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.

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 as of the filing date of Korean Patent Application No. 10-2021-0133395, filed with the Korean Intellectual Property Office on October 7, 2021, and all its contents are incorporated herein by reference.

[0002] This 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 a growing demand for alternative and clean energy sources, and one of the most actively researched areas in this field is the generation and storage of electricity using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses this type of electrochemical energy is the secondary battery, and its range of applications is steadily expanding.

[0005] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, research is actively being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and removes lithium ions released from the positive electrode, and 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, there has been active research on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials, they have the problem that, compared to conventionally used graphite, their volume expands rapidly during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, in order to resolve the problems that arise when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods to adjust the driving potential, methods to further coat a thin film on the active material layer, methods to suppress volume expansion itself such as adjusting the particle size of the silicon-based compound, or methods to prevent the conduction path from being interrupted. However, in the case of the above methods, there are limitations to their application because they can actually degrade the performance of the battery, and there are still limitations to the commercialization of negative electrode battery manufacturing with a high content of silicon-based compounds.

[0009] Therefore, even when using silicon-based compounds as active materials to improve capacity performance, research is needed on conductive materials that can prevent the conduction path from being damaged due to the volume expansion of the silicon-based compound, and on pre-dispersions that can uniformly disperse conductive materials deformed under certain conditions to achieve the above objective. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0011] This application is based on research aimed at maximizing the solid content while maintaining appropriate fluid properties of the negative electrode slurry. It has been found that by including a sheet-like conductive material having a BET specific surface area within a certain range and adjusting the solid content of the pre-dispersion to an appropriate range, the phase stability of the negative electrode slurry itself can be ensured, and furthermore, problems in negative electrodes containing this material can be solved.

[0012] This 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 this specification has a specific surface area (BET) of 100.0 m². 2 A negative electrode pre-dispersion is provided, comprising a pre-dispersant containing a sheet-like conductive material and an aqueous dispersant of 1 / g or more, and a dispersion medium, wherein the solid content of the pre-dispersant is 10% to 30% based on the negative electrode pre-dispersion.

[0014] In another embodiment, a negative electrode composition is provided comprising a silicon-based active material; a negative electrode pre-dispersion according to the present application; a point conductive material; 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 another embodiment, the specific surface area (BET) is 100.0 m². 2 A method for producing a negative electrode composition is provided, comprising the steps of: mixing a sheet-like conductive material of 1 / g or more with an aqueous dispersant to form a pre-dispersant; adding a dispersion medium to the pre-dispersant so that the solid content of the pre-dispersant is 10% to 30%; dispersing the pre-dispersant containing the dispersion medium; mixing the pre-dispersant, a point-like conductive material, and a negative electrode binder to form a mixture; adding water to the mixture for a first mixing; and adding an active material to the mixed mixture for a second mixing.

[0016] In yet another embodiment, there is provided 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, there is provided 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 pre-dispersion liquid according to one embodiment of the present invention, a sheet-like conductive material with a specific surface area (BET) of 100.0 m 2 / g or more is used. Among the materials applied to the negative electrode of the silicon-based active material, conventional carbon black (BET: 40 m 2 / g to 70 m 2 / g) or a sheet-like conductive material (BET: 6 m 2 / g to 20 m 2 / g) can be used without pre-dispersion. However, compared with the case of using this, when a sheet-like conductive material with a specific surface area (BET) of 100.0 m 2 / g or more is used, the output characteristics become even better. However, when changing the specific surface area (BET) to a high specific surface area as described above, an aggregation phenomenon of the conductive material in the negative electrode composition may occur. In the case of the negative electrode pre-dispersion liquid according to the present application, since the sheet-like conductive material with the specific surface area (BET) changed to a high specific surface area is pre-dispersed first and has excellent dispersibility, it is effective in improving the output characteristics of a conventional silicon-based negative electrode.

[0019] 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 fabricate a high-capacity battery, the conductive material includes a dot-like conductive material and a pre-dispersed sheet-like conductive material, and the sheet-like conductive material has a BET specific surface area of 100.0 m 2By meeting the requirement of 1 / g or higher, the battery's lifespan characteristics are not significantly affected, the number of charge and discharge points increases, and it exhibits excellent output characteristics at a high C-rate.

[0020] In particular, the negative electrode composition according to one embodiment of the present invention has a BET specific surface area of ​​100.0 m² as a pre-dispersed sheet-like conductive material. 2 By using materials with a specific surface area of ​​1 / g or higher, and adjusting the specific surface area to be higher than that of commonly used sheet-type conductive materials, while adjusting the specific surface area of ​​conventionally used high-specific-surface-area point-type or linear conductive materials to be lower, the lifespan characteristics are maintained at the same level as conventional secondary batteries, and the output characteristics are excellent.

[0021] Furthermore, compared to conventional silicon-based active materials, the volume expansion during charging and discharging can be minimized by using the negative electrode composition according to the present invention. [Brief explanation of the drawing]

[0022] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0023] Before describing the present invention, let's first define some terms.

[0024] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0025] In this specification, "p~q" means the range "p or greater and q or less".

[0026] In this specification, "specific surface area" refers to the specific surface area measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0027] In this specification, "Dn" means the average particle size, and represents the particle size at the n% point of the cumulative particle number distribution according to the particle size. That is, D50 is the particle size at the 50% point of the cumulative particle number distribution according to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution according to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution according to the particle size. On the other hand, the average particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns according to the particle size as the particles pass through the laser beam.

[0028] In this specification, when a polymer is said to contain a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted in the same way as when the polymer contains a monomer as a monomer unit.

