Secondary battery

Abstract

The present invention relates to a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, in which the negative electrode comprises a silicon-based active material and a carbon-based active material, in which the positive electrode comprises a lithium nickel-based active material in a single particle form and one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in a secondary particle form, and in which the amount of the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material in the lithium nickel-based active material is 100 parts by weight. The content of one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the form of secondary particles is 0.1 parts by weight to 10 parts by weight, and the lithium nickel-based active material in the form of single particles contains 55 mol% or more of nickel with respect to 100 mol% of a metal other than lithium.

Description

[0001] This application is a divisional application of PCT international application PCT / KR2023 / 014828, with an application date of September 26, 2023. The original application is an invention patent application. The application number entering the Chinese national phase is 202380046765.6, and the name is "Secondary Battery". Technical Field

[0002] This application claims priority from Korean Patent Application No. 10-2022-0132117 filed on October 14, 2022, in the Korean Intellectual Property Office and Korean Patent Application No. 10-2023-0127952 filed on September 25, 2023, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a secondary battery. Background Art

[0004] Secondary batteries are commonly used not only in portable devices but also in electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by an electric drive source due to their easy application to various products and electrical characteristics such as high energy density.

[0005] Secondary batteries have attracted attention as a new energy source that improves eco-friendliness and energy efficiency due to a primary advantage of significantly reducing the use of fossil fuels and a secondary advantage of using energy without generating byproducts.

[0006] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, an electrolyte, and the like. Furthermore, the positive electrode and the negative electrode may be formed on a current collector having active material layers each containing a positive electrode active material and a negative electrode active material. Typically, for the positive electrode, a lithium-containing metal oxide (e.g., LiCoO2 and LiMn2O4) is used as the positive electrode active material, and for the negative electrode, a carbon compound, a silicon compound, or a mixture thereof is used as the negative electrode active material.

[0007] Recently, in order to develop batteries that can be quickly charged, a mixture of carbon compounds (such as graphite) and silicon compounds has been used for the negative electrode. However, when a silicon compound is included, the resistance of the negative electrode increases rapidly at the end of discharge, resulting in an increase in the difference between the resistance of the negative electrode and the resistance of the positive electrode, which shortens the life of the battery and deteriorates the room temperature cycle characteristics. Therefore, it is necessary to develop batteries to solve these problems.

[0008] Prior art literature

[0009] [Patent Document]

[0010] (Patent Document 1) Korean Patent Application Publication No. 10-2012-0037409 Summary of the Invention

[0011] [Technical Issues]

[0012] The present invention aims to provide a secondary battery having improved lifespan and room temperature cycle characteristics by reducing the difference between the resistance of the negative electrode and the resistance of the positive electrode at the end of discharge by including a silicon-based compound in a negative electrode active material layer.

[0013] However, the technical problems to be solved by the present invention are not limited to the above problems, and those skilled in the art can clearly understand other problems not described from the following description.

[0014] [Technical solution]

[0015] An exemplary embodiment of the present invention provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a silicon-based active material and a carbon-based active material, wherein the positive electrode comprises: a lithium-nickel-based active material in a single particle form; and one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in a secondary particle form, and wherein the lithium-nickel-based active material in a single particle form comprises 55 mol% or more of nickel relative to 100 mol% of metal other than lithium.

[0016] [Beneficial Effects]

[0017] The secondary battery of the present invention contains a lithium nickel-based active material in the form of single particles and one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the form of secondary particles in the positive electrode active material layer, thereby reducing the rapid decrease in positive electrode resistance at the end of discharge. As a result, a secondary battery with a reduced difference in resistance between the negative electrode and the positive electrode and improved lifespan and room temperature cycling characteristics can be obtained.

