Negative electrode pre-dispersion, negative electrode composition containing the same, negative electrode for lithium secondary battery containing the negative electrode composition, lithium secondary battery containing the negative electrode, and method for producing the negative electrode composition

Abstract

The present application relates to a negative electrode pre-dispersion liquid, a negative electrode composition containing the same, a negative electrode for a lithium secondary battery containing the negative electrode composition, a lithium secondary battery containing 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. 10-2021-0142054, filed with the Korean Intellectual Property Office on October 22, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode pre-dispersion, a negative electrode composition containing the same, a negative electrode for a lithium secondary battery containing the negative electrode composition, a lithium secondary battery containing 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 released 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, which have a capacity 10 times larger than that of graphite-based materials, as anode active materials. However, while 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] Therefore, even when silicon-based compounds are used as active materials to improve capacity performance, research is needed into conductive materials that can prevent damage to the conductive paths due to the volume expansion of the silicon-based compounds, and into pre-dispersion liquids that can uniformly disperse deformed conductive materials under certain conditions to achieve the above-mentioned objectives. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0011] In silicon-based anodes, the degree of dispersion of carbon nanotubes and the subsequent bonding relationship between SWCNTs (single-walled carbon nanotubes) and silicon-based active materials are important. Research has shown that when specific functional groups are included as functional groups in the dispersant contained in the carbon nanotube pre-dispersion liquid, the degree of dispersion is excellent and subsequently hydrogen bonds are formed with -OH groups on the surface of the silicon-based active material, strengthening the bonding strength between the carbon nanotubes and silicon.

[0012] Therefore, the present application relates to a negative electrode pre-dispersion, a negative electrode composition containing the same, a negative electrode for a lithium secondary battery containing the negative electrode composition, a lithium secondary battery containing the negative electrode, and a method for producing the negative electrode composition. [Means for solving the problem]

[0013] One embodiment of the present specification provides a negative electrode pre-dispersion comprising: a pre-dispersion material containing carbon nanotubes and a dispersant; and a dispersion medium; wherein the dispersant contains a carboxyl group as a functional group, and the solids content of the pre-dispersion material is 5% or less based on the negative electrode pre-dispersion material, and the negative electrode pre-dispersion comprises: 20 to 60 parts by weight of the carbon nanotubes, and 40 to 80 parts by weight of the dispersant, based on 100 parts by weight of the pre-dispersion material.

[0014] In another embodiment, there is provided a negative electrode composition comprising: a silicon-based active material; a negative electrode pre-dispersion according to the present application; and a negative electrode binder; wherein the silicon-based active material is present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0015] In yet another embodiment, there is provided a method for manufacturing a negative electrode composition, the method including the steps of: forming a pre-dispersion by mixing carbon nanotubes and a dispersant having a carboxyl group as a functional group; adding a dispersant to the pre-dispersion so that the solid content of the pre-dispersion is 5% or less; dispersing the pre-dispersion containing the dispersant; mixing a negative electrode binder with water to form a mixture, and adding the pre-dispersion to the mixture to perform a first mixing; and adding a silicon-based active material to the mixed mixture to perform a second mixing. The method includes, based on 100 parts by weight of the pre-dispersion, 20 to 60 parts by weight of the carbon nanotubes; and 40 to 80 parts by weight of the dispersant.

[0016] In yet 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 formed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition according to the present application.

[0017] 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]

[0018] In the case of a negative electrode pre-dispersion according to one embodiment of the present invention, the dispersant contains a carboxyl group as a functional group, and the solid content of the pre-dispersion is 5% or less based on the negative electrode pre-dispersion. Based on 100 parts by weight of the pre-dispersion, 20 to 60 parts by weight of the carbon nanotubes and 40 to 80 parts by weight of the dispersant are used.

[0019] The negative electrode pre-dispersion according to the present application is a solution in which carbon nanotubes are dispersed before being incorporated into a negative electrode composition, and is characterized by excellent dispersibility of carbon nanotubes because the solid content of the pre-dispersion material, the content of carbon nanotubes, and the content of the dispersant in the pre-dispersion satisfy certain ranges.

[0020] Furthermore, while no major problems occurred when used as a conventional carbon-based negative electrode, when a silicon-based active material is used, the expansion of the volume causes a problem in which the conductive path between the conductive materials is interrupted. To solve this problem, instead of adding another component to the negative electrode composition according to one embodiment of the present application, a carboxyl group is included as a functional group of the dispersant contained in the carbon nanotube pre-dispersion liquid, which then forms a hydrogen bond with the -OH group on the surface of the silicon-based active material, thereby strengthening the bonding strength between the carbon nanotubes and silicon.