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

[0030] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0031] The present invention will be described in detail below with reference to the drawings so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention may be realized in various different forms and is not limited to the following description.

[0032] One embodiment of this specification has a specific surface area (BET) of 100.0 m². 2 A negative electrode pre-dispersion is provided, comprising a pre-dispersant containing a sheet-like conductive material and an aqueous dispersant of 1 / g or more, and a dispersion medium, wherein the solid content of the pre-dispersant is 10% to 30% based on the negative electrode pre-dispersion.

[0033] In one embodiment of this application, the pre-dispersion refers to a dispersion before the substance is included in the negative electrode composition, and the pre-dispersion and the negative electrode composition are used in different senses.

[0034] The negative electrode composition relating to this application has a specific surface area (BET) of 100.0 m². 2 This applies when using sheet-like conductive material with a specific surface area (BET) of 1 / g or more, resulting in even better output characteristics compared to conventional secondary batteries. However, when the specific surface area (BET) is changed to a high specific surface area as described above, aggregation of the conductive material in the negative electrode composition may occur. In the case of the negative electrode pre-dispersion according to this application, the sheet-like conductive material with a high specific surface area (BET) is pre-dispersed first, resulting in excellent dispersibility, which is even more effective in improving the output characteristics compared to conventional silicon-based negative electrodes.

[0035] In one embodiment of this application, a negative electrode predispersion is provided in which the aqueous dispersant is one or more selected from the group consisting of polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), polyacrylamide (PAM), and H-nitrile butadiene rubber (HNBR).

[0036] In one embodiment of this application, the dispersant refers to an aqueous dispersant and has a structure different from that of an organic dispersant.

[0037] In one embodiment of this application, a negative electrode pre-dispersion is provided, which contains 90 parts by weight or more of the sheet-like conductive material based on 100 parts by weight of the pre-dispersion.

[0038] In another embodiment, the sheet-like conductive material may be included in an amount of 90 parts by weight or more, preferably 92 parts by weight or more, more preferably 95 parts by weight or more, or 99 parts by weight or less, based on 100 parts by weight of the pre-dispersed material.

[0039] In one embodiment of this application, the dispersion medium is preferably a nonionic compound that does not have ionic functional groups, can act as a binder after film formation, does not affect electrical properties, or has a low decomposition temperature that can be removed by heat treatment during electrode fabrication, and more preferably has ionic properties due to a polar solvent, or has a hydroxyl group as a functional group to improve solubility in the solvent.

[0040] In one embodiment of this application, a negative electrode pre-dispersion is provided in which the solid content of the pre-dispersion material is 10% to 30% based on the negative electrode pre-dispersion.

[0041] In another embodiment, the solid content of the predispersant may be 10% to 30%, preferably 15% to 20%, relative to the negative electrode predispersion.

[0042] The solid content of the pre-dispersant is such that it satisfies the above range based on the negative electrode pre-dispersion, and by satisfying the above range, the sheet-like conductive material contained in the pre-dispersant is efficiently dispersed, the viscosity range can be kept within a certain range, and as a result, aggregation of the pre-dispersion does not occur.

[0043] In one embodiment of this application, a negative electrode pre-dispersion is provided, wherein the viscosity of the negative electrode pre-dispersion is 3,000 cP or more and 10,000 cP or less.

[0044] In another embodiment, the viscosity of the negative electrode pre-dispersion may be 3,000 cP or more and 10,000 cP or less, preferably 3,000 cP or more and 7,000 cP or less.

[0045] As described above, the pre-dispersant for the negative electrode pre-dispersion is included in the content portion, and the viscosity is adjusted by a dispersion process described later. By satisfying the above viscosity range, mixing is good when it is subsequently included in the negative electrode composition, which results in an improved output for the secondary battery.

[0046] In one embodiment of this application, the negative electrode pre-dispersion has a specific surface area (BET) of 100.0 m². 2 After mixing a sheet-like conductive material of 1 / g or more with an aqueous dispersant, a dispersion medium is added to adjust the solid content, and the mixture can be dispersed using a homogenizer capable of applying high stress and pressure, a homomixer capable of high-speed mixing, or a milling device using beads.

[0047] Subsequently, after performing PSD particle size analysis to confirm whether a certain particle size is obtained, the shear viscosity curve of the dispersion is checked using a rheometer to confirm whether a certain slope is obtained, thereby enabling the production of the negative electrode pre-dispersion according to this application.

[0048] In one embodiment of the present application, when the negative electrode pre-dispersion liquid is included in the negative electrode, it contains a dispersant and a sheet-like conductive material. Since the content of the dispersant is very small as in the above range, the negative electrode pre-dispersion liquid in the negative electrode described later can be regarded as the pre-dispersed sheet-like conductive material. The dispersion medium may be removed during coating on the negative electrode.

[0049] Provided is a negative electrode composition including a silicon-based active material; a negative electrode pre-dispersion liquid according to the present application; a dot-like conductive material; and a negative electrode binder, wherein the silicon-based active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition. <L

[0050] 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 fabricate a high-capacity battery, the conductive material includes a dot-like conductive material and a pre-dispersed sheet-like conductive material. The pre-dispersed sheet-like conductive material has a BET specific surface area of 100.0 m 2 / g or more, which does not significantly affect the life characteristics of conventional lithium secondary batteries, increases the number of points where charging and discharging are possible, and has the characteristic of excellent output characteristics at a high C-rate.

[0051] Particularly, although an aggregation phenomenon may occur due to an increase in the specific surface area of the sheet-like conductive material, the main feature of the present invention is that the above phenomenon is solved by the negative electrode pre-dispersion liquid and the dispersibility is improved.

[0052] In one embodiment of the present application, provided is a negative electrode composition in which 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 alloys.

