Method for manufacturing cathode active material for lithium secondary battery

Abstract

A method for manufacturing an LMFP-based positive electrode active material is disclosed. A method for manufacturing a positive electrode active material according to the present invention comprises: (a) a step of mixing and grinding a plurality of raw materials and a solvent containing one or more of Li, Mn, Fe, P, Mg, and Ti to form a slurry; (b) a step of spray-drying the slurry to form a powder; and (c) a step of calcining the powder to produce a positive electrode active material represented by Formula 1 below. [Equation 1] LixMnaFebTicMgdPO4(0.9≤x≤1.1, a+b+c+d=1, 0.986

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery, and more specifically, to a method for manufacturing a lithium manganese iron phosphate (LMFP) positive electrode active material for a lithium secondary battery. Background Technology

[0003] Lithium iron phosphate (LFP) cathode active material is an olivine-based structure composed of octahedral sites of FeO6 and tetrahedral sites of PO4, and is a material in which lithium ions are deinserted and inserted through a one-dimensional pathway.

[0004] LFP cathode active material has a main composition of Li, Fe, and P, and offers a cost advantage over NCA or NCM materials, which mainly use Ni and Co, due to the lower cost of metal minerals. In addition, LFP cathode active material has excellent thermal stability and lifespan characteristics because its structure is stable due to strong PO bonds, preventing oxygen dissociation at high temperatures during charging.

[0005] However, LFP cathode active material has a low operating voltage (3.4 V vs. Li + It has the disadvantage of low energy density due to the iron (Fe) group. To overcome this drawback, research is currently being conducted on lithium manganese iron phosphate (LMFP) cathode active materials in which manganese (Mn) is substituted for the iron (Fe) group in LFP cathode active materials.

[0006] Lithium manganese iron phosphate (LMFP) having an olivine crystal structure has some of the iron replaced by manganese compared to lithium iron phosphate (LFP), resulting in improved operating voltage and energy density. However, when iron is replaced by manganese, stability and conductivity are adversely affected, and the degree of capacity development and cycling performance may be degraded. In particular, the fabrication of electrodes requires a process of rolling the electrodes under high pressure, which causes particle breakage in the LMFP cathode active material. Consequently, this leads to an increase in micropores and surface area of ​​the LMFP cathode active material, resulting in a problem of degraded electrochemical performance. The problem to be solved

[0008] The problem that the present invention aims to solve is to provide a method for manufacturing a positive electrode active material for a lithium secondary battery that can reduce particle breakage.

[0009] In addition, the problem that the present invention aims to solve is to provide a method for manufacturing a positive electrode for a lithium secondary battery that can reduce particle breakage.

[0010] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0012] A method for manufacturing a positive electrode active material according to an embodiment of the present invention for solving the above problem comprises: (a) a step of mixing and grinding a plurality of raw materials and a solvent including one or more of Li, Mn, Fe, P, Mg, and Ti to form a slurry; (b) a step of spray-drying the slurry to form a powder; and (c) a step of calcining the powder to manufacture a positive electrode active material represented by Formula 1 below.

[0013] [Equation 1]

[0014] Li x Mn a Fe b Ti c Mg d PO4(0.9≤x≤1.1, a+b+c+d=1, 0.986 <a+b<1, 0<c<0.007, 0<d<0.007)

[0015] For example, the positive active material manufactured by the method according to an embodiment of the present invention is LiMn 0.594 Fe 0.396 Ti 0.005 Mg 0.005 It may be a Ti and Mg-doped LMFP-based cathode active material represented as PO4.

[0016] Preferably, 0.004≤c≤0.006 and 0.004≤d≤0.006 may be possible.

[0017] In step (a) above, one or more of a dispersant and a carbon raw material may be additionally mixed. The carbon raw material may include one or more of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, a material having a crystal structure including graphene, and a material having a crystal structure including graphite. The dispersant may include one or more of citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, maleic acid, oxalic acid, malonic acid, and ascorbic acid.

[0018] One or more of the above-mentioned multiple raw materials may additionally include one or more elements among Al, B, Ca, Si, Sr, V, Cr, Co, Ni, Cu, Zn, Ba, W, Nb, Cd, Pb, Mo, Ta, La, Ce, Er, Ho, Zr, Y, and Sr.

