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 dates 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, and all of its content is included herein.

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

Background Art

[0003] Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, electric vehicles, power tools, and vacuum cleaners, there has been a rapid increase in the demand for secondary batteries that are small, lightweight, yet relatively high-capacity and / or high-output. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for electronic devices. Therefore, research and development efforts for improving the performance of lithium secondary batteries have been actively made.

[0004] A lithium secondary battery generates electrical energy through oxidation and reduction reactions when lithium ions are inserted / desorbed at the positive and negative electrodes in a state where an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of inserting (intercalations) and desorbing (deintercalation) lithium ions.

[0005] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMn2O4), lithium iron phosphate compound (LiFePO4), etc. have been used. Among these, lithium cobalt oxide (LiCoO2) is widely used because of its advantages of high operating voltage and excellent capacity characteristics, and is applied as a positive electrode active material for high voltage. However, due to the price increase and supply instability of cobalt (Co), there is a limit to its large-scale use as a power source in fields such as electric vehicles, and the need for the development of alternative positive electrode active materials is increasing.

[0006] Therefore, a nickel cobalt manganese-based lithium composite transition metal compound (hereinafter, simply referred to as "NCM-based lithium composite transition metal compound") in which a part of cobalt (Co) is replaced with nickel (Ni) and manganese (Mn) has been developed. Recently, technologies for increasing the capacity by increasing the nickel content in the NCM-based lithium composite transition metal compound have been studied. However, in the case of a high-concentration nickel (Ni-rich) positive electrode active material with a high nickel content, there are disadvantages such as a decrease in thermal stability, an increase in resistance due to an increase in side reactions during the electrochemical reaction, and an increase in gas generation.

[0007] On the other hand, as the negative electrode active material of a lithium secondary battery, graphite is mainly used. However, since the capacity per unit mass of graphite is as small as 372 mAh / g, it is difficult to increase the capacity of the lithium secondary battery. Therefore, for the purpose of increasing the capacity of the lithium secondary battery, negative electrode materials such as silicon, tin, and their oxides have been developed as non-carbon-based negative electrode materials having a higher energy density than graphite. However, in the case of such non-carbon-based negative electrode materials, although the capacity is large, there are problems such as low initial efficiency, a large consumption amount of lithium in the initial charge-discharge process, and a large irreversible capacity loss.

[0008] In addition, lithium secondary batteries have a size required according to their applications, and thus need to be designed within a limited space. Although the demand from consumers for an increase in energy density and an improvement in high-output performance is growing, when using a high-capacity positive electrode material, there is no choice but to increase the content of the negative electrode material to suit this, so there is a limit to increasing the battery efficiency within a limited space. Therefore, there is an actual situation where it is necessary to develop a battery with improved performance such as efficiency and lifespan within a limited space.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The inventors of the present invention have found that in a lithium secondary battery designed within a limited space, by adjusting the crystal grain size of the lithium composite transition metal compound of the positive electrode active material and the Si crystal grain size of the negative electrode active material, it is possible to realize optimal battery performance in a specific combination, leading to 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 Problems

[0012] One embodiment of the present invention is a lithium secondary battery including 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 (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 crystal grains of the lithium composite transition metal compound. The silicon-carbon composite includes Si crystal grains. The size of the Si crystal grains in the silicon-carbon composite is 10% or less of the size of the crystal grains of the lithium composite transition metal compound. The single particle is one primary particle or an aggregate of 2 to 30 primary particles. A lithium secondary battery is provided.

[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.

Effect of the Invention

[0015] In the lithium secondary battery according to one embodiment of the present invention, since the size of the Si crystal grains in the silicon-carbon composite contained in the negative electrode active material is 10% or less of the size of the crystal grains of the lithium composite transition metal compound contained in the positive electrode active material, when the crystal grain size is satisfied, the 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, the rapid charging performance, efficiency, life, and / or energy density of the lithium secondary battery designed within a limited space can be easily improved.

Mode for Carrying Out the Invention

[0016] Hereinafter, the present specification will be described in more detail.

[0017] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0018] In this specification, when a certain member is located "above" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is another member between the two members.

[0019] The terms and words used in this specification should not be construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that the inventor himself can appropriately define the concept of the terms in order to explain the invention in the best way, they should be construed in a meaning and concept suitable for the technical idea of the present invention.

[0020] The singular expressions of the terms used in this specification include plural expressions unless the context clearly indicates otherwise.

[0021] In this specification, the term "single particle" is used to distinguish from a positive electrode active material particle in the form of a secondary particle formed by aggregation 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 means including a single particle composed of one primary particle and a similar-single particle form which is an aggregate of 30 or less primary particles.

[0022] In this specification, the average particle diameter (D 50 ) can be defined as the particle diameter corresponding to 50% of the volume cumulative amount in the particle size distribution curve (the graph curve of the particle size distribution diagram). The average particle diameter can be measured, for example, using the laser diffraction method. The laser diffraction method can usually measure particle diameters in the range from the submicron region to about several millimeters, and results with high reproducibility and high resolution can be obtained.

