Anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0183765, filed with the Korean Intellectual Property Office on December 16, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [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 in this area is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses 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. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, active research is being conducted into methods of increasing capacity by using silicon-based compounds such as Si / C and SiOx as negative electrode active materials, which have capacities more than 10 times larger than graphite-based materials. Although silicon-based compounds, which are high-capacity materials, have a higher capacity than conventionally used graphite, they suffer from the problem of rapid volume expansion during charging, which breaks the conductive path and reduces battery performance.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods for suppressing volume expansion itself, such as adjusting the driving potential, coating an additional thin film on the active material layer, and adjusting the particle size of the silicon-based compound, or methods for preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually degrade battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] In other words, anodes using silicon-based active materials must ensure long-term stability. Volume changes in silicon-based active materials occur due to the insertion and desorption of lithium during the reaction between lithium and silicon during charge / discharge, and the degree of cracking of the active material increases during the reaction of large amounts of lithium insertion and desorption.

[0010] In order to improve the cracking phenomenon of silicon-based active materials and ensure their lifespan, relevant research is needed, such as limiting the SOC of silicon-based active materials. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0012] Rather than adjusting the SOC of the silicon-based anode system itself, it was found that when lithium ions react at a higher potential than silicon during cell discharge and a highly reactive metal composite is included in the anode composition, the SOC of the silicon-based active material itself is limited, which is effective in improving lifespan performance.

[0013] Thus, the present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0014] One embodiment of the present specification provides a negative electrode composition including: a silicon-based active material; a negative electrode conductive material; and a negative electrode binder; wherein the negative electrode composition includes a metal composite on which lithium oxide is vapor-deposited, the weight ratio of metal to lithium oxide in the metal composite being 10:1 or more and 800:1 or less, and the metal composite is included in an amount of 1 part by weight to 15 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0015] In another embodiment, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer comprises the negative electrode composition according to the present application or a cured product thereof.

[0016] Finally, there is provided a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0017] An anode composition according to one embodiment of the present invention is characterized in that, when a silicon-based active material, which is a high-capacity material, is used to produce a high-capacity battery, the problem of volume expansion of the silicon-based active material is not limited by the SOC of the battery system, but is improved by including a specific metal composite in the anode composition.

[0018] In particular, the metal composite is characterized in that the weight ratio of metal to lithium oxide in the metal composite is 10:1 or more and 800:1 or less, and the metal composite is 1 part by weight or more and 15 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0019] When using such a metal composite, the SOC of silicon itself is limited compared to when a silicon-based active material is used alone, resulting in an improved lifespan performance. That is, the metal composite has the above-mentioned characteristics, reacts with lithium at a higher potential than the silicon-based active material, has excellent reactivity, and can suppress the volume expansion of the silicon-based active material during charge and discharge compared to when only the silicon-based active material is used, resulting in an excellent improvement in lifespan performance.

[0020] Furthermore, compared to the case where a metal oxide is simply used, when a metal composite on which lithium oxide is deposited is included as in the present invention, when an initial electrochemical reaction occurs, lithium ions are uniformly distributed throughout the entire upper and lower ends of the electrode, and the lithium ions can be more uniformly incorporated, thereby improving the tortuosity within the electrode.

[0021] That is, the negative electrode composition according to the present application has a high content of silicon-based active material particles, and a high-capacity and high-density negative electrode can be obtained. In addition, in order to solve problems such as volume expansion caused by having a high content of silicon-based active material particles, a metal composite of a specific composition and content is used, and this is a main object of the present invention. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. [Figure 3] 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

[0023] Before describing the present invention, some terms will first be defined.

[0024] 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 otherwise specified.

[0025] In this specification, "p to q" means a range of "not less than p and not more than q."

[0026] 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.

[0027] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, particle size distribution 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 according to particle size when the particles pass through a laser beam.

[0028] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, this is interpreted as meaning that the polymer contains the monomer as a monomer unit.

[0029] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0030] 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) of various degrees of polymerization as standard substances for molecular weight measurement. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0031] 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, although the present invention may be embodied in various different forms and is not limited to the following description.