[0019] Step (a) above can be performed in a wet milling machine.

[0020] The above step (b) can be performed in a spray dryer, and preferably, to obtain a spherical positive active material, it can be performed under conditions of a spray pressure of 0.5 to 2.5 bar, a main chamber temperature of 200 to 300°C, and an outlet temperature of 80 to 160°C.

[0021] In step (c) above, firing can be performed at 630 to 700°C.

[0022] The positive active material produced by the method according to the present invention may be in the form of secondary particles. The positive active material may be spherical.

[0024] A method for manufacturing a positive electrode for a lithium secondary battery according to the present invention for solving the above problem includes a process of applying a positive electrode material comprising a positive electrode active material, a conductive material, and a binder manufactured by the above-described method to a current collector, and then compressing it using a 4-ton press process. Effects of the invention

[0026] According to the method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention, Mg and Ti are simultaneously doped into a lithium manganese phosphate positive electrode active material, and the content of Mg and Ti is controlled to less than 0.007 mol, thereby reducing particle breakage during the manufacturing of the positive electrode.

[0027] The cathode for lithium secondary batteries manufactured through this process can improve discharge capacity and enable smooth insertion and extraction of lithium movement.

[0028] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below. Brief explanation of the drawing

[0030] Figure 1 schematically illustrates a method for manufacturing a positive electrode active material according to an embodiment of the present invention. Figure 2 shows an SEM image of the positive electrode active material prepared according to Example 1. Specific details for implementing the invention

[0031] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0032] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to some embodiments of the present invention and a method for manufacturing a positive electrode for a lithium secondary battery including the same will be described.

[0034] Cathode active material for lithium secondary batteries

[0035] Research is underway on lithium manganese iron phosphate (LMFP) cathode active materials in which manganese (Mn) is substituted for the iron (Fe) in lithium iron phosphate (LFP) cathode active materials.

[0036] The positive electrode active material according to the present invention relates to such an LMFP-based positive electrode active material. More specifically, the positive electrode active material according to the present invention relates to an LMFP-based positive electrode active material doped with Mg and Ti.

[0037] The positive active material according to the present invention is represented by the following formula 1.

[0038] [Equation 1]

[0039] Li x Mn a Fe b Ti c Mg d PO4

[0040] (0.9≤x≤1.1, a+b+c+d=1, 0.986 <a+b<1, 0<c<0.007, 0<d<0.007)

[0041] For example, the positive active material according to an embodiment of the present invention is LiMn 0.594 Fe 0.396 Ti 0.005 Mg 0.005 It may be a Ti and Mg-doped LMFP-based cathode active material represented as PO4.

[0042] The cathode active material according to the present invention is an LMFP-based cathode active material comprising Mn and Fe as main metals other than Li. The molar ratio of Fe to Mn may preferably be 1:1 to 1:1.5. When the molar ratio between Fe and Mn is 1:1 to 1:1.5, energy density can be improved without impairing battery stability. If the molar ratio of Mn to Fe is less than 1, the effect of improving energy density is not significant, and if it exceeds 1.5, quality problems may occur as the stability of the lithium secondary battery is reduced.

[0043] In the cathode active material according to the present invention, Ti and Mg are each included in an amount of less than 0.007 moles relative to 1 mole of the total of Mn, Fe, Ti, and Mg. Accordingly, Mn and Fe are included in an amount exceeding 0.986 moles in total. Ti and Mg contribute to reducing particle breakage. However, if Ti or Mg is included in an amount of 0.007 moles or more, particle size control may not be achieved smoothly and discharge capacity characteristics may be impaired.

[0044] Preferably, 0.004≤c≤0.006, 0.004≤d≤0.006, that is, Ti and Mg may be included in amounts of 0.004 to 0.006 moles, for example, 0.005 moles, respectively, with respect to 1 mole of total Mn, Fe, Ti and Mg.

[0045] The above-mentioned cathode active material may additionally contain carbon. In the case of LMFP-based cathode active materials, there is a disadvantage of relatively low electrical conductivity compared to LFP-based cathode active materials as Fe is replaced by Mn. This low electrical conductivity can be improved by introducing a conductive element, such as carbon, into the cathode active material. Carbon may be included as a carbon raw material along with various raw materials during the initial slurry formation stage for manufacturing the cathode active material. Alternatively, it may be introduced separately in subsequent processes, such as by adding to spray-dried powders or by adding to the calcined product.