[0021] When the bonding strength between carbon nanotubes and silicon is strengthened, the pathway between the conductive material is maintained even during repeated charging and discharging, and the use of silicon active material can be made uniform. Therefore, when using conventional silicon-based active materials, the volume expansion during charging and discharging can be minimized by using the anode composition 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 stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 3] FIG. 1 shows the results of initial capacity evaluation of half cells of negative electrodes of Examples 1 and 2 according to the present application. [Figure 4] FIG. 1 shows the results of half-cell evaluation of negative electrodes of Examples 1 and 2 according to the present application. [Figure 5]FIG. 1 is a diagram showing the results of CHC cycle evaluation of negative electrodes produced in Example 1, Example 2, and Comparative Example 1 according to the present application. DETAILED DESCRIPTION OF THE INVENTION

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

[0024] In this specification, "p to q" means a range of "not less than p and not more than q." 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.

[0025] In this specification, "Dn" refers to the average particle size, or 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.

[0026] 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.

[0027] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0028] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization as standard substances for molecular weight measurement. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0029] 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.

[0030] One embodiment of the present specification provides a negative electrode pre-dispersion comprising: a pre-dispersion material containing carbon nanotubes and a dispersant; and a dispersion medium; wherein the dispersant contains a carboxyl group as a functional group, and the solids content of the pre-dispersion material is 5% or less based on the negative electrode pre-dispersion material, and the negative electrode pre-dispersion comprises: 20 to 60 parts by weight of the carbon nanotubes, and 40 to 80 parts by weight of the dispersant, based on 100 parts by weight of the pre-dispersion material.

[0031] In one embodiment of the present application, the pre-dispersion refers to a dispersion before a material is contained in a negative electrode composition, and the pre-dispersion and the negative electrode composition are used in different senses.

[0032] In one embodiment of the present application, the dispersing agent may be one selected from the group consisting of xanthan gum; alginate; and a compound represented by the following chemical formula 1:

[0033] [ka]

[0034] In the above Chemical Formula 1, m is an integer from 1 to 10; n is an integer from 1 to 1000.

[0035] In one embodiment of the present application, m may be an integer of 1 to 10, preferably an integer of 1 to 5, and more preferably an integer of 1 to 3.

[0036] In one embodiment of the present application, there is provided a negative electrode pre-dispersion liquid, in which the dispersant includes one selected from the group consisting of PPBT (poly[3-(potassium-4-butanoate)thiophene-2,5-diyl]); xanthan gum; and alginate.

[0037] In one embodiment of the present application, the dispersant may include CMC. In one embodiment of the present application, the dispersant may be a conjugated polymer containing a carboxyl group as a functional group and having alternating single and double bonds in the molecule.

[0038] In one embodiment of the present application, the dispersant contains a carboxyl group as a functional group, and when the dispersant is used, it has the characteristic of being excellent in dispersibility of carbon nanotubes, and in particular, when the dispersant is subsequently contained in a negative electrode composition, it can strengthen the bond between the carbon nanotubes and the silicon-based active material by hydrogen bonding with Si-OH groups on the surface of the silicon-based active material used together.

[0039] As described above, the dispersant according to the present application contains a carboxyl group as a functional group, which can form hydrogen bonds with the Si-OH groups on the surface of the silicon-based active material. Hydrogen bonds can also be formed with amine groups. However, in the case of the present application, the enthalpy between the functional groups, which is related to the hydrogen bond strength, is 21 kJ / mol or 5.0 kcal / mol when the dispersant has a carboxyl group, and 8 kJ / mol or 1.9 kcal / mol when the dispersant has an amine group. In other words, given the same number of functional groups and circumstances, when a dispersant with an amine group is used, the binding strength with the Si active material is weaker than that of a dispersant with a carboxyl group as intended by the present invention, and the effect of improving electrical connectivity may be significantly reduced. Therefore, when a dispersant with a carboxyl group according to the present invention is used, it is possible to expect both improved dispersion performance and improved binding strength with Si.

[0040] Among these dispersants, the PPBT dispersant in particular is a conjugated polymer with carboxyl groups and alternating single and double bonds in the main chain. The PPBT dispersant effectively wraps SWCNTs through π-π interactions between the π electrons in the main chain and the π electron planes of SWCNTs. The carboxyl groups in the PPBT side chains effectively debundle bundled SWCNTs, thereby improving dispersibility.

