Secondary batteries

Abstract

We provide rechargeable batteries. [Solution] The secondary battery comprises a positive electrode, a negative electrode, a separator membrane, and an electrolyte. The negative electrode comprises a silicon-based active material and a carbon-based active material. The positive electrode comprises a single-particulate lithium nickel-based active material and at least one of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4). The single-particulate lithium nickel-based active material contains 55 mol% or more nickel out of 100 mol% of the metal excluding lithium.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0132117 filed with the Korean Intellectual Property Office on October 14, 2022, and Korean Patent Application No. 10-2023-0127952 filed with the Korean Intellectual Property Office on September 25, 2023, and all of its contents are included herein.

[0002] The present invention relates to a secondary battery.

Background Art

[0003] Secondary batteries with high adaptability according to product groups and having electrical characteristics such as high energy density are widely applied not only to portable devices but also to electric vehicles (EVs), hybrid electric vehicles (HEVs), etc., which are driven by an electric drive source.

[0004] Such secondary batteries have not only the primary advantage of being able to significantly reduce the use of fossil fuels but also the advantage of generating no by-products due to energy use, and thus are attracting attention as an environmentally friendly and new energy source for improving energy efficiency.

[0005] Generally, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Also, on the current collector, an active material layer containing a positive electrode active material and a negative electrode active material may be formed on the positive electrode and the negative electrode, respectively. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material for the positive electrode, and carbon-based compounds, silicon-based compounds, mixtures thereof, etc. are used as the negative electrode active material for the negative electrode.

[0006] In recent years, in order to develop a battery capable of rapid charging, a carbon-based compound such as graphite and a silicon-based compound are mixed and used in the negative electrode. However, when a silicon-based compound is included, at the end of discharge, the negative electrode resistance rapidly increases, the difference between the negative electrode resistance and the positive electrode resistance becomes large, the battery life becomes short, and the room temperature cycle characteristics deteriorate. Therefore, there is a need to develop a battery to solve such problems.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention aims to provide a secondary battery that includes a silicon-based compound in the negative electrode active material layer, reduces the difference between the negative electrode resistance and the positive electrode resistance at the end of discharge, and improves the battery life and room temperature cycle characteristics.

[0009] However, the technical problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the description of the invention described below.

Means for Solving the Problems

[0010] One embodiment of the present invention is a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode includes a silicon-based active material and a carbon-based active material, the positive electrode includes a single-particle lithium nickel-based active material; and at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4), and the single-particle lithium nickel-based active material contains 55 mol% or more of nickel with respect to 100 mol% of the metal excluding lithium.

Effects of the Invention

[0011] The secondary battery of the present invention, by including a single-particulate lithium nickel-based active material and at least one of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the positive electrode active material layer, can reduce the rapid decrease in positive electrode resistance at the end of discharge. This reduces the difference between positive electrode resistance and negative electrode resistance, resulting in a secondary battery with improved lifespan and room-temperature cycle characteristics.

[0012] Specifically, when a single-particle lithium-nickel active material with a high nickel content is used in the positive electrode active material layer to increase the energy density of the battery while reducing active material cracking, and a silicon-based active material is included in the negative electrode active material layer to enable rapid charging, the negative electrode resistance rises sharply at the end of discharge, and the difference between the positive and negative electrode resistances becomes large. This 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), resulting in a decrease in the battery's lifespan. To improve this, by including a single-particle lithium-nickel active material and at least one of the secondary particulate materials LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in the positive electrode active material layer, it is possible to obtain a secondary battery that enables rapid charging, improves the resistance of the positive electrode, reduces the resistance difference between the positive and negative electrodes and the depth of use of the silicon-based active material, and improves the lifespan at room temperature. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below. The following information is intended to aid in understanding the present invention and does not define or limit the scope of the invention's rights in any way.

[0014] In this specification, when a part "includes" a component, this does not exclude other components, unless otherwise stated, but rather means that it may further include other components.

[0015] In this specification, when one member is described as being "on top of" another member, this includes not only cases where one member is in contact with another member, but also cases where another member exists between the two members.

[0016] The terms or words used herein are not to be interpreted in their ordinary or dictionary sense, but rather in a sense and concept consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0017] As used herein, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0018] In this specification, the crystallinity of the structure contained within the active material of the positive or negative electrode can be confirmed by X-ray diffraction analysis. X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker), and other instruments used in this industry may be used as appropriate.

