Olivine cathode active material for lithium secondary battery and manufacturing method thereof

Abstract

An olivine cathode active material for a lithium secondary battery according to the present invention comprises: rod-shaped particles having an average long-side length of 250 nm to 350 nm and a short-side length of 70 nm to 95 nm; and flake-shaped particles having an average long-axis length of 350 nm to 450 nm and a short-axis length of 200 nm to 250 nm in terms of the broad surface, wherein the quantity percentage of the flake-shaped particles to the rod-shaped particles is 10% to 50%.

Description

Olivine-based cathode active material for lithium secondary batteries and method for producing the same

[0001] The present invention relates to an olivine-based positive electrode active material for a lithium secondary battery and a method for manufacturing the same.

[0002] As the electric vehicle market gains momentum, the cathode active material market, which accounts for more than 40% of the cost of lithium-ion batteries, is also experiencing rapid annual growth. Automobiles are categorized into six tiers based on overall length: segment A for vehicles under 3,500 mm and segment F for those over 5,000 mm. Accordingly, even for battery-powered electric vehicles, cathode active materials are used differently depending on the grade and driving range.

[0003] For electric vehicles with a range exceeding 600 km on a single charge, high-energy-density lithium-ion batteries are required, necessitating the use of high-nickel NCM cathode active materials. For ranges around 400 km, mid-nickel NCM cathode active materials are used. However, for electric vehicles with lower ranges and relatively low prices, the use of materials with lower energy density but higher safety and longevity is advantageous from a cost perspective.

[0004] Lithium iron phosphate (LIP) is an olivine structure composed of FeO6 octahedral sites and PO4 tetrahedral sites, and is a material in which lithium ions are inserted and deintercalated through a one-dimensional pathway. This material is mainly composed of Li, Fe, and P, and has a price advantage due to the lower cost of metal minerals compared to NCA or NCM materials that mainly use Ni and Co. In addition, the strong PO bond makes the structure stable, so there is no oxygen dissociation at high temperatures during charging, and it has the advantage of excellent thermal stability. In addition, it has excellent life characteristics, and many electric vehicles using it have been produced in China.

[0005] However, since lithium ion insertion and de-insertion occurs through one-dimensional diffusion, the primary particles must be manufactured in nano-size, and since the material itself has no electrical conductivity, a uniform carbon coating must be applied to the surface, which is a drawback. Nevertheless, with the recent full-scale development of cell-to-pack and even cell-to-chassis technologies for electric vehicles emphasizing high safety, the energy density gap compared to the existing NCM system is gradually narrowing.

[0006] Known methods for producing the above lithium iron phosphate cathode active material include a solid-phase method, a hydrothermal synthesis method, and a liquid-phase method such as a supercritical water method. Recently, a glycothermal method using a non-reacting solution such as ethylene glycol or diethylene glycol as a reaction solvent has been developed. In the case of the hydrothermal synthesis method and the supercritical water method, there were safety issues because the reaction proceeds at high temperature / high pressure when producing lithium iron phosphate nanopowder, and the lithium iron phosphate nanopowder produced by the glycothermal method had the problem that it was difficult to control the particle size and particle size distribution.

[0007] Therefore, there is a need to develop a method for economically and efficiently manufacturing lithium iron phosphate (LFP) cathode active materials with excellent energy density and electrochemical performance without process problems.

[0008]

[0009] The present invention aims to provide an olivine-based positive electrode active material for a lithium secondary battery with improved energy density.

[0010] In addition, the present invention seeks to provide a method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery with improved energy density.

[0011] An olivine-based positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may include rod-shaped particles having an average long side length of 250 nm to 350 nm and an average short side length of 70 nm to 100 nm; and flake-shaped particles having an average long side length of 200 nm to 450 nm and an average short side length of 100 nm to 250 nm.

[0012] The above rod-shaped particles may form round-shaped terminal portions in the longitudinal direction of the long side, and the above flake-shaped particles may have a shape in which the length of the short side gradually decreases in the direction from the center of the long side to the terminal portions on both sides.

[0013] The percentage of the number of flake-shaped particles relative to the total number of rod-shaped particles and flake-shaped particles may range from 1% to 50%.

[0014] The ratio of the long side length to the short side length of the rod-shaped particle may be in the range of 1.5 to 8.0, and the aspect ratio of the wide surface of the flake-shaped particle may be in the range of 1.0 to 3.0.