[0032] One embodiment of the present specification provides a negative electrode composition including: a silicon-based active material; a negative electrode conductive material; and a negative electrode binder; wherein the negative electrode composition includes a metal composite on which lithium oxide is vapor-deposited, the weight ratio of metal to lithium oxide in the metal composite being 10:1 or more and 800:1 or less, and the metal composite is included in an amount of 1 part by weight to 15 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0033] When using the metal composite as described above, since the SOC of silicon itself is limited compared to the case of using the silicon-based active material alone, an improvement effect on the life performance appears. That is, the metal composite has the above-described characteristics, reacts with lithium at a potential higher than that of the silicon-based active material, has excellent reactivity, and can suppress the volume expansion of the silicon-based active material during charge and discharge compared to the case of using only the silicon-based active material. Therefore, it has the characteristic of being excellent in the improvement effect of life performance.

[0034] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0), SiO x (0 < x < 2), SiC, and at least one selected from the group consisting of Si alloys, and includes a negative electrode composition.

[0035] The active material of the present invention includes a silicon-based active material. The silicon-based active material may be SiO x , Si / C, or Si. SiO x may include a compound represented by SiO x (0 ≤ x < 2). In the case of SiO2, since it does not react with lithium ions and cannot store lithium, x is preferably within the above range. The silicon-based active material may be Si / C or Si composed of a composite of Si and C. Also, two or more of the above-described silicon-based active materials may be mixed and used. The negative electrode active material may further include a carbon-based active material together with the above-described silicon-based active material. The carbon-based active material can contribute to the improvement of the excellent cycle characteristics of the negative electrode or secondary battery of the present invention or the battery life performance.

[0036] Generally, it is known that the silicon-based active material has a capacity more than 10 times higher than that of the carbon-based active material. When the silicon-based active material is applied to the negative electrode, it is expected that an electrode having a high level of energy density can be realized even with a thin thickness.

[0037] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0) and SiOx Containing one or more selected from the group consisting of (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x Provided is a negative electrode composition containing 70 parts by weight or more of (x = 0).

[0038] 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 SiO x (x = 0) based on 100 parts by weight of the silicon-based active material.

[0039] The silicon-based active material according to the present application contains 70 parts by weight or more of the SiO x (x = 0), and when compared with a silicon-based active material using a SiO x (0 < x < 2) system as the main substance, there is a drawback that the theoretical capacity is far inferior to that of the silicon-based active material of the present application. That is, when using an active material of the SiO x (0 < x < 2) system, no matter what treatment is applied to the active material itself, it is impossible to achieve the same conditions as the charge and discharge capacity when having the silicon-based active material of the present invention.

[0040] In one embodiment of the present application, the silicon-based active material may use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that when based on a total of 100 parts by weight of the silicon-based active material as described above, pure Si particles (SiO x (x = 0)) may be included within the above range.

[0041] In the case of a silicon-based active material, since the capacity is significantly higher than that of the conventionally used graphite-based active material, attempts to apply it have increased, but due to the high volume expansion rate during the charge and discharge process, it has remained at the level of mixing a small amount with the graphite-based active material and using it.

[0042] Therefore, the present invention is characterized by using a high content of silicon-based active material as the negative electrode active material to improve capacity performance, and by using a metal composite that meets specific conditions to solve the problems of maintaining the conductive path due to the volume expansion and maintaining the bond between the conductive material, binder, and active material.

[0043] 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 falls 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 contact area between the silicon particles and the conductive material is improved by the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of maintaining the conductive network and improving the capacity retention rate. Furthermore, 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.

[0044] 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 m 2 / g~150.0m 2 / g, more preferably 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 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0045] In one embodiment of the present application, silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably non-porous.Silicon particles are preferably spherical or shard particles.Alternatively, but less advantageously, silicon particles can have a fibrous structure or be in the form of silicon-containing film or coating.

[0046] In one embodiment of the present application, there is provided a negative electrode composition, wherein the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0047] In another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included 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.

[0048] The negative electrode composition according to the present application uses a specific metal composite that can suppress the volume expansion rate during charge and discharge even when a silicon-based active material with extremely high capacity is used within the above range, and is therefore characterized by not deteriorating the performance of the negative electrode even when the silicon-based active material is contained within the above range, and by having excellent output characteristics during charge and discharge.

[0049] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0050] In this application, the circularity is determined by the following formula 1-1, where A is the area and P is the perimeter.

[0051] [Formula 1-1] 4πA / P 2

[0052] In one embodiment of the present application, the negative electrode composition may include a metal composite having a lithium oxide deposited thereon.

