Positive electrode and electrochemical device including the same

Abstract

One aspect of the present invention relates to a positive electrode active material for an electrochemical element. The positive electrode active material is a positive electrode granule containing a positive electrode active material and a binder. The positive electrode active material contains a lithium iron phosphate-based compound. The positive electrode active material is bound by the binder. The binder is uniformly distributed in the central portion and the surface portion of the positive electrode granule. The surface portion is a region near the surface of the granule from the surface of the granule to a predetermined depth in the direction of the center of the granule. The central portion is the portion other than the surface portion.

Description

Technical Field

[0001] The present invention relates to a positive electrode and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0110412 filed on August 31, 2022, and all of the content disclosed in the specification and drawings of the application is incorporated into this application.

Background Art

[0003] As the use of fossil fuels has increased rapidly, the demand for the use of alternative energy and clean energy has been increasing, and among them, the most actively studied field is the field of power generation and power storage using electrochemistry. Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually expanding.

[0004] Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used. Lithium secondary batteries are not only an energy source for mobile devices, but in recent years, they are being used as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, and their use area is also expanding as an application such as a power assist power source by grid connection.

[0005] As the positive electrode active material of a lithium secondary battery, a composite oxide of a lithium transition metal is used, and among these, a lithium cobalt composite metal oxide of LiCoO2 having a high operating voltage and excellent capacity characteristics is mainly used. However, LiCoO2 has very poor thermal characteristics due to the destabilization of the crystal structure by delithiation and is expensive, so there is a limit to its mass use as a power source in fields such as electric vehicles.

[0006] As materials to replace LiCoO2, lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate-based compounds (such as LiFePO4), or lithium nickel composite metal oxides (such as LiNiO2) have been developed. Among these, lithium iron phosphate-based compounds are attracting attention as materials that can replace LiCoO2 in terms of low cost, abundance of iron resources, and environmental protection. In addition, lithium iron phosphate has very excellent thermal stability due to the strong covalent bond between P - O, so it has fewer problems with oxygen elution compared to the cathode active materials of conventional materials such as LiCoO2, LiNiO2, and LiMnO4, and it is reported that the crystal lattice rearrangement is less likely to occur, so the structure of the substance is stable.

[0007] However, lithium secondary batteries using such lithium iron phosphate-based compounds (LFP) have a problem that the LiPF6 salt is hydrolyzed by moisture (H2O) present in the battery to generate HF, and the generated HF induces the elution of Fe from the LFP active material, deteriorating the durability of the battery. In addition, the eluted Fe moves to the negative electrode, damages the SEI layer on the surface of the active material, deposits on the negative electrode, and reduces the reaction site(s), inducing a problem of reducing the battery life.

[0008] In addition, the LFP material has a problem that the movement of Li ions is not smooth and is restricted because the oxygen structure is strongly bonded by being filled in the hexagonal closest-packed form, and the flow of electrons is not smooth due to low electrical conductivity. Therefore, it is necessary to improve such problems for the application of the LFP material. For this purpose, research is underway in the direction of adjusting the particle size to control the diffusion rate of lithium or coating the surface with other fibrous metals or carbon to improve the electrical conductivity. However, when the particle size of the active material is small and the surface area is high, and there are defects in the carbon coated on the surface and moisture is adsorbed at the defect positions, it is difficult to remove.

[0009] On the one hand, in the process of manufacturing a battery, the LFP active material is exposed to the outside air. At this time, if the moisture adsorbed on the active material is suppressed, the life characteristics of the battery using it are expected to be improved. Therefore, the development of a new form of LFP active material for suppressing the moisture adsorbed on the surface is required.

Summary of the Invention

Problems to be Solved by the Invention

[0010] The problem to be solved by the present invention is to provide a novel form of cathode active material that suppresses surface moisture adsorption and a method for manufacturing the same as the cathode active material of a lithium iron phosphate-based material.

[0011] Another object of the present invention is to provide a method for manufacturing a cathode active material having the above-described characteristics.

[0012] Furthermore, another object of the present invention is to provide an electrochemical element, for example, a lithium secondary battery, whose life characteristics are improved by suppressing moisture adsorption on the surface of the cathode active material.

Means for Solving the Problems

[0013] To achieve the above problems, According to one aspect of the present invention, cathode granules of the following embodiments are provided.

[0014] The cathode granules according to the first embodiment are cathode granules containing a cathode active material and a binder, wherein the cathode active material contains a lithium iron phosphate-based compound, the cathode active material is bound by the binder, the binder is uniformly distributed in the central portion and the surface portion of the cathode granules, the surface portion is a region near the surface of the granule from the surface of the granule to a predetermined depth in the direction of the center of the granule, and the central portion is the portion other than the surface portion.

[0015] According to the second embodiment, in the first embodiment, the binder may include a hydrophobic binder.

