Lithium secondary battery, battery module, and battery pack

Abstract

The invention relates to a lithium secondary battery, a battery module and a battery pack. In one embodiment, the lithium secondary battery includes: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator between the positive electrode and the negative electrode; and an electrolyte, in which the positive electrode active material contains a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound including at least one of a single particle or a quasi-single particle, the at least one of the single particle or the quasi-single particle having an average particle diameter (D50) of 1 [mu] m or more, the single particle is composed of one agglomerate, the quasi-single particle is a composite composed of 30 agglomerates or less, the negative electrode active material contains a silicon-carbon composite having an average particle diameter (D50) greater than 1 [mu] m, and the average particle diameter (D50) of the silicon-carbon composite is greater than 1 [mu] m. And the average particle size (D50) of at least one of the single particles and the quasi-single particles is smaller than the average particle size (D50) of the silicon-carbon compound.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of July 20, 2023, an application number of 202380015209.2, and an invention title of "Lithium Secondary Battery, Battery Module, and Battery Pack". Technical Field

[0002] This application claims the priority and benefits of Korean Patent Application No. 10-2022-0097491 filed with the Korean Intellectual Property Office on August 4, 2022, and Korean Patent Application No. 10-2023-0091528 filed with the Korean Intellectual Property Office on July 14, 2023. The entire contents of the patent applications are incorporated herein by reference.

[0003] The present invention relates to a lithium secondary battery, a battery module, and a battery pack. Background Art

[0004] In recent years, with the rapid popularization of electronic devices using batteries, such as not only mobile phones, laptop computers, and electric vehicles, but also power tools and cleaners, the demand for small and lightweight secondary batteries with relatively high capacity and / or high output is increasing rapidly. In particular, lithium secondary batteries are lightweight and have a high energy density, and thus have attracted attention as a driving power source for electronic devices. Therefore, active research and development efforts have been made to improve the performance of lithium secondary batteries.

[0005] A lithium secondary battery generates electric power through oxidation and reduction reactions during the insertion or extraction of lithium ions at the positive electrode and the negative electrode in a state where an organic electrolyte or a polymer electrolyte is filled between the positive electrode and the negative electrode. The positive electrode and the negative electrode are composed of active materials capable of inserting and extracting lithium ions.

[0006] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4), etc. have been used. Among them, lithium cobalt oxide (LiCoO2) has been widely used due to its advantages of high working voltage and excellent capacity characteristics, and is used as a high-voltage positive electrode active material. However, because the price of cobalt (Co) has increased and the supply is unstable, its large-scale use as a power source in fields such as electric vehicles is limited, and thus there is an urgent need to develop a positive electrode active material that can replace cobalt.

[0007] 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 by nickel (Ni) and manganese (Mn) has been developed. In recent years, attempts have been made to increase the capacity of NCM-based lithium composite transition metal compounds by increasing the content of Ni in the compounds. However, Ni-rich cathode active materials with a high Ni content have drawbacks such as increased resistance and gas generation due to deteriorated thermal stability and an increase in side reactions during the electrochemical reaction.

[0008] On the other hand, although graphite is generally used as the anode active material of a lithium secondary battery, it is difficult to increase the capacity of the lithium secondary battery because graphite has a small capacity per unit mass of 372 mAh / g. Therefore, in order to increase the capacity of the lithium secondary battery, anode materials such as silicon, tin, and their oxides have been developed as non-carbon-based anode materials having a higher energy density than graphite. However, although these non-carbon-based anode materials have a large capacity, the problem with these materials is that a large amount of lithium is consumed during the initial charge and discharge process and a large irreversible loss of capacity occurs due to low initial efficiency. Summary of the Invention

[0009] Technical Problem

[0010] The inventors have found that in a lithium secondary battery designed in a limited space, optimal battery performance can be achieved through a specific combination of the type, average particle size, and / or component content of the active materials constituting the positive electrode and the negative electrode, thus completing the present invention.

[0011] Technical Solution

[0012] One embodiment of the present disclosure provides a lithium secondary battery, a battery module, and a battery pack including the same, the lithium secondary battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material contains a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound including at least one of single particles or quasi-single particles, wherein each single particle is composed of one agglomerate, wherein each quasi-single particle is a composite of 30 or less agglomerates, and an average particle size (D 50 ) of at least one of the single particles or quasi-single particles is 1 μm or more, the negative electrode active material includes a silicon-carbon composite, the silicon-carbon composite has an average particle size (D 50 ) greater than 1 μm, and the average particle size (D 50 ) of at least one of the single particles or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite.

[0013] Advantageous Effects

[0014] According to the embodiments described in this specification, it is possible to increase the energy density of a lithium secondary battery designed in a limited space, improve its high-output performance, and also improve the cycle performance of the battery. Detailed Embodiments

[0015] Hereinafter, to assist in understanding the present invention, the present invention will be described in more detail. The present invention can be implemented in various different forms and is not limited to the exemplary embodiments described herein. In this case, the terms or words used in the specification and claims should not be construed as being limited to the typical or dictionary meanings, but should be interpreted based on the principle that the inventor can appropriately define the concept of the term to best describe his / her own invention, using meanings and concepts consistent with the technical spirit of the present invention.

[0016] In the present invention, the terms "comprising", "including", or "having" are intended to mean the presence of the implemented features, quantities, steps, components, or any combination thereof, and it should be understood that the possibility of the presence or addition of one or more other features, quantities, steps, components, or any combination thereof is not excluded.

[0017] In a case where a part such as a layer is present "above" or "on" another part, it includes not only the case where the part is present "directly above" the other part, but also the case where another part is present therebetween. On the contrary, the case where a part is present "directly above" another part means that no other part is present therebetween. In addition, in the case of referring to "above" or "on" a reference part, it means being located above or below the reference part and does not necessarily mean "above" or "on" in the direction opposite to gravity.

[0018] In the present invention, a "single particle" is a particle composed of a single agglomerate. An "agglomerate" according to the present invention can be a single crystal lacking any grain boundaries, or can be a polycrystal in which grain boundaries do not appear when observed at a magnification of 5000× to 20000× using a scanning electron microscope (SEM). In the present invention, a "quasi-single particle" refers to a particle of a composite formed by 30 or fewer agglomerates.

[0019] In the present invention, a "secondary particle" refers to a particle formed by the aggregation of dozens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles.

[0020] In the present invention, when describing "particles", it may include any one or all of single particles, quasi-single particles, primary particles, agglomerates, and secondary particles.

[0021] In this specification, "average particle diameter (D 50)” can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The average particle size (D 50 ) can be measured using, for example, the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to about a few millimeters and can obtain highly reproducible and high-resolution results.

[0022] The measurement of the average particle size (D 50 ) can be confirmed by using water and Triton-X100 dispersant and using a Microtrac instrument (manufacturer: Microtrac, model name: S3500). Specifically, the average particle size (D 50 ) of the positive electrode active material can be measured within a refractive index range of 1.5 to 1.7, and the negative electrode active material can be measured under refractive index conditions of 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring device and irradiated with ultrasonic waves at about 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph is obtained. Then, the average particle size can be measured by obtaining the particle size corresponding to 50% of the volume cumulative amount.

[0023] One embodiment of the present invention provides a lithium secondary battery, which includes: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material contains a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound includes single particles and / or quasi-single particles with an average particle size (D 50 ) of 1 μm or more, each single particle is composed of one agglomerate, and each quasi-single particle is a composite of 30 or fewer agglomerates, the negative electrode active material contains a silicon-carbon composite, the silicon-carbon composite has an average particle size (D 50 ) greater than 1 μm, and the average particle size (D 50 ) of the single particle or quasi-single particle is smaller than the average particle size (D 50 ) of the silicon-carbon composite.

[0024] The silicon-carbon composite may be a Si / C-based active material.

[0025] In this specification, the silicon-carbon composite is a composite of Si and C and is different from silicon carbide represented by SiC. Since silicon carbide does not undergo an electrochemical reaction with lithium, all properties such as service life characteristics can be measured as zero.

[0026] The silicon-carbon composite may be a composite of silicon, graphite, etc., or may form a structure in which a core made of a composite of silicon and graphite, etc. is surrounded by graphene, amorphous carbon, etc. In the silicon-carbon composite, the silicon may be nanosilicon. For example, the nanosilicon may be silicon in the range of 1 nm to 999 nm.

