Method for pre-lithification of electrodes, pre-lithified electrodes for lithium secondary batteries, and apparatus for pre-lithification of electrodes

Abstract

The present application relates to a method for prelithiation of an electrode, a prelithiated electrode for a lithium secondary battery, and an electrode prelithiation apparatus.

Description

[Technical Field]

[0001] This application relates to a method for pre-lithiation of electrodes, pre-lithified electrodes for lithium secondary batteries, and an apparatus for pre-lithiation of electrodes.

[0002] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0055970, filed with the Korean Intellectual Property Office on May 6, 2022, and all its contents are incorporated herein by reference. [Background technology]

[0003] The rapid increase in fossil fuel use has led to a growing demand for alternative and clean energy sources, and one of the most actively researched areas in this field is power generation and energy storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes this type of electrochemical energy is the secondary battery, and its range of applications is steadily expanding.

[0005] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly growing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, research is actively underway on methods for manufacturing high-density electrodes with even higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0006] Generally, a secondary battery consists of a positive electrode, electrodes, an electrolyte, and a separation membrane. The electrodes contain an electrode active material that inserts and deinserts lithium ions released from the positive electrode, and silicon-based particles with a large discharge capacity may be used as the electrode active material.

[0007] Generally, carbon materials such as graphite are used for the electrodes of lithium secondary batteries, but the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm³).3 Therefore, in order to improve the energy density of electrodes, silicon (Si), tin (Sn), and their oxides and alloys, which can be alloyed with lithium, are being considered as electrode materials. Among these, silicon-based materials have attracted attention due to their low cost and high capacity (4200 mAh / g).

[0008] However, silicon has a problem in that volume changes (shrinkage or expansion) occur during the insertion / deinsertion process of lithium ions, reducing its mechanical stability and consequently impairing its cycle characteristics. Therefore, there is a need to develop a material that has structural stability, is highly stable when used as an active material in electrochemical elements, and can ensure good cycle characteristics.

[0009] Furthermore, when using silicon-based electrode active materials, a problem arises in that the initial irreversible capacity is large. In the charge-discharge reaction of lithium secondary batteries, lithium released from the positive electrode is inserted into the electrode during charging, and desorbs from the electrode and returns to the positive electrode during discharge. However, in the case of silicon-based electrode active materials, volume changes and surface side reactions are severe, and a large amount of the lithium inserted into the electrode during initial charging does not return to the positive electrode, resulting in a problem of a large initial irreversible capacity. A large initial irreversible capacity leads to a problem of a rapid decrease in battery capacity and cycle life.

[0010] To solve the aforementioned problems, methods for pre-lithifying silicon electrodes containing silicon-based electrode 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, and electrochemical pre-lithification of electrodes.

[0011] Conventional physicochemical methods have inherent risks such as fire and explosion due to environmental factors that require high temperatures, while conventional electrochemical methods cannot uniformly control the initial irreversible capacity, leading to increased production costs.

[0012] In particular, in the lithium metal transfer process, it is difficult to transfer lithium metal safely and easily. Even if it is transferred, the highly reactive lithium metal immediately starts reacting through direct contact with the electrode active material, leading to problems such as particle cracking on the surface of the electrode active material layer.

[0013] Therefore, research is needed on processes and apparatus that are safer and more efficient for pre-lithifying electrodes, and that can uniformly pre-lithify lithium within the electrode active material layer. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0015] This application relates to a method for pre-lithiation of electrodes, pre-lithified electrodes for lithium secondary batteries, and an apparatus for pre-lithiation of electrodes. [Means for solving the problem]

[0016] One embodiment of this specification provides a method for pre-lithiation of an electrode, comprising the steps of: preparing an electrode in which an electrode active material layer is coated on at least one surface of an electrode current collector layer; transferring an intermediate layer by laminating an intermediate layer laminate, in which a first substrate layer, a first release layer, and an intermediate layer are sequentially laminated on the electrode active material layer, so that the intermediate layer is in contact with the electrode active material layer; removing the first substrate layer and the first release layer after the intermediate layer transfer; transferring a lithium metal layer by laminating a lithium metal layer laminate, in which a second substrate layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer to which the intermediate layer has been transferred, so that the lithium metal layer is in contact with the intermediate layer; and removing the second substrate layer after the transfer of the lithium metal layer laminate.

[0017] In another embodiment, an electrode for a lithium secondary battery that has been pre-lithified according to the electrode pre-lithification method described in this application is provided.

[0018] Finally, in one embodiment of this application, an electrode pre-lithiation apparatus is provided, which includes: an electrode extraction unit from which an electrode having an electrode active material layer coated on both sides of an electrode current collector layer is extracted; an intermediate layer transfer unit for laminating an intermediate layer laminate in which a first base layer, a first release layer, and an intermediate layer are sequentially laminated on the electrode active material layers provided on both sides of the electrode; a lithium metal layer transfer unit for laminating a lithium metal layer laminate in which a second base layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer to which the intermediate layer has been transferred; and an electrode recovery unit. [Effects of the Invention]

[0019] One embodiment of the present invention provides a method for pre-lithification of electrodes, which involves manufacturing a pre-lithified electrode through two transfer steps. Specifically, the method includes a step of transferring an intermediate layer to the upper part of the electrode active material layer in order to minimize non-uniform pre-lithification and suppress lithium loss due to side reactions during the electrode pre-lithification process. As a result, the lithium metal does not come into direct contact with the electrode active material layer, and therefore the pre-lithification rate can be adjusted.

[0020] Furthermore, the intermediate layer according to this application is formed not by a wet-on-dry process in which the intermediate layer composition is coated onto the upper part of the electrode active material layer, but by a dry-on-dry process in which the intermediate layer laminate with the intermediate layer formed is transferred onto the upper part of the electrode active material layer. The main feature of this invention is that it solves the problem that occurs when the process proceeds in the wet-on-dry format, in which the intermediate layer composition penetrates into the pores of the electrode active material layer, filling or blocking the electrode pores and increasing the electrode resistance.

