Positive Electrode Composition, Positive Electrode, and Secondary Battery

Abstract

The present invention relates to a positive electrode composition containing a single-particle-shaped first positive electrode active material, a second positive electrode active material having a larger particle size than the first positive electrode active material and a particle strength of 150 Mpa or more, a binder, and a conductive material, a positive electrode containing the same, and a secondary battery.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0125359, filed with the Korean Intellectual Property Office on September 30, 2022, and Korean Patent Application No. 10-2023-0127942, filed with the Korean Intellectual Property Office on September 25, 2023, and all of its contents are included in the specification of this application.

[0002] The present invention relates to a positive electrode composition, a positive electrode, and a secondary battery.

Background Art

[0003] Secondary batteries are widely applied not only to portable devices but also to electric vehicles (EVs) and hybrid electric vehicles (HEVs) 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, so they are environmentally friendly and are attracting 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, an electrolyte, and the like. Also, electrodes such as the positive electrode and the negative electrode may have an electrode active material layer provided on a current collector. As the utilization of secondary batteries increases, various battery performances are required. For example, in order to develop a high-capacity battery, attempts have been made to apply a silicon-based active material to the negative electrode. However, in the case of a silicon-based active material, there is a problem of large initial irreversibility. In order to improve battery performance, attempts have been made to adjust the components of the positive electrode or the negative electrode or to add additives, but an incorrect combination of materials may have an adverse effect on the final battery performance. Therefore, research on improving battery performance by combining materials of the positive electrode or the negative electrode is necessary.

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the present invention is used together with a negative electrode using a silicon-based active material, it can not only provide the irreversible capacity of the negative electrode, but also implement an electrode with a high energy density and improve the gas generation problem due to the reaction with the electrolyte. The present invention provides a positive electrode composition, a positive electrode, and a secondary battery including the same.

Means for Solving the Problems

[0007] An exemplary embodiment of the present invention provides a positive electrode composition including a single particle-shaped first positive electrode active material, a second positive electrode active material having a larger particle size than the first positive electrode active material and a particle strength of 150 Mpa or more, a binder, and a conductive material.

[0008] Another exemplary embodiment of the present invention provides a positive electrode for a secondary battery including a current collector and a positive electrode active material layer provided on the current collector and including the positive electrode composition according to the above-described embodiment.

[0009] Another exemplary embodiment of the present invention provides a secondary battery including the positive electrode, a negative electrode, and a separator according to the above-described embodiment.

[0010] According to another exemplary embodiment of the present invention, the negative electrode includes a silicon-based active material.

Advantages of the Invention

[0011] According to the embodiments described in the present specification, by using a second positive electrode active material with high particle strength together with a single-particle first positive electrode active material as the positive electrode active material, not only can high density be achieved, but also low efficiency can be achieved. Specifically, because it has low efficiency characteristics, when used together with a negative electrode using a silicon-based active material, it can provide the irreversible capacity of the negative electrode. In addition, the first positive electrode active material and the second positive electrode active material can suppress the generation of fine powder due to particle cracking during rolling, so as to prevent an increase in the specific surface area and improve the problem of gas generation due to the reaction with the electrolyte. In addition, since the problems during rolling can be improved as described above, the rolling density can be increased, thereby not only achieving a high energy density, but also reducing the positive electrode thickness and improving the rapid charging performance.

Mode for Carrying Out the Invention

[0012] Hereinafter, in order to facilitate the understanding of the present invention of the application, the present invention of the application will be described in more detail. The present invention of the application can be implemented in various different forms and is not limited to the embodiments described here. Here, the terms or words used in the present specification and the claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor should interpret them in a meaning and concept that does not conflict with the technical idea of the present invention of the application in accordance with the principle that the concept of the terms can be appropriately defined in order to explain his own invention in the best way.

[0013] In the present specification, terms such as "comprise", "include" or "have" are understood to identify the presence of implemented features, numbers, steps, components, or combinations thereof, and do not preclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] Also, when a certain part such as a layer is "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a certain part is "directly on" another part, it means that there is no other part in between. Note that being "on" the reference part refers to being located above or below the reference part, and does not necessarily mean being located "upward" in the opposite direction of gravity.