[0027] The lithium secondary battery has the dimensions required for its use and needs to be designed within a limited space. Although consumers' demands for increasing the energy density and improving the high-output performance are increasing, there is no choice but to increase the content of the negative electrode material to meet the demands when using a high-capacity positive electrode material. Therefore, there are limitations in increasing the battery efficiency within a limited space. In addition, depending on the type of the negative electrode material, it is necessary to design a positive electrode material having an efficiency matching that of the negative electrode material.

[0028] For example, the energy density can be increased. However, when the electrode density is increased by reducing the porosity of the positive electrode, the strong calendering for this purpose may deteriorate the battery performance due to cracks generated on the particles.

[0029] The single particles used in the embodiments of the present invention themselves have high particle rigidity. Thus, even when the electrode density is high, they are relatively excellent in terms of deterioration of the battery performance. Therefore, the energy density can be increased by combining the single particles with the silicon-carbon composite according to the average particle size range.

[0030] According to other embodiments of the present invention, it is characterized in that the positive electrode active material contains a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound contains single particles and / or quasi-single particles, and the average particle size (D 50 ) of the single particles and / or quasi-single particles is 1 μm or more.

[0031] As the average particle size (D 50 ) of the single particles and / or quasi-single particles becomes smaller, the specific surface area increases and the side reaction with the electrolyte increases, which may cause a decrease in the electrochemical performance such as the service life performance. If the average particle size (D 50 ) of the single particles and / or quasi-single particles is less than 1 μm, this may not be within the commercially applicable range. Even so, the service life performance may be very poor due to the increase in the specific surface area, making it difficult to apply.

[0032] When the average particle size (D 50 ) of the single particles and / or quasi-single particles is 1 μm or more, 3 μm or more, or 5 μm or more, the single particles and / or quasi-single particles have excellent service life performance due to the reduction of the side reaction with the electrolyte.

[0033] On the other hand, it is characterized in that the negative electrode active material contains a silicon-carbon composite, and the average particle size (D 50 ) of the silicon-carbon composite is greater than 1 μm, and the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite.

[0034] As the average particle size (D 50 ) of the silicon-carbon composite becomes smaller, the specific surface area increases and the side reactions with the electrolyte increase, which will lead to a decrease in electrochemical performance such as service life performance. If the average particle size (D 50 ) of the silicon-carbon composite is less than 1 μm, due to the increase in side reactions caused by the increase in specific surface area, the life performance may become very low, making it difficult to apply.

[0035] When the average particle size (D 50 ) of the silicon-carbon composite is greater than 1 μm, greater than 3 μm or greater than 5 μm, the side reactions with the electrolyte decrease, resulting in excellent life performance.

[0036] Within the above range, the silicon-carbon composite has excellent service life performance, and the silicon grain size of the silicon-carbon composite can be 10 nm or less. In addition, the silicon-carbon composite has better initial capacity and efficiency than other silicon systems such as SiO, and has excellent electrochemical performance, so that the best battery performance can be achieved under the average value of the combination of single particles and / or quasi-single particles.

[0037] Even if the single particles and / or quasi-single particles are formed with a small particle size, the single particles and / or quasi-single particles can have excellent particle strength, and the excellent particle strength can alleviate the phenomenon of an increase in the number of fine particles in the electrode due to particle breakage, thereby improving the service life characteristics of the battery.

[0038] When the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, the diffusion resistance of the single particles and / or quasi-single particles can be relatively reduced to improve the service life performance. That is, lithium enters the single particles and / or quasi-single particles based on discharge, and the diffusion resistance can increase with the increase in the average particle size (D 50 ) of the single particles and / or quasi-single particles. If the average particle size (D 50 ) of the single particles and / or quasi-single particles is greater than the average particle size (D 50 ) of the silicon-carbon composite, then lithium may not be able to enter the single particles and / or quasi-single particles due to the relative increase in diffusion resistance and may precipitate, resulting in a decrease in battery performance and service life performance.

[0039] When the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, side reactions with the electrolyte can be prevented due to the increased specific surface area of the single particles and / or quasi-single particles, thereby improving the service life performance.

[0040] If the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, the diffusion resistance of the single particles and / or quasi-single particles can be relatively reduced, thereby improving the service life performance.

[0041] Because the single particles and / or quasi-single particles have a greater lithium diffusion resistance than the silicon-carbon composite, if the average particle size (D 50 ) of the single particles and / or quasi-single particles is larger than the average particle size (D 50 ) of the silicon-carbon composite, charge and discharge cannot proceed smoothly due to the increased lithium diffusion resistance, resulting in poor service life performance. Therefore, the average particle size (D 50 ) of the single particles and / or quasi-single particles can be smaller than the average particle size (D 50 ) of the silicon-carbon composite.

[0042] According to other exemplary embodiments of the present invention, the positive electrode active material contains nickel, cobalt, and manganese, and may further contain aluminum.

[0043] According to an embodiment of the present invention, in the lithium composite transition metal compound, the content of nickel relative to the metal other than lithium is 80 mol% or more.

[0044] In another embodiment, in the positive electrode active material, the content of nickel relative to the metal other than lithium is 80 mol% or more and less than 100 mol%, and the lithium composite transition metal compound having a nickel content of 80 mol% or more and less than 100 mol% relative to the metal other than lithium may include one or more mixtures represented by the following Chemical Formula 1.

[0045] The lithium composite transition metal compound may further contain secondary particles on the basis of containing single particles and / or quasi-single particles.

[0046] [Chemical Formula 1]

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

[0048] In the chemical formula, Q is any one or more elements selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, 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, the content of Li can correspond to a, that is, 1 ≤ a ≤ 1.5. The problem is that when a is less than 1, the capacity may decrease, and when a exceeds 1.5, the particles may be sintered during the firing process, making it difficult to prepare the positive electrode active material. Considering the effect of improving the capacity characteristics of the positive electrode active material by controlling the content of Li and the balance of sinterability during the preparation of the active material, the content of Li can be more preferably 1.1 ≤ a ≤ 1.2.

[0050] In the lithium composite transition metal compound of Chemical Formula 1, the content of Ni can correspond 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 becomes a composition of 0.8 or more, a sufficient amount of Ni contributing to charge and discharge can be ensured to achieve a high capacity. Preferably, 1 - (b + c + d) as the Ni content can be 0.88 or more, preferably 0.9 or more, and more preferably 0.93 or more. Preferably, 1 - (b + c + d) as the Ni content can be 0.99 or less or 0.95 or less.

[0051] In the lithium composite transition metal compound of Chemical Formula 1, the content of Co can correspond 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 problem of increased cost. Considering the obvious effect of improving the capacity characteristics by including Co, the content of Co can be more specifically 0.03 ≤ b ≤ 0.2.

[0052] In the lithium composite transition metal compound of Chemical Formula 1, the content of Mn can correspond to c, that is, 0 < c ≤ 0.5. The problem is that when c in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, the output characteristics and capacity characteristics of the battery may deteriorate instead. The content of Mn can be more specifically 0.01 ≤ c ≤ 0.2.

[0053] In the lithium composite transition metal compound of Chemical Formula 1, Q may be a doping element included in the crystal structure of the lithium composite transition metal compound, and the content of Q may correspond 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] According to other exemplary embodiments of the present invention, the lithium composite transition metal compound in the positive electrode active material may include single particles and / or quasi-single particles and secondary particles.

[0055] The single particles and / or quasi-single particles may be prepared by mixing a transition metal precursor and a lithium raw material and firing the resulting mixture. The secondary particles may be prepared by a method different from that of the single particles and / or quasi-single particles, and their composition may be the same as or different from that of the single particles and / or quasi-single particles.

[0056] For example, the firing is performed at a temperature capable of forming single particles and / or quasi-single particles. To form single particles and / or quasi-single particles, the firing needs to be performed at a temperature higher than that in the preparation of secondary particles. For example, when the composition of the precursor is the same, the firing needs to be performed at a temperature about 30°C to 100°C higher than that in the preparation of secondary particles. The firing temperature for forming single particles and / or quasi-single particles may vary depending on the metal composition in the precursor. For example, when it is desired to form a high-Ni NCM-based lithium composite transition metal oxide with a Ni content of 80 mol% or more in the form of single particles and / or quasi-single particles, the firing temperature may be 700°C to 1000°C, preferably about 800°C to 950°C. When the firing temperature satisfies the above range, a positive electrode active material including single particles and / or quasi-single particles with excellent electrochemical performance can be prepared. When the firing temperature is lower than 790°C, a positive electrode active material including a lithium composite transition metal compound in the form of secondary particles can be prepared, and when the firing temperature exceeds 950°C, overfiring may occur, so that a layered crystal structure may not be properly formed, thereby deteriorating the electrochemical performance.

