Negative electrode active material, negative electrode composition comprising same, negative electrode, and secondary battery

Abstract

The present specification relates to a negative electrode active material, and a negative electrode and a secondary battery comprising the same. According to one exemplary embodiment of the present invention, there is provided a negative electrode active material comprising a silicon-based active material and a coating layer disposed thereon, in which the silicon-based active material comprises a compound selected from the group consisting of pure Si, SiOx (0lt; xlt; 2) and Si / C, and the coating comprises an inorganic flame retardant.

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2024-0114080, filed on August 26, 2024, with the Korean Intellectual Property Office, and Korean Patent Application No. 10-2025-0118041, filed on August 25, 2025, the entire contents of which are incorporated herein by reference.

[0002] This application relates to negative electrode active materials, negative electrode compositions, negative electrodes, secondary batteries, battery modules, and battery packs. Background Technology

[0003] The rapid increase in fossil fuel use has led to a growing demand for alternative and clean energy sources. To address this demand, power generation and storage using electrochemical reactions are among the most active research areas. Currently, secondary batteries are a representative example of electrochemical devices utilizing this electrochemical energy, and their applications are gradually expanding.

[0004] With the technological advancements and increasing demands of mobile devices, the need for rechargeable batteries is also rapidly growing. Among these rechargeable batteries, lithium-ion batteries, exhibiting high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, research is actively underway to develop high-density electrodes with even higher energy density per unit volume for the manufacture of electrodes used in high-capacity lithium-ion batteries.

[0005] Typically, a secondary battery comprises a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode comprises a negative electrode active material capable of intercalating and deintercalating lithium ions from the positive electrode; silicon-based particles with high discharge capacity can be used as the negative electrode active material.

[0006] In particular, to address the recent increase in demand for high-density energy batteries, research is actively underway on methods to increase capacity by using silicon-based compounds, such as Si / C or SiOx, with a capacity more than 10 times that of graphite-based materials, as the negative electrode active material. While silicon-based compounds offer the advantage of greater capacity compared to graphite used in related technologies, their problem lies in their tendency to experience thermal runaway within a single cell under actual operating conditions due to rapid volume expansion during charging.

[0007] Therefore, research is needed to develop secondary batteries that offer improved safety while maintaining high capacity.

[0008] Therefore, research is needed to develop secondary batteries that offer improved safety while maintaining high capacity. Summary of the Invention

[0009] Technical Problem

[0010] The present invention is directed to providing a negative electrode active material, a negative electrode, and a secondary battery, which, while having a high capacity by applying a silicon-based active material, provide improved safety under operating conditions.

[0011] Technical Solution

[0012] According to an exemplary embodiment of the present invention, there is provided a negative electrode active material including: a silicon-based active material; and a coating provided on the silicon-based active material, wherein the silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, and the coating includes an inorganic flame retardant.

[0013] Another exemplary embodiment of the present invention provides a negative electrode composition including: a negative electrode active material according to an exemplary embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material.

[0014] Another exemplary embodiment of the present invention provides a negative electrode including: a negative electrode current collector layer; and a negative electrode active material layer formed on one surface or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer includes a negative electrode composition according to an exemplary embodiment of the present invention.

[0015] Another exemplary embodiment of the present invention provides a secondary battery including a negative electrode according to an exemplary embodiment of the present invention.

[0016] Another exemplary embodiment of the present invention provides a battery module including a secondary battery according to an exemplary embodiment of the present invention.

[0017] Another exemplary embodiment of the present invention provides a battery pack including a secondary battery or a battery module according to an exemplary embodiment of the present invention.

[0018] Advantageous Effects

[0019] When the negative electrode active material according to an exemplary embodiment of the present invention is applied to a negative electrode, it is possible to improve the life characteristics while maintaining a high capacity.

[0020] When the negative electrode active material according to an exemplary embodiment of the present invention is applied to a negative electrode, it is possible to suppress ignition at high temperatures without degrading performance, thereby improving thermal safety. Detailed Description

[0021] Before describing the present invention, some terms will be defined.

[0022] As used herein, when a component is described as "comprising," "including," or "having" a constituent element, unless otherwise specifically described, this does not mean that other constituent elements are excluded, but rather that other constituent elements may be included.

[0023] As used in this article, "p to q" refers to the range above p and below q.

[0024] As used herein, "specific surface area" is measured by the BET method, specifically using the BELSORP-mini II, commercially available from BEL Japan, Inc., calculated from the amount of nitrogen adsorbed at liquid nitrogen temperature (77 K). That is, in this specification, BET specific surface area can refer to the specific surface area measured by the above-described method. BET specific surface area can be measured using nitrogen (N2) according to DIN 66131.

[0025] As used herein, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative number distribution of particles based on particle size. That is, D50 is the particle size (center particle size) at the 50% point of the cumulative number distribution of particles based on particle size, D90 is the particle size at the 90% point of the cumulative number distribution of particles based on particle size, and D10 is the particle size at the 10% point of the cumulative number distribution of particles based on particle size. Alternatively, the center particle size can be measured using laser diffraction. Specifically, after dispersing the powder to be tested in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500), where the difference in diffraction pattern based on particle size is measured as the laser beam passes through the particles, and then the particle size distribution is calculated.

[0026] In one exemplary embodiment of the present invention, particle size or particle diameter may refer to the average or representative diameter of the individual particles constituting the metal powder.

[0027] As used herein, describing a polymer as "containing a monomer as a monomeric unit" means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. As used herein, when describing a polymer as containing a monomer, this is interpreted in the same way as when the polymer contains a monomer as a monomeric unit.

[0028] As used herein, unless specified as a homopolymer, the term “polymer” should be interpreted broadly to include copolymers.

[0029] As used herein, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) while using monodisperse polystyrene polymers (standard samples) with different degrees of polymerization commercially available for measuring molecular weights as standard materials. As used herein, unless otherwise specifically described, the molecular weight refers to the weight-average molecular weight.

[0030] Hereinafter, exemplary embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0031] A lithium secondary battery may generate self-heating inside the battery due to an external impact or abnormal single-cell behavior. If the internal temperature of a single cell rises due to self-heating, thermal runaway may occur. In addition, the heat generated inside the single cell may be transferred to adjacent single cells, leading to the spread of thermal runaway throughout the battery.

[0032] In particular, for a negative electrode containing a silicon-based negative electrode active material, thermal runaway is more problematic. The silicon-based negative electrode provides a high energy density but has poor thermal stability, making it more susceptible to single-cell thermal runaway.

[0033] Therefore, in order to prevent the thermal runaway problem of the battery, various methods have been discussed, such as forming a separate coating on the separator on the basis of a polymer substrate, or attaching a sheet to the outside of a battery cell to prevent heat transfer between single cells. However, it has been confirmed that it is difficult to effectively suppress the thermal runaway phenomenon because these methods cannot suppress abnormal heat generation in the electrode unit.

[0034] The present inventors have conceived that by providing a silicon-based active material surface-treated with an inorganic flame retardant as a negative electrode active material, it is possible to obtain the advantages of an electrode using a high-capacity silicon-based negative electrode active material while suppressing the temperature rise from the inside of the negative electrode, thereby delaying the situation where the internal temperature of the battery rises above a certain level.

[0035] Negative electrode active materials

[0036] According to an exemplary embodiment of the present invention, there is provided a negative electrode active material including: a silicon-based active material; and a coating provided on the silicon-based active material, wherein the silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, and the coating includes an inorganic flame retardant.

[0037] According to an exemplary embodiment of the present invention, there is provided a negative electrode active material, the negative electrode active material comprising: a silicon-based active material; and a coating provided on at least one surface of the silicon-based active material, wherein the silicon-based active material comprises one or more selected from the group consisting of Si, SiO x (0 < x < 2) and Si / C, and the coating comprises an inorganic flame retardant.

[0038] According to an exemplary embodiment of the present invention, the negative electrode active material has a structure comprising a core and a coating on the surface of the core, the core comprising a silicon-based active material, the coating comprising an inorganic flame retardant. That is, the coating is provided on at least a part of the surface of the silicon-based negative electrode active material.

[0039] According to an exemplary embodiment of the present invention, the coating is provided on the surface of the silicon-based active material.