[0015] In the present specification, the particle size means the average particle size represented by D 50 . D 50 can be defined as the particle size at the 50% criterion of the particle size distribution and 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, then introduce them into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000), irradiate them with ultrasonic waves of about 28 kHz at an output of 60 W, and then calculate the average particle size (D 50 ) corresponding to 50% of the cumulative volume in the measuring device.

[0016] In the present specification, the "primary particle" means a particle that apparently has no grain boundaries when observed at a magnification of 5000 to 20000 times using a scanning electron microscope.

[0017] In the present specification, the "secondary particle" is a particle formed by aggregation of primary particles.

[0018] In the present specification, the single particle is a term used to distinguish from the secondary particle-shaped positive electrode active material particles formed by aggregation of dozens to hundreds of primary particles that have been generally used in the past, and is a concept including a single particle composed of one primary particle and an aggregate particle of 10 or fewer primary particles.

[0019] In the present specification, when "particles" are described, it may mean including any or all of single particles, secondary particles, and primary particles.

[0020] The positive electrode composition according to an exemplary embodiment of the present specification includes a single-particle-shaped first positive electrode active material, a second positive electrode active material having a larger particle size than the first positive electrode active material and a particle strength of 150 Mpa or more, a binder, and a conductive material.

[0021] In the present specification, the single-particle-shaped first positive electrode active material may be referred to as a small-particle-size positive electrode active material for convenience, and the second positive electrode active material having a larger particle size than the first positive electrode active material and a particle strength of 150 Mpa or more may be referred to as a large-particle-size positive electrode active material.

[0022] In the above embodiment, by using a single-particle shape as the small-particle-size positive electrode active material, the lithium pathway can be lengthened to reduce efficiency. Further, by applying single particles with excellent rolling density, a high-density electrode can be implemented, and by applying single particles with excellent tap density, the rolling rate can be improved and the generation of fine powder due to particle cracking can be suppressed. According to one example, the first positive electrode active material has a tap density of 2 g / cc or more, for example, 2 g / cc or more and 30 g / cc or less. According to one example, the first positive electrode active material has a rolling density of 3 g / cc or more, for example, 3 g / cc or more and 30 g / cc or less.

[0023] The tap density is the apparent density of particles obtained by vibrating under certain conditions and can be measured using a tap density tester (KYT-5000, Seishin). The rolling density can be measured as the rolling density during rolling with a force of 2,000 kgf / cm 2 using a powder resistivity characteristic device HPRM-1000 (HAN TECH CO.).

[0024] In the above-described embodiment, the second positive electrode active material has a larger particle size than the first positive electrode active material and a particle strength of 150 Mpa or more. The particle strength of the second positive electrode active material may preferably be 180 Mpa or more. Although it is more advantageous for the particle strength of the second positive electrode active material to be higher, it may be, for example, 600 Mpa or less.

[0025] The particle strength refers to the force when the compression force is increased after placing the particles on the plate and the particles are broken, and can be measured using a Micro Compression Testing Machine (manufactured by Shimadzu Corporation, MCT-W500).

[0026] According to an exemplary embodiment, the particle strength of the first positive electrode active material is 150 Mpa or more, preferably 180 Mpa or more and less than 250 Mpa. When the particle strength of the first positive electrode active material is 250 Mpa or more, the rolling characteristics may be inferior.

[0027] According to an exemplary embodiment, the second positive electrode active material may be in the form of secondary particles, and in this case, the particle size of the secondary particles is larger than the single particle size of the first positive electrode active material. Even when the second positive electrode active material is in the form of secondary particles, since the particle strength is 150 Mpa or more as described above, particle cracking is alleviated during rolling of the electrode mixed with the single particle first positive electrode active material, generation of fine powder is suppressed, and gas generation is improved. The particle strength of the large particle size positive electrode active material can be adjusted by controlling the firing conditions during the production of the positive electrode active material, such as the firing time and temperature.