[0041] In one embodiment of the present application, the solid content of the pre-dispersion material may be 5% or less based on the negative electrode pre-dispersion liquid.

[0042] In another embodiment, the solid content of the pre-dispersion material may be 5% or less, preferably 3% or less, more preferably 2% or less, and may be 0.1% or more, preferably 1% or more, based on the negative electrode pre-dispersion liquid.

[0043] The solid content of the pre-dispersion material satisfies the above range based on the negative electrode pre-dispersion liquid. By satisfying the above range, the carbon nanotubes contained in the pre-dispersion material can be efficiently dispersed, and the viscosity range can be kept within a certain range, thereby preventing aggregation of the pre-dispersion liquid.

[0044] That is, the pre-dispersion liquid of the present application uses carbon nanotubes with a large specific surface area, and in this case, by satisfying the above-mentioned solid content range, it is possible to exhibit a viscosity range that allows dispersion, and has the characteristic of enabling smooth pre-dispersion.

[0045] In one embodiment of the present application, there is provided a negative electrode pre-dispersion liquid comprising: 20 parts by weight or more and 60 parts by weight or less of the carbon nanotubes; and 40 parts by weight or more and 80 parts by weight or less of the dispersant, based on 100 parts by weight of the pre-dispersion material.

[0046] In another embodiment, the carbon nanotubes may be present in an amount of 20 parts by weight or more and 60 parts by weight or less, preferably 25 parts by weight or more and 55 parts by weight or less, more preferably 30 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the pre-dispersion material.

[0047] In another embodiment, the dispersant may be present in an amount of 40 parts by weight or more and 80 parts by weight or less, preferably 45 parts by weight or more and 75 parts by weight or less, and more preferably 50 parts by weight or more and 70 parts by weight or less, based on 100 parts by weight of the pre-dispersion material.

[0048] As described above, when the content of carbon nanotubes and dispersant in the pre-dispersion material satisfies the above range, the viscosity range of the mixture can be formed to a degree that allows subsequent dispersion. If the content of carbon nanotubes is lower than the above range, the effect of improving conductivity decreases, and if it is higher than the above range, the aggregation phenomenon between carbon nanotubes increases, resulting in poor dispersion.

[0049] In one embodiment of the present application, the dispersion medium is preferably a nonionic compound having no ionic functional groups, capable of acting as a negative electrode binder after the formation of a coating, not affecting the electrical properties, or a compound having a low decomposition temperature that allows it to be removed by heat treatment during the preparation of an electrode, and more preferably, having ionic properties due to the polar solvent, or having a hydroxyl group as a functional group in order to improve solubility in the solvent.

[0050] Specifically, in one embodiment of the present application, the dispersion medium may be water. In one embodiment of the present application, there is provided a negative electrode pre-dispersion having a viscosity of 100 cP or more and 10,000 cP or less.

[0051] In another embodiment, the viscosity of the negative electrode pre-dispersion liquid may be 100 cP or more and 10,000 cP or less, preferably 300 cP or more and 7,000 cP or less.

[0052] The viscosity of the negative electrode pre-dispersion may vary depending on the solid content of the pre-dispersion material and the pre-dispersion substance, but may satisfy the above range when the solid content of the pre-dispersion material and the pre-dispersion substance are used as described above. In particular, the pre-dispersion material for the negative electrode pre-dispersion is contained in the above content, and the viscosity is adjusted by the dispersion process described below. By satisfying the above viscosity range, mixing is favorable when the pre-dispersion material is subsequently added to the negative electrode composition, thereby improving the output power of the secondary battery.

[0053] That is, the negative electrode pre-dispersion according to one embodiment of the present application is a pre-dispersion of carbon nanotubes having high hydrophobic properties, and when the pre-dispersion is subsequently applied to a negative electrode, it can suppress the aggregation phenomenon of the highly hydrophobic point-like conductive material, thereby achieving excellent electrode performance.

[0054] In one embodiment of the present application, the negative electrode pre-dispersion liquid may be prepared by first mixing carbon nanotubes and the dispersant, then adding a dispersion medium to adjust the solid content, and dispersing the mixture using a homogenizer capable of applying high stress or pressure, a homomixer capable of mixing at high speed, or a mill using beads.

[0055] Thereafter, a PSD particle size analysis is performed to determine whether a certain particle size is obtained, and then the dispersion is subjected to a rheometer to determine a shear viscosity curve to determine whether a certain slope is obtained, thereby preparing the negative electrode pre-dispersion according to the present application.