[0016] According to the third embodiment, in the first embodiment or the second embodiment, the positive electrode granules include a main domain having a concave groove portion from the surface to a predetermined depth in the central direction, a sub domain located in the concave groove portion, and a hollow portion formed between the main domain and the sub domain.

[0017] According to the fourth embodiment, in any one of the first to third embodiments, the average particle diameter D of the positive electrode granules 50 may be 20 μm to 300 μm.

[0018] According to the fifth embodiment, in any one of the first to fourth embodiments, the QBR (Quantified Binder Ratio) distribution according to the following formula 1 may have a value of 0.8 to 1.2.

[0019] [Formula 1] QBR = Bs / Bf In Formula 1, Bs represents the average value of the binder content in the region from the surface of the outermost contour of the positive electrode granules to the 15% point of the particle radius of the positive electrode granules, and Bf represents the average value of the binder content in the region from the center inside the positive electrode granules to the 15% point of the particle radius of the positive electrode granules.

[0020] According to the sixth embodiment, in any one of the first to fifth embodiments, the concave groove portion of the positive electrode granules has a circular shape and may have a diameter of 10 μm to 150 μm.

[0021] According to the seventh embodiment, in any one of the first to sixth embodiments, the binder may include a fluorine-based binder.

[0022] According to the eighth embodiment, in any one of the first to seventh embodiments, the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), or a mixture of two or more thereof.

[0023] According to the ninth embodiment, in any one of the first to eighth embodiments, the positive electrode granule may further include a conductive material, and the positive electrode active material and the conductive material may be bound by the binder.

[0024] According to another aspect of the present invention, a method for manufacturing a positive electrode granule of the following embodiment is provided.

[0025] The manufacturing method according to the tenth embodiment is adding a positive electrode active material and a binder to a dispersion medium to produce a slurry, and spray drying the slurry, wherein the positive electrode active material may include a lithium iron phosphate-based compound.

[0026] According to the eleventh embodiment, in the tenth embodiment, the binder may be a hydrophobic binder.

[0027] According to the twelfth embodiment, in the tenth or eleventh embodiment, the binder may include a fluorine-based binder.

[0028] According to the 13th embodiment, in any one of the 10th to 12th embodiments, the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), or a mixture of two or more of these.

[0029] According to another aspect of the present invention, a positive electrode of the following embodiment is provided.

[0030] The positive electrode according to the 14th embodiment is a current collector, and a positive electrode active material layer located on the current collector, and includes the positive electrode active material layer includes a plurality of positive electrode granules according to any one of the 1st to 9th embodiments.

[0031] According to still another aspect of the present invention, an electrochemical element of the following embodiment is provided.

[0032] The electrochemical element according to the 15th embodiment is a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, and the positive electrode includes the positive electrode according to the 14th embodiment.

Effect of the Invention

[0033] The positive electrode active material according to one aspect of the present invention suppresses moisture adsorption on the surface, thereby improving the life characteristics of the electrochemical element using the same.

[0034] The method for manufacturing a positive electrode active material according to another aspect of the present invention can provide a positive electrode active material, a positive electrode, and an electrochemical element having the above-described characteristics.

[0035] The following drawings attached to this specification illustrate desirable embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0036]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0037] Hereinafter, the present invention will be described in detail. However, the present invention is not limited only by the following content, and each component can be variously deformed or selectively mixed as necessary. Therefore, it must be understood that all modifications, equivalents or alternatives included in the spirit and technical scope of the present invention are incorporated.

[0038] In the specification, when a certain configuration "includes" a certain component, it means that, unless otherwise specified, it does not exclude other components, but may further include other components.

[0039] In this specification, the description of "A and / or B" means A or B, or all of these.

[0040] According to one aspect of the present invention, there is provided a positive electrode material that can be used in an electrochemical element, for example, a lithium secondary battery.

[0041] The positive electrode material is positive electrode granules containing a positive electrode active material and a binder, the positive electrode active material contains a lithium iron phosphate-based compound, the positive electrode active material is bound by the binder, the binder is uniformly distributed in the central portion and the surface portion of the positive electrode granules, the surface portion is a region near the surface of the granule from the surface of the granule to a predetermined depth in the direction of the center of the granule, and the central portion can be a portion other than the surface portion.

[0042] The "granule(s)" refers to composite particles containing a positive electrode active material and a binder. Specifically, the granule is one in which the positive electrode active material is bound by a binder and has the form of a group of particles. As will be described later, the granule may further contain a conductive material. When the granule further contains a conductive material, the granule may have the form of a group of particles by binding the positive electrode active material and the conductive material with the binder. The plurality of positive electrode granules can be used to form a positive electrode active material layer through a series of manufacturing processes.

