A negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode

Abstract

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

Description

Technical Field

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

[0002] This application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing, and 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 areas are increasingly expanding.

[0005] As technology development and demand related to 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, high voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, 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 includes 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 having a large discharge capacity can be used.

[0007] In particular, with the recent demand for high-density energy batteries, research is actively being conducted 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. Although silicon-based compounds are high-capacity materials and have a larger capacity than conventionally used graphite, they have the problem of rapidly expanding in volume 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] In other words, negative electrodes using silicon-based active materials require ensuring lifespan stability. Volume changes in silicon-based active materials occur during charging / discharging due to the insertion and removal of lithium during the reaction between lithium and silicon, and the degree of cracking of the active material becomes more severe when large amounts of lithium are inserted and removed.

[0010] To improve the cracking phenomenon of silicon-based active materials as described above and to ensure their lifetime characteristics, related research is needed, such as limiting the state of complexity (SOC) of silicon-based active materials. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] Rather than adjusting the state of charge (SOC) of the silicon-based anode system itself, it was found that including a highly reactive metal composite in the anode composition, where lithium ions react at a higher potential than silicon during cell discharge, limits the SOC of the silicon-based active material itself, thus improving lifespan performance.

[0013] Therefore, this application relates to a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode. [Means for solving the problem]

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

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

[0016] 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]

[0017] One embodiment of the present invention provides a negative electrode composition that, when using a silicon-based active material, which is a high-capacity material, to produce a high-capacity battery, improves upon the problem of volume expansion of the silicon-based active material by including a specific metal composite in the negative electrode composition, rather than limiting the state of charge (SOC) in the battery system.

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

[0019] When using the aforementioned metal composite, the SOC of silicon itself is limited compared to when silicon-based active material is used alone, resulting in an improvement in lifespan performance. In other words, the metal composite has the characteristics described above, reacts with lithium at a higher potential than silicon-based active material, has superior reactivity, and can suppress the volume expansion of silicon-based active material during charging and discharging compared to when silicon-based active material is used alone, thus exhibiting a superior improvement in lifespan performance.

[0020] Furthermore, compared to simply using a metal oxide, when a metal composite with deposited lithium oxide is included, as in the present invention, when the initial electrochemical reaction occurs, lithium ions are uniformly distributed throughout the upper and lower ends of the electrode. This effect allows for more uniform distribution of lithium ions, thereby improving the tortuosity within the electrode.

[0021] In other words, the anode composition according to this application has a high content of silicon-based active material particles, resulting in a high-capacity and high-density anode. Furthermore, to solve problems such as volume expansion caused by having a high content of silicon-based active material particles, the main objective of the present invention is to solve the aforementioned problems by using a metal composite of a specific composition and content. [Brief explanation of the drawing]

[0022] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 3] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

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

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

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

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

[0027] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution corresponding to the particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution corresponding to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution corresponding to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution corresponding to the particle size. On the other hand, the particle size distribution 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 difference in diffraction patterns corresponding to the particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0028] In this specification, the meaning of a polymer containing a monomer as a monomer unit 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 contains a monomer, this is interpreted in the same way as the polymer containing a monomer as a monomer unit.

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

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

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

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

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

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

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

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

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

[0038] In another embodiment, the silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less of the SiO x (x = 0), based on 100 parts by weight of the silicon-based active material.

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

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

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

[0042] Therefore, the present invention is characterized by using a high-content silicon-based active material as the negative electrode active material in order to improve capacity performance, and by using a metal composite under specific conditions in order to resolve the problems of maintaining the conductive path due to volume expansion as described above, and maintaining the bonding between the conductive material, binder, and active material.

[0043] 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. When the average particle size falls within the above range, the specific surface area of ​​the particles falls within a suitable range, and the viscosity of the negative electrode slurry is formed within a suitable range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is greater than or equal to the lower limit range, the contact area between the silicon particles and the conductive material is improved by the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of the conductive network being maintained and increasing the capacity retention rate. In addition, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of non-uniform current density during charging and discharging.

[0044] 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).

[0045] 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.