[0015] The chemical composition of the above rod-shaped particles and flake-shaped particles can be represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] Li x (Fe y M 1-y )PO4

[0018] Here, 0.99≤x≤1.03, 0.2≤y≤0.6, M is at least one selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

[0019] The specific surface area of ​​the olivine-based positive electrode active material for the above lithium secondary battery is 10 m 2 / g to 30m 2 / g can be in the range.

[0020] The above olivine-based positive electrode active material for a lithium secondary battery may include a carbon coating layer positioned on an outer surface, and the mass percentage of carbon with respect to the total mass of the olivine-based positive electrode active material for a lithium secondary battery may be in the range of 1 wt% to 2 wt%.

[0021] Additionally, the carbon coating layer may be positioned in a range of 90% to 100% of the total surface area of ​​the olivine-based positive electrode active material for the lithium secondary battery.

[0022] Another embodiment of the present invention relates to a method for manufacturing an olivine-based cathode active material for a lithium secondary battery, the method comprising the steps of: preparing a first reaction solution in which an iron raw material, a phosphorus raw material, and a doping raw material are dissolved in water, a second reaction solution in which a lithium raw material is dissolved in water, and an organic solvent in which a dispersant is dissolved; introducing the first reaction solution and the second reaction solution into a reactor containing the organic solvent in which the dispersant is dissolved while stirring to obtain an organic solution; heating the reactor to maintain an internal temperature of 160°C to 180°C, performing a reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate; and separating and drying the precipitate and then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material.

[0023] The step of heating the reactor to maintain the internal temperature at 160°C to 180°C and performing a reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate can be performed through a reflux process.

[0024] In the step of preparing each organic solvent in which the dispersant is dissolved, the organic solvent may have a boiling point in the range of 150°C to 200°C.

[0025] In the step of preparing each organic solvent in which the above dispersant is dissolved, the organic solvent may be at least one selected from dimethyl sulfoxide (DMSO), diglyme, triglyme, and dimethylformamide (DMF).

[0026] In the step of preparing each organic solvent in which the above dispersant is dissolved, the dispersant may be at least one selected from polyvinylpyrrodione (PVP), polyvinylphenol (PVPh), polyvinyl alcohol (PVA), polyvinylsulfonic acid, polyvinylsulfate metal salt, polyvinylcarboxylic acid, polyvinylcarboxylate metal salt, polyvinylpyridine (PVPy), copolymers thereof, cyclodextrin, dextran, polysaccharide, or polyacrylic acid (PAA).

[0027] The step of preparing an organic solvent in which the dispersant is dissolved may include a step of stirring and dissolving the organic solvent and the dispersant introduced into the reactor; and a step of heating the organic solvent in which the dispersant is dissolved to a temperature of 50°C to 80°C.

[0028] The step of heating the organic solvent in which the dispersant is dissolved to a temperature in the range of 50°C to 80°C can be performed while continuously introducing an inert gas into the reactor.

[0029] In the step of preparing an organic solvent in which the dispersant is dissolved, the mass percentage of the dispersant with respect to the mass of the organic solvent may be 0.2 wt% to 2 wt%.

[0030] In the step of obtaining an organic solution by stirring while introducing the first reaction solution and the second reaction solution into a reactor containing an organic solvent in which the dispersant is dissolved, the ratio of the number of moles of lithium element to the total number of moles of iron element and doping element in the obtained organic solution may be 1.00 to 1.02.

[0031] The step of obtaining an organic solution by stirring while introducing the first reaction solution and the second reaction solution into a reactor containing an organic solvent in which the dispersant is dissolved may be performed by introducing the first reaction solution and the second reaction solution into the reactor at a predetermined rate, respectively, so that the pH value of the organic solution in the reactor can be maintained constant, and specifically, maintained at 6.0 to 7.0.

[0032] The step of heating the above reactor to a temperature in the range of 160°C to 180°C and performing a reflux reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate can be performed for 3 to 24 hours.

[0033] In the step of separating and drying the above-mentioned precipitate and then calcining it in a reducing atmosphere to obtain an olivine-based positive electrode active material, the step of separating and drying the above-mentioned precipitate and then mixing and milling it with a carbon coating raw material to obtain a mixture may be further included, and the step of calcining the obtained mixture in a reducing atmosphere may be performed.

[0034] In the step of separating and drying the above sediment and then mixing and milling it with a carbon coating raw material to obtain a mixture, the mass percentage of the carbon coating raw material with respect to the mass of the dried sediment may be 5 wt% to 15 wt%.

[0035] The step of separating and drying the above-mentioned sediment and then calcining it in a reducing atmosphere to obtain an olivine-based positive electrode active material can be performed at a temperature of 400°C to 700°C for 1 hour or more in a reducing atmosphere.

