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 of the filing date of Korean Patent Application No. 10-2021-0130950, filed with the Korean Intellectual Property Office on October 01, 2021, and all of its contents are incorporated herein by reference.

[0002] This 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 manufacturing the negative electrode composition.

Background Art

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

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

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

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and as the negative electrode active material, silicon-based particles with a large discharge capacity can be used.

[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 of a negative electrode slurry while maintaining appropriate fluid properties. It has been found that by including a point-like conductive material with a functional group content within a specific 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] Therefore, 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 provides a negative electrode pre-dispersion comprising a pre-dispersant containing a point conductive material and an aqueous dispersant having a functional group content (volatile matter) of 0.01% or more and less than 0.05%, 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 plate-shaped 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, a method for producing a negative electrode composition is provided, comprising the steps of: forming a pre-dispersion by mixing a point-shaped conductive material having a functional group content (volatile matter) of 0.01% or more and less than 0.05% with an aqueous dispersant; adding a dispersion medium to the pre-dispersion so that the solid content of the pre-dispersion is 10% to 30%; dispersing the pre-dispersion containing the dispersion medium; mixing the pre-dispersion, a plate-shaped conductive material, and a negative electrode binder to form a mixture; adding water to the mixture and performing a first mixing; and adding a silicon-based active material to the mixed mixture and performing a second mixing.

[0016] In yet another embodiment, a negative electrode for a lithium secondary battery is provided, comprising a 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 current collector layer.

[0017] Finally, the present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator provided 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, a point-type conductive material having a functional group content (volatile matter) of 0.01% or more and less than 0.05% is used.

[0019] Conventional carbon-based point conductive materials used as anodes generally exhibit hydrophobicity, making them difficult to disperse in water. When used in anodes prepared with water-dispersed slurries, materials with a high functional group content (volatile content) are used for dispersion. This increases the affinity with water and improves dispersibility, but the numerous functional groups lead to problems such as gas generation due to side reactions.

[0020] However, the negative electrode pre-dispersion according to one embodiment of the present invention is applied to silicon-based negative electrodes. Because it has a high proportion of binder, it is easier to disperse compared to conventional carbon-based negative electrodes. By using a point-like conductive material with a functional group content (volatile matter) of 0.01% or more and less than 0.05%, the functional group content is low, the hydrophobicity is strong, and the composite strength with the surrounding conductive material and binder is high. Furthermore, by pre-dispersing a hydrophobic conductive material, the dispersion state is far more dispersible than in solid form, so it does not aggregate, resulting in superior battery performance when silicon-based applications are made later.

[0021] In other words, in the case of a negative electrode composition according to one embodiment of the present invention, when using a silicon-based active material, which is a high-capacity material, to produce a high-capacity battery, the proportion of water-based binder is higher than when used as a conventional carbon-based negative electrode. Therefore, a hydrophobic conductive material with a functional group content (volatile matter) of 0.01% or more and less than 0.05% can be applied as the point conductive material. Furthermore, by applying a pre-dispersion liquid in which the point conductive material is pre-dispersed, the dispersibility is further improved. This improves the bonding strength with the surrounding conductive material / binder, and even if expansion occurs during charging / discharging of the Si-based negative electrode, it strengthens the bonds in the negative electrode composition and improves performance.

[0022] 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]

[0023] [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]

[0024] Before describing the present invention, let us first define some terms.

[0025] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0026] In this specification, "p~q" means the range "p or greater and q or less".

[0027] 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.

[0028] 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.

[0029] 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.

[0030] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense, including copolymers.

[0031] 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.

[0032] 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.

[0033] One embodiment of this specification provides a negative electrode pre-dispersion comprising a pre-dispersant containing a point conductive material and an aqueous dispersant having a functional group content (volatile matter) of 0.01% or more and less than 0.05%, and a dispersion medium, wherein the solid content of the pre-dispersant is 10% to 30% based on the negative electrode pre-dispersion.