[0043] In the positive electrode granules, the binder is uniformly distributed in the central portion and the surface portion. In one embodiment of the present invention, the surface portion may mean a region from the center of the particle size of the granule to the surface of the granule of 70% or more of the radius, preferably, a region to the surface of the granule of 85% or more, or 90% or more, or 95% or more of the radius.

[0044] Explaining the granule in more detail, a plurality of positive electrode active materials contained in the granule form aggregates while being in surface contact, line contact, point contact, or contact of two or more of these with each other and are uniformly distributed throughout the granule, and the binder is distributed throughout the granule so as to bind the uniformly distributed positive electrode active materials, whereby the plurality of positive electrode active materials of the granule can be fixed and bound to each other.

[0045] In one embodiment of the present invention, the granule may have an aspect ratio of 0.5 to 1.0. The aspect ratio means the ratio of the average length of the shortening of the granule to the average length of the major axis. At this time, the average length of the shortening indicates the average value of the lengths in the axial direction having the shortest length among the granules, and the average length of the major axis indicates the average value of the lengths in the axial direction having the longest length among the granules. When the aspect ratio of the granule satisfies such a range, it is advantageous in terms of having sufficient fluidity suitable for the process.

[0046] According to one aspect of the present invention, in order to provide a cathode material of a lithium iron phosphate-based material, the cathode active material contains a lithium iron phosphate-based compound.

[0047] In one embodiment of the present invention, the lithium iron phosphate-based compound may typically include lithium iron phosphate (LFP) having the chemical formula of LiFePO4; LiFe x M1 (1-x) P y M2 (1-y) O4 (where M1 is one or more of Mn, Co, Ni, Al, V, B, Cd, Cu, Mg, Zn, Ti, Nb, Zr, and Cr, 0 < x ≦ 1, M2 is one or more of Si, N, S, Cl, Br, and F, and 0 < y ≦ 1). The lithium iron-metal-phosphate (LMFP) having such a chemical formula; or a mixture thereof may be included. In one embodiment of the present invention, the lithium iron phosphate-based compound may include a compound having the chemical formula of LiFePO4.

[0048] In one embodiment of the present invention, the positive electrode active material may further include materials commonly used for the positive electrode of an electrochemical device in addition to the lithium iron phosphate-based compound. For example, the positive electrode active material may further include, in addition to the lithium iron phosphate-based compound, lithium transition metal oxides; lithium metal iron phosphates; lithium nickel-manganese-cobalt oxides; oxides in which a part of the lithium nickel-manganese-cobalt oxide is substituted with other transition metals; or may further include two or more of these. Specifically, in addition to the lithium iron phosphate-based compound, the positive electrode active material may include, for example, layered compounds such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3), Ni-site type lithium nickel oxides represented by; chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); lithium metal phosphates LiMPO4 (where M = CO, Ni or Mn); lithium nickel-manganese-cobalt oxides Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1); oxides in which a part of the lithium nickel-manganese-cobalt oxide is substituted with aluminum Li a [Ni b Co c Mnd Al e 1-f M 1 f O2 (where M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1); an oxide in which a part of lithium nickel-manganese-cobalt oxide is substituted with another fibrous metal Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, and M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo.). A disulfide compound; It may further contain Fe2(MoO4)3 and the like, but the positive electrode active material that may be further contained is not limited to these.

[0049] Figure 1 is a SEM (scanning electron microscope) image of a positive electrode granule according to an embodiment of the present invention. The SEM image is an image obtained at a magnification of 500.

[0050] Referring to Figure 1, a positive electrode granule according to an embodiment of the present invention may include a main domain having a groove portion from the surface to a predetermined depth in the central direction, a sub domain located in the groove portion, and a hollow portion formed between the main domain and the sub domain.

[0051] ​According to an embodiment of the present invention, although the method for manufacturing the positive electrode granules is not limited thereto, when the positive electrode granules are formed, a solvent trapped inside the granules evaporates while forming concave groove portions on the surface of the positive electrode granules, and granules of a small size can be supported on the concave groove portions. Accordingly, the positive electrode granules may include a main region in which the concave groove portions are formed, a sub-region located in the concave groove portions, and a hollow portion formed between the main region and the sub-region.

[0052] In an embodiment of the present invention, the positive electrode granules may include large-sized granules constituting the main region and small-sized granules constituting the sub-region. At this time, the sub-region may include one small-sized granule or a plurality of small-sized granules.

[0053] FIG. 2 is a SEM image of a cross-section of positive electrode granules according to an embodiment of the present invention. The SEM image is an image obtained at a magnification of 150 times.

[0054] Referring to FIG. 2, it can be confirmed that the positive electrode granules have a main region in which a hollow portion is formed and a sub-region in which a plurality of small-sized granules are included in the hollow portion. Thus, the positive electrode granules may include large-sized granules constituting the main region and a plurality of small-sized granules constituting the sub-region, and a hollow portion may be formed between the main region and the sub-region.