[0046] The cathode active material according to the present invention may be doped or coated with one or more elements selected from Al, B, Ca, Si, Sr, V, Cr, Co, Ni, Cu, Zn, Ba, W, Nb, Cd, Pb, Mo, Ta, La, Ce, Er, Ho, Zr, Y, and Sr, in addition to Mg, Ti, and optionally C, as needed for improving high-temperature lifespan and thermal stability. These elements may be included in an amount of up to 0.1 mol, more preferably 0.05 mol, and even more preferably 0.01 mol or less.

[0047] The above positive active material may be in the form of secondary particles. The above positive active material may be substantially spherical. Here, "spherical" means not only a sphere in the dictionary sense, but also includes those that are intuitively recognized as spherical by those skilled in the art.

[0049] Method for manufacturing positive electrode active material

[0050] Figure 1 schematically illustrates a method for manufacturing a positive electrode active material according to an embodiment of the present invention.

[0051] Referring to FIG. 1, the method for manufacturing an anode active material according to the present invention includes a slurry forming step (S110), a spray drying step (S120), and a calcination step (S130).

[0052] First, in the slurry formation step (S110), a slurry is formed by mixing and grinding the Li raw material, Mn, Fe raw material, P raw material, Mg raw material, Ti raw material, and solvent. At this time, the molar ratio of each raw material is adjusted to satisfy Equation 1.

[0053] Each raw material may be any known material without limitation. Additionally, a single raw material may contain two components, such as LiH2PO4 or FePO4. Examples of Li raw materials may be used, such as LiOH, Li2CO3, LiH2PO4, Li(OH)·H2O, LiNO3, LiH2PO4, etc. Examples of Mn raw materials may be used, such as MnO2, Mn3O4, etc. Examples of Fe raw materials may be used, such as FePO4, Fe2O3, Fe3O4, etc. Examples of P raw materials may be used, such as LiH2PO4, FePO4, etc. Examples of Mg raw materials may be used, such as MgO, Mg(OH)2, etc. Examples of Ti raw materials may be used, such as TiO2.

[0054] Water can be used as the solvent, and one or more types of various organic solvents can also be used.

[0055] Meanwhile, in the slurry formation step (S110), one or more of the carbon raw materials and dispersants may be additionally mixed.

[0056] Carbon raw materials for improving the electrical conductivity of a lithium secondary battery may be mixed in an amount of about 10% by weight or less, more preferably about 5% by weight or less, and most preferably about 2% by weight or less, based on 100% by weight of the total raw materials, and a dispersant for uniform dispersion of raw materials in the slurry may be mixed in an amount of about 10% by weight or less, more preferably about 5% by weight or less. If carbon raw materials and dispersants are added in excess, adverse effects on the crystal growth of the cathode active material may increase.

[0057] The carbon raw material may include one or more of glucose, sucrose, fructose, lactose, maltose, graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, a material having a crystal structure containing graphene, and a material having a crystal structure containing graphite.

[0058] The dispersant may include one or more of glucose, citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, maleic acid, oxalic acid, malonic acid, and ascorbic acid.

[0059] The slurry formation step (S110) can be performed in a known wet milling device, for example, a bead mill. The slurry formation time in the bead mill can be about 1 to 10 hours. The rotation speed in the bead mill, etc. can be performed at 1000 to 5000 rpm.

[0061] Next, in the spray drying step (S120), the formed slurry is spray-dried to form a powder.

[0062] The spray drying step (S120) can be performed using a spray dryer.

[0063] The spray pressure of the spray dryer may be 0.5 to 2.5 bar, preferably 1 to 2 bar. The temperature of the main chamber may be 200 to 300°C, preferably 220 to 260°C. In addition, the discharge port temperature of the spray dryer may be set to 80 to 160°C, preferably 100 to 130°C. By setting the spray pressure of the spray dryer, the main chamber temperature, and the discharge port temperature as described above, spherical powder can be obtained from the slurry through spray drying.

