Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery including a positive electrode; a negative electrode; and a separator provided between the positive electrode and the negative electrode, wherein the positive electrode contains nickel, cobalt, and manganese as a positive electrode active material and monoparticulate lithium composite transition metal compound particles, and the negative electrode contains silicon-based particles as a negative electrode active material, and the silicon-based particles have a specific surface area four or more times the specific surface area of ​​the lithium composite transition metal compound particles.

Description

[Technical Field]

[0001] This specification claims the benefit of Korean Patent Application No. 10-2023-0107196 filed with the Korean Intellectual Property Office on August 16, 2023, and Korean Patent Application No. 10-2024-0108709 filed with the Korean Intellectual Property Office on August 14, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

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

[0003] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have been attracting attention as a driving power source for portable devices. As a result, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Silicon-based negative electrode active materials have attracted attention due to their higher capacity and superior fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to their large irreversible capacity caused by large volume expansion / contraction during charging / discharging.

[0006] Therefore, it is necessary to design materials that can improve battery performance. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a lithium secondary battery with improved performance. [Means for solving the problem]

[0008] One embodiment of the present invention provides a lithium secondary battery including a positive electrode; a negative electrode; and a separator provided between the positive electrode and the negative electrode, in which the positive electrode contains nickel, cobalt, and manganese as a positive electrode active material, and contains single-particle lithium composite transition metal compound particles, and the negative electrode contains silicon-based particles as a negative electrode active material, and the silicon-based particles have a specific surface area four or more times the specific surface area of ​​the lithium composite transition metal compound particles.

[0009] According to one embodiment of the present invention, the silicon-based particles include at least one of silicon carbon composite particles and silicon oxide particles.

[0010] One embodiment of the present invention provides a battery module including the lithium secondary battery according to the above-described embodiment.

[0011] One embodiment of the present invention provides a battery pack including the lithium secondary battery according to the above-described embodiment.

[0012] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment. [Effects of the Invention]

[0013] A lithium secondary battery according to one embodiment of the present invention contains silicon-based particles as an anode active material, which not only provides a lithium secondary battery with a higher capacity than a battery using only a carbon-based anode active material, but also improves battery performance by appropriately matching the cathode material with the anode containing a silicon-based material at the battery level. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present specification will be explained in more detail below.

[0015] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0016] In this specification, when a member is positioned "on" another member, it does not only mean that the member is in contact with the other member, but also that another member exists between the two members.

[0017] As used herein, the term "single particle" may refer to a particle consisting of a single nodule. The "nodule" may be a single crystal without grain boundaries, or may be a polycrystal in which no grain boundaries are apparent when observed under a scanning electron microscope (SEM) at a magnification of 5000x to 20000x. As used herein, the term "single particle" includes quasi-single particles. As used herein, the term "quasi-single particle" may refer to an aggregate consisting of 30 or fewer nodules. As used herein, the term "secondary particle" refers to a particle formed by the aggregation of tens to hundreds of primary particles, and specifically, the secondary particle may include a particle formed by the aggregation of 50 or more primary particles.

[0018] In this specification, the term "particle" may include at least one of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle.

[0019] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

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

[0021] Preferred embodiments of the present invention will be described in detail below. 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.

[0022] <Specific surface area of ​​negative and positive electrode active material particles> According to an embodiment of the present invention, the specific surface area (SSA) of the silicon-based particles contained as the negative electrode active material is at least four times that of the lithium composite transition metal compound particles contained as the positive electrode active material. When the lithium composite transition metal compound particles are single particles, they have low resistance and therefore high lithium input / output. In the above-described embodiment of the present invention, when high-capacity silicon-based particles are used as the negative electrode active material, the specific surface area is designed taking into account the reactivity of the single-particle positive electrode active material with lithium. Specifically, by using silicon-based particles having a larger specific surface area within the above-described range compared to the lithium composite transition metal compound particles, the silicon-based particles can fully react with the lithium ions of the single-particle lithium composite transition metal compound particles. This significantly improves the battery life performance. When silicon-based particles are used as negative electrode active material particles and single-particle positive electrode active material particles and the specific surface area does not satisfy the above-described range, the reaction of lithium ions occurs intensively on the surface of the negative electrode, which increases side reactions with the electrolyte and results in a phenomenon of deterioration (fading) of the battery life performance.