[0036] In the step of preparing a first reaction solution in which iron raw material, phosphorus raw material and doping raw material are dissolved in the water, the doping raw material may be a raw material including at least one selected from among Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W or Ga.

[0037]

[0038] The olivine-based positive electrode active material for a lithium secondary battery according to the present invention has the advantage of having excellent electrical conductivity and high energy density.

[0039] In addition, the method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery according to the present invention has the advantage of being able to obtain an olivine-based positive electrode active material having excellent electrical conductivity and high energy density.

[0040] Figure 1 shows an SME analysis image of LFMP manufactured according to Examples 1 to 3.

[0041] Figure 2 shows SME analysis images of LFMP manufactured according to Comparative Examples 2 to 4.

[0042] Figure 3 shows the XRD analysis results of LFMP manufactured according to Examples 2 and 3.

[0043] Fig. 4 shows the XRD analysis results of LFMP manufactured according to Example 2 and Comparative Example 4.

[0044] Figure 5 shows the XRD analysis results of LFMP manufactured according to Comparative Example 2.

[0045]

[0046] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0047] In the present invention, when it is said that a member is located “on” another member, this includes not only cases where a member is in direct contact with another member, but also cases where another member is interposed between the two members.

[0048] When a part of the present invention is said to "include" a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated.

[0049]

[0050] Olivine-based cathode active material for lithium secondary batteries

[0051] One embodiment of the present invention relates to an olivine-based positive electrode active material represented by the following chemical formula 1.

[0052] [Chemical Formula 1]

[0053] Li x (Fe y M 1-y )PO4

[0054] In the above chemical formula 1,

[0055] Here, 0.99≤x≤1.03, 0.2≤y≤0.6, and M is at least one selected from among Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

[0056] The olivine-based positive electrode active material for a lithium secondary battery according to the present invention may be composed of particles having at least one shape selected from among rod-shaped and flake-shaped.

[0057] The average length of the long side of the rod-shaped particle may be 150 nm to 500 nm, specifically 250 nm to 350 nm. In addition, the average length of the short side of the rod-shaped particle may be 60 nm to 120 nm, specifically 70 nm to 100 nm.

[0058] Meanwhile, the long side length of the rod-shaped particle refers to the length of the long side in the longitudinal direction of a single rod-shaped particle, and the short side length refers to the length of the long side in the width direction perpendicular to the long side. The ratio of the long side length to the short side length of the rod-shaped particle may be in the range of 1.5 to 8.0.

[0059] The above rod-shaped particles may have a rounded end in the longitudinal direction.

[0060] The above flake-shaped particles may have an average length of a major axis of a wide surface of 200 nm to 650 nm, specifically 350 nm to 450 nm. The above flake-shaped particles may have an average length of a minor axis of a wide surface of 150 nm to 350 nm, specifically 200 nm to 250 nm. Meanwhile, the aspect ratio of the flake-shaped particles may be in the range of 1.0 to 3.0.

[0061] Additionally, the flake-shaped particles may have a gradually decreasing length of the short axis from the center of the long axis toward the ends on both sides.

[0062] Meanwhile, the percentage of the number of flake-shaped particles relative to the total number of rod-shaped particles and flake-shaped particles may be in the range of 1% to 50%, specifically in the range of 1% to 30%, and more specifically in the range of 1% to 10%.

[0063] When an olivine-based cathode active material for a lithium secondary battery is mixed with rod-shaped particles and flake-shaped particles of the above size range in the above quantity range, there is an advantage in that the energy density and battery capacity of the battery to which it is applied are improved.

[0064] The specific surface area of ​​the olivine-based positive electrode active material for a lithium secondary battery according to the present invention is 10 m 2 / g to 30m 2 / g can be in the range.

[0065] The above specific surface area was measured using the Brunauer-Emmett-Teller Analysis method according to the nitrogen adsorption method, and the method of measuring the specific surface area of ​​the material by measuring the adsorption amount according to partial pressure by adsorbing and desorbing nitrogen gas on the surface of the solid sample using the BET formula was adopted.

[0066] In addition, the olivine-based positive electrode active material for a lithium secondary battery according to the present invention may include a carbon coating layer positioned on an outer surface, and positioned in an area ranging from 90% to 100% of the total surface area of ​​the olivine-based positive electrode active material particles for a lithium secondary battery. The mass percentage of carbon with respect to the total mass of the olivine-based positive electrode active material for a lithium secondary battery may be from 1 wt% to 2 wt%.