[0034] 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.

[0035] A negative electrode pre-dispersion according to one embodiment of the present invention is applied to silicon-based negative electrodes. Due to the high proportion of binder, it is easier to disperse compared to conventional carbon-based negative electrodes. By using a point-type conductive material with a functional group content (volatile matter) of 0.01% or more and less than 0.05%, the functional group content is low, the hydrophobicity is strong, and the composite strength with the surrounding negative electrode conductive material and negative electrode binder is high. Because the dispersion state is far more dispersible than in solid form by pre-dispersing a hydrophobic conductive material, it does not aggregate, and will have the advantage of superior battery performance when applied to silicon-based systems in the future.

[0036] In one embodiment of this application, the functional group content (volatile content) is a numerical representation of the functional group content contained in the conductive material, and this can be calculated using the weight loss rate as shown below.

[0037] Weight loss rate = [(Weight of material before heat treatment - Weight of material after heat treatment) / Weight of material before heat treatment] × 100

[0038] The amount lost due to heat treatment may be functional groups present on the surface of the substance before heat treatment. The functional group may be at least one functional group selected from the group consisting of hydroxyl group, carboxyl group, aldehyde group, phenol group, ketone group, anhydride group, lactone group, peroxide group, ether group, hemiacetal group, quinone group, and amine group.

[0039] The functional group content (volatile matter) related to this application is determined using an analytical method that allows for confirmation of mass while increasing the temperature using thermal analysis. The method used in this application is the TPD mass method, and specifically, it can be measured by raising the measurement sample to 950°C and confirming the amount of compound that volatilizes. The analyzed amount can be expressed as the content of functional groups present on the surface of the point-like conductive material.

[0040] In one embodiment of this application, a negative electrode predispersion is provided in which the dispersant is one or more selected from the group consisting of polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), polyacrylamide (PAM), and H-nitrile butadiene rubber (HNBR).

[0041] In one embodiment of this application, the dispersant refers to an aqueous dispersant and has a structure different from that of an organic dispersant.

[0042] In one embodiment of this application, a negative electrode pre-dispersion is provided, which contains 90 parts by weight or more of the point-shaped conductive material based on 100 parts by weight of the pre-dispersion material.

[0043] In another embodiment, the predispersant may contain 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, of the point conductive material based on 100 parts by weight of the predispersant.

[0044] 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.

[0045] Specifically, in one embodiment of this application, the dispersion medium may be water.

[0046] 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.

[0047] In another embodiment, the solid content of the predispersant may be 10% to 30%, preferably 15% to 20%, relative to the negative electrode predispersion.

[0048] 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 point conductive material contained in the pre-dispersant is efficiently dispersed, the viscosity range can be kept within a certain range, and as a result, the aggregation phenomenon of the pre-dispersion does not occur.

[0049] 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.

[0050] 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.

[0051] 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 viscosity range, mixing is good when it is subsequently included in the negative electrode composition, which has the characteristic of improving the output of the secondary battery.

[0052] In other words, the negative electrode pre-dispersion according to one embodiment of this application is a substance having a functional group content (volatile matter) of 0.01% or more and less than 0.05%, and possessing high hydrophobic properties. When this pre-dispersion is dispersed in advance, it can suppress the aggregation phenomenon of highly hydrophobic point-type conductive material when subsequently applied to the negative electrode, thereby resulting in an electrode with superior performance.

[0053] In one embodiment of this application, the negative electrode pre-dispersion can be dispersed by first mixing a point-type conductive material having a functional group content (volatile matter) of 0.01% or more and less than 0.05% with an aqueous dispersant, then adding a dispersion medium to adjust the solid content, and using a homogenizer capable of applying high stress or pressure, a homomixer capable of high-speed mixing, or a mill device using beads.

[0054] 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.

