Positive electrode for secondary battery and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode for a secondary battery and a lithium secondary battery comprising same. The positive electrode comprises: a lithium transition metal oxide containing nickel; a first binder containing a linear polymer; and a second binder containing a branched polymer, wherein the linear polymer contains a functional group capable of forming a hydrogen bond, the branched polymer has 3.0 or less branches per 1,000 carbon atoms, and the weight ratio between the first binder and the second binder is 1:0.26 to 1:0.85.

Description

Anode for a secondary battery and a lithium secondary battery including the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0137160 filed on October 8, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0002] The present invention relates to a positive electrode for a secondary battery, the positive electrode for the secondary battery, and a lithium secondary battery comprising the positive electrode for the secondary battery.

[0003] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] The electrode of a lithium secondary battery is manufactured by mixing a positive or negative active material with a binder resin component, dispersing the mixture in a solvent to form a slurry, applying this to the surface of an electrode current collector, drying it, and then forming a composite layer.

[0005] The binder binds electrode active materials ranging in size from several micrometers to tens of micrometers with conductive materials ranging in size from tens of nanometers, and helps the electrode coating layer adhere well to the electrode current collector. The most important characteristic required of the binder is adhesion, so it must not dissolve at all even if swelling occurs in an environment with an excess amount of organic electrolyte, and it must not decompose in electrochemical oxidation or reduction environments.

[0006] Conventionally, polyvinylidene fluoride (PVdF), which has high electrochemical and thermal stability and good oxidation and chemical resistance, has been used as a binder for a long time. However, although PVdF has advantages such as excellent thermal stability, oxidation resistance, and chemical resistance, it lacks adhesion, which can cause problems such as the electrode detaching from the electrode current collector, leading to a degradation of battery characteristics such as capacity reduction.

[0007] Therefore, there is a need to develop a cathode for a secondary battery containing a binder that can achieve improved battery performance by exhibiting excellent dispersibility and enhanced adhesive properties.

[0008] [Prior Art Literature]

[0009] [Patent Literature]

[0010] (Patent Document 1) Korean Published Patent Application No. 2016-0039835

[0011] The problem that the present invention aims to solve is to provide a cathode for a secondary battery that includes a binder capable of exhibiting excellent dispersibility and improved adhesive properties, thereby enabling an improvement in the electrochemical performance of the battery.

[0012] Another problem to be solved by the present invention is to provide a lithium secondary battery comprising the positive electrode for the secondary battery.

[0013] [1] The present invention provides a positive electrode for a secondary battery comprising a lithium transition metal oxide containing nickel; a first binder comprising a linear polymer; and a second binder comprising a branched polymer, wherein the linear polymer comprises hydrogen bondable functional groups, and the branched polymer has 3.0 or fewer branches per 1,000 carbon atoms, and the weight ratio of the first binder to the second binder is 1:0.26 to 1:0.85.

[0014] [2] The present invention provides a positive electrode for a secondary battery, wherein the linear polymer comprises one or more functional groups selected from the group consisting of -COOH, -OH, -COONH-, -NHCONH- and -O-.

[0015] [3] The present invention provides a positive electrode for a secondary battery, wherein, in any one or more of [1] and [2], the branched polymer comprises one or more functional groups selected from the group consisting of -OH, -O-, -CO-, -COO-, aryl and arylene.

[0016] [4] The present invention provides a positive electrode for a secondary battery in which, in one or more of [1] or [3], the linear polymer is a PVdF-based polymer.

[0017] [5] The present invention provides a positive electrode for a secondary battery in which, in any one or more of [1] to [4], the linear polymer has a weight-average molecular weight of 300,000 g / mol to 2,000,000 g / mol.

[0018] [6] The present invention provides a positive electrode for a secondary battery in which, in any one or more of [1] to [5], the branched polymer is a PVdF-based polymer.

[0019] [7] The present invention provides a positive electrode for a secondary battery in which, in any one or more of [1] to [6], the branched polymer has a weight-average molecular weight of 600,000 g / mol to 2,000,000 g / mol.

[0020] [8] The present invention provides a positive electrode for a secondary battery, wherein, in any one or more of [1] to [7], the branched polymer has long chain branches.