[0053] In one embodiment of the present application, provided is a negative electrode composition in which 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 contains 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0054] In another embodiment, the silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, of SiOx(x=0) based on 100 parts by weight, or 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0055] In one embodiment of this application, the silicon-based active material may be pure silicon (Si) in particular. Using pure silicon (Si) as the silicon-based active material means that, based on 100 parts by weight of the total silicon-based active material as described above, it may contain pure Si particles (SiOx(x=0)) that are not bonded to other particles or elements within the above range.

[0056] In the case of silicon-based active materials, the capacity is significantly higher than that of conventionally used graphite-based active materials, and attempts to apply them are increasing. However, because of the high rate of volume expansion during the charge-discharge process, their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0057] Therefore, in the present invention, in order to improve capacity performance, while using only silicon-based active materials as the negative electrode active material, the negative electrode conductive material includes a point conductive material and a sheet conductive material in order to solve the above-mentioned problems, wherein the sheet conductive material has a BET specific surface area of ​​100.0 m². 2 By using materials with a value of / g or higher, the conventional problem was solved.

[0058] On the other hand, the average particle size (D50) of the silicon-based active material in the present invention may be 5 μm to 10 μm, more specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. If the average particle size is less than 5 μm, the specific surface area of ​​the particles increases excessively, and the viscosity of the negative electrode slurry increases excessively. As a result, the dispersion of the particles constituting the negative electrode slurry is not smooth. Also, if the size of the silicon-based active material is excessively small, the contact area between the silicon particles and the conductive material decreases due to the composite consisting of the conductive material and the binder in the negative electrode slurry, increasing the possibility of the conductive network being interrupted and reducing the capacity retention rate. On the other hand, if the average particle size exceeds 10 μm, there will be excessively large silicon particles, resulting in an uneven surface of the negative electrode, which causes non-uniformity of current density during charging and discharging. Also, if the silicon particles are excessively large, the phase stability of the negative electrode slurry becomes unstable, reducing processability. As a result, the capacity retention rate of the battery decreases.

[0059] In one embodiment of this application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m². 2 / g~150.0m 2 / g, more comfortably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0060] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or fragmentary particles. Alternatively, but less conveniently, the silicon particles may have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0061] In one embodiment of this application, a negative electrode composition is provided in which the silicon-based active material is contained in an amount of 60 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0062] In another embodiment, the silicon-based active material may be present in amounts 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 present in amounts of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

[0063] The negative electrode composition according to this application has the characteristic of not degrading the performance of the negative electrode and having excellent output characteristics in charging and discharging, even when a silicon-based active material with a remarkably high capacity is used within the above range, by using a specific conductive material and binder that can suppress the rate of volume expansion during the charging and discharging process.

[0064] In one embodiment of this application, the silicon-based active material may have a non-spherical shape, and its 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.

[0065] In this application, the degree of sphericity is determined by the following formula 1, where A is the area and P is the boundary line.

[0066] [Formula 1] 4πA / P 2

[0067] Traditionally, graphite-based compounds were used exclusively as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have a limitation: their volume expands rapidly during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer and actually degrading the battery's performance.

[0068] Therefore, in one embodiment of this application, the negative electrode conductive material includes a pre-dispersed point conductive material and a sheet-like conductive material, wherein the pre-dispersed sheet-like conductive material has a BET specific surface area of ​​100.0 m². 2 A conductive material of 1 / g or more may also be used. By using the conductive material, even when the silicon-based active material expands, the conductive material can always be located on the surface of the particles, between particles, and between particle aggregates. Therefore, the conductive paths formed by the conductive material are not affected by the volume expansion, and the performance of the battery can be maintained well.

[0069] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity in a negative electrode and means a conductive material in the shape of points or spheres that does not induce chemical changes and is conductive. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably contains carbon black in terms of achieving high conductivity and excellent dispersibility.

[0070] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than / g, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0071] The negative electrode composition relating to this application has a BET specific surface area of ​​100.0 m² in order to improve the output performance of a secondary battery. 2This involves applying a sheet-like conductive material with a density of 1 / g or higher. In the case of a Si negative electrode, output characteristics are the most important factor in obtaining rapid charging characteristics. Conventional secondary batteries use point-type conductive materials or CNT-based conductive materials adjusted to have a high specific surface area for performance purposes. In this case, the lifespan can be improved by reinforcing the conductive material and binder composite as fillers, but the output characteristics will deteriorate.

[0072] Therefore, the conductive material relating to this application includes a point-type conductive material and a sheet-type conductive material, wherein the sheet-type conductive material has a BET specific surface area of ​​100.0 m². 2 By adjusting it to a value of / g or higher, the point-shaped conductive material has a specific surface area that satisfies the above range, thereby maintaining life characteristics at a level equivalent to that of conventional lithium secondary batteries. Furthermore, because the increase in resistance due to life is low, the output characteristics are maintained well for a long period of time.

[0073] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0074] In one embodiment of this application, the conductive material may include a pre-dispersed sheet-like conductive material.

[0075] The pre-dispersed sheet-like conductive material may mean that it is dispersed in the aforementioned negative electrode pre-dispersion. That is, in one embodiment of this application, when the negative electrode pre-dispersion is contained in the negative electrode, it contains a dispersant and a sheet-like conductive material, and since the amount of dispersant is very small as described above, the negative electrode pre-dispersion contained in the negative electrode can be viewed in the same way as the pre-dispersed sheet-like conductive material.

[0076] The aforementioned sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and can also suppress the disruption of the conductive path due to volume expansion.