[0057] In the present invention, single particles and / or quasi-single particles are terms used to distinguish from secondary particles formed by aggregation of dozens to hundreds of primary particles in the prior art.

[0058] Specifically, in the present invention, a single particle is composed of one agglomerate, and a quasi-single particle is an aggregate of 30 or fewer agglomerates. In contrast, secondary particles may be in the form of an aggregate of hundreds of primary particles.

[0059] According to other exemplary embodiments of the present invention, the average particle diameter (D 50) is 1 μm or more, and the silicon-carbon composite has an average particle size (D 50 ).

[0060] According to an exemplary embodiment, the average particle size (D 50 ) of the single particles and / or quasi-single particles can be 1 μm or more, and the silicon-carbon composite can have an average particle size (D 50 ) greater than 1 μm.

[0061] According to other embodiments of the present invention, the average particle size (D 50 ) of the single particles and / or quasi-single particles is 12 μm or less, and the silicon-carbon composite has an average particle size (D 50 ) less than 15 μm.

[0062] For example, the single particles and / or quasi-single particles may have an average particle size (D 50 ) of 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 5 μm or less, greater than 1 μm and 12 μm or less, greater than 1 μm and 8 μm or less, or greater than 1 μm and 5 μm or less.

[0063] Even if the single particles and / or quasi-single particles are formed to have a small particle size with an average particle size (D 50 ) of 1 μm or more and 12 μm or less, the particle strength can be excellent. For example, when calendering with a force of 650 kgf / cm 2 , the single particles and / or quasi-single particles can have a particle strength of 100 to 300 MPa. As a result, even when the single particles and / or quasi-single particles are calendered with a strong force of 650 kgf / cm 2 , the phenomenon of an increase in the number of fine particles in the electrode due to particle rupture is alleviated, thereby improving the service life characteristics of the battery.

[0064] When the average particle size (D 50 ) of the single particles and / or quasi-single particles satisfies the above range, the single particles and / or quasi-single particles have excellent service life performance due to a reduction in side reactions with the electrolyte, and excellent electrochemical performance due to good charge and discharge.

[0065] If the average particle size (D 50 ) of the single particles and / or quasi-single particles is less than 1 μm, the service life performance may be very poor due to an increase in the specific surface area, making it difficult to apply.

[0066] If the average particle size (D 50If it is 12 μm or less, it has excellent electrochemical performance due to good charge and discharge.

[0067] The method for forming the single particle and / or quasi-single particle is not particularly limited. Generally, the single particle and / or quasi-single particle can be formed by increasing the firing temperature to achieve overfiring, and the single particle and / or quasi-single particle can be prepared by using additives such as grain growth promoters that contribute to overfiring or by changing the starting materials.

[0068] According to other embodiments of the present invention, the silicon-carbon composite may have an average particle size (D 50 ) of greater than 1 μm and less than 15 μm, 2 μm or more and 14 μm or less, or 3 μm or more and 13 μm or less.

[0069] Even if the silicon-carbon composite is formed into a small particle size (D 50 ) greater than 1 μm and less than 15 μm, the service life characteristics of the battery can be improved. For example, when the average particle size (D 50 ) of the silicon-carbon composite is greater than 1 μm and less than 15 μm, the volume expansion and shrinkage rates occurring during charge and discharge can be reduced to improve the service life performance. In addition, an excessive increase in the specific surface area is prevented, so as to prevent side reactions with the electrolyte due to the progress of cycling, thereby improving the service life performance. 50 )

[0070] If the average particle size (D 50 ) of the silicon-carbon composite is 1 μm or less, the service life performance may be very poor due to the increase in the specific surface area, making it difficult to apply.

[0071] If the average particle size (D 50 ) of the silicon-carbon composite is less than 15 μm, the particles are small and can easily complete charge and discharge, and the volume expansion and shrinkage rates of the particles generated due to charge and discharge can be reduced, thereby improving the service life performance.

[0072] According to other embodiments of the present invention, the average particle size (D 50 ) of the single particle and / or quasi-single particle is characterized by being smaller than the average particle size (D 50 ) of the silicon-carbon composite. Thus, even if the single particle and / or quasi-single particle is formed of a small particle size, the single particle and / or quasi-single particle can have excellent particle strength, and the excellent particle strength can alleviate the phenomenon of an increase in the number of fine particles in the electrode due to particle rupture, thereby improving the service life characteristics of the battery.

[0073] If the average particle size (D 50) smaller than the average particle size (D 50 ) of the silicon-carbon composite, the diffusion resistance of single particles and / or quasi-single particles having a greater lithium diffusion resistance than the silicon-carbon composite can be relatively reduced, thereby improving the service life performance.

[0074] According to an embodiment of the present invention, the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite by 1 μm to 12 μm.

[0075] The average particle size (D 50 ) of the single particles and / or quasi-single particles may be smaller than the average particle size (D 50 ) of the silicon-carbon composite by 1.5 μm to 11.5 μm, or 2 μm to 11 μm.

[0076] The average particle size (D 50 ) of the single particles and / or quasi-single particles may be smaller than the average particle size (D 50 ) of the silicon-carbon composite by more than 2 μm or more than 4 μm. The average particle size (D 50 ) of the single particles and / or quasi-single particles may be smaller than the average particle size (D 50 ) of the silicon-carbon composite by 11 μm or less, 8 μm or less, or 6 μm or less.

[0077] When the average particle size (D 50 ) of the single particles and / or quasi-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 can be relatively reduced to improve the service life performance. That is, as the average particle size (D 50 ) of the single particles and / or quasi-single particles increases, the diffusion resistance may increase, and when the average particle size (D 50 ) of the single particles and / or quasi-single particles is greater than the average particle size (D 50 ) of the silicon-carbon composite, lithium precipitation etc. may occur due to the relative increase in the diffusion resistance, resulting in deterioration of battery performance and service life performance.

[0078] When the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, for example, when the above range is satisfied, side reactions with the electrolyte due to the increase in specific surface area can be prevented, thereby improving the service life performance.

[0079] According to an embodiment of the present invention, the average particle size (D 50)The ratio of the average particle size (D 50 ) to that of the silicon-carbon composite is in the range of 1.5:2 to 1.5:20.

[0080] In some embodiments, the ratio of the average particle size (D 50 ) of the single particles and / or quasi-single particles to the average particle size (D 50 ) of the silicon-carbon composite can be 1.5:2 to 1.5:19, or 1.5:2 to 1.5:18.

[0081] In some embodiments, the ratio of the average particle size (D 50 ) of the single particles and / or quasi-single particles to the average particle size (D 50 ) of the silicon-carbon composite can be 1.5:2 or more, 1.5:2.5 or more, 1.5:3.5 or more, or 1.5:4.5 or more. In some embodiments, the ratio of the average particle size (D 50 ) of the single particles and / or quasi-single particles to the average particle size (D 50 ) of the silicon-carbon composite can be 1.5:18 or less, 1.5:16 or less, 1.5:14 or less, 1.5:12 or less, or 1.5:10 or less.

[0082] When the above range is satisfied, the diffusion resistance of the single particles and / or quasi-single particles can be relatively reduced to improve the service life performance. That is, as the average particle size (D 50 ) of the single particles and / or quasi-single particles increases more, the diffusion resistance may increase more, and when the average particle size (D 50 ) of the single particles and / or quasi-single particles is greater than the average particle size (D 50 ) of the silicon-carbon composite, lithium precipitation etc. may occur due to the relative increase in diffusion resistance, resulting in deterioration of battery performance and service life performance.

[0083] When the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, for example, when the above range is satisfied, side reactions with the electrolyte due to the increase in specific surface area can be prevented, thereby improving the service life performance.

[0084] In an exemplary 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 particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the secondary particles.

[0085] In the present invention, the single particle is composed of one agglomerate, and the quasi-single particle is an aggregate of 30 or fewer agglomerates, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0086] The above lithium composite transition metal compound may further include secondary particles. The secondary particle refers to a form formed by aggregation of primary particles, and can be distinguished from the concept of a single particle composed of one agglomerate or a quasi-single particle that is an aggregate of 30 or fewer agglomerates.