[0023] The measurement of the average particle size can be confirmed using a Microtrac equipment (manufacturer: Microtrac, model: S3500) with water and triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured in the refractive index range of 1.5 to 1.7, and the negative electrode active material can be measured under the conditions of refractive index 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, they are put into a commercially available laser diffraction particle size analyzer, irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and after obtaining a volume cumulative particle size distribution graph, it can be measured by obtaining the particle size corresponding to 50% of the volume cumulative amount.

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be deformed into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0025] One embodiment of the present invention is a lithium secondary battery including 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, wherein the positive electrode active material includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound includes single particles, the negative electrode active material includes a silicon-carbon composite, the single particles include crystal grains of the lithium composite transition metal compound, the silicon-carbon composite includes Si crystal grains, 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, and the single particles are one primary particle or an aggregate of 2 to 30 primary particles, and a lithium secondary battery is provided.

[0026] Generally, a lithium secondary battery has a size required according to its application, and thus needs to be designed within a limited space. Although the demands of consumers for increased energy density and improved high-power performance are increasing, when using a high-capacity cathode material, the only way is to increase the content of the anode material to suit this, so there is a limit to increasing the battery efficiency within a limited space. Also, depending on the type of anode material, it is necessary to design a cathode material having an efficiency suitable for the efficiency of the anode 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 anode active material is 10% or less of the crystal grain size of the lithium composite transition metal compound contained in the cathode active material.

[0028] Due to the characteristics of the material of the silicon-carbon composite, the larger the crystal grain size, the more difficult it is for crystalline Si to be amorphized during the lithiation process, and a large resistance is generated. As the cycle continues, a larger amount of lithium (Li) remains in the material, and there is a possibility that the cycle performance degradation and the degree of swelling become serious. On the other hand, for the lithium composite transition metal compound, due to the characteristics of the material, the larger the crystal grain size, the more it can maintain a relatively stable crystal structure even when the lithiation / delithiation process is repeated, and it can stably maintain the lithium diffusion path.

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

[0030] Specifically, when the crystal grains of the lithium composite transition metal compound of the positive electrode active material are larger than the Si crystal grain size of the silicon carbon composite within the above-described range, the positive electrode active material retains a relatively stable crystal structure during the lithiation / delithiation process. Therefore, the lithium diffusion path can be stably maintained. As a result, an electrochemical reaction can easily occur even with a small amount of lithium (Li), and relative capacity reduction and expansion can be prevented. Further, when the Si crystal grain size of the silicon carbon composite satisfies the above-described range, during charge and discharge, the stress caused by the volume expansion of the negative electrode active material particles can be reduced, and cracking of the particles can be prevented. Therefore, the cycle characteristics and swelling performance can be improved.

[0031] As described above, by controlling the relationship between the crystal grains of the lithium composite transition metal compound contained in the positive electrode active material and the Si crystal grain size of the negative electrode active material, the crystal structure of the positive electrode active material can be relatively stably maintained, and the degradation of the cycle performance and the degree of expansion due to residual lithium can be reduced. 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, the rapid charging performance, efficiency, life, and / or energy density of the lithium secondary battery designed within a limited space can be easily improved.

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

[0033] In the present specification, the silicon carbon composite exists as a composite of Si and C, where Si and C (for example, graphite) are present respectively. For example, each peak of Si and C can be observed by an elemental analysis method such as XRD or NMR.

[0034] In this specification, the silicon-carbon composite may be denoted as Si / C. The silicon-carbon composite may consist of Si and C that do not bond to each other, but may contain additional components if necessary. For example, the silicon-carbon composite may or may not contain silicon carbide (Silicon carbide) denoted as SiC. When the silicon-carbon composite contains silicon carbide, its content is 3% by weight or less. The silicon-carbon composite may exist in a crystalline, amorphous, or mixed state thereof. According to one example, C in the silicon-carbon composite may exist in an amorphous state.

[0035] The silicon-carbon composite may be one in which silicon and carbon are compounded, etc. A structure surrounded by graphite, graphene, or amorphous carbon, etc. may be formed with a core in which silicon and carbon are compounded as the center. In the silicon-carbon composite, the silicon may be nanosilicon.

[0036] The silicon-carbon composite may be one in which the carbon and the silicon material are physically or chemically compounded, and is not limited as long as the carbon and the silicon material form a composite structure.

[0037] Specifically, the silicon-carbon composite may be a structure in which a carbon substance is coated on the surface of particles by heat-treating (firing) in a state where carbon is bonded to silicon or silicon oxide particles, or a structure in which carbon is dispersed in an atomic state inside silicon particles, or a structure surrounded by graphite, graphene, or amorphous carbon, etc. with a core in which silicon and carbon are compounded as the center.

[0038] In one embodiment of the present invention, the average particle size (D 50 ) of the silicon-carbon composite may be 1 μm or more. Also, 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 ) formed to a small particle size of about 1 μm or more and 15 μm or less, and the life characteristics of the battery can be improved. For example, when the average particle size of the silicon-carbon composite is in the range of 1 μm or more and 15 μm or less, the volume expansion and shrinkage rates due to charge and discharge decrease, and the life performance can be improved. Also, excessive increase in the specific surface area is prevented, side reactions with the electrolyte do not occur during the progress of the cycle, and the life performance can be improved.

