Lmfp cathode active material, method of manufacturing the same and lithium secondary battery including the same

Abstract

A lithium iron manganese phosphate cathode active material, a method for manufacturing the same, and a lithium secondary battery containing the same are disclosed. The lithium iron manganese phosphate cathode active material according to the present invention is expressed by the following Formula 1 and satisfies Formula 2. [Equation 1] LixMnaFeb(PO4)y(0.9≤x≤1.2, 0.9≤y≤1.1, 0.9≤a+b≤1.1) [Equation 2] 0.60 ≤ (D50 / BET) × Compressive Density (PD) ≤ 0.70

Description

Technology Field

[0001] The present invention relates to a lithium manganese iron phosphate (LMFP) positive electrode active material.

[0002] In addition, the present invention relates to a method for manufacturing a lithium manganese iron phosphate cathode active material.

[0003] In addition, the present invention relates to a lithium secondary battery comprising a lithium manganese iron phosphate positive electrode active material. Background Technology

[0005] 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.

[0006] 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.

[0007] 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.

[0008] Lithium manganese iron phosphate (LMFP) having an olivine crystal structure has a portion of the iron substituted with manganese compared to lithium iron phosphate (LFP), resulting in improved operating voltage and energy density. However, the substitution of iron with manganese has an adverse effect on stability and conductivity, and may lead to a decrease in capacity development and cycling performance. The problem to be solved

[0010] The problem that the present invention aims to solve is to provide a lithium manganese phosphate cathode active material with excellent electrochemical properties by controlling the particle size, specific surface area, and compaction density of the lithium manganese phosphate cathode active material.

[0011] In addition, the problem that the present invention aims to solve is to provide a positive electrode comprising the positive electrode active material.

[0012] In addition, the problem that the present invention aims to solve is to provide a lithium secondary battery with excellent electrochemical performance including the above-mentioned positive electrode active material.

[0013] In addition, the problem that the present invention aims to solve is to provide a method for manufacturing the above-mentioned positive electrode active material.

[0014] 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

[0016] A lithium iron manganese phosphate cathode active material according to an embodiment of the present invention for solving the above problem is expressed by the following Equation 1 and satisfies Equation 2.

[0017] [Equation 1]

[0018] Li x Mn a Fe b (PO4)y (0.9≤x≤1.2, 0.9≤y≤1.1, 0.9≤a+b≤1.1)

[0019] [Equation 2]

[0020] 0.60 ≤ (D50 / BET) × Compressive Density (PD) ≤ 0.70

[0021] (In Equation 2, D50 is the 50% particle size by volume (㎛), and BET is the BET (Brunauer Emmett Teller) specific surface area (m²) 2 / g), the compressive density (PD) of 1.1g of cathode active material powder with a cross-sectional area of ​​1.3cm 2 Feed into the pellet generator and approximately 4 ton / cm 2 Density (g / cc) when pressed with force

[0022] Preferably, the above x may be 1.09 to 1.12.

[0023] Preferably, x / y can be 1.06 to 1.08.

[0024] The above lithium iron manganese phosphate cathode active material may additionally include Ti. The above Ti may be included in a molar ratio of 0.005 or less.

[0025] The above lithium iron manganese phosphate cathode active material may additionally contain carbon. The carbon may be included in an amount of approximately 1.8 to 2.0 weight percent.

[0026] Preferably, the lithium iron manganese phosphate cathode active material has a BET value of 23 to 26 m 2 It can be / g.

[0027] The above lithium iron manganese phosphate cathode active material may have a D50 value of 7 to 8 μm.

[0028] The above positive active material may be in the form of secondary particles.

[0030] An anode according to an embodiment of the present invention for solving the above problem comprises a current collector; and an anode material disposed on one or both sides of the current collector, wherein the anode material comprises the aforementioned anode active material, conductive material, and binder.

[0032] A lithium secondary battery according to an embodiment of the present invention for solving the above problem 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 disposed between the positive electrode and the negative electrode.