[0019] In this specification, the presence and content of elements in the active material of the positive or negative electrode can be confirmed by ICP (inductively coupled plasma) analysis, which can be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0020] In this specification, the term "end of discharge" refers to the region where the State of Charge (SOC) of a full cell is 10% or less.

[0021] In this specification, "average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. 50The average particle size (D) of the positive electrode active material can be measured using the laser diffraction method. For example, the average particle size (D) of the positive electrode active material can be measured using the laser diffraction method. 50 The measurement method involves dispersing the positive electrode active material particles in a dispersion medium, then introducing them into a commercially available laser diffraction particle size analyzer (e.g., HORIBA LA-960), irradiating them with ultrasound at approximately 28 kHz with an output of 60 W, and then measuring the average particle size (D) corresponding to 50% of the cumulative volume in the measuring device. 50 It is possible to calculate ).

[0022] In this specification, "single particle" is a concept contrasted with secondary particles formed by the aggregation of tens to hundreds of primary particles, and means a particle consisting of 10 or fewer primary particles. Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle, or it may be a particle in the form of an aggregate of multiple primary particles.

[0023] In this specification, "primary particle" refers to the smallest unit of particle recognized when an active material is observed through a scanning electron microscope, and "secondary particle" refers to a secondary structure formed by the aggregation of tens to hundreds of primary particles.

[0024] In this specification, "particle" refers to a particle measured in micrometers, which, when observed under magnification, can be divided into "grains" having a crystalline structure on the order of tens of nanometers. Further magnification reveals separated regions in which atoms form a lattice structure in a specific direction; these are called "crystal grains." The size of particles observed by XRD is defined as the crystal grain size. The crystal grain size can be quantitatively determined using XRD data through Scherrer's equation.

[0025] The secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator membrane, and an electrolyte. The negative electrode comprises a silicon-based active material and a carbon-based active material. The positive electrode comprises a single-particulate lithium nickel-based active material and at least one of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4). The single-particulate lithium nickel-based active material contains 55 mol% or more nickel per 100 mol% of the metal excluding lithium.

[0026] In this specification, when the negative electrode active material layer contains a silicon-based active material, the negative electrode resistance increases sharply at the end of discharge, and the positive electrode resistance, which uses a positive electrode material with low resistance characteristics, decreases sharply, resulting in a very large difference between the negative electrode resistance and the positive electrode resistance. This leads to problems such as rapid deterioration of the negative electrode, a shortened battery life, and reduced room-temperature cycle characteristics. To solve this, the positive electrode active material layer can be made to contain at least one of the secondary particulate materials LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) along with single-particulate lithium nickel-based active material, thereby reducing the sharp decrease in positive electrode resistance and obtaining a battery with improved lifespan and room-temperature cycle characteristics.

[0027] <Positive electrode> The positive electrode of the present invention includes a positive electrode active material layer, the positive electrode active material layer comprising single-particulate lithium nickel-based active material and at least one of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4). In this case, the single-particulate lithium nickel-based active material contains 55 mol% or more of nickel per 100 mol% of the metal excluding lithium, specifically 55 mol% or more and less than 80 mol%, or 80 mol% or more. The present invention, by including at least one of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4), has the effect of reducing the discharge end voltage of the positive electrode when mixed with the lithium nickel-based active material.

[0028] According to one embodiment of the present invention, the positive electrode includes a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material containing single-particulate lithium nickel-based active material; and at least one of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4).

[0029] According to one embodiment of the present invention, the positive electrode active material layer comprises single-particulate lithium nickel-based active material and secondary-particulate LCO (LiCoO2).

[0030] According to one embodiment of the present invention, the positive electrode active material layer comprises single-particulate lithium nickel-based active material and secondary-particulate LMO (LiMn2O4).

[0031] According to one embodiment of the present invention, the positive electrode active material layer comprises single-particulate lithium nickel-based active material and secondary-particulate LFP (LiFePO4).

[0032] According to one embodiment of the present invention, the positive electrode active material layer comprises a single-particulate lithium nickel-based active material and at least one of secondary-particulate LMO (LiMn2O4) and LFP (LiFePO4).