[0021] [9] The present invention provides a positive electrode for a secondary battery, wherein in any one or more of [1] to [8], the weight ratio of the first binder and the second binder is 1:0.33 to 1:0.67.

[0022]

[0010] The present invention provides a positive electrode for a secondary battery, wherein, in any one or more of [1] to [9], the positive electrode further comprises a conductive material.

[0023]

[0011] The present invention provides a positive electrode for a secondary battery, wherein, in any one or more of [1] to

[0010] , the lithium transition metal oxide has a Ni content of 80 mol% or more among the transition metals.

[0024]

[0012] The present invention provides a positive electrode for a secondary battery, wherein in any one or more of [1] to

[0011] , the lithium transition metal oxide is represented by the following chemical formula 1:

[0025] [Chemical Formula 1]

[0026] Li 1+x (Ni a Co b Mn c ) 1-x O2

[0027] In the above Chemical Formula 1, -0.3≤x≤0.3, 0.8≤a<1, 0 <b<0.2, 0<c<0.2, 및 a+b+c=1임.

[0028]

[0013] The present invention provides a lithium secondary battery comprising a positive electrode for a secondary battery according to one or more of [1] to

[0012] .

[0029] The cathode for a secondary battery according to the present invention comprises a first binder comprising a linear polymer and a second binder comprising a branched polymer. Since the linear polymer includes functional groups involved in adhesive properties and the branched polymer has a structure with high solvent affinity involved in dispersibility, the binders are evenly dispersed, thereby enabling improved adhesive properties. Accordingly, the cathode for a secondary battery comprising the first binder and the second binder together in a certain weight ratio exhibits high electrode adhesion along with excellent electrode uniformity, thereby enabling more stable and improved electrochemical performance. Thus, it can be usefully employed in the manufacture of lithium secondary batteries.

[0030] The present invention will be described in more detail below.

[0031] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0032] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0033] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0034] In this specification, when a part is described as including a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0035] In this specification, the description "A and / or B" means A, or B, or A and B.

[0036] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0037] In this case, "weight-average molecular weight" can be measured using gel permeation chromatography (GPC). For example, after preparing a sample of a certain concentration, the GPC measuring instrument is stabilized. Once the instrument is stabilized, a standard sample and a sample are injected into the instrument to obtain a chromatogram, and then the molecular weight is calculated according to the analysis method.

[0038]

[0039] cathode for secondary batteries

[0040] A positive electrode for a secondary battery according to one embodiment of the present invention comprises: a lithium transition metal oxide containing nickel; a first binder containing a linear polymer; and a second binder containing a branched polymer; wherein the linear polymer contains a hydrogen bonding capable functional group, and the branched polymer has 3.0 or fewer branches per 1,000 carbon atoms, and the weight ratio of the first binder and the second binder is 1:0.26 to 1:0.85.

[0041]

[0042] The first binder comprises a linear polymer having hydrogen bondable functional groups and exhibiting excellent adhesive properties, and the second binder comprises a branched polymer having 0.5 or fewer branches per 1,000 carbon atoms, which has high solvent affinity and exhibits excellent dispersibility; therefore, the positive electrode for a secondary battery according to the present invention, which includes these together, can exhibit improved adhesive properties in the positive electrode active material layer and also exhibit more stable and improved electrochemical properties.

[0043]

[0044] The above linear polymer comprises hydrogen bondable functional groups, wherein the hydrogen bondable functional groups may include one or more selected from the group consisting of -COOH, -OH, -COONH-, -NHCONH-, and -O-, and specifically may include -COOH and -OH. The functional groups may be included in an amount of 0.01 mol% to 10 mol% based on the linear polymer, specifically 0.1 mol% to 8 mol%, and more specifically 1 mol% to 5 mol%. The hydrogen bondable functional groups are included in the chain structure of the linear polymer to form hydrogen bonds with hydroxyl groups on the surface of the aluminum current collector and the surface of the active material, thereby improving adhesion as a binder.

[0045] The content of the above hydrogen bonding-capable functional groups can be confirmed by measuring the elemental composition ratio using X-ray photoelectron XPS.

[0046] The above linear polymer may be a polyvinylidene fluoride (PVdF)-based polymer. The above PVdF-based polymer may contain 60% or more, 70% or more, 80% or more, or 90% or more of vinylidene fluoride units in the polymer.