[0034] A method for manufacturing a lithium iron manganese phosphate cathode 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 containing one or more of Li, Mn, Fe, and P to form a slurry; (b) a step of spray-drying the slurry to form a powder; and (c) a step of calcining the powder at 630 to 670°C to manufacture a cathode active material represented by Formula 1 below.

[0035] [Equation 1]

[0036] Li x Mn a Fe b (PO4) y (0.9≤x≤1.2, 0.9≤y≤1.1, 0.9≤a+b≤1.1)

[0037] Preferably, the above x may be 1.09 to 1.12.

[0038] Preferably, x / y can be 1.06 to 1.08.

[0039] In step (a) above, the plurality of raw materials may include a raw material containing Ti. The Ti may be included in a molar ratio of 0.005 or less. Effects of the invention

[0041] The lithium manganese phosphate cathode active material according to the present invention can exhibit not only capacity but also excellent electrochemical characteristics by controlling the particle size, specific surface area, and compression density related to capacity characteristics in the LMFP cathode active material, thereby adjusting the (D50 / BET) × compression density (PD) value to a specific range.

[0042] Accordingly, the lithium secondary battery using the LMFP-based positive electrode active material of the present invention has the effect of improving initial discharge capacity and Coulomb efficiency.

[0043] 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

[0045] Figure 1 schematically illustrates a method for manufacturing a lithium iron manganese phosphate cathode active material according to an embodiment of the present invention. Specific details for implementing the invention

[0046] 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.

[0047] Hereinafter, a lithium iron manganese phosphate cathode active material according to some embodiments of the present invention, a method for manufacturing the same, and a lithium secondary battery including the same will be described.

[0049] Cathode active material for lithium secondary batteries

[0050] 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.

[0051] 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 is expressed by the following Formula 1.

[0052] [Equation 1]

[0053] Li x Mn a Fe b (PO4) y (0.9≤x≤1.2, 0.9≤y≤1.1, 0.9≤a+b≤1.1)

[0054] The molar ratio (x) of lithium may be 0.9 to 1.2. Preferably, the molar ratio (x) of lithium may be 1.09 to 1.12. The lithium iron manganese phosphate cathode active material according to a preferred embodiment of the present invention may exhibit a lithium content that is relatively higher than that of a general lithium iron manganese phosphate cathode active material, with a lithium molar ratio of 1.09 to 1.12. This high lithium ratio increases the amount of energy that a battery cell can store. This means that more energy can be stored for the same volume and weight. In addition, due to the high lithium ratio, the movement of lithium ions becomes smoother, increasing the efficiency of charging and discharging. This can result in reduced energy loss, leading to an increase in the actual usable capacity and lifespan of the battery.

[0055] The molar ratio (y) of phosphoric acid (PO4) may be 0.9 to 1.1. The lithium iron manganese phosphate cathode active material according to the present invention may have a lithium molar ratio of 1.09 to 1.12, which may exhibit a relatively higher lithium content than a general lithium iron manganese phosphate cathode active material.

[0056] Preferably, in the present invention, the molar ratio (x / y) of lithium to phosphate may be 1.06 to 1.08. When the Li / PO4 ratio is relatively high at 1.06 or higher, the D50 of the secondary particles after spray drying tends to decrease. The main reason is that an excess of Li+ ions induces a supersaturated state, promoting the formation of many small nuclei, and the growth of large crystal grains is inhibited due to the dispersion of growth material resulting from this. In addition, (PO4)3 - The excess presence of ions stabilizes the crystal structure and changes surface energy, allowing small particles to be maintained.

[0057] In addition, the D50 of the secondary particles can also be controlled by the x-size of the primary particles. The smaller the x-size of the primary particles, the more evenly the particles are dispersed and the less cohesive force there is, which allows the secondary particle size to be maintained small during rapid drying using a spray drying method. When the Li / PO4 ratio is the same, the x-size can be controlled by varying the calcination temperature. The higher the calcination temperature, the larger the x-size becomes, and the smaller the x-size, the smaller the average particle size (D50) of the secondary particles becomes. That is, when the Li / PO4 ratio is the same, the x-size can be controlled by varying the calcination temperature, and the average particle size (D50) of the secondary particles can be controlled according to the x-size of the primary particles.

