Lithium secondary battery, battery module, and battery pack

Abstract

The present invention relates to a lithium secondary battery, a battery module, and a battery pack. The lithium secondary battery comprises: 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 includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound contains single particles, the negative electrode active material includes a silicon oxide, and the grain size of Si in the silicon oxide is at most 10% of the grain size of the lithium composite transition metal compound.

Description

Lithium secondary batteries, battery modules and battery packs

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0105599, filed on August 11, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, a battery module, and a battery pack.

[0003] The recent rapid proliferation of battery-powered electronic devices, including mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity and / or high-output secondary batteries. Lithium secondary batteries, in particular, are attracting attention as power sources for electronic devices due to their lightweight design and high energy density. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions, while charging an organic electrolyte or polymer electrolyte between them.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide (LiCoO2) is widely used due to its high operating voltage and excellent capacity characteristics, and is applied as a cathode active material for high voltage. However, due to the rising price of cobalt (Co) and unstable supply, it is difficult to use it in large quantities as a power source in fields such as electric vehicles, and the need for the development of a cathode active material that can replace it has arisen.

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

[0007] Meanwhile, graphite is mainly used as an anode active material for lithium secondary batteries, but because graphite has a low capacity per unit mass of 372 mAh / g, it is difficult to increase the capacity of lithium secondary batteries. Accordingly, non-carbonaceous anode materials with higher energy density than graphite, such as silicon, tin, and their oxides, are being developed to increase the capacity of lithium secondary batteries. However, these non-carbonaceous anode materials have a problem in that although they have a large capacity, they have low initial efficiency, so the amount of lithium consumed during the initial charge and discharge is large, and the irreversible capacity loss is large.

[0008] Furthermore, lithium secondary batteries have specific sizes required for their intended use, and thus must be designed within a limited space. While consumer demand for increased energy density and high-power performance is growing, the use of high-capacity cathode materials necessitates increased anode material content to meet these demands. This limits the ability to increase battery efficiency within a limited space. Consequently, the development of batteries with improved performance, including efficiency and lifespan, within a limited space is urgently needed.

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Korean Patent Publication No. 10-2011-0112215

[0012] The inventors of the present invention have discovered that, in a lithium secondary battery designed within a limited space, optimal battery performance can be achieved in a specific combination by controlling the crystal grain size of a positive electrode active material and the Si crystal grain size of an negative electrode active material, thereby leading to the present invention.

[0013] The present invention relates to a lithium secondary battery, a battery module, and a battery pack.

[0014] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound includes single particles, the negative electrode active material includes silicon oxide, and the Si crystal grain size of the silicon oxide is 10% or less of the crystal grain size of the lithium composite transition metal compound.

[0015] One embodiment of the present invention provides a battery module including the lithium secondary battery.

[0016] One embodiment of the present invention provides a battery pack including the lithium secondary battery.

[0017] One embodiment of the present invention provides a battery pack including the battery module.

[0018] According to one embodiment of the present invention, a lithium secondary battery has a Si crystal grain size of silicon oxide included in an anode active material that is 10% or less of the crystal grain size of a lithium composite transition metal compound included in a cathode active material, and when the above crystal grain size is satisfied, cycle characteristics and swelling performance can be improved. Therefore, by controlling the crystal grains of the lithium composite transition metal compound and the Si crystal grains of the anode active material as described above, the rapid charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed within a limited space can be easily improved.

[0019] Hereinafter, the present specification will be described in more detail.

[0020] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0021] In this specification, when it is said that a member is located “on” another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0022] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0023] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0024] In this specification, the term "single particle" is used to distinguish it from a secondary particle form of a cathode active material particle formed by the aggregation of tens to hundreds of conventional primary particles, and means a single particle formed of one primary particle and a pseudo-single particle form that is an aggregation of 30 or fewer primary particles.

[0025] In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation amount in the particle size distribution curve (graph curve of particle size distribution). The above average particle size can be measured using, for example, the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0026] The above average particle size can be measured using a Microtrac device (manufacturer: Microtrac model number: S3500) using water and a triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured in the range of a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured under the condition of a refractive index of 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, the particles can be introduced into a commercially available laser diffraction particle size measuring device, irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then a volume cumulative particle size distribution graph can be obtained, and then the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0028] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound includes single particles, the negative electrode active material includes silicon oxide, and the Si crystal grain size of the silicon oxide is 10% or less of the crystal grain size of the lithium composite transition metal compound.

[0029] Typically, lithium secondary batteries have specific sizes for their intended use, and thus must be designed within a limited space. While consumer demand for increased energy density and high-power performance is growing, the use of high-capacity cathode materials necessitates increased anode content to meet these demands. This limits the ability to increase battery efficiency within a limited space. Furthermore, depending on the type of anode material, it's necessary to design a cathode material with an efficiency level that matches that of the anode material.

[0030] The lithium secondary battery according to the present invention is characterized in that the Si crystal grain size of the silicon oxide contained in the anode active material is 10% or less of the crystal grain size of the lithium complex transition metal compound contained in the cathode active material. Due to the material properties of silicon oxide, the larger the crystal grain size, the more lithium (Li) remains in the material, which may worsen cycle performance degradation and swelling. The inventors of the present invention have discovered that the aforementioned cycle performance degradation and swelling can be reduced by controlling the crystal grain size of the cathode active material within a specific range relative to the crystal grain size of the silicon oxide. Specifically, the process of Li insertion into the silicon oxide of the anode involves a process in which the crystalline silicon oxide becomes amorphous. Therefore, the larger the crystal grain size of the silicon oxide, the greater the resistance during the lithium insertion and de-insertion process, and the worse the cycle performance degradation and swelling. In contrast, in the case of the cathode active material, the greater the crystallinity, the less the structure changes even when the Li insertion and de-insertion process is repeated, and the more stably the lithium diffusion path can be maintained. When the crystal grains of the positive electrode active material are larger than the crystal grain size of the silicon oxide within the aforementioned range, a relatively stable crystal structure is maintained, so that an electrochemical reaction can easily occur even with a small amount of lithium (Li), thereby preventing relative capacity decrease and swelling. In addition, when the Si crystal grain size of the silicon oxide satisfies the aforementioned range, the stress caused by the volume expansion of the negative electrode active material particles during charge and discharge can be reduced, thereby preventing breakage of the particles, thereby improving cycle characteristics and swelling performance. Therefore, by controlling the crystal grains of the lithium composite transition metal compound and the Si crystal grains of the negative electrode active material as described above, the rapid charging performance, efficiency, lifespan, and / or energy density of a lithium secondary battery designed within a limited space can be easily improved.