[0055] In one embodiment of the present application, the negative electrode pre-dispersion liquid is dispersed by liquid mixing. When comprehensively considering all the processes of slurry transfer / coating and mixing, the most suitable viscosity range can satisfy the above range. Also, although the production time and working power of the negative electrode pre-dispersion liquid can be adjusted to vary according to the current value, the negative electrode pre-dispersion liquid can be manufactured through a process that uses the least amount of energy to satisfy a certain range of particle sizes.

[0056] In one embodiment of the present application, there is provided a negative electrode composition including a silicon-based active material; the negative electrode pre-dispersion liquid according to the present application; a plate-shaped 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.

[0057] In the case of the negative electrode composition according to one embodiment of the present invention, when using a silicon-based active material, which is a high-capacity material, to produce a high-capacity battery, compared with the case of using it as a conventional carbon-based negative electrode, since the proportion of the aqueous binder is low, a hydrophobic conductive material with a functional group content (volatile content) of 0.01% or more and less than 0.05% can be applied as the dot-shaped conductive material. Thereby, the binding force with the conductive material / binder located around it is improved, and even when expansion occurs during charging / discharging of the Si-based negative electrode, strengthening the binding in the negative electrode composition and improving the performance are the main features.

[0058] In particular, although an aggregation phenomenon may occur by adjusting the content of the functional group of the dot-shaped 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.

[0059] In one embodiment of the present application, there is provided a negative electrode composition, 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 alloys.

[0060] 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, it contains 70 parts by weight or more of the SiOx (x = 0), providing a negative electrode composition.

[0061] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0062] In one embodiment of the present application, the silicon-based active material may use particularly pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean that, as described above, when based on a total of 100 parts by weight of the silicon-based active material, it contains pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range.

[0063] In the case of a silicon-based active material, since the capacity is significantly higher compared to the conventionally used graphite-based active material, attempts to apply it have been increasing. However, due to the high volume expansion rate during the charge-discharge process, it has remained at the level of being used by mixing a small amount with the graphite-based active material.

[0064] Therefore, in the case of the present invention, in order to improve the capacity performance and high energy density, while using only the silicon-based active material as the negative electrode active material, in order to solve the above problems, it includes a dot-shaped conductive material and a plate-shaped conductive material as the negative electrode conductive material, and uses a material with a functional group content (volatile matter) of 0.01% or more and less than 0.05%, thereby solving the conventional problems.

[0065] 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.

[0066] 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).

[0067] 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.

[0068] In one embodiment of the present application, there is provided a negative electrode composition 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.

[0069] In another embodiment, the silicon-based active material may be contained 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, and may be contained 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, based on 100 parts by weight of the negative electrode composition.

[0070] Even when the silicon-based active material with a significantly high capacity is used within the above range, the negative electrode composition according to the present application uses a specific conductive material and binder that can suppress the volume expansion rate during the charge and discharge process, so that even when the silicon-based active material is contained within the above range, the performance of the negative electrode is not deteriorated, and it has the characteristic of excellent output characteristics in charging and discharging.

[0071] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and its circularity 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.

[0072] In the present application, the circularity is determined by the following formula 1, where A is the area and P is the boundary line.

[0073] [Formula 1] 4πA / P 2

[0074] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, in recent years, as the demand for high-capacity batteries has increased, attempts have been made to mix and use silicon-based compounds to increase the capacity. However, in the case of silicon-based compounds, there is a limit in that the volume rapidly expands during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer and rather deteriorating the performance of the battery.

[0075] Therefore, in one embodiment of this application, the negative electrode conductive material includes a point-shaped conductive material and a plate-shaped conductive material, and the point-shaped conductive material may have a functional group content (volatile matter) of 0.01% or more and less than 0.05%. 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, so that the conductive paths formed by the conductive material are not affected by volume expansion, and thus the performance of the battery can be maintained well.

[0076] In one embodiment of this application, the dot conductive material means the dot conductive material contained in the negative electrode pre-dispersion described above, and specifically, the dot conductive material contained in the negative electrode composition of the present invention may mean the dot conductive material pre-dispersed as exemplified in the negative electrode pre-dispersion described above.

