Positive electrode active material for lithium secondary battery, and lithium secondary battery using the same

Abstract

To provide a method of preparing a positive electrode active material which is advantageous in terms of energy density by having a bimodal particle size distribution including small and large particles.SOLUTION: A method of preparing a positive electrode active material for a lithium secondary battery comprises: (a) mixing a lithium-containing raw material, an iron-containing precursor, a dopant-containing raw material, a sodium-containing raw material and a carbon-based compound to prepare slurry; (b) pulverizing particles in the slurry; and (c) heat-treating the pulverized particles to obtain a lithium composite phosphorus oxide, where the dopant is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present specification relates to a method for producing a positive electrode active material for a lithium secondary battery, and more specifically, to a method for producing a positive electrode active material for a lithium secondary battery having excellent electrical conductivity and energy density. [Background technology]

[0002] Batteries store electricity by using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example of such batteries is the lithium secondary battery, which stores electrical energy by the difference in chemical potential when lithium ions are intercalated / deintercalated at the positive and negative electrodes.

[0003] The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

[0004] Various materials are used as the positive electrode active material of lithium secondary batteries, among which lithium metal phosphate, for example, lithium iron phosphate (LiFePO4), is widely used in the manufacture of lithium secondary batteries because it has excellent stability, the ability to withstand many charge / discharge cycles, and relatively low manufacturing costs.

[0005] However, due to its olivine crystal structure, lithium iron phosphate has the disadvantage that lithium ions can only diffuse one-dimensionally, resulting in low ionic and electrical conductivity. Therefore, there have been technological attempts to improve this by nano-sizing lithium iron phosphate particles and coating them with carbon.

[0006] However, nano-sized lithium iron phosphate tends to easily aggregate due to the mutual attractive forces between particles and grow into a shape that is disadvantageous in terms of energy density. Also, the carbon coating reduces the fluidity of the lithium iron phosphate particles, which leads to a decrease in the density of the positive electrode active material.

[0007] As technology advances, the demand for lithium secondary batteries, including for electric vehicles, is increasing rapidly, and related industries are demanding increased capacity of lithium secondary batteries that is directly related to the usage time of the products. Summary of the Invention [Problem to be solved by the invention]

[0008] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is driving the market, while the demand for positive electrode active materials used in lithium secondary batteries is also continuously changing, and in particular, the demand for increased capacity of positive electrode active materials is gradually increasing.

[0009] In order to meet such market demands, the present specification aims to provide a method for producing a positive electrode active material that has a bimodal particle size distribution including small particles and large particles and is advantageous in terms of energy density.

[0010] Another object of the present specification is to provide a positive electrode comprising a positive electrode active material produced by the production method defined in the present application. It is a further object of the present specification to provide a lithium secondary battery that uses the positive electrode defined herein. [Means for solving the problem]

[0011] According to one aspect of the present specification, there is provided a method for producing a positive electrode active material for a lithium secondary battery, the method including: (a) mixing a lithium-containing raw material, an iron-containing precursor, a dopant-containing raw material, a sodium-containing raw material, and a carbon-based compound to produce a slurry; (b) pulverizing particles in the slurry; and (c) heat-treating the pulverized particles to obtain a lithium composite phosphate; wherein the dopant is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr.

[0012] In an embodiment, the ratio (Li / Metal) of the number of lithium atoms (Li) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) may be 0.95 to 1.05.

[0013] Furthermore, the ratio (Fe / Metal) of the number of iron atoms (Fe) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) may be 0.96 to 0.98.

[0014] Here, in the step (a), the ratio (D / Metal) of the number of dopant atoms (D) to the total number of atoms (Metal) of metal elements other than lithium in the slurry may be 0.02 to 0.03.

[0015] In addition, the ratio (Na / Metal) of the number of sodium atoms (Na) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) may be 0 to 0.01.

[0016] Moreover, in step (a), at least one of the dopant-containing source material and the sodium-containing source material may be at least one selected from the group consisting of sulfates, carbonates, nitrates, acetates, chlorides, hydroxides, and oxides.

[0017] In addition, the ratio (C / Metal) of the number of carbon atoms (C) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) may be 0.25 to 1.5.

[0018] In another embodiment, the ground particles in step (c) may be obtained by spray drying the slurry obtained in step (b).

[0019] Also, the heat treatment in step (c) may be carried out at a maximum temperature of 600 to 900° C. for 5 to 15 hours in an inert atmosphere.

[0020] According to another aspect of the present specification, there is provided a positive electrode active material including a lithium composite phosphate capable of lithium intercalation / deintercalation, the lithium composite phosphate including secondary particles formed by agglomeration of a plurality of primary particles, the primary particles being in a bimodal form including a first lithium composite phosphate as a small particle and a second lithium composite phosphate as a large particle, and at least one of the first lithium composite phosphate and the second lithium composite phosphate is a lithium composite phosphate having a dopant such as iron, a dopant, or a combination thereof. and sodium element, the dopant being at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, and an amorphous carbon coating layer having a thickness of 1 to 500 nm is formed on the surface of at least a part of the primary particles.

[0021] Furthermore, the content of the second lithium composite phosphate in the positive electrode active material may be 10 to 20% by weight.

[0022] The lithium complex phosphate may be represented by the following Chemical Formula 2:

[0023] [Chemical formula 2] Lip Fe (1-y-z) M y Na z PO4

[0024] In the above formula, M is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, and 0.95≦p≦1.05, 0.02≦y≦0.03, and 0≦z≦0.01.