[0031] According to one embodiment of the present invention, the silicon oxide may include SiOx (0≤x<2).

[0032] The active material containing the above SiOx (0≤x<2) is SiO x (0 <x<2) 및 기공을 포함하는 실리콘 산화물 입자일 수 있다.

[0033] The above SiO x (0 <x<2)는 상기 실리콘 산화물 입자 내에서 매트릭스(matrix)에 해당한다. 상기 SiO x (0 <x<2)는 Si 및 SiO2가 포함된 형태일 수 있으며, 상기 Si는 상(phase)을 이루고 있을 수도 있다. 즉, 상기 x는 상기 SiO x (0 <x<2) 내에 포함된 Si에 대한 O의 개수비에 해당한다. 상기 실리콘 산화물 입자가 상기 SiO x (0 <x<2)를 포함하는 경우, 이차 전지의 방전 용량이 개선될 수 있다.

[0034] The silicon oxide particles may further include at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon oxide particles.

[0035] The above Mg compound and / or Li compound is SiO x (0 <x<2)의 내부 및 / 또는 표면에 존재할 수 있다. 상기 Mg 화합물 및 / 또는 Li 화합물에 의해 전지의 초기 효율이 개선될 수 있다.

[0036] The above Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0037] In one embodiment of the present specification, the Mg element may be included in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon oxide particles. Specifically, the Mg element may be included in an amount of 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be included in an appropriate amount in the silicon oxide particles, so that volume changes of the silicon oxide particles during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0038] The Li compound may include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0039] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate may include Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)로 표시되며, 결정질 리튬 실리케이트와 비정질 리튬 실리케이트로 구분될 수 있다. 상기 결정질 리튬 실리케이트는 상기 실리콘 산화물 입자 내에서 Li2SiO3, Li4SiO4및 Li2Si2O5로 이루어진 군에서 선택된 적어도 1종의 리튬 실리케이트의 형태로 존재할 수 있으며, 비정질 리튬 실리케이트는 Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)의 형태일 수 있고, 상기 형태에 한정되지는 않는다.

[0040] In one embodiment of the present specification, the Li element may be included in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon oxide particles. Specifically, the Li element may be included in an amount of 0.5 wt% to 8 wt%, and more specifically, may be included in an amount of 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound can be included in an appropriate amount in the silicon oxide particles, so that the volume change of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0041] The content of the above Mg element or Li element can be confirmed through ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative electrode active material is precisely aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Thereafter, an inductively coupled plasma electroluminescence spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of the standard solution prepared using a standard solution (5 mg / kg) at the wavelength unique to the Mg element or Li element, thereby creating a reference calibration curve. Thereafter, the pretreated sample solution and blank sample are introduced into the device, and the respective intensities are measured to calculate the actual intensity, and the concentration of each component is calculated against the created calibration curve, and then the content of the Mg element or Li element of the manufactured silicon oxide particles can be analyzed by converting so that the sum of the entire values ​​becomes the theoretical value.

[0042] In one embodiment of the present invention, the silicon oxide may include additional metal atoms. The metal atoms may exist in the silicon oxide in the form of at least one of a metal atom, a metal silicate, a metal silicide, and a metal oxide. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Accordingly, the initial efficiency of the negative electrode active material may be improved.

[0043] In one embodiment of the present invention, a carbon layer is provided on at least a portion of the surface of the silicon oxide. In this case, the carbon layer may be partially coated on at least a portion of the surface, i.e., the particle surface, or may be coated on the entire particle surface. The carbon layer provides conductivity to the negative electrode active material, and the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery can be improved.

[0044] In one embodiment of the present invention, the carbon layer includes amorphous carbon. In addition, the carbon layer may additionally include crystalline carbon.

[0045] The above crystalline carbon can further improve the conductivity of the negative electrode active material. The above crystalline carbon can include at least one selected from the group consisting of fluorene, carbon nanotubes, and graphene.

[0046] The amorphous carbon can appropriately maintain the strength of the carbon layer, thereby suppressing expansion of the silicon oxide. The amorphous carbon can be a carbon-based material formed using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source for chemical vapor deposition.

[0047] The above-mentioned other organic carbonates may be carbonates of organic carbonates selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or kedohexose and combinations thereof.

[0048] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0049] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0050] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on 100 parts by weight of the total silicon oxide. More specifically, it may be included in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0051] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, volume change of the negative electrode active material is easily suppressed, and side reactions between the electrolyte and the negative electrode active material are suppressed, thereby improving the initial efficiency and / or lifespan of the battery.

[0052] Specifically, the carbon layer can be formed by a chemical vapor deposition (CVD) method using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0053] In the present invention, the crystallinity of the carbon layer can be confirmed by calculating the D / G band ratio according to Raman spectroscopy. Specifically, the measurement can be performed using a Renishaw 2000 Raman microscope system and a 532 nm laser excitation, and a 100x optical lens with a low laser power density and an exposure time of 30 seconds to avoid laser thermal effects. In order to reduce positional deviation, a total of 25 points are measured for a 5 μm x 5 μm area, and the calculation can be performed by calculating the average values ​​of the D band and G band after fitting using a Lorentzian function.

[0054] In one embodiment of the present invention, the average particle diameter (D) of the silicon oxide 50 ) may be 1 ㎛ or more. In addition, the average particle diameter of the silicon oxide may be 10 ㎛ or less. For example, the average particle diameter (D of the silicon oxide 50 ) may be 1 ㎛ or more and 10 ㎛ or less, 2 ㎛ or more and 10 ㎛ or less, 3 ㎛ or more and 10 ㎛ or less, 3 ㎛ to 10 ㎛, 4 ㎛ to 8 ㎛, or 5 ㎛ to 8 ㎛.