[0056] In one embodiment of the present application, there is provided a negative electrode pre-dispersion liquid, wherein the weight average molecular weight of the dispersant is 10,000 g / mol or more and 100,000 g / mol or less.

[0057] In another embodiment, the weight average molecular weight of the dispersant may satisfy the range of 10,000 g / mol or more and 100,000 g / mol or less, preferably 10,000 g / mol or more and 50,000 g / mol or less.

[0058] As described above, when the weight average molecular weight of the dispersant satisfies the above range, the viscosity of the pre-dispersion liquid itself can be adjusted within a certain range, which has the advantage of preventing the aggregation phenomenon of carbon nanotubes.

[0059] In one embodiment of the present application, a negative electrode composition comprising a silicon-based active material; a negative electrode pre-dispersion liquid according to the present application; and a negative electrode binder, wherein the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition, is provided.

[0060] Rather than adding another composition to the negative electrode composition according to one embodiment of the present application, a carboxyl group is included as a functional group of the dispersant contained in the carbon nanotube pre-dispersion liquid, and later, it forms a hydrogen bond with the -OH group on the surface of the silicon-based active material, having the characteristic that the bonding force between the carbon nanotube and silicon can be strengthened.

[0061] In one embodiment of the present application, a negative electrode composition is provided, wherein the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloy.

[0062] 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), SiOx (0 < x ≤ 2), and metal impurities, 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, to provide a negative electrode composition.

[0063] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0064] The negative electrode composition contains a silicon-based active material in the above content parts, and by satisfying the above range, later, the carboxyl group-containing dispersion liquid contained in the pre-dispersion liquid forms a hydrogen bond with the OH group on the surface of the silicon-based active material, having the characteristic that the bond between the carbon nanotube and the active material can be strengthened.

[0065] In one embodiment of the present application, the silicon-based active material may be, in particular, pure silicon (Si). Using pure silicon (Si) as the silicon-based active material may mean that, based on 100 parts by weight of the total silicon-based active material as described above, pure Si particles (SiOx (x=0)) not bonded to other particles or elements are contained within the above range.

[0066] 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 and discharge process, they have only been used in small amounts by mixing with graphite-based active materials.

[0067] Therefore, in the present invention, in order to improve capacity performance, only a silicon-based active material is used as the negative electrode active material, but in order to solve the above-mentioned problems, a negative electrode pre-dispersion liquid is prepared to improve the dispersibility of carbon nanotubes and strengthen the bond with the active material, thereby solving the conventional problems.

[0068] 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 is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the above lower limit range, the complex consisting of the conductive material and the negative electrode binder in the negative electrode slurry has 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.

[0069] 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).

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 conductive material and a negative electrode binder that can suppress the volume expansion rate during charging and discharging, even when the silicon-based active material is contained within the above range.

[0074] 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.

[0075] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter. [Formula 1] 4πA / P 2

[0076] While graphite-based compounds have traditionally been used exclusively as anode active materials, attempts to incorporate silicon-based compounds to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, silicon-based compounds have limitations, such as their rapid volume expansion during charge / discharge processes damaging the conductive pathways formed in the anode active material layer and reducing battery performance. Therefore, a certain conductive material may be included.

[0077] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode composition further comprises a negative electrode conductive material, and the negative electrode conductive material comprises one or more selected from the group consisting of a dot-like conductive material and a sheet-like conductive material.

[0078] 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.

[0079] 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.

[0080] 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 40 nm to 60 nm.

[0081] In one embodiment of the present application, the conductive material may include a sheet-shaped conductive material. The sheet-shaped conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode, and can also play a role in preventing the conductive path from being broken due to volume expansion.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] In one embodiment of the present application, the sheet-shaped conductive material has a BET specific surface area of ​​100 m 2 / g or more.

[0086] In another embodiment, the sheet-shaped conductive material has a BET specific surface area of ​​100 m 2 / g or more 500m 2 / g or less, preferably 150m 2 / g or more 300m 2 / g or less, more preferably 200m 2 / g or more 300m 2 / g or less.

[0087] Other conductive materials include linear conductive materials such as carbon nanotubes contained in the negative electrode pre-dispersion liquid. 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 their longitudinal axes substantially aligned in the same direction, forming a bundle or rope-like structure. The carbon nanotube units have graphite sheets with a nanometer-sized diameter and an sp2 bonding structure. Depending on the curved angle and structure of the graphite sheets, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly during negative electrode fabrication, smoothly forming a conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0088] In one embodiment of the present application, the carbon nanotubes may be SWCNTs.

