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

Abstract

The present specification relates to a negative electrode active material, and a negative electrode and a secondary battery comprising same. According to an embodiment of the present invention, provided is a negative electrode active material comprising a silicon-based active material and a coating layer provided thereon, wherein the silicon-based active material comprises at least one selected from the group consisting of pure Si, SiOx (0<x<2) and Si / C, and the coating layer comprises an inorganic flame retardant.

Description

Negative active material, negative electrode composition containing the same, negative electrode and secondary battery

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

[0002] The present application relates to a negative electrode active material, a negative electrode composition, a negative electrode and a secondary battery, and a battery module and a battery pack.

[0003] The rapid increase in fossil fuel use is driving a growing demand for alternative and clean energy sources. To meet this demand, one of the most actively researched areas is the use of electrochemical reactions to generate and store electricity. Secondary batteries are a prime example of electrochemical devices that utilize this electrochemical energy, and their applications are expanding.

[0004] As technological development and demand for mobile devices increase, the demand for secondary batteries is also rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used. Furthermore, active research is underway to develop high-density electrodes with even higher energy density per unit volume to manufacture high-capacity lithium secondary battery electrodes.

[0005] Typically, secondary batteries consist of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative active material that inserts and desorbs lithium ions from the positive electrode. This negative active material can be silicon-based particles with high discharge capacity.

[0006] In particular, with the recent increase in demand for high-density energy cells, research is actively being conducted on methods to increase capacity using silicon-based compounds, such as Si / C or SiOx, which have a capacity more than 10 times greater than graphite-based materials as anode active materials. Silicon-based compounds, which are high-capacity materials, have the advantage of greater capacity compared to conventional graphite, but they have the problem of being vulnerable to thermal runaway problems within the cell in actual operating environments due to rapid volume expansion during the charging process.

[0007] Accordingly, research is needed to develop secondary batteries with high capacity and improved safety.

[0008] Therefore, research is needed to develop secondary batteries with improved safety while having high capacity.

[0009] The present specification aims to provide a negative electrode active material, a negative electrode, and a secondary battery having high capacity and improved safety in an operating environment by applying a silicon-based active material.

[0010] According to one embodiment of the present invention, a silicon-based active material and a coating layer provided on the silicon-based active material are included, and the silicon-based active material is Si, SiOx(0 <x<2) 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함하고 상기 코팅층은 무기 난연제를 포함하는 것인 음극 활물질을 제공한다.

[0011] According to one embodiment of the present invention, a negative electrode composition is provided, which includes a negative electrode active material according to one embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material.

[0012] According to one embodiment of the present invention, there is provided a negative electrode comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode composition according to one embodiment of the present invention.

[0013] According to one embodiment of the present invention, a secondary battery including a negative electrode according to one embodiment of the present invention is provided.

[0014] According to one embodiment of the present invention, a battery module including a secondary battery according to one embodiment of the present invention is provided.

[0015] According to one embodiment of the present invention, a battery pack including a secondary battery or battery module according to one embodiment of the present invention is provided.

[0016] When the negative active material according to one embodiment of the present invention is applied to a negative electrode, the life characteristics can be improved while maintaining a high capacity.

[0017] When the negative electrode active material according to one embodiment of the present invention is applied to the negative electrode, ignition at high temperatures can be suppressed without performance deterioration, thereby improving thermal safety.

[0018] Before explaining the present invention, some terms are first defined.

[0019] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0020] In this specification, “p to q” means a range of p or more and q or less.

[0021] In this specification, "specific surface area" is measured by the BET method, and specifically, it is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan. That is, in this application, the BET specific surface area may refer to the specific surface area measured by the above measurement method. The BET specific surface area may be measured using N2 according to DIN 66131.

[0022] In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size (center particle size) at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the center particle size can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0023] In one embodiment of the present application, particle size or particle diameter may mean the average diameter or representative diameter of each grain forming the metal powder.

[0024] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0025] In this specification, the term “polymer” is understood to be used in a broad sense including copolymers unless “homopolymer” is specified.

[0026] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0027] The following is a detailed description of the present invention so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0028] Lithium secondary batteries can experience internal self-heating due to external shock or abnormal cell behavior. This self-heating can cause internal cell temperatures to rise, potentially leading to thermal runaway. Furthermore, the heat generated within a cell can be transferred to adjacent cells, potentially spreading thermal runaway throughout the entire battery.

[0029] This thermal runaway problem is particularly problematic for anodes containing silicon-based anode active materials. While silicon-based anodes offer high energy density, they have poor thermal stability, making them more susceptible to cell thermal runaway.

[0030] Accordingly, various methods have been discussed to prevent the thermal runaway problem of batteries, such as forming a separate coating layer in addition to the polymer substrate on the separator or attaching a sheet to the outside of the battery cell to prevent cell-to-cell transfer. However, it has been confirmed that it is difficult to effectively suppress the above-mentioned thermal runaway phenomenon because it is impossible to suppress the abnormal heat generation phenomenon occurring at the electrode unit.

[0031] The present inventors have obtained the advantages of an electrode using a silicon-based negative electrode active material having a high capacity by providing a silicon-based negative electrode active material surface-treated with an inorganic flame retardant as a negative electrode active material, and at the same time, suppressing the problem of temperature rise from within the negative electrode, thereby delaying the temperature inside the battery from rising above a certain level.

[0032]

[0033] Negative active material

[0034] According to one embodiment of the present invention, it comprises a silicon-based active material and a coating layer provided on the silicon-based active material, wherein the silicon-based active material comprises Si, SiOx(0 <x<2) 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함하고, 상기 코팅층은 무기 난연제를 포함하는 것인 음극 활물질을 제공한다.

[0035] According to one embodiment of the present invention, it comprises a silicon-based active material and a coating layer provided on at least one surface of the silicon-based active material, wherein the silicon-based active material comprises Si, SiOx(0 <x<2) 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함하고, 상기 코팅층은 무기 난연제를 포함하는 것인 음극 활물질을 제공한다.

[0036] According to one embodiment of the present invention, the negative electrode active material has a structure including a core containing a silicon-based active material and a coating layer containing an inorganic flame retardant on the surface of the core. That is, the coating layer is provided on at least a portion of the surface of the silicon-based negative electrode active material.

[0037] According to one embodiment of the present invention, the coating layer is provided on the surface of the silicon-based active material.

[0038] The negative active material according to the present invention is characterized by directly coating an inorganic flame retardant on the surface of a silicon-based active material, and therefore has the advantage of being able to suppress heat generated by an abnormal situation in a battery operating environment from the surface of the negative active material. For example, compared to a form in which an inorganic flame retardant is evenly dispersed in the negative active material layer, the negative active material can more effectively suppress heat generated on the surface of the negative active material, and has the advantage of being able to minimize the amount of flame retardant applied to the negative electrode. That is, when the negative active material according to one embodiment of the present invention is applied to the negative electrode, heat generation within the cell can be effectively suppressed by applying only a small amount of flame retardant, and there is an advantage in that the active material content can be further increased as the amount of flame retardant is reduced.

[0039] According to one embodiment of the present invention, a negative active material comprises an inorganic flame retardant that undergoes an endothermic reaction at a temperature of 100°C to 250°C. For example, the endothermic reaction may occur at a temperature of 100°C or higher, 150°C or higher, or 180°C or higher.