[0064] After grinding the slurry as described above, secondary particles are generated through spray drying, and the shape of the secondary particles can be maintained during the subsequent calcination stage.

[0066] Next, in the calcination step, the obtained powder is calcined to produce an anode active material represented by Equation 1.

[0067] [Equation 1]

[0068] Li x Mn a Fe b Ti c Mg d PO4(0.9≤x≤1.1, a+b+c+d=1, 0.986 <a+b<1, 0<c<0.007, 0<d<0.007)

[0069] In step (c) above, calcination can be performed at 630 to 700°C. If the calcination temperature is too low, it is difficult to achieve the desired performance of the cathode active material, and if the calcination temperature is too high, energy consumption may increase without improving the effect. Calcination can be performed for about 1 to 10 hours, and preferably for 3 to 8 hours.

[0070] Calcination can be performed under an inert gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere.

[0072] The cathode active material manufactured by the method according to the present invention may exhibit a particle size distribution, specifically a volume-cumulative particle size distribution (PSD) after the press process for electrode manufacturing, where (D90-D10) / D50 is 1.2 or less. D50 can be approximately 7 to 8.5 μm. (D90-D10) / D50 can be viewed as an indicator of the uniformity of the particle distribution. A smaller (D90-D10) / D50 value indicates higher particle distribution uniformity, while a larger (D90-D10) / D50 value indicates lower particle distribution uniformity. Due to the 4-ton press process, significant particle breakage may occur, resulting in an increase in fine particles of approximately 1.4 μm or less; in this case, D10 decreases. Even with a similar D50 particle size, if D10 decreases, the value of D90-D10 increases, which may lead to a decrease in the uniformity of the particle distribution. Therefore, it is desirable to keep (D90-D10) / D50 as low as possible after a press process such as a 4-ton press process. In the present invention, by simultaneously doping Ti and Mg into the LMFP cathode active material and controlling their content to less than 0.007 mol each, this (D90-D10) / D50 can be kept as low as possible, at 1.2 or less.

[0073] Meanwhile, when Ti and Mg are included at a doping concentration of 0.007 moles or more, (D90-D10) / D50 actually increased to 1.2 or more, so it is desirable that Ti and Mg be included at a doping concentration of less than 0.007 moles each, and more preferably at a doping concentration of 0.004 to 0.006 moles.

[0075] In addition, the positive electrode active material prepared by the method according to the present invention may have an I(101) / x-size of 29 or more when, in XRD analysis, the peak intensity (au) of the (101) plane is denoted as I(101) and the lattice size (nm) of the (020) plane having the same direction as the movement direction of the Li ion is denoted as x-size (020).

[0076] In this invention, XRD analysis was performed using an X-ray diffraction analyzer (Rigaku). XRD measurement conditions were: Scan range (10-80°), Scan speed (2.5° / min), and analysis was performed with a reliability of Rwp 2.5 or less and S value 2 or less. After measuring the XRD diffraction pattern, the X-size (crystal size) was determined by performing a precise analysis of the crystal structure using the Rigaku-SmartLab Studio II program. To analyze crystal information regarding the entire diffraction pattern, the Fundamental Parameter (FP) method was used as the functional model, and the average crystal size was calculated by assuming spherical particles.

[0077] I(101) indicates the degree of formation of the channel through which lithium moves, based on the peak intensity (au) of the (101) plane. The higher the peak intensity, the better the channel is formed, allowing for smooth insertion and extraction of lithium.

[0078] x-size (020) refers to the lattice size (nm) of the (020) plane having the same direction as the movement direction of the Li ion.

[0079] The value of b represents the three-dimensional lattice constant defining the crystal structure, specifically the length of the unit cell measured along the b-axis. The value of b can be obtained through XRD measurements. In olivine-structured lithium manganese phosphate cathode active materials, the movement of lithium ions primarily occurs through one-dimensional channels, which are arranged along the b-axis. Therefore, the smaller the value of b—that is, the smaller the size of the unit cell along the b-axis—the shorter the path for lithium movement becomes, enabling faster transport and thereby improving electrochemical performance.