[0023] For reference, in the case of lithium composite transition metal compound particles that are not single particles, the lithium input / output performance is relatively low compared to single particles, and therefore it is unlikely that the life performance of the battery can be significantly improved by controlling the specific surface area relationship with the silicon-based particles of the negative electrode according to the present invention.

[0024] According to one example, the specific surface area of ​​the silicon-based particles is 4 times or more, for example, 4.1 times or more, 4.2 times or more, or 4.3 times or more, that of the lithium composite transition metal compound particles contained as the positive electrode active material. According to another example, the specific surface area of ​​the silicon-based particles is 20 times or less, for example, 15 times or less, or 10 times or less, that of the lithium composite transition metal compound particles contained as the positive electrode active material.

[0025] The specific surface area of ​​the positive or negative electrode active material particles is affected by the particle size, surface treatment, coating structure, coating material, coating method, and the like.

[0026] According to one embodiment, the specific surface area of ​​the single-particulate lithium composite transition metal compound particles is 0.4 m 2 / g~0.8m 2 / g, e.g., 0.6m 2 / g~0.8m 2 / g, or 0.6m 2 / g~0.7m 2 / g.

[0027] According to one embodiment, the silicon-based particles, e.g., silicon carbon composite or silicon oxide particles, have a specific surface area of ​​2 m 2 / g or more, e.g., 3m 2 / g or more.

[0028] The specific surface area can be measured using a BET measurement device (BEL-SORP-MAX, Nippon Bell) by degassing at 200°C for 8 hours and then performing N2 adsorption / desorption at 77K.

[0029] <Negative electrode active material> The negative electrode of the lithium secondary battery according to one embodiment of the present invention contains silicon-based particles as a negative electrode active material.

[0030] The silicon-based particles may include at least one of silicon carbon composite particles and silicon oxide particles. For example, the silicon-based particles may include silicon carbon composite particles, silicon oxide particles, or both.

[0031] According to one embodiment, the silicon carbon composite may be a Si / C based active material.

[0032] In this specification, the silicon carbon composite is a composite of Si and C, and is distinguished from silicon carbide, which is represented as SiC.

[0033] The silicon carbon composite may be a composite of silicon and graphite, or may have a structure in which a core of the composite of silicon and graphite is surrounded by graphene or amorphous carbon, etc. The silicon in the silicon carbon composite may be nanosilicon.

[0034] According to one embodiment, the silicon carbon composite comprises porous carbon-based particles and silicon located on the surface or in the internal pores of the porous carbon-based particles.

[0035] According to one embodiment, the silicon carbon composite has a pore volume of 0.005 cm by the BET method. 3 / g~0.03cm 3 The silicon carbon composite may have a pore volume of 0.005 cm3 measured by mercury penetration method, and the pore size may be 10 nm to 20 nm by BET method. 3 / g~0.03cm 3 / g.

[0036] According to one embodiment, the silicon carbon composite can be produced by a method including the step of forming silicon on the surface and in the internal pores of porous carbon particles.

[0037] The porous carbon-based particles can be prepared by a method known in the art, for example, by carbonizing organic materials such as petroleum-based materials, polymers, etc., or by chemically treating and then carbonizing naturally occurring materials such as palm bark, etc. As another example, the porous carbon-based particles can be prepared by a method including the step of etching carbon-based particles having internal pores to expand the internal pores of the carbon-based particles.

[0038] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2), oxygen (O2), or air atmosphere, and the flow rate of the oxygen (O2) or oxygen-containing air may be controlled to 0.1 L / min to 10 L / min.

[0039] The step of expanding the internal pores of the carbon-based particles may be performed at a temperature ranging from 400° C. to 1200° C. for 30 minutes to 4 hours.

[0040] The pore characteristics of the resulting porous carbon-based particles may vary depending on the conditions for expanding the internal pores of the carbon-based particles.

[0041] The step of forming the silicon may be performed using a chemical vapor deposition method, in which silicon nanoparticles are deposited on the surfaces and / or in the pores of the carbon-based particles with expanded pores, thereby forming silicon in the form of a film, islands, or a mixture thereof.