[0058] 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 Mn (a) and the molar ratio of Fe (b) 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 degraded. For example, the molar ratio of Mn (a) may be 0.5 to 0.58, and the molar ratio of Fe (b) may be 0.33 to 0.39. The combined molar ratio of Fe and Mn (a+b) may be 0.9 to 1.1.

[0059] For example, the positive active material according to an embodiment of the present invention is Li 1.12 Mn 0.504 Fe 0.336 (PO4) 1.04 It can be expressed as.

[0060] The above lithium iron manganese phosphate cathode active material may additionally include Ti. Ti plays a role in suppressing particle breakage during the pressing process for electrode formation. Furthermore, if Ti is included, similar capacity characteristics can be exhibited even if the lithium content is slightly reduced.

[0061] Preferably, the Ti may be included in a molar ratio of 0.005 or less. For example, the cathode active material according to an embodiment of the present invention is Li 1.09 Mn 0.531 Fe 0.354 Ti 0.005 (PO4) 1.02 It can be expressed as follows. If the Ti molar ratio exceeds 0.005, particle size control cannot be performed smoothly due to the excessive Ti content, and discharge capacity characteristics may be impaired.

[0062] The above lithium manganese phosphate 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.

[0063] The above carbon may be included in an amount of approximately 1.8 to 2.0 weight percent based on 100 weight percent of the total positive active material containing carbon.

[0064] 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.

[0066] Preferably, the lithium iron manganese phosphate cathode active material has a BET value of 23 to 26 m 2 / g. Preferably, the lithium iron manganese phosphate cathode active material may have a D50 value of 7 to 8 μm. If the BET value exceeds 26 or the D50 value is less than 7, it is disadvantageous in terms of efficiency. Conversely, if the BET value is less than 26 or the D50 value exceeds 8, it is disadvantageous in terms of discharge capacity.

[0067] The above lithium iron manganese phosphate cathode active material may be in the form of secondary particles. The above cathode 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.

[0069] In addition, the positive active material according to the present invention satisfies Equation 2.

[0070] [Equation 2]

[0071] 0.60 ≤ (D50 / BET) × Compressive Density (PD) ≤ 0.70

[0072] In Equation 2, D50 represents the 50% particle size (μm) based on volume in the Particle Size Distribution (PSD). BET is the BET (Brunauer-Emmett-Teller) specific surface area (m²). 2 It means / g). Compressed density (PD) refers to 1.1g of cathode active material powder with a cross-sectional area of ​​1.3cm² 2 Feed into the pellet generator and approximately 4 ton / cm 2 It refers to the density (g / cc) of the pellet when it is pressed with force to form a pellet.

[0073] In the case of lithium iron manganese phosphate cathode active materials, the compressive density is lower compared to lithium iron phosphate cathode active materials, so it is necessary to increase the compressive density. However, focusing on increasing compressive density improves physical density and mechanical strength, but it can hinder lithium ion movement due to reasons such as reduced porosity, potentially leading to a decrease in discharge capacity as accessibility to electrochemical active sites is reduced. Conversely, focusing on discharge capacity increases the specific surface area of ​​the electrode material and maintains porosity to facilitate electrolyte penetration and smooth lithium ion movement; however, this results in lower physical compressive density, which may lead to a degradation in electrochemical performance.

[0074] In order to comprehensively improve the physical and electrochemical performance of LMFP electrode materials having such a trade-off relationship, the present invention controlled the particle size distribution, specific surface area, and compression conditions to adjust the (D50 / BET) × compression density (PD) to 0.6 to 0.7, and as shown in Table 1, it was found that excellent electrochemical characteristics as well as capacitance could be exhibited.

