Negative electrode for lithium secondary battery, method for manufacturing a negative electrode for lithium secondary battery, and lithium secondary battery including a negative electrode

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same. The negative electrode includes a negative electrode current collector layer, a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, and a ceramic layer provided on the opposite side of the silicon-based negative electrode active material layer that contacts the negative electrode current collector layer, the ceramic layer including a ceramic layer composition or a dried product thereof, the ceramic layer having a thickness of 0.5 μm to 3 μm, the ceramic layer composition including a ceramic and an organic binder, the ceramic being included in an amount of 80 parts by weight to 95 parts by weight and the organic binder being included in an amount of 5 parts by weight to 20 parts by weight, based on 100 parts by weight of the ceramic layer composition.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0054788, filed with the Korean Intellectual Property Office on May 3, 2022, and all of its content is incorporated herein.

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

Background Art

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

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage areas are increasingly expanding.

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

[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 desorbs lithium ions emitted from the positive electrode, and silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In recent years, in response to the demand for high-density energy batteries, research has been actively conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials and have superior capacity characteristics compared to conventionally used graphite, they rapidly expand in volume during the charging process, disrupting the conductive path and degrading battery performance, resulting in a decrease in capacity from the start. Furthermore, with silicon-based negative electrodes, uniform charging of lithium ions does not occur in the depth direction of the negative electrode during repeated charge and discharge cycles, and the reaction proceeds at the surface, accelerating surface degradation. Therefore, performance improvements are needed in terms of battery cycles.

[0008] Therefore, in order to resolve the aforementioned problems when using silicon-based compounds as negative electrode active materials, various methods are being discussed, such as methods to suppress volume expansion itself, including methods to adjust the driving potential, methods to further coat a thin film on the active material layer, and methods to adjust the particle size of the silicon-based compound, or the development of binders that suppress the volume expansion of silicon-based compounds to prevent the conduction path from being interrupted. Research is also underway to complement the lifetime characteristics of silicon-based negative electrodes by limiting the proportion of silicon-based active material used during initial charging and discharging through a method of pre-lithifying the silicon-based active material layer, thereby giving it the role of a reservoir.

[0009] However, the aforementioned method can actually degrade battery performance, limiting its applicability. There are still limitations to the commercialization of negative electrode batteries with a high silicon compound content. In particular, as the proportion of silicon-based active material in the silicon-based active material layer increases, prelithiation concentrates on the negative electrode surface, causing damage to the silicon-based active material on the surface and resulting in uneven prelithiation, which poses a problem in improving lifespan characteristics.

[0010] Therefore, even when silicon-based compounds are used as the active material, it is possible to prevent degradation of the electrode surface during the progression of charge and discharge cycles, improve uniformity during pre-lithiation, and conduct research to improve the cycle performance along with the capacity characteristics of lithium secondary batteries. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0012] This application relates to a negative electrode for a lithium secondary battery, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode, which can prevent the deterioration of the electrode surface during the progression of charge and discharge cycles, a conventional problem, even when using a silicon-based active material as the negative electrode, and in particular can improve the uniformity during pre-lithification, thereby improving the cycle performance along with the capacity characteristics of the lithium secondary battery. [Means for solving the problem]

[0013] One embodiment of this specification provides a negative electrode for a lithium secondary battery comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the side of the silicon-based negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer; wherein the ceramic layer comprises a ceramic layer composition or a dried product thereof, the thickness of the ceramic layer is 0.5 μm or more and 3 μm or less, and the ceramic layer composition comprises a ceramic and an organic binder, wherein, based on 100 parts by weight of the ceramic layer composition, the ceramic is included in an amount of 80 parts by weight or more and 95 parts by weight or less, and the organic binder is included in an amount of 5 parts by weight or more and 20 parts by weight or less.

[0014] In another embodiment, a method for manufacturing a negative electrode for a lithium secondary battery is provided, comprising the steps of: preparing a negative electrode current collector layer; applying a negative electrode active material layer composition to one or both sides of the negative electrode current collector layer to form a negative electrode active material layer; and applying a ceramic layer composition to the side of the negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer to form a ceramic layer, wherein the thickness of the ceramic layer is 0.5 μm or more and 3 μm or less, and the ceramic layer composition comprises a ceramic, an organic binder, and an organic solvent, wherein, based on 100 parts by weight of the ceramic layer composition, the ceramic is included in an amount of 80 parts by weight or more and 95 parts by weight or less, and the organic binder is included in an amount of 5 parts by weight or more and 20 parts by weight or less.

[0015] Finally, the present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0016] A negative electrode for a lithium secondary battery according to one embodiment of the present invention is characterized by having a silicon-based negative electrode active material layer and including a ceramic layer having a specific composition and thickness on top of the silicon-based negative electrode active material layer. The negative electrode according to this application has excellent capacity characteristics and excellent rapid charging capability by using a silicon-based negative electrode.