[0040] The negative electrode active material according to the present invention is characterized in that the inorganic flame retardant is directly coated on the surface of the silicon-based active material, and thus has the advantage of being able to suppress heat generated due to abnormal conditions under battery operating conditions from the surface of the negative electrode active material. For example, compared with the form in which the inorganic flame retardant is uniformly dispersed in the negative electrode active material layer, the negative electrode active material according to the present invention has the advantages of being able to more effectively suppress heat generated on the surface of the negative electrode active material and minimizing the amount of the flame retardant applied to the negative electrode. That is, when the negative electrode active material according to an exemplary embodiment of the present invention is applied to the negative electrode, the advantage is that by applying only a small amount of the flame retardant, heat generation inside the single cell can be effectively suppressed, and as the amount of the flame retardant decreases, the content of the active material can be further increased.

[0041] The negative electrode active material according to an exemplary embodiment of the present invention comprises an inorganic flame retardant that undergoes an endothermic reaction at 100°C to 250°C. For example, the endothermic reaction may occur at 100°C or higher, 150°C or higher, or 180°C or higher.

[0042] The inorganic flame retardant selectively undergoes an endothermic reaction only when the temperature inside the battery abnormally rises due to abnormal heat generation inside the battery, thereby delaying heat generation. That is, since the inorganic flame retardant does not react at the normal operating temperature of the battery, heat generation inside the battery can be effectively suppressed, but the battery performance is not reduced by the flame retardant under normal operating conditions.

[0043] According to an exemplary embodiment of the present invention, the endothermic reaction is a dehydration reaction. The inorganic flame retardant undergoes an endothermic reaction accompanied by dehydration at a specific temperature, and thus is characterized in that in addition to suppressing heat through the endothermic reaction, an additional cooling effect can be obtained through the latent heat of the water generated by the dehydration reaction.

[0044] According to an exemplary embodiment of the present invention, the inorganic flame retardant comprises one or more selected from the group consisting of aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), antimony trioxide (Sb2O3), and zinc borate.

[0045] According to an exemplary embodiment of the present invention, the inorganic flame retardant is aluminum hydroxide (Al(OH)3) or magnesium hydroxide (Mg(OH)2), preferably aluminum hydroxide (Al(OH)3). Aluminum hydroxide is characterized by its ability to absorb a large amount of heat energy during the reaction, its low price, and its non-toxic nature, even when used in batteries, will not harm the user.

[0046] According to an exemplary embodiment of the present invention, the average particle size (D50) of the inorganic flame retardant can be from 0.05 μm to 1.5 μm. For example, the average particle size (D50) of the inorganic flame retardant can be 0.05 μm or more, 0.08 μm or more, 0.1 μm or more, 0.5 μm or more, or 0.6 μm or more, and can be less than 1.5 μm, less than 1.2 μm, less than 1 μm, less than 900 nm, or less than 800 nm. When the average particle size of the inorganic flame retardant falls within the specified range, a coating can be uniformly formed on the surface of the active material.

[0047] The average particle size of the inorganic flame retardant refers to the volume average particle size (sphere equivalent particle size) obtained by converting each inorganic flame retardant particle into a sphere with the same volume, and this value can be obtained by observation with an electron microscope. That is, by observing the inorganic flame retardant with an electron microscope, measuring the diameter of more than 200 inorganic flame retardant particles in a given field of view, calculating the sphere equivalent particle size of each particle, and determining their average value to obtain this value.

[0048] According to an exemplary embodiment of the present invention, the average thickness of the coating can be from 0.02 μm to 10 μm. For example, the average thickness of the coating can be greater than 0.02 μm, greater than 0.05 μm, greater than 0.08 μm, greater than 0.1 μm, greater than 0.2 μm, greater than 0.5 μm, greater than 0.8 μm, greater than 1 μm, or greater than 1.5 μm, and can be less than 10 μm, less than 8 μm, less than 6 μm, less than 4 μm, or less than 3 μm. When the average thickness of the coating is within the specified range, the heat resistance of the negative electrode active material can be improved without affecting the behavior of lithium ions under operating conditions. Furthermore, if the thickness of the coating exceeds the upper limit, the overall size of the negative electrode active material may become too large, making it difficult to uniformly distribute the negative electrode active material within the negative electrode active material layer.

[0049] According to an exemplary embodiment of the present invention, with respect to 100 parts by weight of the coating, the content of the inorganic flame retardant may be 95 parts by weight or more. For example, with respect to 100 parts by weight of the coating, the content of the inorganic flame retardant may be 95 parts by weight or more, 96 parts by weight or more, 97 parts by weight or more, or 98 parts by weight or more, and may be 100 parts by weight or less, 99.5 parts by weight or less, or 99 parts by weight or less. When the content of the inorganic flame retardant is within the specified range, the heat resistance can be improved without reducing the conductivity of the negative electrode active material.

[0050] According to an exemplary embodiment of the present invention, with respect to 100 parts by weight of the negative electrode active material, the content of the inorganic flame retardant may be 0.1 to 20 parts by weight. For example, with respect to 100 parts by weight of the negative electrode active material, the content of the inorganic flame retardant may be 0.1 part by weight or more, 0.5 part by weight or more, or 1 part by weight or more, and may be 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. That is, the content of the inorganic flame retardant may be 1 to 20 parts by weight or 1 to 10 parts by weight. When the content of the inorganic flame retardant is within the specified range, the heat resistance can be improved without reducing the conductivity of the negative electrode active material.

[0051] According to an exemplary embodiment of the present invention, the negative electrode active material contains one or more selected from the group consisting of Si, SiO x (0 < x < 2) and Si / C as the silicon-based active material.

[0052] In an exemplary embodiment of the present invention, the negative electrode active material contains one or more selected from the group consisting of Si and SiO x (0 < x < 2) as the silicon-based active material.

[0053] In an exemplary embodiment of the present invention, the silicon-based active material is Si.

[0054] According to an exemplary embodiment of the present invention, the negative electrode active material contains one or more selected from the group consisting of Si, SiO x (0 < x < 2) and Si / C as the silicon-based active material, the silicon-based active material contains Si, and with respect to 100 parts by weight of the silicon-based active material, the content of Si is 70 to 100 parts by weight.

[0055] In another exemplary embodiment, the Si content relative to 100 parts by weight of the silicon-based active material is 70 parts by weight or more, 75 parts by weight or more, 80 parts by weight or more, 85 parts by weight or more, or 90 parts by weight or more. The Si content relative to 100 parts by weight of the silicon-based active material can be less than 100 parts by weight, less than 100 parts by weight, less than 99.9 parts by weight, less than 99 parts by weight, or less than 95 parts by weight.

[0056] That is, in an exemplary embodiment of the present invention, the negative electrode active material contains Si as a silicon-based active material, and contains more than 70 parts by weight of Si relative to 100 parts by weight of the silicon-based active material.

[0057] According to an exemplary embodiment of the present invention, the silicon-based active material may contain Si, and the content of Si may be 100 parts by weight relative to 100 parts by weight of the silicon-based active material.

[0058] In this specification, Si refers to pure silicon (Si) particles, i.e., pure Si. For example, using pure silicon (Si) particles as a silicon-based active material may mean, as described above, pure Si particles (SiO2) that are not bonded to other particles or elements relative to 100 parts by weight of the total negative electrode active material. x (x=0) is included in the specified range.

[0059] In one exemplary embodiment of the present invention, the silicon-based active material may be formed from silicon-based particles having 100 parts by weight of pure Si relative to 100 parts by weight of the negative electrode active material.

[0060] In one exemplary embodiment of the present invention, the silicon-based active material may contain metallic impurities. In this case, the impurities are metals that are typically present in the silicon-based active material, specifically, the content of which may be less than 0.1 parts by weight relative to 100 parts by weight of the negative electrode active material.

[0061] That is, in an exemplary embodiment of the present invention, the silicon-based active material is different from the Si alloy, and the capacity and structural stability of the silicon-based active material according to an exemplary embodiment of the present invention are higher than those of the silicon-based active material with Si alloy as the main material.

[0062] In another exemplary embodiment, the silicon-based active material comprises SiO2. x (0 <x<2)。

[0063] In SiO xIn the case where [SiO₂ (x = 2)] does not react with lithium ions and cannot store lithium, it is therefore preferred that x be within the range (0 < x < 2). Specifically, in terms of the structural stability of the active material, x can be 0.5 ≤ x ≤ 1.5.

[0064] The [SiO] x (0 < x < 2) may further contain a metal distributed on the surface, inside, or both the surface and inside of the [SiO] x (0 < x < 2) particles. The metal is distributed on the surface and / or inside of the silicon-based active material and may be included in the silicon-based active material in order to reduce the proportion of irreversible phases (e.g., SiO₂) in the silicon-based active material and improve the efficiency of the active material.