[0021] Furthermore, by forming the intermediate layer using the dry-on-dry process as described above, it can be simultaneously transferred onto the electrode active material layers provided on both sides of the electrode current collector layer. When forming the intermediate layer using the wet-on-dry process, it is difficult to proceed with coating on both sides simultaneously, which can cause warping and twisting of the electrodes. However, the intermediate layer formation method described in this application solves these problems by forming the intermediate layer on both sides simultaneously using the dry-on-dry process, and has the advantage of improving the economic efficiency of the process itself.

[0022] In other words, the electrode pre-lithiation method according to the present invention is characterized by forming an intermediate layer for adjusting the pre-lithiation rate on both sides of the electrode active material layer simultaneously through a dry-on-dry process, thereby preventing the electrode from warping or twisting, and preventing the penetration of the intermediate layer composition into the electrode active material layer pores, thereby producing a superior pre-lithified electrode.

[0023] The electrode pre-lithiation apparatus according to this application is characterized by including two R2R steps in order to apply the two transfer steps described above. Specifically, it has an electrode extraction section, an intermediate layer transfer section, a lithium metal layer transfer section, and an electrode recovery section, and two R2R steps are carried out in the intermediate layer transfer section and the lithium metal transfer section, respectively. [Brief explanation of the drawing]

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0025] Before describing the present invention, let us first define some terms.

[0026] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0027] In this specification, "p~q" means the range "p or greater and q or less".

[0028] 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-mini 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.

[0029] In this specification, "Dn" means the average particle size, and represents the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the 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 average particle size can 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 as the particles pass through the laser beam is measured to calculate the particle size distribution.

[0030] 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.

[0031] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense, including copolymers.

[0032] 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.

[0033] 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.

[0034] One embodiment of this specification provides an electrode prelithiation method comprising the steps of: preparing an electrode in which an electrode active material layer is coated on both sides of an electrode current collector layer; transferring an intermediate layer by laminating an intermediate layer laminate, in which a first base layer, a first release layer, and an intermediate layer are sequentially laminated on the electrode active material layers provided on both sides of the electrode, so that the intermediate layer is in contact with the electrode active material layer; removing the first base layer and the first release layer after the intermediate layer transfer; transferring a lithium metal layer by laminating a lithium metal layer laminate, in which a second base layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the active material layer to which the intermediate layer has been transferred, so that the lithium metal layer is in contact with the intermediate layer; removing the second base layer after the transfer of the lithium metal layer laminate; and prelithiating the electrode active material layer.

[0035] Figure 1 shows a method for pre-lithiation of electrodes according to one embodiment of the present application. In Figure 1, the electrode active material layer 20 is shown to be formed on one surface of the electrode current collector layer 10, but it is a simplified representation of a case where the electrode active material layer 20 is formed on both surfaces of the electrode current collector layer 10, but only on one surface. That is, the electrode active material layer 20 can be applied to both surfaces of the electrode current collector layer 10, and the other pre-lithiation methods may be the same.

[0036] One embodiment of the present invention provides a method for pre-lithifying electrodes, which involves manufacturing a pre-lithified electrode following two transfer steps. Specifically, the method includes a step of transferring an intermediate layer to the upper part of the electrode active material layer in order to minimize non-uniform pre-lithification and suppress lithium loss due to side reactions during the electrode pre-lithification process. Since the lithium metal does not come into direct contact with the electrode active material layer, the pre-lithification rate can be adjusted.

[0037] Therefore, in the case of the present invention, when pre-lithiation of electrodes is applied to maximize the improvement of battery performance, the main feature of the present invention is that the intermediate layer is formed in a dry-on-dry manner in order to minimize the problems during pre-lithiation as described above, namely, non-uniform pre-lithiation and lithium loss during the pre-lithiation process.

[0038] The following describes the specific details of the electrode pre-lithiation method of the present invention.

[0039] In one embodiment of this application, the electrode pre-lithiation method includes the step of preparing an electrode in which an electrode active material layer is coated on at least one surface of the electrode current collector layer.

[0040] Specifically, although not shown in Figure 1, electrodes can be prepared by coating at least one surface of the electrode current collector layer with an electrode slurry containing the electrode composition described later.

[0041] In one embodiment of this application, the electrode slurry may comprise an electrode active material layer composition and a slurry solvent.

[0042] In one embodiment of this application, the solid content of the electrode slurry may be 5% or more and 80% or less.

[0043] In another embodiment, the solid content of the electrode slurry may be in the range of 5% to 80%, preferably 10% to 75%, and more preferably 20% to 70%.

[0044] The solid content of the electrode slurry can refer to the content of the electrode active material layer composition contained in the electrode slurry, and can refer to the content of the electrode active material composition based on 100 parts by weight of the electrode slurry.

[0045] When the solid content of the electrode slurry satisfies the aforementioned range, the viscosity is appropriate during electrode active material layer formation, minimizing particle aggregation of the electrode active material layer composition and enabling efficient formation of the electrode active material layer.

[0046] In one embodiment of this application, the slurry solvent is not limited to any solvent that can dissolve the electrode active material layer composition, but specifically, NMP or distilled water can be used.

[0047] An electrode according to one embodiment of this application can be formed by coating and drying the electrode slurry on an electrode current collector layer.

[0048] Through the drying step, the slurry solvent in the electrode slurry can be dried.

[0049] In one embodiment of this application, the slurry solvent can be dried after the drying step, thereby coating at least one surface of the electrode current collector layer with an electrode active material layer.

[0050] In one embodiment of this application, the electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such an 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 electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric.

[0051] In one embodiment of this application, the thickness of the electrode current collector layer may be 1 μm or more and 100 μm or less, and the thickness of the electrode active material layer may be 20 μm or more and 500 μm or less.

[0052] However, the thickness can vary considerably depending on the type and application of the electrodes used, and is not limited to this.

[0053] In one embodiment of this application, the electrode active material layer may include a negative electrode active material; an electrode conductive material; and an electrode binder. The negative electrode active material may contain at least one selected from the group consisting of graphite, soft carbon, hard carbon, SiO x (x = 0), SiO x (0 < x < 2), Si / C, metal impurities, and Si alloys.

