Lithium secondary battery, battery pack, and electronic device including the same

Abstract

The present invention relates to a lithium secondary battery, a battery pack, and an electronic device including the same, which includes a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte. The positive electrode active material includes a lithium composite transition metal compound containing nickel, cobalt, and manganese. The lithium composite transition metal compound includes single particles. The silicon-carbon composite includes Si crystal grains, and the size of the Si crystal grains of the silicon-carbon composite is equal to or smaller than the crystal grains of the lithium composite transition metal compound. The size of lithium is equal to or smaller than the crystal grains of the silicon-carbon composite. The single particle is an aggregate of one primary particle or 2 to 30 primary particles.

Description

[Technical Field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0177120 filed with the Korean Intellectual Property Office on December 16, 2022, and Korean Patent Application No. 10-2023-0180420 filed with the Korean Intellectual Property Office on December 13, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, a battery pack, and an electronic device including the same. [Background technology]

[0003] Recently, with the rapid spread of battery-powered electronic devices, such as mobile phones, laptop computers, and electric vehicles, as well as power tools and vacuum cleaners, the demand for secondary batteries that are small and lightweight yet have relatively high capacity and / or high output has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as a driving power source for electronic devices. Therefore, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Lithium secondary batteries generate electrical energy through oxidation and reduction reactions when lithium ions are inserted into and extracted from the positive and negative electrodes while an organic or polymer electrolyte solution is charged between the positive and negative electrodes, which are made of active materials that allow for the intercalation and deintercalation of lithium ions.

[0005] Positive electrode active materials used in lithium secondary batteries include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compound (LiFePO4). Among these, lithium cobalt oxide (LiCoO2) is widely used due to its advantages of high operating voltage and excellent capacity characteristics, and is applied as a positive electrode active material for high voltage applications. However, rising cobalt (Co) prices and unstable supply have limited its mass use as a power source in fields such as electric vehicles, and there is an increasing need to develop alternative positive electrode active materials.

[0006] Therefore, nickel-cobalt-manganese-based lithium composite transition metal compounds (hereinafter simply referred to as "NCM-based lithium composite transition metal compounds") have been developed, in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). Recently, research has been conducted into increasing the nickel content in NCM-based lithium composite transition metal compounds to increase capacity. However, high-nickel (Ni-rich) positive electrode active materials with a high nickel content have drawbacks, such as reduced thermal stability and increased resistance due to increased side reactions during electrochemical reactions, as well as increased gas generation.

[0007] While graphite is commonly used as the negative electrode active material for lithium secondary batteries, its low capacity per unit mass of 372 mAh / g makes it difficult to increase the capacity of lithium secondary batteries. Therefore, to increase the capacity of lithium secondary batteries, non-carbon-based negative electrode materials with higher energy densities than graphite, such as silicon, tin, and their oxides, have been developed. However, while these non-carbon-based negative electrode materials offer high capacity, they suffer from low initial efficiency, high lithium consumption during the initial charge / discharge process, and large irreversible capacity loss.

[0008] In addition, lithium secondary batteries have a required size depending on the application, and therefore must be designed within a limited space. While consumer demands for increased energy density and improved high-power performance are increasing, when using a high-capacity cathode material, the only way to achieve this is to increase the content of the anode material, which limits the improvement of battery efficiency within a limited space. Therefore, there is a need to develop batteries that can be used in a limited space with improved performance, such as efficiency and lifespan. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2011-0112215 Summary of the Invention [Problem to be solved by the invention]

[0010] The present inventors have discovered that in a lithium secondary battery designed within a limited space, optimal battery performance can be achieved by adjusting the crystal grain size of the lithium transition metal composite compound as a positive electrode active material and the Si crystal grain size of the negative electrode active material in a specific combination, and have arrived at the present invention.

[0011] The present invention relates to a lithium secondary battery, a battery pack, and an electronic device including the same. [Means for solving the problem]

[0012] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material comprises a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound comprising single particles; and the negative electrode active material comprises a silicon carbon composite, the single particles comprising crystal grains of the lithium composite transition metal compound, the silicon carbon composite comprising Si crystal grains, the Si crystal grain size of the silicon carbon composite being 10% or less of the crystal grain size of the lithium composite transition metal compound, and the single particle being a single primary particle or an aggregate of 2 to 30 primary particles.

[0013] One embodiment of the present invention provides a battery pack including the lithium secondary battery.

[0014] One embodiment of the present invention provides an electronic device including the battery pack. [Effects of the Invention]

[0015] In a lithium secondary battery according to one embodiment of the present invention, the Si crystal grain size of the silicon carbon composite included in the negative electrode active material is 10% or less of the crystal grain size of the lithium composite transition metal compound included in the positive electrode active material, and when this crystal grain size is satisfied, cycle characteristics and swelling performance can be improved. Therefore, as described above, by adjusting the crystal grains of the lithium composite transition metal compound and the Si crystal grains of the negative electrode active material, it is possible to easily improve the fast charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed in a limited space. DETAILED DESCRIPTION OF THE INVENTION

[0016] This specification will be explained in more detail below.

[0017] In this specification, when a part is said to "comprise" a certain component, this does not mean that it may further include other components, unless specifically stated to the contrary, but rather that it does not exclude other components.

[0018] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when another member is present between the two members.

[0019] The terms and words used in this specification should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is appropriate to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to best explain the invention.

[0020] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0021] As used herein, the term "single particle" is used to distinguish it from positive electrode active material particles in the form of secondary particles formed by agglomeration of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles, and is meant to include a single particle consisting of one primary particle and a quasi-single particle form that is an agglomeration of 30 or fewer primary particles.

[0022] In this specification, the average particle size (D 50 The average particle size can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (the graph curve of a particle size distribution diagram). The average particle size can be measured, for example, using a laser diffraction method. The laser diffraction method is usually capable of measuring particle sizes from the submicron range to about several mm, and can provide results with high reproducibility and high resolution.

[0023] The average particle size can be measured using a Microtrac device (manufacturer: Microtrac model: S3500) with water and Triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured at a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured at a refractive index of 1.97 or 2.42. For example, the particles can be dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer. Ultrasound of about 28 kHz is irradiated at an output of 60 W to obtain a volume cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to preferred embodiments thereof. However, the present invention may be modified in various ways and the scope of the present invention is not limited to the following embodiments.