[0065] The metal may be at least one selected from the group consisting of Li, Mg, and Al, at least one selected from the group consisting of Li and Mg, or Mg because Mg can effectively achieve the effect of preventing the silicon-based oxide particles from being destroyed and has a low reactivity with moisture, thereby further improving the life characteristics of the negative electrode active material.

[0066] The content of the metal in the silicon-based active material may be 0.1 wt% to 25 wt% or 3 wt% to 15 wt%, which is preferred because it can improve the efficiency of the active material without reducing the capacity.

[0067] In an exemplary embodiment of the present invention, the average particle size (D50) of the silicon-based active material may be 1 μm or more. In addition, the average particle size of the silicon-based active material may be 15 μm or less. For example, the average particle size (D50) of the silicon-based active material may be 1 μm or more, greater than 1 μm, 2 μm or more, 3 μm or more, or 4 μm or more, and may be 15 μm or less, less than 15 μm, 14 μm or less, 13 μm or less, 10 μm or less, or 8 μm or less.

[0068] In an exemplary embodiment of the present invention, the coating is formed on the surface of the silicon-based active material. That is, in an exemplary embodiment of the present invention, when the total area of the silicon-based active material is 100%, the area of the coating is 50% or more. For example, the area of the coating may be 50% or more, 60% or more, 70% or more, or 80% or more, and may be 100% or less, less than 100%, 99% or less, 95% or less, or 90% or less.

[0069] In an exemplary embodiment of the present invention, when the average particle size (D50) of the silicon-based active material is represented as A and the average particle size (D50) of the inorganic flame retardant is represented as B, the following formula 1 is satisfied.

[0070] [Formula 1]

[0071] 3 ≤ A / B ≤ 25

[0072] In one exemplary embodiment of the present invention, Formula 1 is 3 to 25. For example, Formula 1 can be 3 or more, 4 or more, 5 or more, 6 or more, or 7 or more, and can be 25 or less, 20 or less, or 15 or less. When Formula 1 falls within the specified range, the dimensions between the silicon-based active material and the inorganic flame retardant are appropriately controlled, enabling the formation of a uniform and thin inorganic flame retardant coating on the silicon-based active material.

[0073] In Formula 1, the ranges of A and B can be based on the average particle size (D50) of the silicon-based active material and the average particle size (D50) of the inorganic flame retardant.

[0074] In one exemplary embodiment of the present invention, the grain size of the silicon-based active material can be below 600 nm.

[0075] In another exemplary embodiment, the grain size of the silicon-based active material can be less than 600 nm, less than 500 nm, less than 400 nm, less than 300 nm, less than 200 nm, less than 130 nm, less than 110 nm, less than 100 nm, less than 95 nm, or less than 91 nm. The grain size of the aforementioned silicon-based active material can be in the range of more than 10 nm or more than 15 nm.

[0076] The silicon-based active material has the aforementioned grain size, and this grain size can be controlled by changing the process conditions in the manufacturing process. In this case, when the specified range is met, grain boundaries are widely distributed, thereby allowing lithium ions to be uniformly inserted during lithium-ion intercalation, reducing the stress applied during lithium-ion intercalation into silicon particles, and thus mitigating particle breakage. As a result, characteristics that improve the lifetime stability of the anode are obtained. If the grain size exceeds the specified range, the grain boundary distribution within the particles is narrow. In this case, lithium ions are not uniformly intercalated into the particles, resulting in high stress during ion intercalation and thus particle breakage.

[0077] In an exemplary embodiment of the present invention, the silicon-based active material may comprise a crystal structure having a grain distribution of more than 1 nm and less than 600 nm, and the area ratio of the crystal structure to the total area of ​​the silicon-based active material may be less than 5%.

[0078] In another exemplary embodiment, the area ratio of the crystal structure to the total area of ​​the silicon-based active material can be less than 5% or less than 3%, and can be more than 0.1%.

[0079] That is, the silicon-based active material according to an exemplary embodiment of the present invention has a grain size of less than 600 nm, which results in small sizes of the formed crystal structures and satisfies the area ratio. Therefore, the grain boundary distribution can be widened, and thus the above-mentioned effects can be exhibited.

[0080] The silicon-based active material according to an exemplary embodiment of the present invention has a grain size of less than 200 nm, resulting in small sizes of the formed crystal structures and satisfying the area ratio. Therefore, the grain boundary distribution can be widened, and thus the aforementioned effects can be exhibited.

[0081] In one exemplary embodiment of the present invention, the silicon-based active material may contain more than 20 crystal structures.

[0082] In another exemplary embodiment, the number of crystal structures contained in the silicon-based active material may fall within the range of more than 20, more than 30 or more than 35, and less than 60 or less than 50.

[0083] That is, as described above, when the grain size of the silicon-based active material falls within a specified range and the number of crystal structures falls within a specified range, the strength of the silicon-based active material itself is within an appropriate range. Therefore, when such a silicon-based active material is included in an electrode, it can impart flexibility and effectively suppress volume expansion.

[0084] In this invention, a grain refers to a crystalline particle in a metal or material, which is a collection of microscopically irregular shapes, and the grain size can refer to the diameter of the observed grain particles. That is, in this invention, the grain size refers to the size of crystal domains within a particle that have the same crystal orientation, and is a concept different from grain size or particle diameter, which represent the size of a material.

[0085] In one exemplary embodiment of the invention, the grain size can be calculated as a full width at half maximum (FWHM) value by XRD analysis. Except for L, the other values ​​can be measured by XRD analysis of the silicon-based active material, and the grain size can be determined by the Debye-Scherrer equation, which indicates that FWHM is inversely proportional to the grain size. The Debye-Scherrer equation is shown in Equation 1-1 below.

[0086] [Equation 1-1]

[0087] FWHM=Kλ / Lcosθ

[0088] In Equation 1-1, L is the grain size, K is a constant, θ is the Bragg angle, and λ is the X-ray wavelength.

[0089] Furthermore, the shapes of grains are diverse and can be measured in three dimensions. Typically, the size of grains can be measured using commonly used methods for measuring circularity or diameter, but is not limited to these.

[0090] In diameter measurement methods, grain size can be measured by drawing 5 to 10 parallel lines of length L mm on a photomicrograph of the target particle, counting the number of grains z on each line, and taking the average value. In this case, only all grains contained within the lines are counted, excluding some grains located (crossing) the lines. When the number of lines is represented by P and the magnification is represented by V, the average grain size can be calculated according to the following formula 1-2.

[0091] [Equation 1-2]

[0092] Dm = (L P 10 3 ) / (zV) (μm)

[0093] Furthermore, the circular method involves drawing a circle with a predetermined diameter on a photomicrograph of the target particle, and then calculating the average area of ​​the grains by the number of grains in the circle and the number of grains crossing the boundary line. The average area can be calculated using the following formulas 1-3.

[0094] [Equation 1-3]

[0095] Fm = (Fk 10 6 ) / ((0.67n + z)V 2 ) (μm 2 )

[0096] In Equations 1-3, Fm is the average grain area, Fk is the measured area on the photograph, z is the number of grains inside the circle, n is the number of grains spanning the arc, and V is the magnification of the microscope.

[0097] In one exemplary embodiment of the present invention, the specific surface area of ​​the negative electrode active material comprising the silicon-based active material and the inorganic flame retardant coating disposed on the silicon-based active material can be 0.5 m². 2 / g to 5 m 2 / g.

[0098] In another exemplary embodiment, the specific surface area of ​​the negative electrode active material can be 0.5 m². 2 / g or more, 1 m 2 / g or more, 1.25 m2 / g or more, 1.5 m 2 / g or more or 2 m 2 / g or more. The specific surface area of ​​the silicon-based active material can be 5 m². 2 / g or less, 5.5 m 2 / g or less or 4.5 m 2 / g or less. Specific surface area can be measured according to DIN 66131 (using nitrogen).

[0099] The negative electrode active material has the aforementioned specific surface area, and the size of the specific surface area of ​​the silicon-based active material can be controlled by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material. That is, when the silicon-based active material is manufactured using the manufacturing method according to this application, the negative electrode active material has a larger specific surface area due to its surface roughness compared to particles of the same particle size. In this case, by satisfying the specified range, the adhesion strength with the binder is increased, thereby mitigating electrode cracking caused by repeated charge-discharge cycles.