[0055] Even if the silicon oxide is formed into a small particle size, such as an average particle size of 1 ㎛ to 10 ㎛, the life characteristics of the battery can be improved. For example, when the average particle size of the silicon oxide is in the range of 1 ㎛ to 10 ㎛, the volume expansion and shrinkage rate due to charge and discharge are reduced, so that the life performance can be improved. In addition, by preventing the specific surface area from increasing excessively, side reactions with the electrolyte due to the progress of the cycle can be prevented, so that the life performance can be improved.

[0056] In one embodiment of the present invention, the negative active material may further include graphite.

[0057] The above graphite may be natural graphite or artificial graphite, or may be a mixture of natural graphite and artificial graphite.

[0058] When the above graphite is a mixture of natural graphite and artificial graphite, the weight ratio of the natural graphite and the artificial graphite may be 50:50 to 90:10, and specifically 60:40 to 80:20 or 65:35 to 75:25.

[0059] In one embodiment of the present invention, the average particle diameter (D) of the graphite 50 ) may be 10 ㎛ to 20 ㎛. Specifically, it may be 15 ㎛ to 20 ㎛. When the average particle diameter of graphite satisfies the above range, the influence of particle agglomeration is reduced, and the slurry dispersibility can be improved.

[0060] In one embodiment of the present invention, the positive electrode active material may include a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn).

[0061] In one embodiment of the present invention, the positive electrode active material includes nickel, cobalt, and manganese, and may further include aluminum.

[0062] In the present specification, the positive electrode active material contains 80 mol% or more and less than 100 mol% of nickel among metals other than lithium, and the lithium composite transition metal compound containing 80 mol% or more and less than 100 mol% of nickel among metals other than lithium may include one or a mixture of two or more types represented by the following chemical formula 1.

[0063] [Chemical Formula 1]

[0064] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0065] In the above formula, Q is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, and 1≤a≤1.5, 0 <b≤0.5, 0<c≤0.5, 0≤d≤0.1, 0 <b+c+d≤20, -0.1≤δ≤1.0이다.

[0066] In the lithium composite transition metal compound of the above chemical formula 1, Li may be included in an amount corresponding to a, that is, 1≤a≤1.5. If a is less than 1, there is a risk of reduced capacity, and if a exceeds 1.5, the particles may be sintered during the sintering process, making it difficult to manufacture a positive electrode active material. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the Li amount control and the balance of sinterability during the manufacture of the active material, the Li may be more preferably included in an amount of 1.1≤a≤1.2.

[0067] In the lithium composite transition metal compound of the above chemical formula 1, Ni may be included in a content corresponding to 1-(b+c+d), for example, 0.8≤1-(b+c+d) < 1. When the content of Ni in the lithium composite transition metal compound of the above chemical formula 1 is 0.8 or more, a sufficient amount of Ni is secured to contribute to charge / discharge, thereby promoting high capacity. Preferably, the content of Ni, 1-(b+c+d), may be 0.88, preferably 0.9 or more, and more preferably 0.93 or more. Preferably, the content of Ni, 1-(b+c+d), may be 0.99 or less, or 0.95 or less.

[0068] In the lithium complex transition metal compound of the above chemical formula 1, Co is in the content corresponding to b, i.e., 0 <b≤0.5로 포함될 수 있다. 상기 화학식 1의 리튬 복합 전이금속 화합물 내 Co의 함량이 0.5를 초과할 경우 비용 증가의 우려가 있다. Co 포함에 따른 용량 특성 개선 효과의 현저함을 고려할 때, 상기 Co는 보다 구체적으로 0.03≤b≤0.2의 함량으로 포함될 수 있다.

[0069] In the lithium complex transition metal compound of the above chemical formula 1, Mn is in the content corresponding to c, i.e., 0 <c≤0.5의 함량으로 포함될 수 있다. 상기 화학식 1의 리튬 복합 전이금속 화합물 내 c가 0.5를 초과하면 오히려 전지의 출력 특성 및 용량 특성이 저하될 우려가 있으며, 상기 Mn은 보다 구체적으로 0.01≤c≤0.2의 함량으로 포함될 수 있다.

[0070] In the lithium composite transition metal compound of the above chemical formula 1, Q may be a doping element included in the crystal structure of the lithium composite transition metal compound, and Q may be included in a content corresponding to d, that is, 0≤d≤0.1. Q may be one or two or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, and for example, Q may be Al.

[0071] In one embodiment of the present invention, the lithium composite transition metal compound may include single particles.

[0072] In one embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles.

[0073] The above single particles can be manufactured by mixing and calcining a transition metal precursor and a lithium source material. The secondary particles can be manufactured using a different method from the above single particles, and their composition may be the same as or different from that of the single particles.

[0074] For example, the sintering is performed at a temperature capable of forming single particles. To form these, the sintering must be performed at a higher temperature than that during secondary particle production. For example, when the precursor composition is the same, the sintering must be performed at a temperature that is about 30°C to 100°C higher than that during secondary particle production. The sintering temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is intended to be formed into single particles, the sintering temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the sintering temperature satisfies the above range, a cathode active material including single particles having excellent electrochemical properties can be produced. When the sintering temperature is lower than 790°C, a cathode active material including a lithium complex transition metal compound in the form of secondary particles can be manufactured, and when it exceeds 950°C, excessive sintering occurs and a layered crystal structure is not properly formed, which may result in a deterioration in electrochemical properties.

[0075] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle formed of one primary particle and a pseudo-single particle form that is an agglomeration of 30 or fewer primary particles.

[0076] Specifically, in the present invention, the single particle may be in the form of a single particle composed of one primary particle or a quasi-single particle that is an aggregate of 30 or fewer primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles.

[0077] In this specification, the size of Si crystal grains included in the silicon oxide can be confirmed through X-ray diffraction analysis, and the X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analysis device (product name: D4-endavor, manufacturer: bruker). Specifically, the XRD measurement can be performed by sampling a powder-type sample into a holder and measuring it through Cu K alpha X-ray. The size of the Si crystal grains can be calculated by fitting the XRD results using the Scherrer equation, and the grain standard at this time can be measured based on Si (220). (2θ = 47.5° to 48.5°)

[0078] In one embodiment of the present invention, the Si crystal grain size of the silicon oxide may be 0.1 nm or more and 20 nm or less. Specifically, it may be 0.5 nm or more and 15 nm or less, 1 nm or more and 15 nm or less, 1.5 nm or more and 12 nm or less, 1.5 nm or more and 10 nm or less, 2 nm or more and 10 nm or less, 3 nm or more and 10 nm or less, or 4 nm or more and 9 nm or less.