[0042] The silicon nanoparticles may be crystalline, semi-crystalline, amorphous, or a combination thereof.

[0043] According to one embodiment, the silicon oxide is SiO x (0 ≦ x < 2) may be included.

[0044] The active material containing SiO x (0 ≦ x < 2) may be silicon oxide particles containing SiO x (0 < x < 2) and pores.

[0045] The SiO x (0 < x < 2) corresponds to a matrix within the silicon oxide particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon oxide particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0046] The silicon oxide particles may be general silicon oxide particles that do not contain additional metals or metal compounds, and may further contain at least one of Mg compounds and Li compounds as needed. The Mg compounds and Li compounds may correspond to a matrix within the silicon oxide particles.

[0047] The Mg compound and / or Li compound may be present inside and / or on the surface of the SiO x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or Li compound.

[0048] The Mg compound may include at least any one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least any one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0049] In one embodiment of the present specification, the Mg element may be contained in an amount of 0.1 wt% to 20 wt%, or may be contained in an amount of 0.1 wt% to 15 wt%, based on 100 wt% of the silicon oxide particles. Specifically, the Mg element may be contained in an amount of 0.5 wt% to 10 wt%, or 0.8 wt% to 10 wt%. When the above range is satisfied, the Mg compound can be contained in an appropriate content in the silicon oxide particles, so that the volume change 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.

[0050] The Li compound may contain at least any one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain at least any one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may contain Li7Si2. The Li oxide may contain Li2O.

[0051] In one embodiment of the present invention, the Li compound may contain lithium silicate in the form. The lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 in the silicon oxide particles, and the amorphous lithium silicate may be Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0052] In one embodiment of the present specification, the lithium element may be contained in an amount of 0.1 wt % to 20 wt %, or 0.1 wt % to 15 wt %, based on 100 wt % of the silicon oxide particles. Specifically, the lithium element may be contained in an amount of 0.5 wt % to 10 wt %, or more specifically, 0.5 wt % to 10 wt %. When the above range is satisfied, the lithium compound can be contained in the silicon oxide particles in an appropriate amount, which can easily suppress volumetric changes of the negative electrode active material during battery charge and discharge, thereby improving the battery's discharge capacity and initial efficiency.

[0053] The Mg or Li element content can be confirmed by ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative electrode active material is accurately separated and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at a wavelength specific to Mg or Li, creating a reference calibration curve. The pretreated sample solution and a blank sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated using the created calibration curve, and the total is converted to a theoretical value. The Mg or Li element content of the silicon oxide particles can then be analyzed.

[0054] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist in the silicon-based particles in the form of at least one of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This may improve the initial efficiency of the negative electrode active material.

[0055] In one embodiment of the present invention, the silicon-based particles have a carbon layer formed on at least a portion of their surfaces. The carbon layer may cover at least a portion of the surface, i.e., the surface of the particles, or may cover the entire surface of the particles. The carbon layer provides electrical conductivity to the negative electrode active material, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0056] In one embodiment of the present invention, the carbon layer contains amorphous carbon. Alternatively, the carbon layer may further contain crystalline carbon.

[0057] The crystalline carbon may further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0058] The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic substances as a source in a chemical vapor deposition process.

[0059] The carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0060] 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, hexane, or the like. 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, phenanthrene, or the like.

[0061] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0062] 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 silicon-based particles. More specifically, the carbon layer 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 amount is within the above range, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0063] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the thickness is within this range, 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, resulting in improved initial efficiency and / or lifespan of the battery.

[0064] Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0065] In the present invention, the crystallinity of the carbon layer can be confirmed by calculating the D / G band ratio using Raman spectroscopy. Specifically, measurements can be performed using a Renishaw 2000 Raman microscope system with 532 nm laser excitation, a low laser power density to avoid thermal effects, and a 100x optical lens for a 30-second exposure time. To reduce positional deviations, a total of 25 points are measured over a 5 μm × 5 μm area, and the results are fitted using a Lorentzian function to calculate the average values ​​of the D and G bands.