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

[0047] In another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0048] The negative electrode composition according to this application uses a specific metal composite that can suppress the rate of volume expansion during the charge-discharge process even when a silicon-based active material with remarkably high capacity is used within the aforementioned range. This results in a negative electrode composition that does not degrade performance even when a silicon-based active material is included within the aforementioned range, and exhibits excellent output characteristics during charging and discharging.

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

[0050] In this application, the degree of sphericity is determined by the following formula 1-1, where A is the area and P is the boundary line.

[0051] [Formula 1-1] 4πA / P 2

[0052] In one embodiment of this application, the negative electrode composition may include a metal composite on which lithium oxide has been deposited.

[0053] Metal composites with deposited lithium oxide are used with a different concept than conventional metal oxides. That is, metal oxides are represented as MO2 (where M is the metal), while the metal composites with deposited lithium oxide according to this application can have a structure in which lithium oxide is deposited on the metal itself. When a metal oxide (or metal) is used as the negative electrode, lithium ions must enter from the top to the bottom of the electrode during the initial discharge, resulting in a relative imbalance between the upper and lower parts of the electrode, which reduces the lifespan performance. However, in the case of metal composites with deposited lithium oxide according to this application, the lithium oxide can be uniformly mixed, so when the initial electrochemical reaction occurs, lithium ions are distributed throughout the upper and lower ends of the electrode, allowing for more uniform distribution of lithium ions, thereby improving the tortuosity.

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

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

[0056] The metal composite described in this application is a material used to limit the state of charge (SOC) of a silicon-based active material. In the case of the metal composite described in this application, lithium oxide may be deposited on the surface of the metal. In particular, by satisfying the ratio of lithium oxide to metal as described above, it reacts with lithium at a higher potential than silicon-based active materials, exhibits excellent reactivity, and can suppress the volume expansion of the silicon-based active material during charging and discharging compared to using only silicon-based active materials, thus exhibiting excellent improvement in lifespan performance.

[0057] In other words, if the proportion of lithium oxide in the metal composite is low, a problem may arise in that it cannot react uniformly with the Li in the metal during the reaction. If the proportion of lithium oxide exceeds the aforementioned range, these may remain even after the reaction, causing an increase in resistance and potentially leading to a decrease in cell performance.

[0058] In one embodiment of this application, the negative electrode composition is provided, wherein the metal composite is included in an amount of 1 to 15 parts by weight based on 100 parts by weight of the negative electrode composition.

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

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

[0061] The negative electrode composition according to this application is characterized by using a silicon-based active material and containing the aforementioned metal composite, and is characterized by satisfying the weight ratio described above. When the weight ratio described above is satisfied, the content of the silicon-based active material itself does not decrease, and it is possible to exhibit high energy density and high capacity, and the metal composite is included in an appropriate amount to limit the SOC, and the lifetime characteristics can also be improved.

[0062] In other words, if the content of the metal composite is less than the range mentioned above, the degree to which it limits the SOC of Si decreases, and the cracking phenomenon of Si cannot be mitigated. If the content of the metal composite exceeds the range mentioned above, the discharge capacity of Sn relative to Si decreases, which can lead to an increase in electrode resistance due to an increase in the total loading amount in the negative electrode.

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

[0064] In one embodiment of this application, the lithium oxide can be any lithium oxide used in the industry without limitation, but Li2O may also be used.

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

[0066] In one embodiment of this application, a negative electrode composition is provided in which the D50 particle size of the lithium oxide is 200 nm or less.

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

[0068] Lithium oxide is deposited onto the surface of a metal, and when it meets the aforementioned particle size range, it can improve the deposition strength on the metal surface and also has the characteristic of having a suitable degree of dispersion.

[0069] Traditionally, graphite-based compounds have been used exclusively as negative electrode active materials. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, in the case of silicon-based compounds, even if the properties of the silicon-based active material itself are adjusted according to this application, as described above, a problem may still occur where the volume rapidly expands during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer.

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

[0071] In one embodiment of this application, the point-shaped conductive material means a point-shaped or spherical conductive material that can be used to improve conductivity in a negative electrode, does not cause 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 that it achieves high conductivity and has excellent dispersibility.