[0100] Furthermore, during lithium-ion intercalation, lithium ions can be uniformly intercalated, thereby reducing the stress applied during lithium-ion intercalation into silicon particles and thus reducing particle breakage. As a result, properties that improve the lifetime stability of the negative electrode are obtained. If the surface area is less than a specified range, even at the same particle size, the formed surface is smooth, leading to reduced adhesion strength to the binder and electrode cracking. In this case, lithium ions are not uniformly intercalated into the particles, resulting in increased stress and particle breakage due to ion intercalation.

[0101] In one exemplary embodiment of the present invention, the negative electrode active material satisfies the range of the following formula 2-1.

[0102] [Equation 2-1]

[0103] X1 / Y1≤0.960

[0104] In Equation 2-1, X1 refers to the actual area of ​​the negative electrode active material, and Y1 refers to the area of ​​a spherical particle with the same perimeter as the negative electrode active material.

[0105] The measurement of Equation 2-1 can be performed using a particle shape analyzer. Specifically, the negative electrode active material according to an exemplary embodiment of the present invention can be dispersed on a glass plate by air jetting, and then the shape of 10,000 negative electrode active material particles in a photograph obtained by capturing a shadow image of the dispersed particles can be measured. In this case, Equation 2-1 represents the value of averaging 10,000 particles. Equation 2-1 according to the present invention can be measured from this image, and Equation 2-1 can be expressed as the sphericity (roundness) of the negative electrode active material. Sphericity can also be calculated by [4π × actual area of ​​the negative electrode active material / (perimeter)]. 2 ]express.

[0106] In one exemplary embodiment of the present invention, the sphericity of the negative electrode active material may be, for example, 0.960 or less or 0.957 or less. The sphericity of the negative electrode active material may be 0.8 or more, 0.9 or more, 0.93 or more, 0.94 or more, or 0.941 or more.

[0107] In one exemplary embodiment of the present invention, the negative electrode active material satisfies the range of the following formula 2-2.

[0108] [Equation 2-2]

[0109] X² / Y²≤0.996

[0110] In Equation 2-2, Y2 refers to the actual perimeter of the negative electrode active material, and X2 refers to the perimeter of the circumscribed pattern of the negative electrode active material.

[0111] The measurement of Equation 2-2 can be performed using a particle shape analyzer. Specifically, the negative electrode active material according to an exemplary embodiment of the present invention can be dispersed on a glass plate by air jetting, and then the shape of 10,000 negative electrode active material particles in a photograph obtained by taking a shadow image of the dispersed particles can be measured. In this case, Equation 2-2 represents the value of averaging 10,000 particles. Equation 2-2 according to the present invention can be measured from this image, and Equation 2-2 can be expressed as the convexity of the negative electrode active material.

[0112] In one exemplary embodiment of the present invention, the range of X2 / Y2 ≤ 0.996 or X2 / Y2 ≤ 0.995 can be satisfied, and the range of 0.8 ≤ X2 / Y2, 0.9 ≤ X2 / Y2, 0.95 ≤ X2 / Y2 or 0.98 ≤ X2 / Y2 can also be satisfied.

[0113] The smaller the value of Equation 2-1 or Equation 2-2, the greater the roughness of the negative electrode active material. By using a negative electrode active material that meets the specified range, the adhesion strength with the adhesive is increased, thereby mitigating electrode cracking caused by repeated charge-discharge cycles.

[0114] In one exemplary embodiment of the present invention, the particle size distribution of the negative electrode active material is greater than 0.01 μm and less than 30 μm.

[0115] The fact that the negative electrode active material contains negative electrode active material particles with a particle size distribution of 0.01 μm or more and 30 μm or less means that the negative electrode active material contains multiple individual negative electrode active material particles with a particle size within a specified range, and in this case, the number of negative electrode active material particles contained is not limited.

[0116] When the particle is spherical, the particle size can be represented by its diameter. Even if the particle has a non-spherical shape, the particle size can be measured by comparing it to the spherical case. Typically, the particle size of an individual particle can be measured using methods commonly employed in the art.

[0117] negative electrode composition

[0118] An exemplary embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to an exemplary embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material.

[0119] An exemplary embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to an exemplary embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material, and further comprising a carbon-based active material as a second negative electrode active material.

[0120] That is, an exemplary embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to an exemplary embodiment of the present invention as a first negative electrode active material; a carbon-based active material as a second negative electrode active material; a negative electrode binder; and a negative electrode conductive material.

[0121] In one exemplary embodiment of the present invention, the carbon-based active material may comprise one or more selected from the group consisting of natural graphite and artificial graphite. Specifically, the carbon-based active material may be natural graphite, artificial graphite, or a mixture of natural and artificial graphite.

[0122] The negative electrode composition according to an exemplary embodiment of the present invention further includes a carbon-based active material as a second negative electrode active material in addition to the negative electrode active material according to an exemplary embodiment of the present invention. This allows the high capacity advantage of the first negative electrode active material to be utilized, while improving the volume expansion problem caused by the silicon-based active material, and exhibiting high safety and excellent output caused by the second active material.

[0123] Artificial graphite is typically manufactured by carbonizing raw materials such as coal tar, coal tar pitch, or petroleum-based heavy oil at temperatures above 2500°C. After graphitization, the particle size of the artificial graphite is adjusted, such as through crushing and secondary particle formation, before it is used as a negative electrode active material. In the case of artificial graphite, crystals are randomly distributed within the particles, with a lower sphericity than natural graphite and slightly pointed shapes.

[0124] Furthermore, the particle size of artificial graphite can be 5 to 30 μm, preferably 10 to 25 μm.

[0125] Natural graphite is typically in the form of plate-like aggregates before processing, and these plate-like particles are processed into spherical forms with smooth surfaces through post-processing techniques such as particle crushing and reassembly, for use as active materials in the manufacture of electrodes.

[0126] In addition, the particle size of natural graphite can be 5 to 30 μm or 10 to 25 μm.

[0127] When the carbon-based active material is a mixture of artificial graphite and natural graphite, the weight ratio of artificial graphite to natural graphite can be from 9.99:0.01 to 0.01:9.99 or from 9.7:0.3 to 7:3. When this weight ratio range is met, excellent output can be exhibited.

[0128] In one exemplary embodiment of the present invention, the content of the first negative electrode active material may be 1 to 20 parts by weight relative to a total of 100 parts by weight of the first negative electrode active material and the second negative electrode active material. A total of 100 parts by weight of the first negative electrode active material and the second negative electrode active material means that the sum of the first negative electrode active material and the second negative electrode active material is 100 parts by weight. For example, relative to a total of 100 parts by weight of the first negative electrode active material and the second negative electrode active material, the content of the first negative electrode active material may be 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more, and may be 20 parts by weight or less or 18 parts by weight or less.

[0129] In one exemplary embodiment of the present invention, the content of the second negative electrode active material may be from 80 parts by weight to 99 parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material. 100 parts by weight of the first negative electrode active material and the second negative electrode active material refers to the sum of the first negative electrode active material and the second negative electrode active material. For example, relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material, the content of the second negative electrode active material may be 80 parts by weight or more, 83 parts by weight or more, or 85 parts by weight or more, and may be 99 parts by weight or less, 95 parts by weight or less, or 90 parts by weight or less.

[0130] In a negative electrode composition according to an exemplary embodiment of the present invention, the negative electrode adhesive and the negative electrode conductive material are as follows.

[0131] According to an exemplary embodiment of the present invention, the negative electrode composition is provided, wherein the negative electrode composition comprises 60 or more parts by weight of the negative electrode active material relative to 100 parts by weight of the negative electrode composition.

[0132] In another exemplary embodiment, the content of the negative electrode active material relative to 100 parts by weight of the negative electrode composition may be 60 parts by weight or more, 65 parts by weight or more, or 70 parts by weight or more, and may be 97 parts by weight or less, 95 parts by weight or less, or 90 parts by weight or less.

[0133] In one exemplary embodiment of the present invention, the conductive material may comprise one or more selected from the group consisting of point-like conductive materials, planar conductive materials, and linear conductive materials.

[0134] In one exemplary embodiment of the present invention, the dot-shaped conductive material refers to a spherical or dot-shaped conductive material that can be used to improve the conductivity of the negative electrode and has conductivity without causing chemical changes. Specifically, the dot-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 cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black for high conductivity and excellent dispersibility.

[0135] In one exemplary embodiment of the present invention, the BET specific surface area of ​​the dot-shaped conductive material can be 40m². 2 / g or more and 70 m 2 / g or less, 45 m 2 / g or more and 65 m 2 / g or less or 50 m 2 / g or more and 60 m 2 / g or less.