[0025] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material comprises a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium composite transition metal compound comprises a single particle; the negative electrode active material comprises a silicon carbon composite, and the single particle comprises a crystal grain of the lithium composite transition metal compound, the silicon carbon composite comprising Si crystal grains, the Si crystal grain size of the silicon carbon composite being 10% or less of the crystal grain size of the lithium composite transition metal compound, and the single particle is a single primary particle or an aggregate of 2 to 30 primary particles.

[0026] Generally, lithium secondary batteries have a required size depending on the application, and therefore must be designed within a limited space. While consumer demands for increased energy density and improved high-power performance are increasing, the use of high-capacity positive electrode materials requires an increased content of negative electrode material, limiting the improvement of battery efficiency within a limited space. Furthermore, depending on the type of negative electrode material, it is necessary to design a positive electrode material with efficiency that matches the efficiency of the negative electrode material.

[0027] The lithium secondary battery according to the present invention is characterized in that the Si crystal grain size of the silicon carbon composite contained in the negative electrode active material is 10% or less of the crystal grain size of the lithium composite transition metal compound contained in the positive electrode active material.

[0028] Due to the material properties of silicon carbon composites, the larger the crystal grain size, the more difficult it is for crystalline Si to become amorphous during the lithiation process, resulting in greater resistance, and as cycling continues, a larger amount of lithium (Li) remains within the material, which can lead to serious deterioration in cycle performance and expansion.On the other hand, due to the material properties of lithium transition metal composites, the larger the crystal grain size, the more stable the crystalline structure can be maintained even when the lithiation / delithiation process is repeated, and the more stable the lithium diffusion path can be maintained.

[0029] The present inventors have found that the degradation of cycle performance and the degree of expansion can be reduced by adjusting the crystal grain size of the lithium transition metal composite compound of the positive electrode active material to within a specific range relative to the Si crystal grain size of the silicon carbon composite.

[0030] Specifically, when the crystal grains of the lithium transition metal composite compound of the positive electrode active material are larger than the Si crystal grain size of the silicon carbon composite within the aforementioned range, the positive electrode active material maintains a relatively stable crystal structure during the lithiation / delithiation process, thereby stably maintaining lithium diffusion paths. As a result, electrochemical reactions can occur easily even with small amounts of lithium (Li), preventing relative capacity loss and expansion. Furthermore, when the Si crystal grain size of the silicon carbon composite satisfies the aforementioned range, stress due to volumetric expansion of the negative electrode active material particles during charge and discharge can be reduced, preventing particle cracking and improving cycle characteristics and swelling performance.

[0031] As described above, by controlling the relationship between the crystal grain size of the lithium transition metal composite compound contained in the positive electrode active material and the Si crystal grain size of the negative electrode active material, the crystalline structure of the positive electrode active material can be relatively stabilized and deterioration of cycle performance and expansion due to residual lithium can be reduced. Therefore, as described above, by adjusting the crystal grain size of the lithium transition metal composite compound and the Si crystal grain size of the negative electrode active material, it is possible to easily improve the fast charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed within a limited space.

[0032] In one embodiment of the present invention, the silicon carbon composite may be a Si / C-based active material.

[0033] In this specification, the silicon carbon composite is a composite of Si and C, and Si and C (e.g., graphite) are present. For example, peaks of Si and C can be observed by elemental analysis such as XRD or NMR.

[0034] In this specification, the silicon carbon composite may be expressed as Si / C. The silicon carbon composite may consist of Si and C that are not bonded to each other, but may contain additional components as necessary. For example, the silicon carbon composite may or may not contain silicon carbide, expressed as SiC. When the silicon carbon composite contains silicon carbide, its content is 3 wt % or less. The silicon carbon composite may exist in a crystalline state, an amorphous state, or a mixture thereof. According to one example, C in the silicon carbon composite may exist in an amorphous state.

[0035] The silicon carbon composite may be a composite of silicon and carbon, or may have a structure in which a core of the composite of silicon and carbon is surrounded by graphite, graphene, amorphous carbon, etc. In the silicon carbon composite, the silicon may be nanosilicon.

[0036] The silicon carbon composite may be a physical or chemical composite of the carbon and silicon material, and is not limited as long as the carbon and silicon material form a composite.

[0037] Specifically, the silicon carbon composite may be formed by firing carbon bound to silicon or silicon oxide particles, so that the carbon material is coated on the surface of the particles, carbon is dispersed in an atomic state inside silicon particles, or a core of silicon and carbon composite is surrounded by graphite, graphene, amorphous carbon, or the like.

[0038] In one embodiment of the present invention, the average particle size (D 50 ) may be 1 μm or more. The average particle size of the silicon carbon composite may be 15 μm or less. For example, the average particle size (D 50) may be 1 μm or more and 15 μm or less, more than 1 μm and less than 15 μm, 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 3 μm to 10 μm, 4 μm to 8 μm, or 5 μm to 8 μm.

[0039] The silicon carbon composite has an average particle size (D 50 Even if the silicon carbon composite particles are formed to have a small particle size of about 1 μm to 15 μm, the battery life characteristics can be improved. For example, when the average particle size of the silicon carbon composite is in the range of 1 μm to 15 μm, the volume expansion and contraction rate during charge and discharge is reduced, thereby improving the battery life. In addition, an excessive increase in the specific surface area is prevented, and side reactions with the electrolyte as the cycle progresses are prevented, thereby improving the battery life.

[0040] In one embodiment of the present invention, the negative electrode active material may further include graphite.

[0041] The graphite may be natural graphite or artificial graphite, or a mixture of natural and artificial graphite.

[0042] When the graphite is a mixture of natural graphite and artificial graphite, the weight ratio of the natural graphite to the artificial graphite may be 50:50 to 90:10, specifically 60:40 to 80:20 or 65:35 to 75:25.

[0043] In one embodiment of the present invention, the average particle size (D 50 ) may be 10 μm to 20 μm. Specifically, it may be 15 μm to 20 μm. When the average particle size of the graphite is within the above range, the influence of particle agglomeration is reduced, and the dispersibility of the slurry can be improved.

[0044] In one embodiment of the present invention, the positive electrode active material may include a lithium complex transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn).

[0045] In one embodiment of the present invention, the positive electrode active material contains nickel, cobalt, and manganese, and may further contain aluminum.