[0017] However, the aforementioned volume expansion problem caused by using a silicon-based negative electrode can be solved by processes such as pre-lithiation, but in particular, the reaction between silicon and lithium layers during the pre-lithiation process is too fast, leading to a fire problem. However, the negative electrode for lithium secondary batteries according to this application uses a silicon-based active material and includes a ceramic layer of a specific thickness and composition on top of the negative electrode active material layer, thereby stabilizing the process speed during pre-lithiation, and thus significantly increasing the stability during the pre-lithiation process.

[0018] In other words, by reducing the contact points between the silicon-based anode and the lithium metal, as described above, the uniformity of charging and discharging of the silicon-based anode can be increased, thereby improving its performance.

[0019] Furthermore, by having a ceramic layer on top of the silicon-based negative electrode active material layer, the ceramic layer formed on the separation membrane can be eliminated or minimized, reducing the thickness of the separation membrane's raw material, thus offering advantages in terms of process and cost.

[0020] In other words, the negative electrode for lithium secondary batteries according to this application has the advantages of an electrode that uses a single layer of active material with a high content of Si particles, and is characterized by the introduction of a ceramic layer having a specific thickness and composition in order to solve the problems of surface degradation, uniformity during pre-lithiation, and life characteristics that are disadvantages of such electrodes. [Brief explanation of the drawing]

[0021] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0022] Before describing the present invention, let us first define some terms.

[0023] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0024] In this specification, "p~q" means the range "p or greater and q or less".

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

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

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

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

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

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

[0031] One embodiment of this specification provides a negative electrode for a lithium secondary battery comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the side of the silicon-based negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer; wherein the ceramic layer comprises a ceramic layer composition or a dried product thereof, the thickness of the ceramic layer is 0.5 μm or more and 3 μm or less, and the ceramic layer composition comprises a ceramic and an organic binder, wherein, based on 100 parts by weight of the ceramic layer composition, the ceramic is included in an amount of 80 parts by weight or more and 95 parts by weight or less, and the organic binder is included in an amount of 5 parts by weight or more and 20 parts by weight or less.

[0032] The negative electrode for lithium secondary batteries according to this application has the advantages of an electrode that uses a high content of Si particles as a single layer active material, and is characterized by the introduction of a ceramic layer having a specific thickness and composition in order to solve the problems of surface degradation, uniformity during pre-lithiation, and life characteristics that are disadvantages of such electrodes.

[0033] Figure 1 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 and a ceramic layer 10 on one surface of a negative electrode current collector layer 30. Figure 1 shows that the negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer.

[0034] The negative electrode for lithium secondary batteries of the present invention will be described in more detail below.

[0035] The present invention provides a negative electrode for a lithium secondary battery comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the side of the silicon-based negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer.

[0036] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. Furthermore, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric.

[0037] In one embodiment of this application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less.

[0038] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0039] In one embodiment of the present application, the silicon-based negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition provides a negative electrode for a lithium secondary battery including at least one selected from the group consisting of a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0040] In one embodiment of the present application, the silicon-based active material may include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0041] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and metal impurities, and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0042] In another embodiment, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0043] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0044] In one embodiment of the present application, in particular, pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean that, as described above, when based on 100 parts by weight in total of the silicon-based active material, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are included within the above range.

[0045] In one embodiment of this application, the silicon-based active material may consist of SiOx (x=0).

[0046] In the case of silicon-based active materials, the capacity is significantly higher compared to conventionally used graphite-based active materials, and attempts to apply them are increasing. However, the volume expansion rate during the charge-discharge process is high, so their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0047] The negative electrode active material layer according to this application contains a silicon-based active material, specifically containing pure silicon particles with 70 parts by weight or more of SiOx (x=0). In this case, when pure silicon particles are included in a high content, the capacity characteristics are excellent, and in order to solve the problem of reduced lifespan due to surface non-uniform reaction caused by this, the ceramic layer according to the present invention is included, thereby solving the aforementioned problem.

[0048] On the other hand, the average particle size (D50) of the silicon-based active material in the present invention is 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. If the average particle size is less than 5 μm, the specific surface area of ​​the particles increases excessively, and the viscosity of the negative electrode slurry increases excessively. As a result, the dispersion of the particles constituting the negative electrode slurry is not smooth. Also, if the size of the silicon-based active material is too small, the contact area between the silicon particles and the conductive material decreases due to the composite of the conductive material and binder in the negative electrode slurry, increasing the possibility of the conductive network being interrupted and reducing the capacity retention rate. On the other hand, if the average particle size exceeds 10 μm, there are silicon particles that are too large, and the surface of the negative electrode does not become smooth, resulting in non-uniform current density during charging and discharging. Also, if the silicon particles are excessively large, the phase stability of the negative electrode slurry becomes unstable, reducing processability. As a result, the capacity retention rate of the battery decreases.

[0049] In one embodiment of this application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m². 2 / g~150.0m 2 / g, more comfortably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

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

[0051] In one embodiment of this application, the present invention provides a negative electrode composition in which the silicon-based active material is 70 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0052] In another embodiment, the silicon-based active material may be present in an amount of 70 parts by weight or more, preferably 75 parts by weight or more, more preferably 80 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be present in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0053] The negative electrode active material layer composition according to this application solves the problems of surface degradation during charging and discharging, uniformity during pre-lithiation, and lifespan characteristics by using a silicon-based active material with significantly high capacity within the aforementioned range, while also using a ceramic layer described later, without reducing the overall capacity performance of the negative electrode. Furthermore, by using a specific conductive material and binder that can suppress the volume expansion rate during the charge and discharge process, the negative electrode performance is not reduced even within the aforementioned range, and it exhibits excellent output characteristics during charging and discharging.