[0054] The statement that the electrode active material layer contains a negative electrode active material, an electrode conductive material, and an electrode binder may mean that it contains an electrode active material layer composition containing a silicon-based active material, an electrode conductive material, and an electrode binder.

[0055] In one embodiment of the present application, the electrode active material layer contains a silicon-based active material, an electrode conductive material, and an electrode binder, and the silicon-based active material is SiO x (x = 0), SiO x (0 < x < 2), Si / C, metal impurities, and at least one selected from the group consisting of Si alloys, to provide a method for pre-lithiation of an electrode.

[0056] In one embodiment of the present application, the silicon-based active material may contain one or more selected from the group consisting of Si particles (SiO x (x = 0)), SiO x (0 < x < 2), Si / C, metal impurities, and Si alloys.

[0057] In one embodiment of the present application, the silicon-based active material contains at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be contained in an amount of 20 parts by weight or more.

[0058] In one embodiment of the present application, the silicon-based active material can contain metal impurities, which are impurities that can occur during the purification process of the silicon-based active material, and the content thereof may be contained in an amount of 1 part by weight or less based on 100 parts by weight of the silicon-based active material.

[0059] In one embodiment of the present application, in particular, pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, as described above, when based on a total of 100 parts by weight of the silicon-based active material, pure Si particles (SiO xThis could mean that (x=0) is included in the aforementioned range.

[0060] On the other hand, the average particle size (D50) of the active material in the present invention is 100 nm to 20 μm, specifically 500 nm to 15 μm, and more specifically 1 μm to 10 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 electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the electrode slurry. Furthermore, when the size of the active material is greater than or equal to the lower limit of the above range, the composite consisting of the conductive material and binder in the electrode slurry provides excellent contact area between the active material 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 active material particles are excluded, resulting in a smooth electrode surface, which prevents non-uniformity of current density during charging and discharging.

[0061] In one embodiment of this application, the active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the 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~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0062] In one embodiment of this application, the active material may be 60 parts by weight or more based on 100 parts by weight of the electrode active material layer composition.

[0063] In another embodiment, the active material may be present 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, based on 100 parts by weight of the electrode active material layer composition, and may be present 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.

[0064] The electrode active material layer composition according to this application, even when using a silicon-based active material with a remarkably high capacity within the specified range, utilizes a conductive material and binder capable of suppressing the rate of volume expansion during the charge-discharge process, thereby preventing a decrease in electrode performance even when included within the specified range, and exhibiting excellent output characteristics during charging and discharging.

[0065] In one embodiment of this application, the active material may 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.

[0066] In this application, the degree of sphericity is determined by the following formula 1, where A is the area and P is the boundary line.

[0067] [Formula 1] 4πA / P 2

[0068] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, in recent years, 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 electrode active material layer and actually degrading the battery's performance.

[0069] Accordingly, in one embodiment of this application, the electrode conductive material may include at least one selected from the group consisting of point conductive material; linear conductive material; and planar conductive material.

[0070] In one embodiment of this application, the point-like conductive material can be used to improve conductivity to an electrode, and is preferably conductive without inducing chemical changes. Specifically, the 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 contain carbon black in that it exhibits high conductivity and excellent dispersibility.

[0071] 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.

[0072] 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.

[0073] In one embodiment of this application, the conductive material may include a planar conductive material.

[0074] The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. It can be described as a plate-type conductive material or a bulk-type conductive material.

[0075] 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.

[0076] 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 sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0077] In one embodiment of this application, an 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.

[0078] 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.

[0079] 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.

[0080] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0081] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 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.

[0082] 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 80m 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.

[0083] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, with a BET specific surface area of ​​1 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.

[0084] 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 electrode manufacturing, smoothly form a conductive network within the electrode, and improve the conductivity of the electrode.

[0085] In one embodiment of this application, the electrode conductive material may be 10 to 40 parts by weight, based on 100 parts by weight of the electrode active material layer composition.

[0086] In another embodiment, the 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 electrode active material layer composition.

[0087] In one embodiment of this application, the 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.

[0088] An electrode binder according to one embodiment of this application plays a role in suppressing the active material and conductive material in order to prevent twisting and structural deformation of the 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 can be used. A thickening agent may be included together with the binder, and specifically, CMC can be used as the thickening agent.

[0089] In one embodiment of this application, the electrode pre-lithiation method includes the steps of: transferring an intermediate layer by laminating an intermediate layer laminate, in which a first base layer, a first release layer, and an intermediate layer are sequentially laminated on an electrode active material layer provided on at least one surface of the electrode, such that the intermediate layer is in contact with the electrode active material layer; and removing the first base layer and the first release layer after the intermediate layer transfer.

[0090] Specifically, as can be seen from Figure 1, an intermediate layer laminate 200 can be seen in which a first base layer 40, a first release layer 30, and an intermediate layer 35 are sequentially laminated on top of the electrode active material layer 20. At this time, it can be seen that a lamination process is carried out so that the intermediate layer 35 and the electrode active material layer 20 are in contact. After the intermediate layer lamination, the first base layer 40 and the first release layer 30 are removed, and it can be seen that the intermediate layer 35 is formed on top of the electrode active material layer 20.

[0091] In one embodiment of this application, the intermediate layer laminate may include a structure in which a first base layer, a first release layer, and an intermediate layer are sequentially laminated.

[0092] Specifically, in one embodiment of this application, the first 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.

[0093] In one embodiment of this application, the thickness of the first 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 less, and 10 μm or more and 100 μm or less.

[0094] In one embodiment of this application, in order to improve the peelability of the intermediate layer and ensure transferability to the upper part of the electrode active material layer, a first release layer may be further included on the surface of the intermediate layer laminate that is in contact with the first base layer and the intermediate layer.

[0095] In other words, the first substrate layer may have a first release layer formed on at least one surface, or it may have a first release layer formed on both surfaces. During the winding process for transferring the intermediate layer deposited by the first release layer onto the electrode active material layer, the problem of reverse delamination, in which the intermediate layer is transferred onto the first substrate layer, can be prevented, and the first substrate layer can be easily separated after the intermediate layer has been transferred onto the electrode active material layer.