[0025] According to yet another aspect, there is provided a positive electrode comprising the positive electrode active material. According to yet another embodiment, there is provided a lithium secondary battery using the positive electrode. Effect of the Invention

[0026] According to the present specification, a bimodal cathode active material containing both small and large particles can be prepared in one synthesis process by adding a specific dopant element during the preparation of a lithium composite phosphate through the calcination of raw materials. In addition, large particles can be formed even at a low sintering temperature during preparation of the positive electrode active material, and a uniform carbon-based coating layer can be formed with a minimum amount of carbon-based compound. Therefore, the positive electrode active material has a high pellet density and an excellent energy density. The specific effects of the present specification, together with the above-mentioned effects, will be described below together with specific matters for implementing the matters described in the specification. [Brief description of the drawings]

[0027] [Figure 1] 4 shows a particle size distribution of secondary particles of a positive electrode active material prepared according to an embodiment of the present specification. [Diagram 2] 4 shows a particle size distribution of primary particles of a positive electrode active material prepared according to an embodiment of the present specification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] In order to make this specification easier to understand, certain terms are defined herein for convenience.Unless otherwise defined herein, scientific and technical terms used herein have the meanings that are commonly understood by those of ordinary skill in the art.In addition, unless otherwise specified above, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms. Hereinafter, a method for producing a positive electrode active material for a lithium secondary battery according to the present specification, a positive electrode including the positive electrode active material produced by the method, and a lithium secondary battery using the positive electrode will be described in more detail.

[0029] Method for producing positive electrode active material for lithium secondary battery According to one embodiment, a method for producing a positive electrode active material for a lithium secondary battery includes: (a) mixing a lithium-containing raw material, an iron-containing precursor, a dopant-containing raw material, a sodium-containing raw material, and a carbon-based compound to produce a slurry; (b) pulverizing particles in the slurry; and (c) heat-treating the pulverized particles to obtain a lithium composite phosphate. The dopant may be at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr.

[0030] The step (a) is a step of preparing an aqueous solution slurry by mixing raw materials for preparing a lithium composite phosphate with water.

[0031] The lithium-containing raw material used in step (a) is for forming a lithium composite phosphate used as a positive electrode active material, and may be lithium hydroxide, lithium carbonate, lithium nitrate, lithium phosphate, lithium fluoride, lithium acetate, or the like.

[0032] Here, the lithium compounds can be mixed so that the ratio (Li / Metal) of the number of lithium atoms (Li) to the total number of atoms of metal elements other than lithium in the slurry is in the range of 0.95 to 1.05, for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, or a range between two of these values.

[0033] The iron-containing precursor is a precursor of a lithium composite phosphate containing iron element, and can form a lithium composite phosphate by reacting with a lithium-containing raw material.

[0034] In one example, the iron-containing precursor may contain, in addition to iron element, at least one transition metal such as manganese, nickel, cobalt, vanadium, titanium, chromium, copper, zinc, etc., and at least one element such as phosphorus, oxygen, hydrogen, carbon, silicon, sulfur, nitrogen, boron, fluorine, chlorine, iodine, etc.

[0035] Optionally, the iron-containing precursor may be doped with a different element, where the different element may be at least one selected from Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, F, Ga, Hf, I, In, K, La, Mg, Mo, N, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn and Zr.

[0036] In one example, the iron-containing precursor may be an iron complex hydroxide or iron complex oxide containing iron, or an iron complex phosphate containing iron and phosphorus.

[0037] An iron composite hydroxide precursor can be produced through a synthesis reaction in an aqueous solution containing an iron raw material. As an example of such a synthesis reaction, an iron composite hydroxide precursor can be produced by adding a basic aqueous solution dropwise to an aqueous solution containing an iron source material, a phosphorus source material, and an oxidizing agent while stirring the aqueous solution.

[0038] Here, the amount of the iron raw material, the phosphorus raw material, and the oxidizing agent may vary depending on the composition of the target positive electrode active material. For example, when LiFePO4 is produced, the iron raw material, the phosphorus raw material, and the oxidizing agent may be added so that the difference in the amount of each of them is 20% or less on a molar basis, for example, 20%, 15%, 10%, or between two of these values, but is not limited thereto.

[0039] In another example, the molar ratio of the iron source material, the phosphorus source material and the oxidizing agent may be, but is not limited to, 0.8-1.2:0.8-1.2:0.8-1.2, i.e., 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, or a molar ratio in a range between any two of these values.

[0040] Examples of the iron source material include ferrous sulfate, ferrous oxalate, ferrous citrate, ferrous hydroxide, ferrous phosphate, ferrous chloride, ferrous nitrate, and ferrous acetate.

[0041] As the phosphorus source material, phosphoric acid, iron phosphate, lithium dihydrogen phosphate, lithium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, phosphorus pentoxide, etc. can be used.

[0042] Examples of the oxidizing agent include hydrogen peroxide, glycolic acid, citric acid, ammonium persulfate, sodium persulfate, potassium persulfate, potassium permanganate, ammonium peroxydisulfate, nitric acid, chloric acid, chromic acid, manganese dioxide, and ferric chloride.

[0043] As the basic aqueous solution, an aqueous sodium hydroxide solution, an aqueous ammonia solution, an aqueous potassium hydroxide solution, or the like can be used.

[0044] The hydroxide precursor can be produced by adding the basic aqueous solution to an aqueous solution prepared by adding an iron source material, a phosphorus source material, and an oxidizing agent to pure water (DIW), and reacting the solution at a temperature of 40 to 80°C, for example, 40°C, 42.5°C, 45°C, 47.5°C, 50°C, 52.5°C, 55°C, 57.5°C, 60°C, 62.5°C, 65°C, 67.5°C, 70°C, 72.5°C, 75°C, 77.5°C, 80°C, or a temperature in the range between any two of these values.

[0045] The reaction may be carried out under inert conditions, for example, in a reaction system purged with at least one inert gas selected from the group consisting of N2, Ar, He, Rn, Ne and Xe, but is not limited thereto.

[0046] If necessary, a raw material containing a different element may be further added to dope the hydroxide precursor with the different element.

[0047] The iron composite hydroxide precursor can be heat-treated to produce an iron composite oxide precursor. Here, the iron composite oxide precursor may be produced by heat treating the iron composite hydroxide precursor in a calciner at a maximum temperature of 400 to 700°C, for example, 400°C, 425°C, 450°C, 475°C, 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, 700°C, or a temperature in the range between any two of these values, for 3 to 10 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, or a temperature in the range between any two of these values, but is not limited thereto.

[0048] The heat treatment may be performed by increasing the temperature at a rate of 1 to 5° C. per minute, for example, 1° C., 1.5° C., 2° C., 2.5° C., 3° ​​C., 3.5° C., 4° C., 4.5° C., 5° C., or a range between any two of these values, until the maximum temperature is reached. The heat-treated precursor may be obtained by cooling in a furnace.

