Negative electrode composition, negative electrode for lithium secondary battery containing the same, lithium secondary battery containing the negative electrode

Abstract

The negative electrode composition can include a silicon-based active material, a negative electrode conductive material, and a negative electrode binder. The silicon-based active material contains 70 parts by weight or more of SiOx (x = 0) with respect to 100 parts by weight of the silicon-based active material, optionally contains SiOx (0 < x < 2), the crystal grain size of the silicon-based active material is 200 nm or less, and the negative electrode conductive material includes a planar conductive material and a linear conductive material.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0119283, filed with the Korean Intellectual Property Office on September 21, 2022, and all of its contents are incorporated herein by reference. and Korean Patent Application No. 10-2023-0126086, filed with the Korean Intellectual Property Office on September 21, 2023. 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. 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 a high energy density, 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 a higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively underway.

[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 silicon-based particles having a large discharge capacity can be used as the negative electrode active material.

[0007] In recent years, in response to the demand for high-density energy batteries, research has been actively conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx as negative electrode active materials, which have more than 10 times the capacity of graphite-based materials. However, while silicon-based compounds are high-capacity materials, they have the problem of rapidly expanding in volume during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, various methods have been discussed to suppress volume expansion itself or prevent the conduction path from being interrupted, such as adjusting the driving potential to resolve the problems when using silicon-based compounds as negative electrode active materials, further coating a thin film on the active material layer, and adjusting the particle size of the silicon-based compound. However, these methods can actually degrade the performance of the battery, limiting their applicability, and thus limiting the commercialization of negative electrode batteries with a high silicon-based compound content.

[0009] Furthermore, when using silicon-based active materials to fabricate negative electrodes to increase energy density, high swelling during charging and discharging makes it difficult to achieve sufficient cycle performance by using only a small amount of point-type conductive material, as in existing carbon-based active material systems. Consequently, while there is room for improvement in lifespan performance when applying an excessive amount of point-type conductive material, there are limitations, and the high specific surface area of ​​the point-type conductive material leads to problems such as increased slurry viscosity and increased gas generation at high temperatures.

[0010] Therefore, even when silicon-based compounds are used as active materials to improve capacity performance, research is needed to prevent damage to the conductive pathways due to the volume expansion of the silicon-based compounds, and to develop conductive material systems that are particularly suitable for crystalline silicon-based active materials, which are high-capacity anode materials. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] Recognizing the above problems, as a result of research on the conductive material system to reduce the amount of gas generated at high temperatures, instead of using a dot-shaped conductive material for a silicon-based active material that satisfies a certain crystal grain size, when applying a bulk conductive material and a linear conductive material, it was found that the electrical connectivity can be improved and the electrical isolation phenomenon can be prevented.

[0013] Accordingly, the present 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 PROBLEMS

[0014] One embodiment of the present specification is a negative electrode composition containing a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material contains at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 <x <2), based on 100 parts by weight of the silicon-based active material, 70 parts by weight or more of the SiOx (x = 0) is included, the silicon-based active material has a crystal grain size of 200 nm or less, and the negative electrode conductive material includes a bulk conductive material; and a linear conductive material.

[0015] In another embodiment, a negative electrode for a lithium secondary battery including a negative electrode current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one or both surfaces of the negative electrode current collector layer is provided.

[0016] Finally, a lithium secondary battery including a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte is provided. EFFECTS OF THE INVENTION

[0017] A negative electrode composition according to one embodiment of the present invention manufactures a negative electrode using a silicon-based active material with a specific range of crystalline grains to increase energy density. In this case, the negative electrode conductive material uses planar conductive material and linear conductive material to significantly improve the electrical connectivity between silicon-based active materials, and as a result, prevents electrical isolation phenomena that may occur when charging / discharging a negative electrode to which silicon-based active materials are applied, thereby improving the lifespan of the negative electrode.

[0018] In conventional negative electrodes using carbon-based active materials, a small amount of dot-type conductive material is used as the negative electrode conductive material. However, when such dot-type conductive material is applied to the silicon-based active material of the present invention, it is difficult to achieve sufficient cycle performance. If an excessive amount of dot-type conductive material is included, although there is room to improve lifespan performance, the high specific surface area leads to problems such as increased viscosity of the composition and increased high-temperature gas generation. In other words, the negative electrode composition of the present application is characterized by the construction of a system that can be applied together with a high-energy-density silicon-based active material by applying a negative electrode conductive material of a specific composition and content as described above, without using dot-type conductive material. [Brief explanation of the drawing]

[0019] [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. [Figure 3] This shows an enlarged view of a silicon-based active material according to one embodiment of this application. [Modes for carrying out the invention]

[0020] Before describing the present invention, let us first define some terms. In this specification, when a part "includes" a component, this means, unless otherwise stated, that it may include other components rather than excluding them.

