KR20240127080A - Manufacturing method of electrode, electrode laminate and lithium secondary battery comprising electrode - Google Patents

Abstract

The present application relates to a method for manufacturing an electrode, an electrode assembly, and a lithium secondary battery including the electrode.

Description

{MANUFACTURING METHOD OF ELECTRODE, ELECTRODE LAMINATE AND LITHIUM SECONDARY BATTERY COMPRISING ELECTRODE}

The present application relates to a method for manufacturing an electrode, an electrode assembly, and a lithium secondary battery including the electrode.

Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the field being most actively researched is power generation and storage using electrochemical reactions.

A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

As the demand for mobile devices and technological development increases, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, are commercialized and widely used. In addition, research is actively being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

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

Generally, carbon materials such as graphite are used as the negative electrode of lithium secondary batteries, but the theoretical capacity density of carbon is 372 mAh/g (833 mAh/cm ³ ). Therefore, in order to improve the energy density of the negative electrode, silicon (Si), tin (Sn), oxides and alloys thereof that are alloyed with lithium are being considered as negative electrode materials. Among them, silicon-based materials have attracted attention due to their low price and high capacity (3579 mAh/g).

However, when using silicon-based negative electrode active materials, such as Si nanoparticles or SiOx particles, there is a problem of high initial irreversible capacity. In the charge/discharge reaction of a lithium secondary battery, 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 the silicon-based negative electrode active material described above, since the volume change and surface side reaction are severe, a large amount of lithium inserted into the negative electrode during the initial charge does not return to the positive electrode, and thus a problem occurs in which the initial irreversible capacity increases. As a result, the initial capacity and energy density of the battery decrease, and the cycle life is rapidly reduced due to excessive lithium loss during the charge/discharge cycle.

To solve the above problems, a method of lithiating the electrode is known. Known lithiation methods include physical/chemical methods such as electrolytic plating, lithium metal transfer, lithium metal deposition, and electrochemical lithiation.

Since the electrochemical lithiation process uses an electrolyte, it includes an electrode washing and drying process after lithiation, so the process itself is complicated and it is difficult to ensure safety and economy. In addition, even when physically contacting the lithium metal layer, if an electrolyte is used, it is not easy to remove the electrolyte components remaining on the electrode after lithiation, and it is difficult to control the lithiation speed and time. In addition, even if an electrolyte is not used, the lithiation speed and time vary depending on the type of electrode, the electrode/metal interface contact state, etc., making it difficult to secure the fairness and ensuring quality accordingly.

In addition, since electrolytes are hazardous substances and have the risk of explosion, various factors/devices must be reflected in the design and operation of the electrolithiation device to ensure safety. For these reasons, despite its many advantages, the electrochemical electrolithiation method has not been commercialized due to its lack of economic feasibility and safety.

In addition, losses occur due to the volatilization of the electrolyte solvent, and solvent volatilization changes the composition of the electrolyte and increases the risk of vapor explosion. In addition, the electrolyte is also lost due to the interfacial reaction with the electrode, and if the composition of the electrolyte changes due to solvent volatilization or reaction, the quality of the prelithiated electrode changes. To solve this problem, in order to maintain the electrolyte composition constant, the electrolyte composition must be checked in real time and the deficient components must be supplemented, which increases the cost, and it is difficult to maintain the composition of the electrolyte constant.

Therefore, although the prelithiation of the electrode is absolutely necessary according to the above-mentioned necessity, research is required on a method that can solve the above-mentioned problems, simplify the cell manufacturing process, improve the performance of the electrode produced thereby, and reduce the cell manufacturing cost.

Japanese Patent Publication No. 2009-080971

The present invention relates to a novel dry lithiation method. In an electrochemical lithiation method, it has been found that when a solid electrolyte film is formed on an upper portion of an electrode and lithiation is performed electrochemically through an external circuit, more precise lithiation with uniform quality can be performed even without including an electrolyte in the electrode. Accordingly, the present application seeks to provide a method for manufacturing an electrode, an electrode assembly, and a lithium secondary battery including the electrode.

