Secondary battery

Abstract

To provide a secondary battery.SOLUTION: A secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, in which the negative electrode includes a silicon-based active material and a carbon-based active material, and the positive electrode includes a single-particle lithium-nickel-based active material, and at least one of secondary particles of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4), in which the single-particle lithium-nickel-based active material includes 55 mol% or more of nickel in 100 mol% of metals excluding lithium.SELECTED DRAWING: None

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, the entire contents of which are incorporated herein by reference.

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

[0003] Secondary batteries, which are highly adaptable to various product groups and have electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are powered by electrical sources.

[0004] Such secondary batteries have the primary advantage of dramatically reducing the use of fossil fuels, as well as the advantage of not producing any by-products from energy use, making them environmentally friendly and drawing attention as a 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. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, while the negative electrode uses a carbon-based compound, a silicon-based compound, or a mixture thereof as the negative electrode active material.

[0006] In recent years, in order to develop batteries capable of rapid charging, a mixture of carbon-based compounds such as graphite and silicon-based compounds has been used in the negative electrode. However, when a silicon-based compound is included, the negative electrode resistance rises sharply at the end of discharge, increasing the difference between the negative electrode resistance and the positive electrode resistance, resulting in problems such as a shortened battery life and a deterioration in room temperature cycle characteristics. Therefore, there is a need to develop a battery that solves these problems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2012-0037409 Summary of the Invention [Problem to be solved by the invention]

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

[0009] However, the technical problems that the present invention aims to solve 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 problem]

[0010] One embodiment of the present invention provides 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, and the positive electrode includes a single-particulate lithium-nickel-based active material; and at least one of LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO) in secondary particulate form, and the single-particulate lithium-nickel-based active material includes 55 mol % or more of nickel relative to 100 mol % of metals excluding lithium. [Effects of the Invention]

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

[0012] Specifically, if a single-particle lithium-nickel-based active material with a high nickel content is used in the positive electrode active material layer to increase the battery's energy density while reducing cracking of the active material, and a silicon-based active material is included in the negative electrode active material layer to enable rapid charging, the negative electrode resistance increases sharply at the end of discharge, increasing the difference between the positive and negative electrode resistances. This results in excessive use of the silicon-based active material in the negative electrode active material layer (increased depth of use), resulting in reduced battery life. To address this issue, the positive electrode active material layer contains a single-particle lithium-nickel-based active material and at least one of secondary particles of LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO). This allows for rapid charging, improves positive electrode resistance, reduces the difference in resistance between the positive and negative electrodes, and reduces the depth of use of the silicon-based active material, resulting in a secondary battery with improved room-temperature life. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. The following description is provided to aid in understanding the present invention, and is not intended to limit or define the scope of the invention.

[0014] In this specification, when a part is said to "comprise" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0015] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when there is another member between the two members.

[0016] The terms or words used in this specification should not be construed as being limited to their ordinary or dictionary meanings, but should be construed in a meaning and concept that is consistent with the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

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

[0018] In this specification, the crystallinity of the structure contained in the positive or negative electrode active material can be confirmed by X-ray diffraction analysis. X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analysis device (product name: D4-Endavor, manufacturer: Bruker), and in addition to the above device, any device used in the art can be appropriately adopted.

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

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

[0021] In this specification, the term "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) can be measured using a laser diffraction method. For example, the average particle size (D 50 The method for measuring the average particle size (D) is to disperse particles of the positive electrode active material in a dispersion medium, then introduce them into a commercially available laser diffraction particle size measuring device (e.g., HORIBA LA-960), irradiate them with ultrasonic waves of about 28 kHz at an output of 60 W, and measure the average particle size (D) corresponding to 50% of the cumulative volume in the measuring device. 50 ) can be calculated.

[0022] In this specification, the term "single particle" is a concept that contrasts with secondary particles formed by aggregation of tens to hundreds of primary particles, and refers to a particle consisting of 10 or less primary particles. Specifically, in the present invention, the single particle may be a single particle consisting of one primary particle, or may be in the form of a particle formed by aggregation of multiple primary particles.