[0021] In this specification, "p~q" means the range "p or greater and q or less". 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 BELSORP-mini II from BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0022] In this specification, "Dn" refers to the particle size distribution, and means the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. Alternatively, the particle size distribution may be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, then 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 due to particle size as the particles pass through the laser beam.

[0023] In this specification, when a polymer contains a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer contains a monomer, this is interpreted as meaning that the polymer contains monomers as monomer units.

[0024] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as "homopolymer."

[0025] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0026] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0027] One embodiment of this specification is a negative electrode composition containing a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material has a crystal grain size of 200 nm or less, and the negative electrode conductive material includes a planar conductive material; and a linear conductive material, and provides a negative electrode composition.

[0028] One embodiment of this specification is a negative electrode composition containing a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), based on 100 parts by weight of the silicon-based active material, contains 70 parts by weight or more of the SiOx (x = 0), the silicon-based active material has a crystal grain size of 200 nm or less, and the negative electrode conductive material includes a planar conductive material; and a linear conductive material, and provides a negative electrode composition.

[0029] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and provides a negative electrode composition containing 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0030] In another embodiment, the silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, of SiOx(x=0) based on 100 parts by weight of the silicon-based active material, or 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0031] In one embodiment of this application, the silicon-based active material may be one that particularly contains pure silicon (Si) particles. Using pure silicon (Si) particles as the silicon-based active material means that, based on 100 parts by weight of the total silicon-based active material, it contains pure Si particles (SiOx(x=0)) that are not bonded with other particles or elements, within the range described above.

[0032] In one embodiment of this application, the silicon-based active material may consist of silicon-based particles having 100 parts by weight of SiOx(x=0).

[0033] In one embodiment of this application, the silicon-based active material may contain metallic impurities, in which case the impurities are metals that can generally be contained in silicon-based active materials, and specifically, may contain 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0034] In the case of silicon-based active materials, the capacity is significantly higher than that of conventionally used graphite-based active materials, and attempts to apply them are increasing. However, the volume expansion rate during the charge-discharge process is high, so their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0035] However, the negative electrode composition according to the present invention has the characteristic of improving the lifespan performance of the negative electrode and reducing the amount of gas at high temperatures by applying a silicon-based active material whose crystal grain size meets the range described later, as well as including specific planar conductive materials and linear conductive materials.

[0036] In one embodiment of this application, the crystal grain size of the silicon-based active material may be 200 nm or less.

[0037] In this application, the crystal grain size of the silicon-based active material may be 10 nm or more and 150 nm or less.

[0038] In another embodiment, the crystal grain size of the silicon-based active material may be 200 nm or less, preferably 130 nm or less, more preferably 110 nm or less, even more preferably 100 nm or less, specifically 95 nm or less, and more specifically 91 nm or less. The crystal grain size of the silicon-based active material may be in the range of 10 nm or more, preferably 15 nm or more, and 30 nm or more.

[0039] The silicon-based active material has the aforementioned crystal grain size, and the crystal grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. In this case, by satisfying the aforementioned range and ensuring a wide distribution of grain boundaries, lithium ions will be inserted uniformly, reducing the stress applied to the silicon particles during lithium ion insertion, thereby mitigating particle cracking. As a result, the lifetime stability of the negative electrode can be improved. If the crystal grain size exceeds the aforementioned range, the crystal grain system within the particle becomes narrowly distributed, in which case lithium ions are inserted non-uniformly, the stress due to ion insertion is large, and particle cracking occurs.

[0040] Figure 3 shows an enlarged view of a silicon-based active material according to one embodiment of this application. Specifically, the silicon-based active material 1 consists of numerous crystalline structures 2, and it can be confirmed that the crystalline structures have a grain distribution of 1 nm to 200 nm. The space between crystalline structures can be defined as a grain boundary. In general, crystalline structures can be expressed as crystal grains.

[0041] In one embodiment of this application, the silicon-based active material includes a crystalline structure having a grain distribution of 1 nm to 200 nm, and the negative electrode active material is provided such that the area ratio of the crystalline structure is 5% or less based on the total area of ​​the silicon-based active material.

[0042] In another embodiment, the area ratio of the crystal structure to the total area of ​​the silicon-based active material may be 5% or less, 3% or less, or 0.1% or more.

[0043] In other words, the silicon-based active material according to this application has a crystal grain size of 200 nm or less, and the size of each crystal structure is formed to be small, thus satisfying the aforementioned area ratio. As a result, the distribution of crystal grain boundaries can be broadened, thereby achieving the aforementioned effects.

[0044] One embodiment of this application provides a negative electrode active material having 20 or more crystal structures contained in the silicon-based active material.

[0045] In another embodiment, the number of crystal structures contained in the silicon-based active material may be 20 or more, 30 or more, 35 or more, and may satisfy the range of 60 or less, or 50 or less.