[0055] In an embodiment of the present invention, the lithium iron phosphate-based compound may have, for example, an average particle diameter D 50 of 100 nm to 500 nm, specifically 200 nm to 300 nm.

[0056] In one embodiment of the present invention, when a lithium iron phosphate-based compound is used as a conventional cathode active material to form a cathode, problems have been reported that due to the small particle size of the lithium iron phosphate-based compound, the packing density is high, and the diffusion rate of lithium ions and the electrical conductivity are low. To solve this problem, according to one aspect of the present invention, there is provided a cathode granule in the form of composite particles in which the lithium iron phosphate-based compound having the above-described size is bound by the binder. Thereby, the cathode granule has, for example, an average particle diameter D 50 is 20 μm to 300 μm, specifically 20 μm to 250 μm, 20 μm to 200 μm, 20 μm to 150 μm, 20 μm to 100 μm, 25 μm to 80 μm, 30 μm to 75 μm, 30 μm to 70 μm, 30 μm to 60 μm, 30 μm to 50 μm, 40 μm to 75 μm, 50 μm to 75 μm or 60 μm to 80 μm. In the present specification, when the cathode granule includes a main region and a sub-region, the size of the cathode granule may indicate the size of the main region, that is, the size of the large particle diameter granule.

[0057] In one embodiment of the present invention, when the cathode granule has a structure including a main region, a sub-region, and a hollow portion, the concave groove portion formed in the main region has, for example, a circular shape, and the diameter of the concave groove portion may be, for example, 10 μm to 150 μm. Specifically, the diameter of the concave groove portion may be, for example, 10 μm to 110 μm, 10 μm to 100 μm, 10 μm to 80 μm, 10 μm to 60 μm, 10 μm to 50 μm, 10 μm to 30 μm, 10 μm to 20 μm, 10 μm to 15 μm or 15 μm to 20 μm. The term "circular shape" includes not only the shape of a set of points having the same radius from the center as in the normal definition of a "circle", but also similar circular shapes such as an ellipse and a distorted circle.

[0058] In one embodiment of the present invention, when the cathode granule has a structure including a main region, a sub-region, and a hollow portion, the small particle diameter granules constituting the sub-region have, for example, an average particle diameter D of 5 μm to 50 μm, 5 μm to 40 μm, 10 μu to 30 μm, 15 μm to 25 μm or 15 μm to 20 μmm50 may have.

[0059] In this specification, the "average particle size D 50 " means the particle size at the 50% point of the cumulative particle number distribution by particle size, and the particle size may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and when the particles pass through the laser beam, the diffraction pattern difference due to the particle size is measured to calculate the particle size distribution. The D50 particle size can be measured by calculating the particle diameter at the point where the cumulative particle number distribution by particle size in the measuring device reaches 50%.

[0060] In this specification, the "diameter" of the concave groove portion may be measured by SEM image or mercury intrusion method.

[0061] In the present invention, the binder is uniformly distributed in the central part and the surface part of the positive electrode granules. Specifically, in one embodiment of the present invention, the positive electrode granules may have a QBR (Quantified Binder Ratio) distribution value of 0.8 to 1.2 according to the following formula 1.

[0062] [Formula 1] QBR = Bs / Bf In the formula 1, Bs represents the average value of the binder content in the region from the surface of the outermost contour of the positive electrode granule to the 15% point of the particle radius of the positive electrode granule, and Bf represents the average value of the binder content in the region from the inner center of the positive electrode granule to the 15% point of the particle radius of the positive electrode granule.

[0063] According to the definition of Formula 1 above, the closer the QBR distribution is to 1, the more uniform the binder distribution is on the surface and in the center of the positive electrode granules. The positive electrode granules according to one aspect of the present invention may have a QBR distribution value of 0.85 to 1.15, 0.9 to 1.1, or 0.95 to 1.05, but the present invention is not limited thereto.

[0064] In one embodiment of the present invention, the binder content for the QBR measurement can be measured, for example, by a method of measuring the content of an element specific to the binder used or a method of measuring the content of a functional group specific to the binder. For example, when a fluorine-based binder is used as the binder as described later, the binder content can be measured by measuring the content of fluorine element. At this time, the content of the fluorine element can be measured, for example, by FT-IR analysis method or the like.

[0065] In the present specification, the sphericity of the positive electrode granules can be a value obtained by dividing the circumference of a circle having the same area as the projected image by the length around the projected image when the positive electrode granules are projected. Specifically, it can be represented by the following Formula 1. The sphericity can be measured using a particle shape analyzer, for example, Sysmex FPIA3000 manufactured by Malvern.