[0028] According to an exemplary embodiment, the D 50 of the first positive electrode active material is 1 μm to 10 μm, and the D 50 of the second positive electrode active material may be 8 μm to 20 μm. The second positive electrode active material may be 3 μm to 15 μm, for example, 5 μm to 10 μm larger in particle size than the first positive electrode active material. When the particle size difference between the first positive electrode active material and the second positive electrode active material is 3 to 15 μm, it is advantageous in terms of improving particle cracking and improving the generation of fine powder and gas generation.

[0029] According to an exemplary embodiment, the weight ratio of the first cathode active material to the second cathode active material may be from 1:9 to 9:1, specifically from 3:7 to 7:3. In particular, when the contents of the first cathode active material and the second cathode active material are from 3:7 to 7:3, the rolling characteristics of the electrode are improved, which is advantageous for implementing a high-density electrode.

[0030] According to an exemplary embodiment, the first cathode active material and the second cathode active material may each include a lithium composite transition metal compound containing nickel (Ni) and cobalt (Co). The lithium composite transition metal compound may further include at least one of manganese and aluminum. The lithium composite transition metal compound may contain 80 mol% or more, for example, 80 mol% or more and less than 100 mol% of nickel among the metals excluding lithium. For example, the lithium composite transition metal compound is Li a Ni (1-x-y) Co x M1 y M2 w O2 (1.0 ≤ a ≤ 1.5, 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 ≤ w ≤ 0.1, 0 ≤ x + y ≤ 0.2, M1 is one or more metals among Mn and Al, and M2 is one or more metal elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo) may be a cathode active material represented by.

[0031] According to an exemplary embodiment, one or both of the first cathode active material and the second cathode active material may further include a cobalt oxide layer provided on at least a part of the surface. The cobalt raw material of the cobalt oxide layer may contain lithium cobalt oxide by reacting with residual lithium on the surface of the active material. In this case, it can show the effect of reducing the residual lithium on the surface of the active material, and due to the excellent lithium ion conductivity of lithium cobalt oxide, it can show the effect of improving the output. In addition, the cobalt oxide layer can reduce the side reaction with the electrolyte by existing on the surface of the active material.

[0032] According to a further embodiment of the present specification, the positive electrode binder can play a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, those known in the art can be used. Non-limiting 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.

[0033] The positive electrode binder may be contained in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the positive electrode active material layer. For example, preferably 0.3 part by weight or more and 35 parts by weight or less, more preferably 0.5 part by weight or more and 20 parts by weight or less.

[0034] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electron conductivity without undergoing a chemical change in the battery. 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.

[0035] Specifically, in an exemplary embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The conductive material may be included in an amount of 0.1 part by weight or more and 2 parts by weight or less based on 100 parts by weight of the composition for the positive electrode active material layer. For example, it may preferably be included in an amount of 0.3 part by weight or more and 1.5 parts by weight or less, and more preferably 0.5 part by weight or more and 1.2 parts by weight or less.

[0036] According to a further embodiment of the present specification, a positive electrode for a secondary battery is provided, which includes a current collector and a positive electrode active material layer provided on the current collector and containing the above-described positive electrode composition. The thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less.

[0037] According to an exemplary embodiment, among the positive electrode active material layer, fine powder having a particle size of 1 μm or less is 5 vol% or less, preferably 3 vol% or less, and more preferably 1 vol% or less based on 100 vol% of the positive electrode active material layer. The fine powder content in the positive electrode active material layer can be measured using the laser diffraction method after obtaining only the positive electrode active material by heat-treating the rolled electrode in an air atmosphere at 500 °C for 5 hours to remove the conductive material and the binder. For example, after dispersing the lithium composite transition metal oxide powder or the positive electrode active material powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and after obtaining a volume-cumulative particle size distribution graph, it can be measured by determining the volume cumulative amount of 1 μm or less.

[0038] The positive electrode active material in 100 parts by weight of the positive electrode active material layer may be included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0039] The positive current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Further, the positive current collector may usually have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0040] A further embodiment of the present specification provides a secondary battery including the positive electrode according to the above-described embodiment, a negative electrode, and a separator.