[0080] (I(101) / x-size(020) / b) / 10 represents a measure of the ease of lithium migration. In the case of I(101), which indicates the degree of lithium migration channel formation, a higher value indicates easier lithium migration. Conversely, regarding the crystal size, the smaller the x-size(020) and b values, the easier lithium migration is considered to be. In particular, it was confirmed that when the I(101) / x-size(020) value is high (29 or higher), the lithium migration channel is well formed and the lithium migration path is short, thereby exhibiting excellent electrochemical performance. In the present invention, by simultaneously doping Ti and Mg into the LMFP cathode active material and controlling their content to less than 0.007 mol each, this I(101) / x-size(020) can be increased to 29 or higher.

[0081] When the b-axis unit cell length (b value) is 0.6065 nm or less, the lithium transport path can be relatively shortened, allowing for excellent electrochemical performance.

[0082] Meanwhile, when Ti and Mg are included in amounts of 0.007 moles or more, the I(101) / x-size does not reach 29, so it is desirable that Ti and Mg be included in amounts of less than 0.007 moles each, and more preferably in amounts of 0.004 to 0.006 moles.

[0084] Lithium secondary battery

[0085] A lithium secondary battery according to an embodiment of the present invention comprises a positive electrode comprising the aforementioned positive electrode active material; a negative electrode comprising a negative electrode active material; and an electrolyte. A separator may be additionally disposed between the positive electrode and the negative electrode.

[0086] anode

[0087] The anode includes an anode material comprising an anode active material, a conductive material, and a binder, and a current collector.

[0088] The anode according to the present invention comprises a current collector and an anode material disposed on at least one surface of the current collector and comprising the aforementioned anode active material.

[0089] The cathode material acts as a lithium source in lithium-ion batteries and is a key material that determines battery capacity and average voltage.

[0090] The cathode material may include a binder and a conductive material.

[0091] The above binder serves to effectively bond the positive active material particles to each other and also to effectively bond the positive active material to the current collector.

[0092] Representative examples of binders include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0093] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials comprising mixtures thereof.

[0094] The above current collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.

[0095] The above-described positive electrode can be manufactured by applying the aforementioned positive electrode active material, conductive material, and binder to a current collector, and then pressing the positive electrode material onto the current collector through a 4-ton press process.

[0097] cathode

[0098] The above cathode includes a current collector and a cathode material formed on the current collector, and the cathode material may include a cathode active material.

[0099] The above negative electrode active material may include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0100] The material capable of reversibly intercalating / deintercalating the above lithium ions may be, for example, a carbon material, and any carbon-based negative electrode active material generally used in the above lithium secondary battery may be used.

[0101] For example, carbon-based cathode active materials can use crystalline carbon, amorphous carbon, or a combination thereof.

[0102] As the above lithium metal alloy, an alloy of a metal selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0103] Examples of materials capable of doping and dedoping the above lithium include Si, SiOx (0 < x < 2), Si-Y alloy (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn).

[0104] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, etc.

[0105] The above cathode material also includes a binder and may optionally further include a conductive material.

[0106] The above binder can serve to effectively attach the negative electrode active material particles to each other and also effectively attach the negative electrode active material to the current collector.

[0107] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any electronically conductive material that does not cause chemical changes can be used.

[0108] For example, the above current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0109] The above-mentioned cathode can be manufactured by coating an active material, a conductive material, and a binder onto a current collector, and the method of manufacturing the cathode in the present invention is not limited.

[0111] electrolytes

[0112] The above electrolyte may be a non-aqueous electrolyte or a solid electrolyte, and may be used in which a lithium salt is dissolved.

[0113] The above-mentioned non-aqueous electrolyte may include an organic solvent, and the above-mentioned non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0114] The above organic solvent may be, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide. These may be used individually or in combination.

[0115] In particular, a mixed solvent of cyclic carbonates and chain carbonates can be preferably used.

[0116] In addition, as an electrolyte, a gel-type polymer electrolyte in which an electrolyte solution is impregnated into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N, is possible.

[0117] The above lithium salt is a material that is dissolved in an organic solvent and acts as a source of lithium ions within the battery, enabling the operation of a basic lithium secondary battery and facilitating the movement of lithium ions between the positive and negative electrodes.

[0118] The above lithium salt may be applied without limitation to any commonly used in the art, provided that it does not impede the purpose of the present invention.

