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

Abstract

This specification relates to a negative electrode active material and a negative electrode and secondary battery comprising the same. According to one embodiment of the invention, the negative electrode active material is provided, comprising: a silicon-based active material; and a coating disposed on the silicon-based active material, wherein the silicon-based active material comprises materials selected from Si and SiO2. x (0

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2024-0114073, filed on August 26, 2024, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to a negative electrode active material, a negative electrode composition, a negative electrode, a secondary battery, a battery module, and a battery pack. Background Technology

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

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

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

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

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

[0008] <List of References>

[0009] Japanese Patent Application Publication No. 2009-080971 Summary of the Invention

[0010] Technical issues

[0011] The present invention is dedicated to providing a negative electrode active material, a negative electrode, and a secondary battery that employ a silicon-based active material, thereby having a high capacity and improving safety under operating conditions.

[0012] Technical Solution

[0013] An exemplary embodiment of the present invention provides a negative electrode active material comprising: a silicon-based active material; and a coating provided on the silicon-based active material, wherein the silicon-based active material comprises one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, the coating comprises a metal oxide, the content of the metal oxide is 10 parts by weight or more and 30 parts by weight or less relative to 100 parts by weight of the negative electrode active material, and the average thickness of the coating is 0.01 μm or more and 5 μm or less.

[0014] Another exemplary embodiment of the present invention provides a negative electrode composition comprising: a negative electrode active material according to an exemplary embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material.

[0015] Another exemplary embodiment of the present invention provides a negative electrode comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or two surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode composition according to an exemplary embodiment of the present invention.

[0016] Another exemplary embodiment of the present invention provides a secondary battery comprising a negative electrode according to an exemplary embodiment of the present invention.

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

[0018] Another exemplary embodiment of the present invention provides a battery pack comprising a secondary battery or a battery module according to an exemplary embodiment of the present invention.

[0019] Advantageous Effects

[0020] When the negative electrode active material according to an exemplary embodiment of the present invention is applied to a negative electrode, it is possible to improve the life characteristics while maintaining a high capacity.

[0021] When the negative electrode active material according to an exemplary embodiment of the present invention is applied to a negative electrode, it is possible to suppress ignition at high temperatures without deteriorating performance, and thus improve thermal safety.

[0022] Specifically, according to the present invention, the coating contains a specific amount of metal oxide and has a thickness of 0.01 μm or more and 5 μm or less. Therefore, if the thickness of the coating exceeds the range defined by the present invention, the coating exists in a porous form even when the metal oxide content is satisfied, and in this case, a stable barrier cannot be formed on the surface, which may lead to thermal stability problems. Furthermore, if the thickness of the coating is below the range defined by the present invention, the coating is formed in a high-density form, which is detrimental to battery operation in terms of resistance related to lithium-ion transport. Therefore, the present invention is characterized by maintaining the metal oxide content at a level effective for thermal stability by including an optimal amount of metal oxide in the coating and adjusting the thickness of the metal oxide layer. Detailed Implementation

[0023] Before describing the present invention, some terms will be defined.

[0024] As used herein, when a part is described as "including", "containing", or "having" a constituent element, unless otherwise specifically described, this does not mean that other constituent elements are excluded, but rather that other constituent elements may be included.

[0025] As used in this article, "p to q" refers to the range "above p and below q".

[0026] As used herein, "specific surface area" is measured by the BET method, specifically using a BELSORP-mini II commercially available from BEL Japan, calculated from the amount of nitrogen adsorbed at liquid nitrogen temperature (77K). That is, in this specification, BET specific surface area can refer to the specific surface area measured by the above method. BET specific surface area can be measured using nitrogen (N2) according to DIN 66131.

[0027] As used herein, "Dn" refers to the particle size distribution, specifically the particle size at the n% point in the cumulative number distribution of particles according to particle size. That is, D50 is the particle size (center particle size) at the 50% point in the cumulative number distribution of particles according to particle size, D90 is the particle size at the 90% point, and D10 is the particle size at the 10% point. Alternatively, the center particle size can be measured using laser diffraction. Specifically, after dispersing the powder to be tested in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500), where the difference in diffraction pattern according to particle size is measured as the laser beam passes through the particles, and then the particle size distribution is calculated.

[0028] In one exemplary embodiment of the present invention, particle size or particle diameter may refer to the average or representative diameter of the individual particles constituting the metal powder.

[0029] As used herein, describing a polymer as "containing a monomer as a monomeric unit" means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. As used herein, when describing a polymer as containing a monomer, this should be interpreted in the same way as when the polymer contains a monomer as a monomeric unit.

[0030] As used herein, unless specified as a homopolymer, the term “polymer” should be understood in a broad sense to include copolymers.

[0031] As used herein, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers with different degrees of polymerization (standard samples) as standard materials. Unless otherwise specified, molecular weight as used herein refers to weight-average molecular weight.

[0032] Exemplary embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention may be implemented in many different forms and is not limited to the following description.

[0033] Lithium-ion batteries may self-heat due to external impacts or abnormal battery behavior. When the internal temperature of the battery rises due to heat, the separator may shrink when it reaches or exceeds a certain temperature, which may cause an internal short circuit between the positive and negative electrodes. An internal short circuit may lead to thermal runaway and heat propagation within the battery. Thermal runaway may cause the internal temperature of the battery to rise rapidly and generate gas, which may result in a serious fire or explosion.

[0034] In existing lithium-ion batteries, there is no separate material besides the separator to prevent internal short circuits, making it difficult to suppress internal ignition when a certain temperature is reached or exceeded. This is particularly problematic for anodes containing silicon-based anode active materials. Compared to graphite-based anodes, silicon-based anodes offer higher energy density. However, due to the large amount of lithium and lithium oxide per unit area, silicon-based anodes exhibit lower thermal stability and are more prone to battery thermal runaway. In the event of a fire, thermal runaway can propagate more violently than with graphite-based anodes.

[0035] In addition, the negative electrode containing the silicon-based negative electrode active material undergoes significant volume expansion during charge and discharge. Therefore, a SEI layer is continuously formed under operating conditions. Thus, the formed thick SEI layer decomposes under the battery operating conditions, and since the decomposition of the SEI layer may promote ignition, additional measures are required to improve the safety of the lithium secondary battery by enhancing the high-temperature stability and preventing internal short circuits.

[0036] For this purpose, various methods have been considered to prevent thermal runaway in the battery, such as forming a separate coating on the separator. However, even when a separate coating is formed on the separator, it has been confirmed that the separator substrate shrinks within the temperature range where thermal runaway becomes a problem, resulting in an internal short circuit and a rapid increase in the internal temperature of the battery, leading to ignition inside the battery.

[0037] Therefore, the present inventors have envisioned that by providing a silicon-based active material having a surface treated with a metal oxide of a specific thickness as the negative electrode active material, it is possible to obtain the advantages of an electrode using a high-capacity silicon-based negative electrode active material while suppressing the temperature rise inside the negative electrode, thereby delaying the situation where the internal temperature of the battery rises above a certain level.

[0038] Negative electrode active materials

[0039] According to an exemplary embodiment of the present invention, there is provided a negative electrode active material comprising: a silicon-based active material; and a coating provided on the silicon-based active material, wherein the silicon-based active material comprises one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, and the coating comprises a metal oxide.

[0040] According to an exemplary embodiment of the present invention, there is provided a negative electrode active material comprising: a silicon-based active material; and a coating provided on at least one surface of the silicon-based active material, wherein the silicon-based active material comprises one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, and the coating comprises a metal oxide.

[0041] According to an exemplary embodiment of the present invention, the negative electrode active material has a structure comprising a core and a coating on the surface of the core, the core comprising a silicon-based active material, and the coating comprising a metal oxide. That is, the coating is provided on at least a part of the surface of the silicon-based active material.

[0042] According to an exemplary embodiment of the present invention, the coating is provided on the surface of the silicon-based active material.

[0043] According to an exemplary embodiment of the present invention, the metal oxide is a particle with excellent heat resistance, having a melting point equal to or higher than the thermal runaway temperature of a secondary battery (approximately 200°C), and is capable of preventing thermal runaway of batteries containing silicon-based negative electrode active materials under high-temperature conditions. Therefore, it can delay the rapid rise of the battery's internal temperature to the temperature at which the separator contracts, and even when the separator contracts due to the increased internal temperature, it can delay the occurrence of a direct internal short circuit between the positive and negative electrodes, thereby suppressing battery fires.