[0136] In one exemplary embodiment of the present invention, the content of functional groups (volatiles) of the dot-shaped conductive material may fall within the range of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0137] In particular, when the content of functional groups in the dot-shaped conductive material falls within a specified range, the functional groups exist on the surface of the dot-shaped conductive material, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent.

[0138] In one exemplary embodiment of the present invention, the conductive material may comprise a planar conductive material.

[0139] The planar conductive material can be used to improve conductivity by increasing the surface contact between silicon particles in the negative electrode, while suppressing the breakage of the conductive path due to volume expansion, and can be represented as a plate-shaped conductive material or a block-shaped conductive material.

[0140] In one exemplary embodiment of the present invention, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide and graphite flakes, preferably plate graphite.

[0141] In one exemplary embodiment of the present invention, the average particle size (D50) of the planar conductive material can be from 2 μm to 7 μm, specifically from 3 μm to 6 μm, and more specifically from 4 μm to 5 μm. When the specified range is met, sufficient particle size results in easy dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, the dispersion effect is excellent when the same equipment and time are used for dispersion.

[0142] In one exemplary embodiment of the present invention, the planar conductive material can 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.

[0143] In one exemplary embodiment of the present invention, the planar conductive material can be used without limitation either a high specific surface area planar conductive material or a low specific surface area planar conductive material. However, in particular, the planar conductive material according to one exemplary embodiment of the present invention may be affected to some extent by the dispersion effect in terms of electrode performance, thus a low specific surface area planar conductive material that does not cause dispersion problems is particularly preferred.

[0144] In one exemplary embodiment of the present invention, the BET specific surface area of ​​the planar conductive material can be 5m². 2 / g or more.

[0145] In another exemplary embodiment, the BET specific surface area of ​​the planar conductive material can be 5 m². 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0146] In another exemplary embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area can fall within 50 m². 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 Within the range of / g and below.

[0147] In another exemplary embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area can fall within 5 m². 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, preferably 5 m 2 / g or more and 25 m 2 Within the range of / g and below.

[0148] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may comprise multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" herein refers to a secondary shape resembling a bundle or rope, wherein multiple carbon nanotube units are arranged side-by-side or intertwined with substantially the same orientation along their longitudinal axes. The carbon nanotube units have cylindrical graphite sheets with diameters on the nanometer scale and exhibit sp... 2 Bonded structure. In this case, depending on the curl angle and structure of the graphite sheet, it can exhibit the properties of a conductive or semiconductor material. Compared to wound carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during the fabrication of the negative electrode and can more smoothly form a conductive network in the negative electrode, thereby improving the conductivity of the negative electrode.

[0149] In one exemplary embodiment of the present invention, the linear conductive material may comprise SWCNT or MWCNT.

[0150] In one exemplary embodiment of the present invention, the negative electrode composition is provided, wherein the amount of the negative electrode conductive material present is 0.01 parts by weight or more and 20 parts by weight or less relative to 100 parts by weight of the negative electrode composition. For example, the content of the negative electrode conductive material may be 0.01 parts by weight or more, 0.1 parts by weight or more, or 0.5 parts by weight or more relative to 100 parts by weight of the negative electrode composition, and may be 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less.

[0151] The composition of the negative electrode conductive material according to an exemplary embodiment of the present invention is completely different from that of the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material according to an exemplary embodiment of the present invention is used to maintain the contact between silicon-based active materials that undergo significant electrode volume expansion due to charging and discharging, while the positive electrode conductive material is used to provide a certain conductivity while acting as a buffer during rolling. In terms of structure and function, it is completely different from the negative electrode conductive material of the present invention.

[0152] Furthermore, the negative electrode conductive material according to an exemplary embodiment of the present invention is applied to a silicon-based active material, and its composition is completely different from that of the conductive material applied to a negative electrode composition containing only graphite-based active material. That is, the conductive material used in a negative electrode composition containing only graphite-based active material has only smaller particles compared to the active material, and therefore has the characteristics of enhancing output characteristics and imparting partial conductivity. Its composition and function are completely different from the negative electrode conductive material applied together with silicon-based active material in the present invention.

[0153] In one exemplary embodiment of the present invention, the negative electrode adhesive may comprise at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polyacrylamide (PAM), and materials wherein hydrogen is replaced by Li, Na, Ca, etc., and may also comprise various copolymers thereof.

[0154] According to an exemplary embodiment of the present invention, a negative electrode adhesive is used to retain the active and conductive materials to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and mitigation of the silicon-based active material. When the above-described effect is achieved, all common adhesives can be applied; specifically, aqueous adhesives can be used, and more specifically, PAM-based adhesives as single-component aqueous adhesives can be used.

[0155] In one exemplary embodiment of the present invention, a negative electrode slurry is provided, wherein the negative electrode binder comprises an aqueous binder, and the content of the negative electrode binder is 5 parts by weight or more and 12 parts by weight or less relative to 100 parts by weight of the negative electrode composition.

[0156] In another exemplary embodiment, the content of the negative electrode binder may be 5 or more but less than 12 parts by weight, 7 or more but less than 11 parts by weight, or 8 or more but less than 11 parts by weight relative to 100 parts by weight of the negative electrode composition.

[0157] In a lithium secondary battery negative electrode according to an exemplary embodiment of the present invention, the silicon-based active material is used in the above-mentioned weight proportions to maximize capacity characteristics. Compared with the case of related technologies using carbon-based active materials as the main active material, the volume expansion during charge and discharge becomes larger. Therefore, the negative electrode contains the above-mentioned negative electrode binder, thus having the characteristic of effectively controlling the volume expansion caused by the charge and discharge of the high-rigidity silicon-based active material.

[0158] negative electrode

[0159] According to an exemplary embodiment of the present invention, a negative electrode is provided, the negative electrode comprising a negative electrode current collector layer and a negative electrode active material layer comprising the negative electrode active material formed on one or both surfaces of the negative electrode current collector layer.

[0160] In one exemplary embodiment of the present invention, the negative electrode for the secondary battery can be formed by applying the negative electrode slurry to one or both surfaces of the negative electrode current collector layer and drying it.

[0161] In one exemplary embodiment of the present invention, the solid content of the negative electrode slurry can be in the range of 5% or more and 55% or less.

[0162] In another exemplary embodiment, the solid content of the negative electrode slurry may fall within the range of 5% or more and 55% or less, 7% or more and 35% or less, or 10% or more and 30% or less.

[0163] The solid content of a negative electrode slurry can refer to the content of negative electrode active materials, conductive materials and binders other than solvents in the negative electrode slurry, and can also refer to the total amount of negative electrode active materials, conductive materials and binders relative to 100 parts by weight of negative electrode slurry.

[0164] When the solids content of the negative electrode slurry falls within a specified range, the viscosity becomes appropriate during the formation of the negative electrode active material layer, which minimizes particle agglomeration and enables the effective formation of the negative electrode active material layer.

[0165] In one exemplary embodiment of the present invention, the slurry solvent can be used without limitation, as long as it is used in the art; specifically, water, acetone, or NMP can be used.

[0166] In one exemplary embodiment of the present invention, the thickness of the negative electrode current collector layer is typically from 1 μm to 100 μm. There are no particular limitations on the negative electrode current collector layer, as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc., can be used. Furthermore, the negative electrode current collector layer can have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material, and can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0167] In one exemplary embodiment of the present invention, a negative electrode for a 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 10 μm or more and 500 μm or less.

[0168] In this invention, the thickness of the negative electrode active material layer can refer to the thickness of a single negative electrode active material layer when it is formed on one surface of the negative electrode current collector layer.

[0169] However, the thickness can be modified in various ways depending on the type and purpose of the negative electrode used, and is not limited thereto.

[0170] In one exemplary embodiment of the present invention, a negative electrode for a secondary battery is provided, wherein the porosity of the negative electrode active material layer is 40% or more and 60% or less.

[0171] In another exemplary embodiment, the porosity of the negative electrode active material layer may fall within the range of 40% or more and 60% or less, 45% or more and 60% or less, or 50% or more and 55% or less.

[0172] Secondary batteries

[0173] According to an exemplary embodiment of the present invention, a secondary battery is provided, the secondary battery comprising a positive electrode, a negative electrode according to an exemplary embodiment of the present invention, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0174] A secondary battery according to an exemplary embodiment of the present invention may specifically include the aforementioned negative electrode for a secondary battery. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator inserted between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as described above. Since the negative electrode has already been described above, its detailed description is omitted.

[0175] 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 positive electrode active material.