[0075] For example, if the (D50 / BET) × compressive density (PD) value is less than 0.6, the compressive density of the cathode active material is excessively small, resulting in poor physical performance and consequently, reduced electrochemical performance. If the (D50 / BET) × compressive density (PD) value exceeds 0.7, the average particle size of the cathode active material is excessively large or the specific surface area is excessively small, resulting in poor electrochemical performance.

[0077] Method for manufacturing positive electrode active material

[0078] Figure 1 schematically illustrates a method for manufacturing a lithium iron manganese phosphate cathode active material according to an embodiment of the present invention.

[0079] Referring to FIG. 1, the method for manufacturing a lithium iron manganese phosphate cathode active material according to the present invention includes a slurry forming step (S110), a spray drying step (S120), and a calcination step (S130).

[0080] 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, and solvent. At this time, the molar ratio of each raw material is adjusted to satisfy Equation 1.

[0081] Each raw material may be any known material without limitation. Additionally, a single raw material may contain two components, such as LiH2PO4 and 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 and Mn3O4. 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 and FePO4.

[0082] Among the multiple raw materials, a raw material containing Ti may be included. The Ti may be included in a molar ratio of 0.005 or less. For example, TiO2 may be used as the Ti raw material.

[0083] Water can be used as the solvent, and one or more types of various organic solvents can also be used.

[0084] Meanwhile, in the slurry formation step (S110), one or more of the carbon raw materials and dispersants may be additionally mixed.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0090] Next, in the spray drying step (S120), the formed slurry is spray-dried to form a powder.

[0091] The spray drying step (S120) can be performed using a spray dryer.

[0092] 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.

[0093] 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.

[0095] Next, in the calcination step, the obtained powder is calcined to produce an anode active material represented by Equation 1.

[0096] [Equation 1]

[0097] Li x Mn a Fe b (PO4) y

[0098] (0.9≤x≤1.2, 0.9≤y≤1.1, 0.9≤a+b≤1.1)

[0099] In step (c) above, calcination can be performed at 630 to 670°C. If the calcination temperature is too low, it is difficult to achieve the target cathode active material performance, 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.

[0100] Calcination can be performed under an inert gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere.

[0102] Lithium secondary battery

[0103] 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.

[0104] anode

[0105] The anode includes an anode material comprising an anode active material, a conductive material, and a binder, and a current collector.

[0106] 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.

[0107] The cathode material acts as a lithium source in lithium-ion batteries and is a key material that determines battery capacity and average voltage.

[0108] The cathode material may include a binder and a conductive material.

[0109] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. 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.

[0110] 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.

[0111] The above-mentioned anode can be manufactured by coating an active material, a conductive material, and a binder onto a current collector such as stainless steel or aluminum. For the anode and the cathode described below, there are many different methods for manufacturing them, and known methods can be used without limitation.

[0113] cathode

[0114] 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.

[0115] 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.

[0116] 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.

[0117] For example, carbon-based cathode active materials can use crystalline carbon, amorphous carbon, or a combination thereof.

[0118] 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.

[0119] 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).

[0120] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, etc.

[0121] The above cathode material also includes a binder and may optionally further include a conductive material.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] The cathode can be manufactured by coating a cathode material comprising an active material, a conductive material, and a binder onto a current collector, and the present invention does not limit the method of manufacturing the cathode.

[0127] electrolytes

[0128] The above electrolyte may be a non-aqueous electrolyte or a solid electrolyte, and may be used in which a lithium salt is dissolved.

[0129] 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.

[0130] 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.

[0131] In particular, a mixed solvent of cyclic carbonates and chain carbonates can be preferably used.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0137] Separator

[0138] In lithium secondary batteries, a separator may exist between the positive and negative electrodes.

[0139] 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.

[0140] 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, and pouch types depending on their shape; and they can be divided into bulk and thin-film types depending on their size.

[0142] In the case of a lithium secondary battery comprising a positive electrode active material according to the present invention, the 0.1C discharge capacity may be 148 mAh / g or more, preferably 150 mAh / g or more. Additionally, the 10C discharge capacity may be 120 mAh / g or more.