[0087] The secondary particle may have a particle size (D 50 ) of 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The secondary particle may have a specific surface area (BET) of 0.05 m 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, and more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0088] In other exemplary embodiments of the present invention, the secondary particle is an aggregate of primary particles, and the average particle size (D 50 ) of the primary particle may be 0.5 μm to 3 μm. Specifically, the secondary particle may be in the form of an aggregate of several hundred primary particles, and the primary particle may have an average particle size (D 50 ) of 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0089] When the average particle size (D 50 ) of the primary particles aggregated in the secondary particle satisfies the above range, a single-particle cathode active material having excellent electrochemical performance can be formed. When the average particle size (D 50 ) of the primary particles aggregated in the secondary particle is too small, the number of primary particles aggregating to form lithium nickel-based oxide particles increases, thereby reducing the effect of suppressing particle breakage during the rolling process. When the average particle size (D 50 ) of the primary particles aggregated in the secondary particle is too large, the diffusion path of lithium in the primary particle becomes longer, thereby increasing the resistance and the output characteristics may deteriorate.

[0090] According to other embodiments of the present invention, the average particle size (D 50 ) of the single particle and / or the quasi-single particle is characterized by being smaller than the average particle size (D 50) Thus, even if the single particles and / or quasi-single particles are formed with a small particle size, the single particles can have excellent particle strength, and the excellent particle strength can alleviate the phenomenon of an increase in the number of fine particles in the electrode due to particle breakage, thereby improving the service life characteristics of the battery.

[0091] In one embodiment of the present invention, the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the secondary particles by 1 μm to 18 μm.

[0092] For example, the average particle size (D 50 ) of the single particles and / or quasi-single particles may be smaller than the average particle size (D 50 ) of the secondary particles by 1 μm to 16 μm, 1.5 μm to 15 μm, or 2 μm to 14 μm.

[0093] The average particle size (D 50 ) of the single particles and / or quasi-single particles may be smaller than the average particle size (D 50 ) of the secondary particles by more than 1 μm, more than 2 μm, more than 4 μm, or more than 6 μm. The average particle size (D 50 ) of the single particles and / or quasi-single particles may be smaller than the average particle size (D 50 ) of the secondary particles by 18 μm or less, 16 μm or less, 14 μm or less, 12 μm or less, 10 μm or less, or 8 μm or less. When the average particle size (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle size (D 50 ) of the secondary particles, for example, when the above range is satisfied, the single particles and / or quasi-single particles can have excellent particle strength even when formed with a small particle size, and the excellent particle strength alleviates the phenomenon of an increase in the number of fine particles in the electrode due to particle breakage, thereby having the effect of improving the service life characteristics of the battery and increasing the energy density.

[0094] In the lithium secondary battery according to the above exemplary embodiment, the negative electrode active material may further include a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof.

[0095] In one embodiment of the present invention, the negative electrode active material further includes graphite, and the average particle size (D 50 ) of the silicon-carbon composite is smaller than the average particle size (D 50 ) of the graphite.

[0096] When the average particle size (D 50) less than the average particle size (D 50 ) of the graphite, during the charge and discharge process, the volume expansion / shrinkage rate decreases, resulting in less particle breakage, thus having the effect of improving the battery service life performance. According to an embodiment of the present invention, the average particle size (D 50 ) of the silicon-carbon composite is smaller than the average particle size (D 50 ) of the graphite by 1 μm to 25 μm.

[0097] For example, the average particle size (D 50 ) of the silicon-carbon composite can be smaller than the average particle size (D 50 ) of the graphite by 2 μm to 24 μm, 3 μm to 23 μm, or 4 μm to 22 μm.

[0098] The average particle size (D 50 ) of the silicon-carbon composite can be smaller than the average particle size (D 50 ) of the graphite by more than 1 μm, more than 2 μm, more than 3 μm, more than 4 μm, more than 5 μm, more than 6 μm, more than 7 μm, more than 8 μm, more than 9 μm, or more than 10 μm. The average particle size (D 50 ) of the silicon-carbon composite can be smaller than the average particle size (D 50 ) of the graphite by 25 μm or less, 23 μm or less, 22 μm or less, 20 μm or less, 18 μm or less, 16 μm or less, or 14 μm or less.

[0099] When the average particle size (D 50 ) of the silicon-carbon composite is smaller than the average particle size (D 50 ) of the graphite, for example, when the above range is satisfied, there is an effect of improving the battery service life performance.

[0100] In an embodiment of the present invention, the lithium composite transition metal compound further includes secondary particles, the negative electrode active material further includes graphite, and the average particle sizes (D 50 ) of the secondary particles, the single particles and / or quasi-single particles, the graphite, and the silicon-carbon composite are represented by A, B, C, and D respectively, where B < D ≤ A < C.

[0101] Exemplary embodiments of the secondary particles, the single particles and / or quasi-single particles, the graphite, and the silicon-carbon composite are as described above.

[0102] When the average particle sizes (D 50 ) of the secondary particles, the single particles and / or quasi-single particles, the graphite, and the silicon-carbon composite are A, B, C, and D respectively, the case of B < D ≤ A < C has the effect of improving the battery service life performance.

[0103] According to one embodiment of the present invention, the negative electrode active material further includes graphite, and the average particle diameters (D 50 ) of the single particles and / or quasi-single particles, the graphite, and the silicon-carbon composite are represented by B, C, and D respectively, where B < D < C.

[0104] The average particle diameters (D 50 ) of the secondary particles, the single particles and / or quasi-single particles, and the silicon-carbon composite are represented by A, B, and D respectively, and may be B < D ≤ A.

[0105] The average particle diameters (D 50 ) of the secondary particles, the single particles and / or quasi-single particles, and the graphite are represented by A, B, and C respectively, and may be B < A < C.

[0106] The average particle diameters (D 50 ) of the secondary particles, the graphite, and the silicon-carbon composite are represented by A, C, and D respectively, and may be D ≤ A < C.

[0107] When the above ranges are satisfied, there is an effect of improving the battery service life performance.

[0108] In one embodiment of the present invention, in the lithium secondary battery according to the above exemplary embodiment, based on 100 parts by weight of the positive electrode active material, the content of the single particles and / or quasi-single particles is 15 parts by weight to 100 parts by weight, and based on 100 parts by weight of the negative electrode active material, the content of the silicon-carbon composite is 3 parts by weight to 30 parts by weight.

[0109] According to other exemplary embodiments of the present invention, based on 100 parts by weight of the positive electrode active material, the content of the single particles and / or quasi-single particles is 15 parts by weight to 100 parts by weight. Based on 100 parts by weight of the positive electrode active material, the content of the single particles and / or quasi-single particles may be 20 parts by weight to 100 parts by weight, 30 parts by weight to 100 parts by weight, 40 parts by weight to 100 parts by weight, or 50 parts by weight to 100 parts by weight.

[0110] For example, based on 100 parts by weight of the positive electrode active material, the content of the single particles and / or quasi-single particles may be 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, 45 parts by weight or more, or 50 parts by weight or more. Based on 100 parts by weight of the positive electrode active material, the content of the single particles and / or quasi-single particles may be 100 parts by weight or less.

[0111] When the single particles and / or quasi-single particles within the above range are included, excellent battery characteristics can be exhibited by combining them with the above-mentioned negative electrode material. Specifically, when the amount of the single particles and / or quasi-single particles is 15 parts by weight or more, the phenomenon of an increase in the number of fine particles in the electrode due to particle breakage during the calendering process after manufacturing the electrode can be alleviated, thereby improving the service life characteristics of the battery.

[0112] In an exemplary embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles, and based on 100 parts by weight of the positive electrode active material, the content of the secondary particles may be from 0 parts by weight to 85 parts by weight, from 0 parts by weight to 70 parts by weight, or from 0 parts by weight to 50 parts by weight.

[0113] Based on 100 parts by weight of the positive electrode active material, the amount of the secondary particles may be 85 parts by weight or less, 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, 55 parts by weight or less, or 50 parts by weight or less. Based on 100 parts by weight of the positive electrode active material, the amount of the secondary particles may be 0 parts by weight or more or 20 parts by weight or more.

[0114] When the above range is satisfied, the above effects caused by the presence of the positive electrode active material of the single particles and / or quasi-single particles can be maximized. When the positive electrode active material includes secondary particles, the components may be the same as the components exemplified as the single particle positive electrode active material, or may be other components, and may be in the form of aggregates of single particle form.

[0115] In an embodiment of the present invention, the positive electrode further includes a positive electrode active material layer containing the positive electrode active material, and in 100 parts by weight of the positive electrode active material layer, the content of the positive electrode active material may be 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0116] According to an embodiment of the present invention, the positive electrode according to the above exemplary embodiment further includes a positive electrode binder and a conductive material.

[0117] The positive electrode binder is used to improve the binding between positive electrode active material particles and the adhesion between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, binders known in the art can be used, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof can be used.

[0118] Based on 100 parts by weight of the positive electrode active material layer, the content of the positive electrode binder can be 0.1 part by weight or more and 50 parts by weight or less, for example, preferably 0.3 part by weight or more and 35 parts by weight or less, more preferably 0.5 part by weight or more and 20 parts by weight or less.