[0089] In one embodiment of the present application, the average length of the SWCNTs may be in the range of 500 nm or more and 20 μm or less.

[0090] In one embodiment of the present application, the negative electrode pre-dispersion liquid may refer to pre-dispersed carbon nanotubes, and the negative electrode pre-dispersion liquid includes the pre-dispersed carbon nanotubes and a dispersant.

[0091] That is, in one embodiment of the present application, when the negative electrode pre-dispersion liquid is contained in the negative electrode, the dispersion medium may be removed, and the negative electrode pre-dispersion liquid may contain pre-dispersed carbon nanotubes and a dispersant.

[0092] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is contained in an amount of 5 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 5 parts by weight or more and 40 parts by weight or less, preferably 5 parts by weight or more and 30 parts by weight or less, and more preferably 7 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, in which the negative electrode pre-dispersion liquid contains 0.01 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0095] In another embodiment, the negative electrode pre-dispersion liquid may contain 0.01 parts by weight or more and 20 parts by weight or less, preferably 0.02 parts by weight or more and 18 parts by weight or less, and more preferably 0.03 parts by weight or more and 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0096] In one embodiment of the present application, the negative electrode pre-dispersion liquid can be used as a conductive material. In this case, the negative electrode pre-dispersion liquid may have a solid content of 5% or less.

[0097] In one embodiment of the present application, when the negative electrode pre-dispersion liquid satisfies the above-described composition and proportions, it has the characteristics of increasing the number of points at which charging and discharging are possible and providing excellent output characteristics at a high C-rate without significantly affecting the life characteristics of conventional lithium secondary batteries.

[0098] 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 to act as a buffer during rolling and to impart some conductivity, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

[0099] 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. 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.

[0100] 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.

[0101] 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 plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0102] 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.

[0103] 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.

[0104] 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 volume of the silicon-based active material expands and relaxes. 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.

[0105] In one embodiment of the present application, the negative electrode binder may be contained 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, or may be contained in an amount of 5 parts by weight or more, or 10 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0106] Compared to conventional carbon-based negative electrodes, when a Si-based negative electrode is used, a water-based binder is applied in the above weight parts, allowing the use of a dot-like conductive material with a low content of functional groups. Due to the above characteristics, the dot-like conductive material is hydrophobic, and therefore has the characteristic of excellent bonding strength between the conductive material and the binder.

[0107] In one embodiment of the present application, there is provided a negative electrode composition in which hydroxyl groups (—OH) on the surface of the silicon-based active material and carboxyl functional groups of the negative electrode pre-dispersion liquid form hydrogen bonds with each other.

[0108] As a result, the negative electrode pre-dispersion liquid according to the present application is used as a substance that not only acts as a dispersant but also strengthens the bond between the carbon nanotubes and the silicon-based active material, and has the characteristic that the use of the dispersant according to the present application improves the dispersibility of the carbon nanotubes and maintains the conductive path of the conductive material.

[0109] In one embodiment of the present application, there is provided a method for manufacturing an anode composition, the method including the steps of: forming a pre-dispersion by mixing carbon nanotubes and a dispersant having a carboxyl group as a functional group; adding a dispersant to the pre-dispersion so that the solid content of the pre-dispersion is 5% or less; dispersing the pre-dispersion containing the dispersant; mixing a binder with water to form a mixture, and adding the pre-dispersion to the mixture to perform a first mixing; and adding a silicon-based active material to the mixed mixture to perform a second mixing. The method includes, based on 100 parts by weight of the pre-dispersion, 20 to 60 parts by weight of the carbon nanotubes; and 40 to 80 parts by weight of the dispersant.

[0110] In one embodiment of the present application, the method for preparing the negative electrode composition may include forming a negative electrode slurry by adding a slurry-forming solvent to a negative electrode composition including a negative electrode active material, a negative electrode conductive material, and a negative electrode binder. Specifically, the negative electrode slurry is formed by mixing the binder with water to form a mixture, adding the pre-dispersion material to the mixture (first mixing), and adding a silicon-based active material to the mixed mixture (second mixing).

[0111] In one embodiment of the present application, the solid content of the negative electrode slurry may be 10% to 40%, and the negative electrode slurry may be coated on a negative electrode current collector to form a negative electrode.

[0112] In one embodiment of the present application, there is provided a method for producing a negative electrode composition, wherein the negative electrode composition may further include a conductive material, and specifically, in the first mixing step, the negative electrode composition further includes one or more selected from the group consisting of a dot-like conductive material and a sheet-like conductive material.

