Secondary battery

Abstract

This specification 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, 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 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 incorporated herein by reference.

[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. driven by an electric drive source.

[0004] Such secondary batteries have not only the primary advantage of significantly reducing the use of fossil fuels but also the advantage of generating no by-products from 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 for the negative electrode. However, when a silicon-based compound is included, the negative electrode resistance rapidly increases at the end of discharge, 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, it is necessary 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 includes a single-particle lithium nickel-based active material in the positive electrode active material layer; and at least one of secondary particle-shaped LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4), thereby reducing a sharp decrease in the positive electrode resistance at the end of discharge. As a result, the difference between the positive electrode resistance and the negative electrode resistance can be reduced, and a secondary battery with improved life and normal temperature cycle characteristics can be obtained.

[0012] Specifically, in order to reduce the cracking of the active material while increasing the energy density of the battery, a single-particle lithium nickel-based active material with a high nickel content is used in the positive electrode active material layer, and a silicon-based active material is included in the negative electrode active material layer to enable rapid charging. At the end of discharge, the negative electrode resistance increases rapidly, and the difference between the positive electrode resistance and the negative electrode resistance becomes large. Therefore, the use of the silicon-based active material included in the negative electrode active material layer will increase excessively (increase in depth of use), resulting in a decrease in the life performance of the battery. To improve this, a single-particle lithium nickel-based active material is included in the positive electrode active material layer; and at least one of secondary particle-shaped LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) is included, enabling rapid charging, improving the resistance of the positive electrode, reducing the resistance difference between the positive electrode and the negative electrode and the depth of use of the silicon-based active material, and obtaining a secondary battery with improved normal temperature life.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail. The following content is for helping to understand the present invention, and the scope of the rights of the invention is not defined or limited by this.

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

[0015] In this specification, when a member is located "above" another member, this includes not only the case where a member is in contact with another member, but also the case where there is another member between the two members.

[0016] The terms or words used in this specification are not construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that the inventor can appropriately define the concept of the terms in order to best explain his invention, they are construed in meanings and concepts that conform to the technical idea of the present invention.

[0017] The singular form of the terms used in this specification includes the plural form unless the context clearly dictates otherwise.

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

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

[0020] In this specification, the "end of discharge" means the region where the SOC (states of charge) of the battery (Full cell) is 10% or less.

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

[0022] In this specification, the "single particle" is a concept contrasted with the secondary particle state formed by the aggregation of dozens to hundreds of primary particles, and means a particle composed of 10 or fewer primary particles. Specifically, in the present invention, the single particle may be a single particle composed of one primary particle, or may be in the form of a particle in which a plurality of primary particles are aggregated.

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

[0024] In this specification, the "particle" refers to a particle in micrometer units, and when this is magnified and observed, it can be classified into "grains" having a crystal form in nanometer units of dozens. When this is further magnified and observed, it is possible to confirm a separated region in which atoms form a lattice structure in a certain direction, and this is called a "crystallite grain". The size of the particle observed by XRD is defined as the crystallite grain size. The crystallite grain size can be quantitatively determined through the Scherrer equation using XRD data.

[0025] The secondary battery of the present invention includes 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 includes a single-particle lithium nickel-based active material; and at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4). 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.

[0026] In this specification, when the negative electrode active material layer contains a silicon-based active material, the negative electrode resistance rapidly increases at the end of discharge, and the positive electrode resistance using a positive electrode material having low resistance characteristics rapidly decreases. Therefore, the difference between the negative electrode resistance and the positive electrode resistance becomes very large. As a result, there is a problem that the deterioration of the negative electrode progresses rapidly, the life of the battery is shortened, and the normal temperature cycle characteristics are deteriorated. In order to solve this problem, at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) is included together with the single-particle lithium nickel-based active material in the positive electrode active material layer, so as to reduce the rapid decrease in the positive electrode resistance and obtain a battery with improved life and normal 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 includes a single-particle lithium nickel-based active material; and at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4). At this time, 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, specifically 55 mol% or more and less than 80 mol%, or 80 mol% or more. By including at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4), the present invention has the effect of reducing the discharge end voltage of the positive electrode by mixing 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, and the positive electrode active material layer includes a positive electrode active material containing a single-particle lithium nickel-based active material; and at least one of secondary-particle LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4).