[0119] For example, the lithium salt may be one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiSbF6, LiAlO4, LiAlCl4, LiCl, and LiI.

[0120] Separator

[0121] In lithium secondary batteries, a separator may exist between the positive and negative electrodes.

[0122] As such separation membranes, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer membranes of two or more layers thereof may be used, and of course, mixed multilayer membranes such as polyethylene / polypropylene two-layer membranes, polyethylene / polypropylene / polyethylene three-layer membranes, and polypropylene / polyethylene / polypropylene three-layer membranes may be used.

[0123] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used; they can be classified into cylindrical, prismatic, coin, pouch types, etc., depending on their shape; and they can be divided into bulk type and thin-film type depending on their size. The structure of the battery is not limited in the present invention.

[0124] In the case of a lithium secondary battery containing a positive electrode active material according to the present invention, the 0.1C discharge capacity may be 150mAh / g or more, and the 10C discharge capacity may be 120mAh / g or more.

[0125] In addition, the above lithium secondary battery may have a 0.1C charge / discharge efficiency of 97% or higher.

[0127] As such, specific embodiments of the method for manufacturing a positive electrode active material for a lithium secondary battery are as follows.

[0129] 1. Manufacture of cathode active material for lithium secondary batteries

[0130] Example 1

[0131] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO499.3g, Mn3O475.3g, LiH2PO4102.1g, Li2CO326.2g, glucose (C6H) as a carbon source 12 33.2g of O6, 6.1g of citric acid (C6H8O7) as a dispersant, and 0.7g of TiO2 and 0.3g of MgO as dopant raw materials were mixed with 800g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratio of the raw materials corresponds to Li : Mn : Fe : Ti : Mg = 1:0.594 : 0.396 : 0.005 : 0.005.

[0132] Spray drying: The slurry obtained by the above grinding was spray-dried using a spray dryer. The spray pressure of the spray dryer was set to 1.5 bar, the main chamber temperature to 250℃, and the outlet temperature to 110℃.

[0133] Calcination: First, to remove oxygen from the graphite crucible, nitrogen gas was supplied to the graphite crucible at a flow rate of 1.5 L / min for 1 hour and 30 minutes. Subsequently, 30 g of the powder obtained by the above spray drying was calcined in the graphite crucible under a nitrogen atmosphere (nitrogen gas flow rate 1.0 L / min) (heating rate: 5℃ / min, calcination temperature and time: 650℃, 6 hours) to produce LiMn, a Ti and Mg-doped LMFP cathode active material. 0.594 Fe 0.396 Ti 0.005 Mg 0.005 PO4 was manufactured.

[0135] Example 2

[0136] Ti and Mg-doped LMFP cathode active materials were prepared under the same conditions as in Example 1, except that the calcination temperature was set to 670°C.

[0138] Comparative Example 1

[0139] An LMFP cathode active material was prepared under the same conditions as in Example 1, except that TiO2 and MgO were not added as dopant raw materials.

[0141] Comparative Example 2

[0142] An LMFP cathode active material was prepared under the same conditions as in Example 2, except that TiO2 and MgO were not added as dopant raw materials.

[0144] Comparative Example 3

[0145] A Ti-doped LMFP cathode active material was prepared under the same conditions as in Example 1, except that only 1.4 g of TiO2 (0.01 mol of Ti) was applied as the dopant raw material.

[0147] Comparative Example 4

[0148] A Ti-doped LMFP cathode active material was prepared under the same conditions as in Example 2, except that only 1.4 g of TiO2 (0.01 mol of Ti) was applied as the dopant raw material.

[0150] Comparative Example 5

[0151] Ti and Mg-doped LMFP cathode active materials were prepared under the same conditions as in Example 1, except that 0.98 g of TiO2 (0.007 mol of Ti) and 0.42 g of MgO (0.007 mol of Mg) were applied as dopant raw materials.

[0153] Comparative Example 6

[0154] Ti and Mg-doped LMFP cathode active materials were prepared under the same conditions as in Example 2, except that 0.98 g of TiO2 (0.007 mol of Ti) and 0.42 g of MgO (0.007 mol of Mg) were used as dopant raw materials.