[0066] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0067] The negative electrode active material, for example, silicon carbon composite particles or silicon oxide particles, may have an average particle size (D50) of 1 μm to 10 μm. When the average particle size satisfies this range, the active material's structural stability during charge and discharge can be improved, the problem of increased volume expansion / contraction due to an excessively large particle size can be prevented, and the problem of reduced initial efficiency due to an excessively small particle size can be prevented.

[0068] <Negative electrode> The negative electrode of the lithium secondary battery according to one embodiment of the present invention includes the above-described negative electrode active material.

[0069] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder, a thickener, and / or a conductive material.

[0070] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one surface of a current collector, followed by drying and rolling.

[0071] The negative electrode slurry may further include an additional negative electrode active material.

[0072] The additional negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0073] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0074] In one embodiment of the present invention, the silicon-based particles may be contained in an amount of 3 to 30 parts by weight based on 100 parts by weight of the negative electrode active material.

[0075] When the silicon-based particles are contained in an amount of 3 to 30 parts by weight per 100 parts by weight of the negative electrode active material, the inclusion of high-capacity silicon-based particles allows the negative electrode to be made thinner, improving output characteristics, and thereby improving the life characteristics of the secondary battery.

[0076] Specifically, when silicon-based particles are included in an amount of 3 parts by weight or more per 100 parts by weight of anode active material, the anode capacity is increased compared to anodes containing only carbon-based active material, resulting in a thinner electrode and improved output characteristics. While excessive silicon-based active material content can cause problems with reduced lifespan due to volume expansion, when the anode active material is included in an amount of 30 parts by weight or less, this drawback is reduced and the lifespan characteristics of the secondary battery are improved. The anode slurry may also include a solvent for forming the anode slurry. Specifically, the solvent for forming the anode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, to facilitate dispersion of the components.

[0077] According to one embodiment of the present invention, the negative electrode slurry may have a pH of 7 to 11 at 25°C. When the pH of the negative electrode slurry satisfies this range, the rheological properties of the slurry are stabilized. On the other hand, if the pH of the negative electrode slurry is less than 7 or more than 11, decomposition of carboxymethyl cellulose (CMC), which is used as a thickener, occurs, causing a decrease in the viscosity of the slurry and a decrease in the degree of dispersion of the active material contained in the slurry.

[0078] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited to this.

[0079] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0080] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as 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.

[0081] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the technical field may be appropriately adopted.

[0082] In one embodiment of the present invention, the total amount of the negative electrode active material contained in the negative electrode slurry may be 60 parts by weight to 99 parts by weight, specifically 70 parts by weight to 98 parts by weight, based on 100 parts by weight of the solid content of the negative electrode slurry.

[0083] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode slurry.

[0084] In one embodiment of the present invention, the conductive material may be included in an amount of 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode slurry.

[0085] In one embodiment of the present invention, the thickener may be included in an amount of 0.5 parts by weight to 25 parts by weight, specifically 0.5 parts by weight to 20 parts by weight, more specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode slurry.

[0086] The negative electrode slurry according to an embodiment of the present invention may further include a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0087] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the negative electrode slurry.

[0088] <Cathode active material> A positive electrode of a lithium secondary battery according to one embodiment of the present invention includes nickel, cobalt, and manganese as a positive electrode active material, and includes single-particulate lithium transition metal composite compound particles, where the single-particulate state includes similar-single-particulate states.

[0089] The positive electrode active material includes lithium composite transition metal compound particles containing nickel (Ni), cobalt (Co), and manganese (Mn). The lithium composite transition metal compound particles include single particles, and the single particles have an average particle size (D50) of 1 μm or more. The single particles include single particles consisting of one nodule and similar-single particles that are aggregates consisting of 30 or less nodules.

[0090] The single-particle lithium composite transition metal compound particles may be included in an amount of 15 to 100 parts by weight, for example, 50 to 100 parts by weight, or 85 to 100 parts by weight, based on 100 parts by weight of the positive electrode active material.

[0091] When the average particle size (D50) of the single particles is 1 μm or more, 3 μm or more, or 5 μm or more, the single particles have reduced side reactions with the electrolyte solution and excellent life performance. According to one embodiment, the average particle size (D50) of the single-particulate lithium composite transition metal compound particles may be 1 μm or more and 10 μm or less.

