Negative electrode composition, negative electrode for lithium secondary battery including the same, lithium secondary battery including the negative electrode, and method for producing the negative electrode composition

Abstract

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

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0154386, filed with the Korean Intellectual Property Office on November 11, 2021, 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, a lithium secondary battery including the negative electrode, and a method for producing the negative electrode composition. [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 anode 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 associated with 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] Lithium secondary batteries are typically manufactured using lithium-intercalated compounds such as LiCoO2 and LiMn2O4 as the positive electrode and non-lithium-intercalated materials such as carbonaceous and silicon-based materials as the negative electrode. During charging, lithium ions intercalated in the positive electrode migrate to the negative electrode via the electrolyte, and during discharging, lithium ions migrate from the negative electrode to the positive electrode again. During charging, the lithium ions migrate from the positive electrode to the negative electrode react with the electrolyte to form a passivation film called a solid electrolyte interface (SEI) on the surface of the negative electrode. This SEI stabilizes the structure of the negative electrode by inhibiting the transfer of electrons required for the reaction between the negative electrode and the electrolyte and preventing the electrolyte decomposition reaction. However, since this reaction is irreversible, it results in the consumption of lithium ions. Therefore, research is being conducted on SEI layers that can provide greater stability and utilize the above benefits.

[0010] Therefore, even when a silicon-based compound is used as an active material to improve the capacity performance, research is needed on the silicon-based active material itself that can prevent the conduction path from being impaired due to the volume expansion of the silicon-based compound and on the formation of a more stable SEI layer.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] Recognizing the above problems and in order to improve the volume expansion problem of the silicon-based active material, when the silicon-based active material is coated and the coating layer is doped with a specific element, it has been found that the rapid volume expansion during charging and discharging of the silicon-based active material is alleviated and a more stable film is formed on the negative electrode.

[0013] Therefore, the present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, a lithium secondary battery containing the negative electrode, and a method for manufacturing the negative electrode composition.

Means for Solving the Problems

[0014] One embodiment of the present specification is a negative electrode composition containing a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the surface of the silicon-based active material includes a carbon coating layer, the carbon coating layer is doped with fluorine (F), 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, it contains 70 parts by weight or more of SiOx (x = 0).

[0015] In another embodiment, a step of preparing a silicon-based active material including a carbon coating layer doped with fluorine (F) on the surface; a step of mixing a negative electrode conductive material and a negative electrode binder to form a mixture; a step of adding water to the mixture and performing first mixing; and a step of adding a silicon-based active material including a carbon coating layer doped with fluorine (F) to the mixed mixture and performing second mixing; A method for manufacturing a negative electrode composition, wherein 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, provided is a method for manufacturing a negative electrode composition containing 70 parts by weight or more of SiOx (x = 0).

[0016] In yet another embodiment, provided is a negative electrode for a lithium secondary battery, including a negative electrode current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one or both surfaces of the negative electrode current collector layer.

[0017] Finally, provided is a lithium secondary battery including 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.

Advantages of the Invention

[0018] In the case of the negative electrode composition according to an embodiment of the present invention, when using a silicon-based active material, which is a high-capacity material, to manufacture a high-capacity battery, rather than adjusting the characteristics of the conductive material and the binder due to the volume expansion of the silicon-based active material, the characteristics of the silicon-based active material itself are adjusted. The surface of the silicon-based active material includes a carbon coating layer, and the carbon coating layer is doped with fluorine (F), which can relieve the rapid volume expansion during charging and discharging of the silicon-based active material, and fluorine is doped and reacts with FEC to form a more stable LiF film on the negative electrode together with the SEI layer.

[0019] 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 mix and use silicon-based compounds to increase the capacity have been on the rise. Particularly in the case of the negative electrode composition according to one embodiment of the present invention, the silicon-based active material contains one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and contains 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. Since it contains a high content of pure Si particles, it is characterized in that a high-capacity and high-density negative electrode can be produced.

[0020] The negative electrode composition according to the present application contains a high content of pure Si particles, so that a high-capacity and high-density negative electrode can be obtained. In order to solve problems such as volume expansion associated with containing a high content of pure Si particles, the silicon-based active material itself containing a high content of pure Si particles is coated with a carbon layer containing fluorine and used, thereby solving the volume expansion problem and making use of the advantages of the silicon-based active material.