[0079] When the crystal grain size of the Si satisfies the above range, Li ions are uniformly diffused inside the Si particles, which has the effect of stably maintaining the structure of the Si particles during charge and discharge. On the other hand, when the crystal grain size of the Si exceeds the above range, cracks are formed in the particles due to stress caused by shrinkage / expansion of the Si material during charge and discharge, and Li ions are unable to diffuse inside the crystal grains, which causes accelerated deterioration of the material due to reaction non-uniformity, which reduces the cell lifespan.

[0080] In the present specification, the crystal grains of the lithium composite transition metal compound may refer to, for example, the crystal size of the structure itself of the above-described chemical formula 1. In the present specification, the crystal grain size of the lithium composite transition metal compound can be confirmed through X-ray diffraction analysis, and the X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analysis device (product name: D4-endavor, manufacturer: bruker). Specifically, the XRD measurement can be performed by sampling a powder-type sample into a holder and measuring it through Cu K alpha X-ray. The crystal grain size of the lithium composite transition metal compound is calculated by fitting the XRD result using the Scherrer equation, and the crystal grain size at this time can be measured based on the largest peak appearing around 2θ=10° to 12°.

[0081] In one embodiment of the present invention, the crystal grain size of the lithium composite transition metal compound may be 70 nm or more and 200 nm or less. Specifically, it may be 70 nm or more and 180 nm or less, 70 nm or more and 160 nm or less, or 80 nm or more and 130 nm or less.

[0082] When the crystal grain size of the lithium composite transition metal compound satisfies the above range, the lithium composite transition metal compound has excellent phase stability and can react stably with Li. On the other hand, when the crystal grain size of the lithium composite transition metal compound is smaller than the above range, there is a problem that the reaction with Li occurs for a long time, but the efficiency of the positive electrode decreases, and when the crystal grain size of the lithium composite transition metal compound exceeds the above range, there is a problem that the particles of the positive electrode active material break during the rolling stage during the electrode manufacturing process.

[0083] In one embodiment of the present invention, the Si crystal grain size of the silicon oxide may be 10% or less of the crystal grain size of the lithium composite transition metal compound. Specifically, the Si crystal grain size of the silicon oxide may be 0.5% or more and 10% or less, 1% or more and 10% or less, or 1% or more and 9.5% or less of the crystal grain size of the lithium composite transition metal compound. When the Si crystal grain size of the silicon oxide and the crystal grain size of the lithium composite transition metal compound satisfy the above relationship, the stress due to volume expansion of the negative electrode active material particles during charge and discharge can be reduced, thereby preventing breakage of the particles. In addition, depending on the crystallinity of the silicon oxide, degradation of the negative electrode may occur, and some lithium ions may be consumed due to a side reaction with the silicon oxide. However, due to the stable crystal structure caused by the relatively large crystal grain size of the positive electrode active material, an electrochemical reaction can easily occur even with a small amount of lithium (Li), thereby improving cycle characteristics and swelling performance. In other words, not only can the consumption of lithium ions occurring during the insertion / de-insertion process be minimized, but a certain level of capacity can be maintained even with the consumed and reduced lithium ions, thereby compensating for the deterioration of the entire battery cell.

[0084] On the other hand, even if the Si crystal grain size of the silicon oxide and the crystal grain size of the lithium composite transition metal compound satisfy the aforementioned crystal grain sizes, if the Si crystal grain size of the silicon oxide exceeds 10% of the crystal grain size of the lithium composite transition metal compound, the cycle performance may deteriorate and swelling may become severe due to lithium (Li) remaining in the silicon oxide, and cracks may occur in the particles due to an increase in the internal stress of Si according to charge and discharge, which may cause a problem of a decrease in cycle performance.

[0085] In one embodiment of the present invention, the average particle diameter (D) of the single particle 50 ) may be 1 ㎛ or more. In addition, the average particle diameter of the single particles may be 10 ㎛ or less. For example, the average particle diameter of the single particles may be 1 ㎛ or more and 10 ㎛ or less, 1 ㎛ or more and 8 ㎛ or less, 1 ㎛ or more and 6 ㎛ or less, more than 1 ㎛ and 6 ㎛ or less, 2 ㎛ or more and 6 ㎛ or less, or 3 ㎛ or more and 5 ㎛ or less.

[0086] Even if the above single particles are formed with a small average particle size of 1 ㎛ to 10 ㎛, the particle strength can be excellent, and as a result, the phenomenon of fine particles increasing in the electrode due to particle breakage can be alleviated, and thereby the life characteristics of the battery can be improved. For example, the above single particles have a particle strength of 650 kgf / cm. 2 When rolled with a force of 100 to 300 MPa, the particle strength can be achieved. Accordingly, the single particle can be rolled with a force of 650 kgf / cm. 2 Even when rolled with a strong force, the phenomenon of fine particle increase in the electrode due to particle breakage is alleviated, thereby improving the life characteristics of the battery.

[0087] The method for forming the above single particles is not particularly limited, but can generally be formed by increasing the firing temperature to cause underfiring, using additives such as grain growth accelerators that aid underfiring, or by changing the starting material.

[0088] The above single particles have high particle rigidity, so even at high electrode density, their battery performance is relatively poor. Therefore, the energy density can be increased by adjusting the average particle size range of the single particles and the silicon oxide.

[0089] In one embodiment of the present invention, the average particle diameter of the single particle may be smaller than the average particle diameter of the silicon oxide.

[0090] When the average particle diameter of the single particles is smaller than the average particle diameter of the silicon oxide, the diffusion resistance of the single particles may be relatively reduced, thereby improving the life performance. That is, as the average particle diameter of the single particles increases, the diffusion resistance may increase, and when the average particle diameter of the single particles is larger than the average particle diameter of the silicon oxide, the diffusion resistance may relatively increase, thereby causing lithium precipitation, etc. to occur, thereby deteriorating the battery performance and lowering the life performance.

[0091] In addition, when the average particle diameter of the single particle is smaller than the average particle diameter of the silicon oxide, the life performance can be improved by preventing side reactions with the electrolyte due to an increase in the specific surface area.