[0092] According to a further embodiment of the present application, the lithium transition metal composite compound particles contain nickel, cobalt, and manganese, and may further contain aluminum.

[0093] In this specification, the lithium composite transition metal compound particles contain 80 mol % or more and less than 100 mol % of nickel among metals other than lithium, and may contain one or a mixture of two or more types represented by the following chemical formula 1.

[0094] [Chemical formula 1] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ In the above formula, Q is any one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, where 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.

[0095] In the lithium composite transition metal compound of Chemical Formula 1 above, Li may be contained in an amount corresponding to a, that is, 1 ≦ a ≦ 1.5. When a is less than 1, the capacity may decrease. When a exceeds 1.5, the particles may sinter in the firing process, making it difficult to manufacture the positive electrode active material. Considering the improvement effect of the capacity characteristics of the positive electrode active material by controlling the content of Li and the balance of the sinterability during the manufacture of the active material, the Li may be more preferably contained in an amount of 1.1 ≦ a ≦ 1.2.

[0096] In the lithium composite transition metal compound of Chemical Formula 1 above, Ni may be contained in an amount corresponding to 1 - (b + c + d), for example, 0.8 ≦ 1 - (b + c + d) < 1. When the content of Ni in the lithium composite transition metal compound of Chemical Formula 1 is in a composition of 0.8 or more, a sufficient amount of Ni contributing to charge and discharge can be ensured, and high capacity can be achieved. Preferably, 1 - (b + c + d), which is the content of Ni, may be 0.88, preferably 0.9 or more, more preferably 0.93 or more. Preferably, 1 - (b + c + d), which is the content of Ni, may be 0.99 or less, 0.95 or less.

[0097] In the lithium composite transition metal compound of Chemical Formula 1 above, Co may be contained in an amount corresponding to b, that is, 0 < b ≦ 0.5. When the content of Co in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, there is a risk of cost increase. Considering the significance of the improvement effect of the capacity characteristics by containing Co, the Co may be more specifically contained in an amount of 0.03 ≦ b ≦ 0.2.

[0098] In the lithium composite transition metal compound of Chemical Formula 1, Mn may be contained in a content corresponding to c, that is, a content of 0 < c ≤ 0.5. When c in the lithium composite transition metal compound of Chemical Formula 1 exceeds 0.5, the output characteristics and capacity characteristics of the battery may conversely deteriorate. More specifically, Mn may be contained in a content of 0.01 ≤ c ≤ 0.2.

[0099] In the lithium composite transition metal compound of Chemical Formula 1, Q may be a doping element contained in the crystal structure of the lithium composite transition metal compound, and Q may be contained in a content corresponding to d, that is, 0 ≤ d ≤ 0.1. Q may be one or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr. For example, Q may be Al.

[0100] The above-described lithium composite transition metal compound may further contain secondary particles. The secondary particles mean a form formed by aggregation of primary particles and can be distinguished from the concept of similar-single particles that are single particles composed of one nodule or aggregates composed of 30 or fewer nodules.

[0101] According to a further embodiment of the present application, the positive electrode active material may contain single particles and secondary particles of the lithium composite transition metal compound.

[0102] The single particles can be produced by mixing and firing a transition metal precursor and a lithium raw material substance. The secondary particles may be produced by a method different from that of the single particles, and their composition may be the same as or different from the composition of the single particles.

[0103] For example, the calcination is performed at a temperature that allows the formation of single particles. To form the single particles, the calcination may be performed at a temperature higher than that used for producing the secondary particles. For example, when the precursor composition is the same, the calcination may be performed at a temperature about 30°C to 100°C higher than that used for producing the secondary particles. The calcination temperature for forming the single particles may vary depending on the metal composition of the precursor. For example, when a high-nickel (Ni) NCM-based lithium transition metal oxide having a nickel (Ni) content of 80 mol% or more is to be formed into single particles, the calcination temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material including single particles with excellent electrochemical properties can be produced. When the calcination temperature is lower than 790°C, a positive electrode active material including a lithium transition metal compound in the form of secondary particles is produced. When the calcination temperature is higher than 950°C, excessive calcination may occur, resulting in an inadequate formation of a layered crystal structure and reduced electrochemical properties.