An embodiment of the present specification provides a method for manufacturing an electrode, comprising the steps of: preparing an electrode in which an electrode current collector layer and an electrode active material layer are laminated on one or both surfaces of the electrode current collector layer; forming a solid electrolyte film on an opposite surface of a surface of the electrode active material layer facing the electrode current collector layer; forming a lithium metal layer on an opposite surface of the surface of the solid electrolyte film facing the electrode active material layer; and electrically connecting the electrode and the lithium metal layer to form an external electric circuit, wherein the electrode is a dry lithiation electrode.

In another embodiment, an electrode assembly including an electrode current collector layer; an electrode active material layer provided on one or both surfaces of the electrode current collector layer; a solid electrolyte film provided on an opposite surface of a surface of the electrode active material layer facing the electrode current collector layer; and a lithium metal layer provided on an opposite surface of the surface of the solid electrolyte film facing the electrode active material layer; wherein the electrode and the lithium metal layer include an external electric circuit electrically connected thereto, and the electrode assembly is a dry electrolithiation electrode assembly.

Finally, one embodiment of the present application provides a lithium secondary battery including a positive electrode for a lithium secondary battery; an anode for a lithium secondary battery; a separator provided between the positive electrode and the anode; and an electrolyte, wherein at least one of the positive electrode for a lithium secondary battery and the anode for a lithium secondary battery is manufactured according to the method for manufacturing an electrode of the present application.

The electrode manufacturing method according to the present application corresponds to a dry electrochemical lithiation method that does not use an electrolyte. Specifically, the electrode is a dry electrode that does not contain a liquid electrolyte, and a solid electrolyte film is formed on the upper part of the electrode and an external circuit is formed to perform the lithiation process.

Since the present invention does not use a liquid electrolyte, it is possible to fundamentally eliminate electrolyte loss due to solvent volatilization or decomposition reaction during electrode lithiation, and the electrode washing and drying processes are unnecessary during the electrode lithiation process, making the process simple and economical.

In addition, the method for manufacturing an electrode according to the present application is a dry electrochemical method in which lithiation is performed, and thus, compared to other methods, the lithiation speed and time can be controlled as desired, so that the lithiation precision and electrode quality are more uniform and superior.

Figure 1 is a diagram showing an electrode manufacturing method according to one embodiment of the present application.

Before explaining the present invention, some terms are first defined.

When it is said in this specification that a part "includes" a certain component, this does not exclude other components, but rather may include other components, unless otherwise stated.

In this specification, 'p to q' means a range of 'p or more and q or less'.

In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of the number of particles according to particle size. That is, D50 is the particle size (average particle size, center particle diameter) at the 50% point of the cumulative distribution of the number of particles according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of the number of particles according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. Meanwhile, the particle size distribution can be measured using the laser diffraction method. Specifically, the target powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction pattern according to particle size when the particles pass through a laser beam, thereby calculating the particle size distribution.

In this specification, the meaning that a polymer contains a certain monomer as a monomer unit means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when it is said that a polymer contains a monomer, this is interpreted as the same as that the polymer contains a monomer as a monomer unit.

In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials. In this specification, unless otherwise specified, molecular weight means weight average molecular weight.

Hereinafter, the present invention will be described in detail with reference to the drawings so that a person having ordinary skill in the art to which the present invention pertains can easily carry out the present invention. However, the present invention can be implemented in various different forms and is not limited to the following description.

An embodiment of the present specification provides a method for manufacturing an electrode, comprising the steps of: preparing an electrode in which an electrode current collector layer and an electrode active material layer are laminated on one or both surfaces of the electrode current collector layer; forming a solid electrolyte film on an opposite surface of a surface of the electrode active material layer facing the electrode current collector layer; forming a lithium metal layer on an opposite surface of the surface of the solid electrolyte film facing the electrode active material layer; and electrically connecting the electrode and the lithium metal layer to form an external electric circuit, wherein the electrode is a dry lithiation electrode.

The method for manufacturing an electrode according to the present application is a dry electrochemical method in which lithiation is carried out without using an electrolyte, and compared to other methods, the lithiation speed and time can be controlled as desired, so that the lithiation precision and electrode quality are more uniform and superior.

In one embodiment of the present application, the electrode may be a cathode or an anode.

That is, the method for manufacturing an electrode according to the present application relates to a method for prelithiation of a negative electrode or a method for prelithiation of a positive electrode.

Below, the method for manufacturing the electrode is described in detail.