[0046] In other words, as mentioned above, when the silicon-based active material satisfies the aforementioned range in terms of crystal grain size and the number of crystal structures satisfies the aforementioned range, the strength of the silicon-based active material itself will be within an appropriate range, providing flexibility when included in an electrode and having the characteristic of efficiently suppressing volume expansion.

[0047] In this application, a crystal grain refers to a crystalline particle in a metal or material that is a collection of irregularly shaped particles of microscopic size, and the crystal grain size may refer to the diameter of the observed crystal grain. In other words, in this application, the crystal grain size refers to the size of domains within a particle that share the same crystal orientation, and is a different concept from particle size or particle size, which represents the size of a substance.

[0048] In one embodiment of this application, the crystal grain size can be calculated as the FWHM (Full Width at Half Maximum) value through XRD analysis. The remaining value, excluding L, is measured by XRD analysis of the silicon-based active material, and the crystal grain size can be measured using the Debey-Scherrer equation, which shows that FWHM and crystal grain size are inversely proportional. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0049] [Formula 1-1] FWHM = Kλ / LCosθ In the above formula 1-1, L is the crystal grain size, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0050] The shape of the crystal grains is diverse and can be measured three-dimensionally. Generally, the size of the crystal grains can be measured using the commonly used circle method or diameter measurement method, but is not limited to these methods.

[0051] The aforementioned diameter measurement method involves drawing 5 to 10 parallel lines, each with a length of L mm, on a micrograph of the target particle, and counting the number of crystal grains z along each line and averaging the results. Only grains that are entirely within the line are counted, and those that overlap the line are excluded. If the number of lines is P and the magnification is V, the average particle diameter can be calculated using the following equation 1-2.

[0052] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0053] Also, the circle method is a method of obtaining the average area of crystal grains by drawing a circle with a defined diameter on a micrograph of the target particles and then calculating the number of crystal grains inside the circle and the number of crystal grains on the boundary line, and can be calculated by the following formula 1-3.

[0054] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 ) In the above formula 1-3, Fm represents the average particle area, Fk represents the measured area on the photograph, z represents the number of particles inside the circle, n represents the number of particles on the arc, and V represents the magnification of the microscope, respectively.

[0055] One embodiment of the present application may include a silicon-based active material having a surface area of 0.25 m 2 / g or more.

[0056] In another embodiment, the silicon-based active material has a surface area of 0.25 m 2 / g or more, preferably 0.28 m 2 / g or more, more preferably 0.30 m 2 / g or more, specifically 0.31 m 2 / g or more, more specifically 0.32 m 2 / g or more. The silicon-based active material may satisfy the range of having a surface area of 3 m 2 / g or less, preferably 2.5 m 2 / g or less, more preferably 2.2 m 2 / g or less. The surface area can be measured in accordance with DIN 66131 (using nitrogen).

[0057] In one embodiment of the present application, the negative electrode active material may include a silicon-based active material having a surface area of 0.30 m 2 / g or more and 4.00 m 2 / g or less.

[0058] In another embodiment, the silicon-based active material has a surface area of ​​0.30 m². 2 / g or more, preferably 0.31m 2 / g or more, more preferably 0.32m 2 The silicon-based active material may be 1 / g or more. 2 Less than or equal to / g, preferably 2.50m 2 / g or less, more preferably 2.20m 2 The range of / g or less may also be satisfied.

[0059] The silicon-based active material has the aforementioned surface area, and the size of the surface area of ​​the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material. In other words, when the negative electrode active material is manufactured using the manufacturing method according to this application, the rough surface results in a larger surface area compared to particles with the same particle size. In this case, the aforementioned range is satisfied, and the bonding strength with the binder is increased, which has the characteristic of mitigating electrode cracks caused by repeated charge-discharge cycles.

[0060] Furthermore, lithium ions are inserted uniformly, reducing the stress applied during lithium ion insertion into silicon particles, thereby mitigating particle cracking. As a result, the lifespan stability of the negative electrode can be improved. If the surface area size is less than the aforementioned range, even if the particle size is the same, the surface is formed smoothly, reducing the bonding force with the binder and causing electrode cracks. In this case, lithium ions are inserted unevenly within the particles, resulting in high stress due to ion insertion and causing particle cracking.

[0061] In one embodiment of this application, the silicon-based active material may satisfy the range of the following formula 2-1.

[0062] [Formula 2-1] X1 / Y1 ≤ 0.960 In the above equation 2-1, X1 is the actual area of ​​the silicon-based active material. Y1 represents the area of ​​the surrounding spherical particles, similar to that of the silicon-based active material.