[0021] That is, compared with the case of using a conventional silicon-based active material, when using a silicon-based active material having a specific content of silicon particles and surface-treated as in the present invention, the volume expansion during charging and discharging can also be minimized by using the negative electrode composition according to the present invention.

Brief Description of the Drawings

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

Modes for Carrying Out the Invention

[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 the average particle size, which is the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the 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, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in the diffraction pattern according to the 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. 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 the number-average molecular weight (Mn) are the polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0031] Hereinafter, a detailed description will be given with reference to the drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention may be realized in various different forms and is not limited to the following description.

[0032] One embodiment of this specification is a negative electrode composition containing a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the surface of the silicon-based active material includes a carbon coating layer, the carbon coating layer is doped with fluorine (F), 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, it provides a negative electrode composition containing 70 parts by weight or more of SiOx (x = 0).

[0033] In the case of the negative electrode composition according to one embodiment of the present invention, when using a silicon-based active material, which is a high-capacity material, to produce a high-capacity battery, instead of adjusting the characteristics of the conductive material and the binder due to the volume expansion of the silicon-based active material, the characteristics of the silicon-based active material itself are adjusted. The surface of the silicon-based active material includes a carbon coating layer, and by using a carbon coating layer doped with fluorine (F), it has the characteristics of alleviating the rapid volume expansion during charging and discharging of the silicon-based active material, and fluorine is doped and reacts with FEC to form a more stable LiF film on the negative electrode together with the SEI layer.

[0034] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and provides a negative electrode composition containing 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0035] In another embodiment, the SiOx (x = 0) may be contained 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 contained 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, based on 100 parts by weight of the silicon-based active material.

[0036] In one embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the metal impurities are common metals that can be contained in the silicon-based active material, and the content may be 1 part by weight or less, or 0.1 part by weight or less based on 100 parts by weight of the total silicon-based active material.

[0037] In one embodiment of the present application, the silicon-based active material may use particularly pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean containing pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range when based on 100 parts by weight of the total silicon-based active material as described above.

[0038] The silicon-based active material according to the present application contains 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. Compared with a silicon-based active material using a SiOx (0 < x < 2) system as the main substance, the SiOx (0 < x < 2) system has the drawback that its 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 SiOx (0 < x < 2) system, no matter what treatment is applied to the active material itself, it is impossible to achieve the same conditions in terms of charge and discharge capacity as in the case of having the silicon-based active material of the present invention.

[0039] Silicon-based active materials have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them are increasing. However, because of their high volume expansion during the charge / discharge process, they have only been used in small amounts by mixing with graphite-based active materials.

[0040] Therefore, in the case of the present invention, while only a pure silicon-based active material is used as the negative electrode active material to improve capacity performance, the surface of the silicon-based active material is coated with a specific material as described above to solve the above problems. In particular, the carbon coating alleviates the volume expansion of the silicon-based active material, and the fluorine doped into the carbon coating layer reacts with FEC to form a more stable LiF inorganic coating together with the SEI layer, thereby solving the conventional problems. This is a feature of the present invention.

[0041] 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 the above 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 above lower limit range, the complex consisting of the conductive material and the binder in the negative electrode slurry provides an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining the conductive network and improving the capacity retention rate. Meanwhile, when the average particle size is within the above range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0042] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0043] In one embodiment of the present application, the silicon-based active material may be, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or shard-like particles. Alternatively, but less advantageously, the silicon particles may have a fibrous structure or be in the form of a silicon-containing film or coating.

[0044] 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.

[0045] 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 80 parts by weight or less.

[0046] The negative electrode composition according to the present application is characterized in that even when a silicon-based active material with extremely high capacity is used within the above range, the performance of the negative electrode is not reduced and the output characteristics during charging and discharging are excellent, by using a specific surface coating that can suppress the volume expansion rate during charging and discharging, even when the silicon-based active material is contained within the above range.

[0047] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the circularity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0048] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter.

[0049] [Formula 1] 4πA / P 2

[0050] The surface of the silicon-based active material according to the present application includes a carbon coating layer, and the carbon coating layer is doped with fluorine (F). The silicon-based active material itself is formed from a material containing SiOx (x = 0) and SiOx (0 < x < 2). One or more particles selected from the group consisting of the SiOx (x = 0) and SiOx (0 < x < 2) contained in the silicon-based active material each have a carbon coating layer containing fluorine, or both cases where secondary particles formed by aggregation of one or more particles selected from the group consisting of the SiOx (x = 0) and SiOx (0 < x < 2) have a carbon coating layer containing fluorine are included.