[0044] In the case of a negative electrode containing a silicon-based active material, lithium ions migrate during charging and discharging as they insert into and extract from the silicon-based active material under operating conditions. Specifically, lithium ions can form lithium oxide when they escape from the silicon-based active material during discharge. The formation of lithium oxide leads to internal heating in the battery, and due to the continuous occurrence of exothermic reactions, the internal temperature of the battery rises rapidly, resulting in thermal runaway. Therefore, the inventors of this invention have discovered that by providing a coating containing a metal oxide on the surface of the silicon-based negative electrode active material, the exothermic reactions during charging and discharging as described above can be suppressed.

[0045] That is, since the negative electrode active material according to an exemplary embodiment of the present invention is coated with a metal oxide having excellent heat resistance on the surface of the silicon-based active material, it is possible to suppress the rapid rise of the battery internal temperature from the level of the negative electrode active material.

[0046] Furthermore, since the metal oxide has high hardness, it has the property of enhancing the durability of the anode active material and suppressing the rapid volume expansion of the anode active material under working conditions when coated on the surface of the silicon-based anode active material.

[0047] According to an exemplary embodiment of the present invention, the metal oxide is made of M a O b (1≤a≤2,1≤b≤3) represents, where M is any one of Al, Ti and Mg.

[0048] According to an exemplary embodiment of the present invention, the metal oxide comprises one or more selected from the group consisting of Al2O3, TiO2 and MgO.

[0049] According to an exemplary embodiment of the present invention, the metal oxide is Al2O3.

[0050] According to an exemplary embodiment of the present invention, the average particle size (D50) of the metal oxide can be from 5 nm to 1 μm. For example, the average particle size (D50) of the metal oxide can be 5 nm or more, 10 nm or more, 50 nm or more, 100 nm or more, 200 nm or more, or 250 nm or more, and can be less than 1 μm, less than 900 nm, less than 800 nm, less than 700 nm, less than 600 nm, less than 500 nm, or less than 400 nm. When the average particle size of the metal oxide is within this specific range, a coating can be uniformly formed on the surface of the active material without interfering with the behavior of lithium ions under battery operating conditions. That is, if the average particle size of the metal oxide is below the lower limit, the coating formed on the surface of the active material makes it difficult to ensure pores (spaces) for lithium ion migration, thereby interfering with the behavior of lithium ions under battery operating conditions and increasing resistance. If the average particle size is above the upper limit, it is difficult to uniformly distribute the coating on the surface of the active material, making it difficult to control the coating thickness.

[0051] The average particle size of the metal oxide refers to the volume average particle size (sphere-equivalent particle size) obtained by converting each metal oxide particle into a sphere with the same volume, and this value can be obtained by observation with an electron microscope. That is, this value is obtained by observing the metal oxide with an electron microscope, measuring the diameter of more than 200 metal oxide particles in a given field of view, calculating the sphere-equivalent particle size of each particle, and determining their average value.

[0052] According to an exemplary embodiment of the present invention, the average thickness of the coating can be from 0.01 μm to 5 μm. For example, the average thickness of the coating can be greater than 0.01 μm, greater than 0.02 μm, greater than 0.05 μm, greater than 0.1 μm, greater than 0.5 μm, greater than 0.8 μm, greater than 1 μm, greater than 1.5 μm, or greater than 1.9 μm, and can be less than 5 μm, less than 4 μm, less than 3 μm, or less than 2 μm. When the average thickness of the coating is within this specific range, the heat resistance of the negative electrode active material can be improved without affecting the behavior of lithium ions under operating conditions. Furthermore, if the thickness of the coating exceeds this upper limit, the overall size of the negative electrode active material may become too large, making it difficult to uniformly distribute the negative electrode active material within the negative electrode.

[0053] According to an exemplary embodiment of the present invention, relative to 100 parts by weight of the negative electrode active material, the content of the metal oxide may be 10 to 30 parts by weight. For example, relative to 100 parts by weight of the negative electrode active material, the content of the metal oxide may be 10 parts by weight or more, and may be 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less. When the content of the metal oxide is within this specific range, the heat resistance can be improved without reducing the conductivity of the negative electrode active material.

[0054] According to an exemplary embodiment of the present invention, the weight ratio of the silicon-based active material to the metal oxide may be 70:30 to 99.9:0.1, 75:25 to 99.9:0.1, 80:20 to 99.9:0.1, 90:10 to 99.9:0.1, 75:25 to 99:1, 80:20 to 99:1, or 90:10 to 99:1. The weight ratio of the silicon-based active material to the metal oxide can be confirmed by the relationship between the battery capacity of the negative electrode of a coin-type half-cell containing the negative electrode active material and the unit weight capacity (specific capacity). For example, since the metal oxide does not exhibit capacity, the weight ratio can be confirmed by the difference between the battery capacity and the specific capacity.

[0055] According to an exemplary embodiment of the present invention, the negative electrode active material contains one or more selected from the group consisting of Si, SiO x (0 < x < 2) and Si / C as the silicon-based active material.

[0056] In an exemplary embodiment of the present invention, the negative electrode active material contains one or more selected from the group consisting of Si and SiO x (0 < x < 2) as the silicon-based active material.

[0057] In an exemplary embodiment of the present invention, the silicon-based active material is Si.

[0058] According to an exemplary embodiment of the present invention, the negative electrode active material contains one or more selected from the group consisting of Si, SiO x (0 < x < 2) and Si / C as the silicon-based active material, the silicon-based active material contains Si, and relative to 100 parts by weight of the silicon-based active material, the content of Si is 70 to 99 parts by weight.

[0059] In another exemplary embodiment, with respect to 100 parts by weight of the silicon-based active material, the content of Si may be 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, and may be 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.

[0060] That is, in an exemplary embodiment of the present invention, the negative electrode active material contains Si as the silicon-based active material, and with respect to 100 parts by weight of the silicon-based active material, the content of Si is 70 parts by weight or more.

[0061] In the present specification, Si refers to pure silicon (Si) particles, that is, pure Si. For example, using pure silicon (Si) particles as the silicon-based active material may mean that, as described above, with respect to 100 parts by weight of all the negative electrode active materials, the content of pure Si particles (SiO x (x = 0)) is within this specific range.

[0062] In an exemplary embodiment of the present invention, the silicon-based active material may be formed of silicon-based particles having 100 parts by weight of Si with respect to 100 parts by weight of the negative electrode active material.

[0063] In an exemplary embodiment of the present invention, the silicon-based active material may contain metal impurities. In this case, the impurities are metals that may generally be contained in the silicon-based active material. Specifically, with respect to 100 parts by weight of the negative electrode active material, the content thereof may be 0.1 part by weight or less.

[0064] That is, in an exemplary embodiment of the present invention, the silicon-based active material is different from the Si alloy, and the capacity and structural stability of the silicon-based active material according to an exemplary embodiment of the present invention are higher than those of the silicon-based active material in which the Si alloy is used as the main material.

[0065] In another exemplary embodiment, the silicon-based active material contains SiO x (0 < x < 2).

[0066] In the case of SiO x Since SiO2 (x = 2) does not react with lithium ions and cannot store lithium, it is preferably within the range (0 < x < 2). Specifically, with respect to the structural stability of the active material, x may be 0.5 ≤ x ≤ 1.5.

[0067] The SiO x (0 < x < 2) may further contain distributed in SiO xMetal on the surface, inside, or both on the surface and inside of the (0 < x < 2) particles. The metal is distributed on the surface and / or inside of the silicon-based active material, and may be included in the silicon-based active material in order to reduce the proportion of irreversible phases (e.g., SiO2) in the silicon-based active material and increase the efficiency of the active material.

[0068] The metal may be at least one selected from the group consisting of Li, Mg, and Al, at least one selected from the group consisting of Li and Mg, or Mg, because Mg can effectively achieve the effect of preventing damage to the silicon-based oxide particles and has low reactivity with moisture, thereby further improving the life characteristics of the negative electrode active material.

[0069] The content of the metal in the silicon-based active material may be 0.1 wt% to 25 wt% or 3 wt% to 15 wt%, which is preferred because it can increase the efficiency of the active material without reducing the capacity.

[0070] In an exemplary 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.

[0071] In an exemplary embodiment of the present invention, the coating is uniformly provided on the surface of the silicon-based active material. The coating is provided on the surface of the silicon-based active material, thereby reducing the area of the silicon-based active material exposed to the outside, minimizing the heat generation that occurs under battery operating conditions, and preventing excessive volume changes of the silicon-based active material.