[0049] By using the iron composite oxide precursor produced by such a method, primary nanoparticles having an olivine crystal structure can be formed.

[0050] In a specific example, the iron composite oxide precursor may be produced by a method including: (i) a step of introducing a basic aqueous solution into a reaction system containing an iron source material, a phosphorus source material, and an oxidizing agent to produce an iron composite hydroxide precursor; and (ii) a step of heat-treating the iron composite hydroxide precursor to produce an iron composite oxide precursor; but the method is not limited thereto.

[0051] The slurry in the step (a) may contain a dopant-containing raw material, and may dope the lithium composite phosphate with a different element.

[0052] Here, in step (a), the ratio (Fe / Metal) of the number of iron atoms (Fe) to the total number of atoms (Metal) of metal elements other than lithium in the slurry may be 0.96 to 0.98.

[0053] Lithium iron phosphate compounds, which are olivine-based positive electrode materials, are PO4 3- The strong covalent bonds of Li give it a relatively low electrical conductivity. + is known to have one-dimensional diffusion and low ionic conductivity.

[0054] As a means to overcome these shortcomings, we have developed a method to make lithium phosphate nanoparticles. + Techniques have been proposed to improve diffusion.

[0055] However, such techniques reduce the density of the positive electrode active material, which can result in lower energy density of the final product.

[0056] One method for increasing the density of the positive electrode active material is to mix particles of different sizes. For example, it is known that a positive electrode active material that exhibits a bimodal particle distribution in which the particle size distribution graph has two peaks can have a high density. Conventionally, to manufacture such positive electrode active materials, two materials with different average particle sizes are mixed.

[0057] However, in this method, the lithium composite phosphate is synthesized at a high sintering temperature during the production of large particles, so the carbon-based compound disappears during the sintering, and the characteristics of the carbon-based coating between the large particles and the small particles are different. Also, a larger amount of carbon-based compound is required to form the carbon-based coating layer.

[0058] Meanwhile, in the method according to one aspect of the present specification, the particle size of the primary particles of the lithium composite phosphate synthesized using a specific dopant or sodium that can act as a flux that affects particle growth can be controlled.

[0059] Here, the dopant may be at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn and Zr.

[0060] The dopant may grow or inhibit the growth of specific particles of the lithium composite phosphate, thereby realizing a bimodal morphology without physical mixing.

[0061] In addition, the dopant may improve the stability or conductivity of the lithium composite phosphate.

[0062] Here, in the step (a), the ratio (D / Metal) of the number of dopant atoms (D) to the total number of atoms (Metal) of metal elements other than lithium in the slurry may be 0.02 to 0.03.

[0063] The slurry in step (a) may contain a sodium-containing raw material, and the lithium composite phosphate may be doped with sodium element.

[0064] When the lithium composite phosphate is doped with sodium element, large particles of 3 to 20 μm can be formed.

[0065] The sodium element can improve the lattice stability of the lithium composite phosphate.

[0066] Here, in step (a), the ratio (Na / Metal) of the number of sodium atoms (Na) to the total number of atoms (Metal) of metal elements other than lithium in the slurry may be 0 to 0.01.

[0067] In step (a), at least one of the dopant-containing source material and the sodium-containing source material may contain hydrogen and oxygen.

[0068] That is, at least one of the dopant-containing source material and the sodium-containing source material is A(O a H b ) c where A is an element having an oxidation number of +1 or +2.

[0069] In another example, the dopant-containing source material and the sodium-containing source material may be at least one selected from the group consisting of sulfates, carbonates, nitrates, acetates, chlorides, hydroxides, and oxides.

[0070] When a raw material containing a dopant or sodium is introduced into the slurry, the particle size of the lithium composite phosphate can be controlled.

[0071] As a method for improving the conductivity of lithium iron phosphate-based compounds, a technique for forming a carbon coating on at least a portion of the surface has been proposed.

[0072] However, the coated carbon exists in an amorphous phase and can reduce the density of the positive electrode active material.

[0073] When the thickness of the carbon coating layer is minimized and its uniformity is increased, the decrease in flowability caused by amorphous carbon can be minimized and the conductivity of the positive electrode active material can be improved.

[0074] The carbon-based compound included in the slurry in step (a) may be for forming a carbon coating that improves the conductivity of the positive electrode active material.

[0075] Examples of the carbon-based compound include, but are not limited to, sucrose, glucose, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), colloidal carbon, citric acid, tartaric acid, glycolic acid, polyacrylic acid, adipic acid, glycine, and aminobenzoic acid.

[0076] As an example, the carbon-based compound can be added so that the ratio (C / Metal) of the number of carbon atoms (C) to the total number of atoms (Metal) of metal elements other than lithium in the slurry is in the range of 0.25 to 1.5, for example, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, or a range between two of these values.

[0077] The carbon-based compound may be added so that the content of the carbon coating layer is 1.0 to 2.0 wt% based on 100 wt% of the lithium composite phosphate in the final product, for example, 1.0 wt%, 1.05 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.25 wt%, 1.3 wt%, 1.35 wt%, 1.4 wt%, 1.45 wt%, 1.5 wt%, 1.55 wt%, 1.6 wt%, 1.65 wt%, 1.7 wt%, 1.75 wt%, 1.8 wt%, 1.85 wt%, 1.9 wt%, 1.95 wt%, 2.0 wt%, or a range between two of these values.

[0078] When the content of the carbon-based compound in the slurry satisfies the above range, it may be easy to form a thin carbon coating layer.

[0079] The carbon-based compound may be a compound in which the proportion of C element in the molecular structure is 30 to 60% by weight, for example, 30% by weight, 31% by weight, 32% by weight, 33% by weight, 34% by weight, 35% by weight, 36% by weight, 37% by weight, 38% by weight, 39% by weight, 40% by weight, 41% by weight, 42% by weight, 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, or a range between two of these values.

[0080] When a carbon-based compound having a C element ratio within the above range is used, a product with excellent yield and uniformity of carbon coating can be manufactured even if the same content of the compound is used.

