Negative electrode for lithium secondary battery, method for manufacturing lithium secondary battery, and lithium secondary battery

Abstract

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

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0167502, filed with the Korean Intellectual Property Office on November 29, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode for a lithium secondary battery, a method for producing a lithium secondary battery, and a lithium secondary battery. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields is power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources 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, have been commercialized and widely used. In addition, active research is 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.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a high discharge capacity.

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

[0008] However, silicon has poor mechanical stability due to volume changes (shrinkage or expansion) during the lithium ion insertion / extraction process, which results in impaired cycle performance. Therefore, there is a need to develop a material that has structural stability and is therefore stable enough to be used as an active material in electrochemical devices and ensure cycle performance.

[0009] Furthermore, the use of silicon-based negative electrode active materials poses the problem of high initial irreversible capacity. During the charge-discharge reaction of a lithium secondary battery, lithium is released from the positive electrode and inserted into the negative electrode during charging, and then released from the negative electrode and returned to the positive electrode during discharge. However, with silicon-based negative electrode active materials, volume changes and surface side reactions are so severe that much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a high initial irreversible capacity. This high initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0010] To solve the above problems, a method of prelithiating a silicon negative electrode containing a silicon-based negative electrode active material is known. Known prelithiation methods include a method of preparing an electrode after lithiating the negative electrode by a physical / chemical method such as electroplating, lithium metal transfer, or lithium metal vapor deposition, and a method of electrochemically prelithiating the negative electrode.

[0011] Conventional physicochemical methods involve the risk of fire and explosion due to environmental factors, such as the need to perform them at high temperatures, and existing electrochemical methods have the problem of being unable to uniformly control the initial irreversible capacity, which increases production costs.

[0012] In particular, in the lithium metal transfer process, it is difficult to transfer lithium metal safely and easily, and even if it is transferred, the highly reactive lithium metal immediately begins to react with the negative electrode active material, causing problems such as particle cracking on the surface of the negative electrode active material layer.

[0013] Therefore, there is a need for research into processes and materials for prelithiating a negative electrode that are safer and more efficient and that can uniformly prelithiate lithium within the negative electrode active material layer. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0015] Having confirmed the existence of the above-mentioned problems, it was found that the above-mentioned problems can be solved by laminating a layer having a specific composition and thickness on top of the negative electrode active material layer in a pre-lithiation process including a transfer process, which allows lithium metal to be transferred safely and easily and prevents the lithium metal and the negative electrode active material layer from immediately starting to react after transfer.

[0016] Therefore, the present application relates to a negative electrode for a lithium secondary battery, a method for producing a lithium secondary battery, and a lithium secondary battery. [Means for solving the problem]

[0017] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer; and an electrolyte solution-dissolving layer provided on the surface of the negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer; wherein the thickness of the electrolyte solution-dissolving layer is 0.1 μm or more and 5 μm or less, and the electrolyte solution-dissolving layer includes a binder copolymer containing a monomer having a fluoro group, and the content of the monomer is 5 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the binder copolymer.

[0018] In yet another embodiment, there is provided a method for manufacturing a lithium secondary battery, the method including: forming a negative electrode active material layer on one or both sides of a negative electrode current collector layer and the negative electrode current collector layer; coating an electrolyte dissolution layer composition on a side of the negative electrode active material layer opposite to the side that contacts the negative electrode current collector layer to form a negative electrode for a lithium secondary battery, the negative electrode active material layer including an electrolyte dissolution layer; transferring lithium metal to the side of the electrolyte dissolution layer opposite to the side that contacts the negative electrode active material layer; forming a positive electrode active material layer on one or both sides of a positive electrode current collector layer and the positive electrode current collector layer to form a positive electrode for a lithium secondary battery; laminating the negative electrode and the positive electrode with a separator between them, and incorporating the resulting laminate into a battery pouch; and injecting an electrolyte into the battery pouch to prelithiate the negative electrode.

[0019] Finally, in one embodiment of the present application, there is provided a lithium secondary battery manufactured by the method for manufacturing a lithium secondary battery according to the present application. [Effects of the Invention]

[0020] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery includes an electrolyte-dissolving layer on a negative electrode active material layer, the electrolyte-dissolving layer having a thickness of 0.1 μm to 5 μm and including a binder copolymer containing a monomer containing a fluoro group, the electrolyte-dissolving layer being 5 to 20 parts by weight per 100 parts by weight of the binder copolymer. The inclusion of the electrolyte-dissolving layer prevents prelithiation even when lithium metal is transferred onto the negative electrode active material layer. After the battery is assembled, the electrolyte is injected and sealed, and the electrolyte-dissolving layer dissolves in the electrolyte, allowing prelithiation.

[0021] As described above, since the electrolyte solution dissolving layer dissolves in the electrolyte and undergoes prelithiation, the amount of by-reaction products with lithium is reduced and the loss of lithium metal is reduced compared to when prelithiation occurs simultaneously with the manufacture of the negative electrode. Furthermore, since the electrolyte solution dissolving layer can also control the rate of prelithiation, it is possible to prevent lithium loss and achieve uniform prelithiation throughout the negative electrode active material layer.

[0022] That is, the negative electrode for a lithium secondary battery according to the present invention is mainly characterized in that it comprises an electrolyte dissolving layer having a specific composition and thickness on top of the negative electrode active material layer, so that prelithiation during the prelithiation step can be carried out more efficiently, without loss of lithium, and uniformly across the entire negative electrode active material layer. [Brief explanation of the drawings]

[0023] [Figure 1] 1A to 1C are diagrams illustrating a process for transferring lithium metal to a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0024] Before describing the present invention, some terms will first be defined.