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

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

[0042] When the graphite is a mixture of natural graphite and artificial graphite, the weight ratio of natural graphite to artificial graphite may be 50:50 to 90:10. Specifically, it may be 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 ) of the graphite may be 10 μm to 20 μm. Specifically, it may be 15 μm to 20 μm. When the average particle size of the graphite satisfies the above range, the influence due to the aggregation of particles 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 contain a lithium composite 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 the nickel, cobalt, and manganese, and may further contain aluminum.

[0046] In the present specification, the positive electrode active material contains nickel in an amount of 80 mol% or more and less than 100 mol% among the 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 the metals excluding lithium may contain one or more mixtures 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 above formula, Q is any one or more elements 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, and -0.1 ≦ δ ≦ 1.0.

[0049] In the lithium composite transition metal compound of Chemical Formula 1, Li may be contained in an amount corresponding to a, that is, 1 ≦ a ≦ 1.5. When a is less than 1, the capacity may decrease, and when it exceeds 1.5, the particles may be sintered in the firing process, which may make it difficult to manufacture the positive electrode active material. Considering the improvement effect of the capacity characteristics of the positive electrode active material by controlling the Li content and the balance of the sinterability when manufacturing the active material, the Li may more preferably be contained 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 an amount 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 is ensured to contribute to charge and discharge, 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 an amount 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 remarkable effect of improving capacity characteristics by containing Co, more specifically, Co may be contained in an amount of 0.03 ≦ b ≦ 0.2.

[0052] In the lithium composite transition metal compound of Chemical Formula 1, Mn may be contained in an amount corresponding to c, that is, 0 < c ≦ 0.5. When c in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, conversely, there is a risk of deterioration of the output characteristics and capacity characteristics of the battery, and more specifically, Mn may be contained in an amount 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 an amount 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 composite transition metal compound may further include secondary particles.

[0056] The single particles can be manufactured by mixing and firing a transition metal precursor and a lithium raw material. The secondary particles may be manufactured by a method different from that of the single particles, and their composition may be the same as or different from that of the single particles.

[0057] For example, the firing is carried out at a temperature capable of forming single particles. To form this, firing should be carried out at a temperature higher than that during the production of secondary particles. For example, when the composition of the precursor is the same, firing needs to be carried out at a temperature about 30°C to 100°C higher than that during the production of secondary particles. The firing temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when attempting to form a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more into single particles, the firing temperature may be 700°C to 1000°C, preferably 800°C to 950°C. When the firing temperature satisfies the above range, a cathode active material containing single particles with excellent electrochemical properties can be manufactured. When the firing temperature is less than 790°C, a cathode active material containing a lithium composite transition metal compound in the form of secondary particles can be manufactured. When it exceeds 950°C, the firing is overdone and a layered crystal structure cannot be properly formed, and the electrochemical properties may be deteriorated.

[0058] As used herein, the single particles are terms used to distinguish from secondary particles formed by aggregation 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 it is a concept including single particles composed of one primary particle and similar-single particle forms that are aggregates of 30 or fewer primary particles.

[0059] Specifically, in the present invention, the single particle may be a single particle composed of one primary particle and / or an aggregate of 30 or fewer primary particles in a similar-single particle form, and the secondary particle may be in a form in which 30 or more primary particles are aggregated. For example, the secondary particle may be in a form in which 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 are aggregated.

[0060] In this specification, the size of the Si crystal grains contained in the silicon-carbon composite can be confirmed by X-ray diffraction analysis, and the X-ray diffraction analysis may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). Specifically, the XRD measurement can sample a sample in powder form into a holder and measure it with Cu K alpha X-ray. The size of the Si crystal grains can be calculated by fitting to the XRD results using the Scherrer equation, and the reference of the crystal grains at this time can be measured based on Si(220). (2θ = 47.5° to 48.5°)

[0061] In one embodiment of the present invention, the Si crystal grain size of the silicon-carbon composite may be 0.1 nm or more and 20 nm or less. Specifically, it may be 0.5 nm or more and 15 nm or less, 1 nm or more and 15 nm or less, 1.5 nm or more and 12 nm or less, 1.5 nm or more and 10 nm or less, 2 nm or more and 10 nm or less, 3 nm or more and 10 nm or less, or 4 nm or more and 9 nm or less.

[0062] When the crystal grain size of the Si satisfies the above range, Li ions are uniformly diffused inside the Si particles, and there is an effect of stably maintaining the structure of the Si particles during charge and discharge. On the other hand, when the crystal grains of the Si exceed the above range, due to the stress caused by the shrinkage / expansion of the Si material that appears during charge and discharge, cracks are formed in the particles, and Li ions cannot diffuse to the inside of the crystal grains. There is a problem that the life of the cell is reduced due to the acceleration of the degradation of the material caused by the non-uniformity of the reaction.