[0023] In this specification, the term "primary particle" refers to the smallest particle unit that can be recognized when observing an active material through a scanning electron microscope, and the term "secondary particle" refers to a secondary structure formed by aggregation of several tens to several 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" with crystalline forms measured in units of several tens of nanometers. Further magnification reveals separate regions in which atoms form a lattice structure in a specific direction, which are called "crystal grains." The size of particles observed by XRD is defined as the crystal grain size. Crystal grain size can be quantitatively determined using the Scherrer equation based on XRD data.

[0025] 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, and the positive electrode comprises a single-particulate lithium-nickel-based active material; and at least one of LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) in secondary particulate form, and the single-particulate lithium-nickel-based active material contains 55 mol % or more of nickel per 100 mol % of metals excluding lithium.

[0026] In this specification, when the negative electrode active material layer contains a silicon-based active material, the negative electrode resistance rises sharply at the end of discharge, while the positive electrode resistance drops sharply when a low-resistance positive electrode material is used, resulting in a large difference between the negative electrode resistance and the positive electrode resistance. This leads to rapid deterioration of the negative electrode, shortening the battery's lifespan and reducing room-temperature cycle performance. To address this issue, the positive electrode active material layer contains at least one of secondary particles of LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO) along with a single-particle lithium-nickel active material, thereby reducing the rapid decrease in positive electrode resistance and improving the lifespan and room-temperature cycle performance of the battery.

[0027] <Positive electrode> The positive electrode of the present invention includes a positive electrode active material layer, which includes a single-particle lithium-nickel-based active material; and at least one of LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO). The single-particle lithium-nickel-based active material contains 55 mol% or more of nickel, specifically 55 mol% or more but less than 80 mol%, or 80 mol% or more, relative to 100 mol% of metals excluding lithium. The present invention includes at least one of LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO), in the form of secondary particles, which, when mixed with the lithium-nickel-based active material, reduces the end-of-discharge voltage of the positive electrode.

[0028] According to one 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 including a single-particle lithium-nickel-based active material; and at least one of secondary-particle LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO).

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

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

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

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

[0033] In one embodiment of the present invention, the secondary particle-form at least one of LCO (LiCoO), LMO (LiMnO), and LFP (LiFePO) is included in an amount of 0.1 to 10 parts by weight, specifically 0.1 to 5 parts by weight, or 0.1 to 3 parts by weight, based on 100 parts by weight of the total positive electrode active material in the positive electrode active material layer. In this case, the total positive electrode active material may refer to 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 (LiCoO), LMO (LiMnO), and LFP (LiFePO) in the positive electrode active material layer satisfies the above range, an increase in negative electrode potential due to a decrease in the end-of-discharge voltage of the positive electrode is suppressed, thereby suppressing negative electrode degradation. In addition, since the charge / discharge capacity (mAh) per gram of the LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) is lower than the charge / discharge capacity (mAh) per gram of the lithium nickel-based active material, if the content of at least one of the LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) exceeds the above range, the battery capacity may be reduced.

[0034] According to one embodiment of the present invention, the average particle size (D 50 ) is 3μm to 10μm.

[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 (e.g., Li(Ni p Co q Mn r1 )O2(where, 0 <p<1、0<q<1、0<r1<1)、p+q+r1=1)または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 one or more of these compounds may be included, but 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. In this case, 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 a material 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 a film, sheet, foil, net, porous body, foam, non-woven fabric body, 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 any particular limitation as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and the like, and these may be used alone or in combination of two or more.

[0040] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0041] The positive electrode active material layer may be formed by applying a positive electrode slurry containing a single-particle lithium nickel-based active material and at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4), as well as a binder and / or a conductive material, to at least one surface of a positive electrode current collector, followed by drying and rolling.

[0042] The cathode slurry according to an embodiment of the present invention may further include a solvent for forming the cathode slurry. Specifically, the solvent for forming the cathode slurry may include methylpyrrolidone (NMP) to facilitate dispersion of components.

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

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

[0045] The porosity can be calculated by (1-(rolled density / true electrode density)) x 100 (%).