[0119] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be used without particular limitation as long as the conductive material has electron conductivity and does not cause chemical changes in the battery. Specific examples thereof include: graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon 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, and any one of them or a mixture of two or more thereof can be used.

[0120] Specifically, in an exemplary embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). Based on 100 parts by weight of the composition for the positive electrode active material layer, the content of the conductive material can be 0.1 part by weight or more and 2 parts by weight or less, for example, preferably 0.3 part by weight or more and 1.5 parts by weight or less, more preferably 0.5 part by weight or more and 1.2 parts by weight or less.

[0121] In this specification, the silicon-carbon composite is a composite of Si and C, peaks of Si and C (graphite) are observed in the XRD diffraction pattern, and it seems that no second phase Si / C is formed. The silicon-carbon composite is different from silicon carbide insulators represented by SiC.

[0122] According to the above embodiments of the present invention, the negative electrode further includes a negative electrode active material layer containing a negative electrode active material, and based on 100 parts by weight of all the negative electrode active materials, the negative electrode active material layer contains 3 to 30 parts by weight of a silicon-carbon composite. According to one example, based on 100 parts by weight of all the negative electrode active materials, the negative electrode active material layer may contain 3 to 20 parts by weight or 3 to 13 parts by weight, preferably 5 to 10 parts by weight of the silicon-carbon composite.

[0123] Based on 100 parts by weight of all the negative electrode active materials, the negative electrode active material layer may contain more than 3 parts by weight, more than 4 parts by weight or more than 5 parts by weight of the silicon-carbon composite. Based on 100 parts by weight of all the negative electrode active materials, the negative electrode active material layer may contain 30 parts by weight or less, 20 parts by weight or less or 10 parts by weight or less of the silicon-carbon composite.

[0124] By using the silicon-carbon composite within the above range, excellent battery characteristics can be exhibited in combination with the above positive electrode material. In particular, when the content of the silicon-carbon composite is 3 parts by weight or more, the effects resulting from the use of the silicon-carbon composite can be fully exhibited. In addition, since the silicon-carbon composite has a higher capacity than the SiOx-based active material, it may be difficult to balance with the capacity of the positive electrode active material when used in excess. In particular, when the content of the silicon-carbon composite is 30 parts by weight or less, swelling during charge and discharge can be prevented to improve the cycle characteristics.

[0125] The silicon-carbon composite is a material with higher capacity and higher efficiency than silicon-based oxides, and may exhibit excellent effects in terms of resistance even when no conductive material is included, compared to a positive electrode containing a silicon-based oxide and a conductive material. In addition, since the silicon-carbon composite has a higher Si crystallinity than the silicon-based oxide, excellent effects can be exhibited during high-output evaluation.

[0126] According to other embodiments of the present invention, in the lithium secondary battery according to the above exemplary embodiments, the negative electrode active material may further include a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite or a mixture thereof. Based on 100 parts by weight of all the negative electrode active materials contained in the negative electrode active material layer, the content of the graphite may be 70 parts by weight or more and 97 parts by weight or less.

[0127] Based on 100 parts by weight of all the negative electrode active materials, the content of the graphite can be 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 all the negative electrode active materials, the content of the graphite can be 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 content of the artificial graphite and the natural graphite can be 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.

[0128] In one embodiment of the present invention, in 100 parts by weight of the negative electrode active material layer, the content of the negative electrode active material can be 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0129] According to other embodiments of the present invention, in the lithium secondary battery according to the above exemplary embodiment, the negative electrode active material layer may further contain a negative electrode binder on the basis of containing a silicon-carbon composite and graphite.

[0130] The negative electrode binder is used to improve the binding between the negative electrode active material particles and the adhesion between the negative electrode active material particles and the negative electrode current collector. As the negative electrode binder, binders known in the art can be used, and non-limiting examples thereof may include at least one selected from the following: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen thereof is replaced by Li, Na, Ca, etc., and various copolymers thereof may also be included.

[0131] Based on 100 parts by weight of the negative electrode active material layer, the content of the negative electrode binder can be 0.1 part by weight or more and 50 parts by weight or less, for example, preferably 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.

[0132] The negative electrode active material layer may not contain a conductive material, but if necessary, a conductive material may be further included. There is no particular limitation on the conductive material included in the negative electrode active material layer as long as the conductive material has conductivity and does not cause a chemical change in the battery, and substances such as the following may be used, for example: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; carbon fluoride; metal powders such as aluminum powder 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. Based on 100 parts by weight of the negative electrode active material layer, the content of the conductive material in the negative electrode active material layer may be 0.01 part by weight to 30 parts by weight, preferably 0.03 part by weight to 20 parts by weight.

[0133] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing a positive electrode active material.

[0134] There is no particular limitation on the positive electrode current collector as long as the current collector has conductivity and does not cause a chemical change in the battery, and for example, the following may be used: stainless steel, aluminum, nickel, titanium, calcined carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector generally may have a thickness of 1 μm to 500 μm, and the adhesion of the positive electrode active material may also be enhanced by forming fine irregularities on the surface of the current collector. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric body.

[0135] 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 a negative electrode active material.

[0136] The negative electrode current collector is sufficient as long as it has conductivity and does not cause a chemical change in the battery, and there is no particular limitation. For example, as the current collector, the following may be used: copper, stainless steel, aluminum, nickel, titanium, calcined carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal such as copper or nickel that can well adsorb carbon can 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.

[0137] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer containing a positive electrode active material, the negative electrode further includes a negative electrode active material layer containing a negative electrode active material, and the thicknesses of the positive electrode active material layer and the negative electrode active material layer are respectively 10 μm or more and 500 μm or less. The thickness of the positive electrode active material layer can be 90% to 110% of the thickness of the negative electrode active material layer, for example, 95% to 105%, and the thicknesses of the active material layers can be the same. Specifically, the positive electrode active material layer and the negative electrode active material layer can each have a thickness of 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.

[0138] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer containing a positive electrode active material, and the unit volume loading amount of the positive electrode active material layer is 250 mg / 25cm 2 to 900 mg / 25cm 2 The negative electrode further includes a negative electrode active material layer containing a negative electrode active material, and the unit volume loading amount of the negative electrode active material layer is 100 mg / 25cm 2 to 600 mg / 25cm 2 Specifically, the unit volume loading amount of the positive electrode active material layer can be 270mg / 25 cm 2 to 800 mg / 25 cm 2 、285 mg / 25 cm 2 to 700 mg / 25 cm 2 or 300 mg / 25 cm 2 to 600 mg / 25cm 2 And the unit volume loading amount of the negative electrode active material layer can be 120 mg / 25 cm 2 to 500 mg / 25 cm 2 、135 mg / 25 cm 2 to 400 mg / 25 cm 2 or 150 mg / 25 cm 2 to 300 mg / 25 cm 2 。

[0139] The positive electrode and the negative electrode can be manufactured by methods for manufacturing positive and negative electrodes in the relevant art, provided that the above positive electrode active material and negative electrode active material are used. Specifically, after coating a composition for forming an active material layer containing the aforementioned active material and optionally a binder and a conductive material onto a current collector, the positive electrode and the negative electrode can be manufactured by drying and rolling the current collector. In this case, the types and contents of the positive electrode active material, negative electrode active material, binder, and conductive material are as described above. The solvent can be a solvent commonly used in the art, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., and any one or a mixture of two or more thereof can be used. As long as the coating thickness of the slurry and the preparation yield are considered, the amount of the solvent is sufficient if it can dissolve or disperse the active material, conductive material, and binder and has a viscosity capable of exhibiting excellent thickness uniformity in subsequent coatings for manufacturing the positive electrode and the negative electrode. Alternatively, by another method, the positive electrode and the negative electrode can be manufactured by casting a composition for forming an active material layer on a separate carrier and then laminating a film obtained by peeling from the carrier onto a current collector.

[0140] The separator is used to separate the negative electrode and the positive electrode and provide a movement channel for lithium ions, and can be used without particular limitation as long as it is generally used as a separator in a secondary battery. In particular, a separator having excellent moisture retention ability for the electrolyte and low resistance to ion movement in the electrolyte is preferred. Specifically, a porous polymer film, such as a porous polymer film formed from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, can be used; or a laminated structure of two or more layers thereof. In addition, ordinary porous non-woven fabrics, such as non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., can also be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0141] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used to prepare lithium secondary batteries.

[0142] Specifically, the electrolyte can contain a non-aqueous organic solvent and a metal salt.