[0033] In one embodiment of the present invention, at least one of the secondary particle-like LCO (LiCoO₂), LMO (LiMn₂O₄), and LFP (LiFePO₄) is contained in an amount of 0.1 part by weight to 10 parts by weight, specifically 0.1 part by weight to 5 parts by weight, or 0.1 part by weight to 3 parts by weight, based on 100 parts by weight of the total cathode active material in the cathode active material layer. At this time, the total cathode active material can mean the single-particle lithium nickel-based active material; or the single-particle lithium nickel-based active material and an additional active material. When the content of at least one of LCO (LiCoO₂), LMO (LiMn₂O₄), and LFP (LiFePO₄) contained in the cathode active material layer satisfies the above range, it exhibits the effect of suppressing the increase in the anode potential due to the decrease in the end-of-discharge voltage of the cathode and suppressing the deterioration of the anode. Also, since the charge / discharge capacity (mAh) per gram of LCO (LiCoO₂), LMO (LiMn₂O₄), and LFP (LiFePO₄) is lower than the charge / discharge capacity (mAh) per gram of the lithium nickel-based active material, when the content of at least one of LCO (LiCoO₂), LMO (LiMn₂O₄), and LFP (LiFePO₄) exceeds the above range, the battery capacity can be reduced.

[0034] According to one embodiment of the present invention, the average particle diameter (D 50 ) of the single-particle lithium nickel-based active material is 3 μm to 10 μm.

[0035] The lithium nickel-based active material of the present invention may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, or aluminum, nickel, and lithium. More specifically, a lithium-nickel-manganese-cobalt-based oxide (for example, 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 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 the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 ≤ r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and the like, and any one or two or more of these compounds may be included, but are not limited thereto.

[0036] In addition to the above-described positive electrode active material layer, the positive electrode may further include a positive electrode current collector. At this time, the positive electrode active material layer is formed on at least one surface of the positive electrode current collector.

[0037] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0038] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0039] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, 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. One of these alone or a mixture of two or more may be used.

[0040] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-coHFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0041] The positive electrode active material layer may be formed by coating at least one surface of a positive electrode current collector with a positive electrode slurry containing single-particulate lithium nickel-based active material and at least one of secondary-particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) together with a binder and / or conductive material, then drying and rolling the slurry.

[0042] A positive electrode slurry according to one embodiment of the present invention may further contain a solvent for forming the positive electrode slurry. Specifically, the solvent for forming the positive electrode slurry may contain methylpyrrolidone (NMP) or the like, in order to facilitate the dispersion of components.

[0043] In one embodiment of the present invention, the solid content weight of the positive electrode slurry may be 20 to 85 parts by weight, specifically 30 to 80 parts by weight, based on a total of 100 parts by weight of the positive electrode slurry.

[0044] According to one embodiment of the present invention, the porosity of the positive electrode is 19% to 23%.

[0045] The aforementioned porosity can be calculated as (1 - (rolling density / electrode true density)) × 100 (%).

[0046] The aforementioned rolling density can be calculated as follows.

[0047] Rolling density: Electrode weight (g) after electrode rolling, excluding the foil / Electrode volume (area of ​​sample × electrode layer thickness, cm²) 3 )

[0048] The electrode volume excluding the foil refers to the total volume including the pores inside the electrode, and is calculated as the product of the unit area of ​​the sample and the thickness of the electrode layer after roll pressing.

[0049] The electrode true density is the intrinsic density of the electrode active material, meaning the density of only the material-filled portion, excluding the gaps between particles. The electrode true density is calculated by measuring the volume (solid + isolated pores) excluding open pores, and is measured using methods applying Archimedes' principle or a gas pycnometer.

[0050] <Negative electrode> A negative electrode according to one embodiment of the present invention includes a negative electrode active material layer, the negative electrode active material layer includes a silicon-based active material and a carbon-based active material.

[0051] According to one 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.

[0052] In addition to the negative electrode active material layer described above, the negative electrode may further include a negative electrode current collector. At this time, 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 the silicon-based active material and the carbon-based active material. Further, the negative electrode active material layer may further include a binder and / or a conductive material.

[0053] According to one embodiment of the present invention, the carbon-based active material can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite and artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like. The graphite may be natural graphite, artificial graphite, or a mixture thereof. The carbon-based active material may be contained in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer.

[0054] According to one embodiment, the negative electrode includes a silicon-based active material.

[0055] As the silicon-based active material, an active material containing SiO x (0 < x < 2) may be a silicon-based composite particle containing SiO x (0 < x < 2) and pores. ((ID=25]]

[0056] The SiO x (0 < x < 2) corresponds to a matrix in the silicon-based composite particle. The SiO x(0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, x corresponds to the number ratio of O to Si contained within x (0 < x < 2). When the silicon-based composite particles contain x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0057] 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 can correspond to a matrix within the silicon-based composite particles.