[0025] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0026] In this specification, "p to q" means a range of "not less than p and not more than q."

[0027] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0028] In this specification, "Dn" refers to the average particle size, which is the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size when the particles pass through a laser beam.

[0029] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0030] It is understood that the term "polymer" is used in the broad sense herein to include copolymers unless "homopolymer" is specifically stated.

[0031] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0032] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer; and an electrolyte solution-dissolving layer provided on the surface of the negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer; wherein the thickness of the electrolyte solution-dissolving layer is 0.1 μm or more and 5 μm or less, and the electrolyte solution-dissolving layer includes a binder copolymer containing a monomer having a fluoro group, and the content of the monomer is 5 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the binder copolymer.

[0034] The negative electrode for a lithium secondary battery according to the present invention is mainly characterized in that it comprises an electrolyte dissolving layer having a specific composition and thickness on top of the negative electrode active material layer, so that prelithiation during the prelithiation step can be carried out more efficiently, without loss of lithium, and uniformly throughout the negative electrode active material layer.

[0035] The negative electrode for a lithium secondary battery of the present invention will be specifically described below.

[0036] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0037] In one embodiment of the present application, the thickness of the negative electrode current collector layer is 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.

[0038] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0039] In one embodiment of the present application, the negative electrode active material layer may include a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0040] The fact that the negative electrode active material layer includes a silicon-based active material; a negative electrode conductive material; and a negative electrode binder means that it may also include a negative electrode active material layer composition including a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0041] In one embodiment of the present application, the silicon-based active material may include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, metal impurities, and Si alloys.

[0042] In one embodiment of the present application, the silicon-based active material contains at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may contain 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0043] 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, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0044] In one embodiment of the present application, the silicon-based active material may 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 0.1 part by weight or less based on 100 parts by weight of the silicon-based active material.

[0045] In one embodiment of the present application, particularly, pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean containing pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range when based on 100 parts by weight of the total silicon-based active material as described above.

[0046] In the case of silicon-based active materials, compared with the conventionally used graphite-based active materials, the capacity is significantly higher, and attempts to apply it are increasing. However, the volume expansion rate during the charge and discharge process is high, and it has been limited to cases such as mixing a small amount with graphite-based active materials for use.

[0047] Therefore, in the case of the present invention, in order to improve the capacity performance, while using only the silicon-based active material as the negative electrode active material, in order to solve the above problems, the roles of the conductive material and the binder are strengthened to solve the existing problems.

[0048] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of the range, the composite of the conductive material and the binder in the negative electrode slurry has an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network, and thereby increasing the capacity retention. On the other hand, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0049] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0050] In one embodiment of the present application, the silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or shard-like particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0051] In one embodiment of the present application, the silicon-based active material may be included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0052] In yet 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, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 80 parts by weight or less.

[0053] The negative electrode active material layer composition according to the present application uses a conductive material and a binder that can suppress the volume expansion rate during charge and discharge even when a silicon-based active material having an extremely high capacity is used within the above range, and therefore does not deteriorate the performance of the negative electrode even when the range is included, and has the characteristic of excellent output characteristics during charge and discharge.

[0054] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the circularity thereof 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.

[0055] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter.

[0056] [Formula 1] 4πA / P 2

[0057] While graphite-based compounds have traditionally been used exclusively as anode active materials, attempts to incorporate silicon-based compounds into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, silicon-based compounds have limitations, such as their rapid volume expansion during charge / discharge processes, damaging the conductive pathways formed within the anode active material layer and reducing battery performance.

[0058] Thus, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of dot-like conductive material, linear conductive material, and sheet-like conductive material.

[0059] In one embodiment of the present application, the dot-like conductive material may be used to improve the conductivity of the negative 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 fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which realizes high conductivity and excellent dispersibility.

[0060] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 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 / g or less.

[0061] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0062] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0063] The planar conductive material increases the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time, prevents the conductive path from being broken due to volume expansion. The planar conductive material may be classified as a plate-type conductive material or a bulk-type conductive material.

[0064] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0065] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size satisfies this range, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0066] In one embodiment of the present application, the sheet conductive material provides a negative electrode 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.

[0067] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low specific surface area.

[0068] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material or a low-specific surface area planar conductive material without any restrictions. However, the planar conductive material of the present 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.

[0069] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​1 m 2 / g or more.

[0070] In another embodiment, the sheet conductive material has a BET specific surface area of ​​1 m 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 / g or less.

[0071] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having a BET specific surface area of ​​50 m 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 / g or less.

[0072] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of ​​1 m 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 / g or less.

[0073] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with the longitudinal axes of the carbon nanotube units in substantially the same orientation, forming a bundle or rope-like shape. The carbon nanotube units have graphite sheets with nanosized diameters and a cylindrical sp2 bonding structure. Depending on the winding angle and structure of the graphite sheets, the carbon nanotubes may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode, and improving the conductivity of the negative electrode.

[0074] In one embodiment of the present application, the negative electrode conductive material may be included in an amount of 10 parts by weight to 40 parts by weight based on 100 parts by weight of the negative electrode active material layer composition.

[0075] In yet another embodiment, the negative electrode conductive material may be included in an amount of 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 10 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0076] The negative electrode conductive material according to the present application has a structure that is completely different from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact point between the silicon-based active material, which experiences a very large volume expansion in the electrode upon charge and discharge, while the positive electrode conductive material serves as a buffer that has a shock-absorbing function during rolling and also serves to impart partial conductivity, and therefore has a structure and role that are completely different from the negative electrode conductive material of the present invention.