[0077] 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.

[0078] 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.

[0079] In one embodiment of this application, the point-shaped conductive material may satisfy the functional group content (volatile matter) of 0.01% or more and less than 0.05%, preferably 0.01% or more and 0.04%, and more preferably 0.01% or more and 0.03%.

[0080] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, functional groups are present on the surface of the dot-shaped conductive material, and when water is used as the solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, the present invention can lower the functional group content of the dot-shaped conductive material by using silicon particles and a specific binder, thereby having an outstanding effect on improving dispersibility.

[0081] In one embodiment of this application, a point conductive material having a functional group content within the above range is included together with a silicon-based active material, and the content of the functional group can be adjusted according to the degree of heat treatment of the point conductive material.

[0082] In other words, in the production of point-shaped conductive materials, a high functional group content means a large amount of foreign matter, and a low functional group content means that more heat treatment processing has been performed. The point-shaped conductive material according to this application is characterized in that, in order to satisfy the above range of functional group content, the point-shaped conductive material was partially heat-treated to satisfy the above range of functional group content.

[0083] Specifically, by improving the dispersibility of the point-shaped conductive material, even if the content of the point-shaped conductive material is increased in a negative electrode slurry having the same solid content, the viscosity of the negative electrode slurry can be maintained at an appropriate level. This allows for stable processability and improved uniformity of the formed negative electrode.

[0084] 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.

[0085] In one embodiment of this application, the negative electrode conductive material may include a plate-shaped conductive material.

[0086] The plate-shaped 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. The plate-shaped conductive material can also be described as a sheet-shaped conductive material or a bulk conductive material.

[0087] In one embodiment of this application, the plate-shaped conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-shaped graphite.

[0088] In one embodiment of this application, the sheet-like conductive material may be provided in a form bonded to the surface of the silicon-based particles. Specifically, it may be provided in a form in which the -OH groups or -O groups on the surface of the silicon-based particles and the hydrophilic groups of the sheet-like conductive material are bonded to each other.

[0089] In one embodiment of this application, the average particle size (D50) of the plate-shaped 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.

[0090] In one embodiment of this application, a negative electrode composition is provided in which the plate-shaped 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.

[0091] In one embodiment of this application, the plate-shaped conductive material may be a plate-shaped conductive material with a high specific surface area and a high BET specific surface area, or a plate-shaped conductive material with a low specific surface area.

[0092] In one embodiment of this application, the plate-shaped conductive material can be any plate-shaped conductive material with a high specific surface area or a plate-shaped conductive material with a low specific surface area without limitation. However, since dispersion can affect electrode performance to some extent, it is particularly preferable to use a plate-shaped conductive material with a low specific surface area that does not cause dispersion problems.

[0093] In one embodiment of this application, the plate-shaped conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0094] In another embodiment, the plate-shaped conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 300m 2 It may be less than / g.

[0095] In another embodiment, the plate-shaped conductive material is a plate-shaped conductive material with a high specific surface area, and its BET specific surface area is 50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2 Less than / g, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0096] In yet another embodiment, the plate-shaped conductive material is a plate-shaped conductive material with a low specific surface area, and the BET specific surface area is 1 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0097] 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.

[0098] However, the present invention is characterized by not using the linear conductive material described above, but instead including point-shaped and plate-shaped conductive materials as conductive materials, and in particular by adjusting the content of functional groups of the point-shaped conductive material, thereby improving the output characteristics of the secondary battery of the present invention.

[0099] In one embodiment of this application, a negative electrode composition is provided, comprising 45 to 60 parts by weight of the negative electrode pre-dispersion and 40 to 55 parts by weight of the plate-shaped conductive material, based on 100 parts by weight of the negative electrode pre-dispersion and the negative electrode conductive material including the plate-shaped conductive material.