[0046] In this specification, the positive electrode active material contains nickel in an amount of 80 mol % or more and less than 100 mol % among metals excluding lithium, and the lithium composite transition metal compound containing nickel in an amount of 80 mol % or more and less than 100 mol % among metals excluding lithium may include one or a mixture of two or more types represented by the following Chemical Formula 1:

[0047] [Chemical formula 1] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0048] In the formula, Q is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, and 1≦a≦1.5, 0 <b≦0.5、0<c≦0.5、0≦d≦0.1、0<b+c+d≦20、-0.1≦δ≦1.0である。

[0049] In the lithium transition metal composite compound of Formula 1, Li may be included in an amount corresponding to a, i.e., 1≦a≦1.5. If a is less than 1, the capacity may be reduced, and if it exceeds 1.5, the particles may be sintered during the firing process, making it difficult to prepare the positive electrode active material. Considering the effect of controlling the Li content to improve the capacity characteristics of the positive electrode active material and the balance of sinterability during the preparation of the active material, the Li may more preferably be included in an amount of 1.1≦a≦1.2.

[0050] In the lithium composite transition metal compound of Chemical Formula 1, Ni may be contained in a content corresponding to 1-(b + c + d), for example, 0.8 ≦ 1-(b + c + d) < 1. When the content of Ni in the lithium composite transition metal compound of Chemical Formula 1 is 0.8 or more, a sufficient amount of Ni for contributing to charge and discharge is ensured, and high capacity can be achieved. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.88, preferably 0.9 or more, more preferably 0.93 or more. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.99 or less, 0.95 or less.

[0051] In the lithium composite transition metal compound of Chemical Formula 1, Co may be contained in a content corresponding to b, that is, 0 < b ≦ 0.5. When the content of Co in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of increased cost. Considering the significant effect of improving capacity characteristics by containing Co, more specifically, Co may be contained in a content of 0.03 ≦ b ≦ 0.2.

[0052] In the lithium composite transition metal compound of Chemical Formula 1, Mn may be contained in a content corresponding to c, that is, a content of 0 < c ≦ 0.5. When c in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of conversely degrading the output characteristics and capacity characteristics of the battery. More specifically, Mn may be contained in a content of 0.01 ≦ c ≦ 0.2.

[0053] In the lithium composite transition metal compound of Chemical Formula 1, Q may be a doping element contained in the crystal structure of the lithium composite transition metal compound, and Q may be contained in a content corresponding to d, that is, 0 ≦ d ≦ 0.1. Q may be one or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr. For example, Q may be Al.

[0054] In one embodiment of the present invention, the lithium composite transition metal compound may contain single particles.

[0055] In one embodiment of the present invention, the lithium transition metal composite compound may further include secondary particles.

[0056] The single particles may be prepared by mixing a transition metal precursor and a lithium source material and calcining the mixture. The secondary particles may be prepared by a method different from that for the single particles, and the composition thereof may be the same as or different from that of the single particles.

[0057] For example, the calcination is performed at a temperature sufficient to form single particles. To achieve this, the calcination should be performed at a temperature higher than that used for preparing secondary particles. For example, when the precursor composition is the same, the calcination should be performed at a temperature approximately 30°C to 100°C higher than that used for preparing secondary particles. The calcination temperature for forming the single particles may vary depending on the metal composition of the precursor. For example, when forming a high-nickel (Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more into single particles, the calcination temperature may be 700°C to 1000°C, preferably 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be prepared. When the calcination temperature is lower than 790°C, a positive electrode active material containing a lithium composite transition metal compound in the form of secondary particles can be prepared. However, when the calcination temperature exceeds 950°C, excessive calcination may prevent proper formation of a layered crystal structure, resulting in poor electrochemical properties.

[0058] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by agglomeration of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles, and is a concept that includes a single particle consisting of one primary particle and a similar-single particle form that is an agglomeration of 30 or less primary particles.

[0059] Specifically, in the present invention, the single particle may be a single particle consisting of one primary particle and / or a quasi-single particle which is an agglomerate of 30 or less primary particles, and the secondary particle may be an agglomerate of 30 or more primary particles. For example, the secondary particle may be an agglomerate of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles.

[0060] The size of the Si crystal grains contained in the silicon carbon composite can be determined by X-ray diffraction analysis, which may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: Bruker). Specifically, XRD measurement can be performed by placing a powder sample in a holder and measuring using Cu K alpha X-rays. The size of the Si crystal grains can be calculated by fitting the XRD results using the Scherrer equation, and the crystal grains can be measured using Si(220) as the reference (2θ=47.5°~48.5°).

[0061] In one embodiment of the present invention, the silicon carbon composite may have a Si crystal grain size of 0.1 nm to 20 nm, specifically, 0.5 nm to 15 nm, 1 nm to 15 nm, 1.5 nm to 12 nm, 1.5 nm to 10 nm, 2 nm to 10 nm, 3 nm to 10 nm, or 4 nm to 9 nm.

[0062] When the Si crystal grain size satisfies the above range, Li ions are uniformly diffused inside the Si particles, which has the effect of stably maintaining the structure of the Si particles during charge and discharge.On the other hand, when the Si crystal grain size exceeds the above range, cracks are formed in the particles due to stress caused by contraction / expansion of the Si material during charge and discharge, preventing Li ions from diffusing into the inside of the crystal grains, resulting in non-uniform reaction and accelerated degradation of the material, thereby shortening the lifespan of the cell.

[0063] As used herein, the crystal grain size of the lithium composite transition metal compound may refer to the crystal size of the structure of Formula 1. The crystal grain size of the lithium composite transition metal compound may be determined by X-ray diffraction analysis, which may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: Bruker). Specifically, the XRD measurement may be performed by placing a powder sample in a holder and measuring with Cu K alpha X-rays. The crystal grain size of the lithium composite transition metal compound may be calculated by fitting the XRD results using the Scherrer equation, and the crystal grain size may be measured based on the maximum peak appearing around 2θ = 10° to 12°.

[0064] In one embodiment of the present invention, the lithium composite transition metal compound may have a crystal grain size of 100 nm to 200 nm, specifically, 100 nm to 170 nm, 100 nm to 160 nm, or 105 nm to 150 nm.

[0065] When the crystal grain size of the lithium composite transition metal compound satisfies the above range, the lithium composite transition metal compound has excellent phase stability and can stably react with Li. On the other hand, when the crystal grain size of the lithium composite transition metal compound is smaller than the above range, the reaction with Li occurs for a long time, resulting in a decrease in the efficiency of the positive electrode. When the crystal grain size of the lithium composite transition metal compound is larger than the above range, the positive electrode active material may be cracked during the rolling step in the electrode manufacturing process.