[0072] 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.

[0073] In one embodiment of this application, the point-shaped conductive material may satisfy the functional group content (volatile matter) of 0.01% to 1%, preferably 0.01% to 0.3%, and more preferably 0.01% to 0.1%.

[0074] In particular, when the functional group content of the dot-shaped conductive material satisfies the aforementioned 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 excellent effect on improving dispersibility.

[0075] In one embodiment of this application, a silicon-based active material is provided along with a point-type conductive material having a functional group content within the range described above, wherein the content of the functional group can be adjusted according to the degree of heat treatment of the point-type conductive material.

[0076] 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.

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

[0078] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and can also suppress the disruption of the conductive path due to volume expansion. The sheet-like conductive material can also be described as a plate-like conductive material or a bulk conductive material.

[0079] 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.

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

[0081] In one embodiment of this application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When this range is met, 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.

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

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

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

[0085] In one embodiment of this application, the sheet-like conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0086] In another embodiment, the sheet-like 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 250m 2 It may be less than / g.

[0087] The sheet-like conductive material relating to this application may be a sheet-like conductive material with a high specific surface area, or a sheet-like conductive material with a low specific surface area.

[0088] In another embodiment, the sheet-like conductive material is a sheet-like conductive material with a high specific surface area, and has a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2Less than / g, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0089] In another embodiment, the sheet-like conductive material is a low specific surface area sheet-like conductive material, with a BET specific surface area of ​​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.

[0090] Other 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 longitudinal direction of the carbon nanotube units. The carbon nanotube units have a graphite sheet that is cylindrical with a nano-sized diameter, and sp 2 It has a bonded structure. In this case, depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly during the manufacturing of the negative electrode, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0091] Exemplary, linear conductive materials may be single-walled carbon nanotubes (SWCNTs) having a large BET specific surface area, a linear shape, a very small diameter, and a very long length. Linear conductive materials such as SWCNTs cannot be stretched by dispersion and have a strong ability to return to their original shape when dried. As a result, linear conductive materials such as SWCNTs have a strong tendency to return to their original shape when dried, and therefore commonly exist in a form that surrounds or connects the negative electrode active material or secondary aggregates. Bonding can be achieved by adsorption via van der Waals forces.

[0092] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0093] In another embodiment, the negative electrode conductive material may be included in an amount of 10 to 40 parts by weight, preferably 10 to 30 parts by weight, and more preferably 10 to 25 parts by weight, based on 100 parts by weight of the negative electrode composition.

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

[0095] In one embodiment of this application, the negative electrode conductive material is provided, comprising 80 to 99.9 parts by weight of the sheet-like conductive material and 0.1 to 20 parts by weight of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material, as a negative electrode conductive material.

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

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

[0098] In one embodiment of this application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, satisfying the aforementioned composition and proportions, thereby not significantly affecting the lifespan characteristics of conventional lithium secondary batteries. In particular, when a sheet-like conductive material and a linear conductive material are included, the number of charge and discharge points increases, resulting in excellent output characteristics at a high C-rate and reduced high-temperature gas generation.

[0099] The negative electrode conductive material described in this application has a completely different structure from the positive electrode conductive material applied to the positive electrode. Specifically, the negative electrode conductive material described in 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 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.

[0100] 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.

[0101] In one embodiment of this application, the sheet-like conductive material used as the negative electrode conductive material described above has a different structure and role from the carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot shape to facilitate the storage and release of lithium ions.

[0102] In contrast, sheet-like conductive materials used as negative electrode conductive materials are substances that have a sheet-like or plate-like shape and can be described as plate-like graphite. That is, they are substances included in the negative electrode active material layer to maintain conductive pathways, and do not play a role in the storage and release of lithium, but rather are substances that secure conductive pathways in a sheet-like form within the negative electrode active material layer.

[0103] In other words, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a sheet or plate shape and used not to store or release lithium, but as a material to secure a conductive path. In this case, the negative electrode active material 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.

[0104] In contrast, in this application, the use of a carbon-based active material as an active material means that it is processed into a point-like or spherical shape and used as a substance that stores or releases lithium.