[0018] Specifically, a lithium nickel-based active material in the form of a single particle with a high nickel content is used for the positive electrode active material layer to increase the energy density of the battery and reduce the breakage of the active material, and a silicon-based active material is included in the negative electrode active material layer to enable rapid charging. At this time, the resistance of the negative electrode increases rapidly at the end of discharge, resulting in a large difference between the resistance of the positive electrode and the resistance of the negative electrode, which leads to an excessive increase in the use of the silicon-based active material contained in the negative electrode active material layer (increased depth of use) and deterioration of the life performance of the battery. In order to improve the above-mentioned problems, a lithium nickel-based active material in the form of a single particle and one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles are included in the positive electrode active material layer to enable rapid charging, improve the resistance of the positive electrode, and reduce the resistance difference between the positive electrode and the negative electrode and the depth of use of the silicon-based active material, thereby obtaining a secondary battery with improved room temperature life. DETAILED DESCRIPTION

[0019] Hereinafter, the present invention will be described in detail. The following description is intended to help understanding the present invention, but does not determine or limit the scope of the present invention.

[0020] In the present specification, when a part is referred to as “including / comprising” a certain component, this means that the part may further include / comprising another component, without excluding the other component, unless explicitly described otherwise.

[0021] Throughout the specification, when an element is referred to as being “on” another element, the element can be in direct contact with the other element, or intervening elements may also be present.

[0022] It should be understood that the terms or words used throughout the specification should not be interpreted as limited to their general meanings or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the technical ideas of the present invention based on the principle that the inventor can appropriately define the concepts of the words or terms to best explain the present invention.

[0023] As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] In this specification, the crystallinity of the structure contained in the positive electrode or negative electrode active material can be confirmed by X-ray diffraction analysis, and the X-ray diffraction analysis can be performed by using an X-ray diffraction (XRD) analyzer (product name: D4-Endavor, manufacturer: Bruker), or, in addition to the above-mentioned equipment, equipment used in the prior art can also be used.

[0025] In this specification, the presence or absence of an element and the content of the element in the positive or negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed by using an inductively coupled plasma atomic emission spectrometer (ICP AES, Perkin-Elmer 7300).

[0026] In this specification, the end of discharge refers to a period in which the SOC (state of charge) of all cells is 10% or less.

[0027] In this specification, the average particle size (D 50 )” can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle size (D 50 ) can be measured using laser diffraction. For example, the average particle size (D 50 ) may include dispersing particles of the positive electrode active material in a dispersion medium, introducing the dispersion into a commercially available laser diffraction particle size measuring apparatus (e.g., HORIBA LA-960), irradiating the dispersion with ultrasonic waves of about 28 kHz at an output of 60 W, and then calculating the average particle size (D) corresponding to 50% of the cumulative volume in the measuring apparatus. 50 ).

[0028] In this specification, the term "single particle" refers to a particle consisting of 10 or fewer primary particles, as opposed to a secondary particle formed by the aggregation of tens to hundreds of primary particles. Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle, or may be a particle formed by the aggregation of several primary particles.

[0029] In this specification, the term "primary particle" refers to the smallest unit of a particle recognized when an active material is observed through a scanning electron microscope, and "secondary particle" refers to a secondary structure formed by aggregation of tens to hundreds of primary particles.

[0030] In this specification, the expression "particle" refers to micron-sized particles, and when observed under magnification, the particles can be identified as "grains" having a crystalline form with a size of tens of nanometers. When the grains are further magnified, individual regions in which atoms form a lattice structure in a predetermined direction can be identified, wherein such regions are referred to as "crystallites". The size of the particles observed by X-ray diffraction (XRD) is defined as the size of the crystallite. The size of the crystallite can be quantitatively determined by the Scherrer equation using XRD data.

[0031] The secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode comprises a silicon-based active material and a carbon-based active material, wherein the positive electrode comprises a lithium-nickel-based active material in the form of a single particle and one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles, and wherein the lithium-nickel-based active material in the form of a single particle contains more than 55 mol% of nickel relative to 100 mol% of metal other than lithium.