[0066] In one embodiment of the present invention, the Si crystal grain size of the silicon carbon composite is 10% or less of the crystal grain size of the lithium composite transition metal compound. Specifically, the Si crystal grain size of the silicon carbon composite may be 0.5% to 10%, 1% to 10%, or 1% to 9.5% of the crystal grain size of the lithium composite transition metal compound. When the Si crystal grain size of the silicon carbon composite and the crystal grain size of the lithium composite transition metal compound satisfy this relationship, stress due to volumetric expansion of the negative electrode active material particles during charge and discharge can be reduced, preventing particle cracking. Not only that, but also, the stable crystal structure due to the relatively large crystal grain size of the lithium composite transition metal compound of the positive electrode active material facilitates electrochemical reactions even with a small amount of lithium (Li), improving cycle characteristics and swelling performance.

[0067] On the other hand, even if the Si crystal grain size of the silicon carbon composite and the crystal grain size of the lithium transition metal composite compound satisfy the above-mentioned crystal grain sizes, if the Si crystal grain size of the silicon carbon composite exceeds 10% of the crystal grain size of the lithium transition metal composite compound, there are problems in that the deterioration of cycle performance and the degree of expansion may become serious due to lithium (Li) remaining in the silicon carbon composite, and cracks may occur in the particles due to an increase in internal stress of Si during charge and discharge, thereby deteriorating cycle performance.

[0068] In one embodiment of the present invention, the average particle size (D 50) may be 1 μm or more. The average particle size of the single particles may be 12 μm or less. For example, the average particle size of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 6 μm or less, 2 μm or more and 6 μm or less, or 3 μm or more and 5 μm or less.

[0069] The single particles may have excellent particle strength even when formed with a small average particle size of about 1 μm to 12 μm, thereby mitigating the increase in fine particles in the electrode due to particle cracking, thereby improving the lifespan of the battery. For example, the single particles have a resistance of 650 kgf / cm 2 When the single particle is rolled at a force of 650 kgf / cm, it can have a particle strength of 100 to 300 MPa. 2 Even if the electrode is rolled with a strong force, the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, improving the life characteristics of the battery.

[0070] The method for forming the single particles is not particularly limited, but may generally be formed by over-firing at an elevated firing temperature, or by using an additive such as a grain growth promoter that is useful for over-firing, or by changing the starting material.

[0071] The single particles have high rigidity and exhibit relatively low degradation in battery performance even when the electrode density is high. Therefore, the energy density can be increased by adjusting the average particle size range of the single particles and the silicon carbon composite.

[0072] In one embodiment of the present invention, the average particle size (D 50 ) is the average particle size (D 50 ) may be smaller.

[0073] When the average particle size of the single particles is smaller than the average particle size of the silicon carbon composite, the diffusion resistance of the single particles is relatively reduced, thereby improving the lifespan performance. That is, as the average particle size of the single particles increases, the diffusion resistance may increase. When the average particle size of the single particles is larger than the average particle size of the silicon carbon composite, the diffusion resistance may increase relatively, which may cause lithium deposition, resulting in a decrease in battery performance and a decrease in lifespan performance.

[0074] Furthermore, when the average particle size of the single particles is smaller than the average particle size of the silicon carbon composite, side reactions with the electrolyte due to an increase in specific surface area can be prevented, thereby improving the lifespan.

[0075] According to one embodiment of the present invention, the average particle size (D 50 ) is the average particle size (D 50 ) by 1 μm to 12 μm. Specifically, it may be 1.5 μm to 11.5 μm, or 2 μm to 11 μm smaller.

[0076] The average particle size of the single particle (D 50 ) is the average particle size (D 50 ), for example, when the average particle size is smaller than the average particle size of the silicon carbon composite, the diffusion resistance of the individual particles may be relatively reduced, thereby improving the lifespan performance. That is, as the average particle size of the individual particles increases, the diffusion resistance may increase. When the average particle size of the individual particles is larger than the average particle size of the silicon carbon composite, the diffusion resistance may increase relatively, which may cause lithium deposition, resulting in a decrease in battery performance and a decrease in lifespan performance.

[0077] In addition, the average particle size of the single particle (D 50 ) is the average particle size (D 50), for example, when the range is satisfied, the occurrence of side reactions with the electrolyte due to an increase in the specific surface area can be prevented, and the life performance can be improved.

[0078] According to one embodiment of the present invention, the average particle size (D 50 ) and the average particle size (D 50 ) may be 1.5:2 to 1.5:20.

[0079] When the above range is satisfied, the diffusion resistance of the individual particles is relatively reduced, thereby improving the lifespan performance. That is, as the average particle size of the individual particles increases, the diffusion resistance may increase. When the average particle size of the individual particles is larger than the average particle size of the silicon carbon composite, the diffusion resistance increases relatively, which may cause lithium deposition, resulting in a decrease in battery performance and a decrease in lifespan performance.

[0080] In addition, the average particle size of the single particle (D 50 ) is the average particle size (D 50 ), for example, when the range is satisfied, the occurrence of side reactions with the electrolyte due to an increase in the specific surface area can be prevented, and the life performance can be improved.

[0081] In one embodiment of the present invention, the lithium composite transition metal compound further includes secondary particles, and the average particle size (D 50 ) is the average particle size of the secondary particles (D 50 ) is smaller than

[0082] In the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-single particle which is an agglomerate of 30 or less primary particles. The secondary particle may be an agglomerate of 30 or more, 35 or more, 40 or more, 50 or more, 60 or more, 70 or more, 100 or more, 150 or more, or 200 or more primary particles.

[0083] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by agglomeration of primary particles, and can be distinguished from the concept of single particles, which includes one primary particle, one single particle, or a similar-single particle form that is an agglomeration of 30 or less primary particles.

[0084] The average particle size of the secondary particles (D 50 ) may be 1 μm to 20 μm. Specifically, it may be 2 μm to 17 μm, 3 μm to 15 μm, 5 μm to 15 μm, 7 μm to 15 μm, or 9 μm to 15 μm.

[0085] In one embodiment of the present invention, the secondary particles are aggregates of primary particles, and the average particle size (D 50 ) may be 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of an aggregation of 30 or more primary particles, and the average particle size of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0086] When the average particle size of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the primary particles is too large, the lithium diffusion path within the primary particles becomes long, increasing resistance and potentially reducing output characteristics.

[0087] In one embodiment of the present invention, the average particle size (D 50 ) is the average particle size of the secondary particles (D 50 ) Therefore, even if the single particle is formed to have a small particle size, the particle strength is excellent, and thus the phenomenon of an increase in fine particles in the electrode due to particle cracking can be alleviated, thereby improving the life characteristics of the battery.