[0063] The measurement of Equation 2-1 can be performed using a granular analyzer. Specifically, the silicon-based active material according to this application is scattered onto a glass plate by air jetting, and then a shadow image of the scattered silicon-based active material particles is taken to measure the shape of 10,000 silicon-based active material particles in the photograph. In this case, Equation 2-1 represents the average value for 10,000 particles. From the above image, Equation 2-1 according to this application can be measured, and Equation 2-1 can be expressed as the degree of spherulity of the silicon-based active material. The degree of spherulity is given by the formula [4π * actual area of ​​silicon-based active material / (boundary)] 2 It may also be represented as ].

[0064] In one embodiment of this application, the degree of spheroidization of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less. The degree of spheroidization of the silicon-based active material may be 0.8 or more, for example, 0.9 or more, specifically 0.93 or more, and more specifically 0.94 or more, for example, 0.941 or more.

[0065] In one embodiment of this application, the silicon-based active material may satisfy the range of the following formula 2-2.

[0066] [Formula 2-2] X2 / Y2 ≤ 0.996 In the above equation 2-2, Y2 is the actual surrounding area of ​​the silicon-based active material. X2 is the perimeter of the circumscribed figure of the silicon-based active material.

[0067] The measurement of Equation 2-2 can be performed using a granular analyzer. Specifically, the silicon-based active material according to this application can be scattered onto a glass plate by air jetting, and then a shadow image of the scattered silicon-based active material particles can be taken to measure the shape of 10,000 silicon-based active material particles in the photograph. In this case, Equation 2-2 represents the average value for 10,000 particles. From the aforementioned image, Equation 2-2 according to this application can be measured, and Equation 2-2 can be expressed as the convexity of the silicon-based active material.

[0068] In one embodiment of this application, the range X2 / Y2 ≤ 0.996, preferably X2 / Y2 ≤ 0.995, can be satisfied, and the range 0.8 ≤ X2 / Y2, preferably 0.9 ≤ X2 / Y2, more preferably 0.95 ≤ X2 / Y2, specifically 0.98 ≤ X2 / Y2 may also be satisfied.

[0069] The smaller the value of equation 2-1 or equation 2-2, the greater the roughness of the silicon-based active material. By using a silicon-based active material having such a range, the bonding strength with the binder is increased, which has the advantage of mitigating electrode cracks caused by repeated charge-discharge cycles.

[0070] On the other hand, the average particle size (D50) of the silicon-based active material in the present invention is 3 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within the above range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is greater than or equal to the lower limit range, the composite consisting of the conductive material and binder in the negative electrode slurry provides excellent contact area between the silicon particles and the conductive material, increasing the likelihood of a sustained conductive network and improving capacity retention. On the other hand, when the average particle size is within the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing non-uniformity of current density during charging and discharging.

[0071] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragmentary particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0072] In one embodiment of this application, the present invention provides a negative electrode composition 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.

[0073] In another embodiment, the silicon-based active material may contain 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 contain 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0074] The negative electrode composition according to this application, even when using a silicon-based active material with remarkably high capacity within the aforementioned range, utilizes specific conductive materials and binders that suppress the rate of volume expansion during the charge and discharge process, thereby preventing a decrease in negative electrode performance even within the aforementioned range and exhibiting excellent output characteristics during charging and discharging.

[0075] 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.

[0076] In this application, the degree of sphericity is determined by the following formula 3-1, where A is the area and P is the boundary line. [Formula 3-1] 4πA / P 2

[0077] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have a limitation: their volume expands rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer and actually degrading the battery's performance.

[0078] Therefore, the negative electrode conductive material according to one embodiment of the present application may include a planar conductive material and a linear conductive material.

[0079] As described above, the negative electrode conductive material includes planar conductive material and linear conductive material, which greatly improves the electrical connectivity between silicon-based active material particles, prevents isolation of silicon-based active material particles during charging / discharging, and improves the negative electrode lifetime performance.

[0080] In one embodiment of this application, the negative electrode conductive material may include a planar conductive material. The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. It can be described as a plate-type conductive material or a bulk-type conductive material.

[0081] In one embodiment of this application, the planar 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.

[0082] In one embodiment of this application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is met, the particle size is sufficient to disperse the material without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0083] In one embodiment of this application, a negative electrode composition is provided in which the planar 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 6.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0084] In one embodiment of this application, the planar conductive material may be a graphite-based plate-like material. In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0085] In one embodiment of this application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. However, since the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, it is particularly preferable to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0086] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0087] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

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

[0089] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, with a BET specific surface area of ​​5 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] In this application, the planar conductive material may have a thickness in the range of 0.5 μm to 2 μm.

[0091] In this application, the planar conductive material may satisfy a ratio of D50 to thickness of 20% or more and 30% or less. In this case, the ratio of D50 to thickness can be expressed as (thickness of planar conductive material / D50 of planar conductive material) × 100%.

[0092] By using the aforementioned planar conductive material, the lifespan characteristics of the lithium secondary battery are not significantly affected, and charging and discharging are possible in many areas, resulting in a high C-rate and excellent output characteristics.