[0100] The aforementioned negative electrode pre-dispersion may mean a pre-dispersed point-shaped conductive material.

[0101] In one embodiment of this application, the negative electrode composition is provided, wherein the negative electrode conductive material is included in an amount of 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0102] 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.

[0103] In one embodiment of this application, a negative electrode composition is provided, comprising 45 to 60 parts by weight of the negative electrode pre-dispersion and 40 to 55 parts by weight of the plate-shaped conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0104] In another embodiment, the negative electrode pre-dispersion may be included in a quantity of 45 to 60 parts by weight, preferably 47 to 58 parts by weight, and more preferably 50 to 55 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0105] In another embodiment, the plate-shaped conductive material may be included in an amount of 40 to 55 parts by weight, preferably 42 to 53 parts by weight, and more preferably 45 to 50 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0106] In one embodiment of this application, the negative electrode conductive material comprises a plate-shaped conductive material and a negative electrode pre-dispersion (pre-dispersed dot-shaped conductive material), and the ratio of the plate-shaped conductive material to the negative electrode pre-dispersion (pre-dispersed dot-shaped conductive material) may be 1:0.8 to 1:1.2, and more specifically, it may be 1:1.

[0107] In one embodiment of this application, the negative electrode conductive material includes a point-shaped conductive material and a plate-shaped conductive material, and by satisfying the aforementioned composition and proportion, the number of chargeable and dischargeable points increases without significantly affecting the lifespan characteristics of conventional lithium secondary batteries, and the battery exhibits excellent output characteristics at a high C-rate.

[0108] The most significant cause of performance degradation is the continuous cracking of the active material due to the expansion / contraction of silicon volume, and the resulting short circuits caused by the separation of particles. Therefore, when constructing electrodes containing silicon-based active materials, the most important factor is how to maintain the original state of the silicon-based electrode for as long as possible, rather than improving its performance.

[0109] To solve the above problems, various negative electrode conductive materials are used, but generally carbon black / plate-shaped / CNT-based materials are mainly used, and typically a network is constructed using negative electrode conductive materials that connect at various intervals depending on the particle size and aspect ratio.

[0110] The negative electrode conductive material according to this application includes two types: a point-shaped conductive material and a plate-shaped conductive material having the above-described characteristics. Without the plate-shaped conductive material, short circuits occur in the active material at intervals where the conductive network cannot be maintained in the irregularly expanding / contracting silicon particles, which causes performance degradation. In the case of plate-shaped conductive material, graphite material is usually used, which has the advantage of fewer side reactions compared to point-shaped conductive material, and unlike point-shaped conductive material, charging / discharging is partially possible, making it more efficient than using point-shaped conductive material alone in terms of Li ion movement to the periphery. In other words, since the absence of plate-shaped conductive material results in degradation, the main feature of this invention is that it solves the problem of silicon-based active materials by including two specific types: a point-shaped conductive material and a plate-shaped conductive material.

[0111] 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 provides cushioning during rolling and also imparts some conductivity. Thus, its structure and role are completely different from the negative electrode conductive material of the present invention.

[0112] 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.

[0113] In one embodiment of this application, the plate-shaped 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.

[0114] In contrast, plate-shaped conductive materials used as negative electrode conductive materials are substances having a sheet-like or plate-like shape, and can be described as plate-shaped 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.

[0115] In other words, in this application, the use of plate-shaped graphite as a conductive material means that it was 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 included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0116] In contrast, in this application, the use of a carbon-based active material as the active material means that it was processed into a point-like or spherical shape and used as a substance that stores or releases lithium.

[0117] 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.

[0118] 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.

[0119] In one embodiment of this application, the negative electrode composition may contain 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, or 5 parts by weight or more, or 10 parts by weight or more, of the negative electrode binder based on 100 parts by weight of the negative electrode composition.