[0081] In addition, since the manufacturing method forms the carbon coating by a wet coating method, it is necessary to use a raw material having sufficient solubility in water.

[0082] Thus, the carbon-based compound may have a solubility in water at 25° C. of 0 to 3,000 g / L, for example, 3,000 g / L, 2,750 g / L, 2,500 g / L, 2,250 g / L, 2,000 g / L, 1,750 g / L, 1,500 g / L, 1,250 g / L, 1,000 g / L, 750 g / L, 500 g / L, 250 g / L, 200 g / L, 150 g / L, 100 g / L, 50 g / L, or a range between any two of these values.

[0083] When a carbon-based compound having a solubility within the above range is used, a uniform coating can be formed more easily.

[0084] In addition, the carbon-based compound must be carbonized within the heat treatment temperature of step (c). If uncarbonized carbon-based compound remains in the positive electrode active material, the improvement in conductivity may be insufficient or unexpected side effects may occur.

[0085] Next, the step (b) is a step of pulverizing particles in the slurry, in which the lithium-containing raw material, the iron-containing precursor, the dopant-containing raw material, the sodium-containing raw material, etc. may be present in particulate form in the slurry.

[0086] To pulverize the particles, a dry or wet dispersion mill such as a ball mill, a bead mill (beads normally used for pulverizing metallic raw materials, such as Al beads, Fe beads, or Zr beads, can be used), a vibratory mill, an attrition mill, an air jet mill, a disk mill, or an air classifier mill can be used.

[0087] The average particle size (D50) of the particles milled in step (b) may be 1 μm or less, for example, 1.0 μm, 0.9 μm, 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm, 0.4 μm, 0.3 μm, 0.2 μm, 0.1 μm, or a range between any two of these values.

[0088] The particles milled to have an average particle size in the above range can easily aggregate due to surface energy. The aggregated particles grow into an angular shape during the sintering process, which leads to a decrease in the density of the positive electrode active material.

[0089] When the slurry contains a specific dopant-containing source material, the agglomeration of the particles can be suppressed, so that the particles grow spherically and the density characteristics can be improved.

[0090] In addition, at least a portion of the dopant or sodium may be doped during the milling process.

[0091] After the pulverization in step (b), the slurry may be dried to obtain a powder form. For example, the slurry may be dried through spray drying. That is, the particles in step (c) may be obtained by spray drying the slurry pulverized in step (b).

[0092] Spray drying, which is an example of the drying, may be performed in a spray dryer. The spray dryer is not particularly limited as long as it is a spray drying device that can spray-dry the slurry containing the pulverized particles to produce dried particles having a shape close to a sphere, and examples of the spray dryer that can be used include an ultrasonic atomizer, a one-fluid jet nozzle sprayer, a two-fluid jet nozzle sprayer, an ultrasonic nozzle sprayer, a filter expansion droplet generator (FEAG), and a disk-type droplet generator.

[0093] The spray dryer may include a spray nozzle and a drying chamber, and the slurry is atomized into droplets of a predetermined size through the spray nozzle and sprayed into the drying chamber in the presence of a relatively hot gas flow.

[0094] The droplet-formed raw material sprayed into the drying chamber can be dried into particles having a nearly spherical shape under the temperature environment in the drying chamber.

[0095] In addition, when the slurry contains a specific dopant-containing raw material, unwanted aggregation of the particles during spray drying can be suppressed, resulting in particles having a nearly spherical shape.

[0096] Here, by adjusting the viscosity of the slurry after completing the pulverization in step (b), it is possible to shorten the condensation time during drying and minimize the decrease in densification due to moisture loss during drying.

[0097] Water loss during drying can reduce particle densification and form pores, which can result in reduced particle strength and poor stability of the positive electrode active material.

[0098] If the viscosity of the slurry is too high, the fluidity decreases during drying, the process efficiency becomes insufficient, and it may be difficult to obtain spherical particles.

[0099] One of the means for adjusting the viscosity of the slurry is to add a binder.

[0100] In addition, at least a portion of the dopant or sodium may be doped during the spray drying process.

[0101] Next, the step (c) may be a step of heat-treating the particles milled in the step (b) to form a lithium composite phosphate.

[0102] In addition, at least a portion of the dopant or sodium may be doped or coated during the heat treatment in step (c).

[0103] In addition, the carbon-based compound may be carbonized during the heat treatment in step (c) to form a carbon coating layer.

[0104] The heat treatment in step (c) may be performed in an inert atmosphere at a maximum temperature of 600 to 900° C. for 5 to 15 hours, where the maximum temperature may vary depending on the composition of the target positive electrode active material.

[0105] More specifically, the heat treatment in step (c) may be performed in an inert atmosphere in a sintering furnace at a temperature of 600 to 900° C. at a rate of 1 to 10° C. per minute for 5 to 15 hours.

[0106] The heat treatment in step (c) may be performed at a temperature ranging from 600 to 900°C, for example, 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C, 775°C, 800°C, 825°C, 850°C, 875°C, 900°C, or any temperature between any two of these values.

[0107] When a specific dopant is added and heat treatment is performed at a temperature satisfying the above range, localized grain enlargement can be easily achieved.

[0108] If the heat treatment temperature in step (c) is less than 600° C., the calcination of the precursor may be insufficient, resulting in insufficient crystal growth of the lithium composite phosphorus oxide or difficulty in forming a carbon coating layer.

[0109] On the other hand, if the heat treatment temperature in step (c) exceeds 900° C., the lithium composite phosphate may be thermally decomposed, resulting in a decrease in particle strength or particle collapse.

[0110] The heat treatment can be carried out by increasing the temperature by 1 to 10°C per minute, for example, 1°C, 1.5°C, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C, 5°C, 5.5°C, 6°C, 6.5°C, 7°C, 7.5°C, 8°C, 8.5°C, 9°C, 9.5°C, 10°C, or a temperature range between any two of these values.