[0088] In one embodiment of the present invention, the average particle size (D 50) is the average particle size of the secondary particles (D 50 ) is 1 μm to 18 μm smaller.

[0089] For example, the average particle size of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size of the secondary particles.

[0090] When the average particle size of the single particles is smaller than the average particle size of the secondary particles, for example, when the above range is satisfied, the single particles have excellent particle strength even though they are formed to have a small particle size, and thus the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, thereby improving the life characteristics and energy density of the battery.

[0091] In one embodiment of the present invention, the average particle size (D 50 ) is the average particle size (D 50 When the average particle size of the silicon carbon composite is smaller than the average particle size of the graphite, the volume expansion / contraction rate during charging / discharging is reduced, thereby reducing particle cracking and improving the lifespan of the battery.

[0092] In the lithium secondary battery according to the above embodiment, the negative electrode active material may further include a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof.

[0093] According to one embodiment of the present invention, the average particle size (D 50 ) is the average particle diameter (D 50 For example, the average particle size of the silicon carbon composite may be 2 μm to 24 μm, 3 μm to 23 μm, or 4 μm to 22 μm smaller than the average particle size of the graphite.

[0094] When the average particle size of the silicon-carbon composite is smaller than the average particle size of the graphite, for example, when the above range is satisfied, there is an effect that the life performance of the battery is further improved.

[0095] In one embodiment of the present invention, when the average particle sizes (D 50 ) of the secondary particles, the single particles, the graphite, and the silicon-carbon composite contained in the lithium secondary battery are A, B, C, and D, respectively, B < D ≦ A < C may be satisfied.

[0096] The embodiments of the secondary particles, the single particles, the graphite, and the silicon-carbon composite are as described above.

[0097] When the average particle sizes (D 50 ) of the secondary particles, the single particles, the graphite, and the silicon-carbon composite are A, B, C, and D, respectively, when B < D ≦ A < C, there is an effect that the life performance of the battery is improved.

[0098] According to one embodiment of the present invention, the negative electrode active material further contains graphite, and when the average particle sizes of the single particle, the graphite, and the silicon-carbon composite are B, C, and D, respectively, B < D < C may be satisfied.

[0099] When the average particle sizes (D 50 ) of the secondary particles, the single particles, and the silicon-carbon composite are A, B, and D, respectively, B < D ≦ A may be satisfied.

[0100] When the average particle sizes (D 50 ) of the secondary particles, the single particles, and the graphite are A, B, and C, respectively, B < A < C may be satisfied.

[0101] When the average particle sizes (D 50 ) of the secondary particles, the graphite, and the silicon-carbon composite are A, C, and D, respectively, D ≦ A < C may be satisfied.

[0102] When the above range is satisfied, the battery life performance is improved.

[0103] In one embodiment of the present invention, in the lithium secondary battery according to the above embodiment, the single particles may be included in an amount of 15 parts by weight to 100 parts by weight based on 100 parts by weight of the positive electrode active material, and the silicon carbon composite may be included in an amount of 3 parts by weight to 30 parts by weight based on 100 parts by weight of the negative electrode active material.

[0104] In one embodiment of the present invention, the single particles may be contained in an amount of 15 parts by weight to 100 parts by weight, or 20 parts by weight to 100 parts by weight, or 30 parts by weight to 100 parts by weight, relative to 100 parts by weight of the positive electrode active material.

[0105] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. For example, the single particles may be included in an amount of 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0106] When the single particles are contained in the above range, excellent battery characteristics can be exhibited in combination with the above-mentioned negative electrode material. In particular, when the single particles are contained in an amount of 15 parts by weight or more, the increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery life characteristics.

[0107] In one embodiment of the present invention, the lithium composite transition metal compound may further include 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 amount of the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The amount of the secondary particles may be 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, or 40 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0108] In one embodiment of the present invention, the weight ratio of the single particles to the secondary particles may be 1:9 to 9:1, 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4.

[0109] When the above range is satisfied, the effects described above due to the presence of the single particle positive electrode active material can be maximized. When the secondary particle positive electrode active material is included, the components thereof may be the same as or different from those exemplified for the single particle positive electrode active material described above, and may refer to an aggregated form of single particles.

[0110] In one embodiment of the present invention, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the positive electrode active material layer.

[0111] According to one embodiment of the present invention, the positive electrode according to the above embodiment further comprises a positive electrode binder and a conductive material.

[0112] The positive electrode binder may serve to improve adhesion between positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. The positive electrode binder may be any binder known in the art, and non-limiting examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0113] The positive electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, and more preferably 0.5 parts by weight to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0114] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0115] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 to 2 parts by weight, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight, based on 100 parts by weight of the composition for a positive electrode active material layer.

[0116] In this specification, the silicon carbon composite is a composite of Si and C, and Si and C (e.g., graphite) peaks are observed in the XRD diffraction pattern, and it appears that a second phase, Si / C, is not formed.

[0117] According to the above-described embodiment of the present invention, the negative electrode active material layer contains 3 to 30 parts by weight of a silicon carbon composite based on 100 parts by weight of the total negative electrode active material. In one example, the negative electrode active material layer may contain 3 to 20 parts by weight, or 3 to 13 parts by weight, or preferably 5 to 10 parts by weight, based on 100 parts by weight of the total negative electrode active material. By using a silicon carbon composite in this range, excellent battery characteristics can be achieved in combination with the above-described positive electrode material. In particular, when the silicon carbon composite is contained in an amount of 3 parts by weight or more, the effects of using the silicon carbon composite can be fully exhibited. Furthermore, since the silicon carbon composite has a higher capacity than SiOx-based active materials, using an excessive amount can make it difficult to balance the capacity with the positive electrode active material. In particular, when the silicon carbon composite is contained in an amount of 30 parts by weight or less, expansion during charge and discharge can be prevented, improving cycle characteristics.

[0118] The silicon carbon composite is a material with higher capacity and efficiency than silicon-based oxides, and even when it does not contain a conductive material, it can exhibit superior resistance effects compared to anodes containing silicon-based oxides and conductive materials. Furthermore, the silicon carbon composite exhibits higher Si crystallinity than silicon-based oxides, and therefore exhibits superior effects when evaluating high power output.

[0119] In one embodiment of the present invention, in the lithium secondary battery according to the above embodiment, the negative electrode active material may further include a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof. The graphite may be included in an amount of 70 to 97 parts by weight based on 100 parts by weight of the total negative electrode active material included in the negative electrode active material layer.