[0072] In an exemplary embodiment of the present invention, the metal oxide is composed of M a O b(1≤a≤2, 1≤b≤3) indicates that M is any one of Al, Ti, and Mg, and the M / Si elemental ratio on the surface of the negative electrode active material is 70 or more. For example, the M / Si elemental ratio on the surface of the negative electrode active material can be 70 or more, 75 or more, or 85 or more, and can be less than 100, less than 100, less than 99, less than 95, less than 90, or less than 89. The fact that the M / Si elemental ratio on the surface of the negative electrode active material is within this specific range means that the coating containing the metal oxide is formed to almost cover the surface of the silicon-based active material, and the area of ​​silicon-based active material exposed on the surface of the negative electrode active material is small. Therefore, when the elemental ratio is within this specific range, the area of ​​silicon-based active material exposed to the outside can be reduced, thereby minimizing the heat generation that occurs under battery operating conditions and preventing excessive volume change of the silicon-based active material.

[0073] In one exemplary embodiment of the present invention, the coating is formed on the surface of the silicon-based active material. That is, in one exemplary embodiment of the present invention, when the total area of ​​the silicon-based active material is 100%, the area of ​​the coating is 50% or more. For example, the area of ​​the coating can be 50% or more, 60% or more, 70% or more, or 80% or more, and can be less than 100%, less than 100%, less than 99%, less than 95%, or less than 90%.

[0074] The M / Si elemental ratio refers to the ratio or content of M (any one of Al, Ti, and Mg) and Si present on the surface of the negative electrode active material. The M / Si elemental ratio can be measured using surface analysis methods for the negative electrode active material, such as the wide scan method of XPS.

[0075] In an exemplary embodiment of the present invention, when the average particle size (D50) of the silicon-based active material is denoted as A and the average particle size (D50) of the metal oxide is denoted as B, the following formula 1 is satisfied.

[0076] [Formula 1]

[0077] 10 ≤ A / B ≤ 30

[0078] In one exemplary embodiment of the present invention, Formula 1 is 10 to 30. For example, Formula 1 can be 10 or more, 12 or more, 14 or more, or 15 or more, and can be 30 or less, 25 or less, 20 or less, or 18 or less.

[0079] In Equation 1, the ranges of A and B can refer to the average particle size (D50) of the silicon-based active material and the average particle size (D50) of the metal oxide.

[0080] Satisfying Equation 1 means that the average particle size (D50) of the silicon-based active material is greater than the average particle size (D50) of the metal oxide within this specific range. When Equation 1 is satisfied within this specific range, a coating can be uniformly formed on the surface of the active material without interfering with the behavior of lithium ions under battery operating conditions. If Equation 1 is below this lower limit, the average particle size (D50) of the metal oxide becomes relatively large, making it difficult to uniformly distribute the metal oxide on the surface of the active material, thus making it difficult to control the coating thickness. If Equation 1 is above this upper limit, the average particle size (D50) of the metal oxide becomes relatively small, making it difficult for the coating on the surface of the active material to ensure pores (spaces) for lithium ion migration, thereby increasing battery resistance; or the average particle size (D50) of the silicon-based active material becomes too large, which may lead to performance degradation due to uneven charging and discharging of silicon.

[0081] In one exemplary embodiment of the present invention, the grain size of the silicon-based active material can be below 600 nm.

[0082] In another exemplary embodiment, the grain size of the silicon-based active material can be less than 600 nm, less than 500 nm, less than 400 nm, less than 300 nm, less than 200 nm, less than 130 nm, less than 110 nm, less than 100 nm, less than 95 nm, or less than 91 nm. The grain size of the aforementioned silicon-based active material can be in the range of more than 10 nm or more than 15 nm.

[0083] The silicon-based active material has the aforementioned grain size, and this grain size can be controlled by changing the process conditions in the manufacturing process. In this case, when this specific range is met, the grain boundaries are widely distributed, thereby allowing lithium ions to be uniformly inserted during lithium-ion intercalation, reducing the stress applied during lithium-ion intercalation into the silicon particles and thus mitigating particle breakage. As a result, properties that improve the lifetime stability of the anode are obtained. If the grain size exceeds this specific range, the grain boundary distribution within the particles is narrow. In this case, lithium ions are not uniformly intercalated into the particles, resulting in high stress during ion intercalation and thus particle breakage.

[0084] In one exemplary embodiment of the present invention, the silicon-based active material may include a crystal structure having a grain distribution of more than 1 nm and less than 600 nm, and the area ratio of the crystal structure relative to the total area of ​​the silicon-based active material may be less than 5%.

[0085] In another exemplary embodiment, the area ratio of the crystal structure relative to the total area of ​​the silicon-based active material can be less than 5% or less than 3%, and can be more than 0.1%.

[0086] That is, in an exemplary embodiment of the present invention, the grain size of the silicon-based active material is less than 600 nm, which results in small sizes of the formed crystal structures and satisfies the area ratio. Therefore, the distribution of grain boundaries can be widened, thereby exhibiting the above-mentioned effects.

[0087] According to an exemplary embodiment of the present invention, the grain size of the silicon-based active material is less than 200 nm, which results in small sizes of the formed crystal structures and satisfies the area ratio. Therefore, the distribution of grain boundaries can be widened, thereby exhibiting the aforementioned effects.

[0088] In one exemplary embodiment of the present invention, the silicon-based active material may contain more than 20 crystal structures.

[0089] In another exemplary embodiment, the number of crystal structures contained in the silicon-based active material may fall within the range of more than 20, more than 30, or more than 35 and less than 60 or less than 50.

[0090] That is, as described above, when the grain size of the silicon-based active material falls within this specific range and the number of crystal structures falls within this specific range, the silicon-based active material itself has strength within an appropriate range. Therefore, when such a silicon-based active material is included in the electrode, flexibility can be imparted and volume expansion can be effectively suppressed.

[0091] In this invention, a grain refers to a crystalline particle in a metal or material, which is a collection of microscopically irregular shapes, and the grain size can refer to the diameter of the observed grain particles. That is, in this invention, the grain size refers to the size of crystal domains within a particle that have the same crystal orientation, and is a concept different from grain size or particle diameter, which represent the size of a material.

[0092] In one exemplary embodiment of the present invention, the grain size can be calculated as the FWHM (full width at half maximum) value by XRD analysis. The remaining values, except for L, can be measured by XRD analysis of the silicon-based active material, and the grain size can be determined by the Debey-Scherrer equation, which shows that FWHM is inversely proportional to the grain size. The Debey-Scherrer equation is shown in Equation 1-1 below.

[0093] [Equation 1-1]

[0094] FWHM = Kλ / Lcosθ

[0095] Where L is the grain size, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0096] Furthermore, the shapes of grains are diverse and can be measured in three dimensions. Typically, grain size can be measured using the commonly used circularity method or diameter measurement method, but this is not intended to be a limitation.

[0097] In the diameter measurement method, the grain size can be measured by drawing 5 to 10 parallel lines of length L mm on a photomicrograph of the target particle, counting the number of grains z on each line, and taking the average value. In this case, only grains completely contained within the lines are counted, while grains partially located on the lines (crossing) are excluded. When the number of lines is represented by P and the magnification is represented by V, the average grain size can be calculated using the following equations 1-2.

[0098] [Equation 1-2]

[0099] Dm = (L P 10 3 ) / (zV) (μm)

[0100] In addition, the circular method involves drawing a circle with a predetermined diameter on a photomicrograph of the target particle, and then calculating the average area of ​​the grains by the number of grains in the circle and the number of grains crossing the boundary line. The average area can be calculated using the following formulas 1-3.

[0101] [Equation 1-3]

[0102] Fm = (Fk 10 6 ) / ((0.67n + z) V 2 ) (μm 2 )

[0103] In Equations 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles inside the circle, n is the number of particles crossing the circle, and V is the magnification of the microscope.

[0104] In one exemplary embodiment of the present invention, the BET specific surface area of ​​the negative electrode active material comprising the silicon-based active material and the metal oxide coating disposed on the silicon-based active material can be 0.5 m². 2 / g to 20 m 2 / g.