[0092] According to one embodiment of the present invention, the average particle diameter of the single particle may be 0.1 ㎛ to 5 ㎛ smaller than the average particle diameter of the silicon oxide. Specifically, it may be 1 ㎛ to 3 ㎛ smaller.

[0093] When the average particle diameter of the single particles is smaller than the average particle diameter of the silicon oxide, for example, when the above range is satisfied, the diffusion resistance of the single particles may be relatively reduced, thereby improving the life performance. That is, as the average particle diameter of the single particles increases, the diffusion resistance may increase, and when the average particle diameter of the single particles is larger than the average particle diameter of the silicon oxide, as the diffusion resistance relatively increases, lithium precipitation, etc. may occur, thereby deteriorating the battery performance and the life performance may be deteriorated.

[0094] In addition, when the average particle diameter of the single particle is smaller than the average particle diameter of the silicon oxide, for example, when the above range is satisfied, the life performance can be improved by preventing the occurrence of side reactions with the electrolyte due to an increase in the specific surface area.

[0095] According to one embodiment of the present invention, the ratio of the average particle diameter of the single particle to the average particle diameter of the silicon oxide may be 1:1 to 1:2, for example, 1:1.1 to 1:2.

[0096] When the above range is satisfied, the diffusion resistance of the single particle may be relatively reduced, thereby improving the life performance. That is, as the average particle diameter of the single particle increases, the diffusion resistance may increase, and when the average particle diameter of the single particle is larger than the average particle diameter of the silicon oxide, as the diffusion resistance relatively increases, lithium precipitation, etc. may occur, thereby deteriorating the battery performance and the life performance may be deteriorated.

[0097] In addition, when the average particle diameter of the single particle is smaller than the average particle diameter of the silicon oxide, for example, when the above range is satisfied, the life performance can be improved by preventing the occurrence of side reactions with the electrolyte due to an increase in the specific surface area.

[0098] In one embodiment of the present invention, the lithium composite transition metal compound further includes secondary particles, and the average particle diameter of the single particles is smaller than the average particle diameter of the secondary particles.

[0099] In the present invention, the single particle may be in the form of a single particle composed of one primary particle or a quasi-single particle that is an aggregate of 30 or fewer primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles.

[0100] The lithium complex transition metal compound described above may further include secondary particles. The term "secondary particle" refers to a form formed by the aggregation of primary particles, and can be distinguished from the concept of a single particle, which includes a quasi-single particle form that is a single primary particle, a single particle, or an aggregation of 30 or fewer primary particles.

[0101] The average particle diameter of the above secondary particles (D 50 ) may be 1 μm to 20 μm. Specifically, it may be 2 μm to 17 μm, 3 μm to 15 μm, 5 μm to 15 μm, 7 μm to 15 μm, or 9 μm to 15 μm.

[0102] In one embodiment of the present invention, the secondary particles are aggregates of primary particles, and the average particle diameter of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of hundreds of primary particles, and the average particle diameter of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0103] When the average particle size of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, which reduces the effect of suppressing particle breakage during rolling. In addition, if the average particle size of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, which may increase resistance and deteriorate output characteristics.

[0104] In one embodiment of the present invention, the average particle diameter of the single particles may be smaller than the average particle diameter of the secondary particles. Accordingly, even if the single particles are formed with a small particle diameter, their particle strength may be excellent, thereby alleviating the phenomenon of fine particles increasing within the electrode due to particle breakage, thereby improving the life characteristics of the battery.

[0105] In one embodiment of the present invention, the average particle diameter of the single particles is 1 ㎛ to 18 ㎛ smaller than the average particle diameter of the secondary particles.

[0106] For example, the average particle diameter of the single particles may be 1 µm to 16 µm smaller than the average particle diameter of the secondary particles, may be 1.5 µm to 15 µm smaller, may be 2 µm to 14 µm smaller, or may be 5 µm to 8 µm smaller.

[0107] When the average particle diameter of the single particle is smaller than the average particle diameter of the secondary particle, for example, when the above range is satisfied, the single particle can have excellent particle strength even if it is formed into a small particle diameter, and as a result, the phenomenon of fine particles increasing in the electrode due to particle breakage is alleviated, thereby improving the life characteristics of the battery and improving the energy density.

[0108] In the lithium secondary battery according to the above-described 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.

[0109] In one embodiment of the present invention, the average particle diameter of the silicon oxide may be smaller than the average particle diameter of the graphite. When the average particle diameter of the silicon oxide is smaller than the average particle diameter of the graphite, the volume expansion / contraction rate during charge / discharge is reduced, thereby reducing particle breakage, thereby improving the life performance of the battery.

[0110] According to one embodiment of the present invention, the average particle diameter of the silicon oxide may be 1 ㎛ to 25 ㎛ smaller than the average particle diameter of the graphite. For example, the average particle diameter of the silicon oxide may be 2 ㎛ to 24 ㎛ smaller than the average particle diameter of the graphite, may be 3 ㎛ to 23 ㎛ smaller, may be 4 ㎛ to 22 ㎛ smaller, or may be 5 ㎛ to 15 ㎛ smaller.

[0111] When the average particle diameter of the silicon oxide is smaller than the average particle diameter of the graphite, for example, when the above range is satisfied, there is an effect of further improving the life performance of the battery.

[0112] In one embodiment of the present invention, when the average particle diameters of the secondary particles, the single particles, the graphite, and the silicon oxide included in the lithium secondary battery are A, B, C, and D, respectively, B < D ≤ A < C may be satisfied.

[0113] The embodiments of the secondary particles, single particles, graphite and silicon oxide are as described above.

[0114] When the average particle diameters of the secondary particles, single particles, graphite and silicon oxide are A, B, C and D, respectively, and B < D ≤ A < C, there is an effect of improving the life performance of the battery.

[0115] According to one embodiment of the present invention, the negative active material further includes graphite, and when the average particle diameters of the single particle, the graphite, and the silicon oxide are B, C, and , respectively, B < D < C may be satisfied.

[0116] When the average particle diameters of the secondary particles, single particles, and silicon oxide are A, B, and D, respectively, B < D ≤ A may be satisfied.

[0117] When the average particle diameters of the secondary particles, single particles, and graphite are A, B, and C, respectively, B < A < C may be satisfied.

[0118] When the average particle diameters of the secondary particles, the graphite, and the silicon oxide are A, C, and D, respectively, D ≤ A < C may be satisfied.

