Method for preparing positive electrode active material for lithium secondary battery

Abstract

The present specification relates to a method for preparing a positive electrode active material for a lithium secondary battery, and more particularly, to a method for preparing a positive electrode active material for a lithium secondary battery having excellent conductivity and energy density, a positive electrode including the same, and a secondary battery.

Description

Technical Field

[0001] This specification relates to a method for preparing a positive electrode active material for lithium secondary batteries, and more specifically, to an environmentally friendly method for preparing a positive electrode active material for lithium secondary batteries with excellent conductivity and energy density. Background Technology

[0002] Batteries use materials capable of electrochemical reactions at the positive and negative electrodes to store electrical energy. A representative example of such batteries is the lithium-ion secondary battery, which stores electrical energy through the chemical potential difference between the positive and negative electrodes during the insertion / extraction of lithium ions.

[0003] The aforementioned lithium secondary battery is prepared by using materials capable of reversible lithium-ion insertion / extraction as positive and negative electrode active materials, and filling the space between the positive and negative electrodes with organic or polymer electrolytes.

[0004] Various materials are used as positive electrode active materials for lithium secondary batteries. Among them, lithium metal phosphates, such as lithium iron phosphate (LiFePO4), are widely used in the manufacture of lithium secondary batteries due to their excellent stability and ability to withstand multiple charge / discharge cycles, as well as their relatively low manufacturing cost.

[0005] Existing positive electrode active materials are prepared by first synthesizing a precursor, then adding lithium and calcining it. During this process, SO₂ is generated due to components present in the raw materials used to prepare the precursor. x or NO x Pollutants such as lead and precipitates are present. Furthermore, after synthesizing the precursor, dehydration or drying is required before adding lithium, which presents disadvantages in terms of energy efficiency and yield.

[0006] With the development of technology, the demand for lithium secondary batteries, represented by electric vehicles, has grown rapidly. In related industries, the demand for technologies that prepare positive electrode active materials in a more environmentally friendly and energy-efficient manner is also increasing. Summary of the Invention

[0007] Technical issues

[0008] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles plays a leading role, while the demand for positive electrode active materials used in lithium secondary batteries is also constantly changing, especially the demand for increased capacity of positive electrode active materials.

[0009] At the same time, the market is also demanding more environmentally friendly methods to prepare positive electrode active materials. Therefore, the preparation methods of positive electrode active materials urgently need fundamental changes.

[0010] To meet these market demands, the purpose of this specification is to provide a method for preparing positive electrode active materials without the need for a separate process to obtain precursors.

[0011] Furthermore, the purpose of this specification is to provide a positive electrode comprising a positive electrode active material prepared according to the preparation method defined herein.

[0012] Furthermore, the purpose of this specification is to provide a lithium secondary battery using the positive electrode defined herein.

[0013] Solution to the problem

[0014] According to one aspect of this specification, a method for preparing a positive electrode active material for a lithium secondary battery is provided, comprising: step (a) reacting a transition metal raw material with a phosphoric acid raw material to prepare a slurry containing a metal-phosphorus complex; step (b) adding a lithium raw material and a carbon raw material to the slurry, and pulverizing and drying to obtain a powder; and step (c) heat-treating the powder to obtain a lithium composite compound.

[0015] In one embodiment, the transition metal may be Fe, or may include Fe and at least one selected from the group consisting of Mn, Ni and Co.

[0016] On the other hand, the reaction in step (a) above can be carried out at a temperature of 60°C to 150°C.

[0017] Furthermore, in step (b) above, the lithium raw material can be added such that the ratio of the number of lithium atoms (Li) to the total number of metal atoms other than lithium (Metal) in the slurry (Li / Metal) is 0.90 to 1.10.

[0018] In another embodiment, the amount of carbon raw material added in step (b) above can be a molar ratio of 0.01 to 0.5 based on the total molar amount of the lithium composite compound.

[0019] In step (b) above, at least one auxiliary raw material may be added to the slurry, including an element selected from the group consisting of 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.

[0020] In addition, in step (b) above, pulverization can be performed so that the average particle size of the solids in the slurry is less than 1.0 μm.

[0021] As an example, the heat treatment in step (c) above can be carried out at temperatures between 700°C and 950°C.