[0054] In one embodiment of the present application, the silicon-based active material can have a non-spherical shape, and its sphericity can be, 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 the present application, the circularity is determined by the following formula 1, where A is the area and P is the boundary line. [Formula 1] 4πA / P 2

[0056] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, in recent years, as the demand for high-capacity batteries has increased, attempts to use a silicon-based active material in combination to increase the capacity have been increasing. However, in the case of a silicon-based active material, even if the characteristics of the silicon-based active material itself are adjusted as described above, there may be a problem that the volume rapidly expands during the charge / discharge process and breaks the conductive path formed in the negative electrode active material layer.

[0057] Therefore, in one embodiment of the present application, the negative electrode active material layer composition provides a negative electrode for a lithium secondary battery including at least one selected from the group consisting of a negative electrode conductive material; and a negative electrode binder.

[0058] In one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-shaped conductive material; a planar conductive material; and a linear conductive material.

[0059] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity to the negative electrode and has conductivity without inducing chemical changes, and means a spherical or point-shaped conductive material. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and may preferably include carbon black in that it embodies high conductivity and has excellent dispersibility.

[0060] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0061] In one embodiment of this application, the point-shaped conductive material may satisfy a functional group content (volatile matter) of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0062] In particular, when the functional group content of the dot conductive material satisfies the above range, functional groups are present on the surface of the dot conductive material, and when water is used as the solvent, the dot conductive material can be smoothly dispersed in the solvent.

[0063] In one embodiment of this application, a silicon-based active material is provided together with a point-type conductive material having a functional group content within the range described above, wherein the functional group content can be adjusted according to the degree of heat treatment of the point-type conductive material.

[0064] In other words, in the fabrication of point-type conductive materials, a high functional group content may mean that there are many foreign substances, while a low functional group content may mean that more heat treatment processing has been performed.

[0065] In one embodiment of this application, the particle size of the dot-like conductive material is 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0066] In one embodiment of this application, the negative electrode conductive material may include a planar conductive material.

[0067] The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. It can be described as a plate-type conductive material or a bulk-type conductive material.

[0068] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0069] In one embodiment of this application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is met, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same apparatus and time, the dispersion effect is excellent.

[0070] In one embodiment of this application, the planar conductive material may have 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.

[0071] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0072] In one embodiment of this application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. In particular, the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0073] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0074] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0075] In another embodiment, the planar conductive material is a high specific surface area planar conductive material with a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0076] In another embodiment, the planar conductive material is a low specific surface area planar conductive material with a BET specific surface area of ​​5 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0077] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in the form of a bundle or rope, in which multiple carbon nanotube units are arranged in substantially the same orientation along their longitudinal axes, or are intertwined. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be determined by the angle and structure in which the graphite sheet is wound. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during anode manufacturing, smoothly form a conductive network within the anode, and improve the conductivity of the anode.

[0078] In one embodiment of this application, the linear conductive material may include SWCNTs or MWCNTs.

[0079] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0080] In another embodiment, the negative electrode conductive material may be included in an amount of 10 to 40 parts by weight, preferably 10 to 30 parts by weight, and more preferably 10 to 25 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0081] In one embodiment of this application, the negative electrode conductive material comprises a planar conductive material and a linear conductive material, wherein the planar conductive material is included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material, to provide a negative electrode for a lithium secondary battery.

[0082] In another embodiment, the planar conductive material may be 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, and more preferably 95 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0083] In another embodiment, the linear conductive material may be 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 10 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0084] In particular, in one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, and by satisfying the above composition and proportion, the number of points where charging and discharging are possible increases without significantly affecting the life characteristics of existing lithium secondary batteries, and the battery has the characteristic of having excellent output characteristics at a high C-rate.

[0085] The negative electrode conductive material of this application has a completely different structure from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application plays the role of capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer that has a cushioning function when rolled, while also imparting some conductivity. Its structure and role are completely different from the negative electrode conductive material of the present invention.

[0086] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. In other words, conductive materials used in electrodes with graphite-based active materials simply have smaller particles compared to the active material, thus improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0087] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material described above has a different structure and role from carbon-based active materials generally used as existing negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form for use in order to facilitate the storage and release of lithium ions.

[0088] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be described as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0089] In other words, the use of plate-shaped graphite as a conductive material in this application means that it was processed into a planar or plate shape and used not to store or release lithium, but as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0090] On the other hand, in this application, the use of a carbon-based active material as an active material means that it was processed into a point-like or spherical shape and used as a material that stores or releases lithium.

[0091] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, is in a point-like form, and has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 It can satisfy the range of less than / g. In addition, plate-type graphite, which is a planar conductive material, is planar and has a BET specific surface area of ​​5m². 2 It may be more than / g.