[0077] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and their structure and role are completely different from those of negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0078] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a 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 that is processed into a spherical or dot-like shape to facilitate the storage and release of lithium ions.

[0079] Meanwhile, 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. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but rather a material for ensuring a planar conductive path within the negative electrode active material layer.

[0080] That is, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material to ensure a conductive path, rather than to store or release lithium. In this case, the negative electrode active material included therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0081] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dotted or spherical shape and is used as a material that serves to store or release lithium.

[0082] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is dot-like and has a BET specific surface area of ​​0.1 m 2 / g or more 4.5m 2 The plate-shaped graphite, which is a planar conductive material, may have a planar BET specific surface area of ​​5 m 2 / g or more.

[0083] 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0084] The negative electrode binder according to one embodiment of the present application serves to hold down the active material and conductive material to prevent twisting and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. As long as it fulfills this role, any common binder can be used, specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used. A thickener can be included together with the binder, specifically, CMC can be used as the thickener.

[0085] In one embodiment of the present application, the electrolyte-dissolving layer refers to a coating layer having a property of being soluble in an electrolyte, and can be expressed as a coating layer containing an electrolyte-dissolving layer composition.

[0086] As described above, when prelithiating the negative electrode according to the present invention, the electrolyte dissolving layer prevents prelithiation from occurring immediately even when lithium metal is transferred to the top of the negative electrode during the negative electrode manufacturing process. Instead, after the subsequent battery assembly and injection of the electrolyte, the negative electrode prelithiation process can be carried out, thereby reducing lithium loss.

[0087] In one embodiment of the present application, the thickness of the electrolyte solution dissolving layer may be in the range of 0.1 μm or more and 5 μm or less.

[0088] In another embodiment, the thickness of the electrolyte solution-dissolving layer may be in the range of 0.1 μm or more and 5 μm or less, preferably 0.2 μm or more and 3 μm or less, preferably 0.2 μm or more and 2 μm or less, more preferably 0.2 μm or more and 1 μm or less, and most preferably 0.2 μm or more and 0.5 μm or less.

[0089] The electrolyte solution dissolving layer according to the present application has the above thickness range, which minimizes lithium loss and allows lithium to be uniformly pre-lithiated within the negative electrode active material layer. That is, if the thickness of the electrolyte solution dissolving layer exceeds the above range, the rate at which the electrolyte solution dissolving layer dissolves in the electrolyte significantly decreases, and during that time, lithium metal is not uniformly pre-lithiated within the negative electrode active material layer. Instead, lithium metal dissolves in the electrolyte, resulting in increased lithium loss. Furthermore, if the thickness is below the above range, pre-lithiation occurs at the top of the negative electrode active material layer before the electrolyte solution dissolving layer is impregnated with the electrolyte, which may result in phenomena such as the generation of by-products due to a rapid reaction between the lithium metal and the negative electrode and cracking of the negative electrode active material on the surface of the negative electrode active material layer.

[0090] In one embodiment of the present application, the electrolyte solution-dissolving layer may contain a binder copolymer containing a monomer containing a fluoro group.

[0091] The electrolyte-dissolving layer including a binder copolymer containing a monomer containing a fluoro group may be the same as including an electrolyte-dissolving layer composition including a binder copolymer containing a monomer containing a fluoro group.

[0092] In one embodiment of the present application, the weight average molecular weight of the binder copolymer may be in the range of 1,000 g / mol to 10,000,000 g / mol, specifically, in the range of 10,000 g / mol to 5,000,000 g / mol.

[0093] In one embodiment of the present application, the binder copolymer may comprise at least one various copolymer selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid.

[0094] In this case, one embodiment of the present application is characterized in that the binder copolymer contains a monomer containing a fluoro group.

[0095] In one embodiment of the present application, the binder copolymer containing a monomer containing a fluoro group may mean that the monomer unit containing the fluoro group may be contained in the copolymer as a monomer unit in the form of random, alternating, or block.

[0096] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the monomer comprises a perfluoroolefin.

[0097] The fluoro-group-containing monomer may include C2-C8 fluoroolefins or perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, and hexafluoroisobutylene.

[0098] Specifically, in one embodiment of the present application, the monomer containing a fluoro group may be hexafluoropropylene (HFP).

[0099] In particular, the binder copolymer according to the present application may contain 5 to 20 parts by weight of the monomer based on 100 parts by weight of the binder copolymer.

[0100] In another embodiment, the binder copolymer may contain 5 to 20 parts by weight, preferably 8 to 15 parts by weight, of the monomer based on 100 parts by weight of the binder copolymer.

[0101] The content of the monomer based on the binder copolymer may refer to the content of the monomer based on the total binder copolymer formed by the reaction of two or more monomers with each other.

[0102] The electrolyte solution dissolving layer according to the present application has the above-described composition, which allows for an appropriate prelithiation rate for lithium metal during subsequent prelithiation, suppresses side reaction generation, and prevents cracking of negative electrode active material particles. That is, if the monomer content is less than the above-described range, the prelithiation rate becomes significantly faster, causing many side reactions on the active material layer surface and increasing lithium loss. If the content exceeds the above-described range, the surface of the electrolyte solution dissolving layer becomes brittle, which may reduce the lithium migration rate during prelithiation and increase lithium loss.

[0103] In one embodiment of the present application, the binder copolymer may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP).