[0040] The above-mentioned inorganic flame retardant selectively causes an endothermic reaction to delay heat generation only when the internal temperature of the battery abnormally rises due to abnormal heat generation within the battery. In other words, the above-mentioned inorganic flame retardant does not react at the normal operating temperature of the battery, and thus can effectively suppress internal heat generation in the battery without deteriorating battery performance due to the flame retardant under normal operating conditions.

[0041] According to one embodiment of the present invention, the endothermic reaction is a dehydration reaction. Since the inorganic flame retardant undergoes an endothermic reaction accompanied by dehydration at a specific temperature, in addition to heat suppression by the endothermic reaction, it is characterized by being able to obtain an additional cooling effect by the latent heat of the water generated by the dehydration reaction.

[0042] According to one embodiment of the present invention, the inorganic flame retardant includes at least one selected from the group consisting of aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), antimony trioxide (Sb2O3), and zinc borate.

[0043] According to one embodiment of the present invention, the inorganic flame retardant is aluminum hydroxide (Al(OH)3) or magnesium hydroxide (Mg(OH)2), and preferably, the inorganic flame retardant is aluminum hydroxide (Al(OH)3). The aluminum hydroxide has the characteristics of having a large amount of absorbable heat energy per reaction, being inexpensive and thus highly economical, and being a non-toxic substance that does not cause harm to the user even when applied to a battery.

[0044] According to one embodiment of the present invention, the average particle diameter (D50) of the inorganic flame retardant may be 0.05 ㎛ to 1.5 ㎛. For example, the average particle diameter (D50) of the inorganic flame retardant may be 0.05 ㎛ or more, 0.08 ㎛ or more, 0.1 ㎛ or more, 0.5 ㎛ or more, or 0.6 ㎛ or more, and may be 1.5 ㎛ or less, 1.2 ㎛ or less, 1 ㎛ or less, 900 nm or less, or 800 nm or less. When the average particle diameter of the inorganic flame retardant is within the above range, a coating layer can be uniformly formed on the surface of the active material.

[0045] The average particle diameter of the above inorganic flame retardant is the average of the diameters (sphere-converted particle diameters) of the inorganic flame retardant particles when converted to spheres of the same volume, and this value can be obtained by electron microscope observation. That is, when observing an inorganic flame retardant with an electron microscope, the diameters of 200 or more inorganic flame retardant particles within a certain field of view are measured, the sphere-converted particle diameters of each particle are obtained, and the average value is obtained.

[0046] According to one embodiment of the present invention, the average thickness of the coating layer may be 0.02 ㎛ to 10 ㎛. For example, the average thickness of the coating layer may be 0.02 ㎛ or more, 0.05 ㎛ or more, 0.08 ㎛ or more, 0.1 ㎛ or more, 0.2 ㎛ or more, 0.5 ㎛ or more, 0.8 ㎛ or more, 1 ㎛ or more, or 1.5 ㎛ or more, and may be 10 ㎛ or less, 8 ㎛ or less, 6 ㎛ or less, 4 ㎛ or less, or 3 ㎛ or less. When the average thickness of the coating layer is within the above range, the heat resistance of the negative electrode active material can be improved without affecting the behavior of lithium ions in the operating environment. In addition, when the thickness of the coating layer is within the range exceeding the upper limit, the size of the entire negative electrode active material may become excessively large, making it difficult for the negative electrode active material to be evenly distributed within the negative electrode active material layer.

[0047] According to one embodiment of the present invention, the inorganic flame retardant may be included in an amount of 95 parts by weight or more based on 100 parts by weight of the coating layer. For example, the inorganic flame retardant may be included in an amount of 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 included in an amount of 100 parts by weight or less, 99.5 parts by weight or less, or 99 parts by weight or less based on 100 parts by weight of the coating layer. When the inorganic flame retardant is included in the above range, the conductivity of the negative electrode active material is not lowered, and the heat resistance can be improved.

[0048] According to one embodiment of the present invention, the inorganic flame retardant may be included in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the negative electrode active material. For example, the inorganic flame retardant may be included in an amount of 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more, and may be included in an amount of 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less, based on 100 parts by weight of the negative electrode active material. That is, the inorganic flame retardant may be included in an amount of 1 to 20 parts by weight, or may be included in an amount of 1 to 10 parts by weight. When the inorganic flame retardant is included in the above range, the heat resistance function can be improved without lowering the conductivity of the negative electrode active material.

[0049] According to one embodiment of the present invention, the negative electrode active material is a silicon-based active material, such as Si, SiOx(0 <x<2) 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함한다.

[0050] In one embodiment of the present invention, the negative electrode active material is a silicon-based active material including Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함한다.

[0051] In one embodiment of the present invention, the silicon-based active material is Si.

[0052] According to one embodiment of the present invention, the negative electrode active material is a silicon-based active material, such as Si, SiOx(0 <x<2) 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함하고, 상기 실리콘계 활물질은 Si를 포함하고, 상기 Si는 실리콘계 활물질 100 중량부에 대하여, 70 중량부 내지 100 중량부 포함한다.

[0053] In another embodiment, the Si is included in an amount of 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, based on 100 parts by weight of the silicon-based active material. The Si may be included in an amount of 100 parts by weight or less, less than 100 parts by weight, 99.9 parts by weight or less, 99 parts by weight or less, or 95 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0054] That is, in one embodiment of the present invention, the negative electrode active material includes Si as a silicon-based active material, and includes 70 parts by weight or more of Si based on 100 parts by weight of the silicon-based active material.

[0055] According to one embodiment of the present invention, the silicon-based active material includes Si, and the Si may be 100 parts by weight based on 100 parts by weight of the silicon-based active material.

[0056] In this specification, the 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 including pure Si particles (SiOx (x=0)) that are not combined with other particles or elements within the above range, based on the total 100 parts by weight of the negative electrode active material.

[0057] In one embodiment of the present invention, the silicon-based active material may be formed of silicon-based particles having 100 parts by weight of pure Si based on 100 parts by weight of the negative electrode active material.

[0058] In one embodiment of the present invention, the silicon-based active material may include a metal impurity, and at this time, the impurity may include a metal that may be generally included in the silicon-based active material, and specifically, may include 0.1 part by weight or less based on 100 parts by weight of the negative electrode active material.

[0059] That is, in one embodiment of the present invention, the silicon-based active material is distinguished from Si-alloy, and the silicon-based active material according to one embodiment of the present invention has higher capacity and structural stability than the silicon-based active material that uses Si-alloy as a main material.

[0060] In another embodiment, the silicon-based active material is SiOx (0 <x<2)을 포함한다.

[0061] In the above SiOx, in the case of SiO2 (when x = 2), it does not react with lithium ions and therefore cannot store lithium, so x is in the above range (0 <x<2) 내인 것이 바람직하다. 구체적으로 활물질의 구조적 안정 측면에서 x는 0.5≤x≤1.5일 수 있다.

[0062] The above SiOx (0 <x<2)은 상기 SiOx (0<x<2) 입자의 표면, 내부, 또는 표면 및 내부에 분포된 금속을 더 포함할 수 있다. 상기 금속은 실리콘계 활물질의 표면 및 / 또는 내부에 분포되어 실리콘계 활물질의 비가역상(예를 들면 SiO2)의 비율을 낮추어 활물질의 효율을 증가시키기 위한 측면에서 실리콘계 활물질 내에 함유될 수 있다.

[0063] The above 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 in that it can excellently implement a damage prevention effect of the above-described silicon-based oxide particles and has low reactivity with moisture, thereby further improving the life characteristics of the negative electrode active material.