[0143] In addition, a lithium secondary battery containing the positive electrode active material according to the present invention may have a 0.1C charge / discharge efficiency (Coulomb efficiency) of 97% or more.

[0145] As such, specific embodiments of the lithium iron manganese phosphate cathode active material and the lithium secondary battery containing it are as follows.

[0147] 1. Preparation of positive electrode active material specimens for lithium secondary batteries

[0148] Psalm 1

[0149] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO4102.2g, Mn3O477.5g, LiH2PO4105.1g, Li2CO326.9g, glucose (C6H) as a carbon source 12 25.7 g of O6, 4.8 g of citric acid (C6H8O7) as a dispersant, and 0.7 g of TiO2 (Ti 0.005 mol) as a dopant raw material were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are shown in Table 1.

[0150] 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℃.

[0151] 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: 700℃, 6 hours) to prepare the cathode active material according to specimen 1.

[0153] Psalm 2

[0154] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO4100.8g, Mn3O476.4g, LiH2PO4103.6g, Li2CO326.5g, glucose (C6H) as a carbon source 12 28.9 g of O6, 5.4 g of citric acid (C6H8O7) as a dispersant, and 0.7 g of TiO2 (Ti 0.005 mol) as a dopant raw material were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are shown in Table 1.

[0155] After spray drying under the same conditions as spray drying of specimen 1, calcination was carried out under the same conditions as calcination of specimen 1, except that the calcination temperature was set to 630℃, and an anode active material according to specimen 2 was prepared.

[0157] Psalm 3

[0158] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO499.2 g, Mn3O475.3 g, LiH2PO4108.8 g, Li2CO329.2 g, glucose (C6H) as a carbon source 12 27.3 g of O6 and 5.1 g of citric acid (C6H8O7) as a dispersant were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are as shown in Table 1.

[0159] After spray drying under the same conditions as spray drying of specimen 1, calcination was carried out under the same conditions as calcination of specimen 1, except that the calcination temperature was set to 630℃, thereby producing an anode active material according to specimen 3.

[0161] Psalm 4

[0162] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO4 100.3 g, Mn3O 476.1 g, LiH2PO4 106.6 g, Li2CO3 28.9 g, glucose (C6H) as a carbon source 12 25.5 g of O6, 4.7 g of citric acid (C6H8O7) as a dispersant, and 0.7 g of TiO2 (Ti 0.005 mol) as a dopant raw material were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are shown in Table 1.

[0163] After spray drying under the same conditions as spray drying of specimen 1, calcination was carried out under the same conditions as calcination of specimen 1, except that the calcination temperature was set to 670℃, and an anode active material according to specimen 4 was prepared.

[0165] Psalm 5

[0166] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO499.2 g, Mn3O475.3 g, LiH2PO4108.8 g, Li2CO327.4 g, glucose (C6H) as a carbon source 12 27.3 g of O6 and 5.1 g of citric acid (C6H8O7) as a dispersant were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are as shown in Table 1.

[0167] After spray drying under the same conditions as spray drying of specimen 1, calcination was carried out under the same conditions as calcination of specimen 1, except that the calcination temperature was set to 670℃, and an anode active material according to specimen 5 was prepared.

[0169] Psalm 6

[0170] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO499.2 g, Mn3O475.3 g, LiH2PO4108.8 g, Li2CO327.4 g, glucose (C6H) as a carbon source 12 27.3 g of O6 and 5.1 g of citric acid (C6H8O7) as a dispersant were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are as shown in Table 1.

[0171] After spray drying under the same conditions as spray drying of specimen 1, calcination was carried out under the same conditions as calcination of specimen 1, except that the calcination temperature was set to 630℃, and an anode active material according to specimen 6 was prepared.

[0173] Psalm 7

[0174] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO4101.1 g, Mn3O476.7 g, LiH2PO4104.0 g, Li2CO330.3 g, glucose (C6H) as a carbon source 12 25.4 g of O6, 4.7 g of citric acid (C6H8O7) as a dispersant, and 0.7 g of TiO2 (Ti 0.005 mol) as a dopant raw material were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are shown in Table 1.