In one embodiment of the present application, the present invention comprises a step of preparing an electrode in which an electrode current collector layer and an electrode active material layer are laminated on one or both surfaces of the electrode current collector layer.

In one embodiment of the present application, the step of forming an electrode active material layer on the electrode current collector layer and one side or both sides of the electrode current collector layer includes a step of coating an electrode slurry including an electrode active material layer composition on one side or both sides of the electrode current collector layer, and a method for manufacturing an electrode is provided, wherein the electrode active material layer composition includes at least one selected from the group consisting of an electrode active material; an electrode conductive material; and an electrode binder.

In one embodiment of the present application, the electrode active material layer composition may further include a solid electrolyte.

Generally, a dry electrode refers to an electrode manufactured without using a solvent. In the case of a lithium secondary battery, an electrode slurry is made by mixing an NMP solvent, an active material, and a conductive binder, and the electrode slurry is coated on an electrode current collector, and then the solvent is removed through a drying process to manufacture the electrode. Likewise, an all-solid-state battery manufactures an electrode slurry composed of an active material, a solid electrolyte, a conductive material, and a binder using an appropriate solvent, and then the electrode slurry is coated on an electrode current collector, and then the solvent is removed. In other words, a dry electrode can be called a dry electrode if it does not use a solvent, regardless of whether it is a lithium secondary battery or an all-solid-state battery.

The electrode according to the present application is a dry lithiation electrode. The term "dry lithiation electrode" may mean an electrode that does not include a liquid electrolyte inside the electrode when electrode lithiation is performed. Specifically, the dry lithiation electrode according to the present application is characterized in that the electrode active material layer composition comprises at least one selected from the group consisting of an electrode active material, an electrode binder, and an electrode conductive material, and is characterized in that the electrode active material layer composition does not include a liquid electrolyte, and a solid electrolyte instead of a liquid electrolyte may be included.

However, the dry electrolithiation electrode according to this invention corresponds to a dry electrochemical electrolithiation electrode applicable to all electrodes manufactured by a wet process, electrodes manufactured by a dry process, and electrodes including a solid electrolyte.

In one embodiment of the present application, the electrode active material includes at least one selected from the group consisting of a silicon-based active material and a carbon-based active material, the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), Si/C, and Si alloy, and the carbon-based active material includes at least one selected from the group consisting of graphite; soft carbon; and hard carbon. A method for manufacturing an electrode is provided.

At this time, the electrode active material may include a silicon-based active material alone, a carbon-based active material alone, or a mixed active material of a silicon-based active material and a carbon-based active material may be used as the electrode active material.

In addition, in the present application, a method for manufacturing an electrode is provided, wherein the electrode active material includes at least one selected from the group consisting of 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).

In one embodiment of the present application, the electrode may be a negative electrode, and the following describes a method for manufacturing a negative electrode for a lithium secondary battery.

A method for manufacturing an electrode according to one 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 sides of the negative electrode current collector layer.

In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 ㎛ to 100 ㎛. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing a chemical change 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., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

In one embodiment of the present 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.

However, the thickness may vary depending on the type and purpose of the cathode used and is not limited thereto.

In one embodiment of the present application, the step of forming a negative electrode current collector layer and a negative electrode active material layer on one side or both sides of the negative electrode current collector layer includes a step of coating a negative electrode slurry including a negative electrode active material layer composition on one side or both sides of the negative electrode current collector layer, and the negative electrode active material layer composition includes at least one selected from the group consisting of a negative electrode active material; a negative electrode conductive material; and a negative electrode binder; The present invention provides a method for prelithiation of an electrode for a lithium secondary battery.

In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

In one embodiment of the present application, the solid content of the cathode slurry can satisfy 5% or more and 40% or less.

In another embodiment, the solid content of the cathode slurry can satisfy a range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

The solid content of the above negative electrode slurry may mean the content of the negative electrode active material layer composition included in the negative electrode slurry, and may mean the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

When the solid content of the above negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode active material layer composition, thereby enabling efficient formation of the negative electrode active material layer.

In one embodiment of the present application, the slurry solvent is not limited to any solvent capable of dissolving the negative electrode active material layer composition, but specifically distilled water can be used.

According to one embodiment of the present application, a negative electrode can be formed by coating and drying the negative electrode slurry on a negative electrode current collector layer.