[0143] As the non-aqueous organic solvent, for example, an aprotic organic solvent can be used, such as N-methyl-2-pyrrolidone, 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, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0144] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates can be preferably used because the cyclic carbonate has a high dielectric constant as a high-viscosity organic solvent, thereby dissociating the lithium salt well, and the cyclic carbonate can be mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate having low viscosity and low dielectric constant in an appropriate ratio and used to prepare an electrolyte having high conductivity. Therefore, such cyclic carbonates can be more preferably used.

[0145] As the metal salt, a lithium salt can be used. The lithium salt is a material that is easily soluble in the non-aqueous electrolyte. For example, as the anion of the lithium salt, one or more selected from the following can be used: 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 - 。

[0146] In the electrolyte, in order to improve the life characteristics of the battery, suppress the reduction of the battery capacity, and increase the discharge capacity of the battery, on the basis of containing the above electrolyte constituent components, for example, one or more additives such as the following can also be included: haloalkyl carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (poly)ethylene glycol dimethyl ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0147] The lithium secondary battery according to an exemplary embodiment of the present invention has an energy density of 400 Wh / L to 900 Wh / L. Specifically, the lithium secondary battery may have an energy density of 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 in a limited space can be increased, the high output performance of the lithium secondary battery can be improved, and the cycle performance of the battery can also be improved.

[0148] The lithium secondary battery according to an exemplary embodiment of the present invention may be a cylindrical battery. A cylindrical battery means that the form of the battery itself containing components including a positive electrode, a negative electrode, a separator, and an electrolyte is cylindrical. Specifically, it may be composed of a cylindrical can, a battery component disposed in the cylindrical can, and a top cover. However, the lithium secondary battery is not limited thereto, and may be a square battery or a pouch-type battery.

[0149] Other exemplary embodiments of the present invention provide a battery module including the above cylindrical battery as a unit cell and a battery pack including the battery module. Since the battery module and the battery pack include the secondary battery having high capacity, high rate performance, and high cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the following: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0150] Since the lithium secondary battery according to the exemplary embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, the lithium secondary battery can be used as a power source for the following devices: portable devices such as mobile phones, laptop computers, and digital cameras; and medium- to large-sized devices selected from electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery module or battery pack can be used as a power source for one or more of the following medium- to large-sized devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0151] Mode for Carrying Out the Invention

[0152] Hereinafter, preferred embodiments will be presented to assist in understanding the present invention, but these embodiments are provided only for illustrating the present invention, and it will be apparent to those skilled in the art that various alternatives and variations are possible within the scope and spirit of the present invention. Naturally, such alternatives and variations also fall within the scope of the appended claims.

[0153] <Example 1>

[0154] A composition for forming a positive electrode active material layer was prepared, which, based on 100 parts by weight of the positive electrode active material layer, contained: 98.04 parts by weight (weight ratio of single particles and / or quasi-single particles: secondary particles = 80:20) of a lithium composite transition metal compound as the positive electrode active material, which had a content of 93.3 mol% of Ni, 4.9 mol% of Co, and 1.8 mol% of Mn with respect to the metal other than lithium; 1 part by weight of PVDF as a binder; and a CNT pre-dispersion containing 0.8 part by weight of CNT as a conductive material and 0.16 part by weight of a dispersant. In this case, the single particles and / or quasi-single particles were prepared to have a size D 50 = 3 μm by a jet milling method, and the secondary particles were prepared to have a size D 50 = 7 μm. The composition for forming the positive electrode active material layer was coated on an aluminum foil with a thickness of 30 μm so as to have a thickness of 103 μm in the dried state, and then dried to fabricate a positive electrode.

[0155] A composition for forming a negative electrode active material layer was prepared. Based on 100 parts by weight of the negative electrode active material layer, the composition contains: 97.7 parts by weight of graphite as the negative electrode active material (the weight ratio of artificial graphite to natural graphite = 70:30, 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); 1.15 parts by weight of styrene-butadiene rubber (SBR) as a binder and 1 part by weight of carboxymethyl cellulose (CMC), and also contains a CNT pre-dispersion, the CNT pre-dispersion containing 0.09 parts by weight of a dispersant and 0.06 parts by weight of single-walled CNTs. In this case, using the airflow pulverization method, the silicon-carbon composite was prepared to have a size D 50 = 5 μm, and the graphite was prepared to have a size D 50 = 17 μm. The composition for forming a negative electrode active material layer was coated on a copper foil with a thickness of 15 μm so as to have a thickness of 86 μm in the dry state, and then dried to manufacture a negative electrode.

[0156] The positive electrode and the negative electrode were stacked under the condition of having a separator therebetween, and an electrolytic solution (1.0 M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 30 / 70 (volume%), vinylene carbonate (VC) 1.5%) was injected to manufacture a battery.

[0157] <Example 2>

[0158] A positive electrode was manufactured in the same manner as in Example 1, except that based on 100 parts by weight of the positive electrode active material, the weight ratio of single particles and / or quasi-single particles to secondary particles in the lithium composite transition metal compound was adjusted to 50:50. Then, except for using the manufactured positive electrode, a battery was manufactured in the same manner as in Example 1.

[0159] <Example 3>

[0160] A positive electrode was manufactured in the same manner as in Example 1, except that based on 100 parts by weight of the positive electrode active material, the content of single particles and / or quasi-single particles was 100 parts by weight. Then, except for using the manufactured positive electrode, a battery was manufactured in the same manner as in Example 1.

[0161] <Example 4>

[0162] Except that the silicon-carbon composite contained in the negative electrode active material had D 50 = 9 μm, a negative electrode was manufactured in the same manner as in Example 3. Then, except for using the manufactured negative electrode, a battery was manufactured in the same manner as in Example 3.

[0163] <Example 5>

[0164] A negative electrode was fabricated in the same manner as in Example 3, except that the content of the silicon-carbon composite was 5 parts by weight based on 100 parts by weight of the negative electrode active material. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated negative electrode was used.

[0165] <Example 6>

[0166] A negative electrode was fabricated in the same manner as in Example 1, except that the silicon-carbon composite contained in the negative electrode active material had a D 50 = 7 μm. Then, a battery was fabricated in the same manner as in Example 1, except that the fabricated negative electrode was used.

[0167] <Example 7>

[0168] A positive electrode was fabricated in the same manner as in Example 3, except that the single particles and / or quasi-single particles contained in the positive electrode active material had a D 50 = 1 μm. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated positive electrode was used.

[0169] <Example 8>

[0170] A positive electrode and a negative electrode were fabricated in the same manner as in Example 2, except that the single particles and / or quasi-single particles and secondary particles contained in the positive electrode active material had a D 50 = 1 μm and 5 μm, respectively, and the silicon-carbon composite contained in the negative electrode active material had a D 50 = 3 μm. Then, a battery was fabricated in the same manner as in Example 2, except that the fabricated positive electrode and negative electrode were used.

[0171] <Example 9>

[0172] A negative electrode was fabricated in the same manner as in Example 8, except that the graphite contained in the negative electrode active material had a D 50 = 25 μm. Then, a battery was fabricated in the same manner as in Example 8, except that the fabricated negative electrode was used.

[0173] <Example 10>

[0174] A positive electrode and a negative electrode were fabricated in the same manner as in Example 8, except that the secondary particles contained in the positive electrode active material had a D 50 = 7 μm, and the graphite contained in the negative electrode active material had a D 50 = 13 μm. Then, a battery was fabricated in the same manner as in Example 8, except that the fabricated positive electrode and negative electrode were used.

[0175] <Example 11>

[0176] Except that the graphite contained in the negative electrode active material has D 50 = 17 μm, the negative electrode was fabricated in the same manner as in Example 10. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 10.

[0177] <Example 12>

[0178] Except that the graphite contained in the negative electrode active material has D 50 = 25 μm, the negative electrode was fabricated in the same manner as in Example 10. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 10.

[0179] <Example 13>

[0180] Except that the secondary particles contained in the positive electrode active material have D 50 = 9 μm, the positive electrode was fabricated in the same manner as in Example 10. Then, except for using the fabricated positive electrode, the battery was fabricated in the same manner as in Example 10.

[0181] <Example 14>

[0182] Except that the graphite contained in the negative electrode active material has D 50 = 17 μm, the negative electrode was fabricated in the same manner as in Example 13. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 13.

[0183] <Example 15>

[0184] Except that the graphite contained in the negative electrode active material has D 50 = 25 μm, the negative electrode was fabricated in the same manner as in Example 13. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 13.