[0064] The metal may be included in the silicon-based active material in an amount of 0.1 wt% to 25 wt%, or 3 wt% to 15 wt%, and is preferable in that it increases the efficiency of the active material without reducing the capacity when within the above range.

[0065] In one embodiment of the present invention, the average particle diameter (D50) of the silicon-based active material may be 1 μm or more. In addition, the average particle diameter of the silicon-based active material may be 15 μm or less. For example, the average particle diameter (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.

[0066] In one embodiment of the present invention, the coating layer is formed on the surface of the silicon-based active material. That is, in one embodiment of the present invention, when the total area of ​​the silicon-based active material is 100%, the area of ​​the coating layer is 50% or more. For example, the area of ​​the coating layer 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.

[0067] In one embodiment of the present invention, when the average particle diameter (D50) of the silicon-based active material is A and the average particle diameter (D50) of the inorganic flame retardant is B, the following equation 1 is satisfied.

[0068] [Formula 1]

[0069] 3 ≤ A / B ≤ 25

[0070] In one embodiment of the present invention, the above formula 1 is 3 to 25. For example, the above formula 1 may be 3 or more, 4 or more, 5 or more, 6 or more, or 7 or more, and may be 25 or less, 20 or less, or 15 or less. When the formula 1 is included in the above range, the size between the silicon-based active material and the inorganic flame retardant is appropriately controlled, so that an inorganic flame retardant coating layer can be uniformly and thinly formed on the silicon-based active material.

[0071] In the above formula 1, the ranges of A and B can be derived from the average particle diameter (D50) of the above-described silicon-based active material and the average particle diameter (D50) of the inorganic flame retardant.

[0072] In one embodiment of the present invention, the crystal grain size of the silicon-based active material may be 600 nm or less.

[0073] In another embodiment, the crystal grain size of the silicon-based active material may be 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less, 130 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, or 91 nm or less. The crystal grain size of the silicon-based active material may have a range of 10 nm or more and 15 nm or more.

[0074] The above silicon-based active material has the above crystal grain size, and the crystal grain size of the silicon-based active material can be controlled by changing the process conditions in the manufacturing process. At this time, by satisfying the above range and ensuring that the grain boundaries are widely distributed, when lithium ions are inserted, they are inserted uniformly, thereby reducing the stress applied when lithium ions are inserted into silicon particles, and thus alleviating particle breakage. As a result, it has the characteristic of improving the life stability of the negative electrode. When the crystal grain size exceeds the above range, the grain boundaries within the particles become narrowly distributed, and in this case, lithium ions within the particles are inserted unevenly, so that the stress due to ion insertion is large, resulting in particle breakage.

[0075] In one embodiment of the present invention, the silicon-based active material includes a crystal structure having a crystal grain distribution of 1 nm or more and 600 nm or less, and the area ratio of the crystal structure based on the total area of ​​the silicon-based active material may be 5% or less.

[0076] In another embodiment, the area ratio of the crystal structure based on the total area of ​​the silicon-based active material may be 5% or less, 3% or less, or 0.1% or more.

[0077] That is, the silicon-based active material according to the present invention has a crystal grain size of 600 nm or less, so that a single crystal structure can be formed with a small size and satisfy the above-mentioned area ratio. Accordingly, the distribution of grain boundaries can be broadened, and thus the aforementioned effects can be exhibited.

[0078] The silicon-based active material according to the present invention has a crystal grain size of 200 nm or less, so that a single crystal structure can be formed with a small size and satisfy the above-mentioned area ratio. Accordingly, the distribution of grain boundaries can be broadened, thereby exhibiting the aforementioned effects.

[0079] In one embodiment of the present invention, the number of crystal structures included in the silicon-based active material may be 20 or more.

[0080] In another embodiment, the number of crystal structures included in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may satisfy a range of 60 or less, or 50 or less.

[0081] That is, as described above, when the silicon-based active material has a crystal grain size that satisfies the above range and the number of crystal structures that satisfies the above range, the strength of the silicon-based active material itself has an appropriate range, so that when included in an electrode, it can provide flexibility and also has the characteristic of efficiently suppressing volume expansion.

[0082] In the present invention, a crystal grain means a crystal particle that is a collection of irregularly shaped microscopic particles in a metal or material, and the crystal grain size may refer to the diameter of the observed crystal grain. That is, in the present invention, the crystal grain size refers to the size of a domain that shares the same crystal direction within a particle, and is a different concept from the particle size or particle diameter that expresses the size of a material.

[0083] In one embodiment of the present invention, the crystal grain size can be calculated as the FWHM (Full Width at Half Maximum) value through XRD analysis. The remaining values, excluding L, are measured through XRD analysis of a silicon-based active material, and the crystal grain size can be measured through the Debey-Scherrer equation, which states that the FWHM and the crystal grain size are inversely proportional. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0084] [Formula 1-1]

[0085] FWHM=Kλ / LCosθ

[0086] In the above formula 1-1,

[0087] L represents the grain size, K is a constant, θ is the bragg angle, and λ is the wavelength of the X-ray.

[0088] In addition, the shape of the crystal grains is diverse and can be measured three-dimensionally, and the size of the crystal grains can generally be measured using the commonly used circle method and diameter measurement method, but is not limited thereto.

[0089] The above diameter measurement method can be measured by drawing 5-10 equilibrium lines, each of which is L mm long, on a microscopic photograph of the target particle, counting the number of grains z on the lines, and averaging them. At this time, only those that are completely included are counted, and those that intersect are excluded. If the number of lines is P and the magnification is V, the average grain diameter can be calculated using the following equations 1-2.

[0090] [Formula 1-2]

[0091] Dm = (L*P*10 3 ) / (zV) (㎛)

[0092] In addition, the above circle method is a method of calculating the average area of ​​crystal grains by drawing a circle of a set diameter on a microscopic photograph of the target particle and calculating the number of crystal grains within the circle and the number of crystal grains that fall on the boundary line using the following equation 1-3.

[0093] [Formula 1-3]

[0094] Fm = (Fk * 10 6 ) / ((0.67n + z) V 2 ) (㎛ 2 )

[0095] In the above equation 1-3, Fm represents the average particle area, Fk represents the measured area on the photograph, z represents the number of particles inside the circle, n represents the number of particles in the circular arc, and V represents the magnification of the microscope.

[0096] In one embodiment of the present invention, the negative electrode active material including the silicon-based active material and the inorganic flame retardant coating layer provided on the silicon-based active material has a specific surface area of ​​0.5 m 2 / g to 5 m 2 / g could be.

[0097] In another embodiment, the negative active material has a specific surface area of ​​0.5 m 2 / g or more, 1 m 2 / g or more, 1.25 m 2 / g or more, 1.5 m 2 / g or more, or 2 m2 / g or more. The above silicon-based active material has a specific surface area of ​​5 m 2 / g or less, 5.5 m 2 / g or less or 4.5 m 2 / g or less can be satisfied. The specific surface area can be measured according to DIN 66131 (using nitrogen).

[0098] The above negative active material has the above specific surface area, and the size of the specific surface area of ​​the silicon-based active material can be controlled by changing the manufacturing process conditions 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 the present application, it has a wide specific surface area compared to particles having the same particle size due to the rough surface, and at this time, it has the characteristic of being able to alleviate cracks in the electrode due to repeated charge / discharge cycles as the bonding strength with the binder increases by satisfying the above range.