[0063] In this specification, the crystal grains of the lithium composite transition metal compound can mean, for example, the crystal size of the structure itself of Chemical Formula 1 described above. In this specification, the size of the crystal grains of the lithium composite transition metal compound can be confirmed by X-ray diffraction analysis, and the X-ray diffraction analysis may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). Specifically, the XRD measurement can sample a Powder-form sample into a holder and measure it with Cu K alpha X-ray. The size of the crystal grains of the lithium composite transition metal compound is calculated by fitting to the XRD results using the Scherrer equation, and the size of the crystal grains at this time can be measured based on the maximum peak that appears around 2θ = 10° to 12°.

[0064] In one embodiment of the present invention, the crystal grain size of the lithium composite transition metal compound may be 100 nm or more and 200 nm or less. Specifically, it may be 100 nm or more and 170 nm or less, 100 nm or more and 160 nm or less, or 105 nm or more and 150 nm or less.

[0065] When the crystal grain size of the lithium composite transition metal compound satisfies the above range, the phase stability of the lithium composite transition metal compound is excellent and it can react stably with Li. On the other hand, when the crystal grain size of the lithium composite transition metal compound is smaller than the above range, there is a problem that the reaction with Li occurs for a long time and the efficiency of the positive electrode decreases. When it exceeds the above range, there is a problem that particle cracking of the positive electrode active material occurs in the rolling stage during 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% or more and 10% or less, 1% or more and 10% or less, or 1% or more and 9.5% or less 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 the above relationship, the stress due to the volume expansion of the negative electrode active material particles during charge and discharge can be reduced, and not only can particle cracking be prevented, but also an electrochemical reaction can easily occur even with a small amount of lithium (Li) due to the stable crystal structure with a relatively large crystal grain size of the lithium composite transition metal compound as the positive electrode active material, and the cycle characteristics and swelling performance can be improved.

[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 composite transition metal compound satisfy the above-mentioned crystal grain sizes respectively, when the Si crystal grain size of the silicon-carbon composite exceeds 10% of the crystal grain size of the lithium composite transition metal compound, the lithium (Li) remaining in the silicon-carbon composite may cause degradation of the cycle performance and an increase in the degree of swelling, and there is a problem that cracks occur in the particles due to an increase in the internal stress of Si during charge and discharge, resulting in a decrease in the cycle performance.

[0068] In one embodiment of the present invention, the average particle size (D of the single particle 50) may be 1 μm or more. Further, the average particle diameter of the single particle may be 12 μm or less. For example, the average particle diameter of the single particle may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, 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] Even if the single particle is formed to have a small particle diameter with an average particle diameter of about 1 μm or more and 12 μm or less, its particle strength may be excellent. As a result, the phenomenon of an increase in fine particles in the electrode due to cracking of the particles can be alleviated, and the life characteristics of the battery can be improved. For example, when the single particle is rolled with a force of 650 kgf / cm 2 it can have a particle strength of 100 to 300 MPa. Therefore, even if the single particle is rolled with a strong force of 650 kgf / cm 2 the phenomenon of an increase in fine particles in the electrode due to cracking of the particles is alleviated, and the life characteristics of the battery are improved.

[0070] The method for forming the single particle is not particularly limited. Usually, it may be formed by increasing the firing temperature and overfiring, or it may be manufactured by using an additive such as a grain growth accelerator useful for overfiring, or by changing the starting material.

[0071] Even when the single particle has high rigidity of the particle itself and high electrode density, the decrease in battery performance is relatively excellent. Therefore, the energy density can be increased by adjusting the average particle diameter range of the single particle and the silicon-carbon composite.

[0072] In one embodiment of the present invention, the average particle diameter (D 50 ) of the single particle may be smaller than the average particle diameter (D 50 ) of the silicon-carbon composite.

[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 relatively decreases, and the life performance can be improved. That is, the larger the average particle size of the single particles, the more 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 relative increase in diffusion resistance may cause lithium precipitation and the like, resulting in a decrease in battery performance and a possible decrease in life performance.

[0074] Also, when the average particle size of the single particles is smaller than the average particle size of the silicon-carbon composite, the occurrence of side reactions with the electrolyte due to the increase in specific surface area can be prevented, and the life performance can be improved.

[0075] According to one embodiment of the present invention, the average particle size (D 50 ) of the single particles may be 1 μm to 12 μm smaller than the average particle size (D 50 ) of the silicon-carbon composite. Specifically, it may be 1.5 μm to 11.5 μm, or 2 μm to 11 μm smaller.

[0076] When the average particle size (D 50 ) of the single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, for example, when the above range is satisfied, the diffusion resistance of the single particles relatively decreases, and the life performance can be improved. That is, the larger the average particle size of the single particles, the more 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 relative increase in diffusion resistance may cause lithium precipitation and the like, resulting in a decrease in battery performance and a possible decrease in life performance.

[0077] Also, when the average particle size (D 50 ) of the single particles is the average particle size (D 50When it is smaller than , for example, when the above 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 ) of the single particle and the average particle size (D 50 ) of the silicon-carbon composite may be in a ratio of 1.5:2 to 1.5:20.