[0066] [Formula 1] Sphericity = (circumference of a circle having the same area as the image projected by the positive electrode granules / length around the projected image) × 100

[0067] In the present specification, the density of the positive electrode granules can be calculated as the ratio of weight / volume by obtaining the volume from the average particle diameter of the positive electrode granules and measuring the weight of the positive electrode granules.

[0068] The type of the binder that binds the positive electrode active material and / or the conductive material is not particularly limited as long as it is a binder that can be used as a conventional positive electrode binder.

[0069] In one embodiment of the present invention, the binder may include a hydrophobic binder. According to the present invention, in order to prevent or improve the problem that moisture is adsorbed and decomposed on the lithium iron phosphate-based compound, it is desirable to use a hydrophobic binder as the binder for binding the lithium iron phosphate-based compound.

[0070] In one embodiment of the present invention, the binder, specifically the hydrophobic binder, may include, for example, a fluorine-based binder.

[0071] The fluorine-based binder is a binder containing at least one fluorine (F) atom in its structure. For example, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), or a mixture of two or more of these may be mentioned, but the present invention is not limited thereto. When the fluorine-based binder is used as the binder to aggregate and bind the positive electrode active material to form positive electrode granules, it can have an advantageous effect in suppressing and preventing moisture adsorption on the surface of the positive electrode granules. In addition, by using the fluorine-based binder as the binder, it can have an advantageous effect in improving the binding force of the positive electrode active material and the adhesion force between the positive electrode granules and the current collector, but the present invention is not limited thereto.

[0072] In one embodiment of the present invention, using a hydrophobic binder, such as a fluorine-based binder, as the binder is more advantageous in stabilizing the lithium iron phosphate-based active material than using a normal hydrophilic binder, such as polyacrylonitrile (PAN).

[0073] In one embodiment of the present invention, the positive electrode granule may further include a conductive material as necessary in addition to the positive electrode active material and the binder. When the positive electrode granule further includes a conductive material, the conductive material may be fixed in the granule by binding of the conductive material and the positive electrode active material particles or binding of the conductive material particles by the binder.

[0074] As the conductive material, any material that does not induce a chemical change in the battery and has conductivity can be used without particular limitation as to its type.

[0075] In one embodiment of the present invention, examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0076] According to one aspect of the present invention, as described above, a novel positive electrode material containing the lithium iron phosphate-based compound as a positive electrode active material by the positive electrode granule can be provided.

[0077] According to another aspect of the present invention, a method for manufacturing the above-described positive electrode granule is provided.

[0078] The positive electrode granule is not limited to this production method, but can be produced by mixing the positive electrode active material with the binder and then granulating by a spray drying method.

[0079] The manufacturing method includes a step of adding a positive electrode active material and a binder to a dispersion medium to produce a slurry, and a step of spray drying the slurry, and the positive electrode active material includes a lithium iron phosphate-based compound.

[0080] First, the conductive material and additional additives are selectively dispersed or dissolved in a dispersion medium (solvent for the binder) together with the positive electrode active material and the binder to obtain a slurry in which the positive electrode active material and the binder are dispersed or dissolved.

[0081] Water is most preferably used as the dispersion medium used to obtain the slurry, but an organic solvent may also be used. Examples of organic solvents include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, and diglyme; amides such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; sulfur-based solvents such as dimethyl sulfoxide and sulfolane; etc. Among them, alcohols are desirable. When an organic solvent having a boiling point lower than that of water is used in combination, the drying rate can be increased during fluidized granulation. In addition, since the dispersibility or solubility of the negative electrode binder can change, the viscosity and fluidity of the slurry can be adjusted according to the amount or type of the dispersion medium, so that the production efficiency can be improved.

[0082] The amount of the dispersion medium used when preparing the slurry can be an amount such that the solid content concentration of the slurry is usually in the range of 1 to 50 wt%, or 5 to 50 wt%, or 10 to 30 wt%.

[0083] The method or order of dispersing or dissolving the positive electrode active material, the binder, etc. in the dispersion medium is not particularly limited. For example, there are methods of adding the positive electrode active material and the binder to the dispersion medium and mixing them, and methods of dissolving or dispersing the binder in the dispersion medium and then finally adding the positive electrode active material and mixing them. When a conductive material or an additive is included, these components can be added when the positive electrode active material is charged. Examples of the mixing means include a ball mill, a sand mill, a bead mill, a pigment disperser, a stone mill, an ultrasonic disperser, 1737092196677_0.naver?docId=430912&cid=60261&categoryId=60261 Examples of the mixing equipment include a homogenizer and a planetary mixer. The mixing can be carried out, for example, in the range of room temperature to 80 °C for 10 minutes to several hours.