[0120] Compared to conventional carbon-based anodes, when using a Si-based anode, the application of a water-based binder in the aforementioned weight allows for the use of a point-type conductive material with a low functional group content. Due to the aforementioned characteristics, the point-type conductive material is hydrophobic, resulting in excellent bonding strength between the conductive material and the binder.

[0121] One embodiment of this application provides a method for producing a negative electrode composition, comprising the steps of: forming a pre-dispersion by mixing a point-shaped conductive material having a functional group content (volatile matter) of 0.01% or more and less than 0.05% with an aqueous dispersant; adding a dispersion medium to the pre-dispersion so that the solid content of the pre-dispersion is 10% to 30%; dispersing the pre-dispersion containing the dispersion medium; mixing the pre-dispersion, a plate-shaped conductive material, and a binder to form a mixture; adding water to the mixture and performing a first mixing; and adding a silicon-based active material to the mixed mixture and performing a second mixing.

[0122] In the method for producing the negative electrode composition, the composition and content of each component are as described above.

[0123] In one embodiment of this application, a method for producing 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0130] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0131] 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%.

[0132] The aforementioned porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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 to 300 MPa when rolled with this force. This allows the single particle to have a strength of 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.

[0142] 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.

[0143] 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 are useful for over-firing, or by changing the initiating substance.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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-particle forms are aggregated.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0168] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0169] 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.

[0170] 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.

[0171] 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:

[0172] 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.

[0173] 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]

[0174] 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.

[0175] <Examples> <Manufacturing of pre-dispersion> (Example 1 - Pre-dispersion 1) A carbon black conductive material C (Timcal, SB50L) and a dispersant (CHC, DN400H, Daicell) were added to water as a dispersion medium to form a negative electrode pre-dispersion with a solid content of 15%. This negative electrode pre-dispersion was then dispersed using a milling apparatus with a homomixer to produce a negative electrode pre-dispersion 1 with a viscosity of 6710 cp.

[0176] The aforementioned carbon black conductive material C has a specific surface area of ​​58 m². 2 It satisfies the following conditions: / g, diameter: 37nm, volatile content: 0.01%.

[0177] After dispersion of 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 had been manufactured.

[0178] (Example 2 - Pre-dispersion 2) A negative electrode predispersion was formed by adding a carbon black conductive material C (Timcal, SB50L) and a dispersant (CHC, DN400H, Daicell) to water as a dispersion medium so that the solid content was 15%. This negative electrode predispersion was then dispersed using a milling apparatus with a homomixer to produce a negative electrode predispersion 2 with a viscosity of 6710 cp.

[0179] The aforementioned carbon black conductive material C has a specific surface area of ​​58 m². 2 It satisfies the following conditions: / g, diameter: 37nm, volatile content: 0.03%.

[0180] After dispersing the negative electrode pre-dispersion 2, 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 2 had been manufactured.

[0181] (Comparative Example 1 - Pre-dispersion 3) In the above-described embodiment 1, the carbon black conductive material C is replaced with a carbon black conductive material C (specific surface area: 63 m²). 2 Pre-dispersion 3 was prepared in the same manner as in Example 1, except that it was applied with changes to the concentration ( / g, diameter: 35 nm, volatile content: 0.15%).

[0182] (Comparative Example 2 - Pre-dispersion 4) In the above-described embodiment 1, carbon black C (specific surface area: 45 m²) was used as the first conductive material. 2 Pre-dispersion 4 was prepared in the same manner as in Example 1, except that it was applied with changes to the concentration ( / g), diameter: 30-50 nm, and volatile content: 0.05%).

[0183] (Comparative Example 3 - Pre-dispersion 5) In Example 1, the pre-dispersion 5 was prepared in the same manner as in Example 1, except that a carbon black conductive material C (Timcal, SB50L) and a dispersant (CHC, DN400H, Daicell) were added to water as a dispersion medium to form a negative electrode pre-dispersion with a solid content of 5%.