[0032] In this specification, when the negative electrode active material layer contains a silicon-based active material, the resistance of the negative electrode increases rapidly at the end of discharge, and the resistance of the positive electrode using a positive electrode material with low resistance characteristics decreases rapidly, so the difference between the resistance of the negative electrode and the resistance of the positive electrode increases significantly. Therefore, there is the following problem: the degradation of the negative electrode progresses rapidly, shortening the life of the battery and deteriorating the room temperature cycle characteristics. In order to solve this problem, a lithium nickel-based active material in the form of a single particle and one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles are included in the positive electrode active material layer, thereby reducing the rapid decrease in the resistance of the positive electrode and obtaining a battery with improved life and room temperature cycle characteristics.

[0033] <Cathode Material>

[0034] The positive electrode of the present invention includes a positive electrode active material layer, wherein the positive electrode active material layer includes: a lithium nickel-based active material in the form of a single particle, and one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the form of secondary particles. In this case, the lithium nickel-based active material in the form of a single particle contains 55 mol% or more of nickel, specifically 55 mol% or more and less than 80 mol% of nickel, or 80 mol% or more of nickel, relative to 100 mol% of metal other than lithium. The present invention includes one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the form of secondary particles, and mixes them with the lithium nickel-based active material to have the effect of reducing the positive electrode voltage at the end of discharge.

[0035] According to an exemplary embodiment of the present invention, the positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes: a lithium nickel-based active material in the form of a single particle; and one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles.

[0036] According to an exemplary embodiment of the present invention, the positive active material layer includes a lithium nickel-based active material in the form of single particles and LCO (LiCoO 2 ) in the form of secondary particles.

[0037] According to an exemplary embodiment of the present invention, the positive electrode active material layer includes a lithium nickel-based active material in the form of single particles and LMO (LiMn 2 O 4 ) in the form of secondary particles.

[0038] According to an exemplary embodiment of the present invention, the positive active material layer includes a lithium nickel-based active material in the form of single particles and LFP (LiFePO 4 ) in the form of secondary particles.

[0039] According to an exemplary embodiment of the present invention, the positive electrode active material layer includes a lithium nickel-based active material in the form of single particles and one or more of LMO (LiMn 2 O 4 ) and LFP (LiFePO 4 ) in the form of secondary particles.

[0040] In an exemplary embodiment of the present invention, the content of one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the form of secondary particles is 0.1 to 10 parts by weight, specifically 0.1 to 5 parts by weight, or 0.1 to 3 parts by weight, relative to 100 parts by weight of the total amount of the positive electrode active material in the positive electrode active material layer. In this case, the total amount of the positive electrode active material may refer to the lithium nickel-based active material in the form of a single particle, or the lithium nickel-based active material in the form of a single particle and an additional active material. When the content of one or more of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) contained in the positive electrode active material layer satisfies the above range, the effect of suppressing negative electrode degradation is exhibited by suppressing the increase in negative electrode potential caused by the decrease in positive electrode voltage at the end of discharge. In addition, since the charge / discharge capacity (mAh) / g of each of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) is lower than the charge / discharge capacity (mAh) / g of the lithium nickel-based active material, if the content of one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) exceeds the above range, the battery capacity may decrease.

[0041] According to an exemplary embodiment of the present invention, the average particle size (D 50 ) is 3μm to 10μm.

[0042] The lithium nickel active material of the present invention may include a lithium composite metal oxide containing nickel, lithium and one or more metals such as cobalt, manganese or aluminum. More specifically, lithium nickel manganese cobalt oxides (e.g.

[0043] Li(Ni p Co q Mn r1)O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where

[0044] 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), lithium nickel cobalt transition metal (M) oxide (e.g., Li(Ni) p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are each independently the atomic fraction of the element, 0 < p2 < 1, 0 < q2 < 1, 0 ≤ r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc.), etc., and may include any one or more than two of these compounds.

[0045] However, the present invention is not limited thereto.