[0053] Lithium oxide-deposited metal composites are used based on a different concept from conventional metal oxides. That is, metal oxides are represented by MO2 (where M is the metal), and the lithium oxide-deposited metal composites of the present application may have a structure in which lithium oxide is deposited on the metal itself. When a metal oxide (or metal) is used as a negative electrode, lithium ions must enter the electrode from the top to the bottom during the initial discharge, resulting in a relative imbalance between the top and bottom of the electrode, which reduces the lifespan. However, in the case of the lithium oxide-deposited metal composites of the present application, the lithium oxide can be uniformly mixed. Therefore, when the initial electrochemical reaction occurs, lithium ions are distributed throughout the entire top and bottom of the electrode, allowing for more uniform incorporation of lithium ions, thereby improving tortuosity.

[0054] In one embodiment of the present application, the weight ratio of metal to lithium oxide in the metal composite may be 10:1 or more and 800:1 or less.

[0055] In another embodiment, the weight ratio of metal to lithium oxide in the metal composite may be 10:1 or more and 800:1 or less, preferably 15:1 or more and 700:1 or less, more preferably 20:1 or more and 600:1 or less.

[0056] The metal composite according to the present application corresponds to a material used to limit the SOC of a silicon-based active material. In the case of the metal composite according to the present application, the lithium oxide may be vapor-deposited on the surface of the metal. In particular, by satisfying the ratio of lithium oxide to metal as described above, the composite reacts with lithium at a higher potential than the silicon-based active material, exhibiting excellent reactivity. Furthermore, the composite can suppress the volume expansion of the silicon-based active material during charge and discharge compared to when only the silicon-based active material is used, thereby exhibiting an excellent effect of improving the life performance.

[0057] That is, if the proportion of lithium oxide in the metal composite is low, a problem may occur in that the lithium oxide cannot react uniformly with the Li in the metal during the reaction, and if the proportion of lithium oxide exceeds the above range, these may remain even after reacting, causing an increase in resistance and a decrease in cell performance.

[0058] In one embodiment of the present application, there is provided a negative electrode composition, in which the metal composite is contained in an amount of 1 part by weight to 15 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0059] In another embodiment, the metal composite may be included in an amount of 1 part by weight to 15 parts by weight, preferably 2 parts by weight to 14 parts by weight, and more preferably 3 parts by weight to 13.5 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0060] In one embodiment of the present application, there is provided a negative electrode composition, wherein the weight ratio of the metal composite to the silicon-based active material in the negative electrode composition satisfies 1:5 to 1:20.

[0061] The negative electrode composition according to the present application is characterized by using a silicon-based active material and containing the above-mentioned metal composite, and is characterized by satisfying the above-mentioned weight ratio. When the above-mentioned weight ratio is satisfied, the content of the silicon-based active material itself is not reduced, and high energy density and high capacity can be exhibited. At the same time, the metal composite is contained in an appropriate content to limit the SOC, thereby improving life characteristics.

[0062] That is, if the content of the metal composite is less than the above range, the degree of limiting the SOC of Si is reduced, and therefore the cracking phenomenon of Si cannot be alleviated. If the content of the metal composite is more than the above range, the discharge capacity of Sn relative to Si is reduced, and therefore, the total loading amount in the negative electrode increases, and thus the electrode resistance may increase.

[0063] In one embodiment of the present application, the metal may be Sn.

[0064] In one embodiment of the present application, the lithium oxide may be any lithium oxide used in the art without limitation, but Li2O may be used.

[0065] In one embodiment of the present application, the lithium oxide may be contained in an amount of 5 parts by weight or less, preferably 3 parts by weight or less, and more preferably 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0066] In one embodiment of the present application, there is provided a negative electrode composition, wherein the lithium oxide has a D50 particle size of 200 nm or less.

[0067] In another embodiment, the D50 particle size of the lithium oxide may be 200 nm or less, preferably 150 nm or less, and specifically may satisfy the range of 10 nm or more, 30 nm or more.

[0068] Lithium oxide is deposited on the surface of a metal, and when the particle size satisfies the above-mentioned range, it can improve the deposition ability on the metal surface and has the characteristic of having an appropriate degree of dispersion.