[0156] 2. Methods for Evaluating Physical Properties

[0157] (1) Electrochemical properties

[0158] Coin half-cell manufacturing: An electrode slurry was prepared by adding 4.3g of NMP to 4.5g of positive active material prepared according to the example and comparative example, 0.25g of Super P, and 3.125g of liquid binder KF7208 (PVDF 8 wt.%, Kureha). After coating the electrode on an Al foil using a doctor blade, the mixture was dried at 130°C for 2 hours and then rolled to a thickness of 0.2 mm to manufacture a coin half-cell.

[0159] The above positive plate was punched to a size suitable for a CR2032 coin cell, and a coin cell was fabricated using the punched positive plate, a lithium metal negative plate, and an EL5 electrolyte.

[0160] For the electrochemical evaluation, after aging at 25°C for 24 hours immediately after cell fabrication, one formation cycle (2.5-4.4V) was performed with 0.1 C charge / discharge, a fixed charge rate of 0.1 C, and one measurement each at discharge rates of 0.1, 0.33, 1, 2, 5, and 10 C (2.5-4.4V). The cells were then rested for 20 minutes immediately after the charge and discharge steps using CC-CV charge mode (Charge step condition: fixed at 0.1 C, 0.05 C cut-off current).

[0161] The above half-cells were aged at 25°C for 23 hours, after which charge-discharge tests were conducted. Specifically, one formation cycle (2.5–4.4 V) was performed using 0.1 C charge-discharge; then, the charge rate was fixed at 0.1 C, and the discharge rate was measured once each at 0.1, 0.33, 1.0, 2.0, 5.0, and 10.0 C. (The capacity at 1 C was set to 150 mAh / g.)

[0162]

[0163] (2) Measurement of particle size and press density

[0164] Press density and particle size were measured after the 4-ton press process.

[0165] 4-ton press: 1.1g of LMFP powder with a cross-sectional area of ​​1.3cm 2 Put into a pelletizer and approximately 4 ton / cm 2 A pellet was made by compressing it with the force of...

[0166] After the above 4 ton press, the press density was measured.

[0167] ​Particle size measurement: After the above 4-ton press, the pellet was crushed, and D10, D50, and D90 particle sizes were measured using a particle size analyzer (Malvern Panalytical, Mastersizer 3000). The cathode active material used was 0.02 g, and 1 ml of IGEPAL 1.0 wt.% dispersant was used.

[0168]

[0169] (3) XRD analysis

[0170] X-ray diffraction analyzer (Rigaku) ​​was used to analyze peak intensity, X-size (crystal size), and b-value. XRD measurement conditions: Scan range (10-80°), Scan speed (2.5° / min) / Rwp ≤ 2.5, S value ≤ 2.0.

[0171] X-size (crystal size) analysis was performed by measuring the diffraction pattern and then conducting a precise analysis of the crystal structure using the Rigaku-SmartLab Studio II program. To analyze crystal information regarding the entire diffraction pattern, the Fundamental Parameter (FP) method was used as the functional model, and the average size of the crystal was calculated by assuming it to be a spherical particle.

[0173] 3. Results of Material Property Evaluation

[0174] Figure 1 shows an SEM image of the positive electrode active material prepared according to Example 1.

[0175] Referring to Fig. 1, it can be seen that the positive active material prepared according to Example 1 exhibits a spherical shape.

[0176] The results of the physical property evaluation related to the cathode active materials prepared by the methods according to Examples 1-2 and Comparative Examples 1-6 are shown in Table 1.

[0177] [Table 1-1]

[0178] ​

[0179] [Table 1-2]

[0180]

[0181] Referring to Tables 1-1 and 1-2, in the case of Example 1 and Example 2, which are LMFP positive electrode active materials doped with 0.005 mol of Ti and Mg respectively, it can be seen that the 0.1C discharge capacity is 150 mAh / g or more, the 10C discharge capacity is 120 mAh / g or more, and the 0.1C charge / discharge efficiency is 97% or more.

[0182] In contrast, in the case of Comparative Examples 1 and 2, which are LMFP cathode active materials not doped with Ti and Mg, the 0.1C discharge capacity did not reach 150 mAh / g, and the 10C discharge capacity also did not reach 120 mAh / g. Through this, it can be seen that the discharge capacity of the battery is improved through Ti and Mg doping.