[0185] <Example 16>

[0186] Except that the secondary particles contained in the positive electrode active material have D 50 = 15 μm, the positive electrode was fabricated in the same manner as in Example 8. Then, except for using the fabricated positive electrode, the battery was fabricated in the same manner as in Example 8.

[0187] <Example 17>

[0188] Except that the silicon-carbon composite contained in the negative electrode active material has D 50Outside of = 5 μm, a negative electrode was fabricated in the same manner as in Example 10. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 10.

[0189] <Example 18>

[0190] Except that the graphite contained in the negative electrode active material had D 50 = 17 μm, a negative electrode was fabricated in the same manner as in Example 17. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 17.

[0191] <Example 19>

[0192] Except that the graphite contained in the negative electrode active material had D 50 = 25 μm, a negative electrode was fabricated in the same manner as in Example 17. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 17.

[0193] <Example 20>

[0194] Except that the secondary particles contained in the positive electrode active material had D 50 = 9 μm, a positive electrode was fabricated in the same manner as in Example 18. Then, except for using the fabricated positive electrode, a battery was fabricated in the same manner as in Example 18.

[0195] <Example 21>

[0196] Except that the secondary particles contained in the positive electrode active material had D 50 = 3 μm, and the silicon-carbon composite contained in the negative electrode active material had D 50 = 7 μm, a positive electrode and a negative electrode were fabricated in the same manner as in Example 8. Then, except for using the fabricated positive electrode and negative electrode, a battery was fabricated in the same manner as in Example 8.

[0197] <Example 22>

[0198] Except that the silicon-carbon composite contained in the negative electrode active material had D 50 = 9 μm, a negative electrode was fabricated in the same manner as in Example 21. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 21.

[0199] <Example 23>

[0200] Except that the silicon-carbon composite contained in the negative electrode active material had D 50Outside of 12 μm, a negative electrode was fabricated in the same manner as in Example 21. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 21.

[0201] <Example 24>

[0202] Except that the single particles and / or quasi-single particles contained in the positive electrode active material have D 50 = 5 μm, and the silicon-carbon composite contained in the negative electrode active material has D 50 = 7 μm, a positive electrode and a negative electrode were fabricated in the same manner as in Example 10. Then, except for using the fabricated positive electrode and negative electrode, a battery was fabricated in the same manner as in Example 10.

[0203] <Example 25>

[0204] Except that the graphite contained in the negative electrode active material has D 50 = 17 μm, a negative electrode was fabricated in the same manner as in Example 24. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 24.

[0205] <Example 26>

[0206] Except that the graphite contained in the negative electrode active material has D 50 = 25 μm, a negative electrode was fabricated in the same manner as in Example 24. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 24.

[0207] <Example 27>

[0208] Except that the secondary particles contained in the positive electrode active material have D 50 = 9 μm, a positive electrode was fabricated in the same manner as in Example 24. Then, except for using the fabricated positive electrode, a battery was fabricated in the same manner as in Example 24.

[0209] <Example 28>

[0210] Except that the graphite contained in the negative electrode active material has D 50 = 17 μm, a negative electrode was fabricated in the same manner as in Example 27. Then, except for using the fabricated negative electrode, a battery was fabricated in the same manner as in Example 27.

[0211] <Example 29>

[0212] Except that the graphite contained in the negative electrode active material has D 50Outside of = 25 μm, the negative electrode was fabricated in the same manner as in Example 27. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 27.

[0213] <Example 30>

[0214] Except that the secondary particles contained in the positive electrode active material had D 50 = 15 μm, the positive electrode was fabricated in the same manner as in Example 24. Then, except for using the fabricated positive electrode, the battery was fabricated in the same manner as in Example 24.

[0215] <Example 31>

[0216] Except that the graphite contained in the negative electrode active material had D 50 = 17 μm, the negative electrode was fabricated in the same manner as in Example 30. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 30.

[0217] <Example 32>

[0218] Except that the graphite contained in the negative electrode active material had D 50 = 25 μm, the negative electrode was fabricated in the same manner as in Example 30. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 30.

[0219] <Example 33>

[0220] Except that the silicon-carbon composite contained in the negative electrode active material had D 50 = 9 μm, the negative electrode was fabricated in the same manner as in Example 24. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 24.

[0221] <Example 34>

[0222] Except that the graphite contained in the negative electrode active material had D 50 = 17 μm, the negative electrode was fabricated in the same manner as in Example 33. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 33.

[0223] <Example 35>

[0224] Except that the graphite contained in the negative electrode active material had D 50 = 25 μm, the negative electrode was fabricated in the same manner as in Example 33. Then, except for using the fabricated negative electrode, the battery was fabricated in the same manner as in Example 33.

[0225] <Comparative Example 1>

[0226] A positive electrode was fabricated in the same manner as in Example 1, except that, based on 100 parts by weight of the positive electrode active material, the content of the secondary particles contained in the positive electrode active material was 100 parts by weight. Then, a battery was fabricated in the same manner as in Example 1, except that the fabricated positive electrode was used.

[0227] <Comparative Example 2>

[0228] A positive electrode was fabricated in the same manner as in Example 3, except that the single particles and / or quasi-single particles contained in the positive electrode active material had D 50 = 0.5 μm. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated positive electrode was used.

[0229] <Comparative Example 3>

[0230] A positive electrode was fabricated in the same manner as in Example 3, except that the single particles and / or quasi-single particles contained in the positive electrode active material had D 50 = 15 μm. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated positive electrode was used.

[0231] <Comparative Example 4>

[0232] A negative electrode was fabricated in the same manner as in Example 3, except that the silicon-carbon composite contained in the negative electrode active material had D 50 = 0.5 μm. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated negative electrode was used.

[0233] <Comparative Example 5>

[0234] A negative electrode was fabricated in the same manner as in Example 3, except that, based on 100 parts by weight of the negative electrode active material, the content of graphite contained in the negative electrode active material was 100 parts by weight. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated negative electrode was used.

[0235] <Comparative Example 6>

[0236] A negative electrode was fabricated in the same manner as in Example 3, except that, based on 100 parts by weight of the negative electrode active material, the content of SiO contained in the negative electrode active material was 10 parts by weight. Then, a battery was fabricated in the same manner as in Example 3, except that the fabricated negative electrode was used.

[0237] <Comparative Example 7>

[0238] A positive electrode was fabricated in the same manner as in Example 3, except that the single particles and / or quasi-single particles contained in the positive electrode active material had D 50Outside of 12 μm, a positive electrode was fabricated in the same manner as in Example 2. Then, except for using the fabricated positive electrode, a battery was fabricated in the same manner as in Example 2.

[0239] <Comparative Example 8>

[0240] Except that the single particles and / or quasi-single particles contained in the positive electrode active material have a D 50 = 5 μm, and the silicon-carbon composite contained in the negative electrode active material has a D 50 = 3 μm, a positive electrode and a negative electrode were fabricated in the same manner as in Example 2. Then, except for using the fabricated positive electrode and negative electrode, a battery was fabricated in the same manner as in Example 2.

[0241] <Comparative Example 9>

[0242] Except that the single particles and / or quasi-single particles contained in the positive electrode active material have a D 50 = 10 μm, a positive electrode was fabricated in the same manner as in Example 2. Then, except for using the fabricated positive electrode, a battery was fabricated in the same manner as in Example 2.

[0243] <Comparative Example 10>

[0244] Except that the single particles, quasi-single particles, and secondary particles contained in the positive electrode active material have D 50 = 9 μm and 14 μm, respectively, and the silicon-carbon composite contained in the negative electrode active material has a D 50 = 7 μm, a positive electrode and a negative electrode were fabricated in the same manner as in Example 2. Then, except for using the fabricated positive electrode and negative electrode, a battery was fabricated in the same manner as in Example 2.

[0245] <Comparative Example 11>

[0246] Except that the single particles and / or quasi-single particles contained in the positive electrode active material have a D 50 = 11 μm, a positive electrode was fabricated in the same manner as in Comparative Example 10. Then, except for using the fabricated positive electrode, a battery was fabricated in the same manner as in Comparative Example 10.

[0247] <Comparative Example 12>

[0248] Except that the single particles and / or quasi-single particles contained in the positive electrode active material have a D 50 = 10 μm, and the silicon-carbon composite contained in the negative electrode active material has a D 50 = 9 μm, a positive electrode and a negative electrode were fabricated in the same manner as in Comparative Example 11. Then, except for using the fabricated positive electrode and negative electrode, a battery was fabricated in the same manner as in Comparative Example 11.