[0092] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0093] The negative electrode binder according to one embodiment of this application plays a role in suppressing the active material and conductive material in order to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any general binder can be applied as long as it satisfies the above role, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder may be used.

[0094] In one embodiment of this application, the negative electrode binder is 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0095] In particular, the negative electrode binder used in this application is an aqueous binder when using a silicon-based active material with high rigidity. The aqueous binder is a polymer that exhibits very high rigidity after drying. When an aqueous binder is included in the negative electrode active material layer composition of this application, if a ceramic layer made in an aqueous system is coated on top of a silicon-based negative electrode active material layer made in an aqueous system and dried, the surfaces will mix due to the water, resulting in inter-mixing, no matter how quickly it is dried. To solve the above problem, the ceramic layer of this application has the characteristic that, using an organic binder and an organic solvent, the dispersion of ceramic and organic binder can be easily formed without affecting the negative electrode made in an aqueous system, and a very dense coating can be made on the negative electrode active material layer.

[0096] One embodiment of this application includes a ceramic layer provided on the surface of the silicon-based negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer;

[0097] As described above, the negative electrode for lithium secondary batteries according to this application includes a ceramic layer, and by including the negative electrode active material described above, it maintains high capacity and high density characteristics, while solving problems of surface degradation during charging and discharging, uniformity during pre-lithiation, and lifespan characteristics.

[0098] In one embodiment of this application, the ceramic layer may include a ceramic layer composition or a dried product thereof.

[0099] In this context, "containing the ceramic layer composition" can mean that the ceramic layer contains the ceramic layer composition as is. Furthermore, "containing the dried ceramic layer composition" can mean that all organic solvents that may be contained in the ceramic layer composition are removed after drying and are not contained in the ceramic layer.

[0100] In one embodiment of this application, the thickness of the ceramic layer may be 0.5 μm or more and 3 μm or less.

[0101] In another embodiment, the thickness of the ceramic layer may be 0.5 μm or more and 3 μm or less, preferably 0.7 μm or more and 2.5 μm or less.

[0102] As described above, by ensuring the thickness of the ceramic layer meets the aforementioned range, the effect of improving stability through adjustment of the pre-lithiation rate during pre-lithiation can be obtained. If the thickness of the ceramic layer exceeds the aforementioned range, problems such as deterioration of the negative electrode performance may occur, and it may even result in a decrease in efficiency during pre-lithiation. Furthermore, if the thickness of the ceramic layer is less than the aforementioned range, it is not easy to adjust the pre-lithiation rate, and problems such as a shortened lifespan may occur due to electrode deterioration caused by surface reactions on the upper part of the negative electrode active material layer.

[0103] In one embodiment of this application, the ceramic layer composition may include a ceramic and an organic binder.

[0104] In one embodiment of this application, the ceramic can be used without limitation as long as it can perform the role of a ceramic layer, but specifically, Al2O3, ZrO2, SiO2, TiO2, ZnO, BaTiO3, SrTiO3, CaCO3, CaO, CeO2, NiO, MgO, SnO2, Y2O3, Pb(Zr,Ti)O3(PZT), (Pb,La)(Zr,Ti)O3(PLZT), PB(Mg3Nb 2 / 3 The present invention provides a negative electrode for lithium secondary batteries that contains one or more selected from the group consisting of O3-PbTiO3 (PMN-PT) and hafnia (HfO2).

[0105] More specifically, the ceramic may be Al2O3 or CeO2.

[0106] In one embodiment of this application, the ceramic composition further comprises an organic solvent, the organic solvent comprising at least one selected from the group consisting of N-methylpyrrolidone (NMP); dimethylformamide (DMF); acetone; and dimethylacetamide; to provide a negative electrode for a lithium secondary battery.

[0107] More preferably, the organic solvent may be acetone.

[0108] In one embodiment of this application, the organic binder is polyvinylidene fluoride (PVdF) or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) to provide a negative electrode for a lithium secondary battery.

[0109] In particular, as mentioned above, the silicon-based anode active material layer will use an aqueous binder due to the characteristics of the silicon-based active material. This allows for the use of an organic binder and an organic solvent for dispersion in the ceramic layer to ensure the coating properties of the ceramic layer.

[0110] Furthermore, while water-based binders are polymers that exhibit very high rigidity after drying, they generally fall into the category of binders whose adhesive strength decreases after drying. However, in the case of organic binders used in ceramic layers, they are very soft polymers and exhibit a slight amount of viscosity, i.e., adhesive strength, compared to water-based binders.

[0111] As a result, during pre-lithiation, the lithium metal layer is transferred to the top of the ceramic layer. When the ceramic layer contains an organic binder, the resulting slight adhesive force facilitates the transfer of the lithium metal layer to the top of the ceramic layer, thus improving processability.

[0112] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided in which, after bonding the surface of the ceramic layer opposite to the surface in contact with the negative electrode active material layer to a lithium metal, the adhesive strength after being left at 23°C for 10 seconds to 2 minutes is 10 gf / 15 mm or more and 100 gf / 15 mm or less.