[0047] In one embodiment of the present invention, the first binder comprising the linear polymer may be a PVdF-based binder. The weight-average molecular weight of the linear polymer may be 300,000 g / mol to 2,000,000 g / mol, specifically 400,000 g / mol to 1,700,000 g / mol, 500,000 g / mol to 1,500,000 g / mol, and more specifically 800,000 g / mol to 1,000,000 g / mol. When the first binder comprises a linear polymer satisfying the weight-average molecular weight, it may exhibit an even more enhanced adhesive strength enhancement effect. If the weight-average molecular weight of the linear polymer is low, the viscosity of the anode slurry containing it may decrease, causing phase separation, and the adhesion effect between the anode active material layer and the current collector may decrease. In addition, if the weight-average molecular weight of the linear polymer is large, the phase stability of the anode slurry containing the linear polymer may shift to a high-elasticity region, thereby reducing the uniformity of the quality of the anode manufactured using it.

[0048]

[0049] The branched polymer has 3.0 or fewer branches per 1,000 carbon atoms. Specifically, the branched polymer may have 0.1 to 3.0 branches per 1,000 carbon atoms, and more specifically, 1 to 2.5 branches per 1,000 carbon atoms. When the second binder includes a branched polymer satisfying the number of branches, the branched polymer can increase the solvent affinity of the binder, thereby exhibiting excellent dispersibility in the anode slurry and forming a stable dispersed phase. On the other hand, when the second binder includes a linear polymer that does not contain branches rather than a branched polymer, the binders may aggregate locally within the anode slurry, and consequently, interfacial adhesion may be reduced. Furthermore, if the number of branches of the branched polymer falls outside the above range, the solvent affinity of the branched polymer may be reduced, and adhesion may be lowered.

[0050] The number of branches per 1,000 carbon atoms can be obtained by analyzing the branched polymer using Fourier Trans-Infrared Analysis (FT-IR) to derive a distribution curve of the number of branches per 1,000 carbon atoms (right Y-axis) according to the molecular weight (X-axis) of the branched polymer, measuring the number of branches overall, and then calculating the average value, or it can be measured using a known method with NMR.

[0051] The branched polymer has long chain branches in an aliphatic main chain and may include one or more functional groups selected from the group consisting of -OH, -O-, -CO-, -COO-, aryl, and arylene within the chain structure, specifically may include -O- and -CO-. The functional groups may be included in an amount of 0.01 mol% to 10 mol% based on the branched polymer, specifically 0.1 mol% to 5 mol%, and more specifically 1 mol% to 3 mol%.

[0052] When the above branched polymer has long-chain branches in an aliphatic main chain and includes the above functional groups within the chain structure, it can maintain stable dispersibility in an electrode slurry state by increasing solvent affinity, minimize volume expansion of the positive active material layer that may occur due to the electrolyte in the battery, and improve battery performance by forming a uniform ion conduction path.

[0053] The branched polymer may be a PVdF-based polymer. The PVdF-based polymer may contain 60% or more, 70% or more, 80% or more, or 90% or more of vinylidene fluoride units in the polymer.

[0054] In one embodiment of the present invention, the second binder comprising the branched polymer may be a PVdF-based binder. The weight-average molecular weight of the branched polymer may be 600,000 g / mol to 2,000,000 g / mol, specifically 800,000 g / mol to 1,700,000 g / mol, 1,000,000 g / mol to 1,500,000 g / mol, and more specifically 1,300,000 g / mol to 1,450,000 g / mol. When the second binder comprises a branched polymer satisfying the weight-average molecular weight, it can increase solvent affinity and exhibit a viscosity-reducing effect. On the other hand, if the weight-average molecular weight of the branched polymer is small, the viscosity of the anode for a secondary battery may be lowered, which may cause phase separation and make it difficult to properly exhibit the dispersibility enhancement effect. If the weight-average molecular weight of the branched polymer is large, the resistance of the electrode layer within the anode for a secondary battery increases, which may result in inferior output characteristics and shift the phase stability of the slurry to a high-elasticity region, thereby reducing the uniformity of electrode quality.

[0055] The above "weight-average molecular weight" can be measured using gel permeation chromatography (GPC). For example, after preparing a sample of a certain concentration, the GPC measuring instrument is stabilized. Once the instrument is stabilized, a standard sample and a sample are injected into the instrument to obtain a chromatogram, and then the molecular weight is calculated according to the analysis method to obtain the polystyrene equivalent value.