Through the above drying step, the slurry solvent in the cathode slurry can be dried.

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

In one embodiment of the present application, a silicon-based active material may be used as the negative electrode active material, or an negative electrode including both a silicon-based active material and a carbon-based active material may be used. In this case, a lithium secondary battery having improved overall performance, such as cycle life characteristics, can be manufactured.

In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), a Si/C composite, and a Si alloy.

In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and may include at least 70 parts by weight of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

In another embodiment, the silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

In one embodiment of the present application, the silicon-based active material may be, in particular, pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean that, based on 100 parts by weight of the total silicon-based active material, pure Si particles (SiOx (x=0)) that are not combined with other particles or elements are included within the above range.

In the charge and discharge reaction of a lithium secondary battery, 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, the volume change and surface side reactions are severe, so a large amount of lithium inserted into the negative electrode during the initial charge does not return to the positive electrode, and thus the problem of increased initial irreversible capacity occurs. If the initial irreversible capacity increases, the problem of rapid decrease in battery capacity and cycles occurs.

In the case of the present invention, in order to solve the above problems, the negative electrode of a lithium secondary battery is prelithiated to solve the initial irreversible capacity problem and the problem of excessive lithium loss during charge and discharge cycles. Specifically, in the prelithiation process, when the lithium transfer process is performed, the present invention relates to a process for suppressing the production of by-products so that lithium metal is easily transferred from a transfer laminate and lithium in the negative electrode active material layer can be uniformly prelithiated.

Meanwhile, the average particle diameter (D50) of the silicon-based active material of the present invention may be 5 ㎛ to 10 ㎛, specifically 5.5 ㎛ to 8 ㎛, and more specifically 6 ㎛ to 7 ㎛. When the average particle diameter is included in the above range, the specific surface area of the particles is included in an appropriate range, so that the viscosity of the negative electrode slurry is formed in an appropriate range. Accordingly, the dispersion of the particles constituting the negative electrode slurry becomes smooth. In addition, when the size of the silicon-based active material is greater than the range of the lower limit, the contact area between the silicon particles and the conductive material is excellent due to the complex composed of the conductive material and the binder in the negative electrode slurry, so that the possibility of the conductive network being sustained increases, thereby increasing the capacity retention rate. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded, so that the surface of the negative electrode is formed smoothly, and thus the phenomenon of uneven current density during charge and discharge can be prevented.

In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of the silicon-based active material is preferably 0.01 m ² /g to 150.0 m 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, and most preferably 0.2 m ² /g to 18.0 m ² /g. The BET surface area is measured (using nitrogen) according to DIN 66131.

In one embodiment of the present application, the silicon-based active material may be present in, for example, a crystalline or amorphous form. The silicon particles are preferably spherical or fragment-shaped particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

In one embodiment of the present application, the silicon-based active material may be at least 60 parts by weight based on 100 parts by weight of the negative electrode active material layer composition.

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

The negative electrode active material layer composition according to the present application includes a negative electrode conductive agent and a negative electrode binder capable of controlling a volume expansion rate during a charge and discharge process even when a silicon-based active material having a significantly high capacity is used within the above range, so that the performance of the negative electrode is not deteriorated even within the above range, and it has the characteristic of excellent output characteristics during charge and discharge.

Previously, it was common to use only graphite compounds as negative electrode active materials, but recently, as the demand for high-capacity batteries has increased, attempts to mix and use silicon compounds to increase capacity have been increasing. However, in the case of silicon compounds, there is a limitation in that the volume rapidly expands during the charge/discharge process, which damages the conductive path formed within the negative electrode active material layer and lowers the performance of the battery. Therefore, the type of negative electrode conductive material used together with the silicon active material is important.

In one embodiment of the present application, the negative conductive material may include at least one selected from the group consisting of a dot-shaped conductive material; a surface-shaped conductive material; and a linear conductive material.

In one embodiment of the present application, the dot-shaped conductive material can be used to improve conductivity of the cathode, and means a conductive material having conductivity without causing a chemical change. Specifically, the dot-shaped 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, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in that it implements high conductivity and has excellent dispersibility.