[0176] In the positive electrode, there are no particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel that have undergone surface treatments with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and the surface of the current collector can be formed with fine irregularities to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0177] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can be a layered compound, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound replaced by 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 represented by O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5, and Cu2V2O7; and those represented by the chemical formula LiNi. 1-c2 M c2 O2 (where M is at least one of the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c2 ≤ 0.6) represents a Ni-site type lithium nickel oxide; LiMn 2- c3 M c3Lithium-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, and satisfies 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, wherein a portion of the Li in the chemical formula is replaced by alkaline earth metal ions; and so on, but not limited thereto. The positive electrode may be Li metal.

[0178] In an exemplary embodiment of the present invention, the positive electrode active material may contain a lithium composite transition metal compound comprising nickel (Ni), cobalt (Co) and manganese (Mn), the lithium composite transition metal compound may contain single particles or secondary particles, and the average particle size (D50) of the single particles may be greater than 1 μm.

[0179] For example, the average particle size (D50) of the single particle can be greater than 1 μm and less than 12 μm, greater than 1 μm and less than 8 μm, greater than 1 μm and less than 6 μm, greater than 1 μm and less than 12 μm, greater than 1 μm and less than 8 μm, or greater than 1 μm and less than 6 μm.

[0180] Even when the single particles are formed with a small average particle size (D50) of 1 μm or more but less than 12 μm, the particle strength can still be excellent. For example, at 650 kgf / cm², the particle strength is excellent. 2 During force compression, the particle strength of the single particle can be between 100 and 300 MPa. Therefore, even at 650 kgf / cm², 2 The strong rolling of the single particles also reduces the increase of microparticles in the electrode due to particle breakage, which improves the battery's lifespan characteristics.

[0181] The single particles can be manufactured by mixing and calcining a transition metal precursor and a lithium source material. The secondary particles can be manufactured by a different method than the single particles, and their composition can be the same as or different from that of the single particles.

[0182] There are no particular restrictions on the method of forming single particles, but single particles can usually be formed by over-calcining at elevated calcination temperatures, or by using additives that facilitate over-calcination, such as grain growth promoters, or by changing the starting materials.

[0183] For example, calcination is carried out at a temperature that allows single particles to form. For this purpose, calcination should be carried out at a temperature higher than the temperature during the production of secondary particles. For example, when the composition of the precursor is the same, calcination should be carried out at a temperature approximately 30°C to 100°C higher than the temperature during the production of secondary particles. The calcination temperature for forming single particles can vary depending on the metal composition in the precursor. For example, when it is necessary to form high-nickel content (high-Ni) NCM-based lithium complex transition metal oxides with a nickel (Ni) content of 80 mol% or more into single particles, the calcination temperature can be approximately 700°C to 1000°C, preferably approximately 800°C to 950°C. When the calcination temperature falls within the specified range, it is possible to produce a cathode active material containing single particles with excellent electrochemical performance. If the calcination temperature is below 790°C, a cathode active material containing lithium complex transition metal compounds in the form of secondary particles can be produced; if the calcination temperature exceeds 950°C, over-calcination will occur and a layered crystal structure cannot be properly formed, which may degrade the electrochemical performance.

[0184] As used herein, a single particle is a term used to distinguish it from a typical secondary particle, which consists of clusters of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of a primary particle and quasi-single particle forms as clusters of less than 30 primary particles.

[0185] Specifically, in this invention, a single particle can be a single particle composed of a primary particle or a quasi-single particle as an aggregate of 30 or fewer primary particles, and a secondary particle can be an aggregate of hundreds of primary particles.

[0186] In an exemplary embodiment of the present invention, the lithium composite transition metal compound used as the positive electrode active material further comprises secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0187] In this invention, a single particle can be a single particle consisting of a primary particle or a quasi-single particle as an aggregate of 30 or fewer primary particles, and a secondary particle can be an aggregate of hundreds of primary particles.

[0188] The aforementioned lithium complex transition metal compounds may also contain secondary particles. Secondary particles refer to the form formed by the aggregation of primary particles, and can be distinguished from the single-particle concept, which includes a single primary particle, a single particle, and an aggregation of less than 30 primary particles.

[0189] The particle size (D50) of the secondary particles can be 1 to 20 μm, 2 to 17 μm, and preferably 3 to 15 μm. The specific surface area (BET) of the secondary particles can be 0.05 m². 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0190] In another exemplary embodiment of the invention, the secondary particles are aggregates of primary particles, the primary particles having an average particle size (D50) of 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of hundreds of primary particles, the primary particles having an average particle size (D50) of 0.6 to 2.8 μm, 0.8 to 2.5 μm, or 0.8 to 1.5 μm.

[0191] When the average particle size (D50) of the primary particles falls within a specified range, a single-particle positive electrode active material with excellent electrochemical performance can be formed. If the average particle size (D50) of the primary particles is too small, the number of agglomerates of primary particles forming lithium nickel oxide particles increases, thereby reducing the effect of suppressing particle breakage during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path inside the primary particles may be prolonged, thereby increasing resistance and reducing output characteristics.

[0192] According to another exemplary embodiment of the invention, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles. As a result, even if the single particles are formed with a small particle size, they can still have excellent particle strength, thus mitigating the increase in microparticles in the electrode due to particle breakage, which can improve the battery's lifespan characteristics.

[0193] In one exemplary embodiment of the present invention, 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.

[0194] For example, the average particle size (D50) of the single particle can be 1 to 16 μm, 1.5 to 15 μm, or 2 to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0195] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when a specified range is met, even if the single particles are formed to have a small particle size, they can still have excellent particle strength. Therefore, the increase in particles in the electrode due to particle breakage is reduced, which can improve the battery's lifespan characteristics and energy density.

[0196] According to another exemplary embodiment of the present invention, the content of the single particles is 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material. Alternatively, the content of the single particles may be 20 to 100 parts by weight or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0197] For example, relative to 100 parts by weight of the positive electrode active material, the content of the single particles can be 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more. Relative to 100 parts by weight of the positive electrode active material, the content of the single particles can be less than 100 parts by weight.

[0198] When the content of the single particles is within a specified range, the combination with the aforementioned negative electrode material can exhibit excellent battery characteristics. In particular, when the content of the single particles is 15 parts by weight or more, the increase in particulate matter in the electrode due to particle breakage during calendering after electrode manufacturing is reduced, which can improve the battery's lifespan characteristics.

[0199] In one exemplary embodiment of the present invention, the lithium composite transition metal compound may further comprise secondary particles, and the amount of the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The content of the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The content of the secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0200] When the specified range is met, the aforementioned effects due to the presence of the single particles in the positive electrode active material can be maximized. In the case of a positive electrode active material containing the secondary particles, its composition may be the same as or different from those components exemplified in the single-particle positive electrode active materials described above, and may refer to the aggregate form of single particles.

[0201] In one exemplary embodiment of the present invention, in 100 parts by weight of the positive electrode active material layer, the content of the positive electrode active material can be 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.

[0202] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0203] In this context, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular restriction, as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the constructed battery. Specific examples may include graphite, such as natural and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking 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, etc., and any one or a mixture of two or more thereof may be used.

[0204] Furthermore, the positive electrode adhesive is used to improve 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 may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0205] The separator is used to separate the negative electrode from the positive electrode and to provide a migration pathway for lithium ions. Any separator can be used without particular limitation, as long as it is typically used in secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion migration are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be selectively used.

[0206] Examples of the electrolyte may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0207] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0208] Examples of the non-aqueous organic solvents include aprotic organic solvents such as N-methyl-2-pyrrolidone, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, butyl 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, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0209] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are high-viscosity organic solvents and are preferred because they readily dissociate lithium salts due to their high dielectric constant. When the cyclic carbonates are mixed in appropriate proportions with linear carbonates such as dimethyl carbonate and diethyl carbonate, which have low viscosity and low dielectric constant, electrolytes with high conductivity can be prepared, and therefore, they are even more preferred.

[0210] Lithium salts can be used as the metal salts, and the lithium salts are materials that are readily soluble in non-aqueous electrolytes, wherein the anions of the lithium salts can be, for example, one or more selected from the group consisting of: 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 - .

[0211] To improve battery life characteristics, suppress battery capacity decline, and improve battery discharge capacity, the electrolyte may contain one or more additives in addition to the electrolyte components mentioned above, such as alkylene carbonate halide compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0212] Battery modules and battery packs

[0213] An exemplary embodiment of the present invention provides a battery module comprising a secondary battery according to an exemplary embodiment of the present invention.