[0084] Next, the slurry is spray-dried. The spray-drying method is a method of spraying the slurry into hot air for drying. A typical example of the apparatus used in the spray-drying method is an atomizer. There are two types of atomizers: a rotating disk type and a pressure type. The rotating disk type is a method in which the slurry is introduced almost at the center of a disk rotating at high speed, and when the slurry is detached from the disk by the centrifugal force of the disk, it is atomized and dried. The rotation speed of the disk depends on the size of the disk, but is usually 5,000 to 35,000 rpm, preferably 15,000 to 30,000 rpm. On the other hand, the pressure type is a method in which the slurry is pressurized and sprayed in a mist from a nozzle for drying.

[0085] The temperature of the slurry to be sprayed is usually room temperature, but it may be heated to a temperature above room temperature. The hot air temperature during spray drying is usually 80 °C to 250 °C, preferably 100 °C to 200 °C. In the spray-drying method, the method of inhaling the hot air is not particularly limited. For example, there are a method in which the hot air and the spray direction are in a horizontal parallel flow, a method in which the slurry is sprayed from the top of the drying tower and descends together with the hot air, a method in which the sprayed droplets and the hot air are in countercurrent contact, and a method in which the sprayed droplets first flow in parallel with the first hot air and then fall by gravity for countercurrent contact.

[0086] Note that the resultant obtained by selectively spray-drying, that is, the granules may be heat-treated to harden the surface of the granules. In this case, the heat treatment temperature can usually be 80 °C to 300 °C.

[0087] According to another aspect of the present invention, a positive electrode to which the above-described positive electrode granules are applied is provided.

[0088] The positive electrode includes a current collector and a positive electrode active material layer located on the current collector, and the positive electrode active material includes a plurality of the above-described positive electrode granules.

[0089] In one embodiment of the present invention, the positive electrode active material layer is formed by stacking a plurality of the positive electrode granules in a layered structure, and has a plurality of fine pores provided by an interstitial volume, which is a space between the positive electrode granules, and exhibits porosity characteristics derived from such a structure. At this time, the ion diffusion rate of the positive electrode active material layer is determined by factors such as the size and number of the fine pores, and the electrode capacity of the positive electrode active material layer can be determined by the packing density of the granules.

[0090] In this specification, the porosity of the positive electrode active material layer indicates the ratio of the volume occupied by pores to the total volume in the positive electrode active material layer, uses volume% as its unit, and can be used interchangeably with terms such as void fraction and porosity.

[0091] The porosity of the positive electrode active material layer can be measured, for example, by the BET (Brunauer - Emmett - Teller) measurement method using nitrogen gas, the mercury porosimeter method, and ASTM D - 2873. Alternatively, the true density of the electrode can be calculated from the density (apparent density) of the electrode, the composition ratio of the materials contained in the electrode, and the density of each component, and the porosity of the electrode can be calculated and measured from the difference between the apparent density and the true density. For example, the porosity can be calculated by the following Equation 3.

[0092] [Equation 3] Porosity (volume%) = {1 - (apparent density / true density)} × 100 In Equation 3 above, the apparent density can be calculated from the following Equation 4.

[0093] [Equation 4] Apparent density (g / cm 3 ) = (weight of the positive electrode active material layer (g)) / {(thickness of the positive electrode active material layer (cm)) × (area of the positive electrode active material layer (cm 2 ))} According to one embodiment of the present invention, the above-described positive electrode granules suppress the adsorption of moisture on the surface, thereby suppressing the elution of iron (Fe) from the positive electrode active material due to the reaction with moisture.

[0094] According to one embodiment of the present invention, the positive electrode to which the above-described positive electrode granules are applied has an effect of increasing the ion diffusion rate compared to a positive electrode to which a lithium iron phosphate-based compound is applied as a conventional positive electrode active material. The ion diffusion rate can be measured, for example, using the GITT (Galvanostatic Intermittent Titration Technique) method in the charged and discharged states. According to one embodiment of the present invention, the ion diffusion rate is measured by the GITT method under the SOC50% condition and can be expressed in units of cm 2 / s, but is not limited thereto. The ion diffusion rate means the degree of ion diffusion in a specific substance. Specifically, in this specification, unless otherwise specified, the ion diffusion rate indicates the diffusion rate of lithium ions.

[0095] The overall "thickness" of the positive electrode active material layer or the "thickness" of each layer included therein can indicate a value measured by a known method for measuring thickness. The method for measuring the thickness is not limited thereto, and for example, it can be a value measured using a thickness measuring instrument (Mitutoyo, VL-50S-B).

[0096] In one embodiment of the present invention, the current collector can be used without particular limitation as long as it does not induce a chemical change in the battery and has high conductivity. The current collector can be, for example, stainless steel, aluminum, nickel, titanium, fired carbon, copper, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. Further, the current collector can also form fine irregularities on its surface to enhance the adhesive force of the active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body are possible. On the other hand, in one embodiment of the present invention, the current collector can have a thickness of 10 μm to 50 μm, but is not particularly limited thereto. The current collector can have a thickness of, for example, 10 μm to 20 μm.