[0099] In addition, when lithium ions are inserted, they are inserted uniformly, which can reduce the stress applied when lithium ions are inserted into silicon particles, thereby alleviating particle breakage. As a result, it has a characteristic that can improve the life stability of the negative electrode. If the surface area size is less than the above range, even if the particle size is the same, the surface is formed smoothly, so the bonding strength with the binder is reduced, resulting in electrode cracks. In this case, lithium ions are inserted unevenly within the particle, so the stress due to ion insertion is large, resulting in particle breakage.

[0100] In one embodiment of the present invention, the negative active material satisfies the range of the following formula 2-1.

[0101] [Formula 2-1]

[0102] X1 / Y1 ≤ 0.960

[0103] In the above formula 2-1,

[0104] X1 is the actual area of ​​the negative active material,

[0105] Y1 represents the area of ​​a spherical particle of the same circumference as the negative active material.

[0106] The above equation 2-1 can be measured using a particle shape analyzer. Specifically, the negative active material according to the present invention is scattered on a glass plate by spraying air, and then the scattered particles are imaged as shadows to measure the shapes of 10,000 negative active material particles in the photograph. At this time, equation 2-1 is a value expressing the average of 10,000 particles. From the image above, equation 2-1 according to the present invention can be measured, and equation 2-1 can be expressed as the circularity of the negative active material. The circularity is [4π actual area of ​​negative active material / (perimeter) 2 ] may also be displayed.

[0107] In one embodiment of the present invention, the sphericity of the negative active material may be, for example, 0.960 or less, 0.957 or less. The sphericity of the negative 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.

[0108] In one embodiment of the present invention, the negative active material satisfies the range of the following formula 2-2.

[0109] [Formula 2-2]

[0110] X2 / Y2 ≤ 0.996

[0111] In the above equation 2-2,

[0112] Y2 is the actual circumference of the negative active material,

[0113] X2 is the perimeter of the circumscribed figure of the negative active material.

[0114] The above equation 2-2 can be measured using a particle shape analyzer. Specifically, the negative active material according to the present application is scattered on a glass plate by spraying air, and then the scattered particles are imaged as shadows to measure the shapes of 10,000 negative active material particles in the photograph. At this time, equation 2-2 is a value expressing the average of 10,000 particles. From the above image, equation 2-2 according to the present application can be measured, and equation 2-2 can be expressed as the convexity of the negative active material.

[0115] In one embodiment of the present invention, the ranges of X2 / Y2 ≤ 0.996, X2 / Y2 ≤ 0.995 can be satisfied, and the ranges of 0.8 ≤ X2 / Y2, 0.9 ≤ X2 / Y2, 0.95 ≤ X2 / Y2 or 0.98 ≤ X2 / Y2 can be satisfied.

[0116] The smaller the value of the above formula 2-1 or formula 2-2, the greater the roughness of the negative electrode active material. By using a negative electrode active material having the above range, the bonding strength with the binder increases, thereby providing a characteristic that can alleviate cracks in the electrode due to repeated charge and discharge cycles.

[0117] In one embodiment of the present invention, the negative active material has a particle size distribution of 0.01 µm or more and 30 µm or less.

[0118] The above negative active material includes negative active material particles having a particle size distribution of 0.01 ㎛ or more and 30 ㎛ or less, which means that it includes a plurality of individual negative active material particles having a particle size within the above range, and the number of negative active material particles included is not limited.

[0119] The above particle size can be expressed as its diameter if it is spherical, but even if it is a shape other than spherical, the particle size can be measured in comparison with the spherical case, and the particle size of individual particles can be measured by a method generally used in the art.

[0120]

[0121] cathode composition

[0122] One embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material; a negative electrode binder; and a negative electrode conductive material.

[0123] One embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material; 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.

[0124] That is, one embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material 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.

[0125] In one embodiment of the present invention, the carbon-based active material may include at least one 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 graphite and artificial graphite.

[0126] The negative electrode composition according to one 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 one embodiment of the present invention, and is characterized by taking advantage of the high capacity of the first negative electrode active material, while improving the volume expansion problem resulting from the silicon-based active material, and exhibiting high safety and excellent output resulting from the second active material.

[0127] Artificial graphite is typically manufactured by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum heavy oils at temperatures exceeding 2,500°C. After graphitization, the particles undergo particle size adjustments, such as crushing and secondary particle formation, before being used as a negative electrode active material. In the case of artificial graphite, crystals are randomly distributed within the particles, and compared to natural graphite, they have a lower sphericity and a somewhat pointed shape.

[0128] Additionally, the artificial graphite may have a particle size of 5 to 30 μm, preferably 10 to 25 μm.

[0129] The above natural graphite is generally in the form of plate-shaped aggregates before being processed, and the plate-shaped particles are manufactured into a spherical shape with a smooth surface through post-processing such as particle crushing and reassembly processes in order to be used as an active material for manufacturing electrodes.

[0130] Additionally, the natural graphite may have a particle size of 5 to 30 μm, or 10 to 25 μm.

[0131] When the above carbon-based active material is a mixture of artificial graphite and natural graphite, the weight ratio of the artificial graphite and natural graphite may be 9.99:0.01 to 0.01:9.99, or 9.7:0.3 to 7:3. When this weight ratio range is satisfied, excellent output can be exhibited.

[0132] In one embodiment of the present invention, the first negative electrode active material may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the sum of the first and second negative electrode active materials. The sum of 100 parts by weight of the first and second negative electrode active materials 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, the first negative electrode active material may be included in an amount of 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, based on 100 parts by weight of the sum of the first and second negative electrode active materials, and may be included in an amount of 20 parts by weight or less, or 18 parts by weight or less.

[0133] In one embodiment of the present invention, the second negative electrode active material may be included in an amount of 80 to 99 parts by weight based on 100 parts by weight of the first and second negative electrode active materials. 100 parts by weight of the first and second negative electrode active materials refers to the sum of the first negative electrode active material and the second negative electrode active material. For example, the second negative electrode active material may be included in an amount of 80 parts by weight or more, 83 parts by weight or more, or 85 parts by weight or more, and may be included in an amount of 99 parts by weight or less, 95 parts by weight or less, or 90 parts by weight or less based on 100 parts by weight of the first and second negative electrode negative electrode active materials.

[0134] In the negative electrode composition according to one embodiment of the present invention, the negative electrode binder and negative electrode conductive material are described below.

[0135] According to one embodiment of the present invention, a negative electrode composition is provided, which contains at least 60 parts by weight of the negative electrode active material based on 100 parts by weight of the negative electrode composition.

[0136] In another embodiment, the negative electrode active material may be at least 60 parts by weight, at least 65 parts by weight, at least 70 parts by weight, and may be at most 97 parts by weight, at most 95 parts by weight, or at most 90 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0137] In one embodiment of the present invention, the conductive material may include at least one selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0138] In one embodiment of the present invention, the dot-shaped conductive material may be used to improve conductivity of the negative electrode, and refers to a spherical or dot-shaped conductive material that has conductivity without causing chemical change. 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, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of implementing high conductivity and excellent dispersibility.

[0139] In one embodiment of the present invention, the dot-shaped conductive material has a BET specific surface area of ​​40 m 2 / g or more than 70m 2 / g may be less than 45m 2 / g or more than 65m 2 / g or less, or 50m 2 / g or more than 60m 2 / g can be less.