[0077] In this application, the term "sheet-like conductive material" refers to a conductive material encompassing a large area in the form of a sheet, and may be used as a concept that includes both bulk-like conductive materials and plate-like conductive materials.

[0078] In one embodiment of this application, the sheet-like conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0079] In one embodiment of this application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, the sufficient particle size prevents an excessive increase in the viscosity of the negative electrode slurry and facilitates dispersion. Therefore, the dispersion effect is excellent when dispersed using the same apparatus and time.

[0080] In one embodiment of this application, a negative electrode composition is provided in which the sheet-like conductive material has 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.

[0081] In one embodiment of this application, the sheet-like conductive material has a BET specific surface area of ​​100 m². 2 It may be more than / g.

[0082] In another embodiment, the sheet-like conductive material has a BET specific surface area of ​​100 m². 2 / g or more 500m 2 It may be less than / g, preferably 150m 2 / g or more 400m 2 / g or less, more preferably 200m 2 / g or more 350m 2 It may be less than / g.

[0083] As mentioned above, the conductive material relating to this application includes point-type conductive material and sheet-type conductive material, and in particular the sheet-type conductive material has a BET specific surface area of ​​100.0 m². 2 By adjusting the density to above / g, the point-type conductive material can maintain a lifespan at a level equivalent to conventional lithium secondary batteries, as its specific surface area meets the above range. Furthermore, because the resistance increase due to lifespan is low, the output characteristics are maintained well for a long period of time.

[0084] Other negative electrode conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, here, "bundle type" refers to a bundle-like or rope-like secondary shape in which multiple carbon nanotube units are arranged side by side or intertwined with substantially the same orientation along the length direction of the carbon nanotube units. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be exhibited depending on the angle and structure in which the graphite sheet is wound. Compared to entangled-type carbon nanotubes, the bundle-type carbon nanotubes can be dispersed more uniformly during negative electrode manufacturing, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0085] However, the present invention is characterized by improving the output characteristics of the secondary battery of the present invention by not using the linear conductive material described above, but by including point-shaped and sheet-shaped conductive materials as conductive materials and adjusting their specific surface area.

[0086] In one embodiment of this application, a negative electrode composition is provided in which the negative electrode conductive material is contained in an amount of 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0087] In another embodiment, the negative electrode conductive material may be included in an amount of 10 to 40 parts by weight, preferably 10 to 30 parts by weight, and more preferably 15 to 25 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0088] In one embodiment of this application, a negative electrode composition is provided, comprising 35 to 65 parts by weight of the point-shaped conductive material and 35 to 65 parts by weight of the negative electrode pre-dispersion, based on 100 parts by weight of the negative electrode conductive material.

[0089] The aforementioned negative electrode pre-dispersion may mean a pre-dispersed sheet-like conductive material.

[0090] In another embodiment, the negative electrode conductive material may be included in an amount of 35 to 65 parts by weight, preferably 40 to 65 parts by weight, and more preferably 40 to 60 parts by weight, based on 100 parts by weight of

[0091] In another embodiment, the negative electrode pre-dispersion may be included in a quantity of 35 to 65 parts by weight, preferably 40 to 65 parts by weight, and more preferably 40 to 60 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0092] In one embodiment of this application, the negative electrode conductive material comprises a point conductive material and a negative electrode pre-dispersion (pre-dispersed sheet-like conductive material), and the ratio of the point conductive material to the negative electrode pre-dispersion (pre-dispersed sheet-like conductive material) may satisfy 1:0.51 to 1:1.51.

[0093] In one embodiment of this application, the negative electrode conductive material comprises a point conductive material and a negative electrode pre-dispersion (pre-dispersed sheet-like conductive material), and the ratio of the point conductive material to the negative electrode pre-dispersion (pre-dispersed sheet-like conductive material) may be 1:1.

[0094] The aforementioned ratio may refer to a weight ratio.

[0095] In one embodiment of this application, the negative electrode conductive material includes a point-like conductive material and a sheet-like conductive material, each satisfying the above composition and proportion, so that the conductive material is effectively positioned in the form of points and sheets in the silicon-based active material network. In particular, by including two types of point-like and sheet-like conductive materials and satisfying the above range, particles of different sizes are mixed, resulting in a higher packing density, which leads to improved performance of the electrode containing it.

[0096] Furthermore, it does not significantly affect the lifespan characteristics of conventional lithium-ion batteries, and it has the advantage of having many charging and discharging points, as well as excellent output characteristics with a high C-rate.

[0097] The negative electrode conductive material of this application has a completely different structure from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application plays the role of providing contact between silicon-based active materials, which undergo very large volume expansion during charging and discharging, while the positive electrode conductive material plays the role of a buffer that has a cushioning function during rolling and also imparts some conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0098] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and thus have the properties of improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0099] In one embodiment of this application, the sheet-like conductive material used as the negative electrode conductive material described above has a different structure and role from the carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot shape to facilitate the storage and release of lithium ions.

[0100] In contrast, sheet-like conductive materials used as negative electrode conductive materials are substances having a sheet-like or plate-like shape and can be described as plate-like graphite. That is, they are substances included in the negative electrode active material layer to maintain conductive pathways, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a sheet-like form within the negative electrode active material layer.

[0101] In other words, in this application, the use of plate-shaped graphite as a negative electrode conductive material means that it is processed into a sheet or plate shape and used not to store or release lithium, but as a material to secure a conductive path. In this case, the negative electrode active material contained together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0102] In contrast, in this application, the use of a carbon-based active material as an active material means that it is processed into a point-like or spherical shape and used as a substance that stores or releases lithium.

[0103] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these are substituted with Li, Na, or Ca, and may also contain a variety of copolymers thereof.