In one embodiment of the present application, the dot-shaped conductive material may have a BET surface area of 40 m ² /g or more and 70 m ² /g or less, preferably 45 m ² /g or more and 65 m ² /g or less, and more preferably 50 m ² /g or more and 60 m ² /g or less.

In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

In one embodiment of the present application, the negative conductive material may include a planar conductive material.

The above-mentioned planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, suppress disconnection of conductive paths due to volume expansion, and is used as a concept including a bulk conductive material or a plate-shaped conductive material.

In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

In one embodiment of the present application, the average particle diameter (D50) of the surface-shaped conductive agent may be 2 ㎛ to 7 ㎛, specifically 3 ㎛ to 6 ㎛, and more specifically 4 ㎛ to 5 ㎛. When the above range is satisfied, dispersion is easy without causing excessive viscosity increase of the negative electrode slurry due to sufficient particle size. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

In one embodiment of the present application, the surface-shaped conductive material provides a negative electrode active material layer composition having 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.

In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material having a high BET specific surface area; or a low-specific surface area planar conductive material.

In one embodiment of the present application, a high surface area surface-type conductive material; or a low surface area surface-type conductive material may be used without limitation as the surface-type conductive material; however, since the surface-type conductive material according to the present application may be affected to some extent by dispersion influence on electrode performance, it may be particularly preferable to use a low surface area surface-type conductive material that does not cause dispersion problems.

In one embodiment of the present application, the surface-shaped conductive material may have a BET surface area of 5 m ² /g or more.

In another embodiment, the surface-shaped conductive material may have a BET surface area of 5 m ² /g or more and 500 m ² /g or less, preferably 5 m ² /g or more and 300 m ² /g or less, and more preferably 5 m ² /g or more and 250 m ² /g or less.

In another embodiment, the planar conductive material is a high surface area planar conductive material, and the BET surface area can satisfy a range of 50 m ² /g or more and 500 m ² /g or less, preferably 80 m ² /g or more and 300 m ² /g or less, and more preferably 100 m ² /g or more and 300 m ² /g or less.

In another embodiment, the planar conductive material is a low surface area planar conductive material, and the BET surface area can satisfy a range of 5 m ² /g or more and 40 m ² /g or less, preferably 5 m ² /g or more and 30 m ² /g or less, and more preferably 5 m ² /g or more and 25 m ² /g or less.

Other negative 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 include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in a longitudinal direction of the carbon nanotube units or are entangled. The carbon nanotube units have a cylindrical shape of a graphite sheet with a nano-sized diameter and an sp2 bonding structure. In this case, the graphite sheets may exhibit conductor or semiconductor properties depending on the angle and structure at which they are rolled. The above bundled carbon nanotubes can be uniformly dispersed during the manufacture of a cathode compared to entangled type carbon nanotubes, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

In one embodiment of the present application, the negative electrode conductive material may be present in an amount of 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

In another embodiment, the negative electrode conductive material may include 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

The negative electrode conductive material according to the present application has a completely separate composition from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application plays a role of holding the contact point between silicon-based active materials, which greatly expand the volume of the electrode due to charging and discharging, and the positive electrode conductive material plays a role of providing some conductivity while acting as a buffer when rolled, and is completely different in composition and role from the negative electrode conductive material of the present invention.

In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material, and has a completely different composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles compared to the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based active material, as in the present invention.

In one embodiment of the present application, the planar conductive material used as the above-mentioned negative electrode conductive material has a structure and a role different from those of the carbon-based active material generally used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material processed into a spherical or dot-shaped form to facilitate the storage and release of lithium ions.

On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be expressed as plate-like graphite. In other words, it refers to a material included to maintain a conductive path within the negative electrode active material layer, and is not a material that plays a role in storing and releasing lithium, but rather a material that secures a conductive path in a planar shape within the negative electrode active material layer.

That is, in the present application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped form and used as a material that secures a conductive path rather than a role of storing or releasing lithium. At this time, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role of storing and releasing all lithium ions transferred from the positive electrode.

On the other hand, in the present application, the use of a carbon-based active material as an active material means that it is processed into a dot or spherical shape and used as a material that plays a role in storing or releasing lithium.

That is, in one embodiment of the present application, the carbon-based active material, such as artificial graphite or natural graphite, may have a BET surface area satisfying a range of 0.1 m ² /g or more and 4.5 m ² /g or less. In addition, the plate-shaped graphite, which is a surface-shaped conductive material, may have a BET surface area of 5 m ² /g or more in the form of a surface.