[0046] In addition to the above positive electrode active material layer, the positive electrode may further include a positive electrode current collector. In this case, the positive electrode active material layer is formed on at least one surface of the positive electrode current collector.

[0047] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and micro-concavo-convex objects may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous body, foam body, and non-woven fabric body.

[0048] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above positive electrode active material.

[0049] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation, as long as the positive electrode conductive material has electronic conductivity and does not cause chemical changes in the battery to be constructed. Specific examples include: graphite, such as natural graphite and artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and the like, and any one of these or a mixture of two or more thereof can be used.

[0050] In addition, the positive electrode binder is used to improve the adhesion between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may 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 polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0051] The positive electrode active material layer can be formed by applying a positive electrode slurry containing a lithium nickel-based active material in the form of single particles, one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles, and a binder and / or a conductive material to at least one surface of a positive electrode collector, and then drying and rolling the slurry.

[0052] The positive electrode slurry according to the exemplary embodiment of the present invention may further include a solvent for forming the positive electrode slurry. Specifically, the solvent for forming the positive electrode slurry may include methyl pyrrolidone (NMP) or the like to facilitate dispersion of the components.

[0053] In an exemplary embodiment of the present invention, the solid content of the positive electrode slurry may be 20 to 85 parts by weight, specifically 30 to 80 parts by weight, based on 100 parts by weight of the total amount of the positive electrode slurry.

[0054] According to an exemplary embodiment of the present invention, the porosity of the positive electrode is 19% to 23%.

[0055] The porosity can be calculated as: (1-(rolling density / true density of electrode))*100(%).

[0056] The roll density can be calculated as follows.

[0057] Rolling density: weight of the electrode excluding the foil (g) / volume of the electrode excluding the foil (sample area * electrode layer thickness, cm 3 )

[0058] The volume of the electrode excluding the foil refers to the total volume including the pores in the electrode and is calculated as the product of the unit area of the sample and the thickness of the electrode layer after rolling.

[0059] The true density of the electrode is the inherent density of the electrode active material and refers to the density of the part filled only with the material excluding the gaps between the particles. The true density of the electrode is measured by applying Archimedes' principle to measure the volume excluding the open pores (solid + isolated pores) to calculate the density value, or by using a gas pycnometer.

[0060] <Negative electrode>

[0061] The negative electrode of an exemplary embodiment of the present invention includes a negative electrode active material layer, and the negative electrode active material layer includes a silicon-based active material and a carbon-based active material.

[0062] According to an exemplary embodiment of the present invention, the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes a silicon-based active material and a carbon-based active material.

[0063] In addition to the above negative electrode active material layer, the negative electrode may further include a negative electrode current collector. In this case, the negative electrode active material layer is formed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a silicon-based active material and a carbon-based active material. In addition, the negative electrode active material layer may further include an adhesive and / or a conductive material.

[0064] According to an exemplary embodiment of the present invention, the carbon-based active material can be used without particular limitation, and its representative examples may include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon may include graphite, such as natural graphite and artificial graphite in amorphous, plate-like, flaky, spherical, or fibrous forms, and examples of amorphous carbon may include soft carbon (low-temperature sintered carbon), hard carbon, mesophase pitch carbide, sintered coke, etc. The graphite may be natural graphite, artificial graphite, or a mixture thereof. With respect to the total amount of the negative electrode active material contained in 100 parts by weight of the negative electrode active material layer, the content of the carbon-based active material may be 60 parts by weight or more and 99 parts by weight or less.

[0065] According to an exemplary embodiment, the negative electrode includes a silicon-based active material.

[0066] Containing SiO x (0 < x < 2) As the active material of the silicon-based active material, it may be silicon-based composite particles containing SiO x (0 < x < 2) and pores.