[0079] When the above range is satisfied, the diffusion resistance of the single particle is relatively reduced, and the life performance can be improved. That is, as the average particle size of the single particle increases, the diffusion resistance may increase. When the average particle size of the single particle is larger than the average particle size of the silicon-carbon composite, the diffusion resistance increases relatively, which may cause lithium precipitation or the like, resulting in a possible decrease in battery performance and a possible decrease in life performance.

[0080] Also, when the average particle size (D 50 ) of the single particle is smaller than the average particle size (D 50 ) of the silicon-carbon composite, for example, when the above 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 ) of the single particle is smaller than the average particle size (D 50 ) of the secondary particles.

[0082] In the present invention, the single particle may be a single particle composed of one primary particle or an aggregate of 30 or fewer primary particles in a similar-single particle form. The secondary particle may be a form in which 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 are aggregated.

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

[0084] The average particle size (D 50 ) of the secondary particles 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 ) of the primary particles may be 0.5 μm to 3 μm. Specifically, the secondary particles may be in a form in which 30 or more primary particles are aggregated, 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 excellent in electrochemical characteristics can be formed. If the average particle size of the primary particles is too small, the number of aggregated primary particles forming lithium nickel-based oxide particles increases, and the effect of suppressing particle cracking during rolling decreases. If the average particle size of the primary particles is too large, the lithium diffusion path inside the primary particles becomes long and the resistance increases, and the output characteristics may decrease.

[0087] In one embodiment of the present invention, the average particle size (D 50 ) of the single particles may be smaller than the average particle size (D 50 ) of the secondary particles. Thereby, even if the single particles are formed with a small particle size, their particle strength is excellent, whereby the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and the life characteristics of the battery can be improved.

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

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

[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, even if the single particles are formed with a small particle size, their particle strength is excellent, and thereby, the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and the effects of improving the life characteristics of the battery and the energy density are achieved.

[0091] In one embodiment of the present invention, the average particle size (D 50 ) of the silicon-carbon composite may be smaller than the average particle size (D 50 ) of the graphite. When the average particle size of the silicon-carbon composite is smaller than the average particle size of the graphite, there is an effect that particle cracking is reduced due to a decrease in the volume expansion / shrinkage rate during charge and discharge, and the life performance of the battery is improved.

[0092] In the lithium secondary battery according to the above-described embodiment, the negative electrode active material may further contain 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 ) of the silicon-carbon composite may be smaller than the average particle size (D 50 ) of the graphite by 1 μm to 25 μm. For example, the average particle size of the silicon-carbon composite may be smaller than the average particle size of the graphite by 2 μm to 24 μm, may be smaller by 3 μm to 23 μm, or may be smaller by 4 μm to 22 μm.

[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 particles, 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, there is an effect that the life performance of the battery is improved.

[0103] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the single particles are contained in an amount of 15 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material, and the silicon-carbon composite may be contained in an amount of 3 parts by weight to 30 parts by weight with respect to 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 with respect to 100 parts by weight of the positive electrode active material. The single particles may be contained in an amount of 20 parts by weight to 100 parts by weight, or 30 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material.

[0105] For example, the single particles may be contained 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 with respect to 100 parts by weight of the positive electrode active material. For example, the single particles may be contained 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 with respect to 100 parts by weight of the positive electrode active material.

[0106] When the single particles within the above range are included, excellent battery characteristics can be exhibited in combination with the above-described negative electrode material. In particular, when the single particles are 15 parts by weight or more, the phenomenon of an increase in fine particles in the electrode due to particle cracking can be alleviated during the rolling process after fabricating the electrode, and thereby, the life characteristics of the battery can be improved.

[0107] In one embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less based on 100 parts by weight of the positive electrode active material. The secondary particles may be 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less based on 100 parts by weight of the positive electrode active material. 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 based on 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 above-described effects due to the presence of the positive electrode active material of the single particles can be maximized. When the secondary particles contain the positive electrode active material, the components thereof may be the same as or different from those exemplified by the above-described single particle positive electrode active material, and may mean a form in which the single particle form is aggregated.

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

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

[0112] The positive electrode binder can play a role in improving the adhesion between the positive electrode active material particles and the adhesion force between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, those known in the technical field may be used. 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, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0113] The positive electrode binder may be contained in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the positive electrode active material layer. For example, preferably, it may be contained in an amount of 0.3 part by weight or more and 35 parts by weight or less, and more preferably, 0.5 part by weight or more and 20 parts by weight or less.

[0114] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode. As long as it does not cause a chemical change in the battery and has electron conductivity, it can be used without particular limitation. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

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

[0116] In this specification, as a composite of Si and C, the silicon-carbon composite appears to have Si and C (for example, graphite) peaks observed in the XRD diffraction pattern and no Si / C, which is the second phase, formed.

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

[0118] The silicon-carbon composite, as a material having high capacity and high efficiency compared to silicon-based oxides, can exhibit excellent effects in terms of resistance compared to a negative electrode containing a silicon-based oxide and a conductive material even when the conductive material is not included. Further, since the silicon-carbon composite exhibits higher Si crystallinity than silicon-based oxides, it can exhibit excellent effects during high-output evaluation.