[0056]

[0057] A positive electrode for a secondary battery according to one embodiment of the present invention comprises the first binder and the second binder in a weight ratio of 1:0.26 to 1:0.85, wherein the weight ratio of the first binder and the second binder may specifically be 1:0.30 to 1:0.70, and more specifically 1:0.33 to 1:0.67. When the weight ratio of the first binder and the second binder satisfies the above range, the first binder capable of improving adhesive properties and the second binder capable of improving solvent affinity and dispersibility are appropriately combined and included in the positive electrode for the secondary battery, thereby allowing the performance improvement effect of the battery containing the first binder and the second binder together to be more appropriately exhibited. If the weight ratio of the first binder and the second binder deviates from the above range, such that the content of the first binder increases and the content of the second binder decreases, gelation of the anode slurry containing the same may occur, and due to the gelation of the anode slurry, the electrode adhesion strength may decrease despite the high content of the first binder which can improve adhesive properties. Additionally, if the content of the first binder decreases and the content of the second binder increases outside the above weight ratio range, the dispersibility and storage stability of the anode slurry containing the same are maintained, but the electrode adhesion strength may decrease due to the relative decrease in the content of the first binder.

[0058]

[0059] The lithium transition metal oxide containing nickel included in the positive electrode for a secondary battery according to the present invention may be selected from the group consisting of lithium-nickel-based oxides, lithium-nickel-manganese-based oxides, lithium-nickel-cobalt-based oxides, and lithium-nickel-manganese-cobalt-based oxides, and specifically Li 1+x (Ni a Co b Mn c ) 1-x O2(0<a<1, 0 <b<1, 0<c<1, -0.3≤x≤0.3, 및 a+b+c=1), Li(Ni dCo e Mn f )O4(0<d<2, 0<e<2, 0<f<2, d+e+f=2), Li g NiO2(0.5 <g<1.3), LiNi 1-h M h O2(M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, 0≤h<1), LiMn 2-y Ni y O4(0<y<2), LiMn 2-z Co z It may include at least one selected from O4(0<Z<2).

[0060] Preferably, the lithium transition metal oxide is represented by the following chemical formula 1 and may comprise a lithium transition metal oxide having a Ni content of 80% or more, 83% or more, preferably 86% or more.

[0061] [Chemical Formula 1]

[0062] Li 1+x (Ni a Co b Mn c ) 1-x O2

[0063] In the above chemical formula 1,

[0064] -0.3≤x≤0.3, 0.8≤a<1, 0 <b≤<0.2, 0<c<0.2, 및 a+b+c=1임.

[0065]

[0066] As described above, when a lithium transition metal oxide with a nickel content of 80% or more is used as the lithium transition metal oxide, it exhibits high capacity characteristics, whereas, as the nickel content of the lithium transition metal oxide increases, the generation of hydroxyl groups resulting from the reaction between nickel and moisture in the atmosphere may also increase. Accordingly, the higher the nickel content included in the lithium transition metal oxide, the more accelerated the gelation of the anode-forming composition containing it may be.

[0067] Accordingly, by using a second binder comprising a branched polymer capable of improving solvent affinity and dispersibility as a binder, together with a first binder comprising a linear polymer capable of improving adhesion properties through hydrogen bonding with hydroxyl groups, it is possible to prevent gelation of the positive electrode for a secondary battery while improving adhesion properties.

[0068] The above-mentioned positive electrode may additionally include a conductive material. The conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and includes, for example, materials having point, linear, or plate-shaped conductivity. 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 or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. Specific examples of commercially available conductive materials include acetylene black series products such as those from Chevron Chemical Company, Denka Black (Singapore Private Limited), and Gulf Oil Company, Ketjenblack, EC series (Armak Company products), Vulcan XC-72 (Cabot Company products), and Super P (Timcal products).

[0069]

[0070] The above positive electrode may further include a positive current collector and may include a positive active material layer formed on the positive current collector. The positive active material layer may include a lithium transition metal oxide containing nickel, a first binder, and a second binder, and specifically may include a lithium transition metal oxide containing nickel, a first binder, a second binder, and a conductive material.

[0071]

[0072] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used.