[0067] SiO x (0 < x < 2) corresponds to the matrix in the silicon-based composite particles. SiO x (0 < x < 2) can be in the form containing Si and SiO2, and Si can form a phase. That is, x corresponds to the ratio of the number of O to Si contained in SiO x (0 < x < 2). When the silicon-based composite particles contain SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0068] [[ID=,13]]The silicon-based composite particles may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to the matrix in the silicon-based composite particles.

[0069] The Mg compound and / or the Li compound may be present in SiO x (0 < x < 2) and / or on the surface of SiO x (0 < x < 2). Through the Mg compound and / or the Li compound, the initial efficiency of the battery can be improved.

[0070] The 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 or MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0071] In an exemplary embodiment of the present specification, based on the total amount of 100% by weight of the silicon-based active material, the content of the Mg element can be 0.1% to 20% by weight, or 0.1% to 10% by weight. Specifically, the content of the Mg element can be 0.5% to 8% by weight, or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound can be contained in the silicon-based active material in a suitable content, so that the volume change of the silicon-based active material during the charge and discharge processes of the battery can be easily inhibited, and the discharge capacity and the initial efficiency of the battery can be improved.

[0072] 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.

[0073] In an exemplary embodiment of the present invention, the Li compound may be contained in the form of lithium silicate. The lithium silicate is represented as Li a Si[[ID=3,5]] b O c(2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate can exist in the silicon-based composite particles in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5, and the amorphous lithium silicate can be Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5). However, the present invention is not limited thereto.

[0074] In an exemplary embodiment of the present specification, based on the total amount of 100% by weight of the silicon-based active material, the content of the Li element can be 0.1% to 20% by weight, or 0.1% to 10% by weight. Specifically, the content of the Li element can be 0.5% to 8% by weight, and more specifically 0.5% to 4% by weight. When the above range is satisfied, the Li compound can be included in the silicon-based active material in a suitable content, so that the volume change of the negative electrode active material during battery charging and discharging can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0075] The content of the Mg element or the Li element can be confirmed by ICP analysis. For ICP analysis, a predetermined amount (about 0.01 g) of the negative electrode active material is accurately aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid thereto. Then, using an inductively coupled plasma atomic emission spectrometer (ICP-AES, Perkin-Elmer 7300), by measuring the intensity of the standard solution (5 mg / kg) prepared using a standard solution at the inherent wavelength of the Mg element or the Li element, a reference calibration curve is obtained. Subsequently, the pretreated sample solution and the blank sample are introduced into the spectrometer, and by measuring the intensity of each component to calculate the actual intensity, the concentration of each component is calculated based on the obtained calibration curve, and then converted so that the sum of the calculated component concentrations is equal to the theoretical value, whereby the content of the Mg element or the Li element in the prepared silicon-based active material can be analyzed.

[0076] In an exemplary embodiment of the present specification, a carbon layer can be provided on the surface and / or within the pores of the silicon-based composite particles. The carbon layer imparts conductivity to the silicon-based composite particles, thereby improving the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery including the negative electrode active material containing the silicon-based composite particles. Based on the total amount of 100% by weight of the silicon-based composite particles, the total amount of the included carbon layer can be 5% to 40% by weight.

[0077] In an exemplary embodiment of the present specification, the carbon layer can include at least one of amorphous carbon or crystalline carbon.

[0078] In an exemplary embodiment of the present invention, the silicon-based active material may be SiO β (0<β<2) or Si-C complex.

[0079] The average particle size of the silicon active material (D 50 ) can be 2 μm to 15 μm, specifically 3 μm to 12 μm, more specifically 4 μm to 10 μm. When the above range is met, the side reaction between the silicon-based composite particles and the electrolyte solution is controlled, and the discharge capacity and initial efficiency of the battery can be effectively achieved.

[0080] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured using, for example, the laser diffraction method. In the laser diffraction method, particle sizes from submicrometers to several millimeters can generally be measured, and results with high reproducibility and high resolution can be obtained.