[0051] In one embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloy.

[0052] In one embodiment of the present application, the doped fluorine (F) in the carbon coating layer is formed by a single bond between carbon and fluorine (F), providing a negative electrode composition.

[0053] In one embodiment of the present application, the carbon coating layer may satisfy a thickness range of 1 nm or more and 20 nm or less, preferably 5 nm or more and 15 nm or less, and more preferably 10 nm or more and 15 nm or less.

[0054] In one embodiment of the present application, the content of carbon contained in the carbon coating layer may be 5 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the silicon-based active material. <着

[0055] In another embodiment, the content of carbon contained in the carbon coating layer may satisfy a range of 5 parts by weight or more and 20 parts by weight or less, preferably 7 parts by weight or more and 15 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0056] In one embodiment of the present application, there is provided a negative electrode composition comprising 0.1 parts by weight or more and 20 parts by weight or less of fluorine (F) based on 100 parts by weight of the silicon-based active material.

[0057] In another embodiment, the fluorine (F) may be contained in an amount of 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, more preferably 0.2 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the silicon-based active material, and may also satisfy the range of 3 parts by weight or less, 1 part by weight or less.

[0058] The inclusion of fluorine as described above based on the silicon-based active material provides an appropriate thickness for the coating layer, allowing the capacity per weight to be maintained and mitigating rapid volume expansion during charge and discharge of the silicon-based active material. In addition, the fluorine is doped in the content and reacts with FEC to form a more stable LiF coating on the anode together with the SEI layer.

[0059] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based compounds into negative electrode active materials to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of the silicon-based active material itself are adjusted as described above, silicon-based compounds can experience rapid volume expansion during charge / discharge processes, which can damage the conductive paths formed in the negative electrode active material layer.

[0060] 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.

[0061] In one embodiment of the present application, the dot-like conductive material can be used to improve the conductivity of the negative electrode, and preferably does not induce chemical changes and has conductivity. Specifically, the conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black in order to achieve high conductivity and excellent dispersibility.

[0062] 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.

[0063] 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.

[0064] In particular, when the content of functional groups in the dot-like conductive material satisfies the above range, the 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 outstanding effect in improving dispersibility.

[0065] 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.

[0066] In other words, in the preparation of point-like conductive material, a high content of functional groups means that there is a lot of foreign matter, and a low content of functional groups means that more heat treatment processing has been performed. The point-like conductive material of the present application is characterized in that the point-like conductive material has been subjected to a certain partial heat treatment so that the content of functional groups satisfies the above range, thereby satisfying the above range of content of functional groups.

[0067] Specifically, the improved dispersibility of the dot-like conductive material allows the viscosity of the negative electrode slurry to be maintained at an appropriate level even when the content of the dot-like conductive material is increased in a negative electrode slurry having the same solid content, thereby maintaining stable processability and improving the uniformity of the formed negative electrode.

[0068] 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.

[0069] In one embodiment of the present application, the conductive material may include a sheet-shaped conductive material.

[0070] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also serve to prevent the conductive path from being disconnected due to volume expansion, and can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0071] In one embodiment of the present application, the sheet-shaped 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.

[0072] In one embodiment of the present application, the average particle size (D50) of the sheet-shaped conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the 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, excellent dispersion effect is achieved when dispersing using the same device and for the same time.

[0073] In one embodiment of the present application, the sheet-shaped conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0074] 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.

[0075] In one embodiment of the present application, the sheet-like conductive material may 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 may 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.

[0076] 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.

[0077] 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 300m 2 / g or less.

[0078] 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.

[0079] In yet 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.

[0080] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with each other, in a bundle or rope-like configuration. The carbon nanotube units each have a graphite sheet with a nanometer-sized diameter and a cylindrical shape with an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the bundled carbon nanotubes 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.

[0081] In one embodiment of the present application, there is provided a negative electrode composition, in which the negative electrode conductive material is contained in an amount of 10 parts by weight to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0082] 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.