[0119] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material may further contain 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. Based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the graphite may be contained in an amount of 70 parts by weight or more and 97 parts by weight or less.

[0120] Based on 100 parts by weight of the total negative electrode active material, the graphite may be contained 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 contained in an amount of 95 parts by weight or less, 93 parts by weight or less, or 90 parts by weight or less. When the graphite is a mixture of artificial graphite and natural graphite, based on 100 parts by weight of the graphite, the artificial graphite and the natural graphite may be contained 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.

[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, in the lithium secondary battery according to the above-described embodiment, among 100 parts by weight of the negative electrode active material layer, 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 still more preferably 98 parts by weight or more and 99.9 parts by weight or less.

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

[0124] As the negative electrode binder, it can play a role in improving the adhesion between negative electrode active material particles and the adhesion between negative electrode active material particles and the negative electrode current collector. As the negative electrode binder, those known in the art may be used. As non-limiting examples, 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, poly acrylic acid, and at least any one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc. may be included, and various copolymers thereof may also be included.

[0125] The negative electrode binder may be contained in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the negative electrode active material layer. For example, preferably, it may be contained in an amount of 0.3 part by weight or more and 35 parts by weight or less, and more preferably, 0.5 part by weight or more and 10 parts by weight or less.

[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 has conductivity without inducing a chemical change in the battery. For example, 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 fluorocarbons, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used. 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, based on 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 containing the positive electrode active material.

[0128] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. The positive electrode current collector usually may have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[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 containing the negative electrode active material.

[0130] The negative electrode current collector only needs to have conductivity without inducing chemical changes in the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Specifically, a transition metal that adsorbs carbon well, 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 the thickness of the current collector 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, the negative electrode further includes a negative electrode active material layer containing the negative electrode active material, and the thicknesses of the positive electrode and the negative electrode active material layers are each 10 μm or more and 500 μm or less. 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, and these thicknesses may be the same. Specifically, the thicknesses of the positive electrode and the negative electrode active material layers may be each 15 μm or more and 400 μm or less, 20 μm or more and 300 μm or less, 25 μm or more and 200 μm or less, or 30 μm or more and 100 μm or less.

[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 loading amount per unit volume of the positive electrode active material layer is 250 mg / 25 cm 2 ~900 mg / 25 cm 2 and the negative electrode further includes a negative electrode active material layer containing the negative electrode active material, and the loading amount per unit volume of the negative electrode active material layer is 100 mg / 25 cm 2 ~600 mg / 25 cm 2 Specifically, the loading amount per unit volume of the positive electrode active material layer is 270 mg / 25 cm 2 ~800 mg / 25 cm 2 、285 mg / 25 cm 2 ~700 mg / 25 cm 2 、or 300 mg / 25 cm 2 ~600 mg / 25 cm 2It may also be that the loading amount per unit volume of the negative electrode active material layer is 120 mg / 25 cm 2 ~500 mg / 25 cm 2 、135 mg / 25 cm 2 ~400 mg / 25 cm 2 、150 mg / 25 cm 2 ~300 mg / 25 cm 2 It may also be that.

[0133] The positive electrode and the negative electrode may be manufactured by the usual manufacturing methods of positive and negative electrodes, except that the above positive and negative electrode active materials are used. Specifically, it may be manufactured by applying a composition for forming an active material layer containing the above active material and, optionally, a binder and a conductive material onto a current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode and negative electrode active materials, the binder, and the conductive material are as described above. The solvent may be a solvent commonly used in the art, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more thereof may be used. The amount of the solvent used is such that, in consideration of the coating thickness of the slurry and the production yield, the active material, the conductive material, and the binder are dissolved or dispersed, and later, when coating to manufacture the positive electrode and the negative electrode, it has a viscosity that can exhibit excellent thickness uniformity. Also, as another method, the positive electrode and the negative electrode may be manufactured by casting the composition for forming the active material layer on a separate support, and then laminating the film obtained by peeling from this support onto the current collector.

[0134] The separation membrane separates the negative electrode and the positive electrode and provides a migration path for lithium ions. It can be used without particular limitation as long as it is usually used as a separation membrane in a secondary battery. In particular, those with low resistance to ion migration of the electrolyte and excellent electrolyte impregnation ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separation membrane containing a ceramic component or a polymer substance may be used, and it may be selectively used in a single-layer or multi-layer structure.

[0135] Examples of the electrolyte include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery, but are not limited thereto.

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

[0137] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene 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, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

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

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

[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 ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the capacity reduction of the battery, improving the discharge capacity of the battery, etc.

[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 the above range is satisfied, the energy density of the lithium secondary battery designed within a limited space can be increased, the high output performance can be improved, and the 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 means that the form of the battery itself including an assembly containing a positive electrode, a negative electrode, a separator, and an electrolyte is cylindrical. Specifically, it may be composed of a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap. However, the lithium secondary battery is not limited thereto, and it may be a prismatic battery or a pouch-type battery.