[0058] The Mg compound and / or the Li compound may be present inside and / or on the surface of x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0059] The Mg compound may contain at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may contain at least one of Mg2SiO4 and MgSiO3. The Mg silicide may contain Mg2Si. The Mg oxide may contain MgO.

[0060] In one embodiment of the present specification, the Mg element may be contained at 0.1 wt% to 20 wt%, or may be contained at 0.1 wt% to 10 wt%, based on 100 wt% of the total of the silicon-based active material. Specifically, the Mg element may be contained at 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be contained in an appropriate content within the silicon-based active material, so that the volume change of the silicon-based active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and the initial efficiency of the battery can be improved.

[0061] 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 any one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0062] In one embodiment of the present invention, the Li compound may include a form of lithium silicate. 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 can exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based composite particles, and the amorphous lithium silicate can be in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to this form.

[0063] In one embodiment of the present specification, the Li element may be contained at 0.1% to 20% by weight, or may be contained at 0.1% to 10% by weight based on 100% by weight of the total silicon-based active material. Specifically, the Li element may be contained at 0.5% to 8% by weight, and more specifically, may be contained at 0.5% to 4% by weight. When the above range is satisfied, the Li compound can be contained in an appropriate content in the silicon-based active material, the change in the volume of the negative electrode active material can be easily suppressed during charging and discharging of the battery, and the discharge capacity and initial efficiency of the battery can be improved.

[0064] The content of the aforementioned Mg or Li element can be confirmed by ICP analysis. For the ICP analysis, a fixed amount (approximately 0.01 g) of the negative electrode active material is accurately separated, transferred to a platinum crucible, and completely decomposed on a hot plate with nitric acid, hydrofluoric acid, and sulfuric acid. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution prepared using a standard solution (5 mg / kg) at the characteristic wavelength of the Mg or Li element is measured to obtain a reference calibration curve. Subsequently, the pre-treated sample solution and the base sample are introduced into the instrument, their respective intensities are measured to calculate the actual intensities, and after calculating the concentration of each component compared to the calibration curve created above, the Mg or Li element content of the manufactured silicon-based active material can be analyzed by converting the total sum to a theoretical value.

[0065] In one embodiment of this specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon-based composite particles. The carbon layer imparts conductivity to the silicon-based composite particles, thereby improving the initial efficiency, lifespan, and battery capacity characteristics of a secondary battery containing a negative electrode active material that includes the silicon-based composite particles. The total weight of the carbon layer may be 5% to 40% by weight, based on 100% by weight of the total silicon-based composite particles.

[0066] In one embodiment of this specification, the carbon layer may contain at least one of amorphous carbon and crystalline carbon.

[0067] In one embodiment of the present invention, the silicon-based active material is SiO β (0 < β < 2) or a Si-C composite may also be used.

[0068] The average particle size (D) of the silicon-based active material 50 The particle size is 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 4 μm to 10 μm. When the above range is met, the side reactions between the silicon-based composite particles and the electrolyte are controlled, and the discharge capacity and initial efficiency of the battery can be effectively realized.

[0069] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 The particle size can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can obtain highly reproducible and high-resolution results.

[0070] Furthermore, according to one embodiment of the present invention, the silicon-based active material is included in an amount of 1 to 15 parts by weight, preferably 1 to 10 parts by weight, and more preferably 5 to 10 parts by weight, per 100 parts by weight of the total negative electrode active material. In this case, the total negative electrode active material can mean the silicon-based active material and the carbon-based active material; or the silicon-based active material, the carbon-based active material and additional active material. When the content of the silicon-based active material satisfies the above range, it has an improved effect in terms of energy density and cell resistance, while also having an excellent effect in terms of lifespan, with less volume expansion occurring during charging / discharging.

[0071] According to one embodiment of this specification, the negative electrode slurry may further contain additional negative electrode active materials in addition to the silicon-based active material described above.

[0072] As the additional negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO2 β (0<β<2), SnO 2、Examples include lithium-doped and dedoped metal oxides such as vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; composites containing the metallic compound and carbonaceous material, such as Si-C composites or SnC composites; and carbon-based active materials. One or more mixtures of these may be used. Furthermore, a metallic lithium thin film may be used as the negative electrode active material.