[0105] 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 hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0106] The negative electrode binder according to one embodiment of this application plays a role in holding the active material and conductive material to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any general binder can be applied as long as it fulfills the above role, and specifically, an aqueous binder may be used, or more specifically, a PAM-based binder may be used.

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

[0108] 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 formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to this application or a cured product thereof.

[0109] 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, which includes a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10.

[0110] Figure 2, representing another embodiment, shows a laminated structure of a negative electrode for a lithium secondary battery, and specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on both sides of a negative electrode current collector layer 10.

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

[0112] In one embodiment of this application, when a negative electrode active material layer is coated on both sides, the negative electrode active material layer containing the negative electrode composition according to this application can be used without limitation as long as it is coated on only one of the two sides, and the other side may contain a silicon-based negative electrode active material or a carbon-based negative electrode active material, which may be commonly included.

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

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

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

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

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

[0118] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity during the formation of the negative electrode active material layer is suitable, minimizing particle aggregation of the negative electrode composition and enabling efficient formation of the negative electrode active material layer.

[0119] 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 cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, 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.

[0120] 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.

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

[0122] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0123] 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%.

[0124] 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 aforementioned range is satisfied by including the silicon-based active material and conductive material according to this application in specific compositions and content portions, thereby ensuring that the electrical conductivity and resistance of the electrode are within a suitable range.

[0125] 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.

[0126] Figure 3 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 the 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 the 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. The negative electrode active material layer 20 may also be formed on both sides of the negative electrode current collector layer 10. The positive electrode active material layer 40 may also be formed on both sides of the positive electrode current collector layer 50.

[0127] 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.

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

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

[0130] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 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 M c2 Ni-site type lithium nickel oxide represented as O2 (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 thereto. The positive electrode may be Li metal.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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 produced by using additives such as grain growth promoters that are useful for over-firing, or by changing the initiating substance.

[0136] 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 produced. For example, if the composition of the precursor is the same, firing must be performed at a temperature about 30°C to 100°C higher than when secondary particles are produced. The firing temperature for forming the single particles may vary depending on the composition of the metal 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 about 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 produced. 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 produced. 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.

[0137] 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 which is an aggregate of 30 or fewer primary particles.

[0138] 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, and a secondary particle may be in the form of several hundred primary particles aggregated together.

[0139] 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.

[0140] 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, and a secondary particle may be in the form of an aggregate of several hundred primary particles.

[0141] 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 analogous-single particle that is an aggregate of 30 or fewer primary particles.

[0142] 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.

[0143] 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.

[0144] When the average particle size (D50) of the primary particles satisfies the aforementioned 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 output characteristics.

[0145] 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.

[0146] 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.

[0147] For example, the average particle size (D50) of the single particle may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particle.

[0148] 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 met, 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.

[0149] 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.

[0150] 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.

[0151] When single particles within the aforementioned range are included, they can be combined with the aforementioned negative electrode material to exhibit excellent battery characteristics. In particular, when the single particles amount to 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.

[0152] 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.

[0153] When the above range is met, the aforementioned effects due to the presence of single-particle positive electrode active material can be maximized. When secondary-particle positive electrode active material is included, its components may be the same as those exemplified as the single-particle positive electrode active material described above, or they may be different, and may represent a form in which single particles are aggregated.

[0154] In one embodiment of this application, the positive electrode active material may be included 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, per 100 parts by weight of the positive electrode active material layer.

[0155] 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.

[0156] 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.

[0157] 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 of these alone or a mixture of two or more may be used.

[0158] 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 those made from polyolefin polymers like 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 those made from 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.

[0159] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0161] 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.

[0162] 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.

[0163] 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:

[0164] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0165] 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]

[0166] Hereinafter, preferred embodiments are presented to assist in understanding the present invention. However, the following embodiments are merely illustrative of this description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of this description and the scope of the technical idea, and it is needless to say that such variations and modifications belong to the scope of the appended claims.