[0104] In one embodiment of the present application, the electrolyte-dissolving layer further comprises an acrylic polymer, and the electrolyte-dissolving layer comprises 1 part by weight to 20 parts by weight of the binder copolymer based on 100 parts by weight of the electrolyte-dissolving layer.

[0105] In one embodiment of the present application, the acrylic polymer is an acrylic polymer that can be dissolved in an electrolyte solution and may include at least one polymer selected from the group consisting of polymethyl methacrylate (PMMA), polycarbonate, and polystyrene.

[0106] In particular, the acrylic polymer according to the present application may include a polymer that is insoluble in water and easily soluble in the electrolyte solution contained therein.

[0107] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, the method including: forming a negative electrode active material layer on one or both sides of a negative electrode current collector layer and the negative electrode current collector layer; coating an electrolyte dissolving layer composition on a side of the negative electrode active material layer opposite to the side that contacts the negative electrode current collector layer, to form a negative electrode for a lithium secondary battery, the negative electrode active material layer including an electrolyte dissolving layer; transferring lithium metal to the side of the electrolyte dissolving layer opposite to the side that contacts the negative electrode active material layer; forming a positive electrode active material layer on one or both sides of a positive electrode current collector layer and the positive electrode current collector layer, to form a positive electrode for a lithium secondary battery; laminating the negative electrode and the positive electrode with a separator between them, and incorporating the resulting laminate into a battery pouch; and injecting an electrolyte into the battery pouch to prelithiate the negative electrode.

[0108] In one embodiment of the present application, a step of forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer is provided.

[0109] The step is a process of stacking a lithium secondary battery, and the step of forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer may include coating one or both surfaces of the negative electrode current collector layer with a negative electrode slurry including a negative electrode active material layer composition, and the negative electrode active material layer composition may include at least one selected from the group consisting of a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0110] In this case, the above-mentioned contents regarding the silicon-based active material, the negative electrode conductive material, and the negative electrode binder can be applied.

[0111] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0112] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0113] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0114] The solid content of the negative electrode slurry may refer to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and may refer to the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

[0115] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is appropriate, and the particle aggregation phenomenon of the negative electrode active material layer composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0116] In one embodiment of the present application, the slurry solvent is not limited to a solvent that can dissolve the negative electrode active material layer composition, and specifically, distilled water can be used.

[0117] The negative electrode according to one embodiment of the present application can be formed by coating and drying the negative electrode slurry on a negative electrode current collector layer.

[0118] The drying step may allow the slurry solvent in the negative electrode slurry to be dried.

[0119] In one embodiment of the present application, a step of forming a negative electrode for a lithium secondary battery including an electrolyte dissolving layer by coating an electrolyte dissolving layer composition on a surface of the negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer may be included.

[0120] The coating of the electrolyte solution dissolving layer may be performed using a coating method commonly used in the art, for example, the coating method may be selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but is not limited thereto.

[0121] In one embodiment of the present application, after coating the electrolyte solution dissolving layer composition, a step of vacuum drying at a temperature of 100°C to 150°C for 5 hours to 10 hours may be included, and an electrolyte solution dissolving layer is formed by the step.

[0122] In one embodiment of the present application, the method may include transferring lithium metal to a surface of the electrolyte dissolving layer opposite to a surface in contact with the negative electrode active material layer.

[0123] Generally, the prelithiation process is a process of chemically or physically prelithiating lithium metal onto the negative electrode, and specifically may proceed through a lithium metal transfer process, a lithium metal powder deposition process, an electrochemical process, or a lithium metal deposition process. The prelithiation process according to the present application may include a lithium metal transfer process.

[0124] The lithium metal transfer process has the advantage that highly reactive lithium metal can be transferred more stably to the top of the negative electrode active material layer. At this time, a process is required that can easily transfer lithium metal from the transfer laminate to the top of the negative electrode active material layer. By forming the electrolyte solution dissolving layer on the top of the negative electrode active material layer according to the present application, the efficiency of the transfer process can also be improved.

[0125] In one embodiment of the present application, there is provided a method for producing a lithium secondary battery, wherein the step of transferring lithium metal to the surface of the electrolyte solution dissolution layer opposite to the surface that contacts the negative electrode active material layer includes the steps of: preparing a transfer laminate including a substrate layer and lithium metal provided on the substrate layer; laminating the transfer laminate on the electrolyte solution dissolution layer so that the surface of the lithium metal opposite to the surface that contacts the substrate layer contacts the surface of the electrolyte solution dissolution layer opposite to the surface that contacts the negative electrode active material layer; and removing the substrate layer.

[0126] In one embodiment of the present application, the deposition method for depositing the lithium metal on the substrate layer may be selected from among, but not limited to, vacuum deposition, chemical vapor deposition (CVD), and physical vapor deposition, and various deposition methods used in the art may be used.

[0127] 1 is a diagram showing a pre-lithiation method for a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, the process shows the steps of preparing a transfer laminate 100 including a substrate layer 10 and lithium metal 20, forming a negative electrode active material layer 30 on a negative electrode current collector layer 40, and laminating the negative electrode 200 for a lithium secondary battery such that the electrolyte solution dissolving layer 35 is in contact with the lithium metal 20, and then removing the substrate layer 10 to transfer only the lithium metal 20 onto the electrolyte solution dissolving layer 35.