[0104] The particle diameter (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, and preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g~10m 2 / g, preferably 0.1m 2 / g~1m 2 / g, more preferably 0.3m 2 / g~0.8m 2 / g.

[0105] In a further embodiment, the secondary particles may be aggregates of primary particles, and the average particle size (D50) of the primary particles may be 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) 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.

[0106] <Positive electrode> According to one embodiment of the present application, 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 including the positive electrode active material.

[0107] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0108] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0109] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0110] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0111] The positive electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, more preferably 0.5 parts by weight to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0112] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination.

[0113] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 to 2 parts by weight, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight, based on 100 parts by weight of the composition for a positive electrode active material layer.

[0114] <Secondary battery> A secondary battery according to an embodiment of the present invention includes the above-described negative electrode, positive electrode, and a separator interposed between the positive electrode and the negative electrode, and may further include an electrolyte.

[0115] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferred that the separator exhibits low resistance to ion migration in the electrolyte and has excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0116] Examples of the electrolytic solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0117] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0118] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0119] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared, and therefore these cyclic carbonates can be used even more preferably.

[0120] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P- , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0121] In addition to the components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0122] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0123] <Examples and Comparative Examples> Example 1 A positive electrode active material-forming composition was prepared using 98.04 parts by weight of a single-particle lithium composite transition metal compound containing 93.3 mol% Ni, 4.9 mol% Co, and 1.8 mol% Mn (excluding lithium) based on 100 parts by weight of the positive electrode active material, 1 part by weight of PVDF as a binder, and a CNT pre-dispersion containing 0.8 parts by weight of CNTs and 0.16 parts by weight of a dispersant as a conductive material. The single particles were milled to a D50 of 3 μm using an airflow milling method. The positive electrode active material-forming composition was coated onto a 30 μm-thick aluminum foil to a dry thickness of 103 μm and then dried to prepare a positive electrode.

[0124] A negative electrode active material-forming composition was prepared using 100 parts by weight of negative electrode active material. The composition included 97.7 parts by weight of graphite (90 parts by weight based on 100 parts by weight of negative electrode active material), 97.7 parts by weight of methane-CVD carbon-coated silicon oxide active material (10 parts by weight based on 100 parts by weight of negative electrode active material), 1.15 parts by weight of styrene butadiene rubber (SBR) and 1 part by weight of carboxymethyl cellulose (CMC) as binders, 0.1 parts by weight of dispersant, and 0.05 parts by weight of single-walled CNTs. The carbon-coated silicon oxide active material was milled to a size (D50) of 6 μm and the graphite was milled to a size (D50) of 17 μm using an airflow milling method. The negative electrode active material-forming composition was coated onto a 15 μm-thick copper foil to a dry thickness of 86 μm and then dried to prepare a negative electrode.

[0125] The positive electrode and the negative electrode were stacked with a separator interposed therebetween, and an electrolyte (1.0 M LiPF6, EC (ethylene carbonate) / EMC (ethylmethyl carbonate) = 30 / 70 (Vol%), VC (vinylene carbonate) 1.5%) was injected to prepare a battery.

[0126] The specific surface areas of the silicon oxides in the positive and negative active materials were measured using a BET measurement device (BEL-SORP-MAX, Nippon Bell) by degassing at 200°C for 8 hours and then performing N adsorption / desorption at 77K. The specific surface areas were 0.6 m for the positive active material and 0.6 m for the negative active material, respectively. 2 / g, silicon oxide active material 3.0m 2 / g.

[0127] Example 2 A battery was fabricated in the same manner as in Example 1, except that a Mg-containing silicon oxide coated with carbon by methane CVD was used as the silicon-based active material contained in the negative electrode active material. The specific surface area of ​​the active material was 0.6 m² for the positive electrode active material. 2 / g, Mg-silicon oxide active material 6.0m 2 / g.

[0128] Example 3 A battery was fabricated in the same manner as in Example 1, except that a Li-containing silicon oxide coated with carbon by methane CVD was used as the silicon-based active material contained in the negative electrode active material. The specific surface area of ​​the active material was 0.6 m² for the positive electrode active material. 2 / g, Li-silicon oxide active material 3.5m 2 / g.