[0113] The adhesive strength was measured using a peel strength meter with 3M 9070 tape at a 90° angle and a speed of 5 mm / s. Specifically, one side of the lithium metal layer of the negative electrode, which has a lithium metal layer laminated on top of a ceramic layer, was adhered to one side of a glass slide (3M 9070 tape) to which an adhesive film had been attached. Then, it was pressed by moving a 2 kg rubber roller back and forth 5 to 10 times, and the adhesive strength (peel strength) was measured at a 90° angle and a speed of 5 mm / s. At this time, the adhesive strength can be measured under normal conditions of 23°C and atmospheric pressure.

[0114] In one embodiment of this application, normal pressure can mean pressure in a state where no specific pressure is applied or reduced, and can be used synonymously with atmospheric pressure. It can generally be expressed as 1 atmosphere.

[0115] In one embodiment of this application, after bonding the surface of the ceramic layer opposite to the surface in contact with the negative electrode active material layer to the lithium metal, the adhesive strength after being left at 23°C for 10 seconds to 2 minutes may be 10 gf / 15 mm or more and 100 gf / 15 mm or less, preferably 15 gf / 15 mm or more and 95 gf / 15 mm or less, and more preferably 20 gf / 15 mm or more and 50 gf / 15 mm or less.

[0116] As described above, when the adhesive strength between the ceramic layer and the lithium metal satisfies the aforementioned range, the adhesion strength between the lithium metal and the ceramic layer is good, especially when transferring lithium metal using the transfer process in the pre-lithification process, ensuring transferability, preventing problems such as reverse transfer, and enabling a smooth pre-lithification process.

[0117] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the ceramic is contained in an amount of 80 to 95 parts by weight and the organic binder in an amount of 5 to 20 parts by weight, based on 100 parts by weight of the ceramic layer composition.

[0118] In this case, since the organic solvent that may be included in the ceramic layer composition does not qualify as an active substance, the standard of 100 parts by weight of the ceramic layer composition can mean parts by weight containing only ceramic and organic binder.

[0119] In one embodiment of this application, the ceramic may be 80 parts by weight or more and 95 parts by weight or less, preferably 85 parts by weight or more and 95 parts by weight or less, based on 100 parts by weight of the ceramic layer composition.

[0120] In one embodiment of this application, the organic binder may be 5 parts by weight or more and 20 parts by weight or less, preferably 5 parts by weight or more and 15 parts by weight or less, and more preferably 5 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the ceramic layer composition.

[0121] As described above, by including the organic binder and ceramic in the aforementioned content portion of the ceramic layer composition, the dispersibility of the binder and ceramic is improved, and the ceramic layer is formed uniformly. This allows for smooth adjustment of the pre-lithiation rate, satisfying an appropriate viscosity range and improving the coating density during the coating of the ceramic layer.

[0122] In one embodiment of this application, the thickness of the negative electrode active material layer may be 10 μm or more and 200 μm or less.

[0123] In one embodiment of this application, the negative electrode for the lithium secondary battery may be a pre-lithified negative electrode.

[0124] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, comprising the steps of: preparing a negative electrode current collector layer; applying a negative electrode active material layer composition to one or both sides of the negative electrode current collector layer to form a negative electrode active material layer; and applying a ceramic layer composition to the side of the negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer to form a ceramic layer, wherein the thickness of the ceramic layer is 0.5 μm or more and 3 μm or less, and the ceramic layer composition comprises a ceramic, an organic binder, and an organic solvent, wherein, based on 100 parts by weight of the ceramic layer composition, the ceramic is included in an amount of 80 parts by weight or more and 95 parts by weight or less, and the organic binder is included in an amount of 5 parts by weight or more and 20 parts by weight or less.

[0125] In the method for manufacturing the negative electrode, the composition and content included in each step can be as described above.

[0126] One embodiment of this application provides a step of forming a negative electrode active material layer by applying a negative electrode active material layer composition to one or both sides of the negative electrode current collector layer.

[0127] In other words, the aforementioned step is the step of forming a negative electrode active material layer on the negative electrode current collector layer, and can be said to mean the step of forming an active material layer on the surface in contact with the current collector layer.

[0128] In one embodiment of this application, the application of the negative electrode active material layer composition includes the steps of applying and drying a negative electrode slurry containing the negative electrode active material layer composition and a negative electrode slurry solvent.

[0129] In this case, the solid content of the negative electrode slurry may be in the range of 10% to 40%.

[0130] In one embodiment of this application, the step of forming the negative electrode active material layer may include the steps of mixing the negative electrode slurry and coating one or both sides of the negative electrode current collector layer with the mixed negative electrode slurry, wherein the coating may be performed using coating methods commonly used in the industry.

[0131] Subsequently, in one embodiment of this application, a step is provided in which a ceramic layer composition is applied to the surface of the negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to form a ceramic layer.

[0132] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, which includes the step of drying the organic solvent in the ceramic layer composition by drying and rolling after applying the ceramic layer composition.

[0133] In one embodiment of this application, the negative electrode slurry solvent can be used without limitation as long as it can dissolve and disperse the negative electrode active material layer composition, and specifically water or NMP may be used.