[0073] In one embodiment of the present invention, the weight ratio of the silicon-based active material contained in the negative electrode slurry to the additional negative electrode active material is 1:99 to 90:10, and more specifically, it may be 1:99 to 50:50.

[0074] The negative electrode current collector is not particularly limited, as long as it is conductive and does not induce any chemical changes in the battery. For example, the current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that effectively adsorb carbon, such as copper and nickel, can be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0075] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0076] The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. Examples of such materials include 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 powder; metal powders such as 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.

[0077] The negative electrode slurry may further contain thickeners such as Na-CMC (Sodium carboxymethyl cellulose), Li-CMC (Carboxymethyl cellulose lithium), and CNF (Cellulose nanofiber).

[0078] A negative electrode slurry according to one embodiment of the present invention may further contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in terms of facilitating the dispersion of components.

[0079] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on a total of 100 parts by weight of the negative electrode slurry.

[0080] <Secondary battery> A secondary battery according to one embodiment of the present invention may include a positive electrode, a negative electrode, a separation membrane interposed 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 explanation will be omitted.

[0081] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. It can be used without particular limitations as long as it is the type typically used as a separation membrane in secondary batteries. Particularly preferred is a membrane that exhibits low resistance to electrolyte ion movement while maintaining excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0082] Examples of the aforementioned electrolytes 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 the manufacture of lithium secondary batteries.

[0083] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0084] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-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, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0085] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be created, and this mixture is even more preferable.

[0086] The metal salt can be a lithium salt, and the lithium salt is a substance that dissolves easily in the non-aqueous electrolyte. For example, the anion of the lithium salt is F - Cl - , I - NO3 -, N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - One or more types selected from the group consisting of the following can be used.

[0087] In addition to the electrolyte components, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0088] According to yet another embodiment of the present invention, a battery module and a battery pack including the secondary battery as a unit cell are provided. Since the battery module and battery pack include the secondary battery having high capacity, high lifespan characteristics and cycle characteristics, they 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.

[0089] Preferred embodiments are presented below to aid in understanding the present invention, but these embodiments are illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept. Such variations and modifications naturally fall within the scope of the appended claims.

[0090] <Example 1> <Manufacturing example> <Manufacturing of lithium-ion secondary batteries> Manufacturing of positive electrodes Single-particle LiNi 0.86 Co 0.05 Mn 0.08 Al 0.01 O 2、 (Ni: Contains 86 mol% of metal excluding lithium, average particle size (D 50 The cathode active material layer was made using 4 μm (LFP) and secondary particulate LFP (LiFePO4), with LFP (LiFePO4) present at a ratio of 3 parts by weight per 100 parts by weight of the total cathode active material. The cathode active material, binder, and conductive material were added to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation in a weight ratio of 97:1.8:1.2 to produce the cathode slurry.

[0091] The binder is polyvinylidene fluoride (PVDF), and the conductive material is carbon nanotube (CNT).

[0092] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is used, with the positive electrode slurry applied to both sides at a rate of 3.92 mAh / cm². 2The electrode was coated with the specified electrode loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer, thereby manufacturing the positive electrode.

[0093] Manufacturing of negative electrodes A negative electrode slurry was prepared by adding artificial graphite, natural graphite (with a weight ratio of artificial graphite to natural graphite of 8:2, excluding the SiO ratio), SiO (6 parts by weight per 100 parts by weight of negative electrode active material), binder, carboxymethylcellulose (CMC), and conductive material to distilled water as a solvent for forming the negative electrode slurry in a weight ratio of 95.573:2.3:1.127:1.

[0094] The binder is styrene-butadiene rubber (SBR), and the conductive material is carbon nanotube (CNT).

[0095] As the negative electrode current collector, the negative electrode slurry is applied to both sides of a copper current collector (thickness: 6 μm) at a rate of 4.10 mAh / cm². 2 The electrode was coated with the specified load, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form the negative electrode active material layer.

[0096] Manufacturing of lithium-ion batteries A lithium secondary battery was manufactured using the aforementioned positive and negative electrodes, a multilayer polyethylene / polypropylene / polyethylene separation membrane (thickness: 14 μm) as the separation membrane, and a non-aqueous organic solvent containing a lithium salt as the electrolyte. (N / P ratio: 104.7%, weight of finished cell: 502.0 g, thickness of finished cell: 8.24 mm)

[0097] <Examples 1-6 and Comparative Examples 1-5> A lithium secondary battery was manufactured in the same manner as in Example 1, except that only the type and composition of the positive electrode active material or the compound added were changed as shown in Table 1 below.