[0081] Furthermore, in an exemplary embodiment of the present invention, the content of the silicon-based active material is 1 to 15 parts by weight, preferably 1 to 10 parts by weight, and more preferably 5 to 10 parts by weight, relative to 100 parts by weight of the total amount of the negative electrode active material. In this case, the total amount of the negative electrode active material may refer to the silicon-based active material and the carbon-based active material; or the silicon-based active material, the carbon-based active material, and the additional active material. When the content of the silicon-based active material satisfies the above range, an improved effect is achieved in terms of energy density and cell resistance, and an excellent effect is achieved in terms of life due to the small volume expansion that occurs during the charge / discharge process.

[0082] According to the exemplary embodiment of the present specification, the negative electrode slurry may further include an additional negative electrode active material in addition to the above-mentioned silicon-based active material.

[0083] As additional negative electrode active materials, compounds capable of reversibly intercalating and deintercalating lithium can be used. Specific examples include metal materials capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiO β (0 < β < 2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; a composite comprising a metal material and a carbon material, such as a Si-C composite or a SnC composite; a carbon active material, and the like, any one of which or a mixture of two or more thereof can be used. In addition, a metallic lithium thin film can be used as the negative electrode active material.

[0084] In an exemplary embodiment of the present invention, a weight ratio of the silicon-based active material to the additional negative electrode active material contained in the negative electrode slurry may be 1:99 to 90:10, specifically 1:99 to 50:50.

[0085] There is no particular limitation on the negative electrode current collector, as long as it has conductivity and does not cause chemical changes in the battery. For example, for the current collector, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., etc. can be used. Specifically, transition metals that adsorb carbon well (such as copper and nickel) can be used for the current collector. The thickness of the current collector can be 6 μm to 20 μm. However, the thickness of the current collector is not limited thereto.

[0086] The adhesive may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, 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, polyacrylic acid, and the above materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0087] There is no particular limitation on the conductive material as long as it has conductivity without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powders; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0088] The negative electrode slurry may further include a thickener such as sodium carboxymethylcellulose (Na-CMC), lithium carboxymethylcellulose (Li-CMC), and cellulose nanofibers (CNF).

[0089] The negative electrode slurry of the exemplary 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, and may include distilled water in terms of promoting dispersion of components.

[0090] In an exemplary embodiment of the present invention, the solid content of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on 100 parts by weight of the total amount of the negative electrode slurry.

[0091] <Secondary Battery>

[0092] The secondary battery of the exemplary embodiment of the present invention may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode and the negative electrode have been described above, a detailed description is omitted.

[0093] The separator is used to separate the negative electrode and the positive electrode, and provides a migration path for lithium ions, wherein any separator can be used as the separator without particular limitation, as long as it is commonly used for secondary batteries, and in particular, it is preferably possible to use a separator having high water retention capacity for the electrolyte solution and low resistance to the migration of electrolyte ions. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a laminated structure having two or more layers thereof can be used. In addition, conventional porous non-woven fabrics can be used, for example, a non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator with a single layer or multilayer structure can be selectively used.

[0094] Examples of the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a melt-type inorganic electrolyte that can be used to manufacture a lithium secondary battery, but are not limited thereto.

[0095] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0096] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0097] Especially, in carbonate organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonate are high viscosity organic solvents, and can be preferably used because they have high dielectric constant to dissociate lithium salt well.When cyclic carbonate is mixed with linear carbonate (such as dimethyl carbonate and diethyl carbonate) with low viscosity and low dielectric constant in a suitable ratio and used, it is possible to prepare an electrolyte with high conductivity, and therefore it is possible to more preferably use.

[0098] Lithium salt can be used as the metal salt, and lithium salt is a material that is easily soluble in a non-aqueous electrolyte solution, among which, for example, a material selected from 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 kinds of the group consisting of are used as anions of the lithium salt.