[0134] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, which includes a step of pre-lithiation of a negative electrode having a negative electrode active material layer and a ceramic layer formed on the negative electrode current collector, wherein the step of pre-lithiation of the negative electrode includes a lithium electroplating step; a lithium metal transfer step; a lithium metal deposition step; or a stabilized lithium metal powder (SLMP) coating step.

[0135] The negative electrode for lithium secondary batteries described above includes SiOx (x=0) as the negative electrode active material layer to enhance capacity characteristics, and a ceramic layer is provided with the specific composition and thickness mentioned above, thus retaining the advantages of rapid charging. In other words, compared to simply applying only the negative electrode active material layer, the ceramic layer having the aforementioned composition allows for a uniform pre-lithification process at the upper end of the negative electrode, thereby further improving the battery life.

[0136] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0137] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0138] The porosity varies depending on the composition and content of the silicon-based active material, negative electrode conductive material, and negative electrode binder contained in the negative electrode active material layer, thereby ensuring that the electrical conductivity and resistance of the electrode are within an appropriate range.

[0139] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0140] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

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

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

[0143] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be Li metal.

[0144] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0145] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more can be used.

[0146] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0147] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Generally, any membrane used as a separation membrane in secondary batteries is acceptable without particular limitations, and it is especially preferable that it has low resistance to electrolyte ion movement while exhibiting excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0148] In particular, by having a ceramic layer on top of the silicon-based negative electrode active material layer according to this application, the ceramic layer formed on the separation membrane can be eliminated or minimized, the thickness of the original material of the separation membrane can be reduced, and it can have advantages in terms of process and cost.

[0149] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0150] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0151] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0152] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be created, and this mixture is even more preferable.

[0153] The metal salt can be a lithium salt, and the lithium salt is a substance that dissolves easily in the non-aqueous electrolyte. For example, the anion of the lithium salt is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You can use one or more selected from the group consisting of the following.

[0154] In addition to the electrolyte components, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0155] One embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Because the battery module and battery pack include the secondary battery having high capacity, high rate-limiting characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0156] The following are preferred embodiments to aid in understanding the present invention. These embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such variations and modifications fall within the scope of the appended claims.

[0157] <Examples> <Manufacturing of negative electrodes> Example 1: Manufacturing of the negative electrode Manufacturing of the negative electrode active material layer A negative electrode active material layer composition was prepared using silicon-based active material Si (average particle size (D50): 5 μm), and polyacrylamide as the first conductive material, second conductive material, and binder in a weight ratio of 80:9.6:0.4:10. A negative electrode slurry was produced by adding these materials to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 28% by weight).

[0158] The first conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The particle size is 3.5 μm (d / g), and the second conductive material is carbon nanotubes.

[0159] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0160] As the negative electrode current collector, a copper current collector (thickness: 15 μm) is coated with the negative electrode slurry at a rate of 3.00 mg / cm³ on both sides. 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 23 μm).

[0161] Manufacturing of ceramic layers A ceramic layer composition was prepared using Ce(Al2O3, d50:300nm) as the ceramic and PVdF-HFP as the organic binder in a weight ratio of 92:8. This was then added to acetone, an organic solvent, to produce the ceramic layer composition. (Solid content concentration: 18% by weight)

[0162] Subsequently, the ceramic layer composition was coated onto the upper part of the negative electrode active material layer, rolled (roll press), and dried in a vacuum oven at 60°C for 10 hours to form a ceramic layer (thickness: 1 μm).

[0163] In the above-described Example 1, the negative electrode was manufactured in the same manner as in Example 1, except that the manufacturing conditions for the negative electrode active material layer and the ceramic layer were changed as described below.

[0164] [Table 1]

[0165] Pre-lithiation process A transfer laminate consisting of PET / release layer / lithium metal was laminated onto the top of the negative electrode in Examples 1-5 and Comparative Examples 1-6, and the PET layer was removed to transfer the lithium metal onto the top of the ceramic layer.

[0166] Subsequently, the negative electrode for lithium secondary batteries was converted to pre-lithium.

[0167] <Manufacturing of secondary batteries> LiNi 0.6 Co 0.2 Mn 0.2 A cathode slurry was prepared by adding O2 (average particle size (D50): 15 μm), carbon black (product name: SuperC65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0168] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is coated on both sides with the positive electrode slurry at a rate of 537 mg / 25 cm². 2 The cathode was fabricated by coating with the specified loading amount, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0169] The secondary battery of Example 1 was fabricated by injecting an electrolyte between the positive electrode and the negative electrode of Example 1 via a polyethylene separation membrane.

[0170] The electrolyte in question was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 30:70 in an organic solvent, adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0171] Secondary batteries were fabricated in the same manner as described above, except that the negative electrodes of Examples 2-5 and Comparative Examples 1-6 were used.

[0172] Experimental Example 1. Performance evaluation by discharge C-rate To confirm the performance of the secondary batteries of the examples and comparative examples prepared above at different discharge rates, discharge rate experiments were conducted (charge rate fixed, discharge rate changed to 0.2 / 0.5 / 1.0 / 1.5 / 2.0 / 3.0 / 4.0).