[0140] In one embodiment of the present invention, the dot-shaped conductive material can satisfy a volatile matter content 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.

[0141] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, there is a functional group present 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.

[0142] In one embodiment of the present invention, the conductive material may include a planar conductive material.

[0143] The above-mentioned planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, can suppress disconnection of the conductive path due to volume expansion, and can be expressed as a plate-shaped conductive material or a bulk conductive material.

[0144] In one embodiment of the present invention, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0145] In one embodiment of the present invention, the average particle diameter (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, the sufficient particle size facilitates dispersion without causing excessive viscosity increase in the negative electrode slurry. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0146] In one embodiment of the present invention, the planar conductive material may be a high-specific surface area planar conductive material having a high BET specific surface area; or a low-specific surface area planar conductive material.

[0147] In one embodiment of the present invention, a high surface area surface conductive material or a low surface area surface conductive material may be used without limitation as the surface conductive material, but in particular, since the surface conductive material according to the present application may be affected to some extent by dispersion effects on electrode performance, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0148] In one embodiment of the present invention, the surface-shaped conductive material has a BET specific surface area of ​​5 m 2 / g can be more than that.

[0149] In another embodiment, the surface-shaped conductive material has a BET surface area of ​​5 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0150] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 / g can satisfy the range below.

[0151] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​5 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0152] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in parallel or entangled with the longitudinal axes of the carbon nanotube units. The carbon nanotube units have a cylindrical shape with a nano-sized diameter of a graphite sheet, and are sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or semiconductor. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during the manufacture of the cathode, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0153] In one embodiment of the present invention, the linear conductive material may include SWCNT or MWCNT.

[0154] In one embodiment of the present invention, a negative electrode composition is provided in which the negative electrode conductive material is included in an amount of 0.01 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode composition. For example, the negative electrode conductive material may be included in an amount of 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, and may be included in an amount of 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 based on 100 parts by weight of the negative electrode composition.

[0155] The negative electrode conductive material according to the present invention has a completely separate composition from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact between silicon-based active materials, which undergo a large volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer when rolled, and is completely different in composition and role from the negative electrode conductive material of the present invention.

[0156] In addition, the negative electrode conductive material according to the present invention is applied to a silicon-based active material and has a completely different composition from the conductive material applied to a negative electrode composition containing only a graphite-based active material. That is, the conductive material used in a negative electrode composition containing only a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0157] In one embodiment of the present invention, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, 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), fluoroelastomer, poly acrylic acid, polyacrylamide (PAM), and materials in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0158] The negative electrode binder according to one embodiment of the present invention serves to hold the active material and the conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. If the above-mentioned role is satisfied, all general binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder, which is a one-component aqueous binder, can be used.

[0159] In one embodiment of the present invention, a cathode slurry is provided in which the cathode binder includes an aqueous binder, and the cathode binder is included in an amount of 5 parts by weight or more and 12 parts by weight or less based on 100 parts by weight of the cathode composition.

[0160] In another embodiment, the negative electrode binder may be in an amount of 5 parts by weight or more and 12 parts by weight or less, 7 parts by weight or more and 11 parts by weight or less, or 8 parts by weight or more and 11 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0161] In the case of the negative electrode for a lithium secondary battery according to the present invention, since the silicon-based active material is used in the above weight portion to maximize capacity characteristics, the volume expansion during charge and discharge is greater than when a conventional carbon-based active material is used as the main active material. Accordingly, the negative electrode binder in the above content portion is provided with the characteristic of being able to efficiently control the volume expansion of the silicon-based active material with high rigidity during charge and discharge.

[0162]

[0163] cathode

[0164] According to one embodiment of the present invention, a negative electrode is provided, which includes a negative electrode current collector layer and a negative electrode active material layer including the negative electrode active material formed on one or both sides of the negative electrode current collector layer.

[0165] In one embodiment of the present invention, the negative electrode for the secondary battery can be formed by applying and drying the negative electrode slurry on one or both sides of the negative electrode current collector layer.

[0166] In one embodiment of the present invention, the solid content of the cathode slurry can satisfy 5% or more and 55% or less.

[0167] In another embodiment, the solid content of the cathode slurry can satisfy a range of 5% or more and 55% or less, 7% or more and 35% or less, or 10% or more and 30% or less.

[0168] The solid content of the above negative electrode slurry may mean the content of the negative electrode active material, conductive material, and binder excluding the solvent in the negative electrode slurry, and may mean the sum of the negative electrode active material, conductive material, and binder based on 100 parts by weight of the negative electrode slurry.

[0169] When the solid content of the above negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration, and thus has the characteristic of efficiently forming the negative electrode active material layer.

[0170] In one embodiment of the present application, the slurry solvent may be used without limitation as long as it is used in the art, and specifically, water, acetone or NMP may be used.

[0171] In one embodiment of the present invention, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0172] In one 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.

[0173] In the present invention, the negative electrode active material layer may refer to the thickness of a single-layer negative electrode active material layer when formed on one surface of the negative electrode current collector layer.

[0174] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0175] In one 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.

[0176] In another embodiment, the porosity of the negative electrode active material layer can satisfy a range of 40% or more and 60% or less, 45% or more and 60% or less, or 50% or more and 55% or less.

[0177]

[0178] secondary batteries

[0179] According to one embodiment of the present invention, a secondary battery is provided, which includes a positive electrode, a negative electrode according to the present invention, a separator provided between the positive electrode and the negative electrode, and an electrolyte.

[0180] A secondary battery according to one embodiment of the present specification may particularly include the negative electrode for a secondary battery as described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof will be omitted.

[0181] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and including the positive electrode active material.

[0182] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 µm to 500 µm, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0183] The above positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.6); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxide represented by O2 (wherein 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 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0184] In one embodiment of the present invention, the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium composite transition metal compound includes single particles or secondary particles, and the average particle diameter (D50) of the single particles may be 1 μm or more.

[0185] For example, the average particle diameter (D50) of the single particle may be 1 ㎛ or more and 12 ㎛ or less, 1 ㎛ or more and 8 ㎛ or less, 1 ㎛ or more and 6 ㎛ or less, more than 1 ㎛ and 12 ㎛ or less, more than 1 ㎛ and 8 ㎛ or less, or more than 1 ㎛ and 6 ㎛ or less.

[0186] Even if the above single particles are formed with a small particle size of 1 ㎛ or more and 12 ㎛ or less in average particle diameter (D50), the particle strength can be excellent. For example, the above single particles can have a particle strength of 650 kgf / cm. 2 When rolled with a force of 100 to 300 MPa, the particle strength can be achieved. Accordingly, the single particle can be rolled with a force of 650 kgf / cm. 2 Even when rolled with a strong force, the phenomenon of fine particle increase in the electrode due to particle breakage is alleviated, thereby improving the life characteristics of the battery.

[0187] The above single particles can be manufactured by mixing and calcining a transition metal precursor and a lithium source material. The secondary particles can be manufactured using a different method from the above single particles, and their composition may be the same as or different from that of the single particles.

[0188] The method for forming the above single particles is not particularly limited, but can generally be formed by increasing the firing temperature to cause underfiring, using additives such as grain growth accelerators that aid underfiring, or by changing the starting material.