In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and a material in which hydrogen of these is substituted with Li, Na, Ca, or the like, and may also include various copolymers thereof.

According to one embodiment of the present application, a binder serves to hold the negative electrode active material and the negative electrode conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. If the above-mentioned role is satisfied, all general negative electrode binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

In one embodiment of the present application, the negative electrode binder may be included in an amount 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 be included in an amount of 1 part by weight or more, or 3 parts by weight or more.

In one embodiment of the present application, the electrode may be a positive electrode, and the following describes a method for manufacturing a positive electrode for a lithium secondary battery. At this time, the same description as the method for manufacturing an anode for a lithium secondary battery described above may be applied, with the only difference being that it is a positive electrode.

A method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present application may include a 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.

In one embodiment of the present application, the positive electrode current collector layer is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector layer can typically have a thickness of 3 to 500 ㎛, and fine unevenness can be formed on the surface of the positive electrode current collector layer to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector layer can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

The thickness of the above positive electrode current collector layer can vary depending on the type and purpose of the negative electrode used, and is not limited thereto.

In one embodiment of the present application, the step of forming a positive electrode current collector layer and a positive electrode active material layer on one side or both sides of the positive electrode current collector layer includes a step of coating a positive electrode slurry including a positive electrode active material layer composition on one side or both sides of the positive electrode current collector layer, and the positive electrode active material layer composition includes at least one selected from the group consisting of a positive electrode active material; a positive electrode conductive material; and a positive electrode binder; The present invention provides a method for prelithiation of an electrode for a lithium secondary battery.

In one embodiment of the present application, the content of the positive electrode slurry can be applied equally to the content of the negative electrode slurry described above, with the only difference being the positive electrode.

In one embodiment of the present application, the positive electrode active material layer composition may include at least one selected from the group consisting of a positive electrode active material; a positive electrode conductive material; and a positive electrode binder.

The above positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may include at least one selected from the group consisting of 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). At this time, the positive electrode active material is not limited to these.

Specifically, in the present application, a method for manufacturing an electrode is provided, wherein the cathode active material includes at least one selected from the group consisting of 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).

In the present application, LiNi _x Co _y Mn _z O ₂ (x+y+z=1) may refer to a ternary cathode material, LiNi _a Co _b Mn _c Al _d O ₂ (a+b+c+d=1) may refer to a quaternary cathode material, LiMn ₂ O ₄ may refer to a manganese spinel cathode material, LiNi _0.5 Mn _1.5 O ₂ may refer to a high-voltage spinel cathode material, and LiM _x Fe _y PO ₄ (M: transition metal, x+y=1) may refer to an olivine-based cathode material.

At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, if it does not cause a chemical change and has electronic conductivity, it can be used without special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

In addition, the positive electrode binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used.

In addition, the contents of the positive electrode active material, positive electrode conductive material, and positive electrode binder included in the positive electrode active material layer composition may be applied in the same manner as those applied to the negative electrode active material layer composition described above.

In one embodiment of the present application, the electrode manufacturing method may include a step of forming a solid electrolyte film on the opposite surface of the surface of the electrode active material layer facing the electrode current collector layer; and a step of forming a lithium metal layer on the opposite surface of the surface of the solid electrolyte film facing the electrode active material layer.

The electrode manufacturing method according to the present application may include a solid electrolyte membrane on the upper portion of the electrode active material layer. Accordingly, when the cell is discharged during subsequent lithiation, lithium ions and electrons from the lithium metal layer move to the counter electrode along the solid electrolyte membrane and the external circuit, respectively, so that lithiation of the electrode can be achieved.

In one embodiment of the present application, the solid electrolyte membrane may be in a freestanding form or may be formed in a thin film form on top of an electrode active material layer.

In one embodiment of the present application, the solid electrolyte membrane may include at least one selected from the group consisting of a polymer electrolyte, an oxide electrolyte, and a sulfide electrolyte.

In one embodiment of the present application, the thickness of the solid electrolyte membrane can satisfy 0.1 μm or more and 100 μm or less.