[0143] An embodiment of the present invention provides a battery pack and an electronic device including the above-described cylindrical battery as a unit cell. Since the battery pack and the electronic device include the secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they may be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0144] The lithium secondary battery according to an embodiment of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance. Therefore, it can be used not only for portable devices such as mobile phones, notebook computers, and digital cameras, but also as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery module or battery pack may be used as a power source for one or more of medium and large-sized devices such as power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); or power storage systems.

[0145] [Examples] Hereinafter, in order to assist in the understanding of the present invention, preferred examples are presented. However, these examples are only illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the claims.

[0146] <Examples and Comparative Examples> Example 1 Based on 100 parts by weight of the positive electrode active material layer, as the positive electrode active material, among metals excluding lithium, it has 93.3 mol% of Ni, 4.9 mol% of Co, and 1.8 mol% of Mn, and contains 98.04 parts by weight of single particles and secondary particles of a lithium composite transition metal compound (single particle: secondary particle = 50:50 weight ratio). As a binder, 1 part by weight of PVDF, and as a conductive material, 0.8 part by weight of CNT and a CNT pre-dispersion liquid containing 0.16 part by weight of a dispersant were used to produce a composition for forming a positive electrode active material layer.

[0147] The lithium composite transition metal compound used was heat-treated at 750 °C for 8 hours under an Ar atmosphere, and the crystal grain size of the used lithium composite transition metal compound was 110 nm. Also, the size of the single particles was D 50 = 3.57 μm and the size of the secondary particles was D 50 = 9.5 μm by production. The composition for forming the positive electrode active material layer was coated on an aluminum foil with a thickness of 30 μm to a dry thickness of 103 μm, and then dried to produce a positive electrode.

[0148] Based on 100 parts by weight of the negative electrode active material layer, as the negative electrode active material, 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) were 97.7 parts by weight. As a binder, it contained 1.15 parts by weight of SBR (styrene-butadiene rubber) and 1 part by weight of CMC (carboxymethyl cellulose). In addition, it contained 0.09 part by weight of a dispersant and a CNT pre-dispersion liquid containing 0.06 part by weight of single-walled CNT to produce a composition for forming a 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. Also, the size of the silicon-carbon composite was D 50 = 5.2 μm and the size of the graphite was D 50 = 17 μm were manufactured. After coating the composition for forming a negative electrode active material layer on a copper foil with a thickness of 15 μm to a dry thickness of 86 μm, it was dried to manufacture a negative electrode.

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

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

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

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

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

[0155] As the composition for forming the positive electrode active material layer, a composition obtained by heat-treating a lithium composite transition metal compound at 750 °C for 8 hours in an Ar atmosphere was used. The crystal grain size of the used lithium composite transition metal compound was 105 nm. Also, the size of single particles was D 50 = 3.63 μm and the size of secondary particles was D 50 = 10.5 μm were produced by the airflow pulverization method.

[0156] As the composition for forming the negative electrode active material layer, a composition obtained by heat-treating a silicon carbon composite at 400 °C for 2 hours in an Ar atmosphere was used. The Si crystal grain size of the used silicon carbon composite was 9 nm. Also, the size of the silicon carbon composite was D 50 = 7.1 μm and the size of graphite was D 50 = 17 μm were produced by the airflow pulverization method.

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

[0158] As the composition for forming the positive electrode active material layer, a composition obtained by heat-treating a lithium composite transition metal compound at 800 °C for 10 hours in an Ar atmosphere was used. The crystal grain size of the used lithium composite transition metal compound was 150 nm. Also, the size of single particles was D 50 = 3.72 μm and the size of secondary particles was D 50 = 9.5 μm were produced by the airflow pulverization method.

[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 composition for forming the positive electrode active material layer used a lithium composite transition metal compound heat-treated at 800 °C for 10 hours in an Ar atmosphere, and the crystal grain size of the used lithium composite transition metal compound was 140 nm. Also, the size of single particles was D 50 = 3.74 μm and the size of secondary particles was D 50 = 16.5 μm, and it was manufactured accordingly.

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

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

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

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

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

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

[0171] For the composition for forming the negative electrode active material layer, a composition obtained by heat-treating a silicon carbon composite at 700 °C for 2 hours in an Ar atmosphere was used. The Si crystal grain size of the used silicon carbon composite was 17 nm. Also, the size of the silicon carbon composite was D 50 = 5.3 μm and the size of graphite was D 50 = 17 μm were produced by the airflow pulverization method.

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

[0173] For the composition for forming the positive electrode active material layer, a composition obtained by heat-treating a lithium composite transition metal compound at 750 °C for 8 hours in an Ar atmosphere was used. The crystal grain size of the used lithium composite transition metal compound was 120 nm. Also, the size of single particles was D 50 = 3.60 μm and the size of secondary particles was D 50 = 10.5 μm were produced by the airflow pulverization method.

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

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

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

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

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

[0179] A composition for forming a positive electrode active material layer, using a lithium composite transition metal compound heat-treated at 650 °C for 6 hours in an Ar atmosphere, the crystal grain size of the used lithium composite transition metal compound was 80 nm. Also, by the airflow pulverization method, the size of single particles was D 50 = 3.52 μm and the size of secondary particles was D 50 = 12.5 μm was manufactured.