[0069] While graphite-based compounds have traditionally been used alone as negative electrode active materials, attempts to incorporate silicon-based compounds into negative electrode active materials have been increasing in recent years in response to the growing demand for high-capacity batteries. However, even if the properties of the silicon-based active material itself are adjusted as described above, silicon-based compounds may experience rapid volume expansion during charge / discharge processes, potentially damaging the conductive paths formed in the negative electrode active material layer.

[0070] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-shaped conductive materials, sheet-shaped conductive materials, and linear conductive materials.

[0071] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode, does not cause chemical changes, and has conductivity. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which achieves high conductivity and excellent dispersibility.

[0072] 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.

[0073] In one embodiment of the present application, the dot-like conductive material may have 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.

[0074] In particular, when the content of functional groups in the dot-like conductive material satisfies the above range, functional groups are present on the surface of the dot-like conductive material, and when water is used as a solvent, the dot-like conductive material can be smoothly dispersed in the solvent. In particular, the present invention can reduce the content of functional groups in the dot-like conductive material by using silicon particles and a specific binder, thereby having an excellent effect in improving dispersibility.

[0075] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the content of the functional group can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0076] 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.

[0077] In one embodiment of the present application, the negative electrode conductive material may include a sheet-shaped conductive material.

[0078] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also prevent the conductive path from being broken due to volume expansion. The sheet-like conductive material can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0079] In one embodiment of the present application, the sheet-like conductive material may be provided in a form that is bonded to the surface of the silicon-based particle, specifically, the -OH groups or -O groups on the surface of the silicon-based particle and the hydrophilic groups of the sheet-like conductive material may be bonded to each other.

[0080] In one embodiment of the present application, the sheet-like conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0081] In one embodiment of the present application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the above range is satisfied, the sufficient particle size does not cause an excessive increase in viscosity of the negative electrode slurry and dispersion is easy. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0082] In one embodiment of the present application, there is provided a negative electrode composition, wherein the sheet-shaped conductive material has a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0083] In one embodiment of the present application, the sheet-shaped conductive material may be a sheet-shaped conductive material having a high BET specific surface area; or a sheet-shaped conductive material having a low specific surface area.

[0084] In one embodiment of the present application, the sheet-like conductive material can be a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area, without any restrictions. However, since dispersion of the sheet-like conductive material according to the present application can have some effect on electrode performance, it is particularly preferable to use a sheet-like conductive material with a low specific surface area in which dispersion does not cause problems.

[0085] In one embodiment of the present application, the sheet-shaped conductive material has a BET specific surface area of ​​1 m 2 / g or more.

[0086] In another embodiment, the sheet-shaped 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.

[0087] The sheet-shaped conductive material according to the present application may be a sheet-shaped conductive material with a high specific surface area or a sheet-shaped conductive material with a low specific surface area.

[0088] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a high specific surface area, and 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.

[0089] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a low specific surface area, and 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.

[0090] 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 a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape of a bundle or rope in which a plurality of carbon nanotube units are arranged side by side or entangled with each other with the longitudinal axes of the carbon nanotube units substantially aligned in the same direction. The carbon nanotube units are formed by a graphite sheet having a cylindrical shape with a nano-sized diameter, and a sp 2 The bundled carbon nanotubes have a bonded structure. Depending on the angle and structure of the graphite sheet wrapping, they can 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.

[0091] For example, the linear conductive material may be a single-walled carbon nanotube (SWCNT), which has a large BET specific surface area, a linear shape, a very small diameter, and a very long length. Linear conductive materials such as SWCNTs cannot be stretched by dispersion and have a strong ability to return to their original shape when dried. As a result, linear conductive materials such as SWCNTs have a strong tendency to return to their original shape when dried, so they generally exist in a form that surrounds or connects with the negative electrode active material or secondary aggregates. The bonding method can be adsorption via van der Waals forces.

[0092] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0093] In 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 25 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0094] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a sheet-shaped conductive material and a linear conductive material.

[0095] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material comprises, based on 100 parts by weight of the negative electrode conductive material, 80 parts by weight or more and 99.9 parts by weight or less of the sheet-like conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0096] In another embodiment, the negative electrode conductive material may contain 80 parts by weight or more and 99.9 parts by weight or less, preferably 85 parts by weight or more and 99.9 parts by weight or less, and more preferably 95 parts by weight or more and 98 parts by weight or less of the sheet-like conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0097] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 15 parts by weight or less, and more preferably 2 parts by weight or more and 5 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0098] In one embodiment of the present application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, and by satisfying the above-mentioned composition and proportions, the battery does not have a significant effect on the life characteristics of conventional lithium secondary batteries. In particular, when the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, the battery has the characteristics of having more points at which charging and discharging are possible, excellent output characteristics at a high C-rate, and a reduced amount of high-temperature gas generation.