[0184] (Comparative Example 4 - Pre-dispersion 6) In Example 1, the pre-dispersion 6 was prepared in the same manner as in Example 1, except that a carbon black conductive material C (Timcal, SB50L) and a dispersant (CHC, DN400H, Daicell) were added to water as a dispersion medium to form a negative electrode pre-dispersion with a solid content of 45%.

[0185] However, the pre-dispersion of Comparative Example 4 had a solid content of 45%, and because the content of the conductive material was excessively high, dispersion did not occur, the viscosity became high, and the pre-dispersion itself could not be manufactured.

[0186] <Manufacturing of negative electrodes> [Example 1: Manufacturing of the negative electrode] A negative electrode slurry was prepared by adding Si (average particle size (D50): 3.5 μm) as a silicon-based active material, pre-dispersion 1, a second conductive material, and polyacrylamide as a binder in a weight ratio of 70:10:10:10 to distilled water used as a solvent for negative electrode slurry formation (solid content concentration 25% by weight).

[0187] The second conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2 The values ​​were per g, with an average particle size (D50): 3.5 μm.

[0188] As a mixing method, the pre-dispersion 1, the second conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes. After adding the active material, the mixture was dispersed again at 2500 rpm for another 30 minutes to prepare a slurry.

[0189] 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%).

[0190] [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.

[0191] [Comparative Examples 1-3: 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 pre-dispersions 3 to 5 described above were used, respectively.

[0192] [Comparative Example 5: Manufacturing of the negative electrode] A negative electrode slurry was prepared by adding Si (average particle size (D50): 3.5 μm) as a silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 70:10:10:10 to distilled water used as a solvent for negative electrode slurry formation (solid content concentration 25% by weight).

[0193] The first conductive material is carbon black C (specific surface area: 58 m²). 2 The second conductive material is a plate-shaped graphite (specific surface area: 17 m²), with a diameter of 37 nm and a volatile content of 0.01%. 2 The values ​​were per g, with an average particle size (D50): 3.5 μm.

[0194] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added and dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0195] 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. 2The 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%).

[0196] <Manufacturing of secondary batteries> 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 a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the cathode slurry to prepare a cathode slurry (solid content concentration 78% by weight).

[0197] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is coated on both sides with the positive electrode slurry at a rate of 537 mg / 25 cm². 2 The 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 positive electrode active material layer (thickness: 65 μm), thereby manufacturing the positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0198] 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.

[0199] 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.

[0200] The secondary batteries of the examples and comparative examples were manufactured in the same manner as the secondary batteries of the examples and comparative examples, except that the negative electrodes of the examples and comparative examples were used.

[0201] [Experimental Example 1: Evaluation of the capacity retention rate of coin half-cells] Coin half-cells were manufactured using the negative electrodes of the above examples and comparative examples, and the capacity retention rate of the coin half-cells was evaluated using an electrochemical charger / discharger.

[0202] We determined the number of cycles required to reach 80% capacity for the first time under charging (0.5C CC / CV charge 0.005V 0.005C cut) and discharging (0.5C CC discharge 1.0V cut) conditions for a coin half-cell battery.

[0203] The volume retention rate after the Nth cycle was evaluated using the following formula. The results are shown in Table 1 below.

[0204] Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0205] [Table 1]

[0206] As can be seen from Table 1, the example using the pre-dispersion manufacturing method had a higher number of cycles to reach 80% of its volume compared to the comparative example. Therefore, it was confirmed that this method is effective in maintaining volume even in the lifetime evaluation of coin half-cells with a Li metal counter electrode.

[0207] [Experimental Example 2: 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 subjected to 1) charging (0.33C CC / CV charge 4.2V 0.05C cut) and discharging (0.33C CC discharge 3.0V cut), which was considered the first cycle. Then, from the second cycle onwards, charging (1.0C CC / CV charge 4.2V 0.05C cut) and discharging (0.5C CC discharge 3.0V cut) conditions were observed until the capacity retention rate reached 80%.