[0096] The first 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, Si, melamine, and fluorine.

[0097] In one embodiment of this application, the first release layer can be formed by a coating method, which 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 can be used.

[0098] In one embodiment of this application, the present invention provides a method for pre-lithiation of electrodes, wherein the intermediate layer comprises an intermediate layer composition, and the intermediate layer composition comprises at least one selected from the group consisting of polymers; inorganic materials; active materials; and conductive materials.

[0099] In one embodiment of this application, the polymer can be an amorphous thermoplastic polymer, such as polymethyl methacrylate (PMMA), polystyrene (PS), polyvinyl chloride (PVC), polycarbonate (PC), or ABS (acrylonitrile butadiene styrene) resin, and preferably an acrylic polymer such as polymethyl methacrylate (PMMA).

[0100] When a polymer according to one embodiment of this application is used as an intermediate layer composition, it is possible to impart tackiness and improve lithium transfer performance. Furthermore, when the intermediate layer consists only of polymer and does not contain conductive materials, the intermediate layer acts as a barrier layer between lithium and the electrode, suppressing pre-lithification of the electrode. After the electrolyte is injected during battery manufacturing, the intermediate layer dissolves in the electrolyte, and pre-lithification occurs as the electrode and lithium come into contact. Therefore, when the intermediate layer consists only of polymer, the polymer has the property of dissolving in the electrolyte, and the induction of side reactions during battery operation is minimized.

[0101] The polymer according to one embodiment of this application may be included in an amount of 80 parts by weight or more and 100 parts by weight or less, based on 100 parts by weight of the total intermediate layer composition.

[0102] When the polymer is present in an amount of 100 parts by weight per 100 parts by weight of the total intermediate layer composition, in the dry state it acts as a barrier layer against the pre-lithification reaction. When it contains conductive materials, pre-lithification of the electrodes via the intermediate layer becomes possible in the dry state, and the rate of pre-lithification increases as the content of conductive materials increases.

[0103] When an inorganic material is used in the intermediate layer composition according to one embodiment of this application, the inorganic material may be silica (SiO2), alumina (Al2O3), tungsten oxide (WO3), vanadium oxide (V2O5), etc.

[0104] When an active material is used in the intermediate layer composition according to one embodiment of this application, the active material may be a lithium metal oxide such as LiMO2 (M: containing at least one of Ni, Mn, and Co). Other examples of the active material include graphite, soft carbon, and hard carbon.

[0105] In one embodiment of this application, the description of the active material and conductive material can be applied to the description of the electrode active material and electrode conductive material described above.

[0106] When a conductive material is used in the intermediate layer composition according to one embodiment of this application, the conductive material may be a point-shaped conductive material or a linear conductive material, and both point-shaped and linear conductive materials may be used.

[0107] In one embodiment of this application, the conductive material may preferably include, but is not limited to, at least one selected from the group consisting of carbon black, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0108] In one embodiment of this application, the conductive material may preferably include one selected from the group consisting of carbon black, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs) as the first conductive material, and may also include one of the others as the second conductive material, but is not limited thereto.

[0109] In one embodiment of this application, the intermediate layer composition may contain a polymer or a first conductive material:second conductive material in a weight ratio of 100:0 to 60:40, preferably in a weight ratio of 100:0 to 80:20.

[0110] In one embodiment of this application, if the conductive material exceeds 40 parts by weight, based on 100 parts by weight of the total intermediate layer composition, there is a disadvantage that the difficulty and cost of manufacturing the intermediate layer laminate increase.

[0111] An intermediate layer having the composition described above is formed on the upper part of the electrode active material layer, and the intermediate layer can act as a buffer layer that prevents rapid prelithiation by preventing the lithium metal from directly contacting the upper part of the electrode active material layer. In other words, the intermediate layer according to this application can regulate the rate of prelithiation by preventing direct contact between the lithium metal and the electrode active material layer, so that prelithiation in the electrode active material layer proceeds uniformly, and can suppress side reactions associated with rapid prelithiation and reduce lithium loss.

[0112] In one embodiment of this application, a method for pre-electrode lithiumization is provided in which the thickness of the intermediate layer is 200 μm or less.

[0113] In one embodiment of this application, the thickness of the intermediate layer can be in the range of 100 μm or less, 75 μm or less, preferably 50 μm or less, and may be in the range of 100 nm or more, preferably 300 nm or more.

[0114] In another embodiment, the thickness of the intermediate layer can be in the range of 10 μm or less, 5 μm or less, preferably 1 μm or less, and may be in the range of 100 nm or more, preferably 300 nm or more.

[0115] By satisfying the aforementioned thickness of the intermediate layer, the intermediate layer can be easily formed on top of the first substrate layer and the first release layer, and the intermediate layer has the characteristic of being easily transferred to the electrode. Furthermore, by satisfying the aforementioned thickness, the intermediate layer plays an appropriate role as resistance to lithium ions during pre-lithiation, allowing for proper adjustment of the pre-lithiation rate, and even if it remains on top of the electrode active material layer after cell assembly, its role as electrode resistance can be minimized.

[0116] The intermediate layer according to this application is characterized by coating the intermediate layer composition onto the upper part of the first release layer, drying it, and then transferring it again onto the upper part of the electrode active material layer.

[0117] In one embodiment of this application, a pre-electrode lithiumization method is provided, wherein the step of transferring the intermediate layer includes a dry-on-dry step.

[0118] In other words, the intermediate layer is formed not by a wet-on-dry process in which the intermediate layer composition is coated onto the upper part of the electrode active material layer, but by a dry-on-dry process in which the intermediate layer laminate with the intermediate layer formed is transferred onto the upper part of the electrode active material layer.

[0119] The wet-on-dry step can mean a step of applying a coating layer composition to the top of a dry layer to coat it, and the dry-on-dry step can mean a step of transferring the dry layer itself onto the top of a dry layer.