[0119] When the above range is satisfied, there is an effect of improving the life performance of the battery.

[0120] In one embodiment of the present invention, in the lithium secondary battery according to the embodiment described above, the single particle is included in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, and the silicon oxide is included in an amount of 3 to 30 parts by weight relative to 100 parts by weight of the negative electrode active material.

[0121] In one embodiment of the present invention, the single particle is included in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material. The single particle may be included in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0122] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. For example, the single particles may be included in an amount of 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0123] When the single particles in the above range are included, excellent battery characteristics can be exhibited in combination with the aforementioned negative electrode material. In particular, when the single particles are 15 parts by weight or more, the phenomenon of fine particles increasing in the electrode due to particle breakage during the rolling process after electrode production can be alleviated, thereby improving the life characteristics of the battery.

[0124] In one embodiment of the present invention, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, or 40 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0125] In one embodiment of the present invention, the weight ratio of the single particle and the secondary particle may be 1:9 to 9:1, 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4.

[0126] When the above range is satisfied, the aforementioned effect due to the presence of a single-particle positive electrode active material can be maximized. When including a secondary particle positive electrode active material, the component may be the same as the component exemplified by the single-particle positive electrode active material described above, or may be a different component, and may refer to a form in which the single-particle form is aggregated.

[0127] In one embodiment of the present invention, the positive electrode active material may be included in 100 parts by weight of the positive electrode active material layer in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0128] According to one embodiment of the present invention, the positive electrode according to the above-described embodiment further includes a positive electrode binder and a conductive material.

[0129] The above-described positive electrode binder can serve to improve adhesion between positive electrode active material particles and adhesion between positive electrode active material particles and positive electrode current collector. Those known in the art can be used as the positive electrode binder, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0130] The positive electrode binder may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the positive electrode active material layer, for example, preferably 0.3 to 35 parts by weight, more preferably 0.5 to 20 parts by weight.

[0131] The conductive material included in the above-described positive electrode active material layer is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical changes within the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0132] Specifically, in one embodiment, the conductive material may include at least one of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the composition for the positive electrode active material layer, for example, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight.

[0133] According to the above-described embodiment of the present invention, the negative electrode active material layer contains 3 to 30 parts by weight of silicon oxide based on 100 parts by weight of the total negative electrode active material. In one example, the negative electrode active material layer may contain 3 to 20 parts by weight of silicon oxide, or 3 to 13 parts by weight, and preferably 5 to 10 parts by weight of silicon oxide based on 100 parts by weight of the total negative electrode active material. By using silicon oxide in this range, excellent battery characteristics can be exhibited in combination with the above-described positive electrode material. In particular, when silicon oxide is contained in an amount of 3 parts by weight or more, the effects of using the silicon oxide can be sufficiently exhibited. In addition, since silicon oxide has a high capacity, it may be difficult to balance the capacity with the positive electrode active material when used in excess. In particular, when silicon oxide is contained in an amount of 30 parts by weight or less, expansion during charge and discharge can be prevented, thereby improving cycle characteristics.

[0134] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material may further 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 the total negative electrode active material included in the negative electrode active material layer, the graphite may be included in an amount of 70 parts by weight or more and 97 parts by weight or less.

[0135] Based on 100 parts by weight of the total negative electrode active material, the graphite may be included in an amount of 75 parts by weight or more, 80 parts by weight or more, or 85 parts by weight or more. Based on 100 parts by weight of the total negative electrode active material, the graphite may be included in an amount of 95 parts by weight or less, 93 parts by weight or less, or 90 parts by weight or less. When the graphite is a mixture of artificial graphite and natural graphite, based on 100 parts by weight of the graphite, the artificial graphite and natural graphite may be included in an amount of 90:10 parts by weight to 50:50 parts by weight, 85:15 parts by weight to 60:40 parts by weight, or 80:20 parts by weight to 65:35 parts by weight.

[0136] In one embodiment of the present invention, the weight ratio of the carbon-based active material and silicon oxide may be 0.1:99.9 to 30:70, 1:99 to 20:80, 5:95 to 20:80, 5:95 to 15:85, 8:92 to 12:88, or 10:90 to 12:88.

[0137] In one embodiment of the present invention, the negative electrode active material may be included in 100 parts by weight of the negative electrode active material layer in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0138] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material layer may further include a negative electrode binder in addition to silicon oxide and graphite.

[0139] The above negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material particles and the negative electrode current collector. The above-mentioned negative electrode binder may be one known in the art, and non-limiting examples thereof include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and a material in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0140] The above negative electrode binder may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material layer, for example, preferably 0.3 to 35 parts by weight, more preferably 0.5 to 10 parts by weight.

[0141] The above-described negative electrode active material layer may not include a conductive material, but may further include a conductive material as needed. The conductive material included in the negative electrode active material layer is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 to 30 parts by weight, and preferably 0.03 to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0142] In one embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and including the positive electrode active material.

[0143] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 1 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0144] In one embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and including the negative electrode active material.

[0145] The negative current collector may be any conductive material that does not cause a chemical change in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. The current collector may have a thickness of 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0146] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer including the positive electrode active material, and the negative electrode further includes a negative electrode active material layer including the negative electrode active material, and the thicknesses of the positive electrode and negative electrode active material layers are each 10 ㎛ to 500 ㎛. The thickness of the positive electrode active material layer may be 90% to 110%, for example, 95% to 105%, of the thickness of the negative electrode active material layer, and these thicknesses may be the same. Specifically, the thicknesses of the positive electrode and negative electrode active material layers may be 15 ㎛ to 400 ㎛, 20 ㎛ to 300 ㎛, 25 ㎛ to 200 ㎛, or 30 ㎛ to 100 ㎛, respectively.

[0147] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer including the positive electrode active material, and the loading amount per unit volume of the positive electrode active material layer is 250 mg / 25 cm 2 900 mg / 25cm 2, and the negative electrode further includes a negative electrode active material layer including the negative electrode active material, and the loading amount per unit volume of the negative electrode active material layer is 100 mg / 25cm 2 600 mg / 25cm 2 Specifically, the loading amount per unit volume of the positive electrode active material layer is 270 mg / 25cm 2 800 mg / 25cm 2 , 285 mg / 25cm 2 700 mg / 25cm 2 , or 300 mg / 25cm 2 600 mg / 25cm 2 The loading amount per unit volume of the negative active material layer may be 120 mg / 25cm 2 500 mg / 25cm 2 , 135 mg / 25cm 2 400 mg / 25cm 2 , 150 mg / 25cm 2 300 mg / 25cm 2 It could be.