[0041] The negative electrode may include a current collector and a negative electrode active material layer provided on the current collector.

[0042] According to an exemplary embodiment, the negative electrode includes a silicon-based active material.

[0043] The active material containing SiO x (0 ≦ x < 2) may be silicon-based composite particles containing SiO x (0 < x < 2) and pores.

[0044] SiO x (0 < x < 2) corresponds to the matrix within the silicon-based composite particles. SiO x (0 < x < 2) may be in a form containing Si and SiO2, and Si may form a phase. That is, x corresponds to the number ratio of O to Si contained in SiO x (0 < x < 2). When the silicon-based composite particles contain SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0045] The silicon-based composite particles may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon-based composite particles.

[0046] The Mg compound and / or the Li compound may be present inside and / or on the surface of SiO x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0047] 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.

[0048] In one embodiment of the present specification, the Mg element may be contained in an amount of 0.1% by weight to 20% by weight, or may be contained in an amount of 0.1% by weight to 10% by weight, based on 100% by weight of the silicon-based active material. Specifically, the Mg element may be contained in an amount of 0.5% by weight to 8% by weight or 0.8% by weight to 4% by weight. When such a 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 initial efficiency of the battery can be improved.

[0049] The Li compound may contain at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may contain Li7Si2. The Li oxide may contain Li2O.

[0050] In one embodiment of the present invention, the Li compound may contain the form of lithium silicate. The lithium silicate is Li a Si b Oc (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based composite particles. The amorphous lithium silicate may be in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5). However, the present invention is not limited thereto.

[0051] In one embodiment of the present specification, the Li element may be contained in an amount of 0.1% by weight to 20% by weight, or may be contained in an amount of 0.1% by weight to 10% by weight, based on 100% by weight of the silicon-based active material. Specifically, the Li element may be contained in an amount of 0.5% by weight to 8% by weight, and more specifically, may be contained in an amount of 0.5% by weight to 4% by weight. When such a range is satisfied, the Li compound can be contained in an appropriate content within the silicon-based active material, so that 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.

[0052] The content of Mg element or Li element can be confirmed by ICP (Inductively Coupled Plasma) analysis. For ICP analysis, after accurately sampling 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 and completely decomposed on a hot plate. Then, using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of the standard solution (5 mg / kg) prepared with the standard solution at the specific wavelength of Mg element or Li element is measured to create a reference calibration curve. After that, the pretreated sample solution and the substrate sample are introduced into the instrument, the intensity of each is measured to calculate the actual intensity, and after calculating the concentration of each component by comparing with the created calibration curve, the content of Mg element or Li element in the silicon-based active material manufactured by conversion so that the total sum becomes the theoretical value can be analyzed.

[0053] 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 can impart conductivity to the silicon-based composite particles and improve the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery including the negative electrode active material containing the silicon-based composite particles. The total weight of the carbon layer may be included in an amount of 5 wt% to 40 wt% based on 100 wt% of the total of the silicon-based composite particles.

[0054] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0055] 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 such a 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 implemented.

[0056] In the present 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 in the range from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0057] According to an embodiment of the present specification, the negative electrode slurry may further contain an additional negative electrode active material in addition to the above-described silicon-based active material.

[0058] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may 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 oxides, lithium titanate oxides, and lithium vanadate oxides; composites containing metallic compounds and carbonaceous materials such as Si-C composites or SnC composites; carbon-based active materials, etc. may be mentioned, and any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material.

[0059] In one embodiment of the present invention, the weight ratio of the silicon-based active material and the additional negative electrode active material contained in the negative electrode slurry is 1:99 to 90:10, and specifically may be 1:99 to 50:50.

[0060] In one embodiment of the present invention, the carbonaceous active material can be used without particular limitation, and typical examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite and artificial graphite, and examples of 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 carbonaceous active material may be contained in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer.

[0061] In one embodiment of the present specification, the negative electrode active material in 100 parts by weight of the negative electrode active material layer may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0062] According to a further embodiment of the present specification, the negative electrode active material layer may further contain a negative electrode binder in addition to the silicon-based active material and the carbon-based active material.