[0022] According to another aspect of this specification, a positive electrode active material is provided, which is a positive electrode active material prepared according to the above method, comprising a lithium composite compound capable of lithium intercalation / deintercalation, the lithium composite compound comprising a plurality of particulate materials, at least a portion of which has an amorphous carbon coating with a thickness of 1 nm to 500 nm formed on its surface, the lithium composite compound being represented by the following chemical formula 1:

[0023] [Chemical Formula 1]

[0024] Li p Fe 1-x-y M x A y A' z P 1-z O w

[0025] In the above formula, M is at least one selected from the group consisting of Mn, Ni, and Co; A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr; A' is at least one selected from the group consisting of C, Si, S, N, B, F, Cl, and I; 0.5 ≤ p ≤ 1.5, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 <w≤4。

[0026] According to another aspect, a positive electrode containing the aforementioned positive electrode active material is provided.

[0027] According to another aspect, a lithium secondary battery using the above-mentioned positive electrode is provided.

[0028] The effects of the invention

[0029] According to this instruction manual, no harmful substances are produced when the raw materials are calcined, thus making it more environmentally friendly.

[0030] In addition, unnecessary dehydration or drying processes are omitted in the preparation of the above-mentioned positive electrode active material, so that the positive electrode active material can be prepared in a more economical and efficient manner.

[0031] In addition to the effects described above, the specific effects of this instruction manual will be described while explaining the specific details of this instruction manual. Detailed Implementation

[0032] Specific terms are defined herein for ease of understanding. Unless specifically defined herein, scientific and technical terms used herein should have the meanings commonly understood by those skilled in the art. Furthermore, it should be understood that, as used herein, the singular form is intended to include the plural form, and vice versa, unless the context clearly indicates otherwise.

[0033] The following will describe in more detail the method for preparing the positive electrode active material for lithium secondary batteries according to this specification, the positive electrode including the positive electrode active material prepared according to the above preparation method, and the lithium secondary battery using the above positive electrode.

[0034] Preparation method of positive electrode active material for lithium secondary batteries

[0035] A method for preparing a positive electrode active material for a lithium secondary battery according to one aspect of this specification may include: step (a) reacting a transition metal raw material with a phosphoric acid raw material to prepare a slurry containing a metal-phosphorus complex; step (b) adding a lithium raw material and a carbon raw material to the slurry, and pulverizing and drying it to obtain a powder; and step (c) heat-treating the powder to obtain a lithium composite compound.

[0036] In existing methods for preparing lithium phosphate composites, sulfates or nitrates are used as raw materials. First, a precursor in the form of phosphate is prepared, and then lithium is added and calcined to prepare the positive electrode active material.

[0037] However, in this preparation method, energy and yield losses occur during the dehydration and drying processes when preparing the precursor. Furthermore, SO₂ is generated. x or NO x The problem of harmful substances.

[0038] On the other hand, according to the preparation method described above according to one aspect of this specification, SO will not be generated. x or NO x Harmful substances can be eliminated, and by omitting unnecessary dehydration or drying processes, not only can an environmentally friendly method be achieved, but also positive electrode active material products with comparable or better performance can be prepared.

[0039] Step (a) above is a step of reacting a transition metal raw material with a phosphate raw material to form a metal-phosphorus complex. The transition metal raw material and the phosphate raw material can each be one or more of the same type.

[0040] The aforementioned transition metal raw material refers to a substance containing a transition metal. In one embodiment, the transition metal may be Fe, or may include Fe and at least one selected from the group consisting of Mn, Ni, and Co.

[0041] For example, when the transition metal is Fe, the transition metal raw material can be at least one selected from the group consisting of Fe metal, FeOOH, Fe2O3 and Fe3O4.

[0042] On the other hand, when the aforementioned transition metal further includes a transition metal M other than Fe, it may include the aforementioned Fe transition metal raw material and at least one selected from the group consisting of MSO4, HMPO4, MPO4, M3(PO4)2, (CH3COO)2M, M(NO3)2, MCO3, M2CO3 and MO2 as the transition metal raw material.