[0120] The main feature of this invention is that, according to one embodiment of this application, the intermediate layer solves the problem that arises when the process proceeds in a wet-on-dry manner, where the intermediate layer composition penetrates into the electrode active material layer pores, filling or blocking the electrode pores and increasing the electrode resistance.

[0121] In other words, the intermediate layer composition itself is a fluid composition, and when applied and coated onto the upper part of the electrode active material layer where voids are formed, the fluidity and capillary action of the intermediate layer composition cause it to penetrate into the voids in the electrode active material layer, which leads to the aforementioned problem. However, the intermediate layer according to this application is formed on the upper part of the electrode active material layer by a transfer method, and the aforementioned problem can be solved.

[0122] Furthermore, by forming the intermediate layer using the dry-on-dry process as described above, it can be simultaneously transferred to the upper part of the electrode active material layer provided on both sides of the electrode current collector layer. When forming the intermediate layer using the wet-on-dry process, it is difficult to proceed with coating on both sides simultaneously, which can cause warping and twisting of the electrodes. However, the intermediate layer formation method according to this application solves the above-mentioned problems by forming the intermediate layer on both sides simultaneously using the dry-on-dry process, and has the advantage of improving the economic efficiency of the process itself.

[0123] In one embodiment of this application, a method for pre-lithiation of electrodes is provided in which the first adhesive force of the surface in contact between the intermediate layer and the first release layer is 10 gf / inch or more and 150 gf / inch or less.

[0124] In another embodiment, the first adhesive strength may satisfy the range of 10 gf / inch to 150 gf / inch, more specifically 15 gf / inch to 100 gf / inch, and more specifically 20 gf / inch to 100 gf / inch.

[0125] In one embodiment of this application, the first adhesive strength can be measured using equipment consisting of a peel tester (AR-2000), a first release layer (Nitto31B), and a rubber roller (2kg). Specifically, the first release layer is attached to one surface of the intermediate layer, and then the rubber roller is used to press it back and forth once to form a laminated structure of the first release layer and the intermediate layer, which is then stored at room temperature for 24 hours. After that, the first release layer is peeled off in a 25mm width and the force is measured, in which case the peeling speed is 300mm / min and the peeling angle is 180°.

[0126] As described above, when the first adhesive force satisfies the aforementioned range, the intermediate layer is easily transferred to the upper part of the electrode active material layer, the manufacturing of the intermediate layer laminate is easy, and reverse transfer to the first substrate layer is also prevented.

[0127] In one embodiment of this application, the surface roughness (S) of the intermediate layer a ) is the surface roughness (S) of the electrode active material layer. a The present invention provides a pre-electrode lithiumization method in which the surface roughness of the intermediate layer is 1 / 5 or less. a ) refers to the surface roughness of the surface in contact with the lithium metal layer. This is measured using a CLSM (Confocal Laser Scanning Microscope), specifically an Olympus OLS5100, at 50x magnification, with a scan area of ​​260 μm × 260 μm, and the average value after 10 measurements per sample is used.

[0128] Generally, the electrode active material layer containing the active material has a surface roughness (S a The surface roughness of the lithium metal layer is formed to be in the range of approximately 0.4 μm to 0.7 μm, which is significantly higher than the surface roughness of the lithium metal layer, which is 0.04 μm to 0.06 μm.

[0129] In other words, when lithium metal is directly transferred to the upper part of an electrode active material layer with a large surface roughness, the contact points between the lithium metal and the electrode active material layer are non-uniform, and a large amount of by-products are formed during pre-lithiation. To solve this, an intermediate layer having the aforementioned surface roughness may be included.

[0130] This allows the surface roughness of the intermediate layer according to this application to be the same as the surface roughness (S) of the electrode active material layer. a By designing it to be less than 1 / 5 of the original size, lithium metal can be transferred more uniformly to the upper part of the electrode active material layer. 。

[0131] In one embodiment of this application, the process may include the step of removing the first substrate layer and the first release layer after the transfer of the intermediate layer. That is, the first substrate layer and the first release layer serve as a transfer laminate to facilitate the transfer of the intermediate layer onto the electrode active material layer, and also constitute a laminate for carrying out the dry-on-dry process.

[0132] One embodiment of this application provides a step of laminating a lithium metal layer laminate, in which a second base material layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of an active material layer onto which the intermediate layer has been transferred, so that the lithium metal layer is in contact with the intermediate layer, thereby transferring the lithium metal layer; and a step of removing the second base material layer after the transfer of the lithium metal layer laminate.

[0133] In one embodiment of this application, the lithium metal layer is transferred by laminating a lithium metal layer laminate, in which a second substrate layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer to which the intermediate layer has been transferred, so that the lithium metal layer is in contact with the intermediate layer; The step of removing the second substrate layer after transferring the lithium metal layer laminate; or The step of pre-lithifying the electrode active material layer may be further included in at least one of the steps between the step of transferring the lithium metal layer and the step of removing the second substrate layer. That is, the step of pre-lithifying the electrode active material layer may be performed at any stage after the lithium metal layer has been transferred onto the intermediate layer of the electrode active material layer on which the intermediate layer has been transferred.

[0134] Specifically, as can be seen from Figure 1, it can be confirmed that a lithium metal layer laminate 300 is laminated on top of an electrode in which an intermediate layer 35 is formed on top of the electrode active material layer 20, with a second base material layer 41, a second release layer 31, and a lithium metal layer 36 sequentially stacked on top of the electrode. Subsequently, it can be confirmed that by removing the second base material layer 41, a structure is formed in which the electrode current collector layer 10, electrode active material layer 20, intermediate layer 35, lithium metal layer 36, and second release layer 31 are sequentially stacked.

[0135] In one embodiment of this application, the lithium metal layer laminate may include a structure in which a second substrate layer, a second release layer, and a lithium metal layer are sequentially laminated.

[0136] Specifically, in one embodiment of this application, the second 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.

[0137] In one embodiment of this application, the description of the first substrate layer described above may also apply to the second substrate layer.