[0099] In addition to the above-mentioned electrolyte components, the electrolyte may also contain one or more additives, for example, halogenated alkylene carbonate compounds (such as difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycolyl dimethyl ether, 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, so as to improve the life characteristics of the battery, inhibit the capacity reduction of the battery, improve the discharge capacity of the battery, etc.

[0100] Another exemplary embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. Because the battery module and the battery pack include secondary batteries with high capacity and excellent lifespan and cycle characteristics, the battery module and the battery pack 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.

[0101] Embodiments of the present invention

[0102] Hereinafter, preferred embodiments will be provided for a better understanding of the present invention. It will be apparent to those skilled in the art that these embodiments are provided only to illustrate the present invention and that various modifications and variations may be made within the scope and technical concept of the present invention. Such modifications and variations naturally fall within the scope of the claims appended hereto.

[0103] <Example 1>

[0104] <Preparation Example>

[0105] <Preparation of Lithium Secondary Battery>

[0106] Preparation of positive electrode

[0107] As the positive electrode active material, single-particle LiNi 0.86 Co 0.05 Mn 0.08 Al 0.01 O2(Ni: 86 mol% relative to 100 mol% of metals other than lithium, average particle size (D 50 ) (4 μm) and LFP (LiFePO4) in the form of secondary particles, with the LFP (LiFePO4) content being 3 parts by weight relative to 100 parts by weight of the total amount of the positive electrode active material in the positive electrode active material layer. The positive electrode slurry was prepared by adding the positive electrode active material, binder, and conductive material to N-methyl-2-pyrrolidone (NMP), a solvent for forming a positive electrode slurry, at a weight ratio of 97:1.8:1.2.

[0108] The binder is polyvinylidene fluoride (PVDF) and the conductive material is carbon nanotubes (CNTs).

[0109] The positive electrode slurry was heated at 3.92 mAh / cm 2 An electrode loading of 500 Å was coated on both surfaces of an aluminum current collector (thickness: 12 μm) serving as a positive electrode current collector, roll-pressed, and dried in a vacuum oven at 130° C. for 10 hours to form a positive electrode active material layer, thereby preparing a positive electrode.

[0110] Preparation of negative electrode

[0111] A negative electrode slurry was prepared by adding artificial graphite, natural graphite (the weight ratio of artificial graphite to natural graphite was 8:2, excluding the SiO ratio) and SiO (the content was 6 parts by weight relative to 100 parts by weight of the negative electrode active material) as negative electrode active materials, a binder, carboxymethyl cellulose (CMC) and a conductive material in a weight ratio of 95.573:2.3:1.127:1 to distilled water as a solvent for forming a negative electrode slurry.

[0112] The binder is styrene-butadiene rubber (SBR) and the conductive material is carbon nanotubes (CNTs).

[0113] The negative electrode slurry was charged at 4.10 mAh / cm 2 An electrode loading of 500 Å was coated on both surfaces of a copper current collector (thickness: 6 μm) serving as a negative electrode current collector, roll-pressed, and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer.

[0114] Preparation of lithium secondary batteries

[0115] A lithium secondary battery was prepared by using the above-mentioned positive electrode and negative electrode, using a multilayer polyethylene / polypropylene / polyethylene separator (thickness: 14 μm) as a separator, and injecting a non-aqueous organic solvent containing a lithium salt as an electrolyte (N / P ratio: 104.7%, weight of the finished battery cell: 502.0 g, thickness of the finished battery cell: 8.24 mm).

[0116] <Examples 1 to 6 and Comparative Examples 1 to 5>

[0117] A lithium secondary battery was prepared in the same manner as in Example 1, except that only the type and composition of the positive electrode active material or the added compound were different from those in Example 1, as shown in Table 1 below.

[0118] [Table 1]

[0119]

[0120] Using different positive active materials of Examples 1 to 6 and Comparative Examples 1 to 5, the capacity retention rate and resistance increase rate of the batteries were measured as a result of 100 cycles of room temperature life in situ, and the results are shown in Table 2 below.