[0105] In another exemplary embodiment, the BET specific surface area of ​​the negative electrode active material can be 0.5 m². 2 / g or more, 1 m 2 / g or more, 1.25 m 2 / g or more, 1.5 m 2 / g or more or 2 m 2 / g or more. The BET specific surface area of ​​the negative electrode active material can be 20 m². 2 / g or less, 15 m 2 / g or less, 10 m 2 / g or less, 5.5 m 2 / g or less, 5 m 2 / g or less or 4.5m 2 / g or less. The BET specific surface area can be measured according to DIN 66131 (using nitrogen).

[0106] The negative electrode active material has the aforementioned BET specific surface area, and the size of the surface area of ​​the silicon-based active material can be controlled by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material. Because the negative electrode active material has the BET specific surface area described above, the negative electrode active material according to an exemplary embodiment of the present invention has a larger surface area compared to particles of the same particle size. In this case, by satisfying this specific range, the adhesion strength with the binder is increased, thereby mitigating cracking in the electrode due to repeated charge-discharge cycles.

[0107] Furthermore, during lithium-ion intercalation, lithium ions can be uniformly intercalated, thereby reducing the stress applied during lithium-ion intercalation into silicon particles and thus reducing particle breakage. As a result, properties that improve the lifetime stability of the negative electrode are obtained. If the specific surface area is less than this specific range, even with the same particle size, a smooth surface is formed, leading to reduced adhesion strength with the binder and electrode cracking. In this case, lithium ions are not uniformly intercalated into the particles, resulting in increased stress and particle breakage due to ion intercalation.

[0108] In one exemplary embodiment of the present invention, the negative electrode active material satisfies the range of the following formula 2-1.

[0109] [Equation 2-1]

[0110] X1 / Y1 ≤ 0.960

[0111] In Equation 2-1, X1 refers to the actual area of ​​the negative electrode active material, and Y1 refers to the area of ​​a spherical particle with the same perimeter as the negative electrode active material.

[0112] The measurement of Equation 2-1 can be performed using a particle shape analyzer. Specifically, according to an exemplary embodiment of the invention, the negative electrode active material can be dispersed on a glass plate by air spray, and then the shape of 10,000 negative electrode active material particles in a photograph obtained by taking a shadow image of the dispersed particles can be measured. In this case, Equation 2-1 represents the average value of the 10,000 particles. From this image, Equation 2-1 according to the invention can be measured, and Equation 2-1 can be expressed as the sphericity (roundness) of the negative electrode active material. Sphericity can also be calculated by [4π × actual area of ​​the negative electrode active material / (perimeter)]. 2 ]express.

[0113] In one exemplary embodiment of the present invention, the sphericity of the negative electrode active material may be, for example, 0.960 or less or 0.957 or less. The sphericity of the negative electrode active material may be 0.8 or more, 0.9 or more, 0.93 or more, 0.94 or more, or 0.941 or more.

[0114] In one exemplary embodiment of the present invention, the negative electrode active material satisfies the range of the following formula 2-2.

[0115] [Equation 2-2]

[0116] X² / Y² ≤ 0.995

[0117] In Equation 2-2, Y2 refers to the actual perimeter of the negative electrode active material, and X2 refers to the perimeter of the circumscribed pattern of the negative electrode active material.

[0118] The measurement of Equation 2-2 can be performed using a particle shape analyzer. Specifically, according to an exemplary embodiment of the present invention, the negative electrode active material can be dispersed on a glass plate by air spray, and then the shape of 10,000 negative electrode active material particles in a photograph obtained by taking a shadow image of the dispersed particles can be measured.

[0119] In this case, Equation 2-2 represents the average value of 10,000 particles. From this image, Equation 2-2 according to the invention can be measured, and Equation 2-2 can be expressed as the convexity of the negative electrode active material.

[0120] In one exemplary embodiment of the present invention, the range of X2 / Y2 ≤ 0.996 or X2 / Y2 ≤ 0.995 can be satisfied, and the range of 0.8 ≤ X2 / Y2, 0.9 ≤ X2 / Y2, 0.95 ≤ X2 / Y2 or 0.98 ≤ X2 / Y2 can also be satisfied.

[0121] The smaller the value of Equation 2-1 or Equation 2-2, the greater the roughness of the negative electrode active material. By using a negative electrode active material that meets this specific range, the adhesion strength with the binder is increased, thereby mitigating electrode cracking caused by repeated charge-discharge cycles.

[0122] In one exemplary embodiment of the present invention, the particle size distribution of the negative electrode active material is greater than 0.01 μm and less than 30 μm.

[0123] The fact that the negative electrode active material contains negative electrode active material particles with a particle size distribution of 0.01 μm or more and 30 μm or less means that the negative electrode active material contains multiple individual negative electrode active material particles with particle sizes within this specific range. In this case, the number of negative electrode active material particles contained is not limited.

[0124] When the particle is spherical, the particle size can be expressed as its diameter. Even if the particle has a non-spherical shape, the particle size can be measured by comparison with the spherical case. Typically, the particle size of a single particle can be measured using methods commonly employed in the art.

[0125] negative electrode composition

[0126] An exemplary embodiment of the present invention provides a negative electrode composition comprising: a negative electrode active material according to an exemplary embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material.

[0127] An exemplary embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to an exemplary embodiment of the present invention; a negative electrode binder; and a negative electrode conductive material, and further comprising a carbon-based active material as a second negative electrode active material.

[0128] An exemplary embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to an exemplary embodiment of the present invention as a first negative electrode active material; a carbon-based active material as a second negative electrode active material; a negative electrode binder; and a negative electrode conductive material.

[0129] In one exemplary embodiment of the present invention, the carbon-based active material may comprise one or more selected from the group consisting of natural graphite and artificial graphite. Specifically, the carbon-based active material may be natural graphite, artificial graphite, or a mixture of natural and artificial graphite.

[0130] The negative electrode composition according to an exemplary embodiment of the present invention, in addition to containing the negative electrode active material according to an exemplary embodiment of the present invention, further contains a carbon-based active material as a second negative electrode active material, thereby utilizing the high capacity advantage of the first negative electrode active material, while improving the volume expansion problem originating from the silicon-based active material, and exhibiting high safety and excellent output due to the second active material.

[0131] Artificial graphite is typically manufactured by carbonizing raw materials such as coal tar, coal tar pitch, or petroleum-based heavy oil at temperatures above 2,500°C. After graphitization, the particle size of the artificial graphite is adjusted, for example, through crushing and secondary particle formation, before it is used as a negative electrode active material. In the case of artificial graphite, crystals are randomly distributed within the particles, with a lower sphericity than natural graphite and a slightly pointed shape.

[0132] Furthermore, the particle size of artificial graphite can be 5 to 30 μm, preferably 10 to 25 μm.

[0133] Natural graphite is typically in the form of plate-like aggregates before processing, and these plate-like particles are processed by post-processing (e.g., particle crushing and reassembly processes) to form spheres with smooth surfaces for use as active materials in the manufacture of electrodes.

[0134] In addition, natural graphite can have a particle size of 5 to 30 μm or 10 to 25 μm.

[0135] When the carbon-based active material is a mixture of artificial graphite and natural graphite, the weight ratio of artificial graphite to natural graphite can be from 9.99:0.01 to 0.01:9.99 or from 9.7:0.3 to 7:3. When this weight ratio range is met, excellent output can be exhibited.

[0136] In one exemplary embodiment of the present invention, the content of the first negative electrode active material may be 1 to 20 parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material. 100 parts by weight of the first negative electrode active material and the second negative electrode active material refers to the sum of the first negative electrode active material and the second negative electrode active material. For example, the content of the first negative electrode active material may be 1 or more parts by weight, 2 or more parts by weight, 3 or more parts by weight, 4 or more parts by weight, or 5 or more parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material, and may be less than 20 parts by weight or less than 18 parts by weight.

[0137] In one exemplary embodiment of the present invention, the content of the second negative electrode active material may be 80 to 99 parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material. 100 parts by weight of the first negative electrode active material and the second negative electrode active material refers to the sum of the first negative electrode active material and the second negative electrode active material. For example, the content of the second negative electrode active material may be 80 parts by weight or more, 83 parts by weight or more, or 85 parts by weight or more, and may be 99 parts by weight or less, 95 parts by weight or less, or 90 parts by weight or less, relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material.

[0138] In a negative electrode composition according to an exemplary embodiment of the present invention, the negative electrode adhesive and the negative electrode conductive material are as follows.

[0139] According to an exemplary embodiment of the present invention, the negative electrode composition is provided, wherein the negative electrode composition comprises 60 or more parts by weight of the negative electrode active material relative to 100 parts by weight of the negative electrode composition.