[0138] In one embodiment of this application, the description of the first release layer described above may also apply to the second release layer.

[0139] In one embodiment of this application, the deposition method for depositing the lithium metal layer onto the second substrate layer on which the second release layer is formed can be selected from, but is not limited to, vacuum deposition, chemical vapor deposition (CVD), and physical vapor deposition. Various deposition methods used in the industry can be used.

[0140] In one embodiment of this application, the transfer process can be carried out by applying a load of 10 kgf to 500 kgf to the electrode on which the lithium metal layer laminate is stacked and performing roll pressing. Subsequently, a step of removing the second base material layer is included, and by including the second release layer according to this application during removal, direct contact between the lithium metal layer and air can be prevented, thereby protecting the lithium metal layer.

[0141] 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.

[0142] By ensuring the thickness of the lithium metal layer meets the specified range, the transfer of the lithium metal layer to the electrode active material layer occurs efficiently, while preventing reverse transfer.

[0143] In one embodiment of this application, even after the step of laminating and transferring the lithium metal layer onto the intermediate layer, the intermediate layer prevents direct contact between the lithium metal and the electrode active material layer, thereby delaying the progress of the pre-lithification process.

[0144] Furthermore, if the intermediate layer according to this application is first transferred to the upper part of the lithium metal layer and then laminated to the electrode active material layer, unlike in this application, the intermediate layer and the lithium metal layer are laminated to the electrode active material layer simultaneously, causing pre-lithification to proceed simultaneously, which may make it difficult to derive uniform contact conditions on the upper part of the electrode.

[0145] In one embodiment of this application, the electrode prelithiation method includes the step of prelithiating the electrode active material layer;

[0146] The aforementioned step can be understood as the stage from when the lithium metal layer is transferred to the upper part of the electrode active material layer on which the intermediate layer has been formed, until prelithiation is completed, and from the point at which prelithiation occurs until the lithium metal layer is completely gone and visible to the naked eye.

[0147] In one embodiment of this application, the step of pre-lithifying the electrode is performed at a temperature of 60°C to 80°C at a rate of 5 kgf / cm². 2 ~20 kgf / cm² 2 Pre-lithification can be performed under these pressurized conditions.

[0148] Under the conditions described above, the pre-lithiation completion time during pre-lithiation can be within the range of 1 to 24 hours.

[0149] In other words, an intermediate layer is formed on top of the electrode active material layer according to this application, which prevents rapid prelithiation, satisfies the aforementioned prelithiation completion time, and has the characteristic of allowing prelithiation to proceed more uniformly.

[0150] On the other hand, if the intermediate layer is composed of polymers, prelithiation is suppressed in the dry state, but prelithiation may occur after electrolyte injection during battery assembly.

[0151] In one embodiment of this application, an electrode for a lithium secondary battery that has been pre-lithified according to the electrode pre-lithification method described herein is provided.

[0152] One embodiment of this application provides a lithium secondary battery comprising a pre-lithified electrode according to this application; a separation membrane located between the electrode and a counter electrode; and an electrolyte.

[0153] In another embodiment of this application, the electrode active material layer may include a positive electrode active material; an electrode conductive material; and an electrode binder.

[0154] The statement that the electrode active material layer includes a positive electrode active material; an electrode conductive material; and an electrode binder may mean that it includes a positive electrode active material layer composition comprising a positive electrode active material; an electrode conductive material; and an electrode binder.

[0155] In one embodiment of this application, when the electrode is a positive electrode, the positive electrode is formed on a positive electrode current collector and may include a positive electrode active material layer containing the positive electrode active material.

[0156] In the positive electrode, the positive electrode current collector 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 can also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector 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.

[0157] The positive electrode active material layer composition 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), 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 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), chemical formula LiM 1-c4 M' c4Lithium manganese composite oxides represented as PO4 (where M is a transition metal, and M' is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c4 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include, but are not limited to, LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may also be Li-metal.

[0158] In one embodiment of this application, the electrode active material layer may include a positive electrode active material; an electrode conductive material; and an electrode binder. In one embodiment of this application, the positive electrode active material is LiNi x Co y Mn z O2(x+y+z=1);LiNi a Co b Mn c Al d O2(a+b+c+d=1);LiMn2O4;LiNi 0.5 Mn 1.5 O2 and LiM x Fe y The present invention provides a pre-electrode lithiumization method comprising at least one selected from the group consisting of PO4 (M: transition metal, x+y=1).

[0159] 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.

[0160] 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.

[0161] 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.

[0162] In one embodiment of this application, the separation membrane separates the electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is typically used as a separation membrane in secondary batteries, and is particularly preferred if it has low resistance to ion movement of the electrolyte while having excellent electrolyte moisture absorption capacity. 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 of high-melting-point glass fibers or polyethylene terephthalate fibers, may 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 used selectively in single-layer or multi-layer structures.

[0163] 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.

[0164] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0165] 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, ether, methyl propionate, and ethyl propionate may be used.

[0166] 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 low-viscosity, low-dielectric-constant chain carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions, an electrolyte with high electrical conductivity can be produced, and this mixture is even more preferable.

[0167] The metal salt can be a lithium salt, and the lithium salt 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 - One or more selected from the group consisting of can be used.

[0168] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n - glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N - substituted oxazolidinone, N,N - substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2 - methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the reduction of battery capacity, improving the discharge capacity of the battery, etc.

[0169] One embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium - to - large - sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug - in hybrid electric vehicles and power storage systems.

[0170] In one embodiment of the present invention, an electrode pre-lithiation apparatus is provided, comprising: an electrode extraction unit for extracting an electrode having an electrode active material layer coated on both sides of an electrode current collector layer; an intermediate layer transfer unit for laminating an intermediate layer laminate in which a first base layer, a first release layer, and an intermediate layer are sequentially laminated on the electrode active material layers provided on both sides of the electrode; a lithium metal layer transfer unit for laminating a lithium metal layer laminate in which a second base layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer to which the intermediate layer has been transferred; and an electrode recovery unit.