[0173] The discharge rate experiments proceeded as follows: 0.33 / 0.2 > 0.33 / 0.33 > 0.33 / 0.5 > 0.33 / 0.33 > 0.33 / 1.0 > 0.33 / 0.33 > 0.33 / 1.5 > 0.33 / 0.33 > 0.33 / 2.0 > 0.33 / 0.33 > 0.33 / 3.0 > 0.33 / 0.33 > 0.33 / 4.0, and pre-lithiation did not proceed separately. To confirm the ratio, the capacity for each rate was shown with the 0.2C discharge capacity standard set to 100%. The results are shown in Table 2 below.

[0174] [Table 2]

[0175] The ceramic layer according to the present invention, unlike the negative electrode active material layer, lacks conductive material and consists only of an insulating material and a binder. Therefore, it was confirmed that the rate characteristics decrease as the thickness of the ceramic layer increases. Furthermore, the higher the proportion of binder (PVdF-HFP) in the ceramic layer, the more effective it is in forming a void structure in the ceramic layer, resulting in lower resistance. On the other hand, if the proportion of binder decreases, the ceramic material and binder adhere to each other and form a layer, blocking the voids, reducing the ionic conductivity of the electrolyte and degrading performance.

[0176] Furthermore, as can be seen from Comparative Example 5 in Table 2, when a PAM-based binder, which is an aqueous binder, is used instead of PVdF, and water (H2O), which is an aqueous solvent, is used, the performance is significantly inferior. This is because the strength of the binder becomes very high during the drying of the ceramic layer, and the ceramic layer tends to become very hard. Also, because it has a chemical structure similar to the binder used in silicon (Si) electrodes, the ceramic layer and the negative electrode active material layer are strongly adsorbed together, resulting in very low wettability of the electrolyte.

[0177] Comparative Example 6 in Table 2 shows the results of fabricating a graphite electrode with the same capacity. Since the capacity of silicon is more than 10 times that of graphite, in the case of Comparative Example 6, the electrode thickness was extremely thick due to the coating, and it was confirmed that the discharge rate performance was significantly inferior to that of Examples 1 to 5.

[0178] Experiment Example 2: Electrode Ignition Experiment Li metal of the same size and thickness of 6.2 μm was adsorbed onto the negative electrodes of the examples and comparative examples prepared above, and then left to stand for about 12 hours to allow complete pre-lithification to proceed. A plasma lighter was used to artificially induce a spark on the electrode surface of the pre-lithified negative electrodes prepared for the experiment, and the time required for ignition was measured. The results are shown in Table 3 below.

[0179] [Table 3]

[0180] As can be seen from Table 3 above, all negative electrodes having a ceramic layer according to this application are coated with a ceramic layer, and although there are some differences in time, the time required for ignition is longer, the possibility of ignition is lower, and it has been confirmed that they are highly safe.

[0181] The results of Experimental Example 2 confirm that the proportion of ceramics with the main insulating properties and the thickness of the coating affect the insulating properties. This confirmed that Comparative Example 1, in which the insulating layer was less than the thickness range of this application, ignited in the shortest time (6 seconds) and had poor stability.

[0182] In the case of Comparative Example 2, the thickness of the ceramic layer exceeded the scope of this application, and it was confirmed that it took more than 30 seconds until ignition. As can be seen from Table 2 above, the discharge rate performance was very poor, and it was confirmed that this resulted in a decrease in efficiency during pre-lithiation.

[0183] In Comparative Examples 3 and 4, the thickness of the ceramic layer meets the scope of this application, but the binder content falls below or exceeds the scope of this application. In these cases, the dispersibility of the ceramic itself is poor, making it difficult to smoothly adjust the pre-lithification rate, and problems such as fires occur during the pre-lithification process itself. Although the thickness of the ceramic layer satisfies the thickness range of this application, it showed poor results in the safety evaluation.

[0184] Comparative Example 5 is a case where the ceramic layer was prepared using an aqueous binder and an aqueous solvent. Similarly, it satisfied the thickness range in the safety evaluation and obtained results equivalent to the example. However, as can be seen from Experimental Example 1 above, it was confirmed that it was significantly inferior in performance evaluation.

[0185] Finally, Comparative Example 6 uses a graphite-based active material. As mentioned in Experimental Example 1 above, the electrode thickness had to be made very thick in order to achieve the same capacity, and it was confirmed that the discharge rate performance was significantly inferior to that of Examples 1 to 5.

[0186] For reference, when a negative electrode without the ceramic layer described in this application was pre-lithified under the same conditions, it was found to ignite within 2 to 3 seconds during the experiment, confirming that it was not safe.

[0187] In conclusion, through the above-mentioned examples and comparative examples, it was confirmed that the negative electrode for lithium secondary batteries according to this application, by using a silicon-based active material and including a ceramic layer of a specific thickness and composition on top of the negative electrode active material layer, can stabilize the process speed during pre-lithiation, thereby significantly increasing the stability during the pre-lithiation process.