In another embodiment, the thickness of the solid electrolyte membrane can satisfy a range of 0.1 μm or more and 100 μm or less, preferably 0.1 μm or more and 60 μm or less, and more preferably 1 μm or more and 30 μm or less.

The solid electrolyte membrane serves as a passage for lithium ions during lithiation, and by satisfying the above thickness range, it can prevent the lithium metal layer and the electrode active material layer from coming into direct contact, and also has the characteristic of allowing lithiation to proceed to a desired degree.

A method for manufacturing an electrode according to the present application may include a step of electrically connecting the electrode and a lithium metal layer to form an external electric circuit.

After forming an external electric circuit as described above, a step of lithiumizing the electrode active material layer is included.

At this time, a method for manufacturing an electrode is provided, wherein the above-mentioned lithiumation step is performed in a dry room at room temperature, normal pressure, and with a dew point of -70°C to -10°C.

In one embodiment of the present application, the above-described lithiation can be performed in a sealed chamber in which the temperature, gas type, and pressure within the dry room can be controlled.

The lithiation process according to the present application may include a roll-to-roll electrochemical lithiation process.

In the above-described lithium-ion step of the present application, the electrode and the lithium metal layer are separated, and the electrode and the lithium metal layer are connected through an electric circuit.

When the prelithiation proceeds by a spontaneous reaction due to direct contact between lithium and the electrode, it is very difficult to control the prelithiation rate. At this time, the degree of prelithiation is simply determined by the amount of lithium added during battery assembly, and there was a disadvantage in that it was difficult to control the degree of prelithiation because it was difficult to control the thickness of lithium. However, the prelithiation according to the present application more easily controlled the degree of prelithiation through an electrochemical method as described above.

In one embodiment of the present application, a method for manufacturing an electrode is provided, wherein the current density of the electric circuit is 0.1 mA/cm ² or more, and the time for flowing the current is 300 min or less.

For example, if prelithiation is performed at 10% (0.5 mAh/ ^cm2 ) for an electrode with an electrode loading of 5 mAh/ ^cm2 , this means that when the current density is adjusted to 1 mA/ ^cm2 , the current is passed for 0.5 h (30 min), and when it is adjusted to 5 mA/ ^cm2 , the current is passed for 0.1 h (6 min). In other words, the amount of current is a value that changes depending on various factors such as the width of the electrode, the traveling speed of the electrode, and the amount of prelithiation, and the current density value as described above can correspond to a meaningful value.

In another embodiment, the current density of the electric circuit is 0.1 mA/cm ² or more, preferably 0.5 mA/cm ² or more and 100 mA/cm ² or less, and the time for flowing the current may be 300 min or less, 120 min or less, 60 min or less, preferably 30 min or less, and more preferably 10 min or less. The time for flowing the current may be 1 min or more.

As described above, by specifically controlling the amount of current flowing in the circuit and the time for which the current is supplied, the degree of lithiumization in the electrode can be specified, and accordingly, the performance of the manufactured electrode is improved.

FIG. 1 is a diagram showing a method for manufacturing an electrode according to the present application. Specifically, an electrode in which an electrode current collector layer (1) and an electrode active material layer (2) are laminated can be confirmed, and a solid electrolyte film (3) and a lithium metal layer (4) can be confirmed to be sequentially laminated on top. Although not shown in FIG. 1, when an external circuit is connected to discharge the cell, lithium ions and electrons are generated from the lithium metal layer and move to a counter electrode along the solid electrolyte film and the external conductor, respectively, so that electrolithiation of the electrode occurs.

In one embodiment of the present application, a method for manufacturing an electrode is provided, wherein in the step of lithiumizing the electrode, the lithiumization amount is 0.1 mAh/cm ² or more and 5 mAh/cm ² or less.

In addition, a method for manufacturing an electrode is provided, wherein the electrode active material layer has a thickness of 5 μm or more and 100 μm or less.

As described above, the present application is characterized in that precise prelithiation is possible by controlling the current and time flowing in the electric circuit, and prelithiation can be performed to a desired degree without lithium loss by using lithium and an electrode active material layer having the prelithiation amount and thickness in the above range.