[0129] Example 4 A battery was fabricated in the same manner as in Example 1, except that a silicon-based active material contained in the negative electrode active material was a silicon-carbon composite coated with carbon by methane CVD. The specific surface area of ​​the active material was 0.6 m² for the positive electrode active material. 2 / g, silicon carbon composite active material 3.0m 2 / g.

[0130] Example 5 A battery was manufactured in the same manner as in Example 1, except that the positive electrode active material was pulverized to D50 = 3.5 μm. The specific surface area of ​​the active material was 0.7 m 2 / g, silicon oxide active material 3.0m2 / g.

[0131] Example 6 A battery was manufactured in the same manner as in Example 2, except that the positive electrode active material was pulverized to D50 = 3.5 μm. The specific surface area of ​​the active material was 0.7 m 2 / g, Mg-silicon oxide active material 6.0m 2 / g.

[0132] Example 7 A battery was manufactured in the same manner as in Example 3, except that the positive electrode active material was pulverized to D50 = 3.5 μm. The specific surface area of ​​the active material was 0.7 m 2 / g, Li-silicon oxide active material 3.5m 2 / g.

[0133] Example 8 A battery was manufactured in the same manner as in Example 4, except that the positive electrode active material was pulverized to D50 = 3.5 μm. The specific surface area of ​​the active material was 0.7 m 2 / g, silicon carbon composite active material 3.0m 2 / g.

[0134] Comparative Example 1 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was silicon oxide with a D50 of 12 μm and carbon coating by methane CVD. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, Mg-silicon oxide active material 1.5m 2 / g.

[0135] Comparative Example 2 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was a magnesium-containing silicon oxide with a D50 of 12 μm and carbon-coated by methane CVD. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, Mg-silicon oxide active material 2.0m 2 / g.

[0136] Comparative Example 3 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was a Li-containing silicon oxide with a D50 of 12 μm and carbon-coated by methane CVD. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, Li-silicon oxide active material 2.0m 2 / g.

[0137] Comparative Example 4 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was a silicon-carbon composite with a D50 of 12 μm and carbon-coated by methane CVD. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, silicon carbon composite active material 1.0m 2 / g.

[0138] Comparative Example 5 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was silicon oxide carbon-coated with pitch, with a D50 of 6 μm. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, silicon oxide active material 1.8m 2 / g.

[0139] Comparative Example 6 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was a magnesium-containing silicon oxide carbon-coated with pitch, with a D50 of 6 μm. The specific surface area of ​​the active material was 0.6 m² for the positive electrode active material. 2 / g, Mg-silicon oxide active material 2.3m 2 / g.

[0140] Comparative Example 7 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was a Li-containing silicon oxide that had a D50 of 6 μm and was carbon-coated with pitch. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, Li-silicon oxide active material 2.0m 2 / g.

[0141] Comparative Example 8 A battery was fabricated in the same manner as in Example 1, except that the silicon-based active material contained in the negative electrode active material was a silicon-carbon composite coated with pitch carbon and had a D50 of 6 μm. The specific surface area of ​​the active material was 0.6 m for the positive electrode active material. 2 / g, silicon carbon composite active material 1.2m 2 / g.

[0142] Comparative Example 9 A battery was fabricated in the same manner as in Example 1, except that the negative electrode active material was artificial graphite. The specific surface area of ​​the active material was 0.6 m 2 / g, artificial graphite active material 0.6m 2 / g.

[0143] Comparative Example 10 A battery was fabricated in the same manner as in Example 1, except that the positive electrode active material was a secondary particle. The specific surface area of ​​the active material was 0.6 m 2 / g, silicon carbon composite active material 3.0m 2 / g.

[0144] Comparative Example 11 A battery was fabricated in the same manner as in Example 1, except that the positive electrode active material was a secondary particle. The specific surface area of ​​the active material was 0.8 m 2 / g, silicon carbon composite active material 3.0m 2 / g.

[0145] <Experimental Example 1> Evaluation of life (capacity retention rate) characteristics The manufactured batteries were charged and discharged to evaluate the capacity retention rate, which is shown in Table 1 below.

[0146] The first and second cycles were charged and discharged at 0.1 C, and from the third cycle onwards, the charge and discharge rate was 1.0 C. The 300th cycle ended in a discharged state (with lithium in the positive electrode).