[0067] When the carbon coating layer is within the above range, the phenomenon of lower volume energy density can be suppressed as the carbon coating layer is minimized while exhibiting excellent electrical conductivity. In addition, the excessive carbon content is advantageous in preventing detachment from the current collector during the manufacture of the electrode plate.

[0068]

[0069] <Method for Manufacturing Olivine-Based Cathode Active Materials for Lithium Secondary Batteries>

[0070] Another embodiment of the present invention provides a method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery, the method comprising the steps of: preparing a first reaction solution in which an iron raw material, a phosphorus raw material, and a doping raw material are dissolved in water, a second reaction solution in which a lithium raw material is dissolved in water, and an organic solvent in which a dispersant is dissolved; introducing the first reaction solution and the second reaction solution into a reactor containing the organic solvent in which the dispersant is dissolved while stirring to obtain an organic solution; heating the reactor to a temperature in the range of 160°C to 180°C, performing a reflux reaction under atmospheric pressure conditions without sealing the reactor, to obtain a precipitate; and separating and drying the precipitate and then calcining it in a reducing atmosphere to obtain an olivine-based positive electrode active material.

[0071]

[0072] The method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery of the present invention includes the steps of preparing a first reaction solution in which an iron raw material, a phosphorus raw material, and a doping raw material are dissolved in water, a second reaction solution in which a lithium raw material is dissolved in water, and an organic solvent in which a dispersant is dissolved.

[0073] The above first reaction solution may be a reaction solution in which iron raw material, phosphorus raw material, and doping raw material are added to water and then stirred to dissolve them. The iron raw material may be at least one selected from FeCl2.4H2O, FeSO4.7H2O, and Fe(NO3)2.6H2O, and specifically, may be FeSO4.7H2O.

[0074] The above raw material may be at least one selected from among H3PO4, NH4H2PO4, (NH4)2HPO4, NaH2PO4, Na2HPO4, LiH2PO4, and Li2HPO4.

[0075] The above doping raw material may be a raw material including at least one selected from among Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

[0076] The above second reaction solution may be a reaction solution in which a lithium raw material is added to water and then dissolved by stirring.

[0077] The above lithium raw material may be, but is not limited to, LiOH, Li2CO3, LiH2PO4, Li2HPO4, Li3PO4.

[0078] In the step of preparing each organic solvent in which the dispersant is dissolved, the organic solvent may be an organic solvent having a boiling point in the range of 150°C to 200°C. Specifically, it may be at least one selected from dimethyl sulfoxide (DMSO), diglyme, triglyme, and dimethylformamide (DMF), and more specifically, it may be dimethyl sulfoxide (DMSO).

[0079] The above dispersant may be a polymer dispersant, and specifically, the polymer dispersant may be at least one selected from polyvinylphenol (PVPh), polyvinylpyrodione (PVP), polyvinyl alcohol (PVA), polyvinylsulfonic acid, polyvinylsulfate metal salt, polyvinylcarboxylic acid, polyvinylcarboxylate metal salt, polyvinylpyridine (PVPy), copolymers thereof, cyclodextrin, dextran, polysaccharide, or polyacrylic acid (PAA).

[0080] The mass percentage of the dispersant relative to the mass of the organic solvent may be 0.2 wt% to 2 wt%.

[0081] When a dispersant is mixed into an organic solvent in an amount within the above range, the particle shape and size are controlled, which has the advantage of efficiently producing an olivine-based positive electrode active material with improved energy density, and the advantage of preventing particle agglomeration or generation of by-products during the reaction process.

[0082]

[0083] The method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery of the present invention includes a step of obtaining an organic solution by adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved and stirring the same.

[0084] After the dispersant is introduced into a reactor containing the organic solvent, it is dissolved while stirring at room temperature, and then the reactor is heated so that the temperature of the internal material is 80°C, specifically, it can be heated to 50°C to 80°C. This is advantageous in ensuring that the coprecipitation reaction of the Li(FeMn)PO4 element is uniform within the reactor when the first reaction solution and the second reaction solution described later are introduced.

[0085] When heating the above reactor, an inert gas may be continuously supplied to maintain an inert atmosphere within the reactor. This is advantageous because it prevents oxidation caused by the introduction of active ingredients such as oxygen during the heating process, thereby preventing the generation of side reaction products.

[0086] The first reaction solution, in which the iron raw material, phosphorus raw material, and doping raw material are dissolved in the prepared water, is introduced into a reactor containing an organic solvent in which the heated dispersant is dissolved at a predetermined introduction rate. At this time, the interior of the reactor can be continuously stirred by a separate stirring member or stirring device.

[0087] At the same time, a second reaction solution containing lithium raw material dissolved in water is added at a predetermined rate.