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

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

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

[0032] According to one embodiment of the present invention, the positive electrode active material layer includes a single-particle lithium nickel-based active material and at least one of secondary-particle 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 parts by weight to 10 parts by weight, specifically 0.1 parts by weight to 5 parts by weight, or 0.1 parts 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-like lithium nickel-based active material; or the single particle-like 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 negative electrode potential due to the decrease in the end-of-discharge voltage of the positive electrode and suppressing the deterioration of the negative electrode. 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-like 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) oxides (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] The positive electrode may further include a positive electrode current collector in addition to the aforementioned positive electrode active material layer. 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 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 can 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, and non-woven fabrics.

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

[0039] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances 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. Among these, one kind alone or a mixture of two or more kinds may be used.

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

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

[0042] The positive electrode slurry according to an embodiment of the present invention may further include a solvent for forming the positive electrode slurry. Specifically, the solvent for forming the positive electrode slurry may include N-methylpyrrolidone (NMP) or the like from the aspect of facilitating the 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 density of the electrode)) × 100 (%).

[0046] The rolled density can be calculated as follows.

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

[0048] The volume of the electrode excluding the foil means the total volume including pores inside the electrode, and is calculated by the product of the unit area of the sample and the thickness of the electrode layer after roll press.

[0049] The true density of the electrode is the inherent density of the electrode active material, and means the density of only the part filled with the material excluding the gaps between particles. The true density of the electrode is a method of measuring the volume (solid + isolated pores) excluding open pores to calculate the density value, and is measured by a method applying Archimedes' principle or using a gas pycnometer.

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

[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 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] The silicon-based active material such as SiO x (0 < x < 2) may be silicon-based composite particles including SiO x (0 < x < 2) and pores.

[0056] The SiO x (0 < x < 2) corresponds to a matrix in the silicon-based composite particles. The SiO x(0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained within (0 < x < 2). When the silicon-based composite particles contain x (0 < x < 2), the discharge capacity of the secondary battery can be improved. 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 this specification, the Mg element may be contained in an amount of 0.1 wt% to 20 wt%, or may be contained in an amount of 0.1 wt% to 10 wt%, based on 100 wt% of the total of the silicon-based active material. Specifically, the Mg element may be contained in an amount of 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be 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 included in an amount of 0.1 wt% to 20 wt%, or may be included in an amount of 0.1 wt% to 10 wt% based on 100 wt% of the total of the silicon-based active material. Specifically, the Li element may be included in an amount of 0.5 wt% to 8 wt%, and more specifically, may be included in an amount of 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound can be included in an appropriate 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 Mg element or Li element can be confirmed by ICP analysis. For the ICP analysis, after accurately weighing a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, and nitric acid, hydrofluoric acid, and sulfuric acid are added, followed by complete decomposition on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300) device, the intensity of a standard solution (5 mg / kg) prepared using a standard solution at the specific wavelength of the Mg element or Li element is measured to obtain a calibration curve. Subsequently, the pretreated sample solution and the substrate sample are introduced into the device, the intensities of each are measured to calculate the actual intensity, and after calculating the concentration of each component by comparing with the prepared calibration curve, the content of the Mg element or Li element in the silicon-based active material produced by conversion so that the total sum becomes the theoretical value can be analyzed.

[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 imparts conductivity to the silicon-based composite particles, and the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including the negative electrode active material containing the silicon-based composite particles can be improved. The total weight of the carbon layer may be included at 5% to 40% based on 100% by weight of the total 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, etc. may also be used.