[0121] [Table 2]

[0122]

[0123] From the results of Examples 1 to 6 in Table 1, it can be seen that when one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles is added to a lithium nickel-based active material containing 55 mol% or more of nickel relative to 100 mol% of metals other than lithium, the positive electrode potential drops rapidly at the end of discharge to suppress the increase in the negative electrode potential, resulting in a decrease in the resistance increase rate of the negative electrode and an excellent capacity retention rate. As shown in Table 1 above, Comparative Example 1 corresponds to a lithium nickel-based active material containing only LiNi 0.86 Co 0.05 Mn 0.08 Al 0.01 O2(Ni: 86 mol% relative to 100 mol% of metals other than lithium, average particle size (D 50 ) (4μm) as the positive electrode active material. In this case, compared to a positive electrode containing LFP (LiFePO4) in the form of secondary particles, the negative electrode resistance increase rate increased by approximately 25%, the negative electrode's usage depth increased, and capacity retention evaluation confirmed a decrease of approximately 10% after 100 cycles.

[0124] Comparative Examples 2 and 3 correspond to the case where the positive electrode active material contains LFP (LiFePO4) in the form of secondary particles, but the weight ratio exceeds 10 parts by weight relative to 100 parts by weight of the positive electrode active material. In this case, it can be confirmed that the resistance increase rate and capacity retention rate are inferior to those of Examples 1 to 6, and the battery capacity is inferior to that of the battery containing less than 10 parts by weight of the positive electrode active material.

[0125] Comparative Example 4 uses a secondary particle-based lithium nickel active material. While the capacity is similar to that of Examples 1 to 6, the resistance increase is approximately 5% higher than that of Examples 1 to 6, resulting in a poorer capacity retention.

[0126] Comparative Example 5 corresponds to the case of using a compound containing less than 55 mol% nickel in the lithium nickel-based active material. In this case, it can be confirmed that the results are similar to those of Examples 1 to 6 in terms of resistance increase rate and capacity retention rate, but the capacity is significantly lower.

Claims

1. A secondary battery comprising: positive electrode; negative electrode; diaphragm; and electrolytes, Wherein, the negative electrode comprises silicon-based active materials and carbon-based active materials, in, The positive electrode comprises: Lithium nickel-based active materials in single particle form, and One or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles, wherein the content of one or more of LCO (LiCoO2), LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles is 0.1 to 10 parts by weight relative to 100 parts by weight of the positive electrode active material, and The lithium nickel-based active material in the form of a single particle contains 55 mol % or more of nickel relative to 100 mol % of metals other than lithium.

2. The secondary battery according to claim 1, wherein The positive electrode has a porosity of 19% to 23%.

3. The secondary battery according to claim 1, wherein The silicon-based active material may be present in an amount of 1 to 15 parts by weight relative to 100 parts by weight of the negative electrode active material.

4. The secondary battery according to claim 1, wherein The average particle size D of the lithium nickel-based active material in the form of a single particle 50 3μm to 10μm.

5. The secondary battery according to claim 1, wherein The positive electrode comprises: Lithium nickel-based active materials in single particle form, and One or more of LMO (LiMn2O4) and LFP (LiFePO4) in the form of secondary particles.

6. The secondary battery according to claim 1, wherein The content of one or more of LCO (LiCoO 2 ), LMO (LiMn 2 O 4 ) and LFP (LiFePO 4 ) in the form of secondary particles is 0.1 to 3 parts by weight relative to 100 parts by weight of the positive electrode active material.

7. The secondary battery according to claim 1, wherein The lithium nickel-based active material in the form of a single particle contains 55 mol % or more and less than 80 mol % of nickel relative to 100 mol % of metals other than lithium.

8. The secondary battery according to claim 1, wherein The lithium nickel-based active material in the form of a single particle contains 80 mol % or more of nickel relative to 100 mol % of metals other than lithium.

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