[0088] At this time, the pH value of the material inside the reactor is maintained constant, specifically, between 6.0 and 7.0. When the pH value is maintained within the above range, the particle shape and size are controlled, which is advantageous in that it allows for efficient production of an olivine-based positive electrode active material with improved energy density.

[0089] The ratio of the molar number of lithium elements to the total molar number of iron elements and doping elements in the organic solution obtained above may be 1.00 to 1.02, and specifically, may be 1.00 to 1.01.

[0090] When the ratio of the number of moles of lithium elements to the total number of moles of iron elements and doping elements in the organic solution is within the above range, it is advantageous in producing an olivine-based positive electrode active material with fewer impurities, which is preferable.

[0091]

[0092] The method for producing an olivine-based positive electrode active material for a lithium secondary battery of the present invention includes a step of heating the reactor to maintain the internal temperature at 160°C to 180°C, performing a reaction under atmospheric pressure conditions without sealing the reactor, and obtaining a precipitate.

[0093] After the first reaction solution and the second reaction solution are completely introduced into a reactor containing an organic solvent in which the dispersant is dissolved, the reactor is heated so that the internal temperature of the material contained in the reactor reaches 160°C to 180°C, and then the reactor is allowed to react at an atmospheric pressure without sealing the reactor for 3 hours or more, specifically 3 hours to 24 hours, to obtain a precipitate. At this time, a Dean-Stark device may be connected to the reactor and a reflux condenser may be installed thereon to perform a reflux process.

[0094] After the above-mentioned precipitate obtaining reaction is completed, the precipitate can be separated through centrifugation or a filter press, and the separated precipitate can be washed with distilled water at least twice. Through the two or more washes, impurities such as organic solvents and dispersants remaining in the precipitate can be removed.

[0095] The above washed sediment can be dried in a drying device, and an inert gas can be continuously supplied to the drying device.

[0096] The above dried sediment is loaded into a kiln, and then calcined at a temperature of 550°C to 750°C for 12 hours or more while continuously supplying reducing gas, thereby obtaining a carbon-coated olivine-based positive electrode active material.

[0097] In another embodiment of the present invention, a process of disintegrating the lithium iron phosphate compound may be further included, but is not limited thereto.

[0098] In another embodiment of the present invention, the dried precipitate may be mixed with a carbon coating raw material, milled, and then reduced and calcined to obtain a carbon-coated olivine-based positive electrode active material. The mass percentage of the carbon coating raw material relative to the mass of the dried precipitate may be 5 wt% to 15 wt%. When the carbon coating raw material is mixed within the above range, an olivine-based positive electrode active material with a controlled carbon content as desired in the present invention can be produced, which is advantageous and preferable.

[0099] The above carbon coating raw material may be at least one selected from cellulose, glucose, sucrose, fructose, lactose, or maltose, and the type thereof is not particularly limited as long as a carbon coating layer can be effectively formed by the method according to the present invention.

[0100] Specifically, the carbon coating raw material may be cellulose.

[0101] The carbon-coated olivine-based positive electrode active material obtained through the above process has been specifically described above, and is therefore omitted here.

[0102]

[0103] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0104]

[0105] (Manufacturing of olivine-based positive electrode active materials)

[0106] 3.371 g of FeSO4.7H2O, 8.196 g of MnSO4.H2O, and 6.9714 g of 85% H3PO4 were added to 200 g of distilled water (H2O), and stirred to prepare a first reaction solution.

[0107] Additionally, 7.6297 g of LiOH.H2O was added to 200 g of distilled water (H2O), and stirred to dissolve, thereby preparing a basic lithium solution, which is a second reaction solution.

[0108] An organic solution is prepared by dissolving 200 g of DMSO and 1 g of PVP (Polyvinyl pyrrolidone, dispersant) in a co-precipitation reactor equipped with a condenser, then argon gas is purged and the reactor is heated while stirring the solution inside the reactor until the solution temperature reaches 80°C.

[0109] The first reaction solution is introduced into the heated co-precipitation reactor at a constant rate, and at the same time, the second reaction solution is introduced while adjusting the introduction rate so as to maintain the pH at about 6.5.

[0110] After the first reaction solution and the second reaction solution are added, the reactor is heated until the temperature of the mixture contained inside the reactor reaches 160°C, and a reflux reaction is performed for a predetermined period of time while maintaining the temperature at 160°C.