[0111] The heat treatment can also be carried out while maintaining the maximum temperature for 15 hours or less, for example, 15 hours, 14.5 hours, 14 hours, 13.5 hours, 13 hours, 12.5 hours, 12 hours, 11.5 hours, 11 hours, 10.5 hours, 10 hours, 9.5 hours, 9 hours, 8.5 hours, 8 hours, 7.5 hours, 7 hours, 6.5 hours, 6 hours, 5.5 hours, 5 hours, or a range between any two of these values.

[0112] Here, the inert atmosphere may be composed by replacing air with at least one inert gas selected from the group consisting of, for example, N2, Ar, He, Rn, Ne, and Xe, but is not limited thereto.

[0113] Optionally, in step (c), before the particles pulverized in step (b) are heat-treated, at least one selected from at least one sub-raw material containing an element selected from Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, F, Fe, Ga, Hf, I, In, K, La, Mg, Mo, N, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr and a lithium-containing raw material may be added. The sub-raw material may be provided in at least one form selected from sulfate, carbonate, nitrate, acetate, chloride, hydroxide, and oxide.

[0114] Here, the amount of the sub-raw material added in step (c) may vary depending on the composition of the particles and the composition of the target positive active material.

[0115] Accordingly, in the step (c), when the mixture of the particles and the sub-raw material is heat-treated, the lithium composite phosphate may be doped with the element contained in the sub-raw material or may be coated on at least a portion of the surface of the lithium composite phosphate.

[0116] The lithium composite phosphate obtained in step (c) may include primary particles and secondary particles formed by aggregation of the primary particles. The lithium composite phosphate may be represented by, but is not limited to, Formula 2 below.

[0117] [Chemical formula 2] Li p Fe (1-y-z) M y Na z PO4 (In the above formula, M is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, and 0.95≦p≦1.05, 0.02≦y≦0.03, and 0≦z≦0.01.)

[0118] Furthermore, before or after the step (c), the lithium composite phosphorus oxide may be subjected to a disintegration, distribution, and / or water washing process.

[0119] Positive electrode active material for lithium secondary batteries The positive electrode active material for a lithium secondary battery according to another embodiment may include a lithium composite phosphate capable of intercalating / deintercalating lithium.

[0120] The lithium composite phosphate included in the positive electrode active material includes secondary particles formed by agglomeration of a plurality of primary particles.

[0121] That is, the positive electrode active material is provided as an aggregate including primary particles made of a lithium composite phosphate capable of lithium intercalation / deintercalation and secondary particles in which a plurality of the primary particles are aggregated.

[0122] For example, the primary particles may have a spherical shape. Since the lithium composite phosphate has a smooth surface, the positive electrode active material may have an excellent pellet density.

[0123] Here, the average particle size of the primary particles (here, the average particle size of the primary particles may be the average major axis length of the primary particles) may be within a range of 0.05 to 0.5 μm, for example, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, or a range between two of these values, thereby enabling the optimal density of a positive electrode manufactured using the positive electrode active materials according to various embodiments to be realized.

[0124] The primary particles may be of a bimodal form, including a first lithium composite phosphate as a small particle and a second lithium composite phosphate as a large particle.

[0125] In this case, the gaps between the large particles can be filled with small particles having a relatively small average particle size, thereby improving the integration density of the lithium composite phosphate within a unit volume, and increasing the energy density per unit volume.

[0126] Here, the large particles may refer to primary particles having a particle size of 3 to 20 μm.

[0127] The small particles may refer to primary particles having a particle size of 1 μm or less.

[0128] The lithium composite phosphate may include particles having a particle size outside the above-mentioned range, but the peak of the particle size distribution may fall within each of the particle size ranges of the large particles and the small particles.

[0129] The secondary particles may have gaps and / or grain boundaries between the primary particles. In another embodiment, the positive electrode active material may include a lithium composite phosphate that exists in a single crystal form having an average particle size of 0.05 μm or more.

[0130] The primary particles may be separated from adjacent primary particles within the secondary particle to form internal voids. Also, the primary particles may contact adjacent primary particles without forming grain boundaries and contact internal voids to form a surface present inside the secondary particle. The surface of the primary particles present at the outermost surface of the secondary particle and exposed to the outside air forms the surface of the secondary particle.

[0131] The average particle size of the secondary particles formed by agglomeration of a plurality of the primary particles may vary depending on the number of agglomerated primary particles, but may generally be 30.0 to 40.0 μm, for example, 30.0 μm, 30.5 μm, 31.0 μm, 31.5 μm, 32.0 μm, 32.5 μm, 33.0 μm, 33.5 μm, 34.0 μm, 34.5 μm, 35.0 μm, 35.5 μm, 36.0 μm, 36.5 μm, 37.0 μm, 37.5 μm, 38.0 μm, 38.5 μm, 39.0 μm, 39.5 μm, 40.0 μm, or a range between any two of these values.

[0132] The content of the first lithium composite phosphate in the positive electrode active material may be 80 to 90% by weight, for example, 80% by weight, 80.5% by weight, 81% by weight, 81.5% by weight, 82% by weight, 82.5% by weight, 83% by weight, 83.5% by weight, 84% by weight, 84.5% by weight, 85% by weight, 85.5% by weight, 86% by weight, 86.5% by weight, 87% by weight, 87.5% by weight, 88% by weight, 88.5% by weight, 89% by weight, 89.5% by weight, 90% by weight, or a range between any two of these values.

[0133] Furthermore, the content of the second lithium composite phosphate in the positive electrode active material may be 10 to 20% by weight, for example, 10% by weight, 10.5% by weight, 11% by weight, 11.5% by weight, 12% by weight, 12.5% ​​by weight, 13% by weight, 13.5% by weight, 14% by weight, 14.5% by weight, 15% by weight, 15.5% by weight, 16% by weight, 16.5% by weight, 17% by weight, 17.5% by weight, 18% by weight, 18.5% by weight, 19% by weight, 19.5% by weight, 20% by weight, or a range between two of these values.

[0134] When the contents of the first lithium composite phosphate and the second lithium composite phosphate satisfy the above-mentioned ranges, the density of the positive electrode active material is high.

[0135] At least one of the first lithium composite phosphate and the second lithium composite phosphate may contain iron, a dopant, and sodium elements.