[0083] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material comprises: a sheet-like conductive material; and a linear conductive material; and the negative electrode composition comprises, based on 100 parts by weight of the negative electrode conductive material, 80 parts by weight or more and 99.5 parts by weight or less of the sheet-like conductive material; and 0.5 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0084] In another embodiment, the negative electrode conductive material may contain 80 parts by weight or more and 99.5 parts by weight or less, preferably 85 parts by weight or more and 99 parts by weight or less, and more preferably 90 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.

[0085] In another embodiment, the negative electrode conductive material may contain 0.5 parts by weight or more and 20 parts by weight or less, preferably 1 part by weight or more and 15 parts by weight or less, and more preferably 2 parts by weight or more and 10 parts by weight or less, of the linear conductive material based on 100 parts by weight of the negative electrode conductive material.

[0086] In one embodiment of the present application, the negative electrode conductive material includes dot-like conductive material, sheet-like conductive material, and linear conductive material, each of which satisfies the above-mentioned composition and proportion, so that it does not have a significant effect on the life characteristics of conventional lithium secondary batteries. In particular, when it includes sheet-like conductive material and linear conductive material, it has the characteristics of having more points at which charging and discharging are possible, excellent output characteristics at high C-rates, and reduced gas generation at high temperatures.

[0087] The negative electrode conductive material according to the present application has a completely different structure from the 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 charging and discharging, while the positive electrode conductive material serves as a buffer that has a shock-absorbing function during rolling and also serves to impart some conductivity, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

[0088] 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.

[0089] In one embodiment of the present application, the plate-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 dot-like shape to facilitate the storage and release of lithium ions.

[0090] In contrast, the plate-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.

[0091] That is, in this application, the use of plate-like graphite 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.

[0092] 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 is used as a material that stores or releases lithium.

[0093] 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.

[0094] The negative electrode binder according to an embodiment of the present application serves to hold the active material and the conductive material in order to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. If the above role is satisfied, all general binders can be applied. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0095] In one embodiment of the present application, based on 100 parts by weight of the negative electrode composition, the negative electrode binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and may also be included in an amount of 5 parts by weight or more, 10 parts by weight or more.

[0096] Compared with the conventional carbon-based negative electrode, when a Si-based negative electrode is used, by applying an aqueous binder in the above parts by weight, a point-like conductive material with a low functional group content can be used. Due to the above characteristics, the point-like conductive material has hydrophobicity, so it has the characteristic of excellent bonding strength between the conductive material and the binder.

[0097] In one embodiment of the present application, a method for manufacturing a negative electrode composition includes: preparing a silicon-based active material including a carbon coating layer doped with fluorine (F) on the surface; mixing a negative electrode conductive material and a negative electrode binder to form a mixture; adding water to the mixture and performing a first mixing; and adding a silicon-based active material including a carbon coating layer doped with fluorine (F) to the mixed mixture and performing a second mixing. 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) is included in an amount of 70 parts by weight or more.

[0098] In the method for manufacturing the negative electrode composition, each composition included in the negative electrode composition is the same as the description above.

[0099] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode composition, wherein the step of preparing a silicon-based active material having a carbon coating layer doped with fluorine (F) on its surface includes the steps of: adding the silicon-based active material to a polymer solution containing fluorine (F); adding ethanol to the polymer solution to bond the fluorine (F)-containing polymer to the surface of the silicon-based active material; and carbonizing the bonded polymer.

[0100] In one embodiment of the present application, the step of carbonizing the bound polymer may be a step of carbonizing a polymer containing fluorine (F) on the surface of the silicon-based active material.

[0101] In one embodiment of the present application, the fluorine (F)-containing polymer may be any substance that provides fluorine (F) and carbon (C) atoms, and specifically, polyvinylidene fluoride (PVdF) or Teflon (registered trademark) may be used, but is not limited thereto.

[0102] In one embodiment of the present application, the fluorine (F)-containing polymer solution may be any solution that can dissolve the fluorine (F)-containing polymer, and specifically, dimethylformamide (DMF) may be used.

[0103] In one embodiment of the present application, the step of adding the silicon-based active material to the polymer solution containing fluorine (F) may include a step of adding the silicon-based active material according to the present application to the polymer solution containing fluorine (F), and may further include a step of stirring within a range of 1 hour to 12 hours after the addition.

[0104] In one embodiment of the present application, a fluorine-doped carbon coating layer may be formed on the surface of the silicon-based active material of the present application by carbonizing the polymer.