[0111] After the reaction is completed, the obtained precipitate is separated through centrifugation or a filter press, washed twice with water, and then dried in a drying oven. 10 wt% cellulose is mixed based on the mass of the dried powder and dry-mixed and milled using a mixer. Next, the mixture is placed in a 650°C furnace and calcined for 1 hour in a nitrogen gas atmosphere to produce a carbon-coated LFMP, which is an olivine-based positive electrode active material for lithium secondary batteries.

[0112] The mixing amounts of raw materials according to Examples 1 to 3 and Comparative Examples 1 to 4 according to the above manufacturing method are shown in Table 1 below, and the operating conditions are shown in Table 2 below.

[0113] First reaction solutionSecond reaction solutionOrganic solutionFeSO4-7H2OMnSO4-H2O85%H3PO4H2OLiOHH2OPVPDMSO(g)(g)(g)(g)(g)(g)(g)Example 13.378.26.972007.632001300Example 23.378.26.972007.632001300Example 33.378.26.972007.632001300Comparative example 13.378.26.972007.632001300Comparative example 23.378.26.972007.632000200 (DEG)Comparative example 33.378.26.972007.632001300Comparative example 43.388.26.972007.882001300

[0114] In Table 1 above, Comparative Example 2 mixed DEG (diethylene glycol) instead of DMSO. Meanwhile, in Comparative Example 2, an experiment was performed in which the reaction time was maintained at 3 hours, 6 hours, 9 hours, 15 hours, and 30 hours instead of 24 hours.

[0115] The first reaction solution and the second reaction solution are added to the organic solution. Reflux reaction pH maintenance injection time Final pH Reflux temperature Reflux time (hr) (hr) (℃) (hr) Example 17 26.71 1603 Example 26 26.85 1803 Example 36 26.75 18024 Comparative example 16 26.81 503 Comparative example 28 26.85 18024 Comparative example 35 26.85 1803 Comparative example 48 28.18 1803

[0116] (SEM analysis)

[0117] FIG. 1 shows an SME analysis image of LFMP manufactured according to Examples 1 to 3, and FIG. 2 shows an SME analysis image of LFMP manufactured according to Comparative Examples 2 to 4.

[0118] Referring to FIG. 1, it can be confirmed that the LFMP manufactured according to Examples 1 to 3 is formed as a single entity of rod-shaped particles having an average long side length in the range of 250 nm to 350 nm and an average short side length in the range of 70 nm to 100 nm, and flake-shaped particles having an average long side length in the range of 350 nm to 450 nm and an average short side length in the range of 200 nm to 250 nm. In addition, it can be confirmed that the percentage of the number of flake-shaped particles with respect to the total number of rod-shaped particles and flake-shaped particles is 50% or less.

[0119] On the other hand, referring to FIG. 2, the LFMP manufactured according to Comparative Examples 2 to 4 was found to have rod-shaped particles and flake-shaped particles agglomerated to form a single particle. In addition, it can be confirmed that, in addition to rod-shaped particles and flake-shaped particles, particles in the form of small-sized powders exhibit a shape in which the rod-shaped particles and flake-shaped particles are agglomerated.

[0120]

[0121] (XRD analysis)

[0122] FIG. 3 shows the results of XRD analysis of LFMP manufactured according to Examples 2 and 3, FIG. 4 shows the results of XRD analysis of LFMP manufactured according to Example 2 and Comparative Example 4, and FIG. 5 shows the results of XRD analysis of LFMP manufactured according to Comparative Example 2.

[0123] Meanwhile, Fig. 5 additionally shows the XRD analysis results of LFMP manufactured by a method different from Comparative Example 2 except for the Reflux reaction time.

[0124] Referring to FIG. 3, it can be confirmed that the LFMPs manufactured according to Example 2, where the pH was maintained at 6 and the reflux reaction time was 3 hours, and Example 3, where the reflux reaction time was 3 hours, exhibit almost similar crystal structures.

[0125] Referring to Fig. 4, in the case of Comparative Example 4, where LiOH was added at a ratio of 1.03 for the molar number of lithium element to the total molar number of iron element and manganese element, it can be confirmed that a Li3PO4 peak due to excess Li was observed, and impurities were generated. On the other hand, in the case of Example 4, where LiOH was added at a ratio of 1.00 for the molar number of lithium element to the total molar number of iron element and manganese element, it can be confirmed that almost no impurities were generated.

[0126] Referring to Figure 5, when DEG is used as an organic solvent instead of DMSO, the LFMP XRD analysis results according to the reflux reaction time in the XRD analysis confirm that the (Mn,Fe)5H2(PO4)4·4H2O phase is generated up to 15 hours of reaction time, and LIFe after 24 hours of reaction time. 0.2 Mn 0.8 You can see that it has been converted to PO4. If the reflux reaction time is less than 24 hours, you can see that impurities are generated, and if the reaction time is 24 hours or less, you can see that it has been converted to LFMP.