[0140] In another exemplary embodiment, the content of the negative electrode active material relative to 100 parts by weight of the negative electrode composition may be 60 parts by weight or more, 65 parts by weight or more, or 70 parts by weight or more, and may be 97 parts by weight or less, 95 parts by weight or less, or 90 parts by weight or less.

[0141] In one exemplary embodiment of the present invention, the conductive material may comprise one or more selected from the group consisting of point-like conductive materials, planar conductive materials, and linear conductive materials.

[0142] In one exemplary embodiment of the present invention, the dot-shaped conductive material refers to a spherical or dot-shaped conductive material that can be used to improve the conductivity of the negative electrode and has conductivity without causing chemical changes. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may contain carbon black for high conductivity and excellent dispersibility.

[0143] In one exemplary embodiment of the present invention, the BET specific surface area of ​​the dot-shaped conductive material can be 40m². 2 / g or more and 70 m 2 / g or less, 45 m 2 / g or more and 65 m 2 / g or less or 50 m 2 / g or more and 60 m2 / g or less.

[0144] In one exemplary embodiment of the present invention, the content of functional groups (volatiles) of the dot-shaped conductive material may fall within the range of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0145] In particular, when the functional group content of the dot-shaped conductive material falls within this specific range, the functional groups exist on the surface of the dot-shaped conductive material, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent.

[0146] In one exemplary embodiment of the present invention, the conductive material may comprise a planar conductive material.

[0147] The planar conductive material can be used to improve conductivity by increasing the surface contact between silicon particles in the negative electrode, while suppressing the breakage of the conductive path caused by volume expansion, and can be represented as a plate-shaped conductive material or a block-shaped conductive material.

[0148] In one exemplary embodiment of the present invention, the planar conductive material may comprise at least one selected from the group consisting of plate graphite, graphene, graphene oxide and graphite flakes, and preferably plate graphite.

[0149] In one exemplary embodiment of the invention, the average particle size (D50) of the planar conductive material can be from 2 μm to 7 μm, specifically from 3 μm to 6 μm, and more specifically from 4 μm to 5 μm. When this specific range is met, the particle size is sufficient to result in easy dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, the dispersion effect is excellent when the same equipment and time are used for dispersion.

[0150] In one exemplary embodiment of the present invention, the planar conductive material can be a high specific surface area planar conductive material or a low specific surface area planar conductive material with a high BET specific surface area.

[0151] In one exemplary embodiment of the present invention, the planar conductive material can be used without limitation either a high specific surface area planar conductive material or a low specific surface area planar conductive material. However, in particular, the planar conductive material according to one exemplary embodiment of the present invention may be affected to some extent by the dispersion effect in terms of electrode performance, thus a low specific surface area planar conductive material that does not cause dispersion problems is particularly preferred.

[0152] In one exemplary embodiment of the present invention, the BET specific surface area of ​​the planar conductive material can be 5m². 2 / g or more.

[0153] In another exemplary embodiment, the BET specific surface area of ​​the planar conductive material can be 5 m². 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0154] In another exemplary embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area can fall within 50 m². 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 Within the range of / g and below.

[0155] In another exemplary embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area can fall within 5 m². 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, preferably 5 m 2 / g or more and 25 m 2 Within the range of / g and below.

[0156] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. A bundled carbon nanotube may comprise multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" herein refers to a bundle or rope-like secondary shape in which multiple carbon nanotube units are arranged side-by-side or intertwined with substantially the same orientation along their longitudinal axes. The carbon nanotube units have cylindrical graphite sheets with diameters on the nanometer scale and exhibit sp... 2 Bonded structure. In this case, depending on the curl angle and structure of the graphite sheet, it can exhibit the properties of a conductive or semi-conductive material. Compared to wound carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during the fabrication of the negative electrode and can form a conductive network more smoothly in the negative electrode, thereby improving the conductivity of the negative electrode.

[0157] In one exemplary embodiment of the present invention, the linear conductive material may comprise SWCNT or MWCNT.

[0158] In one exemplary embodiment of the present invention, the negative electrode composition is provided, wherein the amount of the negative electrode conductive material present is 0.01 parts by weight or more and 20 parts by weight or less relative to 100 parts by weight of the negative electrode composition. For example, the content of the negative electrode conductive material may be 0.01 parts by weight or more, 0.1 parts by weight or more, or 0.5 parts by weight or more relative to 100 parts by weight of the negative electrode composition, and may be 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less.

[0159] The negative electrode conductive material according to an exemplary embodiment of the present invention is composed entirely differently from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material according to an exemplary embodiment of the present invention is used to maintain the contact between silicon-based active materials that expand greatly in electrode volume due to charging and discharging, while the positive electrode conductive material is used to act as a buffer during rolling and to impart a certain conductivity, and is completely different from the negative electrode conductive material of the present invention in terms of structure and function.

[0160] Furthermore, the negative electrode conductive material according to an exemplary embodiment of the present invention is applied to a silicon-based active material, and its composition is completely different from that of the conductive material applied to a negative electrode composition containing only a graphite-based active material. That is, compared with the active material, the conductive material used in the negative electrode composition containing only a graphite-based active material simply has smaller particles, thus possessing the characteristics of enhanced output characteristics and imparting partial conductivity, and its composition and function are completely different from the negative electrode conductive material applied together with the silicon-based active material in the present invention.

[0161] In one exemplary embodiment of the present invention, the negative electrode adhesive may comprise at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polyacrylamide (PAM), and materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also comprise various copolymers thereof.

[0162] According to an exemplary embodiment of the present invention, a negative electrode adhesive is used to retain the active material and the conductive material to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and mitigation of the silicon-based active material. When the above-described effect is achieved, all common adhesives can be applied; specifically, aqueous adhesives can be used, and more specifically, PAM-based adhesives, a one-component aqueous adhesive, can be used.

[0163] In one exemplary embodiment of the present invention, a negative electrode slurry is provided, wherein the negative electrode binder comprises an aqueous binder, and the content of the negative electrode binder is 5 parts by weight or more and 12 parts by weight or less relative to 100 parts by weight of the negative electrode composition.

[0164] In another exemplary embodiment, the content of the negative electrode binder may be 5 or more but less than 12 parts by weight, 7 or more but less than 11 parts by weight, or 8 or more but less than 11 parts by weight relative to 100 parts by weight of the negative electrode composition.

[0165] In a lithium secondary battery negative electrode according to an exemplary embodiment of the present invention, the silicon-based active material is used in the aforementioned weight proportions to maximize capacity characteristics, and the volume expansion during charge and discharge is greater compared to the case where a carbon-based active material is used as the main active material. Therefore, the negative electrode contains the aforementioned amount of negative electrode binder, thereby effectively controlling the volume expansion caused by the charge and discharge of the highly rigid silicon-based active material.

[0166] negative electrode

[0167] According to an exemplary embodiment of the present invention, a negative electrode is provided, the negative electrode comprising a negative electrode current collector layer and a negative electrode active material layer containing the negative electrode active material, the negative electrode active material layer being formed on one or both surfaces of the negative electrode current collector layer.

[0168] In one exemplary embodiment of the present invention, the negative electrode for the secondary battery can be formed by applying a negative electrode slurry to one or both surfaces of the negative electrode current collector layer and drying it.

[0169] In one exemplary embodiment of the present invention, the solid content of the negative electrode slurry can be in the range of 5% or more and 55% or less.

[0170] In another exemplary embodiment, the solid content of the negative electrode slurry may fall within the range of 5% or more and 55% or less, 7% or more and 35% or less, or 10% or more and 30% or less.

[0171] The solid content of a negative electrode slurry can refer to the content of negative electrode active materials, conductive materials and binders other than solvents in the negative electrode slurry, and can refer to the sum of negative electrode active materials, conductive materials and binders relative to 100 parts by weight of negative electrode slurry.

[0172] When the solids content of the negative electrode slurry falls within this specific range, the viscosity becomes appropriate during the formation of the negative electrode active material layer, which minimizes particle aggregation and enables the effective formation of the negative electrode active material layer.

[0173] In one exemplary embodiment of the present invention, the slurry solvent can be used without limitation, as long as it is used in the art; specifically, water, acetone, or NMP can be used.

[0174] In one exemplary embodiment of the present invention, the thickness of the negative electrode current collector layer is typically 1 μm to 100 μm.