[0099] 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 form a contact between the silicon-based active materials, which undergo a very large volume expansion of the electrode upon charge and discharge, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and therefore has a structure and role that are completely different from the negative electrode conductive material of the present invention.

[0100] 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 are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0101] In one embodiment of the present application, the sheet-like 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 dotted shape to facilitate the storage and release of lithium ions.

[0102] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a material having a sheet or plate 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 refers to a material that ensures a conductive path in a sheet shape inside the negative electrode active material layer.

[0103] That is, in this application, the term "platy graphite is used as a conductive material" means that it is processed into a sheet or plate 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 contained therein has high capacity characteristics for storing and releasing lithium, and serves to store and release all lithium ions transferred from the positive electrode.

[0104] In contrast, in the present application, the term "carbon-based active material is used as an active material" means that the carbon-based active material is processed into a dotted or spherical shape and used as a material that stores or releases lithium.

[0105] 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.

[0106] The negative electrode binder according to one embodiment of the present application plays a role in holding the active material and the conductive material together to prevent distortion and structural deformation of the negative electrode structure when the silicon-based active material expands and relaxes in volume. As long as the binder fulfills the above role, any common binder can be used. Specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0107] In one embodiment of the present application, the amount of the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, or may be 5 parts by weight or more, or 10 parts by weight or more.

[0108] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode composition according to the present application or a cured product thereof.

[0109] 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 including a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10 can be seen.

[0110] FIG. 2 shows a laminated structure of a negative electrode for a lithium secondary battery according to another embodiment. Specifically, a negative electrode for a lithium secondary battery 100 including a negative electrode active material layer 20 on both sides of a negative electrode current collector layer 10 can be seen.

[0111] As described above, there are two types: one in which a negative electrode active material layer is coated on one side of the negative electrode current collector layer (see FIG. 1), and one in which a negative electrode active material layer is coated on both sides of the negative electrode current collector layer (see FIG. 2). In this case, the compositions of the negative electrode active material layers coated on both sides may be the same or different.

[0112] In one embodiment of the present application, when a negative electrode active material layer is coated on both sides, the negative electrode active material layer including the negative electrode composition according to the present application may be used without limitation as long as it is coated on only one of the two sides, and the other side may include a silicon-based negative electrode active material or a carbon-based negative electrode active material that may be generally included therein.

[0113] In one embodiment of the present application, the negative electrode may be formed by coating one or both sides of a current collector with a negative electrode slurry containing the negative electrode composition.

[0114] In one embodiment of the present application, the negative electrode slurry may include: a negative electrode composition; and a slurry solvent.

[0115] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0116] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, more preferably 10% to 30%.

[0117] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0118] 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 suitable, and particle aggregation of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0119] 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 does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0120] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein 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 is 20 μm or more and 500 μm or less.

[0121] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0122] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0123] In another embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% to 60%, preferably 20% to 50%, more preferably 30% to 45%.

[0124] The porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to the present application are contained in a specific composition and content, thereby satisfying the above range, and the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0125] In one embodiment of the present application, there is provided a lithium secondary battery comprising: a positive electrode; 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.

[0126] 3 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10 can be seen, and a positive electrode 200 for a lithium secondary battery including a positive electrode active material layer 40 on one side of a positive electrode current collector layer 50 can be seen, and the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are stacked with a separator 30 interposed therebetween. In addition, the negative electrode active material layer 20 may be formed on both sides of the negative electrode current collector layer 10. In addition, the positive electrode active material layer 40 may be formed on both sides of the positive electrode current collector layer 50.

[0127] A secondary battery according to an embodiment of the present 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 interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0128] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0129] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0130] 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; 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 satisfying 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.

[0131] 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 includes single particles or secondary particles, and the single particles may have an average particle size (D50) of 1 μm or more.

[0132] 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 more than 1 μm and 6 μm or less.

[0133] The single particles can have excellent particle strength even when formed to have a small average 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 The particle strength may be 100 to 300 MPa when the particle is 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 particle cracking is alleviated, thereby improving the life characteristics of the battery.