[0063] As a negative electrode binder, it can play a role in improving the adhesion between negative electrode active material particles and the adhesion between negative electrode active material particles and the negative electrode current collector. As the negative electrode binder, those known in the art can be used. Non-limiting examples include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and may contain at least one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also contain various copolymers thereof.

[0064] The negative electrode binder may be contained in an amount of 0.1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode active material layer. For example, it may preferably be contained in an amount of 0.3 part by weight or more and 20 parts by weight or less, and more preferably 0.5 part by weight or more and 10 parts by weight or less.

[0065] The negative electrode active material layer may not contain a conductive material, but may further contain a conductive material as needed. The conductive material contained in the negative electrode active material layer 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 or 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; fluorocarbons; 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 may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0066] In one embodiment of the present specification, the thickness of the negative electrode active material layer may be 10 μm or more and 500 μm or less.

[0067] In an exemplary embodiment, the negative electrode current collector may be any material that 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 treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Specifically, a transition metal that can effectively adsorb carbon such as copper or nickel may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0068] The positive electrode and the negative electrode may be manufactured according to the ordinary manufacturing methods of positive and negative electrodes, except that positive electrode active material and negative electrode active material are used. Specifically, after applying a composition for forming an active material layer, which contains the above-described active material and, optionally, a binder and a conductive material, onto a current collector, it may be manufactured by drying and rolling. At this time, the types and contents of the positive electrode active material, negative electrode active material, binder, and conductive material are as described above. As the solvent, a solvent generally used in the art may be used, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more thereof may be used. The amount of the solvent used is such that, in consideration of the coating thickness of the composition and the production yield, the active material, conductive material, and binder are dissolved or dispersed, and then, at the time of coating for manufacturing the positive electrode and the negative electrode, it has a viscosity capable of showing excellent thickness uniformity. As another method, the positive electrode and the negative electrode may be manufactured by casting a composition for forming an active material layer onto another support, and then laminating a film obtained by peeling from the support onto a current collector.

[0069] As the separator, it 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, those with low resistance to ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven 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 be used, and it may be selectively used in a single-layer or multi-layer structure.

[0070] 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 the manufacture of lithium secondary batteries.

[0071] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0072] Examples of the non-aqueous organic solvents 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc.

[0073] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents and have a high dielectric constant, which enables good dissociation of lithium salts. Therefore, they are preferably used. When such cyclic carbonates are mixed with linear carbonates having a low viscosity and a low dielectric constant, such as dimethyl carbonate and diethyl carbonate, at an appropriate ratio and used, an electrolyte having a high electrical conductivity can be produced, and they may be more preferably used.

[0074] As the metal salt, a lithium salt can be used. Lithium salts are substances that are easily dissolved in non-aqueous electrolytes. For example, as an 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 - , (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0075] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric 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 the reduction of the battery capacity, improving the discharge capacity of the battery, etc.

[0076] A further embodiment of the present invention provides a battery module including the above-described lithium secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include a secondary battery having a high capacity, high rate characteristics and cycle characteristics, they may 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.

[0077] The lithium secondary battery according to the embodiment of the present invention can stably exhibit excellent discharge capacity, output characteristics, and cycle performance. Therefore, it can be used not only as a power source for portable devices such as mobile phones, notebook computers, and digital cameras, but also 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. For example, the battery module or battery pack can be used as a power source for a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or one or more medium and large-sized device power sources in a power storage system.

[0078] Mode of the present invention Hereinafter, preferred examples are presented to facilitate the understanding of the present invention. However, it is obvious to those skilled in the art that the examples are illustrative of the description of the present application, and various changes and substitutions are possible within the scope of the description of the present application and the scope of the technical idea. It goes without saying that such changes and substitutions belong to the scope of the appended claims.