[0147] Charging conditions: CC (constant current) / CV (constant voltage) (4.25V / 0.05C current cut-off) Discharge condition: CC (constant current) condition 2.5V The capacity retention rate was calculated as follows.

[0148] Capacity retention rate (%) = (300 times discharge capacity / 1 time discharge capacity) × 100

[0149] [Table 1-1] [Table 1-2]

[0150] As shown in the table, it was confirmed that Examples 1 to 8, in which the specific surface area of ​​the silicon-based particles was four times or more the specific surface area of ​​the lithium composite transition metal compound particles, had superior capacity retention rates after 300 cycles compared to Comparative Examples 1 to 9 and 11, in which the specific surface area of ​​the silicon-based particles was less than 4.0 times the specific surface area of ​​the lithium composite transition metal compound particles. Specifically, when the capacity retention rates of Example 1, in which the specific surface area of ​​the silicon-based particles was 5.0 times the specific surface area of ​​the lithium composite transition metal compound particles, and Comparative Example 1, in which the specific surface area of ​​the silicon-based particles was 2.5 times the specific surface area of ​​the lithium composite transition metal compound particles, were compared, the capacity retention rate of Example 1 was found to be 12.8% higher.

[0151] It was found that Examples 1 to 8, which contained silicon-based particles as the negative electrode active material, had superior capacity retention rates compared to Comparative Example 9, which did not contain silicon-based particles as the negative electrode active material. Specifically, when Example 4, which contained a silicon carbon composite as the negative electrode active material, was compared with Comparative Example 9, which contained only artificial graphite as the negative electrode active material, the capacity retention rate increased by up to 74%.

[0152] Furthermore, it was found that Examples 1 to 8, which used single-particulate lithium composite transition metal compound particles, were superior in capacity retention rate to Comparative Examples 10 and 11, which used secondary-particulate lithium composite transition metal compound particles. Specifically, when Example 1, which contains a single-particulate lithium composite transition metal compound, is compared with Comparative Example 10, which used secondary-particulate lithium composite transition metal compound, the result showed that the capacity retention rate increased by 12.8%.

[0153] Therefore, it was confirmed that by using an active material in which the specific surface area of ​​the silicon-based particles of the negative electrode active material is 4.0 times or more the specific surface area of ​​the lithium composite transition metal compound particles of the positive electrode active material, the silicon-based particles can sufficiently react with the lithium ions of the single-particle lithium composite transition metal compound particles, thereby making it possible to significantly improve the battery life performance.

Claims

1. A lithium secondary battery comprising: a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode, the positive electrode contains nickel, cobalt, and manganese as a positive electrode active material, and contains single-particle lithium composite transition metal compound particles; the negative electrode contains silicon-based particles as a negative electrode active material, a specific surface area of ​​the silicon-based particles being at least four times the specific surface area of ​​the lithium composite transition metal compound particles;

2. The lithium secondary battery according to claim 1 , wherein the silicon-based particles include at least one of silicon carbon composite particles and silicon oxide particles.

3. The specific surface area of ​​the lithium composite transition metal compound particles is 0.4 m ２ / g to 0.8m ２ / g, and the specific surface area of ​​the silicon carbon composite or the silicon oxide particles is 2 m ２ 3. The lithium secondary battery according to claim 2, wherein the SiO2 content is 1 / g or more.

4. the lithium composite transition metal compound particles are contained in an amount of 15 parts by weight to 100 parts by weight relative to 100 parts by weight of the positive electrode active material; 3. The lithium secondary battery according to claim 2, wherein the silicon carbon composite particles or the silicon oxide particles are contained in an amount of 3 to 30 parts by weight based on 100 parts by weight of the negative electrode active material.

5. The lithium transition metal composite compound particles have a D50 of 1 μm or more and 10 μm or less, 3. The lithium secondary battery according to claim 2, wherein the silicon carbon composite particles or the silicon oxide particles have a D50 of 1 μm or more and 10 μm or less.

6. A battery module comprising the lithium secondary battery according to any one of claims 1 to 5.

7. A battery pack comprising the lithium secondary battery according to any one of claims 1 to 5.

8. A battery pack comprising the battery module according to claim 6.

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