[0105] In one embodiment of the present application, the carbonizing step may include a step of performing a heat treatment at 500° C. to 1000° C. for 30 minutes to 3 hours in an inert gas atmosphere in a high-temperature furnace.

[0106] Through the carbonization process described above, the silicon-based active material according to the present application can be surface-modified into a silicon-based active material having a carbon coating layer doped with fluorine (F) on the surface.

[0107] In one embodiment of the present application, there is provided a method for producing a negative electrode composition, wherein the first mixing and second mixing steps are steps of mixing at 2,000 rpm to 3,000 rpm for 10 minutes to 60 minutes.

[0108] In one embodiment of the present application, a negative electrode for a lithium secondary battery may be formed by coating one or both sides of a current collector with a negative electrode slurry containing the negative electrode composition.

[0109] In one embodiment of the present application, the negative electrode slurry may include: a negative electrode composition; and a slurry solvent.

[0110] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0111] 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%.

[0112] 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.

[0113] 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.

[0114] 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 current collector layer, the negative electrode active material layer comprising the negative electrode composition according to the present application.

[0115] 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 can be seen, including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows a negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0116] In one embodiment of the present application, the negative electrode current collector generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector is not particularly limited as long as it does not induce 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, aluminum-cadmium alloy, etc. 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 may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, nonwoven fabric, etc.

[0117] 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.

[0118] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0119] 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.

[0120] 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%.

[0121] 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.

[0122] 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.

[0123] 2 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.

[0124] A secondary battery according to an embodiment of the present specification may include 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.

[0125] 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.

[0126] The positive electrode current collector in the positive electrode 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 surface-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 the surface of the current collector may be formed with fine irregularities 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.

[0127] 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 Ni-site type lithium nickel oxide represented by the chemical formula LiMn 2-c3 M c3 Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0128] 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.

[0129] 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.

[0130] The single particles can have excellent particle strength even when formed into small particle sizes with an 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.

[0131] 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.

[0132] The method for forming the single particles is not particularly limited, but may generally be formed by over-firing at an elevated firing temperature, using an additive such as a grain growth promoter that aids in over-firing, or by changing the starting material.

[0133] 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 the production of 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 the production of 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 including single particles with excellent electrochemical properties can be produced. When the calcination temperature is lower than 790°C, a positive electrode active material including a lithium transition metal compound in the form of secondary particles is produced. When the calcination temperature exceeds 950°C, excessive calcination may result in an inadequate formation of a layered crystal structure, resulting in poor electrochemical properties.

[0134] 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 quasi-single particle form that is an agglomeration of 30 or less primary particles.

[0135] Specifically, in the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-single particle form 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.

[0136] 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.

[0137] In the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-single particle form 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.

[0138] 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 form that is an agglomeration of 30 or less primary particles.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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 have 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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 the form of aggregation of single particles.

[0151] In one embodiment of the present application, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, in 100 parts by weight of the positive electrode active material layer.

[0152] 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.

[0153] 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 materials may be used alone or in combination.

[0154] 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. One or more of these may be used alone or in combination.

[0155] The separator separates the negative electrode and positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferred 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 laminate 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 coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0156] 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.

[0157] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0158] 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.

[0159] 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.

[0160] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0161] 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 derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0162] 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 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]

[0163] Below, preferred examples are presented to help understand the present invention, but these examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0164] Example 1 [Production of negative electrode] Polyvinylidene fluoride (PVDF) was added to dimethylformamide (DMF) at a concentration of 0.5 wt%, sonicated for 1 hour, and then stirred overnight. Then, 2 wt% Si was added to the solution, stirred for 3 hours, and then ethanol was added dropwise and stirred for another hour. After centrifuging the ethanol solution three times, the solution was vacuum dried at 70°C for 12 hours and then heat-treated in a high-temperature furnace under an Ar atmosphere at 700°C for 1 hour to obtain carbon-coated Si. The amount of carbon coated was 7% relative to the Si, the coating thickness was 10 nm, and the amount of F was 0.2 wt% relative to the Si.

[0165] The above-prepared Si was used as the active material (100% Si with a carbon coating layer containing F), and a plate-shaped graphite conductive material (average particle size 3.5 μm) as the first conductive material, SWCNT as the second conductive material, and acrylamide as the binder were added to distilled water as the solvent in a weight ratio of 79.5:10:0.5:10 to prepare a negative electrode slurry.