[0046] The rolling density can be calculated as follows:

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

[0048] The electrode volume excluding the foil means 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 true density of an electrode is the inherent density of an electrode active material, and refers to the density of only the portion filled with the material, excluding the gaps between particles. The true density of an electrode is calculated by measuring the volume (solid + isolated pores) excluding open pores, and is measured using a method applying Archimedes' principle or a gas pycnometer.

[0050] <Negative electrode> An anode according to one embodiment of the present invention includes an anode active material layer, the anode active material layer including 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] The negative electrode may further include a negative electrode current collector in addition to the negative electrode active material layer described above. 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, and typical 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, and 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 with respect to 100 parts by weight of the entire 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] The silicon-based active material such as SiO x (0 < x < 2) may be a silicon-based composite particle containing SiO x (0 < x < 2) and pores.

[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 (0 < x < 2). When the silicon-based composite particles contain (0 < x < 2), the discharge capacity of the secondary battery can be improved. x (0 < x < 2) corresponds to the number ratio of O to Si contained within. 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 (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound. 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 this 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 at 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 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 included at 0.1 wt% to 20 wt%, or may be included at 0.1 wt% to 10 wt% based on 100 wt% of the total silicon-based active material. Specifically, the Li element may be included at 0.5 wt% to 8 wt%, and more specifically, may be included at 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound can be included in an appropriate content within 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 Mg or Li element content 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 and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectroscopy (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at the wavelength specific to Mg or Li element to obtain a reference calibration curve. The pretreated sample solution and the base sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated relative to the calibration curve, and the total is converted to a theoretical value to analyze the Mg or Li element content of the silicon-based active material.

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

[0066] In one embodiment of the present specification, the carbon layer may include 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.

[0068] The average particle size (D 50 ) may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 4 μm to 10 μm. When the above range is satisfied, side reactions between the silicon-based composite particles and the electrolyte solution 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 ) can be measured using, for example, the laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0070] 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, based on 100 parts by weight of the total negative electrode active material. In this case, the total 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 an additional active material. When the content of the silicon-based active material satisfies the above range, improved energy density and cell resistance are achieved, and volume expansion during charge / discharge is minimized, resulting in excellent lifespan.

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

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

[0074] The negative electrode current collector is not particularly limited as long as it is conductive and does not induce 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 surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used as the current collector. The thickness of the current collector can be 6 μm to 20 μm, but is not limited thereto.

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

[0076] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powder 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 may be used.

[0077] The negative electrode slurry may further include a thickener such as sodium carboxymethyl cellulose (Na-CMC), carboxymethyl cellulose lithium (Li-CMC), or cellulose nanofiber (CNF).

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

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

[0080] <Secondary battery> A secondary battery according to an embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode and the negative electrode have been described above, detailed description thereof will be omitted.

[0081] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without limitation. It is particularly preferable that the separator has low resistance to electrolyte ion movement and excellent electrolyte humidification capability. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and it can be used in a single-layer or multi-layer structure.

[0082] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

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

[0084] Examples of the non-aqueous organic solvent that may be used include 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0085] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be produced, and therefore, these cyclic carbonates are more preferably used.

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

[0087] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0088] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, excellent life characteristics, and excellent cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0089] In the following, preferred embodiments are presented to aid in understanding the present invention, but these embodiments are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the technical spirit of the present invention. Such changes and modifications are naturally intended to fall within the scope of the appended claims.

[0090] Example 1 <Production example> <Manufacturing lithium secondary batteries> Cathode manufacturing Single particle LiNi as the positive electrode active material 0.86 Co 0.05 Mn 0.08 Al 0.01 O 2、 (Ni: Contains 86 mol% of 100 mol% of metals excluding lithium, average particle size (D 50 The positive electrode active material, binder, and conductive material were added in a weight ratio of 97:1.8:1.2 to N-methyl-2-pyrrolidone (NMP), which was used as a solvent for forming a positive electrode slurry.

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

[0092] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) as a positive electrode current collector at 3.92 mAh / cm 2The coated electrode was rolled 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.