[0120] The graphite may be included in an amount of 75 parts by weight or more, 80 parts by weight or more, or 85 parts by weight or more, based on 100 parts by weight of the total negative electrode active material. The graphite may be included in an amount of 95 parts by weight or less, 93 parts by weight or less, or 90 parts by weight or less, based on 100 parts by weight of the total negative electrode active material. When the graphite is a mixture of artificial graphite and natural graphite, the artificial graphite and natural graphite may be included in an amount of 90:10 parts by weight to 50:50 parts by weight, 85:15 parts by weight to 60:40 parts by weight, or 80:20 parts by weight to 65:35 parts by weight, based on 100 parts by weight of the graphite.

[0121] In one embodiment of the present invention, the weight ratio of the carbon-based active material to the silicon carbon composite may be 0.1:99.9 to 30:70, 1:99 to 20:80, 5:95 to 20:80, 5:95 to 15:85, 8:92 to 12:88, or 10:90 to 12:88.

[0122] In one embodiment of the present invention, the negative electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, out of 100 parts by weight of the negative electrode active material layer.

[0123] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material layer may further include a negative electrode binder in addition to the silicon carbon composite and graphite.

[0124] The negative electrode binder may serve to improve adhesion between negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. The negative electrode binder may be any binder known in the art, and non-limiting examples thereof may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or various copolymers thereof.

[0125] The negative electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, more preferably 0.5 parts by weight to 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0126] The negative electrode active material layer may not contain a conductive material, but may further contain a conductive material if necessary. The conductive material contained in the negative electrode active material layer is not particularly limited as long as it is conductive without inducing chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. The content of the conductive material in the negative electrode active material layer may be 0.01 to 30 parts by weight, preferably 0.03 to 25 parts by weight, per 100 parts by weight of the negative electrode active material layer.

[0127] In one embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0128] The positive electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0129] In one embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and including the negative electrode active material.

[0130] The negative electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited thereto.

[0131] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer containing the positive electrode active material, and the negative electrode further includes a negative electrode active material layer containing the negative electrode active material, and the positive electrode and negative electrode active material layers each have a thickness of 10 μm to 500 μm. The thickness of the positive electrode active material layer may be 90% to 110%, for example, 95% to 105%, of the thickness of the negative electrode active material layer, or these thicknesses may be the same. Specifically, the thickness of the positive electrode and negative electrode active material layers may each be 15 μm to 400 μm, 20 μm to 300 μm, 25 μm to 200 μm, or 30 μm to 100 μm.

[0132] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer containing the positive electrode active material, and the amount of the positive electrode active material layer loaded per unit volume is 250 mg / 25 cm 2 ~900mg / 25cm 2 The negative electrode further includes a negative electrode active material layer containing the negative electrode active material, and the amount of the negative electrode active material layer loaded per unit volume is 100 mg / 25 cm 2 ~600mg / 25cm 2 Specifically, the amount of the positive electrode active material layer carried per unit volume is 270 mg / 25 cm 2 ~800mg / 25cm 2 , 285mg / 25cm 2 ~700mg / 25cm 2 , or 300 mg / 25 cm 2 ~600mg / 25cm 2The amount of the negative electrode active material layer carried per unit volume may be 120 mg / 25 cm 2 ~500mg / 25cm 2 , 135mg / 25cm 2 ~400mg / 25cm 2 , 150mg / 25cm 2 ~300mg / 25cm 2 may be.

[0133] The positive and negative electrodes may be fabricated by a conventional method for fabricating positive and negative electrodes, except for using the positive and negative electrode active materials. Specifically, they may be fabricated by coating a composition for forming an active material layer containing the active material and, optionally, a binder and a conductive material on a current collector, followed by drying and rolling. The types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used should be sufficient to dissolve or disperse the active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to fabricate positive and negative electrodes, taking into account the coating thickness and manufacturing yield. Alternatively, the positive electrode and the negative electrode may be produced by casting the active material layer-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on a current collector.

[0134] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte impregnation capacity is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be used in a single-layer or multi-layer structure.

[0135] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in producing lithium secondary batteries.

[0136] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0137] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0138] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, may be preferably used because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. If such a cyclic carbonate is mixed with a linear carbonate having a low viscosity and a low dielectric constant, such as dimethyl carbonate or diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore may be more preferably used.

[0139] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0140] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the battery discharge capacity.

[0141] The energy density of the lithium secondary battery according to one embodiment of the present invention may be 400 Wh / L to 900 Wh / L. Specifically, the energy density of the lithium secondary battery may be 425 Wh / L to 875 Wh / L, 450 Wh / L to 850 Wh / L, 475 Wh / L to 825 Wh / L, or 500 Wh / L to 800 Wh / L. When this range is satisfied, the energy density of the lithium secondary battery designed in a limited space can be increased, and high-power performance and battery cycle performance can also be improved.

[0142] The lithium secondary battery according to an embodiment of the present invention may be a cylindrical battery. The cylindrical battery refers to a battery having a cylindrical shape, which includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte. Specifically, the battery may be composed of a cylindrical can, a battery assembly housed inside the cylindrical can, and a top cap. However, the lithium secondary battery is not limited thereto and may be a prismatic battery or a pouch-type battery.

[0143] One embodiment of the present invention provides a battery pack and an electronic device that include the cylindrical battery as a unit cell. The battery pack and the electronic device include the secondary battery that has high capacity and excellent rate and cycle characteristics, and therefore may be used as a power source for a medium- to large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[0144] The lithium secondary battery according to the embodiment of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore may be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, as well as portable devices such as mobile phones, laptop computers, and digital cameras. For example, the battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0145] [Example] Below, preferred examples are presented to help understand the present invention, but these examples are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present description, and it is natural that such changes and modifications fall within the scope of the claims.

[0146] <Examples and Comparative Examples> Example 1 A positive electrode active material layer-forming composition was prepared, which included, based on 100 parts by weight of a positive electrode active material layer, 98.04 parts by weight of a lithium composite transition metal compound containing single particles and secondary particles (single particles:secondary particles=50:50 weight ratio) as the positive electrode active material, which contained 93.3 mol % Ni, 4.9 mol % Co, and 1.8 mol % Mn among metals excluding lithium, 1 part by weight of PVDF as a binder, and 0.8 parts by weight of CNTs and 0.16 parts by weight of a dispersant as a conductive material.