[0128] In this case, the negative electrode for a lithium secondary battery having the transfer laminate laminated thereon can be subjected to a transfer process by roll pressing with a load of 10 kgf to 500 kgf applied thereto. A subsequent process of removing the substrate layer is included, and the inclusion of the electrolyte solution dissolving layer according to the present application during removal can prevent direct contact with the silicon-based active material, thereby allowing for easy transfer of lithium metal.

[0129] The reason for this is that in the case of a conventional battery without an electrolyte dissolving layer, lithium metal comes into direct contact with the top of the negative electrode active material layer, generating a large number of by-products such as Li nitride, which makes it difficult to transfer to the negative electrode active material layer, resulting in detachment of lithium metal. However, the inclusion of a metal layer satisfying the thickness and composition of the present application solves this problem.

[0130] In one embodiment of the present application, the substrate layer may be any material that can withstand process conditions such as high temperatures in the step of depositing lithium metal and that can prevent a reverse peeling problem in which lithium metal is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal.

[0131] Specifically, in one embodiment of the present application, the base layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0132] In one embodiment of the present application, the thickness of the substrate layer may be in the range of 1 μm or more and 300 μm or less, 5 μm or more and 200 μm or less, or 10 μm or more and 100 μm or less.

[0133] In one embodiment of the present application, the thickness of the lithium metal may be 1 μm or more and 10 μm or less, and preferably 3 μm or more and 10 μm or less.

[0134] When the thicknesses of the substrate layer and the lithium metal satisfy the above ranges, the lithium metal can be efficiently transferred to the negative electrode active material layer side, and reverse transfer can be prevented.

[0135] In one embodiment of the present application, in order to improve the releasability of the lithium metal and ensure its transferability to the negative electrode active material layer, the transfer laminate may further include a release layer on the surface where the base material layer and the lithium metal come into contact.

[0136] That is, the substrate layer may have a release layer formed on at least one surface thereof, or may have release layers formed on both surfaces thereof. The release layer can prevent reverse peeling, in which lithium metal is transferred to the substrate layer during a winding process for transferring the deposited lithium metal to the negative electrode, and can also facilitate separation of the substrate layer after the lithium metal is transferred to the negative electrode active material layer.

[0137] The release layer may contain at least one selected from the group consisting of silicon-modified polyester in which silicon chains are graft-bonded to a polyester main chain, Si, melamine, and fluorine.

[0138] In one embodiment of the present application, the release layer may be formed by a coating method. For example, the coating method may be a method 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 various coating methods known in the art for forming a coating layer may be used.

[0139] In one embodiment of the present application, even after the step of depositing and transferring the lithium metal onto the metal layer, the electrolyte dissolving layer may prevent direct contact with the negative electrode active material layer, thereby delaying the progress of the pre-lithiation process.

[0140] In one embodiment of the present invention, the method may include 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 to form a positive electrode for a lithium secondary battery; laminating the negative electrode and the positive electrode with a separator between them, and incorporating the resulting laminate into a battery pouch.

[0141] The positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0142] The positive electrode current collector layer in the positive electrode is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector layer may typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector layer to enhance the adhesive strength of the positive electrode active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0143] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.6 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0144] In one embodiment of the present application, the positive electrode active material includes a lithium transition metal composite compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium transition metal composite compound may include single particles or secondary particles, and the single particles may have an average particle size (D50) of 1 μm or more.

[0145] For example, the average particle size (D50) of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 12 μm or less, more than 1 μm and 8 μm or less, or 1 μm or 6 μm or less.

[0146] The single particles can have excellent particle strength even when they are formed with a small particle size (D50) of 1 μm or more and 12 μm or less. For example, the single particles can have a strength of 650 kgf / cm 2 This allows the single particles to have a particle strength of 100 to 300 MPa when rolled with a force of 650 kgf / cm. 2 Even if the electrode is rolled with a strong force, the phenomenon of an increase in fine particles in the electrode due to cracking of particles is alleviated, thereby improving the life characteristics of the battery.

[0147] The single particles may be prepared by mixing a transition metal precursor and a lithium source material and calcining the mixture. The secondary particles may be prepared by a method different from that for the single particles, and the composition thereof may be the same as or different from that of the single particles.

[0148] The method for forming the single particles is not particularly limited, but generally, the particles can be formed by over-firing at an elevated firing temperature, and can be prepared by using additives such as grain growth promoters that are useful for over-firing, or by changing the starting material.

[0149] For example, the calcination is performed at a temperature sufficient to form single particles. To achieve this, the calcination must be performed at a temperature higher than that used for producing secondary particles. For example, when the precursor composition is the same, the calcination temperature should be approximately 30°C to 100°C higher than that used for producing secondary particles. The calcination temperature for forming the single particles may vary depending on the metal composition of the precursor. For example, when forming a high-nickel (Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more as single particles, the calcination temperature may be approximately 700°C to 1000°C, preferably 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. If the calcination temperature is lower than 790°C, a positive electrode active material containing a lithium composite transition metal compound in the form of secondary particles may be produced. However, if the calcination temperature exceeds 950°C, excessive calcination may occur, resulting in an improper formation of a layered crystal structure and reduced electrochemical properties.

[0150] In this specification, the term "single particle" is used to distinguish it from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and a pseudo-single particle form that is an agglomeration of 30 or less primary particles.

[0151] Specifically, the single particle in the present invention may be in the form of a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0152] In one embodiment of the present application, the lithium transition metal composite compound serving as the positive electrode active material further includes secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0153] In the present invention, the single particle may be in the form of a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0154] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by aggregation of primary particles, and can be distinguished from the concept of single particles, which includes one primary particle, one single particle, or a quasi-single particle form that is an aggregation of 30 or less primary particles.