[0214] An exemplary embodiment of the present invention provides a battery pack comprising a secondary battery according to an exemplary embodiment of the present invention.

[0215] An exemplary embodiment of the present invention provides a battery pack comprising a battery module according to an exemplary embodiment of the present invention.

[0216] An exemplary embodiment of the present invention provides a battery module comprising the secondary battery as a unit cell and a battery pack comprising the secondary battery or the battery module. Because the battery module and the battery pack comprise secondary batteries with high capacity, high rate capability, and high cycle performance, they can be used as power sources for medium to large-sized devices selected from groups consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0217] Although the present invention has been described with reference to exemplary embodiments thereof, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above description.

[0218] Preferred embodiments will be provided below to better understand the invention. It will be apparent to those skilled in the art that the embodiments described are merely illustrative and that various modifications and variations can be made within the scope and spirit of the invention. Such modifications and variations naturally fall within the scope of the claims contained herein.

[0219] Model for implementing invention

[0220] <Preparation Example>

[0221] Example 1

[0222] 1) Preparation of negative electrode active materials

[0223] Pure Si powder (average particle size (D50): 5.0 μm) was prepared as the silicon-based active material, and Al(OH)3 (average particle size (D50): 700 nm) was prepared as the inorganic flame retardant. The silicon-based active material and the inorganic flame retardant were mixed at a weight ratio of 90:10, and then an inorganic flame retardant coating was formed on the surface of the silicon-based active material by dry ball milling to prepare the negative electrode active material (average coating thickness: 1.5 μm).

[0224] 2) Preparation of the negative electrode

[0225] Prepare the negative electrode active material, single-walled carbon nanotubes (SWCNTs) as conductive material, and polyacrylamide (PAM) as binder in a weight ratio of 90:0.8:9.2 to prepare a negative electrode composition, and add the mixture to distilled water as a solvent to prepare a negative electrode slurry (solid content 26% by weight).

[0226] Specifically, SWCNT and PAM were dispersed in distilled water at 2,500 rpm for 30 minutes using a homogenizer, and then the negative electrode active material was added and the mixture was dispersed at 2,500 rpm for 30 minutes to prepare the negative electrode slurry.

[0227] The BET specific surface area of ​​the SWCNTs used is 1000 m². 2 / g to 1500 m 2 / g, with an aspect ratio of 10,000 or higher, and using a solution in which SWCNT is dispersed in carboxymethyl cellulose (CMC).

[0228] The PAM used was in aqueous form, with a weight-average molecular weight (Mw) of 500,000 g / mol to 800,000 g / mol, a number-average molecular weight (Mn) of 100,000 g / mol to 400,000 g / mol, and a PDI value of 20 to 50. The binder was in aqueous form, and its weight-average and number-average molecular weights were measured using aqueous gel permeation chromatography (GPC).

[0229] The negative electrode slurry was prepared at 87.7 mg / 25 cm⁻¹. 2The loading amount was coated on both surfaces of a copper current collector (thickness: 26 μm) used as the negative electrode current collector layer, and then rolled and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), thereby preparing the negative electrode (negative electrode thickness: 59 μm, porosity: 55.0%).

[0230] 3) Preparation of secondary batteries

[0231] LiNi was prepared as the positive electrode active material in a weight ratio of 97:1.5:1.5. 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 are added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the positive electrode slurry, thereby preparing a positive electrode slurry (solid concentration: 78 wt%).

[0232] The positive electrode slurry was prepared at 537 mg / 25 cm⁻¹ 2 The loading amount was coated onto both surfaces of an aluminum current collector (thickness: 12 μm) used as the positive electrode current collector, and then rolled and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), thereby preparing the positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0233] A lithium secondary battery is prepared by inserting a polyethylene separator between the positive and negative electrodes and injecting an electrolyte.

[0234] The electrolyte used was prepared by adding 3% by weight of vinylene carbonate (VC) relative to the total weight of the electrolyte to an organic solvent obtained by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90, and adding 1 M of LiPF6 as a lithium salt.

[0235] Example 2

[0236] The secondary battery was prepared in the same manner as in Example 1, but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, the silicon-based active material was prepared in the following manner.

[0237] SiO particles were prepared as silicon-based particles. The SiO particles were mixed with Mg as a metallic material, and the mixture was heat-treated at 1200°C for 3 hours to prepare SiO particles in which Mg is distributed on the surface and / or inside the SiO particles. During preparation, a carbon layer was formed on the SiO particles in which Mg is distributed on the surface and / or inside the SiO particles using methane as a hydrocarbon gas at 950°C via chemical vapor deposition (CVD), thereby preparing a silicon-based active material (average particle size (D50): 6 μm). In the silicon-based active material, the weight ratio of silicon particles:metal (Mg):carbon layer was 85:10:5 (average coating thickness: 1.5 μm).

[0238] That is, compared with Example 1, Example 2 uses Mg-doped SiO instead of Si powder as the silicon-based active material for preparation.

[0239] Example 3

[0240] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 0.2 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, Al(OH)3 (average particle size (D50): 100 nm) was used as an inorganic flame retardant.

[0241] That is, compared with Example 1, Example 3 was prepared using inorganic flame retardants with different average particle sizes.

[0242] Example 4

[0243] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 3 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, Mg(OH)2 (average particle size (D50): 900 nm) was used as an inorganic flame retardant.

[0244] That is, compared with Example 1, Example 4 uses Mg(OH)2 instead of Al(OH)3 as an inorganic flame retardant with a different average particle size to prepare the flame retardant.

[0245] Example 5

[0246] The secondary battery was prepared in the same manner as in Example 1, but in step 2) of the preparation method in Example 1, the negative electrode composition was prepared in the following manner.

[0247] A negative electrode composition was prepared by preparing the negative electrode active material prepared in Example 1 as the first negative electrode active material (15 parts by weight relative to a total of 100 parts by weight of the first and second negative electrode active materials) and the carbon-based active material as the second negative electrode active material, namely graphite (artificial graphite: natural graphite = 70:30 by weight, 85 parts by weight relative to a total of 100 parts by weight of the first and second negative electrode active materials), as a conductive material, single-walled carbon nanotubes (SWCNTs), and polyacrylamide (PAM) as a binder, in a weight ratio of 90:0.8:9.2.

[0248] That is, Example 5 uses a negative electrode composition mixed with carbon-based active materials to prepare it.

[0249] Example 6

[0250] The secondary battery was prepared in the same manner as in Example 1, but Si / C particles (average particle size (D50): 7.0 μm) were used as silicon-based active materials in the preparation method of Example 1.

[0251] That is, compared with Example 1, Example 6 uses Si / C particles instead of Si powder as the silicon-based active material for preparation.

[0252] Example 7

[0253] The secondary battery was prepared in the same manner as in Example 1, except that in Example 1, when preparing the negative electrode active material, the average thickness of the inorganic flame retardant coating was 20 nm.

[0254] Example 8

[0255] The secondary battery was prepared in the same manner as in Example 2, except that in Example 2, when preparing the negative electrode active material, the average thickness of the inorganic flame retardant coating was 20 nm.

[0256] Comparative Example 1

[0257] The secondary battery was prepared in the same manner as in Example 1, but in step 2) of the preparation method in Example 1, when preparing the negative electrode, pure Si powder (average particle size (D50): 5.0 μm) was used instead of the negative electrode active material prepared in step 1) as the negative electrode active material.

[0258] That is, Comparative Example 1 was prepared using a negative electrode active material that does not contain an inorganic flame retardant coating.

[0259] Comparative Example 2

[0260] The secondary battery was prepared in the same manner as in Example 1, but in the preparation method of Example 1, in step 2) above, when preparing the negative electrode, pure Si (average particle size (D50): 5.0 μm) was used instead of the negative electrode active material prepared in step 1) above, and the negative electrode slurry also contained Al(OH)3 (average particle size (D50): 700 nm) as an inorganic flame retardant.

[0261] That is, Comparative Example 2 was prepared using a negative electrode in which the negative electrode active material does not contain a coating and the inorganic flame retardant is uniformly dispersed and distributed on the negative electrode active material layer.

[0262] Comparative Example 3

[0263] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 3 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, a halogen-based flame retardant (average particle size (D50): 100 nm) was used.

[0264] That is, Comparative Example 3 was prepared using a halogenated flame retardant instead of an inorganic flame retardant.

[0265] Comparative Example 4

[0266] The secondary battery was prepared in the same manner as in Example 6, but in the preparation method of Example 6, a negative electrode active material without an inorganic flame retardant coating was used on the surface of the silicon-based active material.