[0098] [Table 1]

[0099] By changing the positive electrode active material according to Examples 1-6 and Comparative Examples 1-5, the capacity retention rate and the resistance increase rate of the battery were measured in situ at room temperature after 100 cycles, and the results are shown in Table 2 below.

[0100] [Table 2]

[0101] As can be seen from the results of Examples 1 to 6 in Table 1, when one or more of secondary particulate LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) are added to a lithium nickel-based active material containing 55 mol% or more nickel per 100 mol% of metal excluding lithium, it was confirmed that the positive electrode discharge end potential is rapidly reduced, the rise in negative electrode potential is suppressed, and thereby the rate of increase in negative electrode resistance is reduced, resulting in excellent capacity retention. Comparative Example 1, as can be seen from Table 1, uses LiNi as the positive electrode active material. 0.86 Co 0.05 Mn 0.08 Al 0.01 O2(Ni: Contains 86 mol% of metals excluding lithium, average particle size (D 50 This corresponds to a positive electrode containing only (4μm) particles. In this case, the resistance increase rate of the negative electrode was about 25% greater than that of a positive electrode with secondary particulate LFP (LiFePO4) added, and capacity retention rate evaluation confirmed that the depth of use of the negative electrode increased, resulting in a decrease of about 10% in capacity retention rate after 100 cycles.

[0102] Comparative Examples 2 and 3 contain secondary particulate LFP (LiFePO4) in the positive electrode active material, but the weight ratio exceeds 10 parts by weight per 100 parts by weight of 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 batteries containing less than 10 parts by weight.

[0103] Comparative Example 4 represents the case where the lithium nickel-based active material is changed to secondary particulate form. In this case, similar results to Examples 1-6 are observed in terms of capacity, but the resistance increase rate is about 5% greater than that of Examples 1-6, so it can be confirmed that it shows an inferior effect in terms of capacity retention rate.

[0104] Comparative Example 5 is a lithium nickel-based active material in which a compound with less than 55 mol% nickel by weight is used. In this case, the results are similar to those of Examples 1 to 6 in terms of resistance increase rate and capacity retention rate, but it can be confirmed that the capacity is definitely lower.

Claims

1. Single-particulate lithium nickel-based active material, and LCO (LiCoO) ２ ) and LMO (LiMn ２ O ４ ) and LFP (LiFePO ４ ) including at least one of the following, The aforementioned LCO(LiCoO) ２ ) and LMO (LiMn ２ O ４ ) and LFP (LiFePO ４ A positive electrode active material comprising at least one of the above in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the positive electrode active material.

2. The above-mentioned LCO (LiCoO ２ ), LMO (LiMn ２ O ４ ), and LFP (LiFePO ４ ), at least one of which is contained in an amount of 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of the positive electrode active material, is the positive electrode active material according to claim 1.

3. The average particle size (D) of the single-part lithium nickel-based active material ５０ The positive electrode active material according to claim 1, wherein the diameter is 3 μm to 10 μm.

4. The positive electrode active material is a single-particulate lithium nickel-based active material and LCO(LiCoO ２ ) and LMO (LiMn ２ O ４ The positive electrode active material according to claim 1, comprising at least one of the following:

5. The positive electrode active material is the LCO(LiCoO ２ ) and LMO (LiMn ２ O ４ ) and LFP (LiFePO ４ The positive electrode active material according to claim 1, comprising at least one of the above in an amount of 0.1 to 3 parts by weight per 100 parts by weight of the positive electrode active material.

6. The positive electrode active material according to claim 1, wherein the single-particulate lithium nickel-based active material contains 55 mol% or more nickel with respect to 100 mol% of the metal excluding lithium.

7. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 6.

8. The positive electrode according to claim 7, wherein the porosity of the positive electrode is 19% to 23%.

9. A secondary battery comprising the positive electrode described in claim 7.

10. The aforementioned secondary battery includes a negative electrode, The secondary battery according to claim 9, wherein the negative electrode contains a silicon-based active material.

11. A battery module including the secondary battery described in claim 9.

12. A battery pack including the secondary battery described in claim 9.

13. A battery pack comprising the battery module described in claim 11.

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