[0155] The particle diameter (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g~10m 2 / g, preferably 0.1m 2 / g~1m 2 / g, and more preferably 0.3m 2 / g~0.8m 2 / g.

[0156] In a further embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0157] When the average particle size (D50) of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially reducing output characteristics.

[0158] According to a further embodiment of the present invention, the average particle size (D50) of the single particles is smaller than the average particle size D50 of the secondary particles. As a result, the single particles can have excellent particle strength even when formed with a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, thereby improving the life characteristics of the battery.

[0159] In one embodiment of the present application, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles by 1 μm to 18 μm.

[0160] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0161] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when the above range is satisfied, the single particles can have excellent particle strength even though they are formed with a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and thereby improving the battery life characteristics and energy density.

[0162] According to a further embodiment of the present application, the single particles are contained in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, or may be contained in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0163] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. The single particles may be included in an amount of 100 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0164] When the single particles are contained in the above range, excellent battery characteristics can be exhibited in combination with the above-mentioned negative electrode material. In particular, when the single particles are contained in an amount of 15 parts by weight or more, the increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication is mitigated, thereby improving the battery life characteristics.

[0165] In one embodiment of the present application, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0166] When the above range is satisfied, the above-described effects due to the presence of the single particle positive electrode active material can be maximized. When the secondary particle positive electrode active material is included, the components thereof may be the same as or different from those exemplified for the single particle positive electrode active material, and may refer to an aggregated form of single particles.

[0167] In one embodiment of the present application, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, in 100 parts by weight of the positive electrode active material layer.

[0168] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0169] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0170] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0171] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable for the separator to have low resistance to electrolyte ion movement and excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and it can be used in either a single-layer or multi-layer structure.

[0172] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, the method comprising the step of prelithiating the negative electrode by introducing an electrolyte into the battery pouch.

[0173] As described above, when the electrolyte is poured into the battery pouch, the electrolyte dissolving layer begins to dissolve in the electrolyte, thereby allowing prelithiation to proceed.

[0174] In one embodiment of the present application, the step of prelithiating the negative electrode by injecting an electrolyte into the battery pouch is carried out under a temperature condition of 60°C to 80°C and a pressure of 5 kgf / cm 2 ~20kgf / cm 2 The present invention provides a method for producing a lithium secondary battery in which the battery is prelithiated under a pressurized condition of

[0175] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, wherein the pre-lithiation completion time in the step of pre-lithiating the negative electrode by introducing an electrolyte solution into the battery pouch is 6 hours or more and 24 hours or less.

[0176] That is, the prelithiation according to the present application is not carried out in air simultaneously with the manufacture of a negative electrode for a lithium secondary battery and lithium metal transfer, but is carried out in a sealed secondary battery. Since the prelithiation rate is slower than in air, it is possible to suppress the generation of by-products and achieve more uniform prelithiation.

[0177] In one embodiment of the present application, there is provided a lithium secondary battery manufactured by the method for manufacturing a lithium secondary battery.

[0178] In one embodiment of the present application, the lithium secondary battery may include a positive electrode for a lithium secondary battery; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0179] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 200 including an anode active material layer 30 on one side of an anode current collector layer 40 can be seen, and a lithium secondary battery cathode 300 including a cathode active material layer 70 on one side of a cathode current collector layer 60 can be seen, and the lithium secondary battery anode 200 and lithium secondary battery cathode 100 are stacked with a separator 50 sandwiched between them.

[0180] In this case, the electrolyte dissolution layer used during the pre-lithiation can be completely removed depending on the electrolyte used, and therefore does not remain on the top of the negative electrode, thereby preventing an unnecessary increase in resistance.

[0181] In one embodiment of the present application, the electrolytic solution may be an organic liquid electrolytic solution, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolytic solution, a solid inorganic electrolytic solution, or a molten inorganic electrolytic solution that can be used in manufacturing a lithium secondary battery, but is not limited to these.

[0182] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0183] Examples of the non-aqueous organic solvent that may be used include 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0184] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore, these cyclic carbonates are more preferably used.

[0185] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -, CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0186] In addition to the components of the electrolyte solution, the electrolyte solution 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, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0187] According to one embodiment of the present invention, there is provided 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 a secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and 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. [Example]

[0188] Below, preferred examples are presented to help understand the present invention, but these examples are for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0189] Example 1 [Production of negative electrode] A negative electrode slurry was prepared by adding 81 wt % of Si as a negative electrode active material, 9.1 wt % of Denka Black as a conductive material, 9.3 wt % of SBR as a binder, and 0.6 wt % of CMC as a thickener to water.

[0190] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 15 μm), dried in a vacuum oven at 130°C for 12 hours, and roll-pressed to produce a negative electrode coated with a negative electrode active material layer on both sides. The negative electrode was then wound into a separate roll. A 0.5 μm-thick electrolyte solution layer containing 15% PVDF-HFP (100 parts by weight of binder copolymer and 15 parts by weight of fluoro-group-containing monomer) as a binder copolymer was coated on the negative electrode active material layer, and then dried at 80°C.

[0191] A pre-lithiation device was prepared for the negative electrode produced above. Specifically, the pressure of the roll press was set to 100 kgf, the roll temperature was set to 80°C, and the electrode was rolled at a speed of 1 m / min. The electrodes were placed in the following order: PET substrate / Li metal / negative electrode / Li metal / PET substrate, with the Li metal facing both sides of the negative electrode.