[0079] Examples 1 to 3 A positive electrode was prepared by coating, drying, and rolling a positive electrode active material layer on a positive electrode current collector. As a composition for manufacturing the positive electrode active material layer, a Ni-based positive electrode active material (Li 1.0 Ni 0.84 Co 0.08 Mn 0.08 O2) having a cobalt oxide layer on a part of the particle surface, a conductive material (CNT), and a binder (PVDF) were put into a N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1:2 to produce a positive electrode slurry (the solid content of the positive electrode slurry is 70 parts by weight of the total positive electrode slurry).

[0080] The produced positive electrode slurry was coated on an Al current collector, dried at a high temperature, and then rolled at room temperature to produce a positive electrode.

[0081] Here, the positive electrode active material is the D of a single particle in Table 1 below50、 A first positive electrode active material having a tap density, a rolling density, and a particle strength shown in Table 2 below, and D shown in Table 2 below 50 and a second positive electrode active material having a particle strength are included at a weight ratio of 6:4.

[0082] The tap density, the rolling density, and the particle strength were produced by the following methods.

[0083] * Tap density After charging 10 g of the positive electrode active material obtained in Example 1 and Comparative Example 1 respectively into a 300 cc container, the apparent density of the particles obtained by vibrating under certain conditions was measured. Specifically, the tap density of the lithium transition metal oxide particles was measured using a tap density tester (KYT-5000, Seishin).

[0084] * Rolling density The rolling density during rolling of the positive electrode active material (die area: 2.3 cm 2 ) was measured using a powder resistance characteristic device HPRM-1000 (HAN TECH CO.) with a force of 2,000 kgf / cm 2 respectively.

[0085] * Particle strength After placing the particles on a plate, the compression force was increased using a Micro Compression Testing Machine (Shimadzu, MCT-W500), and the force when the particles were broken was measured, which was taken as the particle strength value.

[0086] A negative electrode active material containing SiO and graphite on a negative electrode current collector (the SiO-based active material is included at 5 parts by weight of the total negative electrode active material), a conductive material (carbon black), a binder (SBR), and a thickener (CMC) were put into a distilled water solvent at a weight ratio of 96:1:2:1 to produce a negative electrode slurry (the solid content of the negative electrode slurry is included at 50 parts by weight of the total negative electrode slurry).

[0087] The produced negative electrode slurry was applied onto a Cu current collector, dried at a high temperature, and then cold-rolled to produce a negative electrode.

[0088] The positive electrode and the negative electrode were laminated with a separator in between, and an electrolyte solution (1M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), vinylene carbonate (VC) / propane sultone (PS, propane sultone) (3 parts by weight and 1.5 parts by weight respectively based on 100 parts by weight of the electrolyte)) was injected to fabricate a lithium secondary battery.

[0089] The electrode density, rolling rate, degree of fine powder generation of the positive electrode, and the 0.1C efficiency and degree of gas generation of the lithium secondary battery are shown in Table 2 below.

[0090] The electrode density, rolling rate, degree of fine powder generation, and degree of gas generation were measured by the following methods.

[0091] * Electrode density: Electrode weight / (Electrode thickness × Electrode area) - Electrode weight: Slurry weight excluding the weight of the aluminum foil - Electrode thickness: Thickness of the slurry layer excluding the aluminum foil thickness * Rolling rate: [(Pre-rolling thickness - Aluminum foil thickness) - (Post-rolling thickness - Aluminum foil thickness)] / (Pre-rolling thickness - Aluminum foil thickness) * Fine powder generation: After obtaining a volume particle size distribution graph of the positive electrode active material obtained by heat-treating the rolled electrode in an air atmosphere at 500 °C for 5 hours using Microtrac MT 3000, the volume cumulative amount of 1 μm or less was determined. * Gas generation: The fabricated cell was charged at a constant current / constant voltage (CC / CV) to 4.2 V at 0.33C (0.05C-cut), stored at a high temperature (60 °C) for 8 weeks, and the amount of gas generated was measured using gas chromatography (gc agilent 7890b).

[0092] Comparative Example 1 It was carried out in the same manner as in Example 1 except that secondary particles instead of single particles were used as the first positive electrode active material, and single particles with a strength of 149 Mpa were used as the first positive electrode active material. The first positive electrode active material which is secondary particles has the D of the secondary particles in Table 1 below 50 , tap density, and rolling density.