[0171] In one embodiment of this application, the present invention provides a pre-electrode lithiumization apparatus in which the intermediate layer transfer unit includes an intermediate layer laminate recovery unit for recovering the first substrate layer and the first release layer, and the lithium metal layer transfer unit includes a lithium metal layer laminate recovery unit for recovering the second substrate layer.

[0172] The electrode pre-lithiation apparatus according to this application is characterized by including two R2R steps in order to apply the two transfer steps described above. Specifically, it has an electrode extraction section, an intermediate layer transfer section, a lithium metal layer transfer section, and an electrode recovery section, and two R2R steps are carried out in the intermediate layer transfer section and the lithium metal transfer section, respectively.

[0173] Figure 2 is a diagram relating to an electrode pre-lithiation apparatus according to one embodiment of the present application. Specifically, it has an electrode extraction section 1a including an electrode roll having an electrode current collector layer coated on both sides with an electrode active material layer, from which the electrode is extracted. The electrode then passes through an intermediate layer transfer section 1b, where an intermediate layer can be transferred to both sides of the electrode active material layer. Specifically, the intermediate layer transfer section 1b may include an intermediate layer laminate lamination section 2a and an intermediate layer laminate removal section 2b. It can be confirmed that R2R lamination is performed once in the intermediate layer laminate lamination section. After that, it passes through a lithium metal layer transfer section 1c, where a lithium metal layer is transferred to the upper part of the intermediate layer. At this time, the lithium metal layer transfer section 1c includes a lithium metal layer laminate lamination section 2c and a lithium metal layer laminate removal section 2d. At this time, it can be confirmed that R2R lamination is carried out in the lithium metal layer laminate lamination section. After that, it consists of an electrode recovery section 1d for recovering the electrode.

[0174] In other words, the pre-electrode lithiumization apparatus according to this application is characterized by performing two R2R processes: transferring the intermediate layer in a dry-on-dry process and transferring the lithium metal layer. [Examples]

[0175] 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.

[0176] Manufacturing example Electrode manufacturing A cathode electrode slurry was prepared using NMP as the solvent, with a solid content ratio of 96 wt%:2 wt%:2 wt% for the cathode material (NCMA):conductive material (MWCNT):binder (PVDF-HFP) of the cathode. The volume per standard area of ​​the cross-sectional coating was 4.2 mAh / cm². 2To achieve this, the electrode slurry was coated on both sides of an aluminum current collector (thickness: 15 μm), dried in a vacuum oven at 130°C for 12 hours, and then rolled (roll pressed) to produce an electrode with an electrode active material layer coated on both sides.

[0177] Manufacturing of intermediate layer laminates Table 1 below shows the composition and thickness of the intermediate layer laminate. The intermediate layer laminate is a PET film substrate coated with an adhesive acrylic polymer. The intermediate layer laminate was manufactured by varying the thickness of the PET film and the intermediate layer.

[0178] [Table 1]

[0179] Manufacturing of lithium vapor-deposited films Table 2 below shows the composition and thickness of the lithium vapor-deposited film. The lithium vapor-deposited film has a structure in which a 500 nm thick release layer made of acrylic polymer is coated on a 25 μm thick PET substrate, and a 6.2 μm thick lithium layer is deposited on this release layer using a thermal evaporation method.

[0180] [Table 2]

[0181] Example 1 After roll lamination of the electrode and intermediate layer laminate A manufactured as described above, the base film (PET) and release layer were removed to produce an electrode with the intermediate layer transferred. The intermediate layer was peeled off at the interface between the release layer and the intermediate layer and transferred to the electrode. After roll lamination of the electrode with the transferred intermediate layer and the lithium vapor-deposited film (C), the base layer (PET) of the lithium vapor-deposited film was removed to produce a multi-layer electrode (release layer / lithium layer / intermediate layer / electrode layer) with the lithium layer / release layer transferred (dry-on-dry method). (See Figure 3)

[0182] Example 2 In the above-described Example 1, a multilayer electrode was manufactured by sequentially transferring the intermediate layer and the lithium layer (including the release layer) in the same manner as in Example 1, except that intermediate layer B was used instead of intermediate layer A. (See Figure 4)

[0183] Comparative Example 1 In Example 1, the electrode in which the intermediate layer (A or B) and the lithium metal layer were not transferred was named the Pristine electrode (Comparative Example 1).

[0184] Comparative Example 2 The manufacturing process was the same as in Example 1, except that the intermediate layer (A or B) was not formed on top of the electrode active material layer, and the lithium metal layer was directly transferred to the top of the electrode active material layer provided on both sides of the electrode current collector layer.

[0185] Coin half-cells were manufactured using electrodes produced by the methods of Example 1, Comparative Example 1, and Comparative Example 2, and their initial charge / discharge capacity and cycle performance were evaluated. The results are shown in Table 3 and Figure 5 below. The electrolyte used for manufacturing the coin half-cells was 1M LiPF6 in EC / EMC (30:70 vol%), and a 150 μm thick lithium metal foil was used as the counter electrode. During initial charge / discharge capacity measurement, the C-rate was set to 0.1C, charging was performed with an upper voltage limit of 4.3V, CCCV conditions, and a cutoff current of 0.005C, and discharging was performed with a lower voltage limit of 3.0V and CC conditions. Cycle capacity measurements were performed with upper and lower voltage limits of 4.3V / 3.0V, a C-rate of 0.33C, CCCV charging, and CC discharging conditions.

[0186] [Table 3]

[0187] According to Table 3 and Figure 5, the electrode produced by Example 1, which involves manufacturing an electrode containing a lithium metal layer in a sequential transfer process, was found to have a significantly higher initial charge capacity compared to the electrodes produced by Comparative Examples 1 and 2. Specifically, the method according to Example 1 includes a step of transferring an intermediate layer to the upper part of the electrode active material layer in order to solve the problem of surface active material cracking for high-capacity positive electrode active materials. This prevents the lithium metal from directly contacting the electrode active material layer, thus preventing rapid pre-lithification of the active material.