[0208] The volume retention rate after the Nth cycle was evaluated using the following formula. The results are shown in Table 5 below.

[0209] Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0210] [Table 2]

[0211] As can be seen from Table 2, the number of cycles required to reach 80% capacity was higher in the example using the pre-dispersion manufacturing method compared to the comparative example. Therefore, it was confirmed that this method is effective in maintaining capacity even in secondary batteries using positive electrode active material as the counter electrode.

[0212] In other words, as can be seen from the above examples and comparative examples, the negative electrode pre-dispersion according to one embodiment of the present invention is applied to silicon-based negative electrodes. Because the proportion of binder is high, dispersion is easier compared to conventional carbon-based negative electrodes. By using a point-type conductive material with a functional group content (volatile matter) of 0.01% or more and less than 0.05%, the functional group content is low, the hydrophobicity is strong, and the composite strength with the surrounding conductive material and binder is high. Furthermore, by pre-dispersing a hydrophobic conductive material, the dispersion state is far more dispersible than in solid form, so it does not aggregate, and it was confirmed that it has the characteristic of having excellent battery performance when silicon-based is applied later.

[0213] For reference, in the cases of Comparative Examples 1 and 2, the content of functional groups in the point-like conductive material exceeds the range specified in this application. When manufactured as described above, the dispersion of the pre-dispersion itself becomes difficult, and it was confirmed that the performance evaluation of the negative electrode manufactured as a result (Tables 1 and 2) was poor. In the case of Comparative Example 3, the solid content falls below the range specified in this application. Because it falls within the above range, the viscosity can be lowered, making it easier to manufacture, and the lower viscosity resulted in an even better dispersion state. However, the solid content of the pre-dispersion itself was excessively low, and the solid content of the final negative electrode slurry was also low, resulting in a significant decrease in the phase stability of the negative electrode slurry. As a result, it was confirmed that the performance evaluation of the negative electrode (Tables 1 and 2) was inferior to that of the examples. For reference, for reasons such as those described in Comparative Example 3, research aimed at maximizing the solid content while maintaining appropriate fluid properties of the negative electrode slurry led to the discovery of the pre-dispersion specified in this application.

[0214] The pre-dispersion in Comparative Example 4 had a solid content of 45%, and because the conductive material content was excessively high, dispersion did not occur smoothly, resulting in extremely high viscosity, making it impossible to manufacture the pre-dispersion itself. As a result, it was not possible to manufacture the negative electrode slurry for forming the negative electrode active material layer, and therefore evaluation could not be performed.

[0215] Comparative Example 5 is a case where no pre-dispersion solution was applied, and the point-shaped conductive material according to the present invention was not dispersed. In this case, the capacity characteristics and lifespan were found to be higher than in the other Comparative Examples 1 to 4, but it was confirmed that the performance was inferior to that of the pre-dispersed examples. [Explanation of Symbols]

[0216] 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 batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. A step of forming a pre-dispersant by mixing a point-type conductive material having a functional group content (volatile matter) of 0.01% or more and less than 0.05% with an aqueous dispersant; A step of adding a dispersion medium to the predispersant such that the solid content of the predispersant is 10% to 30%; A step of dispersing a pre-dispersant containing the aforementioned dispersion medium; The step of mixing the pre-dispersant, plate-shaped 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 a silicon-based active material to the mixed mixture and perform a second mixing; Includes, The aqueous dispersant is carboxymethylcellulose (CMC), The pre-dispersed material is used as a basis, and the pre-dispersed material contains 92 parts by weight or more of the point-shaped conductive material. The aforementioned point-shaped conductive material is carbon black, The dispersion medium is water, A method for producing a negative electrode composition, wherein the negative electrode binder is contained in an amount of 5 to 30 parts by weight, based on 100 parts by weight of the negative electrode composition obtained through the above steps.

2. The method for producing a negative electrode composition according to claim 1, 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.

3. The method for producing a negative electrode composition according to claim 1, 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.

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