[0093] Anode manufacturing Negative electrode slurry was prepared by adding artificial graphite, natural graphite (weight ratio of artificial graphite to natural graphite 8:2 excluding the SiO ratio), and SiO (6 parts by weight per 100 parts by weight of the negative electrode active material), binder, carboxymethyl cellulose (CMC), and 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.

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

[0095] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 6 μm) as a negative electrode current collector at a rate of 4.10 mAh / cm 2 The coated electrode was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer.

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

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

[0098] [Table 1]

[0099] The positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 5 were changed, and the capacity retention rate and the resistance increase rate of the battery were measured in situ as a result of 100 cycles at room temperature. 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 of nickel relative to 100 mol% of metals excluding lithium, the positive electrode end-of-discharge potential is rapidly reduced, the negative electrode potential rise is suppressed, and the rate of increase in negative electrode resistance is reduced, resulting in an excellent capacity retention rate. As can be seen from Table 1, Comparative Example 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 100 mol% of metals excluding lithium, average particle size (D 50 In this case, the negative electrode resistance increase rate was about 25% higher than that of a positive electrode containing secondary particle LFP (LiFePO4), and the negative electrode's usage depth increased, resulting in a decrease in capacity retention rate after 100 cycles of about 10%.

[0102] In Comparative Examples 2 and 3, the positive electrode active material contained secondary particulate LFP (LiFePO4) at a weight ratio exceeding 10 parts by weight per 100 parts by weight of the positive electrode active material. In these cases, not only were the resistance increase rate and capacity retention rate inferior to those of Examples 1 to 6, but the battery capacity was also inferior to that of batteries containing less than 10 parts by weight of LFP.

[0103] Comparative Example 4 corresponds to a case where the lithium nickel-based active material was changed to a secondary particle form. In this case, similar results were observed in terms of capacity to Examples 1 to 6, but the resistance increase rate was about 5% larger than in Examples 1 to 6, confirming that an inferior effect was shown in terms of capacity retention rate.

[0104] Comparative Example 5 corresponds to a case where a lithium nickel-based active material containing less than 55 mol% nickel was used. In this case, similar results to Examples 1 to 6 were observed in terms of the resistance increase rate and capacity retention rate, but the capacity was significantly lower.

Claims

1. A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, the negative electrode includes a silicon-based active material and a carbon-based active material, The positive electrode is a single-particle lithium nickel-based active material; and Secondary particle LCO (LiCoO ２ ) and LMO(LiMn ２ O ４ ) and LFP (LiFePO ４ ) and The secondary battery comprises the single-particulate lithium-nickel active material containing 55 mol % or more of nickel relative to 100 mol % of metals excluding lithium.

2. The secondary particle LCO (LiCoO ２ ) and LMO(LiMn ２ O ４ ) and LFP (LiFePO ４ 2. The secondary battery according to claim 1, wherein at least one of the above is contained in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the positive electrode active material.

3. The secondary battery according to claim 1, wherein the porosity of the positive electrode is 19% to 23%.

4. 2. The secondary battery according to claim 1, wherein the silicon-based active material is contained in an amount of 1 to 15 parts by weight per 100 parts by weight of the negative electrode active material.

5. The average particle size (D ５０ 2. The secondary battery according to claim 1, wherein the thickness of the first electrode is 3 μm to 10 μm.

6. The positive electrode is The single-particle lithium nickel-based active material, and The secondary particle-form LMO (LiMn ２ O ４ ) and LFP (LiFePO ４ 2. The secondary battery according to claim 1, comprising at least one of:

7. The positive electrode is made of the secondary particle LCO (LiCoO ２ ) and LMO(LiMn ２ O ４ ) and LFP (LiFePO ４ 2. The secondary battery 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.

8. 2. The secondary battery according to claim 1, wherein the single-particulate lithium-nickel active material contains 55 mol % or more and less than 80 mol % of nickel relative to 100 mol % of metals excluding lithium.

9. 2. The secondary battery according to claim 1, wherein the single-particulate lithium nickel-based active material contains 80 mol % or more of nickel relative to 100 mol % of metals excluding lithium.

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