[0097] In one embodiment of the present invention, a primer layer that covers all or at least a part of the surface can be formed on at least one surface of the current collector. The primer layer can be introduced to improve the bonding strength and electrical conductivity between the current collector and the positive electrode active material layer. The primer layer may contain a binder and a conductive material, and the contents of the binder and the conductive material in the positive electrode active material layer described above can be incorporated.

[0098] In one embodiment of the present invention, the primer layer can further contain, for example, a dispersant for dispersing these in addition to the binder and the conductive material.

[0099] In one embodiment of the present invention, the primer layer contains the above-described composition and can have a thickness of 300 nm to 1.5 μm, specifically 700 nm to 1.3 μm, but is not limited thereto.

[0100] In one embodiment of the present invention, the positive electrode can be manufactured by a method including a step of forming a positive electrode active material layer on at least one surface of a current collector.

[0101] In one embodiment of the present invention, the positive electrode active material layer can be formed without using another solvent by a method of applying the positive electrode granules onto one surface of a current collector and then pressing (press), but the method for manufacturing the positive electrode is not limited thereto.

[0102] In one embodiment of the present invention, the temperature and pressure conditions for each of the granule coating step and the pressing step for manufacturing the positive electrode can be carried out under normal conditions and are not particularly limited in the present invention.

[0103] According to still another aspect of the present invention, there is provided an electrochemical device including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes the one described above as the positive electrode.

[0104] In one embodiment of the present invention, the negative electrode, the separator, and the electrolyte can be used without particular limitation as long as they can be used in a normal electrochemical device within a range not inhibiting the object of the present invention, and thus the description of this specific type is omitted.

[0105] In one embodiment of the present invention, the outer shape of the electrochemical device may be, for example, a coin type, a cylindrical type, a pouch type, or a rectangular type, and the outer shape of the battery is not particularly limited. Further, the electrochemical device can be used not only as a battery cell used as a power source for a small device but also as a unit cell for a medium- or large-sized battery module including a plurality of battery cells, and its usage form is not particularly limited.

[0106] Hereinafter, examples will be given for a detailed description in order to specifically explain the present invention. However, the examples according to the present invention can be deformed into various forms, and the scope of the present invention is not limited by the following examples. The examples of the present invention are provided to more fully explain the present invention to those having average knowledge in the art.

[0107] Preparation of Positive Electrode Granules and Positive Electrode The positive electrodes of Example 1, Example 2, and Comparative Example 1 were manufactured by the following method.

[0108] Example 1 [Manufacture of Positive Electrode Granules] As the positive electrode active material, LFP (LiFePO4), as the conductive material, carbon black (SuperC65), and as the binder, PVDF were mixed together with water as the dispersion medium, and a slurry was produced using a homogenizer.

[0109] The produced slurry was dried using a spray dryer to produce positive electrode granules containing a plurality of positive electrode active materials and conductive materials and including a binder that binds the positive electrode active material and the conductive material. At this time, as the conditions of the spray dryer, the raw material supply rate was 30 rpm, the spray method was the disk method, and the rotation speed was controlled to 5,000 rpm.

[0110] The obtained positive electrode granules were separated and removed of coarse powder exceeding 100 μm and fine powder less than 50 μm using an industrial sieve to obtain positive electrode granules with a size of 50 to 100 μm.

[0111] The SEM images of the obtained positive electrode granules are shown in FIGS. 1 and 2. The average particle size D of the obtained positive electrode granules 50 is 75 μm. Referring to FIGS. 1 and 2, the positive electrode granules are formed with circular concave groove portions having an average diameter of 15 μm in the direction from the surface to the center, and the concave groove portions are confirmed to be in a form containing granules of fine powder with an average particle size D 50 of 8 μm.

[0112] [Manufacture of Positive Electrode] Each of the manufactured positive electrode granules was applied to an aluminum current collector and pressed at a linear pressure of 1 ton to form a positive electrode active material layer, thereby manufacturing a positive electrode (loading amount 550 mg / 25 cm 2 , thickness 115 μm) Example 2 As the conditions of the spray dryer, the raw material supply rate was 30 rpm, the spray method was the disk method, and the rotation speed was controlled to 10,000 rpm to obtain positive electrode granules with a size of 10 to 50 μm (average particle size D 50A positive electrode was manufactured in the same manner as in Example 1, except that a positive electrode granule having a particle size of 30 μm was obtained.

[0113] Comparative Example 1 Instead of the positive electrode granules, LFP (LiFePO4) was applied onto the current collector at the same loading amount and rolled to manufacture a positive electrode.