[0104] The negative electrode binder according to one embodiment of this application plays a role in holding the silicon-based active material and the negative electrode 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. As long as the above role is fulfilled, all general negative electrode binders can be applied, and specifically, an aqueous binder may be used, or more specifically, a PAM-based binder may be used.

[0105] In one embodiment of this application, the negative electrode binder may be included in 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may also be included in 5 parts by weight or more, or 10 parts by weight or more.

[0106] In one embodiment of this application, the specific surface area (BET) is 100.0 m². 2A method for producing a negative electrode composition is provided, comprising the steps of: mixing a sheet-like conductive material of 1 / g or more with an aqueous dispersant to form a pre-dispersant; adding a dispersion medium to the pre-dispersant so that the solid content of the pre-dispersant is 10% to 30%; dispersing the pre-dispersant containing the dispersion medium; mixing the pre-dispersant, a point-like conductive material, and a negative electrode binder to form a mixture; adding water to the mixture for a first mixing; and adding an active material to the mixed mixture for a second mixing.

[0107] In the method for producing the negative electrode composition, the composition and content of each component are as described above.

[0108] In one embodiment of this application, a method for manufacturing a negative electrode composition is provided, wherein the first mixing and second mixing steps are steps of mixing at 2,000 rpm to 3,000 rpm for 10 to 60 minutes.

[0109] In one embodiment of this application, the step of dispersing the pre-dispersed material is performed using a dispersion device capable of dispersion under high stress, high pressure, or high speed, thereby providing a method for manufacturing a negative electrode composition.

[0110] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer containing the negative electrode composition according to this application, formed on one or both sides of the negative electrode current collector layer.

[0111] Figure 1 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen in which a negative electrode active material layer 20 is included on one surface of the negative electrode current collector layer 10. Figure 1 shows a case where the negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer.

[0112] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it 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, etc., and aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0113] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, 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.

[0114] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0115] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0116] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0117] The aforementioned porosity varies depending on the composition and content of the silicon-based active material, negative electrode conductive material, and negative electrode binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to this application are included in specific compositions and content portions to satisfy the above range, thereby providing suitable electrical conductivity and resistance in the electrode.

[0118] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0119] Figure 2 shows a stacked 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, can be seen on one side of a negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery, including a positive electrode active material layer 40, can be seen on one side of a positive electrode current collector layer 50. The negative electrode 100 and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separator 30 in between.

[0120] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0121] 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 containing the positive electrode active material.

[0122] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0123] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 Ni-site type lithium nickel oxide represented as Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.6); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be Li-metal.

[0124] In one embodiment of this application, the positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium composite transition metal compound comprises single particles or secondary particles, and the average particle size (D50) of the single particles may be 1 μm or more.

[0125] For example, the average particle size (D50) of the single particle 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, greater than 1 μm and 12 μm or less, greater than 1 μm and 8 μm or less, or greater than 1 μm and 6 μm or less.

[0126] Even when the single particle is formed to have a small particle size with an average particle size (D50) of 1 μm or more and 12 μm or less, it can still exhibit excellent particle strength. For example, the single particle can have a strength of 650 kgf / cm². 2 The particle may have a particle strength of 100 MPa to 300 MPa when rolled with this force. This allows the single particle to be rolled at 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increasing fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0127] The single particle can be produced by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particle may be produced by a method different from that of the single particle, and its composition may be the same as or different from that of the single particle.

[0128] The method for forming the single particles is not particularly limited, but generally they may be formed by increasing the firing temperature and over-firing, and can be manufactured by using additives such as grain growth promoters that help with over-firing, or by changing the initiating substance.

[0129] For example, the firing is performed at a temperature at which single particles can be formed. In order to form them, firing must be performed at a higher temperature than when secondary particles are manufactured. For example, if the precursor composition is the same, firing must be performed at a temperature about 30°C to 100°C higher than when secondary particles are manufactured. The firing temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when trying to form single particles of a high-nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, the firing temperature may be 700°C to 1000°C, preferably 800°C to 950°C. When the firing temperature is within the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be manufactured. If the firing temperature is below 790°C, a positive electrode active material containing a lithium composite transition metal compound in the form of secondary particulate matter will be manufactured. If it exceeds 950°C, the firing may be excessive, the layered crystal structure may not be properly formed, and the electrochemical properties may deteriorate.

[0130] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the aggregation of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and an analogous-single particle form which is an aggregate of 30 or fewer primary particles.

[0131] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in an analogous-single particle form, and a secondary particle may be in a form in which several hundred primary particles are aggregated.

[0132] In one embodiment of this application, the lithium composite transition metal compound, which is the positive electrode active material, further contains secondary particles, wherein the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0133] In the present invention, a single particle may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in an analogous-single particle form, and a secondary particle may be in a form in which several hundred primary particles are aggregated.

[0134] The lithium-complex transition metal compounds described above may further contain secondary particles. Secondary particles refer to forms formed by the aggregation of primary particles and can be distinguished from the concept of single particles, which includes a single primary particle, a single particle, or an aggregate of 30 or fewer primary particles.

[0135] The particle size (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles is 0.05 m². 2 / g~10m 2 It may be / g, preferably 0.1m 2 / g~1m 2 It may be / g, and more preferably 0.3m 2 / g~0.8m 2 / g is also acceptable.

[0136] In a further embodiment of this 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.

[0137] When the average particle size (D50) of the primary particles meets 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 excessively small, the number of aggregates of primary particles forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is excessively large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially degrading the power characteristics.

[0138] According to a further embodiment of this application, the average particle size (D50) of the single particle is smaller than the average particle size (D50) of the secondary particle. As a result, even when the single particle is formed with a small particle size, it can have excellent particle strength, thereby mitigating the phenomenon of increasing fine particles in the electrode due to particle cracking, and thereby improving the battery life characteristics.