[0073] The above positive current collector can generally have a thickness of 3 μm to 500 μm.

[0074] In one embodiment of the present invention, the positive active material may be included in an amount of 80% to 99.6% by weight based on the total weight of the positive active material layer, the binder may be included in an amount of 0.1% to 19.9% ​​by weight based on the total weight of the positive active material layer, and the conductive material may be included in an amount of 0.1% to 19.9% ​​by weight based on the total weight of the positive active material layer.

[0075] In one embodiment of the present invention, the positive active material may be included in an amount of 90% to 99.5% by weight based on the total weight of the positive active material layer, the binder may be included in an amount of 0.1% to 9.9% by weight based on the total weight of the positive active material layer, and the conductive material may be included in an amount of 0.1% to 9.9% by weight based on the total weight of the positive active material layer.

[0076] In one embodiment of the present invention, the positive active material may be included in an amount of 90% to 99.5% by weight based on the total weight of the positive active material layer, the binder may be included in an amount of 0.1% to 5% by weight based on the total weight of the positive active material layer, and the conductive material may be included in an amount of 0.1% to 5% by weight based on the total weight of the positive active material layer.

[0077] The above positive active material layer can be manufactured by preparing a positive slurry by adding an additive containing a positive active material, a binder, and optionally a conductive material to a solvent, and then coating, drying, and rolling it onto the positive current collector.

[0078] The above solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone) and may be used in an amount that results in a desirable viscosity when including the anode active material and optionally a binder and a conductive material. For example, the concentration of the solid component including the anode active material and optionally a binder and a conductive material may be 50% to 95% by weight, preferably 70% to 90% by weight.

[0079] The cathode for a secondary battery according to the present invention may be manufactured in the atmosphere, and the lithium transition metal oxide containing nickel included in the cathode for the secondary battery may react with moisture contained in the atmosphere to form hydroxyl groups, and even if the pH is increased, the gelation of the cathode for the secondary battery is suppressed by including the second binder as described above, and accordingly, the viscosity of the cathode for the secondary battery may not increase.

[0080]

[0081] lithium secondary battery

[0082] In addition, the present invention provides an electrochemical device comprising the anode. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, may be a lithium secondary battery.

[0083] Specifically, the lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. Additionally, the lithium secondary battery may optionally further comprise a battery container housing an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

[0084]

[0085] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0086] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0087] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0088] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; 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; and SiO₂β Examples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0089] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), sodium carboxymethylcellulose, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0090]

[0091] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0092]

[0093] The above-mentioned cathode active material layer may be manufactured, for example, by applying a composition for forming a cathode active material layer, prepared by dissolving or dispersing a cathode active material, a binder, and a conductive material in a solvent onto a cathode current collector and drying it, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0094]

[0095] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0096]

[0097] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0098] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0099] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0100] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0101] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0102]

[0103] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0104] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0105] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0106] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0107] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0108]

[0109] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0110]

[0111] Examples

[0112]

[0113] Example 1

[0114] Preparation of Anode Slurry

[0115] Li(Ni) 0.86 Co 0.08 Mn 0.06 Linear polyvinylidene fluoride (Mw: 900,000 g / mol, functional groups -COOH, -OH) with a functional group content of 3.6 mol%; branched polyvinylidene fluoride (Mw: 1,380,000 g / mol, functional groups -O-, -CO-) with 2.1 long-chain branches per 1,000 carbon atoms in the polymer chain and a functional group content of 2.0 mol%; and CNT were added to the solvent NMP at a concentration of 9 wt% in a weight ratio of 95:2.1:0.9:2, and an anode slurry was prepared by stirring at 1,500 rpm for 2 hours at room temperature using a homo disper mixer. The maximum temperature measured during stirring was approximately 50℃.

[0116] <Manufacture of Cathodes for Secondary Batteries>

[0117] The above anode slurry was applied to an aluminum thin film with a thickness of 15 μm, dried at 150°C for 1 hour, and then rolled to produce an anode for a secondary battery.