[0180] A composition for forming a negative electrode active material layer, using a silicon-carbon composite heat-treated at 400 °C for 2 hours in an Ar atmosphere, the Si crystal grain size of the used silicon-carbon composite was 10 nm. Also, by the airflow pulverization method, the size of the silicon-carbon composite was D 50 = 6.9 μm and the size of graphite was D 50 = 17 μm was manufactured.

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

[0182] A composition for forming a positive electrode active material layer, using a lithium composite transition metal compound heat-treated at 650 °C for 6 hours in an Ar atmosphere, the crystal grain size of the used lithium composite transition metal compound was 88 nm. Also, by the airflow pulverization method, the size of single particles was D 50 = 3.52 μm and the size of secondary particles was D 50 = 12.7 μm was manufactured.

[0183] A composition for forming a negative electrode active material layer, using a silicon-carbon composite heat-treated at 400 °C for 2 hours in an Ar atmosphere, the Si crystal grain size of the used silicon-carbon composite was 10 nm. Also, by the airflow pulverization method, the size of the silicon-carbon composite was D 50 = 6.8 μm and the size of graphite was D 50 = 17 μm was manufactured.

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

[0185] As the composition for forming the positive electrode active material layer, a composition obtained by heat-treating a lithium composite transition metal compound at 650 °C for 6 hours in an Ar atmosphere was used. The crystal grain size of the used lithium composite transition metal compound was 80 nm. Also, the size of single particles was D 50 = 3.52 μm and the size of secondary particles was D 50 = 12.5 μm by a jet milling method.

[0186] As the composition for forming the negative electrode active material layer, a composition obtained by heat-treating a silicon carbon composite at 400 °C for 2 hours in an Ar atmosphere was used. The Si crystal grain size of the used silicon carbon composite was 9 nm. Also, the size of the silicon carbon composite was D 50 = 7.1 μm and the size of graphite was D 50 = 17 μm by a jet milling method.

[0187] The compositions of the negative electrode active material and the positive electrode active material produced in the above Examples and Comparative Examples are as shown in Table 1 below.

[0188]

Table 1A

[0189]

Table 1B

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

[0191] <Experimental Example: Discharge Capacity, Initial Efficiency, Life (Capacity Retention Rate) Characteristic Evaluation> Charge and discharge were performed on the lithium secondary batteries manufactured in the examples and comparative examples, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated and described in Table 2 below.

[0192] For the 1st cycle and 2nd cycle, charge and discharge were performed at 0.1C, and from the 3rd cycle to the 199th cycle, charge and discharge were performed at 0.5C. The 200th cycle ended in a charged state (with lithium in the negative electrode).

[0193] Charging condition: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharging condition: CC (constant current) condition 1.5V Based on the results of one charge-discharge cycle, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation.

[0194] Initial efficiency (%) = (discharge capacity in one cycle / charge capacity in one cycle) × 100

[0195] The capacity retention rate was derived by the following calculations respectively.

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

[0197] <Experimental Example: Cell Thickness Evaluation> The thickness of the fabricated secondary battery was compared before and after cycling as follows.

[0198] For the 1st cycle and the 2nd cycle, charging and discharging were performed at 0.1C, and from the 3rd cycle to the 200th cycle, charging and discharging were performed at 0.5C. Taking the cell thickness after the 2nd cycle as the initial thickness and the cell thickness after the 200th cycle as the post-thickness, the thickness was calculated by the following formula. The cell thickness of Example 1 calculated was set to 100%, and based on this, the cell thicknesses of Examples 2-6 and Comparative Examples 1-7 were calculated relatively and listed in Table 2 below.

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

[0200]

Table 2

[0201] According to Tables 1 and 2 above, it was confirmed that the secondary batteries of Examples 1 to 6, in which the Si crystal grain size of the silicon carbon composite satisfies 10% or less of the crystal grain size of the lithium composite transition metal compound, show an excellent capacity retention rate with a thinner cell thickness compared to Comparative Examples 1 to 7. This is because 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, so that during charge and discharge, the stress due to the volume expansion of the negative electrode active material particles can be reduced. As a result, it seems that the cracking of the particles is reduced and the cycle characteristics and swelling performance are improved. On the other hand, in the case of Comparative Examples 1 to 7, since the Si crystal grain size of the silicon carbon composite exceeds 10% of the crystal grain size of the lithium composite transition metal compound, it was confirmed that cracks are generated in the particles due to the increase in the internal stress of Si during charge and discharge, resulting in a decrease in the cycle performance.

[0202] In particular, in the case of Example 5 and Comparative Example 5, Example 6 and Comparative Example 1, and Example 3 and Comparative Example 7, even when the Si crystal grain size of the silicon carbon composite is the same, different effects are derived depending on the crystal grain size of the positive electrode active material. Therefore, it can be confirmed that the cycle characteristics and the degree of swelling can be improved by the relative sizes of the Si crystal grain size of the silicon carbon composite and the crystal grain size of the lithium composite transition metal 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.

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