[0188] In the first embodiment described above, forming the intermediate layer using the dry-on-dry process as described above has the advantage of simultaneously transferring the lithium metal layer to the upper part of the electrode active material layer provided on both sides of the electrode current collector layer, unlike the wet-on-dry process.

[0189] In the case of the above-described embodiment 2, the intermediate layer is formed to a thin thickness, which allows for appropriate adjustment of the pre-lithiation rate. Even if some of the intermediate layer remains on top of the electrode active material layer after cell assembly, its role as electrode resistance is minimized.

[0190] In the case of the pristine electrode without a lithium metal layer as in Comparative Example 1, it was found that the cycle performance was inferior compared to that of Example 1 (see Figure 6).

[0191] In the case of Comparative Example 2, since no intermediate layer is formed and the process involves directly transferring the lithium metal layer to the upper part of the electrode, it was confirmed that when the process proceeds as in Comparative Example 2, cracking of the active material particles on the electrode surface side occurs due to rapid pre-lithiation of the electrode, resulting in a decrease in cycle performance compared to Example 1 (see Figure 6). [Explanation of Symbols]

[0192] 10 ···Electrode current collector layer 20...electrode active material layer 30...1st release layer 35 ···Middle class 40...1st base layer 31...Second release layer 41...Second base material layer 36 ···Lithium metal layer 100...electrode 200 ···Intermediate layer laminate 300 ···Lithium metal layer laminate 1a ···Electrode extraction section 1b ···Intermediate layer transfer section 1c ···Lithium metal layer transfer section 1d ···Electrode retrieval section 2a ···Intermediate layer laminated section 2b ···Removal section of the intermediate layer laminate 2c ···Lithium metal layer laminated section 2d ···Lithium metal layer laminate removal section

Claims

1. A step of preparing an electrode in which an electrode active material layer is coated on at least one surface of the electrode current collector layer; A step of transferring the intermediate layer by laminating an intermediate layer laminate, in which a first substrate layer, a first release layer, and an intermediate layer are sequentially laminated on the electrode active material layer, such that the intermediate layer is in contact with the electrode active material layer; The step of removing the first substrate layer and the first release layer after the transfer of the intermediate layer; A step of transferring the lithium metal layer by laminating a lithium metal layer laminate, in which a second substrate layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer onto which the intermediate layer has been transferred, so that the lithium metal layer is in contact with the intermediate layer; and A step of removing the second substrate layer after transferring the lithium metal layer laminate; A method for pre-lithiation of electrodes, including, The surface roughness of the intermediate layer (S ａ ) is the surface roughness (S) of the electrode active material layer. ａ A pre-electrode lithiumization method that is less than 1 / 5 of the cost of the previous method.

2. A step of transferring the lithium metal layer by laminating a lithium metal layer laminate, in which a second substrate layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer onto which the intermediate layer has been transferred, so that the lithium metal layer is in contact with the intermediate layer; The step of removing the second substrate layer after transferring the lithium metal layer laminate; or The step of pre-lithifying the electrode active material layer is performed in at least one of the steps between the step of transferring the lithium metal layer and the step of removing the second substrate layer. The electrode pre-lithiation method according to claim 1, further comprising:

3. The intermediate layer comprises an intermediate layer composition, The electrode prelithiation method according to claim 1, wherein the intermediate layer composition comprises at least one selected from the group consisting of polymers; inorganic materials; active materials; and conductive materials.

4. The electrode pre-lithiation method according to claim 1, wherein the thickness of the intermediate layer is 50 μm or less.

5. The pre-electrode lithiumization method according to claim 1, wherein the step of transferring the intermediate layer includes a dry-on-dry step.

6. The electrode pre-lithiation method according to claim 1, wherein the first adhesive force of the surface in contact with the intermediate layer and the first release layer is 10 gf / inch or more and 150 gf / inch or less.

7. The electrode active material layer comprises a negative electrode active material; an electrode conductive material; and an electrode binder. The negative electrode active material is graphite, soft carbon, hard carbon, SiO ｘ (x=0), SiO ｘ The electrode pre-lithiation method according to claim 1, comprising at least one selected from the group consisting of (0 < x < 2), Si / C, and Si alloy.

8. The electrode active material layer includes a positive electrode active material, an electrode conductive material, and an electrode binder, and the positive electrode active material is LiNi ｘ Co ｙ Mn ｚ O ２ (x + y + z = 1); LiNi ａ Co ｂ Mn ｃ Al ｄ O ２ (a + b + c + d = 1); LiMn ２ O ４ ; LiNi ０．５ Mn １．５ O ２ ; and LiM ｘ Fe ｙ PO ４ (M: transition metal, x + y = 1), and the method for pre-lithiation of an electrode according to claim 1, comprising at least one selected from the group consisting of.

9. The electrode prelithiation method according to claim 1, wherein the first substrate layer and the second substrate layer are one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), polymethylmethacrylic acid (PMMA), polypropylene, polyethylene, and polycarbonate.

10. The electrode pre-lithiation method according to claim 1, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

11. An electrode extraction section from which electrodes coated with electrode active material layers on both sides of the electrode current collector layer are drawn out; An intermediate layer transfer unit for laminating an intermediate layer laminate, in which a first substrate layer, a first release layer, and an intermediate layer are sequentially laminated on electrode active material layers provided on both sides of the electrode; A lithium metal layer transfer section for laminating a lithium metal layer laminate in which a second substrate layer, a second release layer, and a lithium metal layer are sequentially laminated on the intermediate layer of the electrode active material layer onto which the intermediate layer has been transferred; and Electrode retrieval section; A pre-electrode lithium-ion device, including, The surface roughness of the intermediate layer (S ａ ) is the surface roughness (S) of the electrode active material layer. ａ A pre-electrode lithiumization device with a power consumption of less than 1 / 5 of that of other devices.

12. The intermediate layer transfer unit includes an intermediate layer laminate recovery unit for recovering the first substrate layer and the first release layer. The pre-electrode lithiumization apparatus according to claim 11, wherein the lithium metal layer transfer unit includes a lithium metal layer laminate recovery unit for recovering the second substrate layer.

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