[0175] After spray drying under the same conditions as spray drying of Specimen 1, calcination was carried out under the same conditions as calcination of Specimen 1 to prepare the positive active material according to Specimen 7.

[0177] Psalm 8

[0178] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO4102.2g, Mn3O477.5g, LiH2PO4105.1g, Li2CO326.9g, glucose (C6H) as a carbon source 12 25.7 g of O6, 4.8 g of citric acid (C6H8O7) as a dispersant, and 0.7 g of TiO2 (Ti 0.005 mol) as a dopant raw material were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are shown in Table 1.

[0179] After spray drying under the same conditions as spray drying of specimen 1, calcination was carried out under the same conditions as calcination of specimen 1, except that the calcination temperature was set to 630℃, and an anode active material according to specimen 8 was prepared.

[0181] Psalm 9

[0182] In a bead mill (NETZSCH MINISERIES model) containing 500g of zirconia beads with an average diameter of approximately 0.3 mm, FePO4102.2g, Mn3O477.5g, LiH2PO4105.1g, Li2CO326.9g, glucose (C6H) as a carbon source 12 25.7 g of O6, 4.8 g of citric acid (C6H8O7) as a dispersant, and 0.7 g of TiO2 (Ti 0.005 mol) as a dopant raw material were mixed with 800 g of ultrapure water and ground at 3000 rpm for 4 hours. The molar ratios of the raw materials are shown in Table 1.

[0183] After spray drying under the same conditions as spray drying of Specimen 1, calcination was carried out under the same conditions as calcination of Specimen 1 to prepare the positive active material according to Specimen 9.

[0184] [Table 1]

[0185]

[0187] 2. Methods for Evaluating Physical Properties

[0188] (1) Particle size

[0189] The particle size of the cathode active material according to specimens 1 to 9 was measured using a Malvern Panalytical Mastersizer 3000 instrument.

[0190] D50: Particle size at 50% of the total particle size distribution by volume

[0191] D(4,3): Area average particle size

[0192] D(3,2): Volume average particle size

[0194] (2) BET specific surface area

[0195] The specific surface area was measured using the ASAP2400 nitrogen adsorption BET specific surface area measuring device from Micromeritex.

[0197] (3) Compressed density

[0198] The compressive density of the anode active material according to specimens 1 to 9 is a cross-sectional area of ​​1.3 cm² 2 Feed into the pellet generator and approximately 4 ton / cm 2 After making pellets by pressing with the force, they were measured.

[0200] (4) X-size

[0201] X-size was determined by measuring XRD diffraction patterns using an X-ray diffraction analyzer (Rigaku) ​​and then 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 size of the crystal was calculated by assuming it to be a spherical particle.

[0203] 3. Results of Material Property Evaluation

[0204] Table 2 shows the results of the physical property evaluation of the cathode active materials according to specimens 1 to 9 and the values ​​of Equation 2.

[0205] [Table 2]

[0206]

[0207] [Equation 2] 0.60 ≤ (D50 / BET) × Compressed Density (PD) ≤ 0.70

[0209] (2) Results of electrochemical property evaluation

[0210] The electrochemical characteristics of lithium secondary batteries using positive active materials according to specimens 1 to 9 were evaluated by the following method.

[0211] Coin half-cell fabrication: An electrode slurry was prepared by adding 4.3g of NMP to 4.5g of positive active material according to specimens 1 to 9, 0.25g of Super P, and 3.125g of liquid binder KF7208 (PVDF 8 wt.%, Kureha). After coating the electrodes 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 fabricate a coin half-cell.

[0212] 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.

[0213] 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).

[0214] 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.)

[0215] Coulomb efficiency was defined as the percentage of the initial discharge capacity relative to the initial charge capacity.

[0216] Table 3 shows the results of the electrochemical characteristic evaluation of lithium secondary battery specimens with positive electrode active materials according to specimens 1 to 9.