[0093] In one embodiment of this application, the linear conductive material may be a linear conductive material such as a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may contain a plurality of carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in the form of a bundle or rope, in which a plurality of carbon nanotube units are arranged side by side or intertwined with substantially the same orientation of their longitudinal axes. The carbon nanotube unit has a graphite sheet in the shape of a cylinder 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 bundled carbon nanotube can be uniformly dispersed during anode manufacturing, smoothly forming a conductive network within the anode and improving the conductivity of the anode.

[0094] In one embodiment of this application, the linear conductive material may be SWCNT or MWCNT.

[0095] In one embodiment of this application, the linear conductive material may be SWCNT. In one embodiment of this application, the average particle size of the linear conductive material may be 1 μm or more and 5 μm or less.

[0096] In one embodiment of this application, the BET specific surface area of ​​the linear conductive material is 500 m². 2 / g or more 1500m 2 It may be less than / g.

[0097] In one embodiment of this application, the Raman IG / ID of the linear conductive material may satisfy the range of 100 to 150.

[0098] The negative electrode conductive material relating to this application may include, based on 100 parts by weight of the negative electrode conductive material, 90 to 99.9 parts by weight of the planar conductive material, and 0.1 to 10 parts by weight of the linear conductive material.

[0099] In another embodiment, the negative electrode conductive material may include 100 parts by weight of the negative electrode conductive material, 90 to 99.9 parts by weight of the planar conductive material; preferably 92 to 99.9 parts by weight, and more preferably 93 to 98 parts by weight.

[0100] In another embodiment, the negative electrode conductive material may be included in an amount of 0.1 to 10 parts by weight of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material; preferably 0.1 to 8 parts by weight; more preferably 0.5 to 7 parts by weight.

[0101] The negative electrode conductive material according to this application is characterized by not containing point-type conductive materials such as carbon black. When point-type conductive materials are used, there is room for improvement in lifespan performance, but there is a limit, and when excessive amounts of point-type conductive materials are used, the viscosity of the negative electrode slurry increases due to the high specific surface area of ​​the point-type conductive materials, which leads to the problem of increased gas generation at high temperatures.

[0102] Therefore, the negative electrode composition of this application does not use point-shaped conductive material, but contains two types of conductive material: a planar conductive material and a linear conductive material. By including the aforementioned content, the viscosity of the negative electrode slurry containing it can be reduced, and the amount of high-temperature storage gas can be reduced.

[0103] In one embodiment of this application, a negative electrode composition is provided in which the volume resistance (Ω·cm@1g / cc) of the linear conductive material is 0.0005 or more and 0.003 or less.

[0104] The linear conductive material will satisfy the aforementioned volume resistance and will have the characteristic of improving the conductivity of the negative electrode containing it. In other words, it corresponds to a factor indicating the electrical network retention performance of the linear conductive material.

[0105] In one embodiment of this application, the negative electrode conductive material is provided to be 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0106] In another embodiment, the negative electrode conductive material may contain 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.

[0107] In one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each satisfying the aforementioned composition and proportion, thereby increasing the number of charging and discharging points without significantly affecting the life characteristics of existing lithium secondary batteries, and resulting in a high C-rate and excellent output characteristics.

[0108] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material described above has a different structure and role from carbon-based active materials generally used as negative electrode active materials. 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 point-like form for use in order to facilitate the storage and release of lithium ions.

[0109] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and may be described as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0110] In other words, the use of plate-shaped graphite as a negative electrode conductive material in this application means that it was processed into a planar 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.

[0111] On the other hand, the use of carbon-based active materials as active materials means that they were processed into point-like or spherical shapes and used as substances that serve to store or release lithium.

[0112] In other words, artificial graphite or natural graphite, which are carbon-based active materials, have a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 It can satisfy the range of less than / g. In addition, plate-shaped graphite, which is a planar conductive material, has a BET specific surface area of ​​5m². 2 It may be more than / g.

[0113] 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 capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer during rolling while also providing some conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0114] 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, thus improving output characteristics and imparting some conductivity. As with the present invention, its structure and role are completely different from negative electrode conductive materials applied together with silicon-based active materials.

[0115] 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 thereof are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0116] The negative electrode binder according to one embodiment of this application plays a role in suppressing the active material and conductive material in order to prevent twisting 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 satisfies the above role, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0117] In one embodiment of this application, the negative electrode binder may contain 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may also contain 5 parts by weight or more, or 10 parts by weight or more.

[0118] Compared to existing carbon-based anodes, when using a Si-based anode, a water-based binder is applied in the aforementioned weight, and a negative electrode conductive material with a low functional group content can be used. Due to these characteristics, the negative electrode conductive material becomes hydrophobic and exhibits excellent bonding strength with the conductive material / binder.

[0119] 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.