[0192] The PET substrate was then immediately removed.

[0193] [Manufacturing of lithium secondary batteries] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the cathode slurry to prepare a cathode slurry (solid concentration: 78 wt%).

[0194] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at a rate of 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to prepare a positive electrode (thickness: 77 μm, porosity: 26%).

[0195] An electrolyte was injected between the positive electrode and the negative electrode of Example 1 via a polyethylene separator, to prepare the secondary battery of Example 1.

[0196] Prelithiation of the Negative Electrode After the electrolyte was injected, prelithiation was carried out in a low dew point dry room at -50°C until all the Li metal disappeared.

[0197] <Example 2> The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte-dissolving layer was formed using a binder copolymer of 8% PVDF-HFP (containing 8 parts by weight of a monomer containing a fluoro group per 100 parts by weight of the binder copolymer) to a thickness of 0.5 μm.

[0198] Example 3 The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte dissolving layer was coated to a thickness of 0.2 μm.

[0199] Example 4 The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte-dissolving layer was formed using a binder copolymer of PMMA:PVDF-HFP 8% (containing 8 parts by weight of a fluoro group-containing monomer per 100 parts by weight of the binder copolymer) = 15:85, coated to a thickness of 0.5 μm.

[0200] <Example 5> The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte dissolving layer was coated to a thickness of 2.5 μm.

[0201] Example 6 The same preparation and pre-lithiation process as in Example 1 were carried out, except that the electrolyte dissolving layer in Example 2 was coated to a thickness of 2.5 μm.

[0202] <Comparative Example 1> A negative electrode was prepared in the same manner as in Example 1, except that a negative electrode without an electrolyte dissolving layer was prepared and rolled at room temperature (25°C). Then, a pre-lithiation process was carried out.

[0203] <Comparative Example 2> The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte dissolving layer was coated to a thickness of 10 μm.

[0204] <Comparative Example 3> The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte-dissolving layer was formed using a binder copolymer of 30% PVDF-HFP (containing 30 parts by weight of a fluoro group-containing monomer per 100 parts by weight of the binder copolymer) to a thickness of 0.5 μm.

[0205] <Comparative Example 4> The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte-dissolving layer was formed using a binder copolymer of 3% PVDF-HFP (containing 3 parts by weight of a fluoro group-containing monomer per 100 parts by weight of the binder copolymer) to a thickness of 0.5 μm.

[0206] <Comparative Example 5> The same preparation and pre-lithiation process were carried out as in Example 1, except that the electrolyte-dissolving layer was formed using PMMA as the binder copolymer to a thickness of 0.5 μm.

[0207] The configuration of the electrolyte dissolving layer, the thickness of the electrolyte dissolving layer, the rolling temperature, the electrode ICE deviation (%), and the Li metal loss (%) of Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Table 1 below.

[0208] [Table 1]

[0209] In Table 1, the electrode ICE deviation (%) can be calculated by (initial discharge capacity / initial charge capacity) × 100 (%), and the Li metal loss (%) can be calculated by 1 - (measured initial charge capacity / lithium capacity used during pre-lithiation) × 100 (%).

[0210] As can be seen from Table 1, the negative electrodes for lithium secondary batteries of Examples 1 to 6 comprise an electrolyte solution-dissolving layer on top of a negative electrode active material layer, the electrolyte solution-dissolving layer having a thickness of 0.1 μm to 5 μm and including a binder copolymer containing a fluoro group-containing monomer, and the electrolyte solution-dissolving layer is composed of 5 to 20 parts by weight of the monomer per 100 parts by weight of the binder copolymer. The inclusion of the electrolyte solution-dissolving layer prevents prelithiation even when lithium metal is transferred onto the negative electrode active material layer. Furthermore, it was confirmed that the electrolyte solution-dissolving layer is dissolved in the electrolyte and prelithiated when the battery is later assembled and sealed.

[0211] As described above, since the electrolyte solution dissolving layer dissolves in the electrolyte and undergoes prelithiation, the amount of by-reaction products with lithium may be reduced and the loss of lithium metal may be reduced compared to when prelithiation occurs simultaneously with the manufacture of the negative electrode. Furthermore, it has been confirmed that the electrolyte solution dissolving layer can also control the rate of prelithiation, preventing lithium loss and enabling uniform prelithiation throughout the negative electrode active material layer.

[0212] Specifically, Comparative Example 1 in Table 1 does not include an electrolyte dissolution layer, and since there is no reaction retardant on the top of the negative electrode, it was confirmed that prelithiation with Li metal proceeded before assembling the lithium secondary battery. As a result, it was confirmed that the prelithiation rate was fast, and prelithiation proceeded in air, generating a lot of heat and forming by-products, resulting in electrode ICE deviation and a large amount of Li metal loss.

[0213] Comparative Example 2 in Table 1 includes an electrolyte dissolving layer, but its thickness exceeds the upper limit (10 μm). Because the electrolyte dissolving layer is too thick, the rate at which the coating layer dissolves in the electrolyte is significantly reduced. During this time, the coating is not uniformly pre-lithiated, and instead, lithium metal dissolves in the electrolyte, resulting in electrode ICE deviation and significant loss of lithium metal.

[0214] In addition, in the case of Comparative Example 3, the binder copolymer used in the preparation of the electrolyte solution-dissolving layer was 30% PVDF-HFP (containing 30 parts by weight of a monomer containing a fluoro group per 100 parts by weight of the binder copolymer). Since the amount of the monomer containing a fluoro group was large, the surface of the electrolyte solution-dissolving layer was unstable, the lithium migration rate during prelithiation was reduced, and the amount of lithium loss was very large.