[0189] For example, the sintering is performed at a temperature capable of forming single particles. To form these, the sintering must be performed at a higher temperature than that during secondary particle production. For example, when the precursor composition is the same, the sintering must be performed at a temperature that is about 30°C to 100°C higher than that during secondary particle production. The sintering temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is intended to be formed into single particles, the sintering temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the sintering temperature satisfies the above range, a cathode active material including single particles having excellent electrochemical properties can be produced. When the sintering temperature is lower than 790°C, a cathode active material including a lithium complex transition metal compound in the form of secondary particles can be manufactured, and when it exceeds 950°C, excessive sintering occurs and a layered crystal structure is not properly formed, which may result in a deterioration in electrochemical properties.

[0190] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle formed of one primary particle and a pseudo-single particle form that is an agglomeration of 30 or fewer primary particles.

[0191] Specifically, in the present invention, the single particle may be in the form of a single particle composed of one primary particle or a quasi-single particle that is an aggregate of 30 or fewer primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles.

[0192] In one embodiment of the present invention, the lithium composite transition metal compound, which is the positive electrode active material, further includes secondary particles, and the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles.

[0193] In the present invention, the single particle may be in the form of a single particle composed of one primary particle or a quasi-single particle that is an aggregate of 30 or fewer primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles.

[0194] The lithium complex transition metal compound described above may further include secondary particles. The term "secondary particle" refers to a form formed by the aggregation of primary particles, and can be distinguished from the concept of a single particle, which includes a quasi-single particle form that is a single primary particle, a single particle, or an aggregation of 30 or fewer primary particles.

[0195] The particle diameter (D50) of the secondary particles may be 1 ㎛ to 20 ㎛, 2 ㎛ to 17 ㎛, and preferably 3 ㎛ to 15 ㎛. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g to 10 m 2 / g can be, preferably 0.1 m 2 / g to 1 m 2 / g may be, more preferably 0.3 m 2 / g to 0.8 m 2 / g could be.

[0196] In a further embodiment of the present invention, the secondary particles are aggregates of primary particles, and the average particle diameter (D50) of the primary particles is 0.5 µm to 3 µm. Specifically, the secondary particles may be in the form of aggregates of hundreds of primary particles, and the average particle diameter (D50) of the primary particles may be 0.6 µm to 2.8 µm, 0.8 µm to 2.5 µm, or 0.8 µm to 1.5 µm.

[0197] When the average particle diameter (D50) of the primary particles satisfies the above range, a single-particle positive electrode active material having excellent electrochemical properties can be formed. If the average particle diameter (D50) of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, which reduces the effect of suppressing particle breakage during rolling. In addition, if the average particle diameter (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, which may increase resistance and deteriorate output characteristics.

[0198] According to a further embodiment of the present invention, the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles. Accordingly, even if the single particles are formed with a small particle diameter, their particle strength can be excellent, and thus, the phenomenon of an increase in fine particles within the electrode due to particle breakage can be alleviated, thereby improving the life characteristics of the battery.

[0199] In one embodiment of the present invention, the average particle diameter (D50) of the single particles is 1 ㎛ to 18 ㎛ smaller than the average particle diameter (D50) of the secondary particles.

[0200] For example, the average particle diameter (D50) of the single particles may be 1 ㎛ to 16 ㎛ smaller than the average particle diameter (D50) of the secondary particles, may be 1.5 ㎛ to 15 ㎛ smaller, or may be 2 ㎛ to 14 ㎛ smaller.

[0201] When the average particle diameter (D50) of the single particle is smaller than the average particle diameter (D50) of the secondary particle, for example, when the above range is satisfied, the single particle can have excellent particle strength even if it is formed into a small particle diameter, and as a result, the phenomenon of an increase in fine particles in the electrode due to particle breakage is alleviated, thereby improving the life characteristics of the battery and improving the energy density.

[0202] According to a further embodiment of the present invention, the single particles are included in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material. The single particles may be included in an amount of 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.

[0203] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more relative to 100 parts by weight of the positive electrode active material. The single particles may be included in an amount of 100 parts by weight or less relative to 100 parts by weight of the positive electrode active material.

[0204] When the single particles in the above range are included, excellent battery characteristics can be exhibited in combination with the aforementioned negative electrode material. In particular, when the single particles are 15 parts by weight or more, the phenomenon of fine particles increasing in the electrode due to particle breakage during the rolling process after electrode production can be alleviated, thereby improving the life characteristics of the battery.

[0205] In one embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. 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 secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0206] When the above range is satisfied, the aforementioned effect due to the presence of a single-particle positive electrode active material can be maximized. When including a secondary particle positive electrode active material, the component may be the same as the component exemplified by the single-particle positive electrode active material described above, or may be a different component, and may refer to a form in which the single-particle form is aggregated.

[0207] In one embodiment of the present invention, the positive electrode active material may be included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 98 parts by weight or more and 99.9 parts by weight or less, in 100 parts by weight of the positive electrode active material layer.

[0208] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0209] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0210] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0211] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0212] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0213] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0214] As the above non-aqueous organic solvent, for example, aprotic solvents such as N-methyl-2-pyrrolidinone, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate Organic solvents may be used.

[0215] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0216] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - , Cl - , I - , NO3- , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0217] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0218]

[0219] Battery modules and battery packs

[0220] One embodiment of the present invention provides a battery module including a secondary battery according to one embodiment of the present invention.

[0221] One embodiment of the present invention provides a battery pack including a secondary battery according to one embodiment of the present invention.

[0222] One embodiment of the present invention provides a battery pack including a battery module according to one embodiment of the present invention.

[0223] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack using the secondary battery or the battery module. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0224] Although the present invention has been described with reference to 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 contents.

[0225] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0226]

[0227] <Manufacturing Example>

[0228] Example 1

[0229] 1) Manufacturing of negative active material

[0230] Pure Si powder (average particle diameter (D50): 5.0 ㎛) was prepared as a silicon-based active material, and Al(OH)3 (average particle diameter (D50): 700 nm) was prepared as an inorganic flame retardant. The silicon-based active material and the inorganic flame retardant were mixed at a weight ratio of 90:10, and then a dry ball mill method was used to form an inorganic flame retardant coating layer on the surface of the silicon-based active material, thereby manufacturing a negative electrode active material (average thickness of the coating layer: 1.5 ㎛).

[0231] 2) Manufacturing of cathode

[0232] A negative electrode composition was prepared by preparing the negative electrode active material manufactured in the above 1), SWCNT (single-walled carbon nanotube) as a conductive material, and polyacrylamide (PAM) as a binder in a weight ratio of 90:0.8:9.2, and adding it to distilled water as a solvent to prepare a negative electrode slurry (solid content 26 wt%).

[0233] Specifically, SWCNT, PAM, and distilled water were dispersed using a homogenous mixer at 2,500 rpm for 30 minutes, and then the negative electrode active material was added and dispersed at 2,500 rpm for 30 minutes to prepare a negative electrode slurry.

[0234] The above SWCNT has a BET surface area of ​​1000 m 2 / g to 1500m 2 / g, and an aspect ratio of 10,000 or more was used, and a solution dispersed in CMC (Carboxymethyl Cellulose) was used.

[0235] The above PAM was used in an aqueous form, having 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 an aqueous form, and the weight average molecular weight and number average molecular weight were measured using aqueous GPC (Gel permeation chromatography).

[0236] The negative electrode slurry was applied to both sides of a copper current collector (thickness 26㎛) as a negative electrode current collector layer at 87.7mg / 25cm 2 The negative electrode was manufactured by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness 33 μm) (negative electrode thickness 59 μm, porosity 55.0%).