[0134] The single particles can be prepared by mixing a transition metal precursor and a lithium source material and calcining the mixture. The secondary particles can be prepared by a method different from that for the single particles, and the composition of the secondary particles can be the same as or different from that of the single particles.

[0135] The method for forming the single particles is not particularly limited, but may generally be formed by over-firing at an elevated firing temperature, or may be prepared by using an additive such as a grain growth promoter that is useful for over-firing, or by changing the starting material.

[0136] For example, the calcination is performed at a temperature that allows the formation of single particles. To form single particles, 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 must be performed at a temperature about 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 a high-nickel (Ni) NCM-based lithium transition metal oxide having a nickel (Ni) content of 80 mol% or more is to be formed into single particles, the calcination temperature may be about 700°C to 1000°C, preferably about 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. When the calcination temperature is lower than 790°C, a positive electrode active material containing a lithium transition metal compound in the form of secondary particles is produced. When the calcination temperature exceeds 950°C, excessive calcination may occur, resulting in an inadequate formation of a layered crystal structure and reduced electrochemical properties.

[0137] 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 similar-single particle that is an agglomeration of 30 or less primary particles.

[0138] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle or a similar-single particle which is an aggregate of 30 or less primary particles, and a secondary particle may be in the form of an aggregate of several hundred primary particles.

[0139] 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.

[0140] In the present invention, the single particle may be a single particle consisting of one primary particle or a similar-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.

[0141] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by agglomeration of primary particles, and can be distinguished from the concept of single particles, which includes one primary particle, one single particle, or a similar-single particle that is an agglomeration of 30 or less primary particles.

[0142] The particle diameter (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, and 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, more preferably 0.3m 2 / g~0.8m 2 / g.

[0143] 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.

[0144] 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.

[0145] 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 to 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.

[0146] 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.

[0147] 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.

[0148] 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 when formed to a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and improving the life characteristics and energy density of the battery.

[0149] 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.

[0150] 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.

[0151] 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 phenomenon of an increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery life characteristics.

[0152] 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.

[0153] 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 as the single particle positive electrode active material, and may refer to an aggregated form of single particles.

[0154] 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, relative to 100 parts by weight of the positive electrode active material layer.

[0155] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0156] 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.

[0157] 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.

[0158] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin polymers 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. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0159] Examples of the electrolyte 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 manufacturing lithium secondary batteries.

[0160] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0161] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-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.

[0162] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be used more preferably.

[0163] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0164] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0165] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore 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]

[0166] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0167] <Production example> <Production of negative electrode composition> A negative electrode slurry was prepared by adding Si (average particle size (D50): 5 μm) as a silicon-based active material, a metal composite satisfying the composition and content shown in Table 1 below, a second conductive material, SWCNT as a linear conductive material, and polyacrylamide (PAM) as a binder in the weight ratio shown in Table 1 below to distilled water as a solvent for forming a negative electrode slurry (solid concentration: 28 wt %).

[0168] In this case, based on 100 parts by weight of the negative electrode slurry, 9.685 parts by weight of the second conductive material, 0.315 parts by weight of the SWCNTs, and 10 parts by weight of the binder were used.

[0169] Specifically, the first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0170] As a specific mixing method, the first conductive material, the second conductive material, the binder, and the water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0171] The negative electrode current collector layer was made of a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0172] [Table 1]

[0173] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (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 a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0174] 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%).

[0175] A polyethylene separator was interposed between the positive electrode and the negative electrode of each of the examples and comparative examples, and an electrolyte was injected into the separator to prepare a lithium secondary battery.

[0176] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90, to which vinylene carbonate was added in an amount of 3 wt % based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1 M.

[0177] [Experimental Example 1: Evaluation of Mono-Cell Life] The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the capacity retention. The secondary batteries were subjected to an in-situ cycle test at 4.2-3.0 V and 1 C / 0.5 C, and the capacity retention was measured every 50 cycles during the test by charging / discharging at 0.33 C / 0.33 C (4.2-3.0 V). The results are shown in Table 2. Lifetime retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0178] [Table 2]

[0179] [Experimental Example 2: Evaluation of discharge resistance during initial cycle @SOC50 2.5C 0.1s (measurement of electrode resistance using a mono cell)] In Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during the test, and then the resistance was measured for a certain period of time (0.1s to 10s) when discharging at 2.5C pulse at SOC50. The results are shown in Table 3 below.