[0147] The lithium composite transition metal compound used was heat-treated at 750°C for 8 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 110 nm. 50 = 3.57 μm and the size of the secondary particles is D 50 The composition for forming a positive electrode active material layer was coated on an aluminum foil having a thickness of 30 μm to a dry thickness of 103 μm, and then dried to prepare a positive electrode.

[0148] A composition for forming a negative electrode active material layer was prepared, containing 97.7 parts by weight of graphite (artificial graphite:natural graphite = 70:30 weight ratio, 90 parts by weight based on 100 parts by weight of the negative electrode active material) and a silicon carbon composite (10 parts by weight based on 100 parts by weight of the negative electrode active material) as the negative electrode active materials, 1.15 parts by weight of styrene-butadiene rubber (SBR) and 1 part by weight of carboxymethyl cellulose (CMC) as binders, 0.09 parts by weight of a dispersant, and 0.06 parts by weight of a CNT pre-dispersion liquid containing single-walled CNTs, based on 100 parts by weight of the negative electrode active material layer.

[0149] The silicon carbon composite used was heat-treated at 300°C for 2 hours in an Ar atmosphere, and the Si crystal grain size of the silicon carbon composite used was 6 nm. 50 = 5.2 μm and the size of the graphite is D 50 The composition for forming a negative electrode active material layer was coated on a copper foil having a thickness of 15 μm to a dry thickness of 86 μm, and then dried to prepare a negative electrode.

[0150] The positive electrode and negative electrode were stacked with a separator in between, and an electrolyte (1.0M LiPF6, EC (ethylene carbonate) / EMC (ethylmethyl carbonate) = 30 / 70 (Vol%), VC (vinylene carbonate) 1.5%) was injected to fabricate a battery.

[0151] Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0152] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 120nm. 50 = 3.58 μm and the size of the secondary particles is D 50 = 14.7 μm.

[0153] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 200°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 1.5 nm. The size of the silicon carbon composite was D 50 = 6.2 μm and the size of graphite is D 50 = 17 μm.

[0154] Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0155] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 105 nm. 50 = 3.63 μm and the size of the secondary particles is D 50 = 10.5 μm.

[0156] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 400°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 9 nm. 50 = 7.1 μm and the size of graphite is D 50 = 17 μm.

[0157] Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0158] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 800°C for 10 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 150 nm. 50 = 3.72 μm and the size of the secondary particles is D 50 = 9.5 μm.

[0159] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 300°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 4 nm. 50 = 6.3 μm and the size of graphite is D 50 = 17 μm.

[0160] Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0161] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 110 nm. 50 = 3.57 μm and the size of the secondary particles is D 50 = 9.5 μm.

[0162] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 400°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 10 nm. 50 = 6.9 μm and the size of graphite is D 50 = 17 μm.

[0163] Example 6 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0164] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 800°C for 10 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 140 nm. 50 = 3.74 μm and the size of the secondary particles is D 50 = 16.5 μm.

[0165] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 500°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 12 nm. 50 = 7.0 μm and the size of the graphite is D 50 = 17 μm.

[0166] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0167] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 110 nm. 50 = 3.63 μm and the size of the secondary particles is D 50 = 9.6 μm.

[0168] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 500°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 12 nm. 50 = 7.0 μm and the size of the graphite is D 50 = 17 μm.

[0169] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0170] The composition for forming the positive electrode active material layer was prepared by heat-treating a lithium composite transition metal compound at 650°C for 6 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 100 nm. 50 = 3.57 μm and the size of the secondary particles is D 50 = 9.5 μm.

[0171] The silicon carbon composite used in the negative electrode active material layer formation composition was heat treated at 700°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 17 nm. 50 = 5.3 μm and the size of graphite is D 50 = 17 μm.

[0172] Comparative Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0173] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 750°C for 8 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 120nm. 50 = 3.60 μm and the size of the secondary particles is D 50 = 10.5 μm.

[0174] The silicon carbon composite used in the negative electrode active material layer formation composition was heat treated at 700°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 20 nm. 50 = 5.1 μm and the size of graphite is D 50 = 17 μm.

[0175] Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0176] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 800°C for 10 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 140 nm. 50 = 3.74 μm and the size of the secondary particles is D 50 = 16.5 μm.

[0177] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 900°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 41 nm. 50 = 6.8 μm and the size of graphite is D 50 = 17 μm.

[0178] Comparative Example 5 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0179] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 650°C for 6 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 80 nm. 50 = 3.52 μm and the size of the secondary particles is D 50 = 12.5 μm.

[0180] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 400°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 10 nm. 50 = 6.9 μm and the size of graphite is D 50 = 17 μm.

[0181] Comparative Example 6 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0182] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 650°C for 6 hours in an Ar atmosphere. The crystal grain size of the lithium composite transition metal compound used was 88 nm. 50 = 3.52 μm and the size of the secondary particles is D 50 = 12.7 μm.

[0183] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 400°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 10 nm. 50 = 6.8 μm and the size of graphite is D 50 = 17 μm.

[0184] Comparative Example 7 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the lithium transition metal composite compound and the silicon carbon composite were prepared as follows.

[0185] The positive electrode active material layer-forming composition used was a lithium composite transition metal compound that had been heat-treated at 650°C for 6 hours in an Ar atmosphere, and the crystal grain size of the lithium composite transition metal compound used was 80 nm. 50 = 3.52 μm and the size of the secondary particles is D 50 = 12.5 μm.

[0186] The silicon carbon composite used in the negative electrode active material layer forming composition was heat treated at 400°C for 2 hours in an Ar atmosphere. The silicon carbon composite used had a Si crystal grain size of 9 nm. 50 = 7.1 μm and the size of graphite is D 50 = 17 μm.

[0187] The compositions of the negative electrode active materials and positive electrode active materials prepared in the examples and comparative examples are as shown in Table 1 below.

[0188] [Table 1A]

[0189] [Table 1B]

[0190] The size of the crystal grains of the lithium transition metal composite compound and the Si crystal grains contained in the silicon carbon composite can be confirmed by X-ray diffraction analysis, which was performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: Bruker). Specifically, the XRD measurement was performed by placing a powder sample in a holder and measuring it using Cu K alpha X-rays. The size of the crystal grains of the lithium transition metal composite compound was calculated by fitting the XRD results using the Scherrer equation, and the crystal grain size was measured based on the peak that appeared at that position (2θ=10°~12°). The size of the Si crystal grains was calculated by fitting the XRD results using the Scherrer equation, and the crystal grains were measured based on Si(220) (2θ=47.4°~48.5°). D of the positive electrode active material and the negative electrode active material 50 was analyzed using a microtrac device and the PSD measurement method.