[0113] In the method for preparing the negative electrode composition, the components and contents are as described above. 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.

[0114] In one embodiment of the present application, there is provided a method for producing a negative electrode composition, wherein the step of dispersing the pre-dispersed material is performed using a dispersing device capable of dispersing at high stress, high pressure, or high speed.

[0115] The step of dispersing the pre-dispersed material may specifically include a step of adding a pre-dispersed material containing carbon nanotubes and a dispersant containing a carboxyl group as a functional group to water and dispersing the pre-dispersed material using an ultrasonic grinder.

[0116] 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 active material layer comprising the negative electrode composition according to the present application.

[0117] 1 is a diagram showing the 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, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0118] 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 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 layer may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, nonwoven fabric, etc.

[0119] 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.

[0120] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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 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.

[0126] 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 Mc3 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 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 lithium metal (Li-metal).

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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 that is an agglomeration of 30 or less primary particles.

[0134] Specifically, in the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-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.

[0135] 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.

[0136] In the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-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.

[0137] 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, which is an agglomeration of 30 or less primary particles.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0156] 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.

[0157] 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.

[0158] 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:

[0159] 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.

[0160] 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]

[0161] 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.

[0162] <Example> Example 1 The SWCNT pre-dispersion used to fabricate the negative electrode was prepared by adding 0.4 wt% SWCNT and 0.6 wt% dispersant (PPBT) to water (HO) as the solvent, and then dispersing the mixture using an ultrasonic grinder (ultrasonicator) to prepare a pre-dispersion (solid content 1%) (amplitude 40%, 10 min).

[0163] Next, binder A (weight average molecular weight 650,000 to 700,000 g / mol) was mixed with water to form a mixture, and the pre-dispersion liquid and sheet-shaped conductive material (graphite-based, D10>2.5 μm, D50=5 to 6 μm, D90<11 μm) were added to the mixture and dispersed at 2500 rpm for 30 minutes using a homomixer. After that, a silicon-based active material (Si, D50: 3 μm to 8 μm) was added to the mixed mixture and dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0164] The negative electrode current collector was 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%).

[0165] Example 2 The SWCNT pre-dispersion used to fabricate the negative electrode was prepared by adding 0.4 wt% SWCNTs and 0.6 wt% dispersant (alginate / PVP) to water (HO) as the solvent, and then dispersing the mixture using an ultrasonic grinder (ultrasonicator) to prepare a pre-dispersion (solid content 1%) (amplitude 40%, 10 min).

[0166] Next, binder A (weight average molecular weight 650,000 to 700,000 g / mol) was mixed with water to form a mixture, and the pre-dispersion material and sheet-like conductive material (graphite-based, D10>2.5 μm, D50=5 to 6 μm, D90<11 μm) were added to the mixture and dispersed at 2500 rpm for 30 minutes using a homomixer. After that, a silicon-based active material (Si, D50: 3 μm to 8 μm) was added to the mixed mixture and dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0167] The negative electrode current collector was 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%).

[0168] Comparative Example 1 The SWCNT pre-dispersion used to fabricate the negative electrode was prepared by adding 0.4 wt% SWCNTs and 0.6 wt% dispersant (tannic acid / PVP) to water (HO) as the solvent, and then dispersing the mixture using an ultrasonic grinder (ultrasonicator) to prepare a pre-dispersion material (solid content 1%) (amplitude 40%, 10 min).

[0169] Next, binder A (weight average molecular weight 650,000 to 700,000 g / mol) was mixed with water to form a mixture, and the pre-dispersion material and sheet-like conductive material (graphite-based, D10>2.5 μm, D50=5 to 6 μm, D90<11 μm) were added to the mixture and dispersed at 2500 rpm for 30 minutes using a homomixer. After that, a silicon-based active material (Si, D50: 3 μm to 8 μm) was added to the mixed mixture and dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0170] The negative electrode current collector was 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%).

[0171] Comparative Example 2 The negative electrode was manufactured in the same manner as in Example 1, except that the SWCNT pre-dispersion used to manufacture the negative electrode in Example 1 was prepared by adding 0.7 wt % of SWCNTs and 0.3 wt % of a dispersant (PPBT) to water (HO) as a solvent and dispersing the mixture using an ultrasonic grinder (ultrasonicator) to prepare a pre-dispersion (solid content: 1%) (amplitude 40%, 10 min).