[0120] 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. Figure 1 shows that the negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode active material layer.

[0121] 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 has high conductivity without inducing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or 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, net, porous body, foam, nonwoven fabric.

[0122] In one embodiment of this application, the negative electrode for the lithium secondary battery may be formed by coating and drying a negative electrode slurry containing the negative electrode composition on one or both sides of a negative electrode current collector layer.

[0123] In one embodiment of this application, a negative electrode composition is provided having a viscosity of 1,000 cP or more and 6,000 cP or less.

[0124] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0125] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0126] 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%.

[0127] The solid content of the negative electrode slurry can refer to the content of the negative electrode composition contained in the negative electrode slurry, and can refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0128] 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 appropriate, minimizing particle aggregation of the negative electrode composition and enabling efficient formation of the negative electrode active material layer. Furthermore, by including the aforementioned specific conductive material in the negative electrode composition, viscosity increases can be suppressed, improving the dispersibility of the negative electrode slurry.

[0129] In one embodiment of this application, the viscosity of the negative electrode slurry may be 1,000 cP or more and 8,000 cP or less.

[0130] In another embodiment, the viscosity of the negative electrode slurry may be in the range of 1,000 cP or more and 8,000 cP or less, preferably 1,500 cP or more and 6,000 cP or less, and more preferably 2,000 cP or more and 4,000 cP or less.

[0131] 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.

[0132] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0133] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0134] 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%.

[0135] 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 an appropriate range.

[0136] 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 separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0137] 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 separation membrane 30 in between.

[0138] 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 membrane interposed between the positive and negative electrodes, 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.

[0139] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, which contains the positive electrode active material.

[0140] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can 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, net, porous material, foam, or nonwoven fabric.

[0141] 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 by 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 also be metallic lithium (Li-metal).

[0142] 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.

[0143] 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.

[0144] Even when the single particle is formed with a small particle size (average particle size (D50) of 1 μm or more and 12 μm or less), it can exhibit excellent particle strength. For example, the single particle can have a strength of 650 kgf / cm². 2 With this force, the particle strength can be increased to 100 MPa to 300 MPa during rolling. This allows the single particle to be rolled to 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increased fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0145] 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 different method than that of the single particle, and its composition may be the same as or different from that of the single particle.

[0146] The method for forming the single particles is not particularly limited, but generally they can be formed by increasing the firing temperature and over-firing. They may also be produced by using additives such as grain growth promoters that aid in over-firing, or by changing the initiating substance.

[0147] For example, the firing is performed at a temperature at which single particles can be formed. In order to form these, firing must be performed at a higher temperature than that used for secondary particle production. For example, if the precursor composition is the same, firing must be performed at a temperature approximately 30°C to 100°C higher than that used for secondary particle production. The firing temperature for single particle formation may vary depending on the metal composition in the precursor. For example, when attempting 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 satisfies 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 secondary particulate form may be produced. If the temperature exceeds 950°C, excessive firing may occur, the layered crystal structure may not be properly formed, and the electrochemical properties may deteriorate.

[0148] 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 a pseudo-single particle form which is an aggregate of 30 or fewer primary particles.

[0149] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or fewer primary particles, and a secondary particle may be an aggregate of several hundred primary particles.

[0150] In one embodiment of this application, the lithium composite transition metal compound, which is the positive electrode active material, further contains secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0151] In the present invention, a single particle may be a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or fewer primary particles, and a secondary particle may be an aggregate of several hundred primary particles.

[0152] The aforementioned lithium-complex transition metal compounds 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 a pseudo-single particle form that is an aggregate of 30 or fewer primary particles.

[0153] 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 is / g, preferably 0.1m 2 / g~1m 2 / g, and more preferably 0.3m 2 / g~0.8m 2 / g is also acceptable.

[0154] In another embodiment of this application, the primary 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.

[0155] 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 too small, the number of aggregated 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 too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially degrading the output characteristics.

[0156] 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 if 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.

[0157] 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.

[0158] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller than the average particle size (D50) of the secondary particles, or it may be 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller.

[0159] 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 within the electrode due to particle fracture, resulting in improved battery life characteristics and energy density.

[0160] 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.

[0161] For example, the single particles may be present in amounts 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 particles may be present in amounts of 100 parts by weight or less per 100 parts by weight of the positive electrode active material.

[0162] When single particles within the aforementioned range are included, they can be combined with the negative electrode material described above 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.

[0163] 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.

[0164] When the above range is satisfied, 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 in the single-particle positive electrode active material described above, or they may be different, and can represent a form in which the single-particle form is aggregated.

[0165] 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.

[0166] 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.

[0167] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. 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.

[0168] 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.

[0169] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Any membrane commonly used as a separation membrane in secondary batteries is generally acceptable, but those with low resistance to electrolyte ion movement while exhibiting excellent electrolyte moisture absorption capacity are particularly preferred. 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, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0170] 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. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0171] 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, gamma-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.