[0136] The dopant is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn and Zr.

[0137] According to the above-mentioned manufacturing method, the particle size can be adjusted by using a dopant and sodium during the growth of the lithium composite phosphate particles using an iron-containing precursor.

[0138] That is, the lithium composite phosphate may contain iron, a dopant, and sodium elements, and may be synthesized in a bimodal form containing small particles and large particles.

[0139] In addition, the dopant and sodium element can adjust the crystallinity of the lithium composite phosphate. The lithium complex phosphate may be represented by the following Chemical Formula 2:

[0140] [Chemical formula 2] Li p Fe (1-y-z) M y Na z PO4 In the above formula, M is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, and 0.95≦p≦1.05, 0.02≦y≦0.03, and 0≦z≦0.01.

[0141] The composition of the lithium composite phosphate may vary depending on the composition of the raw materials used in the above-mentioned preparation method and the types and compositions of the sub-raw materials further used therein. The positive electrode active material may also include a coating layer that covers at least a portion of the surfaces of the primary particles (e.g., interfaces between the primary particles) and / or secondary particles formed by aggregation of the primary particles.

[0142] Furthermore, an amorphous carbon coating layer having a thickness of 1 to 500 nm, for example, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 12.5 nm, 15 nm, 17.5 nm, 20 nm, 22.5 nm, 25 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range between two of these values, may be formed on the surface of at least a part of the primary particles.

[0143] For example, the coating layer may be present so as to cover at least a portion of the exposed surface of the primary particles, particularly, the coating layer may be present so as to cover at least a portion of the exposed surface of the primary particles present at the outermost portion of the secondary particles.

[0144] Thus, the coating layer may exist as a layer that coats the surfaces of the primary particles and / or the secondary particles formed by agglomeration of the primary particles continuously or discontinuously. When the coating layer exists discontinuously, it may exist in the form of islands.

[0145] In some cases, the oxide may be present not only at the interfaces between the primary particles and at least a portion of the surfaces of the secondary particles, but also in internal voids formed inside the secondary particles.

[0146] The coating layer thus present can contribute to improving the electrochemical properties and stability of the positive electrode active material.

[0147] In this case, the coating layer may be in the form of a solid solution that does not form a boundary with the primary particles and / or the secondary particles formed by agglomeration of the primary particles, but this is not necessarily the case.

[0148] In particular, lithium iron phosphate-based positive electrode active materials, which have low electrical conductivity, can be supplemented with a carbon coating, but an uneven carbon coating layer can reduce the properties of the positive electrode active material, such as the BET specific surface area, pellet density, and energy capacity.

[0149] Here, the content of the carbon coating layer may be 1.0 to 2.0 wt % based on 100 wt % of the lithium composite phosphate, for example, 1.0 wt %, 1.05 wt %, 1.1 wt %, 1.15 wt %, 1.2 wt %, 1.25 wt %, 1.3 wt %, 1.35 wt %, 1.4 wt %, 1.45 wt %, 1.5 wt %, 1.55 wt %, 1.6 wt %, 1.65 wt %, 1.7 wt %, 1.75 wt %, 1.8 wt %, 1.85 wt %, 1.9 wt %, 1.95 wt %, 2.0 wt %, or a range between two of these values.

[0150] When the range is satisfied, the conductivity of the lithium composite phosphate can be improved and a decrease in pellet density of the positive electrode active material can be minimized.

[0151] In the positive electrode active material, the first lithium composite phosphate and the second lithium composite phosphate may be coated with the same amount of carbon.

[0152] Here, the thickness of the carbon coating layer can be adjusted according to the balance between the fluidity and the conductivity of the lithium composite phosphate.

[0153] The thickness of the carbon coating layer can be measured by various known methods. For example, it can be measured from a TEM or SEM image, or confirmed from a line scanning result of carbon in a specific direction from an EDX analysis result. Such a thickness can be an average value obtained by measuring at least three times.

[0154] Lithium secondary battery According to yet another aspect, a positive electrode may be provided, the positive electrode including a positive current collector and a positive active material layer formed on the positive current collector. Here, the positive active material layer may include a positive active material manufactured by the manufacturing method according to any of the various embodiments described above.

[0155] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0156] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0157] In this case, the positive electrode active material may be included in an amount of 80 to 99 wt %, more specifically, 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer. When included in this content range, excellent capacity characteristics can be exhibited, but the amount is not necessarily limited thereto.

[0158] The conductive material is used to impart electrical conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials such as carbon fibers, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in combination. The conductive material may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0159] The binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and among these, one type alone or a mixture of two or more types may be used. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0160] The positive electrode may be manufactured by a typical method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0161] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when applied to manufacture a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0162] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the positive electrode slurry composition from the support, and laminating the resulting film on a positive electrode current collector.

[0163] According to yet another aspect, an electrochemical device including the above-mentioned positive electrode may be provided. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0164] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

[0165] The lithium secondary battery may be provided as an anode-free secondary battery. Here, since the positive electrode is as described above, detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below. Also, it should be understood that the description related to the negative electrode described below will be described on the assumption that the lithium secondary battery includes a negative electrode.

[0166] In addition, the lithium secondary battery may have a separator replaced with a solid electrolyte. In this case, an electrode slurry composition further containing a solid electrolyte may be used when preparing the positive and negative electrodes.

[0167] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container. The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0168] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may generally have a thickness of 3 to 500 μm, and like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0169] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0170] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon, metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys, and SiO β(0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, may be used. A metallic lithium thin film may be used as the negative electrode active material. Low-crystalline carbon and high-crystalline carbon may both be used as the carbon material. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0171] The negative electrode active material may be included in an amount of 80 to 99 wt % based on the total weight of the negative electrode active material layer. The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and may be added in an amount of usually 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0172] The conductive material may be added as a component for further improving the conductivity of the negative electrode active material in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and may be, for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride, aluminum, or nickel powder, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives.