[0175] There are no particular limitations on the negative electrode current collector layer, as long as it has high conductivity and will not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector layer can have micro-textured irregularities formed on its surface to enhance the adhesion of the negative electrode active material, and it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0176] In an exemplary embodiment of the present invention, a negative electrode for a secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 10 μm or more and 500 μm or less.

[0177] In this invention, the thickness of the negative electrode active material layer can refer to the thickness of a single negative electrode active material layer when it is formed on one surface of the negative electrode current collector layer.

[0178] However, the thickness can be modified in various ways depending on the type and purpose of the negative electrode used, and is not limited thereto.

[0179] In one exemplary embodiment of the present invention, a negative electrode for a secondary battery is provided, wherein the porosity of the negative electrode active material layer is 40% or more and 60% or less.

[0180] In another exemplary embodiment, the porosity of the negative electrode active material layer may fall within the range of 40% or more and 60% or less, 45% or more and 60% or less, or 50% or more and 55% or less.

[0181] Secondary batteries

[0182] According to an exemplary embodiment of the present invention, a secondary battery is provided, the secondary battery comprising a positive electrode, a negative electrode according to an exemplary embodiment of the present invention, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0183] According to an exemplary embodiment of the present invention, the secondary battery further comprises an electrolyte.

[0184] A secondary battery according to an exemplary embodiment of the present invention may specifically include the aforementioned negative electrode for a secondary battery. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, and the negative electrode is the same as described above. Since the negative electrode has already been described above, its detailed description is omitted.

[0185] The positive electrode may include a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is formed on the positive electrode current collector and contains positive electrode active material.

[0186] In the positive electrode, there are no particular limitations on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the thickness of the positive electrode current collector is typically from 3 μm to 500 μm, and the surface of the current collector can be formed with fine irregularities to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0187] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can be a layered compound, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound replaced by one or more transition metals; lithium iron oxide, such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides represented by O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5, and Cu2V2O7; and those represented by the chemical formula LiNi. 1-c2 M c2 O2 (where M is at least one of the following groups: Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c2 ≤ 0.6) represents a Ni-site type lithium nickel oxide; represented by the chemical formula LiMn 2-c3 M c3Lithium-manganese composite oxides represented by O2 (where M is selected from at least one of the following: Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≤ c3 ≤ 0.6) or Li2Mn3MO8 (where M is selected from at least one of the following: Fe, Co, Ni, Cu, and Zn); LiMn2O4, wherein a portion of the Li in the chemical formula is replaced by alkaline earth metal ions; and so on, but not limited thereto. The positive electrode may be Li metal.

[0188] In an exemplary embodiment of the present invention, the positive electrode active material may contain a lithium composite transition metal compound comprising nickel (Ni), cobalt (Co) and manganese (Mn), the lithium composite transition metal compound may contain single particles or secondary particles, and the average particle size (D50) of the single particles may be greater than 1 μm.

[0189] For example, the average particle size (D50) of the single particle can be greater than 1 μm and less than 12 μm, greater than 1 μm and less than 8 μm, greater than 1 μm and less than 6 μm, greater than 1 μm and less than 12 μm, greater than 1 μm and less than 8 μm, or greater than 1 μm and less than 6 μm.

[0190] Even when the single particles are formed with a small average particle size (D50) of 1 μm or more and 12 μm or less, the particle strength can still be excellent. For example, when the particle strength is 650 kgf / cm², the particle strength can be very high. 2 During force compression, the particle strength of the single particle can be between 100 and 300 MPa. Therefore, even at 650 kgf / cm², 2 The strong rolling of single particles also alleviates the increase of microparticles in the electrode caused by particle breakage, which improves the battery's lifespan characteristics.

[0191] The single particles can be manufactured by mixing and calcining a transition metal precursor and a lithium source material. The secondary particles can be manufactured by a different method than the single particles, and their composition can be the same as or different from that of the single particles.

[0192] There are no particular limitations on the method of forming the single particles, but generally the single particles can be formed by over-calcination at elevated calcination temperatures, or by using additives such as grain growth promoters that facilitate over-calcination, or by changing the starting materials.

[0193] For example, calcination is performed at a temperature capable of forming single particles. To form these single particles, calcination should be carried out at a higher temperature than that used when producing secondary particles; for example, with the same precursor composition, calcination should be performed at a temperature approximately 30°C to 100°C higher than that used when producing secondary particles. The calcination temperature for forming single particles can vary depending on the metal composition in the precursor. For example, when it is desired to form high-content nickel (high-Ni) NCM-based lithium composite transition metal oxides with a nickel (Ni) content of 80 mol% or more into single particles, the calcination temperature can be approximately 700°C to 1000°C, preferably approximately 800°C to 950°C. When the calcination temperature falls within this specific range, a cathode active material containing single particles with excellent electrochemical performance can be produced. If the calcination temperature is below 790°C, a cathode active material containing lithium composite transition metal compounds in the form of secondary particles can be produced; if the calcination temperature exceeds 950°C, over-calcination occurs and a layered crystal structure cannot be properly formed, potentially leading to deterioration of electrochemical performance.

[0194] As used herein, the term "single particle" is used to distinguish it from secondary particles, which are typically composed of condensations of tens to hundreds of primary particles, and is a concept that includes single particles consisting of a single primary particle and quasi-single particle forms as condensations of fewer than 30 primary particles.

[0195] Specifically, in this invention, the single particle can be a single particle composed of a primary particle or a quasi-single particle as an aggregate of 30 or fewer primary particles, and the secondary particle can be an aggregate of hundreds of primary particles.

[0196] In an exemplary embodiment of the present invention, the lithium composite transition metal compound used as the positive electrode active material further comprises secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0197] In this invention, the single particle can be a single particle composed of a primary particle or a quasi-single particle as an aggregate of 30 or fewer primary particles, and the secondary particle can be an aggregate of hundreds of primary particles.

[0198] The aforementioned lithium complex transition metal compounds may further contain secondary particles. These secondary particles refer to those formed by the aggregation of primary particles, and can be distinguished from the concept of a single particle, which includes a single primary particle, a single particle, and a quasi-single-particle form of an aggregation of 30 or fewer primary particles.

[0199] The particle size (D50) of the secondary particles can be 1 to 20 μm, 2 to 17 μm, and preferably 3 to 15 μm. The specific surface area (BET) of the secondary particles can be 0.05 m². 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0200] In another exemplary embodiment of the invention, the secondary particles are an aggregate of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of an aggregate of hundreds of primary particles, and the average particle size (D50) of the primary particles may be 0.6 to 2.8 μm, 0.8 to 2.5 μm, or 0.8 to 1.5 μm.

[0201] When the average particle size (D50) of the primary particles falls within this specific range, a single-particle positive electrode active material with excellent electrochemical performance can be formed. If the average particle size (D50) of the primary particles is too small, the number of primary particles that agglomerate to form lithium nickel oxide particles increases, thereby reducing the effect of suppressing particle breakage during compression delay. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path inside the primary particles may be prolonged, thereby increasing resistance and reducing output characteristics.

[0202] According to another exemplary embodiment of the invention, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles. As a result, even if the single particles are formed with a small particle size, they can still have excellent particle strength, thus mitigating the increase of microparticles in the electrode due to particle breakage, which can improve the battery's lifespan characteristics.

[0203] In one exemplary embodiment of the present invention, the average particle size (D50) of the single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particle.

[0204] For example, the average particle size (D50) of the single particle may be 1 to 16 μm smaller, 1.5 to 15 μm smaller, or 2 to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0205] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when this specific range is met, even if the single particles are formed with small particle sizes, they can still have excellent particle strength. Therefore, the increase of microparticles in the electrode due to particle breakage is mitigated, which can improve the battery's lifespan characteristics and energy density.

[0206] According to another exemplary embodiment of the present invention, the content of the single particles is 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material. Alternatively, the content of the single particles may be 20 to 100 parts by weight or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0207] For example, relative to 100 parts by weight of the positive electrode active material, the content of the single particles can be 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more. Relative to 100 parts by weight of the positive electrode active material, the content of the single particles can be less than 100 parts by weight.

[0208] When the content of the single particles is within this specific range, it can exhibit excellent battery characteristics when combined with the aforementioned negative electrode material. In particular, when the content of the single particles is 15 parts by weight or more, the increase of microparticles in the electrode due to particle breakage during the calendering process after electrode manufacturing is reduced, which can improve the battery's lifespan characteristics.