[0188] In other words, it was confirmed that this method has the characteristic of reducing the contact point between the silicon-based anode and the lithium metal, thereby increasing the uniformity of the charging and discharging of the silicon-based anode and improving its performance.

[0189] By further including a ceramic layer on top of the silicon-based negative electrode active material layer, the ceramic layer formed on the separation membrane can be eliminated or minimized, thereby reducing the thickness of the original material for the separation membrane, resulting in advantages in terms of process and cost. [Explanation of Symbols]

[0190] 10 ···Ceramic layer 20...Negative electrode active material layer 30 ···Negative electrode current collector layer

Claims

1. A negative electrode for a lithium secondary battery comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the side of the silicon-based negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer; The ceramic layer comprises a ceramic layer composition or a dried product thereof. The thickness of the ceramic layer is 0.5 μm or more and 3 μm or less. The ceramic layer composition comprises a ceramic and an organic binder. Based on 100 parts by weight of the ceramic layer composition, the ceramic is included in an amount of 80 parts by weight or more and 95 parts by weight or less, and the organic binder is included in an amount of 5 parts by weight or more and 20 parts by weight or less. The silicon-based negative electrode active material layer comprises a negative electrode active material layer composition, The negative electrode active material layer composition comprises a planar conductive material and a negative electrode conductive material including a linear conductive material, Based on 100 parts by weight of the negative electrode conductive material, the planar conductive material is included in an amount of 80 parts by weight or more and 99.9 parts by weight or less. The aforementioned planar conductive material is a negative electrode for a lithium secondary battery, having a BET specific surface area of ​​5 m² / g or more and 300 m² / g or less.

2. The ceramic is Al ２ O ３ ZrO ２ SiO ２ TiO ２ ZnO, BaTiO ３ SrTiO ３ CaCO ３ CaO, CeO ２ NiO, MgO, SnO ２ Y ２ O ３ Pb(Zr,Ti)O ３ (PZT), (Pb,La)(Zr,Ti)O ３ (PLZT), Pb(Mg 1／３ Nb ２／３ O ３ -PbTiO ３ (PMN-PT) and hafnia (HfO ２ ) and includes one or more selected from the group consisting of, the negative electrode for a lithium secondary battery according to claim 1.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein the organic binder is polyvinylidene fluoride (PVdF); or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP).

4. The ceramic layer composition further comprises an organic solvent, The negative electrode for a lithium secondary battery according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of N-methylpyrrolidone (NMP); dimethylformamide (DMF); acetone; and dimethylacetamide.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein the adhesive strength after bonding the surface of the ceramic layer opposite to the surface in contact with the silicon-based negative electrode active material layer to the lithium metal and leaving it at 23°C for 10 seconds to 2 minutes is 10 gf / 15 mm or more and 100 gf / 15 mm or less.

6. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer composition comprises at least one selected from the group consisting of a silicon-based active material and a negative electrode binder.

7. The silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0 < x < 2), and comprises 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material, the negative electrode for a lithium secondary battery according to claim 6.

8. The negative electrode for a lithium secondary battery according to claim 1, wherein the planar conductive material is included in an amount of 95 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

9. The negative electrode for a lithium secondary battery according to claim 6, wherein the silicon-based active material is contained in an amount of 70 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition.

10. The step of preparing the negative electrode current collector layer; A step of forming a negative electrode active material layer by applying the negative electrode active material layer composition to one or both sides of the negative electrode current collector layer; and A step of forming a ceramic layer by applying the ceramic layer composition to the surface of the negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer; A method for manufacturing a negative electrode for a lithium secondary battery, including, The thickness of the ceramic layer is 0.5 μm or more and 3 μm or less. The ceramic layer composition comprises a ceramic, an organic binder, and an organic solvent. Based on 100 parts by weight of the ceramic layer composition, the ceramic is included in an amount of 80 parts by weight or more and 95 parts by weight or less, and the organic binder is included in an amount of 5 parts by weight or more and 20 parts by weight or less. The negative electrode active material layer composition comprises a planar conductive material and a negative electrode conductive material including a linear conductive material, Based on 100 parts by weight of the negative electrode conductive material, the planar conductive material is included in an amount of 80 parts by weight or more and 99.9 parts by weight or less. The planar conductive material has a BET specific surface area of ​​5 m² / g or more and 300 m² / g or less, and is a method for manufacturing a negative electrode for a lithium secondary battery.

11. A method for manufacturing a negative electrode for a lithium secondary battery according to claim 10, comprising the step of drying the organic solvent in the ceramic layer composition by drying and rolling after applying the ceramic layer composition.

12. The negative electrode, on which a negative electrode active material layer and a ceramic layer are formed on the negative electrode current collector layer, is pre-lithified. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10, wherein the step of pre-lithifying the negative electrode includes a lithium electroplating step; a lithium metal transfer step; a lithium metal deposition step; or a stabilized lithium metal powder (SLMP) coating step.

13. positive electrode; A negative electrode for a lithium secondary battery according to any one of claims 1 to 9; A separation membrane provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

14. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 12, wherein the step of pre-lithifying the negative electrode includes the lithium metal transfer step.

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