[0068] The average particle size (D 50 ) of the silicon-based active material is 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically may be 4 μm to 10 μm. When the above range is satisfied, the side reaction between the silicon-based composite particles and the electrolyte can be 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 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0070] Also, according to one embodiment of the present invention, the silicon-based active material is contained in an amount of 1 to 15 parts by weight, preferably 1 to 10 parts by weight, more preferably 5 to 10 parts by weight, based on 100 parts by weight of the entire negative electrode active material. At this time, the entire 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 an additional active material. When the content of the silicon-based active material satisfies the above range, it has the effect of improving in terms of energy density and cell resistance, while having less volume expansion during charge / discharge and also having an excellent effect in terms of lifespan.

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

[0072] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. 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, or Al alloys; SiO β (0 < β < 2), SnO 2、Metal oxides capable of doping and undoping lithium, such as vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; composites containing the metallic compound and a carbonaceous material, such as an Si-C composite or an SnC composite; carbon-based active materials, etc. may be mentioned, and a mixture of any one or two or more of these may be used. Further, 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 contained in the negative electrode slurry to the additional negative electrode active material is 1:99 to 90:10, and specifically may be 1:99 to 50:50.

[0074] The negative electrode current collector may be any material as long as it has conductivity without inducing a chemical change in the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Specifically, a transition metal that can adsorb carbon well, such as copper or nickel, can be used as the current collector. The thickness of the current collector can be 6 μm to 20 μm, but the thickness of the current collector 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, poly acrylic acid, and substances in which their hydrogens are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0076] The conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, 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; conductive materials such as polyphenylene derivatives can be used.

[0077] The negative electrode slurry may further contain a thickener such as Na-CMC (Sodium carboxymethyl cellulose), Li-CMC (Carboxymethyl cellulose lithium), CNF (Cellulose nano fiber).

[0078] The negative electrode slurry according to an 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 be at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol in terms of facilitating the dispersion of components, and specifically, may contain distilled water.

[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> The 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, specific descriptions thereof are omitted.

[0081] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolyte while having excellent electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may also be used, and it may be selectively 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 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 contain a non-aqueous organic solvent and a metal salt.

[0084] Examples of the non-aqueous organic solvent 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, triphosphate ester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

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

[0086] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, as the anion of the lithium salt, 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 can be used.

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

[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. Since the battery module and the battery pack include the secondary battery having high capacity, high life characteristics, and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0089] Hereinafter, preferred examples are presented to assist in understanding the present invention. However, it is obvious to those skilled in the art that the examples are illustrative of the description and various changes and modifications are possible within the scope of the description and the scope of the technical idea. It is natural that such variations and modifications belong to the appended claims.

[0090] <Example 1> <Production Example> <Manufacture of Lithium Secondary Battery> Manufacture of Positive Electrode Single-particle LiNi as a positive electrode active material 0.86 Co 0.05 Mn 0.08 Al 0.01 O 2、 (Ni: containing 86 mol% with respect to 100 mol% of the metal excluding lithium, average particle diameter (D 50 ): 4 μm) and secondary particle LFP (LiFePO4) were used, and LFP (LiFePO4) was included at 3 parts by weight with respect to 100 parts by weight of the total positive electrode active material of the positive electrode active material layer. The positive electrode active material, binder, and conductive material were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 97:1.8:1.2 to produce a positive electrode slurry.

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

[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 2Coated with the 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, and a positive electrode was manufactured.

[0093] Manufacture of Negative Electrode Artificial graphite as the negative electrode active material, natural graphite (excluding the SiO ratio, weight ratio of artificial graphite to natural graphite 8:2), SiO (contained at 6 parts by weight per 100 parts by weight of the negative electrode active material): binder: carboxymethyl cellulose (CMC): conductive material were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 95.573:2.3:1.127:1 to manufacture a negative electrode slurry.