[0166] Then, a negative electrode active material layer was coated to a thickness of 30 μm on a copper foil (Cu foil) having a thickness of 15 μm, dried at 130° C. for 12 hours, and rolled to a porosity of 40% to prepare a negative electrode.

[0167] <Example 2> The same method as in Example 1 was used to prepare the silicon nanoparticles, except that polyvinylidene fluoride (PVDF) was added to dimethylformamide (DMF) at 2 wt %, and the amount of carbon coated was 12% relative to Si, the coating thickness was 13 nm, and the amount of F was 0.4 wt % relative to Si.

[0168] Example 3 The same method as in Example 1 was used to prepare the silicon nanoparticles, except that polyvinylidene fluoride (PVDF) was added to dimethylformamide (DMF) at a concentration of 0.25 wt %, and the amount of carbon coated was 4% relative to Si, the coating thickness was 5 nm, and the amount of F was 0.003 wt % relative to Si.

[0169] Example 4 An anode was fabricated in the same manner as in Example 1, except that the Si prepared above was used as the active material (100% Si with a carbon coating layer containing F), SWCNT as the conductive material, and acrylamide as the binder were added to distilled water as the solvent in a weight ratio of 89.5:0.5:10 to prepare an anode slurry.

[0170] <Example 5> An anode was fabricated in the same manner as in Example 1, except that the Si prepared above was used as the active material (100% Si with a carbon coating layer containing F), dot-like carbon black (Super-P) as a conductive material, plate-like graphite conductive material (average particle size 3.5 μm), SWCNTs, and acrylamide as a binder were added to distilled water as a solvent in a weight ratio of 79.5:5:5:0.5:10 to prepare an anode slurry.

[0171] <Comparative Example 1> A negative electrode was prepared in the same manner as in Example 1, except that a Si active material (Si 100%) without an F-doped carbon coating layer was used.

[0172] <Comparative Example 2> A negative electrode was prepared in the same manner as in Example 1, except that SiO 2 was used as the active material.

[0173] <Comparative Example 3> A negative electrode was prepared in the same manner as in Example 1, except that SiO containing no F and 5 wt % of a carbon coating layer (SiO 100% containing a carbon coating layer) was used.

[0174] <Comparative Example 4> A negative electrode was prepared in the same manner as in Example 1, except that a Si active material (Si 100%) including a carbon coating layer not doped with F was used.

[0175] <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%).

[0176] 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%).

[0177] 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.

[0178] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70, to which 3 wt % vinylene carbonate was added based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1 M.

[0179] [Experimental Example 1: Evaluation of initial efficiency of lithium secondary batteries] The initial charge / discharge capacity and initial efficiency of the lithium secondary batteries prepared in the Examples and Comparative Examples were evaluated using an electrochemical charge / discharge device.

[0180] The capacity and efficiency per gram of the lithium secondary battery were calculated under the conditions of charging (0.1C CC / CV charging, 0.005V, 0.005C cut) and discharging (0.1C CC discharging, 1.5V cut), and the results are shown in Table 1 below.

[0181] [Table 1]

[0182] [Experimental Example 2: Evaluation of capacity retention rate of lithium secondary battery] The capacity retention rate of the lithium secondary batteries manufactured in the Examples and Comparative Examples was evaluated using an electrochemical charge / discharge device.

[0183] The number of cycles required to reduce the capacity to 80% was confirmed under the conditions of charging (0.5C CC / CV charging, 0.005V, 0.005C cutoff) and discharging (0.5C CC discharging, 1.0V cutoff) the lithium secondary battery.

[0184] The capacity retention rate after the Nth charge was evaluated using the following formula, and the results are shown in Table 2 below.

[0185] [formula] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0186]

Table 2

[0187] Comparative Example 1 in Table 1 and Table 2 uses pure Si as the active material and does not include a carbon coating layer doped with F. Comparitive Example 4 uses pure Si as the active material and includes only a simple carbon coating layer. That is, in Comparitive Example 1 and Comparitive Example 4, the same type of active material is used, and the initial efficiency is in a range similar to that of the examples. However, it was confirmed that the capacity retention rate and discharge capacity in Table 2 decreased. This is the result of being unable to relieve the expansion of the volume of the active material and being unable to form a stable LiF film.