[0172] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used because they are high-viscosity organic solvents with high dielectric constants and readily dissociate lithium salts. When such cyclic carbonates are mixed with low-viscosity, low-dielectric-constant chain carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions, an electrolyte with high electrical conductivity can be produced, and this method is even more preferable.

[0173] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte. For example, the anion of the lithium salt is 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 can use one or more selected from the group consisting of the following.

[0174] In addition to the electrolyte components, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate 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.

[0175] 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-limiting 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]

[0176] Preferred embodiments are presented below to aid in understanding the present invention, but these embodiments are illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept. Such variations and modifications will naturally fall within the scope of the appended claims.

[0177] <Manufacturing example> <Example 1> Manufacturing of negative electrodes After MG-Si silicon ingots were converted into silane gas, a silicon-based active material was formed on a substrate by deposition following a chemical reaction. During this process, the crystal grain size of the silicon-based active material could be controlled by controlling the process conditions (temperature range of 800°C to 1100°C, pressure range of 10 Pa to 150 Pa), resulting in the production of a silicon-based active material with a crystal grain size of 62 nm.

[0178] Subsequently, a negative electrode composition was formed from the silicon-based active material (Si, average particle size (D50): 3.5 μm, crystal grain size 62 nm), the first conductive material, the second conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10, and it was added to distilled water as a solvent for forming a negative electrode slurry to produce a negative electrode slurry.

[0179] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm, thickness to D50 ratio 28%), and the second conductive material is SWCNT (number of layers: 1 ea, average particle size: 1.6 μm, BET 1160 m 2 / g, IG / ID ratio: 143).

[0180] As a specific mixing method, the conductive material, the binder, and water were dispersed at 2500 rpm for 30 min using a homomixer, then the silicon-based active material was added, and then dispersed at 2500 rpm for 30 min to prepare a negative electrode slurry.

[0181] 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 the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity 40.0%).

[0182] <Example 2> In Example 1 above, after the silicon mass of MG-Si was silanized and chemically reacted, a silicon-based active material was formed on the substrate by vapor deposition. At this time, the crystal grain size of the silicon-based active material could be controlled through the control of process conditions (temperature conditions 800 °C to 1100 °C, pressure conditions 10 pa to 150 pa range). As a result, except that a silicon-based active material with a crystal grain size of 30 nm was produced, it was carried out in the same manner as in Example 1.

[0183] <Example 3> In Example 1, after silane gasification of the MG-Si silicon mass, a chemical reaction was carried out, and then a silicon-based active material was formed on the substrate by vapor deposition. In this process, the crystal grain size of the silicon-based active material could be controlled by controlling the process conditions (temperature range of 800°C to 1100°C, pressure range of 10 Pa to 150 Pa), and as a result, a silicon-based active material with a crystal grain size of 90 nm was produced. The process was carried out in the same manner as in Example 1, except that the result was the same as in Example 1.

[0184] <Comparative Example 1> In Example 1, the cooling and gas deposition environments were changed during the production of the MG-Si silicon ingot. Subsequently, physical force was applied to crush it, resulting in the production of a silicon-based active material with a crystal grain size of 212 nm. The negative electrode was then produced in the same manner as in Example 1, except that the silicon-based active material used met the aforementioned crystal grain size requirement.

[0185] <Comparative Example 2> The negative electrode composition was formed in the same manner as in Example 1, except that the silicon-based active material (Si, average particle size (D50): 3.5 μm, crystal grain size 62 nm), point conductive material (carbon black), and polyacrylamide as a binder were arranged in a weight ratio of 80:10:10.

[0186] <Comparative Example 3> The negative electrode composition was formed in the same manner as in Example 1, except that the silicon-based active material (Si, average particle size (D50): 3.5 μm, crystal grain size 62 nm), the first conductive material, and polyacrylamide as a binder were arranged in a weight ratio of 80:10:10.

[0187] <Comparative Example 4> The negative electrode composition was formed in the same manner as in Example 1, except that the silicon-based active material (Si, average particle size (D50): 3.5 μm, crystal grain size 62 nm), the second conductive material, and polyacrylamide as a binder were arranged in a weight ratio of 84:0.5:15.5.

[0188] <Comparative Example 5> In the above-described Example 1, the negative electrode was manufactured in the same manner as in Example 1, except that a point-type conductive material (carbon black) was used instead of the first conductive material as the conductive material.

[0189] <Comparative Example 6> The negative electrode composition was formed in the same manner as in Example 1, except that the silicon-based active material (Si, average particle size (D50): 3.5 μm, crystal grain size 62 nm), point conductive material (carbon black), first conductive material, and polyacrylamide as a binder were arranged in a weight ratio of 80:5:5:10.