[0139] In one embodiment of this application, the average particle size (D50) of the single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particle.

[0140] For example, the average particle size (D50) of the single particle 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 particle.

[0141] When the average particle size (D50) of a single particle is smaller than the average particle size (D50) of a secondary particle, for example, when the above range is satisfied, the single particle can have excellent particle strength even when formed with a small particle size. This mitigates the phenomenon of increasing fine particles in the electrode due to particle fracture, resulting in improved battery life characteristics and improved energy density.

[0142] According to further embodiments of this application, the single particles are included in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material. The single particles may also be included in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight per 100 parts by weight of the positive electrode active material.

[0143] For example, the single particle 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 per 100 parts by weight of the positive electrode active material. The single particle may also be included in an amount of 100 parts by weight or less per 100 parts by weight of the positive electrode active material.

[0144] When single particles within the above range are included, they can be combined with the aforementioned negative electrode material to exhibit excellent battery characteristics. In particular, when the amount of single particles is 15 parts by weight or more, the phenomenon of increased fine particles within the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery's lifespan characteristics.

[0145] In one embodiment of this application, the lithium composite transition metal compound may further contain secondary particles, the amount of which may be 85 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 0 parts by weight or more per 100 parts by weight of the positive electrode active material.

[0146] If the above range is met, the aforementioned effects due to the presence of single-particle positive electrode active material can be maximized. If secondary-particle positive electrode active material is included, its components may be the same as those exemplified as the single-particle positive electrode active material described above, or they may be different, and may represent a form in which single particles are aggregated.

[0147] In one embodiment of this application, the positive electrode active material in 100 parts by weight of the positive electrode active material layer may be present 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.

[0148] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0149] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0150] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0151] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries is acceptable without particular limitations, and it is especially preferable that it has low resistance to electrolyte ion movement and excellent electrolyte moisture retention capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and these may be selectively used as single-layer or multi-layer structures.

[0152] 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 the manufacture of lithium secondary batteries.

[0153] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0154] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0155] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents because they have high dielectric constants and dissociate lithium salts well. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, and therefore they can be used even more preferably.

[0156] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as the anion of the lithium salt, F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2- (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , and (CF3CF2SO2)2N - You may use one or more selected from the group consisting of the following:

[0157] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0158] One embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Because the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Examples]

[0159] The following are preferred embodiments to aid in understanding the present invention, but these embodiments are merely illustrative of the description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the technical concept, and such variations and modifications will naturally fall within the scope of the appended claims.

[0160] <Examples> <Manufacturing of negative electrodes> (Example 1 - Pre-dispersion 1) Plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 235 m²) is dispersed in water as a dispersion medium. 2 A negative electrode predispersion was formed by adding a solid content of 18% (1 / g, average particle size (D50): 3.2 μm) and a dispersant (CHC, H1496A, Daiichi Kogyo Seiyaku) to a solid content of 18%. The negative electrode predispersion was then dispersed through a milling apparatus using a homomixer to produce a negative electrode predispersion 1 with a viscosity of 6250 cp.

[0161] After dispersing the negative electrode pre-dispersion 1, the viscosity curve due to shear rate among the rheological properties was checked to confirm whether there was no curvature in the curve and whether a constant slope was observed, whether there were any large particles that were not dispersed, the viscosity (G'') and elasticity (G') were checked by frequency sweep, and whether the tangent delta (=G'' / G') was close to 0.8 to 1.2 was checked to confirm whether the solid and liquid properties were similar and whether the dispersion was good, thereby confirming that the negative electrode pre-dispersion 1 was manufactured.

[0162] (Example 2 - Pre-dispersion 2) Plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 295 m²) is dispersed in water as a dispersion medium. 2A negative electrode predispersion was formed by adding a solid content of 18% (1 / g, average particle size (D50): 3.2 μm) and a dispersant (CHC, H1496A, Daiichi Kogyo Seiyaku) to a negative electrode predispersion. This negative electrode predispersion was then dispersed through a milling apparatus using a homomixer to produce a negative electrode predispersion 2 with a viscosity of 6250 cp.

[0163] After dispersing the negative electrode pre-dispersion 2, the viscosity curve due to shear rate among the rheological properties was checked to confirm whether the curve was not bent and showed a constant slope, whether there were any large particles that were not dispersed, the viscosity (G'') and elasticity (G') were checked by frequency sweep, and whether the tangent delta (=G'' / G') was close to 0.8 to 1.2, and whether the solid and liquid properties were similar and the dispersion was good, thereby confirming that the negative electrode pre-dispersion 2 was manufactured.

[0164] (Comparative Example 1 - Pre-dispersion 3) In the above-mentioned Example 1, the plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 235 m²) 2 Instead of using plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 90 m²) instead of 3.2 μm / g (average particle size (D50): 3.2 μm), use plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 90 m²). 2 Pre-dispersion 3 was prepared in the same manner as in Example 1, except that a 2 / g (average particle size (D50): 3.2 μm) was used.

[0165] (Comparative Example 2 - Pre-dispersion 4) In the above-mentioned Example 1, plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 235 m²) was used as the dispersion medium in water. 2 Pre-dispersion 4 was prepared in the same manner as in Example 1, except that a negative electrode pre-dispersion was formed by adding a solid content of 5% (1 / g, average particle size (D50): 3.2 μm) and a dispersant (CHC, H1496A, Daiichi Kogyo Seiyaku) to a solid content of 5%.