[0237] 3) Manufacturing of secondary batteries

[0238] LiNi as a cathode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15㎛), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were prepared in a weight ratio of 97:1.5:1.5, and added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a cathode slurry to prepare a cathode slurry (solid content concentration: 78 wt%).

[0239] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12㎛) as a positive electrode collector at a density of 537mg / 25cm. 2 A positive electrode was manufactured by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) (positive electrode thickness: 77 μm, porosity 26%).

[0240] A lithium secondary battery was manufactured by interposing a polyethylene separator between the positive electrode and the negative electrode and injecting an electrolyte.

[0241] The above electrolyte was used in an organic solvent containing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) mixed in a volume ratio of 10:90, vinylene carbonate (VC) added at 3 wt% based on the total weight of the electrolyte, and LiPF6 added at a concentration of 1 M as a lithium salt.

[0242]

[0243] Example 2

[0244] In the manufacturing method of Example 1, when manufacturing the negative active material in 1), a secondary battery was manufactured in the same manner as Example 1, except that a silicon-based active material was manufactured in the following manner.

[0245] SiO particles were prepared as silicon-based particles. The SiO particles were mixed with Mg as a metal-containing material, and the mixture was heat-treated at 1,200°C for 3 hours to produce SiO particles having Mg distributed on the surface and / or inside. During the preparation, a carbon layer was formed on the SiO particles having Mg distributed on the surface and / or inside by chemical vapor deposition (CVD) using methane as a hydrocarbon gas at 950°C, thereby producing a silicon-based active material (average particle diameter (D50): 6 μm). In the silicon-based active material, the weight ratio of silicon-based particles: metal (Mg): carbon layer was 85:10:5 (average thickness of the coating layer: 1.5 μm).

[0246] That is, Example 2 was manufactured using Mg-doped SiO instead of Si powder as a silicon-based active material, compared to Example 1.

[0247]

[0248] Example 3

[0249] In the manufacturing method of Example 1, when manufacturing the negative active material in the above 1), a secondary battery was manufactured in the same manner as Example 1 (average thickness of the coating layer: 0.2 ㎛), except that Al(OH)3 (average particle diameter (D50): 100 nm) was used as an inorganic flame retardant.

[0250] That is, Example 3 was manufactured using an inorganic flame retardant having a different average particle size compared to Example 1.

[0251]

[0252] Example 4

[0253] In the manufacturing method of Example 1, when manufacturing the negative active material in the above 1), a secondary battery was manufactured in the same manner as Example 1 (average thickness of the coating layer: 3 ㎛), except that Mg(OH)2 (average particle diameter (D50): 900 nm) was used as an inorganic flame retardant.

[0254] That is, Example 4 was manufactured using Mg(OH)2 instead of Al(OH)3 as an inorganic flame retardant having a different average particle size compared to Example 1.

[0255]

[0256] Example 5

[0257] Among the manufacturing methods of Example 1, a secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode composition was manufactured in the following manner in 2).

[0258] The negative electrode active material includes the negative electrode active material manufactured in Example 1 as the first negative electrode active material (15 parts by weight based on 100 parts by weight of the sum of the first and second negative electrode active materials), graphite as the second negative electrode active material (artificial graphite: natural graphite = 70:30 weight ratio, 85 parts by weight based on 100 parts by weight of the sum of the first and second negative electrode active materials), and SWCNT (single-walled carbon nanotube) as a conductive material and polyacrylamide (PAM) as a binder were prepared in a weight ratio of 90:0.8:9.2 to manufacture a negative electrode composition.

[0259] That is, Example 5 was manufactured using a negative electrode composition mixed with a carbon-based active material.

[0260]

[0261] Example 6

[0262] A secondary battery was manufactured using the same method as Example 1, except that Si / C particles (average particle diameter (D50): 7.0 μm) were used as the silicon-based active material in the manufacturing method of Example 1.

[0263] That is, Example 6 was manufactured using Si / C particles instead of Si powder as a silicon-based active material, compared to Example 1.

[0264]

[0265] Example 7

[0266] In Example 1, when manufacturing the negative active material, a secondary battery was manufactured in the same manner as in Example 1, except that the average thickness of the inorganic flame retardant coating layer was 20 nm.

[0267]

[0268] Example 8

[0269] In Example 2, when manufacturing the negative active material, a secondary battery was manufactured in the same manner as in Example 2, except that the average thickness of the inorganic flame retardant coating layer was 20 nm.

[0270]

[0271] Comparative Example 1

[0272] A secondary battery was manufactured in the same manner as in Example 1, except that when manufacturing the negative electrode in the above 2) of the manufacturing method of Example 1, Pure Si powder (average particle size (D50): 5.0 ㎛) was used as the negative electrode active material instead of the negative electrode active material manufactured in the above 1).

[0273] That is, Comparative Example 1 was manufactured using a negative electrode active material that did not include an inorganic flame retardant coating layer.

[0274]

[0275] Comparative Example 2

[0276] In the manufacturing method of Example 1, when manufacturing the negative electrode in the above 2), a secondary battery was manufactured in the same manner as Example 1, except that Pure Si (average particle diameter (D50): 5.0 ㎛) was used as the negative electrode active material instead of the negative electrode active material manufactured in the above 1), and Al(OH)3 (average particle diameter (D50): 700 nm) was further included as an inorganic flame retardant in the negative electrode slurry.

[0277] That is, Comparative Example 2 was manufactured using a negative electrode in which the negative active material did not include a coating layer and the inorganic flame retardant was evenly dispersed and distributed on the negative active material layer.

[0278]

[0279] Comparative Example 3

[0280] In the manufacturing method of Example 1, when manufacturing the negative active material in the above 1), a secondary battery was manufactured in the same manner as Example 1 (average thickness of the coating layer: 3 ㎛), except that a halogen-based flame retardant (average particle diameter (D50): 100 nm) was used.

[0281] That is, Comparative Example 3 was manufactured using a halogen-based flame retardant as an inorganic flame retardant.

[0282]

[0283] Comparative Example 4

[0284] A secondary battery was manufactured in the same manner as in Example 6, except that a negative active material was used that did not include an inorganic flame retardant coating layer on the surface of the silicon-based active material in the manufacturing method of Example 6.

[0285] That is, Comparative Example 4 was manufactured using only Si / C particles without a coating layer as a negative active material.

[0286]

[0287] Comparative Example 5

[0288] In Example 1, when manufacturing the negative active material, a secondary battery was manufactured in the same manner as in Example 1, except that the average thickness of the inorganic flame retardant coating layer was 5 nm.

[0289]

[0290] Comparative Example 6

[0291] In Example 1, when manufacturing the negative active material, a secondary battery was manufactured in the same manner as in Example 1, except that the average thickness of the inorganic flame retardant coating layer was 15 nm.

[0292]

[0293] Comparative Example 7

[0294] In Example 2, when manufacturing the negative active material, a secondary battery was manufactured in the same manner as in Example 1, except that the average thickness of the inorganic flame retardant coating layer was 5 nm.

[0295]

[0296] Comparative Example 8

[0297] In Example 2, when manufacturing the negative active material, a secondary battery was manufactured in the same manner as in Example 1, except that the average thickness of the inorganic flame retardant coating layer was 15 nm.

[0298]

[0299] The following items were evaluated for the manufactured examples and comparative examples, and the results are shown in Table 1.