[0249] <Comparative Example 13>

[0250] Except that the single particles and / or quasi-single particles contained in the positive electrode active material have D 50 = 12 μm, a positive electrode was produced in the same manner as in Comparative Example 12. Then, except for using the produced positive electrode, a battery was produced in the same manner as in Comparative Example 12.

[0251] <Experimental Example 1> Evaluation of energy density characteristics

[0252] The energy density of the produced battery was evaluated and shown in Table 1 below.

[0253] The energy density of Example 1 was derived by the following calculation.

[0254] Battery volume measurement (unit: L): width (100 mm) × length (300 mm) × thickness (8 mm)

[0255] Battery energy measurement (unit: Wh): battery capacity (40 Ah) × average voltage (3.65 V)

[0256] Energy density measurement (unit Wh / L): battery energy (Wh) / battery volume (L) = 608 Wh / L

[0257] <Experimental Example 2> Evaluation of service life (capacity retention rate) characteristics

[0258] The capacity retention rate was evaluated by charging and discharging the produced battery and shown in Table 1 below.

[0259] For the first and second cycles, the battery was charged and discharged at 0.1 C, and starting from the third cycle, the battery was charged and discharged at 0.5 C. The 100th cycle was completed in the charged state (lithium is included in the negative electrode).

[0260] Charging condition: CC (constant current) / CV (constant voltage) (4.25 V / 0.005 C current cut-off)

[0261] Discharging condition: CC (constant current) condition 2.5 V

[0262] The capacity retention rates were each derived by the following calculation.

[0263] Capacity retention rate (%) = (discharge capacity at the 100th time / discharge capacity at the first time) × 100

[0264] Table 1 below shows the values of the energy density (based on Example 1, %) and capacity retention rate (100 cycles, %) of Examples 1 to 7 and Comparative Examples 1 to 13.

[0265]

[0266] Table 2 below shows the energy density (based on Example 1, %) and capacity retention rate (100 cycles, %) when the content of the positive electrode single particles and / or quasi-single particles:secondary particles = 50:50 and the negative electrode silicon-carbon composite:graphite = 10:90 in Examples 8 to 35.

[0267]

[0268] It is characterized in that the lithium composite transition metal compound contained in the positive electrode active material according to the present invention includes single particles and / or quasi-single particles with an average particle diameter (D 50 ) of 1 μm or more, the negative electrode active material includes a silicon-carbon composite with an average particle diameter (D 50 ) greater than 1 μm, and the average particle diameter (D 50 ) of the single particles and / or quasi-single particles is smaller than the average particle diameter (D 50 ) of the silicon-carbon composite. The single particles and / or quasi-single particles and the silicon-carbon composite have a particle size distribution with an appropriate average particle diameter (D 50 ) to suppress side reactions with the electrolyte and promote charge / discharge. Therefore, because the capacity / efficiency is appropriately achieved, there is an effect of increasing the energy density and stabilizing the service life characteristics.

[0269] In Examples 1 to 35, positive electrode active materials and negative electrode active materials that satisfy the particle size range according to the present invention were used, and it was confirmed that the energy density and capacity retention rate were excellent.

[0270] In contrast, in Comparative Examples 1 and 5, the single particles contained in the positive electrode active material of the present invention and the silicon-carbon composite contained in the negative electrode active material were not included, and it was confirmed that the energy density and capacity retention rate deteriorated.

[0271] In Comparative Example 2, the average particle diameter (D 50 ) range of the single particles and / or quasi-single particles contained in the positive electrode active material of the present invention was not satisfied, and it was confirmed that the total particle size was too small, resulting in low life performance and difficulty in charge and discharge, thus leading to a decrease in capacity, efficiency, and life compared with the examples.

[0272] In addition, in Comparative Examples 3 and 8 to 13, the average particle diameter (D 50 ) of the single particles and / or quasi-single particles was larger than the average particle diameter (D 50 ) of the silicon-carbon composite contained in the negative electrode active material, and it was confirmed that the capacity, efficiency, and service life deteriorated.

[0273] In Comparative Example 4, the average particle size (D 50 ) of the silicon-carbon composite contained in the negative electrode active material of the present invention is not satisfied. It can be confirmed that the total particle size is too small, resulting in low life performance and difficulty in charge and discharge, thereby causing a decrease in capacity, efficiency, and life compared with the examples.

[0274] That is, in Comparative Example 4, the average particle size (D 50 ) of the silicon-carbon composite is less than 1 μm, which increases the specific surface area, resulting in a decrease in service life performance due to reaction with the electrolyte as the cycle progresses, and because the D 50 of the silicon-carbon composite is less than the D 50 of single particles and / or quasi-single particles, the capacity, efficiency, and service life decrease.

[0275] In Comparative Example 6, the silicon-carbon composite contained in the negative electrode active material used in the present invention is not contained, but an SiO composite is contained. It can be confirmed that the energy density and capacity retention rate deteriorate.

Claims

1. A lithium secondary battery, the lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material contains a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium composite transition metal compound contains at least one of single particles or quasi-single particles having an average particle diameter (D 50 ) of 1 μm or more, wherein each single particle consists of one agglomerate, and wherein each quasi-single particle is a composite of 30 or less agglomerates, wherein the negative electrode active material comprises a silicon-carbon composite, and wherein the silicon-carbon composite has an average particle size (D 50 ) greater than 1 μm wherein the average particle size (D 50 ) of at least one of the single particles or quasi-single particles is smaller than the average particle size (D 50 ) of the silicon-carbon composite, and wherein the silicon-carbon composite has a core of a composite of silicon and carbon, wherein the lithium composite transition metal compound further includes secondary particles, wherein the negative electrode active material further includes graphite, wherein the average particle sizes (D 50 ) of at least one of the secondary particles, the single particles or quasi-single particles, the graphite, and the silicon-carbon composite are represented by A, B, C, and D, respectively, and wherein B < D ≤ A < C.

2. The lithium secondary battery according to claim 1, wherein an average particle diameter (D 50 ) of at least one of the single particles or quasi-single particles is 12 μm or less, and wherein an average particle size (D 50 ) of the silicon-carbon composite is less than 15 μm.

3. The lithium secondary battery according to claim 1, wherein the average particle size (D 50 ) of at least one of the single particles or quasi-single particles is 1 μm to 12 μm smaller than the average particle size (D 50 ) of the silicon-carbon composite.

4. The lithium secondary battery according to claim 1, wherein the average particle diameter (D 50 ) of at least one of the single particles or quasi-single particles is 1 μm to 18 μm smaller than the average particle diameter (D 50 ) of the secondary particles.

5. The lithium secondary battery according to claim 1, wherein an average particle diameter (D 50 ) of the silicon-carbon composite is 1 μm to 25 μm smaller than an average particle diameter (D 50 ) of the graphite.

6. The lithium secondary battery according to claim 1, wherein the positive electrode active material further includes aluminum.

7. The lithium secondary battery according to claim 1, wherein based on 100 parts by weight of the positive electrode active material, the content of at least one of the single particles or quasi-single particles is 15 parts by weight to 100 parts by weight, and wherein based on 100 parts by weight of the negative electrode active material, the content of the silicon-carbon composite is 3 parts by weight to 30 parts by weight.

8. The lithium secondary battery according to claim 1, wherein in the lithium composite transition metal compound, the content of nickel relative to other metals except lithium is 80 mol% or more.

9. The lithium secondary battery according to claim 1, wherein the positive electrode further includes a positive electrode binder and a conductive material.

10. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is a cylindrical battery.

11. The lithium secondary battery according to claim 1, wherein the ratio of the average particle diameter (D 50 ) of at least one of the single particles or quasi-single particles to the average particle diameter (D 50 ) of the silicon-carbon composite is in the range of 1.5:2 to 1.5:

20.

12. The lithium secondary battery according to claim 1, wherein the positive electrode further includes a positive electrode active material layer having the positive electrode active material, the negative electrode further includes a negative electrode active material layer having the negative electrode active material, and the positive electrode active material layer and the negative electrode active material layer each have a thickness of 10 μm or more and 500 μm or less.

13. The lithium secondary battery according to claim 1, wherein the positive electrode further includes a positive electrode active material layer having the positive electrode active material, and the unit volume loading amount of the positive electrode active material layer is 250 mg / 25 cm 2 to 900 mg / 25 cm 2 and The negative electrode further includes a negative electrode active material layer having 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 to 600 mg / 25 cm 2 .

14. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has an energy density of 400 Wh / L to 900 Wh / L.

15. A battery module, the battery module including the lithium secondary battery according to claim 1.

16. A battery pack, the battery pack including the battery module according to claim 15.

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