[0209] In one exemplary embodiment of the present invention, the lithium composite transition metal compound may further comprise secondary particles, and the amount of the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The content of the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The content of the secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0210] When this specific range is met, the aforementioned effects due to the presence of the single particles in the positive electrode active material can be maximized. In the case of a positive electrode active material containing secondary particles, its composition may be the same as or different from the composition exemplified in the single-particle positive electrode active material described above, and may refer to the aggregate form of single particles.

[0211] In one exemplary embodiment of the present invention, the content of the positive electrode active material relative to 100 parts by weight of the positive electrode active material layer can be 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0212] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0213] In this context, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular restriction, as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the constructed battery. Specific examples may include graphite, such as natural and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, etc., and any one or a mixture of two or more thereof may be used.

[0214] Furthermore, the positive electrode adhesive is used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0215] The separator is used to separate the negative electrode and the positive electrode and to provide a migration path for lithium ions. Any separator can be used without particular limitation, as long as it is typically used in secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion migration are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be selectively used.

[0216] Examples of the electrolyte may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0217] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0218] Examples of the non-aqueous organic solvents include aprotic organic solvents such as N-methyl-2-pyrrolidone, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0219] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, being cyclic carbonates, are high-viscosity organic solvents. Due to their high dielectric constant, they readily dissociate lithium salts and are therefore preferred for use. When the cyclic carbonates are mixed and used with straight-chain carbonates such as dimethyl carbonate and diethyl carbonate, which have low viscosity and low dielectric constant, in an appropriate ratio, electrolytes with high conductivity can be prepared, and therefore, they are even more preferred for use.

[0220] As the metal salt, a lithium salt can be used, which is a material readily soluble in non-aqueous electrolytes. The anion of the lithium salt can be, for example, one or more selected from the group consisting of: F... - Cl- I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - .

[0221] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, the electrolyte may contain, in addition to the aforementioned electrolyte components, one or more additives, such as alkylene carbonate halide compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds. Zolpidemone, N,N-substituted imidazolidinyl ether, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0222] Battery modules and battery packs

[0223] An exemplary embodiment of the present invention provides a battery module comprising a secondary battery according to an exemplary embodiment of the present invention.

[0224] An exemplary embodiment of the present invention provides a battery pack comprising a secondary battery according to an exemplary embodiment of the present invention.

[0225] An exemplary embodiment of the present invention provides a battery pack comprising a battery module according to an exemplary embodiment of the present invention.

[0226] An exemplary embodiment of the present invention provides a battery module comprising the secondary battery as a unit cell, and a battery pack comprising the secondary battery or the battery module. Because the battery module and the battery pack comprise a secondary battery having high capacity, high rate capability, and high cycle performance, the battery module and the battery pack 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 energy storage systems.

[0227] Although the present invention has been described with reference to exemplary embodiments thereof, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above description.

[0228] Preferred embodiments will be provided below to better understand the invention. It will be apparent to those skilled in the art that the embodiments described are merely illustrative, and various modifications and alterations are possible within the scope and spirit of the invention. Such modifications and alterations naturally fall within the scope of the claims included herein.

[0229] <Example>

[0230] <Preparation Example>

[0231] Example 1

[0232] 1) Preparation of negative electrode active materials

[0233] A negative electrode active material was prepared by mixing pure Si powder (average particle size (D50): 5.0 μm) as the silicon-based active material and aluminum isopropoxide (Al(OCH(CH3)2)3) powder as the coating metal oxide source at a weight ratio of 80:20, and then coating the pure Si surface with Al2O3 (average particle size (D50): 300 nm) by surface modification through calcination at 1,000 °C in an Ar atmosphere, thereby forming a metal oxide coating on the surface of the silicon-based active material. In the prepared negative electrode active material, the weight ratio of pure Si powder to Al2O3 (i.e., the weight ratio of the silicon-based active material to the coating) was 90:10, the average thickness of the metal oxide coating was 2 μm, and the BET specific surface area of ​​the negative electrode active material was 4 m². 2 / g.

[0234] 2) Preparation of the negative electrode

[0235] A negative electrode composition was prepared by using the negative electrode active material prepared in Example 1), SWCNT (single-walled carbon nanotubes) as a conductive material, and polyacrylamide (PAM) as a binder in a weight ratio of 90:0.8:9.2, and then added to distilled water as a solvent to prepare a negative electrode slurry (solid content 26% by weight).

[0236] Specifically, SWCNT and PAM were dispersed in distilled water at 2,500 rpm for 30 minutes using a homogenizer, and then the negative electrode active material was added and the mixture was dispersed at 2,500 rpm for 30 minutes to prepare the negative electrode slurry.

[0237] The BET specific surface area of ​​the SWCNTs used is 1000 to 1500 m². 2 / g, with an aspect ratio of 10,000 or higher, and using a solution in which SWCNT is dispersed in CMC (carboxymethyl cellulose).

[0238] The PAM used was in aqueous form, with a weight-average molecular weight (Mw) of 500,000 g / mol to 800,000 g / mol, a number-average molecular weight (Mn) of approximately 100,000 to 400,000, and a PDI value of 20 to 50. The binder was in aqueous form, and its weight-average and number-average molecular weights were measured using aqueous GPC (gel permeation chromatography).

[0239] The negative electrode slurry was prepared at 87.7 mg / 25 cm⁻¹. 2 The loading amount was coated on a surface of a copper current collector (thickness: 26 μm) used as the negative electrode current collector layer, and then rolled and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), thereby preparing the negative electrode (thickness: 59 μm, porosity: 55.0%).

[0240] 3) Preparation of secondary batteries

[0241] LiNi was prepared as the positive electrode active material at a weight ratio of 97:1.5:1.5. 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the positive electrode slurry, thereby preparing a positive electrode slurry (solid concentration: 78 wt%).

[0242] The positive electrode slurry was prepared at 537 mg / 25 cm⁻¹ 2The loading amount was coated on one surface of an aluminum current collector (thickness: 12 μm) used as the positive electrode current collector, and then rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), thereby preparing the positive electrode (thickness: 77 μm, porosity: 26%).

[0243] A lithium secondary battery is prepared by inserting a polyethylene separator between the positive and negative electrodes and injecting an electrolyte.

[0244] The electrolyte used was prepared by adding 3% by weight of vinylene carbonate (VC) relative to the total weight of the electrolyte to an organic solvent obtained by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90, and adding LiPF6 as a lithium salt at a concentration of 1 M.

[0245] Example 2

[0246] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 2 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, the weight ratio of silicon-based active material to coating was 80:20.

[0247] Example 3

[0248] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 0.02 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, Al2O3 (average particle size (D50): 10 nm) was coated on the surface of pure Si.

[0249] Example 4

[0250] The secondary battery was prepared in the same manner as in Example 1, but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, the negative electrode active material was prepared in the following manner.

[0251] SiO particles were prepared as silicon-based particles. The SiO particles were mixed with Mg as a metallic material, and the mixture was heat-treated at 1200°C for 3 hours to prepare SiO particles with Mg distributed on the surface and / or inside the SiO particles. During the preparation, a carbon layer was formed on the SiO particles with Mg distributed on the surface and / or inside the SiO particles by chemical vapor deposition (CVD) at 950°C using methane as the hydrocarbon gas, thereby preparing a silicon-based active material (average particle size (D50): 6 μm). In this silicon-based active material, the weight ratio of silicon particles:metal (Mg):carbon layer was 85:10:5 (average coating thickness: 1 μm).

[0252] That is, compared with Example 1, Example 4 uses Mg-doped SiO with a carbon layer instead of Si powder as the silicon-based active material.

[0253] Example 5

[0254] The secondary battery was prepared in the same manner as in Example 1, but the negative electrode composition was prepared in the manner described in step 2) of the preparation method in Example 1.

[0255] The negative electrode composition is prepared by preparing a negative electrode active material, SWCNTs (single-walled carbon nanotubes) as a conductive material, and polyacrylamide (PAM) as a binder in a weight ratio of 90:0.8:9.2. The negative electrode active material comprises the negative electrode active material prepared in Example 1 as the first negative electrode active material (15 parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material) and graphite as the carbon-based active material as the second negative electrode active material (artificial graphite:natural graphite = 70:30 weight ratio, 85 parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material).

[0256] Comparative Example 1

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

[0258] That is, Comparative Example 1 was prepared using a negative electrode active material that does not contain a metal oxide coating.