[0300]

[0301] <Experimental Example: Capacity Retention Rate Evaluation>

[0302] Lithium secondary batteries were subjected to in-situ cycling tests at 4.2-3.0 V 1C / 0.5C, and 0.33C / 0.33C charge / discharge (4.2-3.0 V) was performed every 50 cycles. Capacity retention was measured after 200 cycles through this process.

[0303] Capacity retention rate (%) = {(discharge capacity in the Nth cycle) / (discharge capacity in the first cycle)} x 100 %

[0304]

[0305] <Experimental Example: Evaluation of Resistance Increase Rate>

[0306] In the capacity retention rate evaluation, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33c (4.2-3.0V) every 50 cycles during the test, and then the resistance was measured by discharging at 2.5C pulse at 50% of SOC after 200 cycles, and the resistance increase rate was compared and analyzed.

[0307] For the above resistance increase rate measurement evaluation, data at 200 cycles were calculated for each.

[0308]

[0309] <Experimental Example: Evaluation of Maximum Temperature at Ignition>

[0310] The maximum temperature at ignition was measured for the secondary battery manufactured as described above.

[0311] In the manufactured secondary battery, the temperature of the charged cell was gradually increased using a heat pad to induce cell ignition. The cathode surface temperature was measured, and the maximum temperature measured is shown in Table 1.

[0312]

[0313] Capacity retention rate after 200 cycles (%) Resistance increase rate after 200 cycles (%) (3.0-4.2 V, 1 C / 0.5 C) Maximum temperature at cell ignition (℃) Example 1857532 Example 2876502 Example 3856545 Example 4848581 Example 5899449 Example 6887490 Example 7857555 Example 8876526 Comparative Example 1858679 Comparative Example 2857610 Comparative Example 3867635 Comparative Example 4876603 Comparative Example 5857620 Comparative Example 6857611 Comparative Example 7876588 Comparative Example 8876580

[0314] Referring to Table 1, in the case of Examples 1 to 8 including a negative active material including an inorganic flame retardant coating layer on the surface of a silicon-based active material, it was confirmed that the maximum temperature upon ignition was lower than in Comparative Example 1 which did not include an inorganic flame retardant coating layer on the surface of a silicon-based active material. This is interpreted as being because, as the temperature of the cell rises, the inorganic flame retardant decomposes above a certain temperature, suppressing ignition through an endothermic reaction, and exhibiting an additional ignition suppression effect due to the latent heat of the water generated by the decomposition reaction of the inorganic flame retardant. In addition, in the case of Examples 1 to 8 including a negative active material including an inorganic flame retardant coating layer on the surface of a silicon-based active material, the maximum temperature upon cell ignition was lower, while the capacity retention rate and resistance increase rate showed characteristics equivalent to or improved compared to Comparative Example 1. It was confirmed that the inorganic flame retardant coating layer on the surface of a silicon-based active material can delay ignition within the cell and improve the thermal safety of the cell without degrading the performance of the cell.

[0315] Meanwhile, in the case of Comparative Example 2, the maximum temperature upon ignition was lower than in Comparative Example 1, but it was confirmed that the maximum temperature upon ignition was higher than in Examples 1 to 8. This is due to the method of applying the inorganic flame retardant, and it is understood that in the case of the form in which the inorganic flame retardant is evenly dispersed throughout the electrode (Comparative Example 2), the heat generated on the surface of the silicon-based active material cannot be effectively suppressed.

[0316] Furthermore, in the case of Example 6, since the negative active material includes an inorganic flame retardant coating layer on the surface of the silicon-based active material, it was confirmed that the maximum temperature at the time of cell ignition was lower than that of Comparative Example 4, which is an negative active material using the same type of silicon-based active material.

[0317] In addition, in the case of Examples 7 and 8, a 20 nm thick inorganic flame retardant coating layer was applied to Pure Si and SiOx, respectively, and it was confirmed that an excellent thermal stability improvement effect was shown compared to Comparative Examples 5 to 8, in which relatively thinner 5 nm and 15 nm thick inorganic flame retardant coating layers were applied. That is, when the average thickness of the inorganic flame retardant coating layer was 20 nm or more, for example, 0.02 ㎛ or more, it was confirmed that the heat resistance effect was excellent. On the other hand, when the average thickness of the inorganic flame retardant coating layer was less than 20 nm, for example, less than 0.02 ㎛, it was confirmed that the maximum temperature at the time of cell ignition was higher due to the inorganic flame retardant coating layer having a thinner thickness than the examples.

[0318] In the case of Comparative Example 3 (when a halogen-based flame retardant is used), the inorganic flame retardant of Examples 1 to 8 decomposes at a relatively low temperature, which may cause a change in the structure of the coating layer. Therefore, it was confirmed that the effect of improving thermal stability was reduced in the thermal runaway situation of an actual cell, resulting in a lower effect compared to the Examples.

[0319] The detailed description above exemplifies and explains the present invention. Furthermore, the foregoing merely illustrates and describes preferred embodiments of the present invention. As described above, the present invention can be used in various other combinations, modifications, and environments, and changes or modifications can be made within the scope of the invention disclosed herein, the scope equivalent to the above-described disclosure, and / or the scope of technology or knowledge in the art. Therefore, the detailed description of the invention above is not intended to limit the present invention to the disclosed embodiments. Furthermore, the appended claims should be construed to include other embodiments.

Claims

1. Silicon-based active material; and It includes a coating layer provided on a silicon-based active material, The above silicon-based active material is Si, SiOx(0 <x<2) 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함하고, A negative electrode active material, wherein the coating layer contains an inorganic flame retardant.

2. In claim 1, The above inorganic flame retardant is a negative electrode active material in which an endothermic reaction occurs at 100°C to 250°C.

3. In claim 2, A negative electrode active material wherein the above endothermic reaction is a dehydration reaction.

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

5. In claim 1, The above silicon-based active material contains Si, The negative electrode active material, wherein the Si is contained in an amount of 70 to 100 parts by weight based on 100 parts by weight of the silicon-based active material.

6. In claim 1, The above SiOx(0 <x<2)는 상기 SiOx(0<x<2)의 표면, 내부, 또는 표면 및 내부에 분포된 금속을 더 포함하고, A negative electrode active material, wherein the metal comprises at least one selected from the group consisting of Li, Mg, and Al.

7. In claim 1, A negative electrode active material, wherein the average thickness of the coating layer is 0.02 ㎛ to 10 ㎛.

8. In claim 1, A negative electrode active material containing 95 parts by weight or more of an inorganic flame retardant based on 100 parts by weight of the above coating layer.

9. In claim 1, A negative electrode active material, wherein the average particle diameter (D50) of the above-mentioned inorganic flame retardant is 0.05 ㎛ to 1.5 ㎛.

10. A negative active material according to any one of claims 1 to 9; negative binder; and A cathode composition comprising a cathode conductive material.

11. In claim 10, The above negative electrode active material is a first negative electrode active material, A negative electrode composition further comprising a carbon-based active material as a second negative electrode active material.

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

13. In claim 11, A negative electrode composition, wherein the first negative electrode active material is 1 to 20 parts by weight based on 100 parts by weight of the sum of the first and second negative electrode active materials.

14. Negative current collector layer; and Including a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, A negative electrode comprising the negative electrode composition according to claim 10, wherein the negative electrode active material layer is a negative electrode.

15. Bipolar; A cathode according to claim 14; and A secondary battery comprising a separator provided between the positive electrode and the negative electrode; and an electrolyte.

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

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

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