[0127]

[0128] (Coin-shaped half-cell manufacturing)

[0129] Using the LFP cathode active material manufactured according to the above examples and comparative examples, a CR2032 coin cell was manufactured and then electrochemical evaluation was conducted.

[0130] Specifically, a slurry for manufacturing an electrode plate was prepared by mixing LFP cathode active material:conductive material (Super P):binder (PVDF) in a mass ratio of 90:5:5 in an NMP (N-Methyl-2-pyrrolidone) solvent and adjusting the slurry viscosity.

[0131] The above-mentioned slurry was coated on a 15 μm thick Al foil using a doctor blade, dried, and rolled to manufacture a positive electrode plate. Here, the electrode loading amount was approximately 10 mg / cm 2 The ideal was the density of the polar plate was about 2 g / cm 3 That's all for now.

[0132] 1M LiPF6 and EC:DMC:EMC=3:4:3 (vol%) were mixed as electrolyte, and then 1.5 wt% of vinylene carbonate (VC) was added. Coin-type half-cells were manufactured using PP separators and lithium anodes (200 μm, Honzo metal), and aged at room temperature for 10 hours. The measured voltage range was 4.3 V to 2.5 V, and the 1C reference capacity was 150 mAh / g, and the evaluation was conducted. The results are shown in Table 3 below.

[0133] Charge capacityDischarge capacityEfficiencyCharge capacityDischarge capacityEfficiency1CDischarge capacity(mAh / g@0.1C)(mAh / g@0.1C)%(wh / kg@0.1C)(wh / kg@0.1C)%(wh / kg@0.1C)Example 1146.1141.897.1%550.9550.399.9%342.6Example 2146.3145.599.5%554.1553.599.9%341.1Example 3147.6143.897.4%556.1550.999.1%284.1Comparative example 1123.0123.1100.1%476.6468.798.3%330.6Comparative example 2110.2109.699.5%416.1401.196.4%167Comparative Example 347.645.395.2%151.3147.497.4%50.3Comparative Example 4110.9109.899.0%366.3365.199.7%184.9Comparative Example 5120.3118.598.5%385.6380.898.8%194.3

[0134] Referring to Table 3, it can be confirmed that the battery manufactured according to the example of the present invention has superior charge capacity and discharge capacity compared to the battery manufactured according to the comparative example.

[0135]

[0136] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Rod-shaped particles having an average long side length of 250 nm to 350 nm and an average short side length of 70 nm to 100 nm; and Flake-shaped particles having a major axis average length of 200 nm to 450 nm and a minor axis average length of 100 nm to 250 nm; The percentage of the number of flake-shaped particles relative to the total number of rod-shaped particles and flake-shaped particles is in the range of 1% to 50%. Olivine-based cathode active material for lithium secondary batteries.

2. In paragraph 1 The ratio of the long side length to the short side length of the above rod-shaped particle is in the range of 1.5 to 8.0, Olivine-based cathode active material for lithium secondary batteries.

3. In paragraph 1 The aspect ratio of the wide surface of the above flake-shaped particles is in the range of 1.0 to 3.0, Olivine-based cathode active material for lithium secondary batteries.

4. In paragraph 1 The chemical composition of the above rod-shaped particles and flake-shaped particles is represented by the following chemical formula 1. Olivine-based cathode active material for lithium secondary batteries. [Chemical Formula 1] Li x (Fe y M 1-y )PO4 Here, 0.99≤x≤1.03, 0.2≤y≤0.6, M is at least one selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W or Ga.

5. In paragraph 1, The specific surface area of ​​the olivine-based positive electrode active material for the above lithium secondary battery is 10 m 2 / g to 30m 2 / g range, Olivine-based cathode active material for lithium secondary batteries.

6. In paragraph 1, The above olivine-based positive electrode active material for lithium secondary batteries is comprising a carbon coating layer located on the outer surface, Olivine-based cathode active material for lithium secondary batteries.

7. In paragraph 6, The mass percentage of carbon with respect to the total mass of the olivine-based positive electrode active material for the above lithium secondary battery is in the range of 1 wt% to 2 wt%. Olivine-based cathode active material for lithium secondary batteries.

8. In paragraph 6, The carbon coating layer is located in a range of 90% to 100% of the total surface area of ​​the olivine-based positive electrode active material for the lithium secondary battery. Olivine-based cathode active material for lithium secondary batteries.

9. In paragraph 1, The above rod-shaped particles form a round-shaped terminal portion in the longitudinal direction of the long side. Olivine-based cathode active material for lithium secondary batteries.