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

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

[0096] Manufacture of Lithium Secondary Battery Using the positive electrode and negative electrode, a polyethylene / polypropylene / polyethylene separator with a multilayer structure (thickness: 14 μm) was used as the separator, and a non-aqueous organic solvent containing a lithium salt was injected as the electrolyte to manufacture a lithium secondary battery. (N / P ratio: 104.7%, weight of the finished product cell: 502.0 g, thickness of the finished product cell: 8.24 mm)

[0097] <Examples 1 to 6 and Comparative Examples 1 to 5> In Example 1, a lithium secondary battery was manufactured in the same manner as in Example 1, except that only the types and compositions of the positive electrode active material or the added compounds were changed as shown in Table 1 below.

[0098]

Table 1

[0099] By changing the cathode active materials according to the above Examples 1 to 6 and Comparative Examples 1 to 5, the capacity retention rate and the battery resistance increase rate were measured as the results of the normal temperature life at 100 cycles in-situ, and the results are shown in Table 2 below.

[0100]

Table 2

[0101] As can be confirmed from the results of Examples 1 to 6 in Table 1 above, when adding one or more of secondary particle-like LCO (LiCoO2), LMO (LiMn2O4), and LFP (LiFePO4) to a lithium nickel-based active material containing 55 mol% or more of nickel with respect to 100 mol% of the metal excluding lithium, the cathode discharge end potential drops rapidly, suppressing the potential rise of the anode, and it was confirmed that this reduces the increase rate of the anode resistance and results in excellent capacity retention rate. As can be confirmed from Table 1 above, Comparative Example 1 uses, as the cathode active material, LiNi 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 (Ni: containing 86 mol% with respect to 100 mol% of the metal excluding lithium, average particle size (D 50 ): 4 μm), which corresponds to a cathode containing only this. In this case, it was confirmed by capacity retention rate evaluation that the increase rate of the anode resistance is about 25% greater than that of the cathode to which secondary particle-like LFP (LiFePO4) was added, the depth of use of the anode increases, and the capacity retention rate after 100 cycles decreases by about 10%.

[0102] Comparative Examples 2 and 3 correspond to the case where the cathode active material contains secondary particle-like LFP (LiFePO4), but the weight ratio exceeds 10 parts by weight with respect to 100 parts by weight of the cathode active material. In this case, it can be confirmed that it is not only inferior to Examples 1 to 6 in terms of the resistance increase rate and the capacity retention rate, but also inferior to the battery containing less than 10 parts by weight in terms of battery capacity.

[0103] Comparative Example 4 corresponds to the case where the lithium nickel-based active material is changed into secondary particles. In this case, similar results to those of Examples 1 to 6 are obtained in terms of capacity, but since the resistance increase rate is about 5% higher than that of Examples 1 to 6, it can be confirmed that the effect is inferior in terms of capacity retention rate.

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

Claims

1. 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-particle lithium nickel-based active material, and Secondary particulate LCO (LiCoO ２ ), LMO (LiMn ２ O ４ ), and LFP (LiFePO ４ ), and includes at least one of them, 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, a secondary battery.

2. The secondary particulate 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 part by weight to 10 parts by weight based on 100 parts by weight of the positive electrode active material, the secondary battery according to claim 1.

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

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

5. The average particle size (D ５０ ) of the single-particle lithium nickel-based active material is 3 μm to 10 μm, and the secondary battery according to claim 1.

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

7. The positive electrode contains at least one of the secondary particle-like LCO (LiCoO ２ ), LMO (LiMn ２ O ４ ), and LFP (LiFePO ４ ) in an amount of 0.1 part by weight to 3 parts by weight based on 100 parts by weight of the positive electrode active material. The secondary battery according to claim 1.

8. The secondary battery according to Claim 1, wherein the single-particle lithium nickel-based active material contains 55 mol% or more and less than 80 mol% of nickel with respect to 100 mol% of the metal excluding lithium.

9. The secondary battery according to Claim 1, wherein the single-particle lithium nickel-based active material contains 80 mol% or more of nickel with respect to 100 mol% of the metal excluding lithium.

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