[0118]

[0119] Example 2: Preparation of a positive electrode for a secondary battery

[0120] Li(Ni) 0.86 Co 0.08 Mn 0.06A positive electrode slurry and a positive electrode for a secondary battery were prepared in the same manner as in Example 1, except that linear polyvinylidene fluoride (functional groups -COOH, -OH) with a functional group content of 3.6 mol%; branched polyvinylidene fluoride (functional groups -O-, -CO-) with a long chain branching number of 2.1 per 1,000 carbon atoms in the polymer chain and a functional group content of 2.0 mol%; and CNTs were used in a weight ratio of 95:1.8:1.2:2.

[0121]

[0122] Comparative Example 1: Preparation of a cathode for a secondary battery

[0123] Li(Ni) 0.86 Co 0.08 Mn 0.06 A positive electrode slurry and a positive electrode for a secondary battery were prepared in the same manner as in Example 1, except that linear polyvinylidene fluoride (functional groups -COOH, -OH) with a functional group content of 3.6 mol% and CNT were used in a weight ratio of 95:3:2.

[0124]

[0125] Comparative Example 2: Preparation of a cathode for a secondary battery

[0126] Li(Ni) 0.86 Co 0.08 Mn 0.06 A positive electrode slurry and a positive electrode for a secondary battery were prepared in the same manner as in Example 1, except that linear polyvinylidene fluoride (functional groups -COOH, -OH) with a functional group content of 3.6 mol%; branched polyvinylidene fluoride (functional groups -O-, -CO-) with a long chain branching number of 2.1 per 1,000 carbon atoms in the polymer chain and a functional group content of 2.0 mol%; and CNTs were used in a weight ratio of 95:1.5:1.5:2.

[0127]

[0128] Comparative Example 3: Preparation of a cathode for a secondary battery

[0129] Li(Ni) 0.86 Co0.08 Mn 0.06 A positive electrode slurry and a positive electrode for a secondary battery were prepared in the same manner as in Example 1, except that linear polyvinylidene fluoride (functional groups -COOH, -OH) with a functional group content of 3.6 mol%, branched polyvinylidene fluoride (functional groups -O-, -CO-) with 2.1 long-chain branches per 1,000 carbon atoms in the polymer chain and a functional group content of 3.6 mol%, and CNTs were used in a weight ratio of 95:2.25:0.75:2.

[0130]

[0131] Experimental Example 1: Evaluation of Storage Stability

[0132] The anode slurries prepared in Examples 1 and 2 and Comparative Examples 1 to 3, respectively, were stored in an environment of 25°C for 7 days, and then gelation was checked.

[0133]

[0134] Experimental Example 2: Measurement of Adhesion Strength

[0135] Each anode prepared in Examples 1 and 2 and Comparative Examples 1 to 3 was die-cut to a size of 150 mm × 20 mm, the anode surface was attached to a slide glass with double-sided tape, and lamination was performed to prepare three samples for a peel test.

[0136] Adhesion strength measurement

[0137] The above samples were loaded onto a UTM at intervals of 20 mm, and a 90° peel test (propagation speed: 300 mm / min) was performed to measure the peel resistance (gf / cm). The adhesion of each electrode was calculated from this, and the results are shown in Table 1 below.

[0138]

[0139] Experimental Example 3: Measurement of Dose Retention Rate

[0140] Manufacturing of half-cells

[0141] The positive electrodes for secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were each coated onto an aluminum thin film with a thickness of 15 μm, dried at 150°C for 1 hour, and then rolled to produce each positive electrode.

[0142] After stacking the anode prepared above together with Li-metal (anode) and a separator, an electrolyte solution in which 1M LiPF6 is dissolved in a solvent mixed in a volume ratio of 1:2:1 of EC:DMC:EMC was injected to prepare a lithium secondary battery (coin half cell) according to Examples 1 and 2 and Comparative Examples 1 to 3.

[0143] Measurement of capacity retention rate

[0144] For each of the lithium secondary batteries prepared above, charging was performed at 25°C with a constant current of 0.2C to 4.2V with a 1 / 200C cut-off. Afterward, discharging was performed with a constant current of 0.2C until the voltage reached 2.5V. Charging and discharging were considered as one cycle, and this cycle was repeated 100 times.

[0145] In addition, for each of the lithium secondary batteries manufactured above, charging was performed at 25°C with a constant current of 0.2C to 4.2V with a 1 / 200C cut-off, and then discharging was performed with a constant current of 0.2C until it reached 2.5V to measure the initial discharge capacity. Next, the lithium secondary battery was charged at 5°C with a constant current of 0.2C to 4.2V with a 1 / 200C cut-off, stored at 60°C for 4 weeks, and then discharged with a constant current of 0.2C until it reached 2.5V to measure the discharge capacity, thereby measuring the discharge capacity after 4 weeks.