[0093] Comparative Example 2 The procedure of Example 1 was repeated, except that secondary particles with a strength of 121 Mpa were used as the second positive electrode active material, and single particles with a strength of 149 Mpa were used as the first positive electrode active material.

[0094] Comparative Example 3 The procedure of Example 1 was repeated, except that secondary particles with a strength of 121 Mpa were used as the second positive electrode active material.

[0095]

Table 1

[0096] As shown in Table 1, even when D 50 is the same, it can be confirmed that the tap density and rolling density of single particles are higher than those of secondary particles.

[0097]

Table 2

[0098] Since the first positive electrode active materials of Example 1 and Comparative Example 1 are single particles and secondary particles, respectively, as shown in Table 1, a difference in the tap density of the first positive electrode active material occurs, and as a result, the coating thickness before rolling of the first positive electrode active material layer coated with the same loading amount changes, and a difference in the rolling rate occurs when rolling to the final target thickness. That is, similar to Example 1, when single particles are used as the first positive electrode active material, the tap density is excellent, the coating thickness of the first positive electrode active material layer is thin, and the rolling rate for rolling to the target thickness can be improved.

[0099] In Examples 2 and 3, the particle sizes of the first and second positive electrode active materials are the same as those in Example 1, but the particle strengths are different. The second positive electrode active materials of Examples 2 and 3 have different particle strengths from the second positive electrode active material of Example 1, and are manufactured under firing conditions different from those of Example 1. The tab density is relatively lower than that of the second positive electrode active material of Example 1, and there is a slight difference in the rolling rate.

[0100] As shown in Table 2, in the cases of Examples 1 to 3, it was confirmed that less fine powder was generated, the efficiency was low, and the generation of gas was also significantly reduced compared to Comparative Examples 1 to 3.

[0101] Comparative Example 1 corresponds to the case where secondary particles are used as the first positive electrode active material. It can be confirmed that the tap density is relatively inferior compared to the case where single particles are used, rolling is not performed well, and more fine powder and gas are generated compared to Examples 1 to 3.

[0102] Comparative Examples 2 and 3 correspond to the case where the particle strength of the second positive electrode active material is less than 150 Mpa. It can be confirmed that the particle strength of the second positive electrode active material is weak, cracks occur during rolling, and more fine powder and gas are generated compared to Examples 1 to 3.

Claims

1. A single-particle first positive electrode active material, a second positive electrode active material having a particle size larger than that of the first positive electrode active material and a particle strength of 150 MPa or more, a binder, and a conductive material, and a positive electrode composition containing the same.

2. The positive electrode composition according to Claim 1, wherein the second positive electrode active material is in the form of secondary particles.

3. The D of the first positive electrode active material ５０ is from 1 μm to 10 μm, The D of the second positive electrode active material ５０ is 8 μm to 20 μm, and the positive electrode composition according to claim 1.

4. The positive electrode composition according to Claim 1, wherein the first positive electrode active material has a tap density of 2 g / cc or more.

5. The positive electrode composition according to Claim 1, wherein the first positive electrode active material has a rolling density of 3 g / cc or more.

6. The positive electrode composition according to Claim 1, wherein the particle strength of the first positive electrode active material is 150 MPa or more.

7. The positive electrode composition according to Claim 1, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is 1:9 to 9:

1.

8. A current collector, and a positive electrode active material layer provided on the current collector and containing the positive electrode composition according to any one of Claims 1 to 7, and a positive electrode for a secondary battery.

9. In the positive electrode active material layer, fine powder having a particle size of 1 μm or less is 5 vol% or less based on 100 vol% of the positive electrode active material layer. The positive electrode according to Claim 8.

10. A secondary battery including the positive electrode according to Claim 8, a negative electrode, and a separator.

11. The secondary battery according to Claim 10, wherein the negative electrode contains a silicon-based active material.

12. The secondary battery according to Claim 11, wherein the negative electrode further contains a carbon-based active material.

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