[0148] The positive electrode and the negative electrode can be manufactured according to a conventional method for manufacturing positive and negative electrodes, except that the positive and negative electrode active materials described above are used. Specifically, the composition for forming an active material layer, which includes the active material described above and optionally a binder and a conductive material, is applied to a current collector, followed by drying and rolling. At this time, the types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be a solvent generally used in the relevant technical field, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water. One type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive and negative electrodes. Alternatively, the positive and negative electrodes may be manufactured by casting the composition for forming the active material layer on a separate support, then peeling the film from the support and laminating the resulting film on a current collector.

[0149] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0150] The electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0151] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0152] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0153] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0154] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -, CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0155] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0156] The energy density of a lithium secondary battery according to one embodiment of the present invention may be 400 Wh / L to 900 Wh / L. Specifically, the energy density of the lithium secondary battery may be 425 Wh / L to 875 Wh / L, 450 Wh / L to 850 Wh / L, 475 Wh / L to 825 Wh / L, or 500 Wh / L to 800 Wh / L. When the above range is satisfied, the energy density of a lithium secondary battery designed within a limited space can be increased, high-output performance can be improved, and battery cycle performance can also be improved.

[0157] A lithium secondary battery according to one embodiment of the present invention may be a cylindrical battery. The cylindrical battery may mean that the battery itself, which includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, has a cylindrical shape, and specifically, may be composed of a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap. However, the lithium secondary battery is not limited thereto, and may be a square battery or a pouch-type battery.

[0158] One embodiment of the present invention provides a battery module including the aforementioned cylindrical battery as a unit cell and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0159] The lithium secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0160] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0161] <Examples and Comparative Examples>

[0162] Example 1

[0163] A composition for forming a positive electrode active material layer was prepared, which includes 98.04 parts by weight of a lithium composite transition metal compound containing 93.3 mol% of Ni, 4.9 mol% of Co, and 1.8 mol% of Mn as metals other than lithium as a positive electrode active material and including single particles and secondary particles (single particle:secondary particle = 50:50 weight ratio), 1 part by weight of PVDF as a binder, and a CNT pre-dispersion liquid containing 0.8 parts by weight of CNT as a conductive agent and 0.16 parts by weight of a dispersant, based on 100 parts by weight of a positive electrode active material layer.

[0164] The above lithium complex transition metal compound was used with a crystal grain size of 110 nm, and the single particles were D by the airflow grinding method. 50 =3.57㎛ size was manufactured, and the secondary particles were D 50 = It was manufactured to a size of 11.1㎛. The composition for forming the positive electrode active material layer was coated on aluminum foil having a thickness of 30㎛ to a dry thickness of 103㎛, and then dried to manufacture a positive electrode.

[0165] Based on 100 parts by weight of the negative active material layer, a composition for forming a negative active material layer was prepared, which included 97.7 parts by weight of graphite (artificial graphite: natural graphite = 70:30 weight ratio, 90 parts by weight based on 100 parts by weight of the negative active material) as a negative active material and silicon oxide (SiOx, x=0.9~1, the carbon coating amount and Mg doping amount based on 100 wt% of carbon-coated silicon oxide are shown in Table 1 below, 10 parts by weight based on 100 parts by weight of the negative active material), 1.15 parts by weight of SBR (styrene-butadiene rubber) as a binder and 1 part by weight of CMC (carboxymethyl cellulose), and, in addition, a CNT pre-dispersion liquid including 0.09 parts by weight of a dispersant and 0.06 parts by weight of single-wall CNT.

[0166] The silicon oxide having Si crystal grains of 5 nm was used, and the silicon oxide was D by the airflow grinding method. 50 = It was manufactured in a size of 5.2㎛, and the graphite was D 50 = It was manufactured to a size of 17㎛. The composition for forming the negative electrode active material layer was coated on a copper foil having a thickness of 15㎛ to a dry thickness of 86㎛, and then dried to manufacture the negative electrode.

[0167] The above positive and negative electrodes were laminated with a separator between them, and an electrolyte (1.0 M LiPF6, EC(ethylene carbonate) / EMC(ethylmethyl carbonate)=30 / 70 (Vol%), VC(vinylene carbonate) 1.5%) was injected to manufacture a battery.

[0168]

[0169] Examples 2 to 4

[0170] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a positive electrode active material and a negative electrode active material having crystal grains of a lithium composite transition metal compound, Si crystal grains of silicon oxide, and particle sizes thereof having the values ​​described in Table 1 below were used.

[0171]

[0172] Comparative Examples 1 and 2

[0173] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material and the negative electrode active material were used, with the crystal grains of the lithium composite transition metal compound, the Si crystal grains of the silicon oxide, and the particle size having the values ​​described in Table 1 below.

[0174]

[0175] The composition of the negative active material manufactured in the above examples and comparative examples is as shown in Table 1 below.

[0176] Crystalline active material, anode active material, lithium composite transition metal compound, crystalline (A) (nm), silicon oxide, Si crystalline (B) (nm), ratio of B to A (%), single particle D 50 (㎛) Single particle content (wt%) Secondary particle D 50 (㎛) Secondary particle content (wt%) Silicon oxide D 50 (㎛) Silicon oxide content (wt%) Graphite D 50 (㎛) Graphite content (wt%) Silicon oxide Mg doping amount (wt%) Silicon oxide carbon coating amount (wt%) Example 1 110 54.54 3.57 50 11.15 05.2 10 179 06.25 Example 2 88 56.25 3.6 3 50 10.5 5 05.7 10 179 06.25 Example 3 110 98.18 3.6 3 50 9.5 5 06.2 10 179 07.5 3.5 Example 4 110 1110 3.5 7 50 9.5 5 05.9 10 179 084.5 Comparative example 183 911.25 3.5 2 50 12.5 5 06.2 10 179 07.5 3.5 Comparative example 21001113.753.525012.5505.910179084.5

[0177] The size of the crystal grains of the above lithium complex transition metal compound and the Si crystal grains included in the silicon oxide can be confirmed through X-ray diffraction analysis, and the X-ray diffraction analysis was performed using an X-ray diffraction (XRD) analysis device (product name: D4-endavor, manufacturer: bruker). Specifically, the XRD measurement was performed by sampling a powder-type sample onto a holder and measuring it through Cu K alpha X-ray.