[0217] [Table 3]

[0218]

[0219] [Equation 2] 0.60 ≤ (D50 / BET) × Compressed Density (PD) ≤ 0.70

[0221] Referring to Table 3, specimens 3 and 4 satisfying Equation 2 showed relatively high discharge capacity and Coulomb efficiency.

[0222] In contrast, for specimens 1, 2, 5 to 9 that did not satisfy Equation 2, the initial discharge capacity was relatively poor, and the Coulomb efficiency also showed a relatively lower value compared to the specimens in the examples.

[0223] Based on the results of Table 3, it can be seen that in the lithium iron manganese phosphate cathode active material, by controlling the particle size, specific surface area, and compressive density to adjust the (D50 / BET) × compressive density (PD) value to 0.6 to 0.7, excellent electrochemical characteristics as well as capacity can be exhibited.

[0225] 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 positive electrode active material expressed by the following Equation 1 and satisfying Equation 2. [Equation 1] Li x Mn a Fe b (PO4) y (0.9≤x≤1.2, 0.9≤y≤1.1, x / y is 1.06∼1.08, 0.9≤a+b≤1.1)[Equation 2] 0.60 ≤ (D50 / BET) × Compressed Density (PD) ≤ 0.70 (In Equation 2, D50 is the 50% particle size by volume (㎛), and BET is the BET (Brunauer-Emmett-Teller) specific surface area (m²) 2 / g), the compressive density (PD) is 1.1g of cathode active material powder with a cross-sectional area of ​​1.3cm 2 Feed into the pellet generator and approximately 4 ton / cm 2 Density (g / cc) when pressed with the force of Claim 2 In claim 1, the lithium iron manganese phosphate positive electrode active material, wherein x is 1.09 to 1.

12. Claim 3 In claim 1, the lithium iron manganese phosphate cathode active material further comprises Ti, wherein the Ti is included in a molar ratio of 0.005 or less. Claim 4 In claim 1, the lithium manganese iron phosphate positive electrode active material further comprises carbon. Claim 5 In claim 1, the lithium iron manganese phosphate cathode active material has a BET value of 23 to 26 m 2 / g, and the lithium iron manganese phosphate positive electrode active material is a lithium iron manganese phosphate positive electrode active material having a D50 value of 7 to 8 μm. Claim 6 In claim 1, the positive active material is a lithium iron manganese phosphate positive active material in the form of secondary particles. Claim 7 A current collector; and a positive material disposed on one or both sides of the current collector, wherein the positive material comprises a positive active material, a conductive material, and a binder according to any one of claims 1 to 6. Claim 8 A lithium secondary battery comprising: a positive electrode comprising a positive active material according to any one of claims 1 to 6; a negative electrode comprising a negative active material; and an electrolyte. Claim 9 A method for manufacturing a lithium iron manganese phosphate cathode active material according to claim 1, comprising: (a) a step of mixing and grinding a plurality of raw materials and a solvent containing one or more of Li, Mn, Fe, and P to form a slurry; (b) a step of spray-drying the slurry to form a powder; and (c) a step of calcining the powder at 630 to 670°C to manufacture a cathode active material represented by the following Formula 1; [Formula 1] Li x Mn a Fe b (PO4) y A method for manufacturing a lithium iron manganese phosphate cathode active material comprising (0.9≤x≤1.2, 0.9≤y≤1.1, x / y is 1.06∼1.08, 0.9≤a+b≤1.1). Claim 10 A method for manufacturing a lithium iron manganese phosphate cathode active material, wherein x is 1.09 to 1.12 in claim 9. Claim 11 A method for manufacturing a lithium iron manganese phosphate cathode active material, wherein, in step (a) above, the plurality of raw materials includes a raw material containing Ti. Claim 12 A method for manufacturing a lithium iron manganese phosphate cathode active material according to claim 11, wherein the above Ti is included in a molar ratio of 0.005 or less. Claim 13 delete Claim 14 delete

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