[0173] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, and then peeled off from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0174] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a passage for lithium ions to move. Any separator generally used in lithium secondary batteries may be used without any particular limitation. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte and has excellent electrolyte humidification ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used. In addition, in order to ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0175] Examples of the electrolyte used in the lithium secondary battery include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used during the manufacture of lithium secondary batteries. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0176] The organic solvent may be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone, an ether solvent such as dibutyl ether or tetrahydrofuran, a ketone solvent such as cyclohexanone, an aromatic hydrocarbon solvent such as benzene or fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that may be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte may be excellent if the cyclic carbonate and the chain carbonate are mixed at a volume ratio of about 1:1 to about 1:9.

[0177] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

[0178] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc. In this case, the additives may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0179] The electrolyte may include a solid electrolyte such as a solid polymer electrolyte, a gel polymer electrolyte, or a solid inorganic electrolyte.

[0180] In the case of a lithium secondary battery including a solid electrolyte, the separator described above can be omitted. However, since the electrolyte is difficult to permeate into the positive and negative electrodes, the solid electrolyte can be mixed into the positive and negative electrodes during the manufacture of the electrodes.

[0181] The solid polymer electrolyte or gel polymer electrolyte may be a composite of a salt of a metal ion of Group 1 or Group 2 of the periodic table used in secondary batteries and a polymer resin, for example, a solvated lithium salt to which a polymer resin is added.

[0182] The salt of the metal ion may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc.

[0183] Examples of the polymer resin include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives such as polyethylene oxide, phosphate polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, branched copolymers in which amorphous polymers such as PMMA, polycarbonate, polysiloxane (PDMS) and phosphazene are copolymerized with a comonomer on a PEO (poly ethylene oxide) main chain, comb-like polymers, and crosslinked polymer resins.

[0184] The solid inorganic electrolyte can be broadly classified into sulfide-based solid electrolytes and oxide-based solid electrolytes.

[0185] The sulfide-based solid electrolyte may be a material that contains sulfur (S) and has the conductivity of metal ions of Group 1 or Group 2 of the periodic table used in secondary batteries, such as Li-PS-based glass or Li-PS-based glass ceramics that have the conductivity of lithium ions.

[0186] An example of the sulfide-based solid electrolyte may be at least one selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2OP2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS.

[0187] The oxide-based solid electrolyte may be a material that contains oxygen (O) and has the electrical conductivity of metal ions in Group 1 or Group 2 of the periodic table used in secondary batteries. For example, LLTO-based compounds, Li6La2CaTa2O 12 , Li6La2ACaNb2O 12 , Li6La2ASrNb2O 12 , Li2Nd3TeSbO 12 , LiBO 2.5 N 0.5 , Li9SiAlO8, a LAGP-based compound, a LATP-based compound, a LISICON-based compound, a LIPON-based compound, a perovskite-based compound, a NASICO-based compound, and a LLZO-based compound.

[0188] As described above, a lithium secondary battery including the positive electrode active material stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0189] The external shape of the lithium secondary battery is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also preferably as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0190] According to yet another aspect, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0191] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (Electric Vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0192] The above-mentioned matters will be described in more detail below with reference to examples. However, these examples are merely illustrative and are not to be construed as limiting the scope of the present specification.

[0193] Production Example 1. Production of positive electrode active material (1) Comparative Example 1 FeSO4·7H2O, H3PO4 and H2O2 were added to the reactor in a molar ratio of 1:1:1, followed by adding deionized water (DIW) to prepare an aqueous solution. NaOH and NH4OH were added to the aqueous solution and stirred. At this time, the temperature inside the reactor was maintained at 60°C, and N2 gas was added to synthesize the precursor. After the reaction was completed, the mixture was washed and dehydrated to obtain a transition metal hydroxide precursor with the composition FePO4·xH2O.

[0194] The temperature of the calcination furnace in the N2 atmosphere was increased at a rate of 2° C. / min, and the transition metal hydroxide precursor was heat-treated for 5 hours while maintaining the temperature at 550° C. Then, the furnace was cooled to obtain an iron-containing precursor.

[0195] The iron-containing precursor, the lithium-containing raw material Li2CO3, and the carbon-based compound glucose were mixed in a molar ratio of 2:1:1 to prepare a slurry, which was then pulverized in a ball mill so that the precursor and raw material in the slurry had a D50 of 1.0 μm or less. The slurry was then dried using a spray dryer (Toshin Giken, DJE003R).

[0196] The temperature of the furnace in the N2 atmosphere was increased at a rate of 2° C. / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 850° C. The furnace was then cooled and classified to obtain a positive electrode active material containing lithium iron phosphate having a D50 of 30.0 to 40.0 μm.

[0197] (2) Comparative Example 2 A positive active material was prepared in the same manner as in Comparative Example 1, except that the titanium-containing raw materials were mixed so that the molar ratio of iron to titanium in the slurry was 97:3.

[0198] (3) Example 1 A positive electrode active material was prepared in the same manner as in Comparative Example 1, except that the titanium-containing raw material and the sodium-containing raw material were mixed so that the molar ratio of iron, titanium and sodium in the slurry was 97:2.5:0.5.

[0199] (4) Example 2 A positive active material was prepared in the same manner as in Comparative Example 1, except that the vanadium-containing raw material and the sodium-containing raw material were mixed so that the molar ratio of iron, vanadium, and sodium in the slurry was 97:2.5:0.5.

[0200] (5) Example 3 A positive electrode active material was prepared in the same manner as in Comparative Example 1, except that the magnesium-containing raw material and the sodium-containing raw material were mixed so that the molar ratio of iron, magnesium, and sodium in the slurry was 97:2.5:0.5.

[0201] (6) Example 4 A positive electrode active material was prepared in the same manner as in Comparative Example 1, except that the aluminum-containing raw material and the sodium-containing raw material were mixed so that the molar ratio of iron, aluminum, and sodium in the slurry was 97:2.5:0.5.

[0202] (7) Example 5 A positive active material was prepared in the same manner as in Comparative Example 1, except that the zinc-containing raw material and the sodium-containing raw material were mixed so that the molar ratio of iron, zinc, and sodium in the slurry was 97:2.5:0.5. In the above-mentioned Examples 1 to 5, sulfates, carbonates, nitrates, acetates, chlorides, hydroxides and oxides were used as raw materials containing specific elements.