[0178] The crystal grain size of the above lithium complex transition metal compound was calculated by fitting the XRD results using the Scherrer equation, and the crystal grain standard was measured based on the peak appearing at the corresponding position. (2θ=10° to 12°)

[0179] The size of the Si crystal grains above was calculated by fitting the XRD results using the Scherrer equation, and the grain size was measured based on Si(220). (2θ=47.4° to 48.5°)

[0180] D of the above positive electrode active material and negative electrode active material 50 The PSD was analyzed using a microtrac device.

[0181]

[0182] <Experimental Example: Evaluation of discharge capacity, initial efficiency, and lifespan (capacity retention rate) characteristics>

[0183] Charging and discharging were performed on the lithium secondary batteries manufactured in the examples and comparative examples, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated, which are listed in Table 2 below.

[0184] The 1st and 2nd cycles were charged and discharged at 0.1C, and from the 3rd to the 199th cycles, the charging and discharging was performed at 0.5C. The 200th cycle was terminated in a charged state (with lithium in the negative electrode).

[0185] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0186] Discharge conditions: CC (constant current) condition 1.5 V

[0187] Based on the results of a single charge / discharge cycle, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived using the following calculation.

[0188] Initial efficiency (%) = (1-time discharge capacity / 1-time charge capacity) × 100

[0189] The capacity retention rate was derived by the following calculations.

[0190] Capacity retention rate (%) = (199 discharge capacity / 1 discharge capacity) × 100

[0191]

[0192] <Experimental Example: Cell Thickness Evaluation>

[0193] The thickness of the secondary battery manufactured above was compared before and after the cycle was performed as follows.

[0194] The 1st and 2nd cycles were charged and discharged at 0.1C, and the 3rd to 200th cycles were charged and discharged at 0.5C. The thickness of the cell after the 2nd cycle was taken as the Initial thickness, and the thickness of the cell after the 200th cycle was taken as the After thickness, and the thickness was calculated using the following formula. The calculated cell thickness of Example 1 was set to 100%, and based on this, the cell thicknesses of Examples 2 to 4 and Comparative Examples 1 and 2 were relatively calculated and are shown in Table 2 below.

[0195] Cell thickness = (After thickness - Initial thickness) / (Initial thickness) X 100

[0196] Total discharge capacity (mAh / g) Initial efficiency (%) Capacity retention (200 cycles at room temperature, %) Cell thickness (based on Example 1) (200 cycles at room temperature, %) Example 1 49 295.29 2.2100 Example 2 49 294.59 1.8110 Example 3 49 293.19 1.5107 Example 4 49 291.59 1.2113 Comparative example 149 289.88 8.2117 Comparative example 249 289.58 6.3125

[0197] According to Tables 1 and 2 above, it was confirmed that the secondary batteries of Examples 1 to 4, in which the Si crystal grain size of the silicon oxide satisfies 10% or less of the crystal grain size of the lithium composite transition metal compound, have thinner cell thicknesses and exhibit superior capacity retention rates compared to Comparative Examples 1 and 2. This is because the Si crystal grain size of the silicon oxide is 10% or less of the crystal grain size of the lithium composite transition metal compound, so that the stress due to volume expansion of the negative electrode active material particles during charge and discharge can be reduced, and accordingly, the breakage of the particles is reduced, which appears to improve the cycle characteristics and swelling performance.

[0198] On the other hand, in the case of Comparative Examples 1 and 2, since the Si crystal grain size of the silicon oxide exceeds 10% of the crystal grain size of the lithium composite transition metal compound, it was confirmed that cracks occurred in the particles due to an increase in the internal stress of Si according to charge and discharge, resulting in a decrease in cycle performance.

Claims

1. A lithium secondary battery comprising: a positive electrode including a positive active material; a negative electrode including a negative active material; a separator provided between the positive electrode and the negative electrode; and an electrolyte. The above positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co) and manganese (Mn), The above lithium complex transition metal compound comprises a single particle, The above negative active material includes silicon oxide, A lithium secondary battery, wherein the Si crystal grain size of the silicon oxide is 10% or less of the crystal grain size of the lithium composite transition metal compound.

2. In claim 1, A lithium secondary battery, wherein the Si crystal grain size of the above silicon oxide is 0.1 nm or more and 20 nm or less.

3. In claim 1, A lithium secondary battery, wherein the crystal grain size of the lithium composite transition metal compound is 70 nm or more and 200 nm or less.

4. In claim 1, A lithium secondary battery wherein the lithium composite transition metal compound further comprises secondary particles.

5. In claim 1, A lithium secondary battery wherein the negative active material further contains graphite.

6. In claim 1, A lithium secondary battery wherein the average particle diameter of the above single particles is 1 ㎛ or more and 10 ㎛ or less.

7. In claim 1, A lithium secondary battery, wherein the average particle size of the silicon oxide is 1 ㎛ or more and 10 ㎛ or less.

8. In claim 1, A lithium secondary battery wherein the average particle diameter of the above single particles is smaller than the average particle diameter of the above silicon oxide.

9. In claim 5, A lithium secondary battery wherein the average particle diameter of the silicon oxide is smaller than the average particle diameter of the graphite.

10. In claim 1, The above single particles are included in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, A lithium secondary battery wherein the silicon oxide is contained in an amount of 3 to 30 parts by weight relative to 100 parts by weight of the negative active material.

11. In claim 1, A lithium secondary battery wherein the above lithium composite transition metal compound contains nickel at 80 mol% or more among metals other than lithium.

12. In claim 1, The above positive electrode further includes a positive electrode active material layer including the positive electrode active material, The above negative electrode further includes a negative electrode active material layer including the above negative electrode active material, A lithium secondary battery, wherein the thickness of the positive electrode active material layer and the negative electrode active material layer is each 10 ㎛ or more and 500 ㎛ or less.

13. A battery module comprising a lithium secondary battery according to any one of claims 1 to 12.

14. A battery pack comprising a lithium secondary battery according to any one of claims 1 to 12.

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