One embodiment of the present application provides an electrode assembly including an electrode current collector layer; an electrode active material layer provided on one or both sides of the electrode current collector layer; a solid electrolyte film provided on an opposite side of a side of the electrode active material layer facing the electrode current collector layer; and a lithium metal layer provided on an opposite side of a side of the solid electrolyte film facing the electrode active material layer, wherein the electrode and the lithium metal layer include an external electric circuit electrically connected, and the electrode assembly is a dry electrolithiation electrode assembly.

Each layer and related composition included in the electrode assembly are the same as described above.

In one embodiment of the present application, a lithium secondary battery is provided, which comprises a positive electrode for a lithium secondary battery; an anode for a lithium secondary battery; a separator provided between the positive electrode and the anode; and an electrolyte, wherein at least one of the positive electrode for a lithium secondary battery and the negative electrode for a lithium secondary battery is manufactured according to the method for manufacturing an electrode of the present application.

In one embodiment of the present application, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphoric acid, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, and ethyl propionate can be used.

In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high permittivity and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-permittivity linear carbonates, such as dimethyl carbonate and diethyl carbonate, are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

The metal salt may use a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, and for example, the anion of the lithium salt includes F ^- , Cl ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ -, (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF3CF2(CF3)2CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) At least one selected from the group consisting of ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- can be used.

In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery.

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. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, and therefore can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

1: Electrode current collector layer
2: Electrode active material layer
3: Solid electrolyte membrane
4: Lithium metal layer

Claims (11)

A step for preparing an electrode having an electrode current collector layer and an electrode active material layer laminated on one or both sides of the electrode current collector layer;
A step of forming a solid electrolyte film on the opposite surface of the surface of the electrode active material layer facing the electrode current collector layer;
A step of forming a lithium metal layer on the opposite surface of the surface of the solid electrolyte membrane facing the electrode active material layer; and
A method for manufacturing an electrode, comprising: a step of electrically connecting the electrode and the lithium metal layer to form an external electric circuit;
A method for manufacturing an electrode, wherein the above electrode is a dry lithium electrode. In claim 1,
A step of lithiumizing the above electrode active material layer is included.
A method for manufacturing an electrode, wherein the above-mentioned lithiumation step is performed in a dry room at room temperature, normal pressure, and a dew point of -70°C to -10°C. In claim 1,
A method for manufacturing an electrode, wherein the above dry lithium electrode does not contain a liquid electrolyte. In claim 1,
The step of forming an electrode active material layer on the electrode current collector layer and one or both sides 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 sides of the electrode current collector layer.
A method for manufacturing an electrode, wherein the electrode active material layer composition comprises at least one selected from the group consisting of an electrode active material; an electrode conductive material; and an electrode binder. In claim 4,
The above electrode active material comprises at least one selected from the group consisting of a silicon-based active material and a carbon-based active material;
The above silicon-based active material comprises at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), Si/C, and Si alloy,
A method for manufacturing an electrode, wherein the carbon-based active material comprises at least one selected from the group consisting of graphite; soft carbon; and hard carbon. In claim 4,
A method for manufacturing an electrode, wherein the electrode active material includes at least one selected from the group consisting of 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). In claim 1,
A method for manufacturing an electrode, wherein the thickness of the electrode active material layer is 5 μm or more and 100 μm or less. In claim 2,
A method for manufacturing an electrode, wherein the amount of lithium in the step of lithiumizing the electrode active material layer is 0.1 mAh/cm ² or more and 5 mAh/cm ² or less. In claim 1,
A method for manufacturing an electrode, wherein the current density of the above electric circuit is 0.1 mA/cm ² or more and the time for flowing the current is 300 min or less. Electrode current collector layer;
An electrode active material layer provided on one or both sides of the electrode current collector layer;
A solid electrolyte film provided on the opposite side of the surface of the electrode active material layer facing the electrode current collector layer; and
An electrode assembly including a lithium metal layer provided on the opposite side of the surface of the solid electrolyte membrane facing the electrode active material layer;
The above electrode and the lithium metal layer include an external electrical circuit electrically connected thereto,
An electrode assembly wherein the above electrode assembly is a dry lithium electrode assembly. A lithium secondary battery comprising a cathode for a lithium secondary battery; an anode for a lithium secondary battery; a separator provided between the cathode and the anode; and an electrolyte.
A lithium secondary battery, wherein at least one of the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery is manufactured according to a method for manufacturing an electrode according to any one of claims 1 to 9.