[0166] (Comparative Example 3 - Pre-dispersion 5) In the above-mentioned Example 1, plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 235 m²) was used as the dispersion medium in water. 2 Pre-dispersion 5 was prepared in the same manner as in Example 1, except that a negative electrode pre-dispersion was formed by adding a dispersant (CHC, H1496A, Daiichi Kogyo Seiyaku) ( / g, average particle size (D50): 3.2 μm) and a dispersant (CHC, H1496A, Daiichi Kogyo Seiyaku) to a solid content of 45%.

[0167] <Manufacturing of negative electrodes> [Example 1: Manufacturing of the negative electrode] A silicon-based active material (Si, average particle size (D50): 3.5 μm), a first conductive material, a negative electrode pre-dispersion 1, and polyacrylamide as a binder were added to distilled water as a solvent for forming the negative electrode slurry to produce a negative electrode slurry (solid content concentration 25% by weight).

[0168] The first conductive material is carbon black A (specific surface area: 63 m²). 2 The sample size was 35 nm in diameter and contained 0.15% volatile matter.

[0169] As a mixing method, the pre-dispersion 1, the first conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added and dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0170] The negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm) which serves as the negative electrode current collector, at a rate of 85 mg / 25 cm². 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was then used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0171] [Example 2: Manufacturing of the negative electrode] In the production of the negative electrode in Example 1, the negative electrode was manufactured in the same manner as in Example 1, except that the aforementioned pre-dispersion 2 was used.

[0172] [Comparative Examples 1 to 3: Production of negative electrode] In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that the pre-dispersion liquids 3 to 5 described above were used respectively.

[0173] [Comparative Example 4: Production of negative electrode] In Example 1, except that plate-shaped graphite A (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm) was applied as the second conductive material that was not produced in the pre-dispersion liquid, a negative electrode of Comparative Example 4 was produced in the same manner as in Example 1.

[0174] [Comparative Example 5: Production of negative electrode] In Example 1, except that no pre-dispersion liquid was produced and plate-shaped graphite (NIPPON Graphite, SP270, specific surface area: 235 m 2 / g, average particle size (D50): 3.2 μm) was applied as the second conductive material, a negative electrode of Comparative Example 5 was produced in the same manner as in Example 1.

[0175] [Production of secondary battery] As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent for forming the positive electrode slurry at a weight ratio of 97:1.5:1.5 to produce a positive electrode slurry (solid content concentration: 78% by weight).

[0176] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as the positive electrode current collector at a loading amount of 537 mg / 25 cm 2 , rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), and a positive electrode was produced (thickness of the positive electrode: 77 μm, porosity: 26%).

[0177] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte was injected to manufacture the secondary battery of Example 1.

[0178] The electrolyte in question was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 30:70 in an organic solvent, adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0179] Secondary batteries were manufactured in the same manner as described above, except that the negative electrodes of the above examples and comparative examples were used.

[0180] [Experimental Example 1: Evaluation of the lifespan of a secondary battery] The secondary batteries manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries were 1) charged (0.33C CC / CV charge 4.2V 0.05C cut) and discharged (0.33C CC discharge 3.0V cut), which was considered the first cycle. From the second cycle onwards, charging and discharging were performed under the conditions of 2) charging (1.0C CC / CV charge 4.2V 0.05C cut) and discharge (0.5C CC discharge 3.0V cut).

[0181] The volume retention rate after the Nth cycle was evaluated using the following formula. The results are shown in Table 1 below.

[0182] Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0183] [Table 1]

[0184] [Experimental Example 2: Evaluation of the Resistance Increase Rate of a Secondary Battery] The secondary batteries manufactured in the above examples and comparative examples were evaluated for life using an electrochemical charger / discharger, and the resistance increase rate was confirmed by measuring the resistance every 50 cycles during the evaluation. Resistance evaluation is performed after the completion of 50 life cycle evaluations by charging (0.33C CC / CV charge 4.2V 0.05C cut) to fully charge the secondary battery. Then, discharge (0.33C CC discharge, cut at 50% of the charge capacity) is performed to bring the charge state to 50%, and then discharge (2.5C CC discharge, 30s cut) is performed. After that, the same 50-cycle life evaluation is performed, followed by the same resistance evaluation.

[0185] The resistance is calculated using the following formula.

[0186] Resistance (R) = (Voltage in idle state before 2.5C discharge (V) - Voltage after 30s discharge (V)) / Discharge current (A)

[0187] The resistance increase rate measured before the life evaluation was confirmed using the 0-cycle baseline, and the results are shown in Table 2.

[0188] [Table 2]

[0189] As can be confirmed from the above experiment, the lifetime evaluation results showed that the capacity retention rate was similar for Example, Comparative Examples 4 and 5, but the resistance increase rate for each lifetime was even better for Example 1. Example uses a pre-dispersed sheet-like conductive material, while Comparative Examples 4 and 5 use an undispersed sheet-like conductive material. A low resistance increase rate indicates excellent current transfer in the Si electrodes, suggesting that the conductive network between active materials is formed by the conductive material of Example, which has a larger specific surface area. However, the improvement in lifetime performance is small because, although it is excellent in network configuration and effective for current transmission, it is not a material that can suppress the expansion and contraction of silicon.

[0190] Comparative Example 1 corresponds to the case where, although pre-dispersed, the specific surface area of the sheet-like conductive material is low. In the case of Comparative Example 1, as can be confirmed from Table 1, the specific surface area is small, but the application effect of the pre-dispersion liquid is added, and the life evaluation result shows the same level as that of the Example. However, it was confirmed that the resistance increase rate in Table 2 is higher than that of the Example. This corresponds to the result that the conductive network is not maintained due to the specific surface area of the sheet-like conductive material.