[0259] Comparative Example 2

[0260] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 2 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, Si-Fe alloy powder (average particle size (D50): 10 μm) was used instead of pure Si powder (average particle size (D50): 5.0 μm).

[0261] That is, compared with Example 1, Comparative Example 2 uses Si-Fe alloy powder instead of Si powder as the silicon-based active material for preparation.

[0262] Comparative Example 3

[0263] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 2 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, the weight ratio of silicon-based active material to coating was 95:5.

[0264] Comparative Example 4

[0265] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 2 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, the weight ratio of silicon-based active material to coating was 65:35.

[0266] Comparative Example 5

[0267] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 8 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, Al2O3 (average particle size (D50): 1000 nm) was coated on the surface of pure Si.

[0268] Comparative Example 6

[0269] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 0.005 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, Al2O3 (average particle size (D50): 5 nm) was coated on the surface of pure Si.

[0270] Comparative Example 7

[0271] The secondary battery was prepared in the same manner as in Example 1 (average coating thickness: 8 μm), but in the preparation method of Example 1 above 1), when preparing the negative electrode active material, the weight ratio of silicon-based active material to coating was 95:5, and Al2O3 (average particle size (D50): 1000 nm) was coated on the surface of pure Si.

[0272] The following items were evaluated for the prepared examples and comparative examples, and the results are shown in Table 2.

[0273] <Experimental Example: Evaluation of Capacity Retention>

[0274] In-situ cycle tests were conducted on the lithium secondary battery at 1 C / 0.5 C charge / discharge conditions within the range of 4.2–3.0 V. During the test, the battery was charged and discharged at 0.33 C / 0.33 C (4.2–3.0 V) every 50 cycles. The capacity retention was measured after 200 cycles.

[0275] Capacity retention (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the 1st cycle)} × 100%

[0276] <Experimental Example: Evaluation of Resistance Increase Rate>

[0277] In capacity retention evaluation, capacity retention was measured by charging and discharging at 0.33 C / 0.33 C (4.2-3.0V) every 50 cycles during the test. After 200 cycles, resistance was measured by discharging at 50% SOC with a 2.5 C pulse, and the rate of increase in resistance was compared and analyzed.

[0278] For evaluating the rate of increase in resistance, data were calculated for each of the 200 cycles.

[0279] <Experimental Example: Evaluation of the Highest Temperature During a Fire>

[0280] For the secondary battery prepared as described above, the highest temperature during the fire was measured.

[0281] In the prepared secondary battery, a heating pad was used to gradually raise the temperature of the charging battery to induce a fire. In this case, the surface temperature of the negative electrode was measured, and the highest measured temperature is shown in Table 1.

[0282] [Table 1]

[0283] Referring to Table 1, in Examples 1 to 5 where a metal oxide coating is included on the surface of the silicon-based active material, the highest temperature during ignition is lower than the highest temperature during ignition in Comparative Example 1 where no metal oxide coating is included on the surface of the silicon-based active material.

[0284] Furthermore, in Examples 1 to 5, where a metal oxide coating is included on the surface of the silicon-based active material, the maximum temperature during battery ignition was lower, while the capacity retention rate and resistance increase rate were comparable to or improved compared to Comparative Example 1. This confirms that the metal oxide coating on the surface of the silicon-based active material can delay battery ignition and improve battery thermal safety, without reducing battery performance.

[0285] In Comparative Example 2, the highest temperature during ignition was lower than in Comparative Example 1, but higher than in Examples 1 and 2. This is understood to be because, in the case of Si-Fe alloy powder, it is difficult to uniformly coat its surface with metal oxides, resulting in unstable coating formation. Therefore, the effect of improving thermal safety through metal oxide coating is insufficient. Furthermore, in Comparative Example 2, Si-Fe alloy powder was used as the silicon-based active material. Therefore, it was confirmed that compared with the negative electrode active material according to an exemplary embodiment of the present invention, it exhibited a lower capacity retention rate and a higher resistance increase rate.

[0286] Furthermore, in Comparative Examples 3 and 4, the content of metal oxides in the negative electrode active material was outside the scope of the present invention, and in both cases, a significant decrease in thermal stability was confirmed. Additionally, in Comparative Example 4, a deterioration in electrical performance was also confirmed. In Comparative Example 3, due to insufficient metal oxide content, the strengthening effect of the metal oxides during cycling was reduced, leading to decreased electrode structure stability. Furthermore, if the content of metal oxides is sufficiently high, the amount of inactive components that do not contribute to the electrochemical reaction increases, resulting in a decrease in theoretical capacity, which in turn inhibits ion and electron transport.

[0287] In Comparative Examples 5 and 6, the average thickness of the coating was outside the scope of the present invention. If the coating thickness exceeds the scope of the present invention, the coating exists in a porous form. In this case, it is known that a stable barrier cannot be formed on the surface, resulting in thermal stability problems. Furthermore, if the coating thickness is below the scope of the present invention, the coating is formed in a high-density form, resulting in poor battery performance in terms of resistance related to lithium-ion flow.

[0288] In Comparative Example 7, the content of metal oxide was lower than that of the present invention, and the thickness exceeded that of the present invention. In this case, it was confirmed that the effects of containing metal oxide were reduced, and the thermal stability was reduced compared to the examples.

[0289] The foregoing detailed description is intended to illustrate and explain the invention. Furthermore, the foregoing description only illustrates and explains preferred exemplary embodiments of the invention. As mentioned above, the invention can be used in various other combinations, variations, and environments, and can be changed or modified within the scope of the invention disclosed in this specification, the scope equivalent to the foregoing disclosure, and / or the scope of technology or knowledge in the art. Therefore, the foregoing detailed description of the invention is not intended to limit the invention to the disclosed embodiments. Moreover, the appended claims should be interpreted as including other embodiments.

Claims

1. A negative electrode active material, said negative electrode active material comprising: Silicon-based active materials; and A coating disposed on the silicon-based active material, wherein The silicon-based active material includes one or more selected from the group consisting of Si, SiO x (0 < x < 2), and Si / C, The coating comprises a metal oxide. The content of the metal oxide is 10 parts by weight or more and 30 parts by weight or less relative to 100 parts by weight of the negative electrode active material, and The average thickness of the coating is greater than 0.01 μm and less than 5 μm.

2. The negative electrode active material according to claim 1, wherein the metal oxide is represented by M a O b (1≤a≤2, 1≤b≤3) wherein M is any one of Al, Ti, and Mg.

3. The negative electrode active material according to claim 1, wherein the average particle size (D50) of the metal oxide is 5 nm to 1 μm.

4. The negative electrode active material according to claim 1, wherein... The silicon-based active material contains Si, and The content of Si is 70 to 99 parts by weight relative to 100 parts by weight of the silicon-based active material.

5. The negative electrode active material according to claim 1, wherein when the average particle size (D50) of the silicon-based active material is denoted as A and the average particle size (D50) of the metal oxide is denoted as B, the following formula 1 is satisfied. [Formula 1] 10 ≤ A / B ≤ 30.

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

7. The negative active material of claim 1, wherein the BET specific surface area of the negative active material is 0.5 m 2 / g to 20 m 2 / g.

8. A negative electrode composition, said negative electrode composition comprising: The negative electrode active material according to any one of claims 1 to 7; Negative electrode adhesive; and Negative electrode conductive material.

9. The negative electrode composition according to claim 8, wherein the negative electrode active material is a first negative electrode active material, and further comprises a carbon-based active material as a second negative electrode active material.

10. The negative electrode composition according to claim 9, wherein the carbon-based active material comprises at least one selected from the group consisting of natural graphite and artificial graphite.

11. The negative electrode composition according to claim 9, wherein the content of the first negative electrode active material is 1 to 20 parts by weight relative to 100 parts by weight of the first negative electrode active material and the second negative electrode active material.

12. A negative electrode, said negative electrode comprising: Negative current collector layer; and A layer of negative electrode active material is formed on one or both surfaces of the negative electrode current collector layer, wherein The negative electrode active material layer comprises the negative electrode composition according to claim 8.

13. A secondary battery, the secondary battery comprising: positive electrode; The negative electrode according to claim 12; A diaphragm disposed between the positive electrode and the negative electrode, and Electrolytes.

14. A battery module comprising the secondary battery according to claim 13.

15. A battery pack comprising a secondary battery according to claim 13.

16. A battery pack comprising the battery module according to claim 14.

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