[0114] Physical Property Evaluation of Electrodes The life characteristics of the manufactured positive electrodes of Example 1, Example 2, and Comparative Example 1 were evaluated by the following method, and the results are shown in Table 1 and Figure 3 below.

[0115] First, as the positive electrode, the positive electrode manufactured above was prepared, and as the negative electrode, a negative electrode (thickness: 60 μm) using graphite as the active material on the current collector was prepared. An electrode assembly was manufactured with a porous polyethylene separator (15 μm) interposed between the positive electrode and the negative electrode manufactured as described above, and after positioning the electrode assembly inside the case, an electrolytic solution was injected into the case to manufacture a lithium secondary battery. At this time, the electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3).

[0116] For each of the lithium secondary battery cells manufactured as described above, charging was performed at 45 °C in CC / CV mode to 3.6 V at 0.33C, and discharging was performed at a constant current of 0.33C to 2.5 V, and the capacity retention rate when performing 100 charge-discharge experiments was measured.

[0117]

Table 1

[0118] From the results in Table 1 and Figure 3, it was confirmed that by using the positive electrode granules manufactured using the positive electrode active material of the lithium iron phosphate-based material, the life characteristics of the battery using the lithium iron phosphate-based material can be improved.

[0119] Evaluation of Elution Amount of Iron (Fe) The elution amount of iron (Fe) was measured from the battery using the positive electrodes of the manufactured Example 1 and Comparative Example 1, and the results are shown in Table 2 below.

[0120] The elution amount of iron was evaluated by a method of separating the negative electrode from the battery and measuring the content of Fe by ICP elemental analysis of the negative electrode.

[0121]

Table 2

[0122] From the results in Table 2 above, it can be seen that by using the positive electrode according to one aspect of the present invention, the moisture adsorption on the surface of the positive electrode is suppressed and the elution of iron is suppressed, thereby improving the life characteristics during the driving of the battery using LFP.

Claims

1. A positive electrode granule containing a positive electrode active material and a binder, wherein the positive electrode active material contains a lithium iron phosphate-based compound, the positive electrode active material is bound by the binder, the binder is uniformly distributed in the central portion and the surface portion of the positive electrode granule, the surface portion is a region near the surface of the granule from the surface of the granule to a predetermined depth in the direction of the center of the granule, and the central portion is the portion other than the surface portion, and the positive electrode granule is characterized by this.

2. The positive electrode granule according to claim 1, wherein the binder contains a hydrophobic binder.

3. The positive electrode granule has a main region having a concave groove portion from the surface to a predetermined depth in the central direction, a sub-region located in the concave groove portion, and a hollow portion formed between the main region and the sub-region, and the positive electrode granule according to claim 1 is characterized by including these.

4. The average particle diameter D of the positive electrode granules ５０ The positive electrode granule according to claim 1, characterized in that the average particle diameter D is 20 μm or more and 300 μm or less.

5. The positive electrode granule according to claim 1, wherein the QBR (Quantified Binder Ratio) distribution according to the following formula 1 has a value of 0.8 to 1.

2. 【Formula 1】 QBR = Bs / Bf In the formula 1, Bs represents the average value of the binder content in the region from the outermost surface of the positive electrode granule to the 15% point of the particle radius of the positive electrode granule, and Bf represents the average value of the binder content in the region from the center inside the positive electrode granule to the 15% point of the particle radius of the positive electrode granule.

6. The positive electrode granule according to claim 3, wherein the concave groove portion of the positive electrode granule has a circular shape and a diameter of 10 μm to 150 μm.

7. The positive electrode granule according to claim 1, wherein the binder contains a fluorine-based binder.

8. The positive electrode granule according to claim 1, wherein the binder contains polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), or a mixture of two or more of these.

9. The positive electrode granule further contains a conductive material, and the positive electrode active material and the conductive material are bound by the binder, and the positive electrode granule according to claim 1 is characterized by this.

10. A step of adding a positive electrode active material and a binder to a dispersion medium to produce a slurry; A step of spray-drying the slurry, and including; A method for producing positive electrode granules, characterized in that the positive electrode active material contains a lithium iron phosphate-based compound.

11. The method for producing positive electrode granules according to claim 10, characterized in that the binder is a hydrophobic binder.

12. The method for producing positive electrode granules according to claim 10, characterized in that the binder contains a fluorine-based binder.

13. The method for producing positive electrode granules according to claim 10, characterized in that the binder contains polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), or a mixture of two or more of these.

14. A current collector; A positive electrode active material layer located on the current collector, and including; A positive electrode, characterized in that the positive electrode active material layer contains a plurality of positive electrode granules according to any one of claims 1 to 9.

15. An electrochemical element, including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution; The electrochemical element, characterized in that the positive electrode contains the positive electrode according to claim 14.

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