10. In paragraph 1, The above flake-shaped particles have a shape in which the length of the short axis gradually decreases from the center of the long axis to the ends on both sides. Olivine-based cathode active material for lithium secondary batteries.

11. A step of preparing a first reaction solution in which iron raw material, phosphorus raw material and doping raw material are dissolved in water, a second reaction solution in which lithium raw material is dissolved in water and an organic solvent in which a dispersant is dissolved, respectively; A step of obtaining an organic solution by adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved and stirring the solution; A step of heating the reactor to maintain the internal temperature at 160°C to 180°C, performing a reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate; and A step of obtaining an olivine-based positive electrode active material by separating and drying the above-mentioned sediment and then calcining it in a reducing atmosphere; A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

12. In paragraph 11, The step of heating the above reactor to maintain the internal temperature at 160°C to 180°C and performing the reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate is as follows. It is performed through a reflux process, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

13. In paragraph 11, In the step of preparing each organic solvent in which the above dispersant is dissolved, The above organic solvent has a boiling point in the range of 150°C to 200°C, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

14. In paragraph 11, In the step of preparing each organic solvent in which the above dispersant is dissolved, The above organic solvent is at least one selected from dimethyl sulfoxide (DMSO), diglyme, triglyme, and dimethylformamide (DMF). A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

15. In paragraph 11, In the step of preparing each organic solvent in which the above dispersant is dissolved, The above dispersant is at least one selected from polyvinylpyrrodione (PVP), polyvinylphenol (PVPh), polyvinyl alcohol (PVA), polyvinylsulfonic acid, polyvinylsulfate metal salt, polyvinylcarboxylic acid, polyvinylcarboxylate metal salt, polyvinylpyridine (PVPy), copolymers thereof, cyclodextrin, dextran, polysaccharide, or polyacrylic acid (PAA). A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

16. In paragraph 11, The step of preparing an organic solvent in which the above dispersant is dissolved is: A step of dissolving the organic solvent and dispersant introduced into the reactor by stirring; A step of heating the organic solvent in which the dispersant is dissolved to a temperature of 50°C to 80°C; A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

17. In paragraph 16, The step of heating the organic solvent in which the dispersant is dissolved to a temperature in the range of 50°C to 80°C is as follows: Heating is performed while continuously introducing an inert gas into the above reactor. A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

18. In paragraph 11, In the step of preparing an organic solvent in which the above dispersant is dissolved, The mass percentage of the dispersant relative to the mass of the organic solvent is 0.2 wt% to 2 wt%, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

19. In paragraph 11, In the step of obtaining an organic solution by stirring while adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved, The ratio of the number of moles of lithium element to the total number of moles of iron element and doping element in the organic solution obtained above is 1.00 to 1.

02. A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

20. In paragraph 11, The step of obtaining an organic solution by stirring while introducing the first reaction solution and the second reaction solution into a reactor containing an organic solvent in which the dispersant is dissolved is as follows: The first reaction solution and the second reaction solution are each injected into the reactor at a predetermined speed, Maintaining the pH value of the organic solution in the above reactor at a constant level, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

21. In paragraph 11, The pH value of the organic solution in the above reactor is 6.0 to 7.

0. A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

22. In paragraph 11, The step of heating the above reactor to a temperature in the range of 160°C to 180°C and performing a reflux reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate is as follows. It is performed for 3 to 24 hours, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

23. In paragraph 11, In the step of separating and drying the above sediment and then calcining it in a reducing atmosphere to obtain an olivine-based positive electrode active material, It further includes a step of separating and drying the above sediment and then mixing and milling it with carbon coating raw materials to obtain a mixture. A step of calcining the obtained mixture in a reducing atmosphere is performed, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

24. In paragraph 23, In the step of separating and drying the above sediment and then mixing and milling it with carbon coating raw materials to obtain a mixture, The mass percentage of the carbon coating raw material with respect to the mass of the dried sediment is 5 wt% to 15 wt%, A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

25. In paragraph 11, The step of separating and drying the above sediment and then calcining it in a reducing atmosphere to obtain an olivine-based positive electrode active material is as follows. It is calcined at a temperature of 400℃ to 700℃ for more than 1 hour in a reducing atmosphere. A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

26. In paragraph 11, In the step of preparing a first reaction solution in which iron raw material, phosphorus raw material and doping raw material are dissolved in the above water, The above doping raw material is a raw material containing at least one selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W or Ga. A method for producing an olivine-based positive electrode active material for a lithium secondary battery.

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