[0203] Experimental Example 1. Characterization of Positive Electrode Active Material In order to confirm the characteristics of the positive active material prepared in Preparation Example 1, the crystal size was analyzed by XRD and the results are shown in Table 1 below.

[0204] [Table 1]

[0205] In addition, the average particle size and particle size distribution of the primary particles and secondary particles of the positive active material were measured using a laser diffraction scattering particle size distribution analyzer (Cilas PSA 1060) to obtain a cumulative particle size distribution curve based on volume, which is shown in Table 2 and Figures 1 and 2.

[0206] [Table 2]

[0207] The ratio of particles having a particle size of 1 μm or less and the ratio of particles having a particle size of 3 μm or more in the primary particles in the examples are shown in Table 3 below.

[0208] [Table 3]

[0209] In addition, the primary particle sizes of the positive active materials prepared in the comparative examples and examples were measured from cross-sectional SEM images, and are shown in Table 4 below.

[0210] [Table 4]

[0211] From the above results, it can be seen that bimodal primary particles were prepared in the positive electrode active material of the embodiment doped with a dopant capable of acting as a flux.

[0212] In particular, referring to Comparative Example 2 and Examples 1 to 5, it can be confirmed that adding Na as a dopant makes it possible to produce large particles. Furthermore, even when Na dopant was added, no problems such as lattice distortion or residual impurities were found.

[0213] Manufacturing Example 2. Manufacturing of lithium secondary batteries A positive electrode slurry was prepared by dispersing 94 wt% of each positive electrode active material prepared in Preparation Example 1, 3 wt% of artificial graphite, and 3 wt% of PVDF binder in 3.5 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was applied to a 20 μm-thick aluminum (Al) thin film serving as a positive electrode current collector, dried, and roll-pressed to prepare a positive electrode.

[0214] A coin battery was fabricated according to a commonly known manufacturing process using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and a liquid electrolyte of LiPF6 at a concentration of 1.15 M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0215] Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries In Production Example 2, a charge / discharge experiment was performed on the coin battery using an electrochemical analyzer (Toyo, Toscat 3100) at 25°C, voltage range of 2.0 to 3.65 V, and discharge rate of 0.1 to 5.0 C, and the initial charge capacity, initial discharge capacity, initial reversible efficiency, and energy density were measured. The pellet density was measured after weighing 3 g of the positive electrode active material into a pelletizer and applying pressure of 4.5 tons for 5 seconds. The energy density was calculated by multiplying the initial discharge capacity by the average voltage (3.4 V) and the pellet density.

[0216] [Table 5]

[0217] When using the positive electrode active material of the embodiment to which a dopant having a flux effect was added, the pellet density was increased, and as a result, the electrochemical properties such as the energy density could be improved.

[0218] This is believed to be due to the change in shape of the primary particles such that the positive electrode active material is formed to have a bimodal particle size.

[0219] Although the embodiments of the present specification have been described above, a person having ordinary knowledge in the art may modify and change the present specification in various ways, such as by adding, changing, deleting or adding elements, without departing from the gist of the present specification as set forth in the claims, and this may also be said to be within the scope of the present specification.

Claims

1. (a) mixing a lithium-containing source material, an iron-containing precursor, a dopant-containing source material, a sodium-containing source material, and a carbon-based compound to produce a slurry; (b) milling the particles in the slurry; and (c) heat-treating the ground particles to obtain a lithium composite phosphate; Including, The dopant is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr.

2. 2. The method of claim 1, wherein the ratio (Li / Metal) of the number of lithium atoms (Li) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) is 0.95 to 1.

05.

3. 2. The method of claim 1, wherein a ratio (Fe / Metal) of the number of iron atoms (Fe) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) is 0.96 to 0.

98.

4. 2. The method of claim 1, wherein a ratio (D / Metal) of the number of dopant atoms (D) to the total number of metal atoms (Metal) other than lithium in the slurry in step (a) is 0.02 to 0.

03.

5. 2. The method of claim 1, wherein a ratio (Na / Metal) of the number of sodium atoms (Na) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) is 0 to 0.

01.

6. 2. The method of claim 1, wherein in step (a), at least one of the dopant-containing raw material and the sodium-containing raw material is at least one selected from the group consisting of sulfates, carbonates, nitrates, acetates, chlorides, hydroxides, and oxides.

7. 2. The method of claim 1, wherein the ratio (C / Metal) of the number of carbon atoms (C) to the total number of atoms (Metal) of metal elements other than lithium in the slurry in step (a) is 0.25 to 1.

5.

8. 2. The method of claim 1, wherein the pulverized particles in step (c) are obtained by spray-drying the slurry obtained in step (b).

9. 2. The method of claim 1, wherein the heat treatment in step (c) is performed at a maximum temperature of 600 to 900° C. for 5 to 15 hours in an inert atmosphere.

10. A positive electrode active material including a lithium composite phosphate capable of lithium intercalation / deintercalation, The lithium composite phosphate includes secondary particles formed by agglomeration of a plurality of primary particles, The primary particles are in a bimodal form including a first lithium composite phosphate as a small particle and a second lithium composite phosphate as a large particle; At least one of the first lithium composite phosphate and the second lithium composite phosphate contains iron, a dopant and sodium elements; the dopant is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr; The positive electrode active material for a lithium secondary battery comprises an amorphous carbon coating layer having a thickness of 1 to 500 nm formed on at least a portion of the surface of the primary particles.

11. The positive electrode active material for lithium secondary batteries according to claim 10, wherein the content of the second lithium composite phosphate in the positive electrode active material is 10 to 20% by weight.

12. The positive electrode active material for a lithium secondary battery according to claim 10, wherein the lithium composite phosphate is represented by the following Chemical Formula 2: [Chemical formula 2] Li ｐ Fe （１－ｙ－ｚ） M ｙ Na ｚ PO ４ In the above formula, M is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr; 0.95≦p≦1.05, 0.02≦y≦0.03, and 0≦z≦0.

01.

13. A positive electrode comprising the positive electrode active material according to claim 10 .

14. A lithium secondary battery using the positive electrode according to claim 13.

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