[0215] In the case of Comparative Example 4, when the electrolyte dissolving layer was manufactured, the binder copolymer had a composition of 3% PVDF-HFP (containing 3 parts by weight of a monomer containing a fluoro group per 100 parts by weight of the binder copolymer), and since the amount of the monomer containing a fluoro group was small, it was confirmed that the amount of lithium loss was large, similar to Comparative Example 3.

[0216] Finally, Comparative Example 5 in Table 1 contains an acrylic polymer alone, rather than the electrolyte solution dissolving layer composition of the present invention. Although the electrolyte dissolves when the electrolyte is introduced, the dissolution is not uniform. Therefore, lithium is not uniformly pre-lithiated throughout, resulting in a large amount of lithium loss.

[0217] For reference, Examples 5 and 6 correspond to cases in which the electrolyte dissolving layer is thicker than Examples 1 to 4. In these cases, it can be seen that the amount of lithium loss is lower than in Comparative Examples 1 to 5, but the electrode ICE deviation and Li metal loss rate are higher than in Examples 1 to 4. This is because the thicker the electrolyte dissolving layer, the slower the rate at which lithium dissolves in the electrolyte. During this time, lithium metal is not uniformly pre-lithiated within the negative electrode active material layer, but rather dissolves in the electrolyte, resulting in increased lithium loss. In other words, it was confirmed that the thickness of the electrolyte dissolving layer according to the present application is most effective when it is between 0.2 μm and 2 μm. [Explanation of symbols]

[0218] 10...Base material layer 20 Lithium metal 30...Negative electrode active material layer 35...electrolyte dissolved layer 40 Negative electrode current collector layer 50...Separation membrane 60 Positive electrode current collector layer 70...Cathode active material layer 100 Transfer laminate 200 ···Anode for lithium secondary battery 300 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode for a lithium secondary battery for producing a lithium secondary battery containing an electrolyte solution, comprising: The negative electrode for the lithium secondary battery is a negative electrode current collector layer; a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer; and a coating layer provided on the surface of the negative electrode active material layer opposite to the surface that comes into contact with the negative electrode current collector layer; Including, the negative electrode active material layer includes a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and a Si alloy; The thickness of the coating layer is 0.1 μm or more and 5 μm or less, the coating layer is made of a binder copolymer containing a monomer having a fluoro group, or made of a binder copolymer containing a monomer having a fluoro group and an acrylic polymer; the monomer comprises a perfluoroolefin, The binder copolymer contains 5 to 20 parts by weight of the monomer based on 100 parts by weight of the binder copolymer, The coating layer contains 85 to 100 parts by weight of the binder copolymer based on 100 parts by weight of the coating layer, The coating layer is completely dissolved in the electrolyte solution.

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material comprises at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the silicon-based active material comprises 70 parts by weight or more of the SiOx (x=0) per 100 parts by weight of the silicon-based active material.

3. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

4. forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer; forming a negative electrode for a lithium secondary battery including a coating layer by coating a coating layer composition on a surface of the negative electrode active material layer opposite to a surface thereof in contact with the negative electrode current collector layer; transferring lithium metal to a surface of the coating layer opposite to a surface that contacts the negative electrode active material layer; 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 to form a positive electrode for a lithium secondary battery; a separator between the negative electrode and the positive electrode, laminating the resulting laminate, and placing the laminate in a battery pouch; and pouring an electrolyte solution into the battery pouch to dissolve the coating layer in the electrolyte solution and prelithiate the negative electrode; Including, The thickness of the coating layer is 0.1 μm or more and 5 μm or less, the coating layer is made of a binder copolymer containing a monomer having a fluoro group, or made of a binder copolymer containing a monomer having a fluoro group and an acrylic polymer; the monomer comprises a perfluoroolefin, The content of the monomer is 5 to 20 parts by weight based on 100 parts by weight of the binder copolymer, The method for manufacturing a lithium secondary battery includes the binder copolymer in an amount of 85 parts by weight to 100 parts by weight based on 100 parts by weight of the coating layer.

5. The step of prelithiating the negative electrode by injecting an electrolyte into the battery pouch is carried out under a temperature condition of 60° C. to 80° C. and a pressure of 5 kgf / cm ２ ~20 kgf / cm ２ 5. The method for producing a lithium secondary battery according to claim 4, wherein the prelithiation is carried out under a pressurized condition of 1000 .mu.m.sup.-1000 .mu.m.sup.

6. 5. The method of claim 4, wherein the time required for completing pre-lithiation in the step of pre-lithiating the negative electrode by introducing an electrolyte into the battery pouch is 6 hours or more and 24 hours or less.

7. The step of transferring lithium metal to a surface of the coating layer opposite to a surface contacting the negative electrode active material layer includes: providing a transfer laminate including a substrate layer and lithium metal disposed on the substrate layer; laminating the transfer laminate on the coating layer such that the surface of the lithium metal opposite to the surface in contact with the substrate layer is in contact with the surface of the coating layer opposite to the surface in contact with the negative electrode active material layer; and removing the substrate layer; The method for producing the lithium secondary battery according to claim 4, comprising:

8. The method for producing a lithium secondary battery according to claim 7 , further comprising a release layer on a surface of the transfer laminate in contact with the base layer and the lithium metal.

9. The method for producing a lithium secondary battery according to claim 4 , wherein the thickness of the lithium metal is 1 μm or more and 10 μm or less.

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