[0188] Also, in the case of the present invention, pure Si (the silicon-based active material includes SiOx (x = 0) and SiOx (0 < x < 2), and contains 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the silicon-based active material) is used as the active material. When comparing Examples 1 to 4 with Comparitive Example 2 (SiO active material) and Comparitive Example 3 (SiO active material), it was confirmed that the initial efficiency decreased.

[0189] Specifically, Comparitive Example 2 is the case of using a carbon layer doped with F in SiO, and Comparitive Example 3 is the case of using only a carbon coating layer in SiO. In both cases, the initial efficiency can be increased by 1 to 2% compared to the SiO active material without other treatments. However, it was confirmed that the initial efficiency is inferior to that of the examples, and the charge / discharge capacity is very inferior compared to the case of having pure Si as the active material.

[0190] That is, Comparative Examples 2 and 3 using SiO active material are 1:1 composites of Si and SiO2, and exhibit low initial efficiency due to an irreversible reaction between the oxide and Li. However, due to the subsequent reversible reaction, the capacity retention rate can be evaluated as being better than that of Si active material (see Table 2). However, as can be seen from Table 1, the theoretical capacity is far inferior to that of Si, and when SiO active material is used, it is not possible to achieve conditions equivalent to the charge and discharge capacity of Example 1 of the present invention. Therefore, it was confirmed that it was not possible to manufacture a high-capacity lithium secondary battery as intended by the present application.

[0191] As a result, as can be seen from Tables 1 and 2, in the case of the anode composition according to one embodiment of the present invention, when a silicon-based active material, which is a high-capacity material, is used to prepare a high-capacity lithium secondary battery, the characteristics of the silicon-based active material itself are adjusted rather than adjusting the characteristics of the conductive material and binder due to the volume expansion of the silicon-based active material. The surface of the silicon-based active material includes a carbon coating layer, and the carbon coating layer is doped with fluorine (F), which alleviates the rapid volume expansion of the silicon-based active material during charge and discharge. In addition, the doped fluorine reacts with FEC to form a more stable LiF coating on the anode together with the SEI layer.

[0192] Furthermore, in Examples 1 and 2, the amount of F doped was larger than that in Example 3, and it was confirmed that the thickness of the coating layer was appropriate due to the fluorine content, and the capacity per weight was better than that of Example 3. [Explanation of symbols]

[0193] 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 surface of the silicon-based active material includes a carbon coating layer; The carbon coating layer is doped with fluorine (F), The silicon-based active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and includes 70 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material; the negative electrode conductive material includes a sheet-shaped conductive material and a linear conductive material; The negative electrode conductive material contains 80 parts by weight or more and 99.5 parts by weight or less of the sheet-like conductive material, and 0.5 parts by weight or more and 20 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material, The doped fluorine (F) in the carbon coating layer is formed by a single bond between carbon and fluorine (F).

2. The negative electrode composition according to claim 1 , comprising 60 parts by weight or more of the silicon-based active material based on 100 parts by weight of the negative electrode composition.

3. 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.

4. The negative electrode composition according to claim 1 , comprising 0.1 to 20 parts by weight of fluorine (F) based on 100 parts by weight of the silicon-based active material.

5. preparing a silicon-based active material having a carbon coating layer doped with fluorine (F) on its surface; mixing a negative electrode conductive material and a negative electrode binder to form a mixture; adding water to the mixture and performing a first mixing; and adding a silicon-based active material including a fluorine (F)-doped carbon coating layer to the mixed mixture and performing a second mixing; A method for producing a negative electrode composition, comprising: The silicon-based active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and includes 70 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material; The step of preparing a silicon-based active material including a carbon coating layer doped with fluorine (F) on the surface thereof includes: Adding a silicon-based active material to a polymer solution containing fluorine (F); Adding ethanol to the polymer solution to bond the fluorine (F)-containing polymer to the surface of the silicon-based active material; and carbonizing the bound polymer; A method for producing a negative electrode composition, comprising:

6. 6. The method for producing a negative electrode composition according to claim 5, wherein the first mixing and the second mixing are performed at 2,000 rpm to 3,000 rpm for 10 minutes to 60 minutes.

7. a negative electrode current collector layer; and a negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 4, formed on one or both surfaces of the negative electrode current collector layer; A negative electrode for a lithium secondary battery comprising:

8. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 8. The negative electrode for a lithium secondary battery according to claim 7, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

9. Positive electrode; The negative electrode for a lithium secondary battery according to claim 7; a separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

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