[0167] <Production Example> <Production of Negative Electrode Composition> Si (average particle size (D50): 5 μm) as a silicon-based active material, a metal composite satisfying the composition and content in Table 1 below, a second conductive material, SWCNT as a linear conductive material, and polyacrylamide (PAM) as a binder were added to distilled water as a solvent for forming a negative electrode slurry at the weight ratios in Table 1 below to produce a negative electrode slurry (solid content concentration: 28% by weight).

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

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

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

[0171] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector layer at a loading amount of 85 mg / 25 cm 2 , 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 used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity 40.0%).

[0172] [Table 1]

[0173] <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).

[0174] 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%).

[0175] A polyethylene separator was interposed between the positive electrode and the negative electrodes of the above-mentioned examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

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

[0177] [Experimental Example 1: Evaluation of Monocell Lifespan] The secondary batteries containing the negative electrodes 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 underwent in-situ cycle testing at 4.2-3.0V 1C / 0.5C, and during the test, they were charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles to measure the capacity retention rate. The results are shown in Table 2. Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0178] [Table 2]

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

[0180] [Table 3]

[0181] As can be seen from Tables 1 to 3 above, when using the metal composite according to this application, the SOC of silicon itself is limited compared to when silicon-based active material is used alone (compared to Comparative Example 1), and it was confirmed that an improvement in lifespan performance is observed. In other words, the metal composite has the characteristics described above, reacts with lithium at a higher potential than silicon-based active material, has excellent reactivity, and can suppress the volume expansion of silicon-based active material during charging and discharging compared to when silicon-based active material is used alone, and it was confirmed that it has the characteristic of having an excellent improvement in lifespan performance.

[0182] Comparative Example 1 is a case where the metal composite described in this application is not included, and Comparative Example 2 is a case where the metal (Sn) is used alone, without using the metal composite described in this application. Furthermore, Comparative Example 3 is a case where the proportion of metal in the metal composite is small, and Comparative Example 4 is a case where the proportion of metal in the metal composite is high.

[0183] When comparing Comparative Example 1 with the Example, an improvement in lifespan performance was observed, and it was confirmed that the resistance of the electrode in the Example remained low. This is a result of the lifespan performance improvement being achieved by limiting the State of Charge (SOC) of the silicon itself.

[0184] Furthermore, in Comparative Example 2, a metal was used as the negative electrode, and since lithium ions had to enter from the top to the bottom of the electrode during the initial discharge, a relative imbalance occurred between the upper and lower parts of the electrode, which resulted in a decrease in lifespan performance. However, in the example, since the lithium oxide could be mixed uniformly, when the initial electrochemical reaction occurred, lithium ions were distributed throughout the entire upper and lower ends of the electrode, allowing for more uniform distribution of lithium ions. This resulted in an improvement in tortuosity.

[0185] In Comparative Examples 3 and 4, the weight ratio of metal to lithium oxide in the metal oxide was adjusted, and it was confirmed that the desired effect could not be obtained if the ratio exceeded or fell below the range specified in this application. [Explanation of Symbols]

[0186] 10. Negative electrode current collector layer 20 Negative electrode active material layer 30 Separators 40 Cathode active material layer 50 Positive electrode current collector layer 100 Negative electrodes for lithium secondary batteries 200 Positive electrode for lithium secondary batteries

Claims

1. A negative electrode composition comprising a silicon-based active material; a negative electrode conductive material; and a negative electrode binder; The negative electrode composition comprises a metal composite on which lithium oxide is deposited. The weight ratio of metal to lithium oxide in the metal composite satisfies 20:1 or more and 800:1 or less. The metal composite is included in an amount of 1 to 15 parts by weight based on 100 parts by weight of the negative electrode composition. A negative electrode composition wherein the metal in the metal composite is Sn.

2. The negative electrode composition according to claim 1, 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.

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

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

5. The negative electrode composition according to claim 1, wherein the D50 particle size of the lithium oxide is 200 nm or less.

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

20.

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

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

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

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

11. A negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, The negative electrode for a lithium secondary battery comprises a negative electrode composition or a cured product thereof according to any one of claims 1 to 10, wherein the negative electrode active material layer includes the negative electrode composition or a cured product thereof according to any one of claims 1 to 10.

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

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

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