[0267] That is, Comparative Example 4 was prepared using only Si / C particles without coating as the negative electrode active material.

[0268] Comparative Example 5

[0269] The secondary battery was prepared in the same manner as in Example 1, except that in Example 1, the average thickness of the inorganic flame retardant coating was 5 nm when the negative electrode active material was prepared.

[0270] Comparative Example 6

[0271] The secondary battery was prepared in the same manner as in Example 1, except that in Example 1, the average thickness of the inorganic flame retardant coating was 15 nm when the negative electrode active material was prepared.

[0272] Comparative Example 7

[0273] The secondary battery was prepared in the same manner as in Example 2, except that in Example 2, the average thickness of the inorganic flame retardant coating was 5 nm when the negative electrode active material was prepared.

[0274] Comparative Example 8

[0275] The secondary battery was prepared in the same manner as in Example 2, except that in Example 2, the average thickness of the inorganic flame retardant coating was 15 nm when the negative electrode active material was prepared.

[0276] The following items were evaluated for the prepared examples and comparative examples, and the results are shown in Table 1.

[0277] <Experimental Example: Evaluation of Capacity Retention>

[0278] In-situ cycling tests were conducted on the lithium secondary battery at 1 C / 0.5 C charge / discharge conditions within the range of 4.2–3.0 V. During the test, the battery was charged and discharged at 0.33 C / 0.33 C (4.2–3.0 V) every 50 cycles. The capacity retention was measured after 200 cycles.

[0279] Capacity retention (%) = {(Discharge capacity at Nth cycle) / (Discharge capacity at 1st cycle)} × 100%

[0280] <Experimental Example: Evaluation of Resistance Increase Rate>

[0281] In capacity retention evaluation, capacity retention was measured by charging and discharging at 0.33 C / 0.33 C (4.2-3.0V) every 50 cycles during the test. After 200 cycles, resistance was measured by discharging at 50% SOC with a 2.5 C pulse, and the rate of increase in resistance was compared and analyzed.

[0282] For the evaluation of the resistance increase rate, the data were calculated for 200 cycles.

[0283] <Experimental Example: Evaluation of the Highest Temperature During Fire Ignition>

[0284] For the secondary battery prepared as described above, the highest temperature at which it ignites is measured.

[0285] In the prepared secondary battery, a heating pad was used to gradually raise the temperature of the charged single cell to induce a fire. In this case, the surface temperature of the negative electrode was measured, and the highest measured temperature is shown in Table 1.

[0286] [Table 1]

[0287] Referring to Table 1, in Examples 1 to 8, which contained an inorganic flame retardant coating on the surface of a silicon-based active material, it was confirmed that the maximum ignition temperature was lower than that of Comparative Example 1, which did not contain an inorganic flame retardant coating on the surface of the silicon-based active material. This is understood to be because, as the cell temperature increases, the endothermic reaction that occurs when the inorganic flame retardant decomposes above a certain temperature suppresses ignition, and the latent heat of water generated by the decomposition reaction of the inorganic flame retardant provides additional ignition suppression. Furthermore, in Examples 1 to 8, which contained an inorganic flame retardant coating on the surface of a silicon-based active material, the maximum ignition temperature of the single cell was lower, while the capacity retention rate and resistance increase rate were comparable to or improved compared to Comparative Example 1. Therefore, it was confirmed that the inorganic flame retardant coating on the surface of the silicon-based active material can delay ignition within the single cell and improve the thermal safety of the single cell, without reducing the performance of the single cell.

[0288] On the other hand, in Comparative Example 2, the highest temperature at ignition was lower than that in Comparative Example 1, but it was confirmed that the highest temperature at ignition was higher than that in Examples 1 to 8. This is understood to be due to the method of applying inorganic flame retardants, because when inorganic flame retardants are uniformly dispersed throughout the electrode (Comparative Example 2), they cannot effectively suppress the heat generated on the surface of the silicon-based active material.

[0289] Furthermore, in Example 6, which included an inorganic flame retardant coating on the surface of a silicon-based active material, it was confirmed that the highest temperature at which a single cell ignited was lower than that in Comparative Example 4, which involved a negative electrode active material using the same type of silicon-based active material.

[0290] Furthermore, in Examples 7 and 8, where 20 nm thick inorganic flame retardant coatings were applied to both pure Si and SiOx, it was confirmed that they exhibited superior performance in improving thermal stability compared to Comparative Examples 5 to 8, which applied relatively thinner inorganic flame retardant coatings of 5 nm and 15 nm, respectively. Specifically, it was confirmed that when the average thickness of the inorganic flame retardant coating is 20 nm or more, for example, 0.02 μm or more, the heat resistance effect is excellent. On the other hand, when the average thickness of the inorganic flame retardant coating is less than 20 nm, for example, less than 0.02 μm, it was confirmed that the maximum temperature at which a single cell ignites is higher, because the thickness of the inorganic flame retardant coating is smaller than in the examples.

[0291] In Comparative Example 3 (using a halogen-based flame retardant), the coating may have undergone structural changes due to decomposition at a relatively lower temperature compared to the inorganic flame retardants of Examples 1 to 8. It was also confirmed that the effect of improving thermal stability was reduced in actual single-cell thermal runaway conditions, resulting in a worse effect compared to the examples.

[0292] The foregoing detailed description is intended to illustrate and explain the present invention. Furthermore, the foregoing description only illustrates and explains preferred exemplary embodiments of the invention. As mentioned above, the invention can be used in various other combinations, variations, and environments, and can be changed or modified within the scope of the invention disclosed in this specification, the equivalent scope of the foregoing disclosure, and / or the scope of technology or knowledge in the art. Therefore, the foregoing detailed description of the invention is not intended to limit the invention to the disclosed embodiments. Moreover, the appended claims should be interpreted as including other embodiments.

Claims

1. A negative electrode active material, said negative electrode active material comprising: Silicon-based active materials; and A coating disposed on the silicon-based active material, wherein The silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, and The coating contains an inorganic flame retardant.

2. The negative electrode active material according to claim 1, wherein the inorganic flame retardant undergoes an endothermic reaction at 100°C to 250°C.

3. The negative electrode active material according to claim 2, wherein the endothermic reaction is a dehydration reaction.

4. The negative electrode active material according to claim 1, wherein the inorganic flame retardant comprises one or more selected from the group consisting of aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), antimony trioxide (Sb2O3), and zinc borate.

5. The negative electrode active material according to claim 1, wherein the silicon-based active material comprises Si, and the content of Si is 70 to 100 parts by weight relative to 100 parts by weight of the silicon-based active material.

6. The negative electrode active material according to claim 1, wherein the SiO x (0 < x < 2) further contains a metal distributed on the surface, inside, or both the surface and inside of the SiO x (0 < x < 2), and The metal comprises one or more selected from the group consisting of Li, Mg and Al.

7. The negative electrode active material according to claim 1, wherein the average thickness of the coating is from 0.02 μm to 10 μm.

8. The negative electrode active material according to claim 1, wherein the content of the inorganic flame retardant is 95 parts by weight or more relative to 100 parts by weight of the coating.

9. The negative electrode active material according to claim 1, wherein the average particle size (D50) of the inorganic flame retardant is from 0.05 μm to 1.5 μm.

10. A negative electrode composition, said negative electrode composition comprising: The negative electrode active material according to any one of claims 1 to 9; Negative electrode adhesive; and Negative electrode conductive material.

11. The negative electrode composition according to claim 10, wherein the negative electrode active material is a first negative electrode active material, and further comprises a carbon-based active material as a second negative electrode active material.

12. The negative electrode composition according to claim 11, wherein the carbon-based active material comprises at least one selected from the group consisting of natural graphite and artificial graphite.

13. The negative electrode composition according to claim 11, wherein the content of the first negative electrode active material is 1 to 20 parts by weight relative to a total of 100 parts by weight of the first negative electrode active material and the second negative electrode active material.

14. A negative electrode, said negative electrode comprising: Negative current collector layer; and A layer of negative electrode active material formed on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer comprises the negative electrode composition according to claim 10.

15. A secondary battery, the secondary battery comprising: positive electrode; The negative electrode according to claim 14; A membrane disposed between the positive electrode and the negative electrode; and Electrolytes.

16. A battery module comprising the secondary battery according to claim 15.

17. A battery pack comprising a secondary battery according to claim 15.

18. A battery pack comprising the battery module according to claim 16.

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