[0190] <Manufacturing of secondary batteries> LiNi 0.6 Co 0.2 Mn 0.2 A cathode slurry was prepared by adding 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 in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0191] 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 cathode was fabricated by coating with the specified loading amount, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0192] A lithium secondary battery was fabricated by injecting an electrolyte between the positive electrode and the negative electrode of the above example and comparative example via a polyethylene separation membrane.

[0193] The electrolyte in question was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) 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.

[0194] <Example of experiment> Experimental Example 1: Lifespan Evaluation The lithium 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 4.2-3.2V 1C / 1C, and the capacity retention rate was measured every 50 cycles by charging / discharging at 1C / 1C (4.2-3.2V). The results are shown in Table 1. Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0195] Experimental Example 2: Measurement and Evaluation of Resistance Increase Rate In Experimental Example 1, during testing, the capacitance retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. Then, the resistance was measured by discharging with a 2.5C pulse using SOC50, and the resistance increase rate was compared and analyzed. The results are shown in Table 1 below.

[0196] Experimental Example 3: Volume change due to gas generation using a pouch test. A 1Ah pouch cell containing the negative electrode manufactured in the above examples and comparative examples was fully charged to 4.2V at 0.33C and then stored in a 60°C oven for 8 weeks. After that, it was fully discharged to 2.5V, and the gas generated inside the pouch cell was extracted by GC / MS for quantitative gas analysis. The results are shown in Table 1 below.

[0197] [Table 1]

[0198] As can be seen from the above examples and comparative examples, the negative electrode composition of the present invention uses a silicon-based active material with a specific range of crystalline grains to produce the negative electrode in order to increase energy density. In this case, the negative electrode conductive material uses planar conductive material and linear conductive material to significantly improve the electrical connectivity between silicon-based active materials, and as a result it has been confirmed that the electrical isolation phenomenon that may occur when charging / discharging the negative electrode to which the silicon-based active material is applied is prevented, thereby improving the lifespan of the negative electrode.

[0199] In the case of Comparative Example 1, the crystal grain size was outside the range specified in this application, resulting in a decrease in the strength of the silicon-based active material itself, making it difficult to provide flexibility when incorporated into the electrode. Furthermore, it was confirmed that volume expansion could not be suppressed, leading to a decrease in lifetime performance and an increase in resistance.

[0200] In the case of Comparative Example 2, which contained an excessive amount of point-like conductive material, there was room for improvement in lifespan performance, but it showed a high resistance increase rate, and the high specific surface area caused problems such as increased viscosity of the composition and increased high-temperature gas generation.

[0201] In addition, in Comparative Examples 3 to 6, although the crystal grain size was the same, planar and linear conductive materials were not used as in the present invention. Even in these cases, it was confirmed that electrical connectivity could not be ensured, resulting in reduced lifetime performance and a high rate of resistance increase.

[0202] Among these, Comparative Examples 2, 5, and 6 involved the use of a dot-type conductive material alone, and the use of a combination of dot-type and linear or dot-type and planar conductive materials. It was found that including a dot-type conductive material resulted in higher gas generation at high temperatures compared to the other examples and comparative examples.

[0203] In other words, the anode composition relating to this application is primarily characterized by its ability to construct a system that can be applied together with a high-energy-density silicon-based active material by applying a specific composition and content of anode conductive material as described above. [Explanation of symbols]

[0204] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 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 negative electrode composition comprising a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, The silicon-based active material comprises at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material. The silicon-based active material has a crystal grain size of 30 nm or more and 200 nm or less. The D50 particle size of the silicon-based active material is 3 μm or more and 8 μm or less. The surface area of ​​the silicon-based active material is 0.25 m². ２ / g or more 4.00m ２ / g or less, The negative electrode conductive material is a negative electrode composition comprising a planar conductive material and a linear conductive material.

2. The negative electrode composition according to claim 1, wherein the crystal grain size of the silicon-based active material is 30 nm or more and 150 nm or less.

3. The negative electrode composition according to claim 1, wherein the viscosity of the negative electrode composition is 1,000 cP or more and 6,000 cP or less.

4. The anode composition according to claim 1, wherein the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the anode composition.

5. 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.

6. The negative electrode composition according to claim 1, wherein the negative electrode conductive material comprises 100 parts by weight of the negative electrode conductive material, 90 parts by weight or more and 99.9 parts by weight or less of the planar conductive material, and 0.1 parts by weight or more and 10 parts by weight or less of the linear conductive material.

7. The negative electrode composition according to claim 1, wherein the planar 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 6.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

8. Negative electrode current collector layer; and A negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 7, formed on one or both sides of the negative electrode current collector layer; A negative electrode for lithium secondary batteries, including...

9. 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 8, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

10. Positive electrode; A negative electrode for a lithium secondary battery according to claim 8; A separation membrane provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

Images