[0180] [Table 3]

[0181] As can be seen from Tables 1 to 3, when the metal composite according to the present application is used, the SOC of silicon itself is limited compared to when a silicon-based active material is used alone (compared to Comparative Example 1), and therefore it was confirmed that an improvement in life performance is achieved. That is, it was confirmed that the metal composite has the above-mentioned characteristics, reacts with lithium at a higher potential than the silicon-based active material, has excellent reactivity, and can suppress the volume expansion of the silicon-based active material during charge and discharge compared to when only the silicon-based active material is used, and therefore has the characteristic of having an excellent improvement in life performance.

[0182] Comparative Example 1 corresponds to a case where the metal composite according to the present application is not included, Comparative Example 2 corresponds to a case where the metal composite according to the present application is not used but a metal (Sn) is used alone, Comparative Example 3 corresponds to a case where the proportion of metal in the metal composite is low, and Comparative Example 4 corresponds to a case where the proportion of metal in the metal composite is high.

[0183] When comparing Comparative Example 1 with the Examples, it was confirmed that there was an improvement in lifespan performance, and that the resistance of the electrode in the Examples was maintained low. This corresponds to the result of the improvement in lifespan performance being achieved by limiting the SOC of silicon itself.

[0184] In Comparative Example 2, where a metal was used for the anode, lithium ions had to move from the top to the bottom of the electrode during the initial discharge, resulting in a relative imbalance between the top and bottom of the electrode, which resulted in a decrease in lifespan. However, in the Example, the lithium oxide was uniformly mixed, so when the initial electrochemical reaction occurred, lithium ions were distributed throughout the top and bottom of the electrode, allowing for more uniform incorporation of lithium ions, resulting in improved tortuosity.

[0185] In Comparative Examples 3 and 4, the weight ratio of the metal to lithium oxide in the metal oxide was adjusted, and it was confirmed that the desired effect could not be obtained when the weight ratio was above or below the range of the present application. [Explanation of symbols]

[0186] 10 Negative electrode current collector layer 20 Negative electrode active material layer 30 Separator 40 Cathode active material layer 50 Positive electrode current collector layer 100 Negative electrode for lithium secondary battery 200 Positive electrode for lithium secondary battery

Claims

1. A negative electrode composition comprising: a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, the negative electrode composition comprises a metal composite having a lithium oxide deposited thereon; The weight ratio of metal to lithium oxide in the metal composite is 10:1 or more and 800:1 or less, The negative electrode composition, wherein the metal composite is included in an amount of 1 part by weight to 15 parts by weight based on 100 parts by weight of the negative electrode composition.

2. The negative electrode composition according to claim 1 , wherein the silicon-based active material is included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

3. The silicon-based active material is SiO ｘ (x=0), SiO ｘ The negative electrode composition of claim 1 , comprising one or more selected from the group consisting of (0<x<2), SiC, and a Si alloy.

4. The silicon-based active material is SiO ｘ (x=0) and SiO ｘ (0<x<2), and based on 100 parts by weight of the silicon-based active material, the SiO ｘ The negative electrode composition according to claim 1 , comprising 70 parts by weight or more of (x=0).

5. 2. The negative electrode composition of claim 1, wherein the lithium oxide has a D50 particle size of 200 nm or less.

6. 2. The negative electrode composition according to claim 1, wherein the weight ratio of the metal composite to the silicon-based active material in the negative electrode composition is 1:5 to 1:

20.

7. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material is present in an amount of 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

8. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material comprises a sheet-shaped conductive material and a linear conductive material.

9. 9. The negative electrode composition according to claim 8, wherein the negative electrode conductive material comprises, based on 100 parts by weight of the negative electrode conductive material, 80 parts by weight or more and 99.9 parts by weight or less of the sheet-like conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

10. The negative electrode composition according to claim 1 , wherein the negative electrode binder is present in an amount of 5 parts by weight to 30 parts by weight based on 100 parts by weight of the negative electrode composition.

11. a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, The negative electrode active material layer comprises the negative electrode composition according to any one of claims 1 to 10 or a cured product thereof.

12. the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, 12. The negative electrode for a lithium secondary battery according to claim 11, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

13. positive electrode; The negative electrode for a lithium secondary battery according to claim 11; a separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

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