[0172] Comparative Example 3 The negative electrode was manufactured in the same manner as in Example 1, except that the SWCNT pre-dispersion used to manufacture the negative electrode in Example 1 was prepared by adding 0.1 wt % of SWCNTs and 0.9 wt % of a dispersant (PPBT) to water (HO) as a solvent and dispersing the mixture using an ultrasonic grinder (ultrasonicator) to prepare a pre-dispersion (solid content: 1%) (amplitude: 40%, 10 min).

[0173] Comparative Example 4 In Example 1, the negative electrode pre-dispersion was prepared to have a solid content of 7%. However, in Comparative Example 4, the solid content exceeded 5%, and the SWCNT content was too high, which prevented proper dispersion and resulted in a very high viscosity, making it impossible to prepare a pre-dispersion. As a result, a negative electrode slurry for forming a negative electrode active material layer could not be prepared, and evaluation was not possible.

[0174] <Experimental Example 1> The initial capacity evaluation results (0.005V-1.0V, 0.1C / 0.1C) of the negative electrode half cells prepared in the above examples and comparative examples show that the capacity close to the theoretical capacity of the active material (up to 3500mAh / g) is observed with equivalent performance, as can be seen from Table 1 below. It was also confirmed that the capacity values ​​were similar to those of electrodes using conventional CMC dispersants.

[0175] [Table 1]

[0176] In Table 1, three types of identical half cells were produced in the same manner as in Example 1, and the evaluation results were divided into 1-#1 to 1-#3, with the average value being recorded as "average."

[0177] In Table 1, two identical half cells were prepared in the same manner as in Example 2, and the evaluation results were divided into 2-#1 and 2-#2, and the average value was recorded as "average."

[0178] In the remaining Comparative Examples 1 to 4, the average values ​​are described as "average" in the same manner as in Example 1.

[0179] FIG. 3 is a diagram showing the results of initial capacity evaluation of half cells of the negative electrodes of Examples 1 and 2 according to the present application.

[0180] <Experimental Example 2> The results of half-cell evaluation (0.005 V-1.0 V, 0.1 C, 50 cycles) of the negative electrodes prepared in the examples and comparative examples are shown in Table 2 below. It can be seen that the electrode performance of Examples 1 and 2 was particularly improved. In particular, in the case of the negative electrode of Example 1, PPBT was used as a dispersant, and the SWCNTs were well wrapped through π-π interactions between the π electrons in the main chain and the faces of the SWCNTs where the π electrons are present. Furthermore, the carboxyl groups in the side chains of PPBT effectively debundled the bundled SWCNTs, resulting in particularly improved dispersibility and further improved electrode performance.

[0181] FIG. 4 is a diagram showing the results of half-cell evaluation of the negative electrodes of Examples 1 and 2 according to the present application.

[0182] [Table 2]

[0183] In Table 2, two types of identical half cells were prepared in the same manner as in Example 1, and the evaluation results were divided into 1-#2 and 1-#2, and the average value was recorded as "average."

[0184] In Table 2, two types of identical half-cells were prepared in the same manner as in Example 2, and the evaluation results were shown as 2-#1 and 2-#2, with the average value being recorded as "average."

[0185] In the remaining Comparative Examples 1 to 4, the average values ​​are described as "average" in the same manner as in Example 1.

[0186] As can be seen from Experimental Examples 1 and 2, the anode pre-dispersion according to the present invention has the characteristic of excellent carbon nanotube dispersibility, since the solid content of the pre-dispersion material, the carbon nanotube content, and the dispersant content in the pre-dispersion satisfy certain ranges. As a result, when the binding strength between the carbon nanotubes and silicon is strengthened, the pathway between the conductive material is maintained even during repeated charge and discharge, and the silicon active material can be used uniformly. Therefore, when a conventional silicon-based active material is used, the volume expansion during charge and discharge can be minimized by using the anode composition according to the present invention.

[0187] <Experimental Example 3> The CHC cycle evaluation results of the negative electrodes prepared in Example 1, Example 2, and Comparative Example 1 (0.005 V-1.0 V, charge / discharge: 0.5 C / 0.5 C, limited capacity evaluation was performed by using only half the capacity (SOC 50%) based on the evaluation result value of the initial capacity) can be seen in FIG. 5.

[0188] Specifically, as can be seen from FIG. 5, as the number of cycles of the negative electrode increases, the capacity retention rate in Comparative Example 1 decreases first at a smaller number of cycles than in Examples 1 and 2.

[0189] In particular, as can be seen from FIG. 5, Example 1 differs from the other dispersants in that it has a carboxyl group as a functional group and a conjugation structure within the molecule, which contributes to improving the lifespan of the electrode and is therefore confirmed to have particularly excellent performance.