[0191] <Experimental example: Discharge capacity, initial efficiency, and life (capacity retention rate) characteristic evaluation> The lithium secondary batteries produced in the examples and comparative examples were charged and discharged, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated. The results are shown in Table 2 below.

[0192] The first and second cycles were charged and discharged at 0.1 C, and the third to 199th cycles were charged and discharged at 0.5 C. The 200th cycle was completed in a charged state (with lithium in the negative electrode).

[0193] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows:

[0194] Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100

[0195] The capacity retention rates were calculated as follows:

[0196] Capacity retention rate (%) = (199 discharge capacity / 1 discharge capacity) × 100

[0197] <Experimental example: Cell thickness evaluation> The thickness of the fabricated secondary battery was compared before and after the following cycles.

[0198] The first and second cycles were charged and discharged at 0.1 C, and the third to 200th cycles were charged and discharged at 0.5 C. The cell thickness after the second cycle was defined as the initial thickness, and the cell thickness after the 200th cycle was defined as the post-thickness, and the thickness was calculated using the following formula. The calculated cell thickness of Example 1 was set as 100%, and the cell thicknesses of Examples 2 to 6 and Comparative Examples 1 to 7 were calculated relative to this, and are shown in Table 2 below.

[0199] Cell thickness = (post-thickness - initial thickness) / (initial thickness) x 100

[0200] [Table 2]

[0201] Tables 1 and 2 show that the secondary batteries of Examples 1 to 6, in which the Si crystal grain size of the silicon carbon composite was 10% or less of the crystal grain size of the lithium composite transition metal compound, had thinner cell thicknesses and better capacity retention than those of Comparative Examples 1 to 7. This is because the Si crystal grain size of the silicon carbon composite was 10% or less of the crystal grain size of the lithium composite transition metal compound, which reduced stress caused by volumetric expansion of the negative electrode active material particles during charge and discharge. This reduced particle cracking and improved cycle characteristics and swelling performance. On the other hand, in Comparative Examples 1 to 7, the Si crystal grain size of the silicon carbon composite exceeded 10% of the crystal grain size of the lithium composite transition metal compound, which resulted in increased internal stress of Si during charge and discharge, causing cracks in the particles and degrading cycle performance.

[0202] In particular, in the cases of Example 5 and Comparative Example 5, Example 6 and Comparative Example 1, and Example 3 and Comparative Example 7, even though the Si crystal grain size of the silicon carbon composite was the same, different effects were obtained depending on the crystal grain size of the positive electrode active material. This confirms that the cycle characteristics and expansion degree can be improved depending on the relative size of the Si crystal grain size of the silicon carbon composite and the crystal grain size of the lithium transition metal composite compound of the positive electrode active material.

Claims

1. A lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte, The positive electrode active material includes a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), The lithium composite transition metal compound includes a single particle, the negative electrode active material includes a silicon carbon composite, the single particle includes a crystal grain of the lithium composite transition metal compound, The silicon carbon composite contains Si crystal grains, the silicon carbon composite has a Si crystal grain size of 10% or less of the lithium composite transition metal compound; The lithium secondary battery, wherein the single particle is one primary particle or an aggregate of 2 to 30 primary particles.

2. The average particle size of the primary particles (D ５０ 2. The lithium secondary battery according to claim 1, wherein the thickness of the first electrode is 0.5 μm or more and 3 μm or less.

3. The single particle has a resistance of 650 kgf / cm ２ 2. The lithium secondary battery according to claim 1, wherein the particle strength is 100 MPa or more and 300 MPa or less when ...

4. 2. The lithium secondary battery according to claim 1, wherein the silicon carbon composite has a Si crystal grain size of 0.1 nm or more and 20 nm or less.

5. 2. The lithium secondary battery according to claim 1, wherein the lithium composite transition metal compound has a crystal grain size of 100 nm or more and 200 nm or less.

6. The lithium composite transition metal compound further includes secondary particles, The lithium secondary battery according to claim 1 , wherein the secondary particles are aggregates of 30 or more primary particles.

7. The average particle size of the secondary particles (D ５０ 7. The lithium secondary battery according to claim 6, wherein the thickness of the first electrode is 1 μm or more and 20 μm or less.

8. The lithium secondary battery according to claim 1 , wherein the negative electrode active material further comprises graphite.

9. 9. The lithium secondary battery according to claim 8, wherein the graphite is natural graphite, artificial graphite, or a mixture of natural graphite and artificial graphite.

10. The graphite is a mixture of natural graphite and artificial graphite, 9. The lithium secondary battery according to claim 8, wherein the weight ratio of the natural graphite to the artificial graphite is 50:50 to 90:

10.

11. The average particle diameter (D ５０ 9. The lithium secondary battery according to claim 8, wherein the thickness of the first electrode is 10 μm or more and 20 μm or less.

12. The average particle size of the single particle (D ５０ 2. The lithium secondary battery according to claim 1, wherein the thickness of the first and second electrodes is 1 μm or more and 12 μm or less.

13. The average particle size (D ５０ 2. The lithium secondary battery according to claim 1, wherein the thickness of the first and second electrodes is 1 μm or more and 15 μm or less.

14. The average particle size of the single particle (D ５０ ) is the average particle size (D ５０ 2. The lithium secondary battery according to claim 1, wherein the capacitance is smaller than 1 / 2.

15. The average particle size (D ５０ ) is the average particle diameter (D ５０ 9. The lithium secondary battery according to claim 8, wherein the capacitance is smaller than 1 / 2.

16. the single particles are included in an amount of 15 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of the positive electrode active material, The lithium secondary battery according to claim 1 , wherein the silicon carbon composite is contained in an amount of 3 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the negative electrode active material.

17. 2. The lithium secondary battery according to claim 1, wherein the lithium composite transition metal compound contains nickel in an amount of 80 mol % or more and less than 100 mol % of metals excluding lithium.

18. the positive electrode includes a positive electrode active material layer containing the positive electrode active material, the negative electrode includes a negative electrode active material layer containing the negative electrode active material, 2. The lithium secondary battery according to claim 1, wherein the thickness of each of the positive electrode active material layer and the negative electrode active material layer is 10 μm or more and 500 μm or less.

19. A battery pack comprising the lithium secondary battery according to any one of claims 1 to 18.

20. An electronic device comprising the lithium secondary battery according to any one of claims 1 to 18.

Images