[0191] Comparative Example 2 and Comparative Example 3 correspond to the cases where the solid content of the pre-dispersion liquid is less than or exceeds that of the present invention. Particularly in the case of Comparative Example 2, the solid content is low, and there is no major problem with the pre-dispersion liquid itself. However, since the solid content of the entire slurry is low, it affects the dispersion level of the entire slurry, and it was confirmed that the life performance is inferior. In the case of Comparative Example 3, the solid content is high, and due to the excessive viscosity of the pre-dispersion liquid itself being produced, the dispersion of the pre-dispersion liquid itself is excessively reduced, showing the result that the final life performance is extremely reduced.

[0192] That is, in the case of the negative electrode pre-dispersion liquid according to an embodiment of the present invention, a sheet-like conductive material having a specific surface area (BET) of 100.0 m 2 / g or more is used. Among the materials applied to the negative electrode of the silicon-based active material, conventional carbon black (BET: 40 m 2 / g to 70 m 2 / g) or a sheet-like conductive material (BET: 6 m 2 / g to 20 m 2 / g) can be used without pre-dispersion. However, compared to the case of using this, when using a sheet-like conductive material having a specific surface area (BET) of 100.0 m 2 / g or more, as can be confirmed from the above experiment, it does not have a major influence on the life characteristics of the secondary battery as in the conventional case, and the number of points where charging and discharging are possible increases due to the sheet-like conductive material, and it was confirmed that it has the characteristic of excellent output characteristics at a high C-rate.

[0193] However, when the specific surface area (BET) is changed to a high specific surface area, aggregation of the conductive material in the negative electrode composition may occur. In the case of the negative electrode pre-dispersion according to this application, it was confirmed that pre-dispersing a sheet-like conductive material with a high specific surface area (BET) beforehand provides excellent dispersibility, which is even more effective in improving the output characteristics compared to conventional silicon-based negative electrodes. [Explanation of Symbols]

[0194] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30 ···Separator 40...Cathode active material 50 ···Positive electrode current collector layer 100 ···Negative electrode for lithium secondary batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. Specific surface area (BET) of 100.0 m² ２ A pre-dispersant consisting of a sheet-like conductive material and an aqueous dispersant of 1 / g or more; and Dispersion medium; A negative electrode pre-dispersion comprising, The solid content of the predispersant is 10% to 30% based on the negative electrode predispersion. The aforementioned sheet-like conductive material includes at least one selected from the group consisting of plate-like graphite, graphene, and graphite flakes. The aqueous dispersant is one or more selected from the group consisting of polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), and polyacrylamide (PAM). The dispersion medium is a nonionic compound that does not have an ionic functional group, and has a hydroxyl group, A negative electrode pre-dispersion liquid containing 92 parts by weight or more of the sheet-like conductive material, based on 100 parts by weight of the pre-dispersion material.

2. Silicon-based active materials; The negative electrode pre-dispersion according to claim 1; Point-type conductive material; and Negative electrode binder; A negative electrode composition comprising, The silicon-based active material is included in an amount of 60 parts by weight or more, based on 100 parts by weight of the negative electrode composition. The silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0) and SiC. The anode binder is a water-based binder in the anode composition.

3. The negative electrode composition according to claim 2, comprising 35 to 65 parts by weight of the point conductive material and 35 to 65 parts by weight of the sheet conductive material, based on 100 parts by weight of the negative electrode conductive material including the sheet conductive material and the point conductive material.

4. The negative electrode composition according to claim 3, wherein the negative electrode conductive material is included 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.

5. The negative electrode composition according to claim 2, wherein the sheet-like conductive material has 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.

6. The negative electrode composition according to claim 2, comprising 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

7. Specific surface area (BET) of 100.0 m² ２ A step of forming a pre-dispersion by mixing a sheet-like conductive material and an aqueous dispersant at a concentration of 1 / g or more, wherein the pre-dispersion consists of a sheet-like conductive material and an aqueous dispersant; A step of forming a negative electrode predispersion by adding a dispersion medium to the predispersion so that the solid content of the predispersion is 10% to 30%; A step of dispersing a pre-dispersant containing the aforementioned dispersion medium; The step of mixing the pre-dispersant, point conductive material, and negative electrode binder to form a mixture; The steps include adding water to the mixture and performing a first mixing; and The first step is to add an active substance to the mixed mixture and perform a second mixing; Includes, The aforementioned sheet-like conductive material includes at least one selected from the group consisting of plate-like graphite, graphene, and graphite flakes. The aqueous dispersant is one or more selected from the group consisting of polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), and polyacrylamide (PAM). The dispersion medium is a nonionic compound that does not have an ionic functional group, and has a hydroxyl group, A method for producing a negative electrode composition, comprising 92 parts by weight or more of the sheet-like conductive material based on 100 parts by weight of the pre-dispersant.

8. The method for producing a negative electrode composition according to claim 7, wherein the first mixing and second mixing steps are steps of mixing at 2,000 rpm to 3,000 rpm for 10 to 60 minutes.

9. The method for producing a negative electrode composition according to claim 7, wherein the step of dispersing the pre-dispersed material is performed using a dispersion device capable of dispersion under high stress, high pressure, or high speed.

10. Negative electrode current collector layer; and A negative electrode active material layer comprising the negative electrode composition according to claim 2 (provided that the dispersion medium is not included) formed on one or both sides of the negative electrode current collector layer; A negative electrode for lithium secondary batteries, including...

11. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The negative electrode for a lithium secondary battery according to claim 10, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

12. positive electrode; A negative electrode for a lithium secondary battery according to claim 11; A separator provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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