[0146]

[0147] 1st Binder:2nd Binder Adhesion Strength (gf / mm) Slurry Storage Stability Cell Capacity Retention Rate (%) After 100 Cycles at Room Temperature After 4 Weeks of Storage at 60℃ Example 170: 302.51 Good 98.7 98.2 Example 260: 402.12 Good 99.1 98.9 Comparative Example 150: 501.37 Good 90.6 93.8 Comparative Example 280: 201.57 Gelation 88.7 89.2 Comparative Example 3100: 01.44 Gelation 83.5 85.5

[0148] Referring to Table 1 above, the cathodes for secondary batteries of Examples 1 and 2 exhibited excellent storage stability and superior adhesion compared to the cathodes for secondary batteries of Comparative Examples 1 to 3. Furthermore, when cathodes and lithium secondary batteries were manufactured using these, it was confirmed that cycle characteristics and capacity characteristics after high-temperature storage were also excellent. On the other hand, as in Comparative Example 1, when the content of the first binder is excessively low compared to the content of the second binder, it was confirmed that although the slurry storage stability is excellent, the adhesion is significantly reduced due to the low content of the first binder, which is related to adhesion. Additionally, as in Comparative Example 2, when the content of the second binder is excessively low compared to the content of the first binder, the low content of the second binder, which is related to slurry stability, results in reduced slurry storage stability, gelation, reduced binder dispersibility, and a decrease in adhesion. In addition, in the case of Comparative Example 3, which does not include the second binder, it was confirmed that, similar to Comparative Example 2, the storage stability of the slurry was lowered, causing gelation, and the dispersibility of the binder was also lowered, resulting in a decrease in adhesive strength.

Claims

1. Lithium transition metal oxide containing nickel; A first binder comprising a linear polymer; and A second binder comprising a branched polymer; comprising, The above linear polymer includes hydrogen bonding-capable functional groups, and The above branched polymer has 3.0 or fewer branches per 1,000 carbon atoms, and A positive electrode for a secondary battery, wherein the weight ratio of the first binder and the second binder is 1:0.26 to 1:0.

85.

2. In Paragraph 1, A positive electrode for a secondary battery, wherein the linear polymer comprises one or more functional groups selected from the group consisting of -COOH, -OH, -COONH-, -NHCONH-, and -O-.

3. In Paragraph 1, A positive electrode for a secondary battery, wherein the branched polymer comprises one or more functional groups selected from the group consisting of -OH, -O-, -CO-, -COO-, aryl, and arylene.

4. In Paragraph 1, The above linear polymer is a positive electrode for a secondary battery, which is a PVdF-based polymer.

5. In Paragraph 1, The above linear polymer is a positive electrode for a secondary battery having a weight-average molecular weight of 300,000 g / mol to 2,000,000 g / mol.

6. In Paragraph 1, The above branched polymer is a positive electrode for a secondary battery, which is a PVdF-based polymer.

7. In Paragraph 1, The above branched polymer is a positive electrode for a secondary battery having a weight-average molecular weight of 600,000 g / mol to 2,000,000 g / mol.

8. In Paragraph 1, The above branched polymer is a positive electrode for a secondary battery having long-chain branches.

9. In Paragraph 1, A positive electrode for a secondary battery, wherein the weight ratio of the first binder and the second binder is 1:0.33 to 1:0.

67.

10. In Paragraph 1, The above-mentioned anode is a cathode for a secondary battery that additionally includes a conductive material.

11. In Paragraph 1, The above lithium transition metal oxide is a cathode for a secondary battery having a Ni content of 80 mol% or more among the transition metals.

12. In Paragraph 1, A cathode for a secondary battery, wherein the above lithium transition metal oxide is represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x (Ni a Co b Mr c ) 1-x O2 In the above chemical formula 1, -0.3≤x≤0.3, 0.8≤a<1, 0 <b<0.2, 0<c<0.2, 및 a+b+c=1임.

13. A lithium secondary battery comprising a positive electrode for a secondary battery according to any one of claims 1 to 12.