[0190] When using a silicon-based active material, the expansion of its volume can cause the conductive path between the conductive materials to be interrupted. To solve this problem, instead of adding another component to the negative electrode composition according to one embodiment of the present application, a carboxyl group is included as a functional group in the dispersant contained in the carbon nanotube pre-dispersion liquid. This allows hydrogen bonding with the -OH group on the surface of the silicon-based active material, thereby strengthening the bonding strength between the carbon nanotubes and silicon.

[0191] In other words, when the bonding strength between carbon nanotubes and silicon is strengthened, the pathway between the conductive material is maintained even during repeated charging and discharging, and the silicon active material can be used uniformly. Therefore, it was confirmed that the volume expansion during charging and discharging, which occurs when using conventional silicon-based active materials, can be minimized by using the anode composition according to the present invention. [Explanation of symbols]

[0192] 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 pre-dispersion liquid, and a negative electrode binder, The negative electrode pre-dispersion liquid is a pre-dispersion material containing carbon nanotubes and a dispersant; A dispersion medium represented by the following chemical formula 1: The solid content of the pre-dispersion material is 5% or less based on the negative electrode pre-dispersion liquid, The pre-dispersion agent contains 20 to 60 parts by weight of the carbon nanotubes and 40 to 80 parts by weight of the dispersant, based on 100 parts by weight of the pre-dispersion agent, the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition; 【Chemistry 1】 In the above Chemical Formula 1, m is an integer from 1 to 10, n is an integer from 1 to 1000, The silicon-based active material comprises 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

2. 2. The negative electrode composition according to claim 1, wherein the weight average molecular weight of the dispersant is 10,000 g / mol or more and 100,000 g / mol or less.

3. The negative electrode composition according to claim 1 , wherein the viscosity of the negative electrode pre-dispersion is 100 cP or more and 10,000 cP or less.

4. The negative electrode composition further includes a negative electrode conductive material, The negative electrode composition according to any one of claims 1 to 3, wherein the negative electrode conductive material comprises at least one selected from the group consisting of dot-like conductive materials and sheet-like conductive materials.

5. The negative electrode composition according to claim 4 , wherein the negative electrode conductive material is present in an amount of 5 parts by weight to 40 parts by weight based on 100 parts by weight of the negative electrode composition.

6. The negative electrode composition according to any one of claims 1 to 3, wherein the negative electrode pre-dispersion liquid is contained in an amount of 0.01 parts by weight to 20 parts by weight based on 100 parts by weight of the negative electrode composition.

7. 4. The negative electrode composition according to claim 1, wherein the silicon-based active material further comprises one or more selected from the group consisting of SiOx (0<x<2) and metal impurities.

8. The negative electrode composition according to any one of claims 1 to 3, wherein a hydroxyl group (-OH) on the surface of the silicon-based active material and a carboxyl functional group of the negative electrode pre-dispersion liquid form a hydrogen bond with each other.

9. mixing carbon nanotubes and a dispersant represented by the following Chemical Formula 1 to form a pre-dispersion material; adding a dispersion medium to the pre-dispersion so that the solid content of the pre-dispersion is 5% or less; Dispersing the pre-dispersion material containing the dispersion medium; Mixing a negative electrode binder with water to form a mixture, and adding the pre-dispersion material to the mixture to perform a first mixing; and adding a silicon-based active material to the first mixed mixture and performing a second mixing; A method for producing a negative electrode composition, comprising: The pre-dispersion material contains 20 to 60 parts by weight of the carbon nanotubes and 40 to 80 parts by weight of the dispersant, based on 100 parts by weight of the pre-dispersion material, The silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition, 【Chemistry 2】 In the above Chemical Formula 1, m is an integer from 1 to 10, n is an integer from 1 to 1000, The method for producing a negative electrode composition, wherein the silicon-based active material contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

10. 10. The method for producing a negative electrode composition according to claim 9, wherein the first mixing step further comprises one or more selected from the group consisting of dot-like conductive materials and sheet-like conductive materials.

11. 10. The method of claim 9, wherein the first mixing step and the second mixing step are performed at 2,000 rpm to 3,000 rpm for 10 minutes to 60 minutes.

12. The method for producing a negative electrode composition according to claim 9 , wherein the step of dispersing the pre-dispersed material is performed using a dispersing device capable of dispersing at high stress, high pressure, or high speed.

13. 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 active material layer comprising the negative electrode composition according to any one of claims 1 to 3; A negative electrode for a lithium secondary battery comprising:

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

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