[0183] In addition, in the case of Comparative Examples 3 and 4, which are LMFP cathode active materials doped with only 0.01 mole of Ti, the 0.1C discharge capacity did not reach 150 mAh / g, and the 10C discharge capacity also did not reach 120 mAh / g. Through this, it can be seen that doping with 0.005 moles each of Ti and Mg is more helpful in improving discharge capacity than doping with only 0.01 mole of Ti.

[0184] In addition, in the case of Comparative Examples 5 and 6, which are LMFP cathode active materials doped with 0.007 moles of Ti and Mg respectively, the 0.1C discharge capacity was 150 mAh / g or higher, but the 10C discharge capacity was significantly lower. Through this, it can be seen that both the 0.1C discharge capacity and the 10C discharge capacity can be improved only when Ti and Mg are doped to less than 0.007 moles each.

[0185] In addition, for Examples 1 and 2, the (D90-D10) / D50 value was 1.2 or less, and the I(101) / x-size(020) value was 29 or more. For Comparative Examples 1 to 6, the (D90-D10) / D50 value exceeded 1.2, and the I(101) / x-size(020) value was less than 29. The fact that only Examples 1 and 2 showed a (D90-D10) / D50 value of 1.2 or less and the I(101) / x-size(020) value exceeded 29 can be attributed to the fact that the particle breakage during the press process was significantly lower in the case of Examples 1 and 2, which are LMFP cathode active materials doped with less than 0.007 moles of Ti and Mg, respectively.

[0186] Meanwhile, in the case of Examples 1 and 2, a b value of 0.6065 nm or less was exhibited. As previously mentioned, the b value represents the length that lithium ions must pass through in the channel, and the shorter the value, the easier it is for lithium to move.

[0188] Although the present invention has been described above with reference to the illustrated drawings, the present invention is not limited by the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration according to the present invention were not explicitly described while explaining the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized.

Claims

Claim 1 (a) a step of mixing and grinding a plurality of raw materials and a solvent to form a slurry, wherein each of the plurality of raw materials comprises one or more of Li, Mn, Fe, P, Mg, and Ti and is mixed to have a molar ratio satisfying Formula 1 below; (b) a step of spray-drying the slurry to form a powder; and (c) a step of calcining the powder to produce an anode active material represented by Formula 1 below; [Formula 1] Li x Mn a Fe b Ti c Mg d PO4(0.9≤x≤1.1, a+b+c+d=1, 0.986 <a+b<1, 0<c<0.007, 0<d<0.007)를 포함하는, 양극 활물질 제조 방법. Claim 2 A method for manufacturing a positive electrode active material according to claim 1, wherein 0.004≤c≤0.006 and 0.004≤d≤0.

006. Claim 3 A method for manufacturing an anode active material according to claim 1, wherein in step (a), one or more of a dispersant and a carbon raw material are additionally mixed. Claim 4 A method for manufacturing a positive electrode active material according to claim 1, wherein one or more of the plurality of raw materials further comprises one or more elements selected from Al, B, Ca, Si, Sr, V, Cr, Co, Ni, Cu, Zn, Ba, W, Nb, Cd, Pb, Mo, Ta, La, Ce, Er, Ho, Zr, Y, and Sr. Claim 5 A method for manufacturing an anode active material according to claim 1, wherein step (a) is performed in a wet milling apparatus. Claim 6 A method for manufacturing an anode active material according to claim 1, wherein step (b) is performed in a spray dryer under conditions of a spray pressure of 0.5 to 2.5 bar, a main chamber temperature of 200 to 300°C, and an outlet temperature of 80 to 160°C. Claim 7 A method for manufacturing an anode active material according to claim 1, wherein secondary particles are generated through step (a) and step (b). Claim 8 A method for manufacturing an anode active material according to claim 1, wherein in step (c), the calcination is performed at 630 to 700°C. Claim 9 A method for manufacturing a positive electrode for a lithium secondary battery, comprising a process of applying a positive electrode material comprising a positive electrode active material, a conductive material, and a binder manufactured by any one of claims 1 to 8 onto a current collector, and then compressing it using a 4-ton press process.

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