[0043] In addition, the aforementioned phosphoric acid raw materials include anions, salts, functional groups, or esters derived from phosphoric acid. For example, the aforementioned phosphoric acid raw materials may be at least one selected from the group consisting of H3PO4, Li3PO4, NH4H2PO4, and (NH4)2HPO4.

[0044] Regarding the ratio of the aforementioned transition metal raw material to the aforementioned phosphoric acid raw material, based on 1 mole of transition metal element, the phosphorus element can be from 0.90 moles to 1.10 moles, for example, it can be 0.90 moles, 0.91 moles, 0.92 moles, 0.93 moles, 0.94 moles, 0.95 moles, 0.96 moles, 0.97 moles, 0.98 moles, 0.99 moles, 1.00 moles, 1.01 moles, 1.02 moles, 1.03 moles, 1.04 moles, 1.05 moles, 1.06 moles, 1.07 moles, 1.08 moles, 1.09 moles, 1.10 moles, or any two of these values ​​within a range.

[0045] On the other hand, the reaction in step (a) above can be carried out at temperatures ranging from 60°C to 150°C, for example, at 60°C, 62.5°C, 65°C, 67.5°C, 70°C, 72.5°C, 75°C, 77.5°C, 80°C, 82.5°C, 85°C, 87.5°C, 90°C, 92.5°C, 95°C, 97.5°C, 100°C, 102.5°C, 105°C, 107.5°C, 110°C, 112.5°C, 115°C, 117.5°C, 120°C, 122.5°C, 125°C, 127.5°C, 130°C, 132.5°C, 135°C, 137.5°C, 140°C, 142.5°C, 145°C, 147.5°C, 150°C, or any two of these values.

[0046] Here, the above reaction can be carried out by stirring the slurry within a time range of 4 hours to 48 hours, for example, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, 48 ​​hours, or any two of these values.

[0047] In step (a) above, transition metal ions can react with phosphate ions to form a metal-phosphorus complex. For example, when iron ions (Fe...) react with phosphate ions... 3+ ) and phosphate ions (PO4) 3- During the reaction, various metal-phosphorus complexes can be formed. These metal complexes may include FePO4·nH2O (0≤n≤9), anhydrous FePO4, Fe3(PO4)2, Fe2(HPO4)3, etc. Among these, the aforementioned metal-phosphorus complexes can also exist in the slurry in precipitated form. Furthermore, FePO4·2H2O typically constitutes the largest proportion of these metal-phosphorus complexes.

[0048] On the other hand, step (b) above can be a step of adding lithium raw material and carbon raw material to the slurry containing the above metal-phosphorus composite without the need for additional dehydration or drying processes.

[0049] Furthermore, in conventional methods for preparing lithium iron phosphate compounds using precursors, omitting dehydration or drying processes can result in sulfur (S) and nitrogen (N) compounds remaining as impurities in the slurry. These impurities not only generate SO2 during calcination but also contribute to the formation of sulfur dioxide. x NO x These harmful substances may also hinder the carbonization of carbon raw materials and the growth of olivine crystals. Furthermore, if the components from these sources remain in the positive electrode active material, they may trigger gas generation in the battery, thereby reducing stability.

[0050] The aforementioned lithium raw materials can be used to introduce lithium, enabling the aforementioned metal-phosphorus complex to function as a lithium cathode active material.

[0051] The lithium raw material in step (b) above may be added such that the ratio (Li / Metal) of the number of lithium atoms (Li) to the total number of atoms of other metal elements (Metal) in the slurry is 0.90 to 1.20, for example, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, or any two of these values. Alternatively, depending on the purpose, the mixture may be prepared such that the ratio (Li / Metal) is 0.5 to 1.5, but is not limited thereto.

[0052] On the other hand, the carbon raw material added in step (b) above can be used to form a carbon coating to improve the conductivity of the positive electrode active material. By minimizing the thickness of the carbon coating while increasing its uniformity, the reduction in fluidity due to amorphous carbon can be minimized, and the conductivity of the positive electrode active material can be improved.

[0053] For example, lithium iron phosphate compounds, which are olivine-based cathode materials, are affected by PO4. 3- The strong covalent bonds in Li result in relatively low electrical conductivity. Furthermore, it is understood that due to its crystal structure, Li... + It can only diffuse in one dimension, so its ionic conductivity is low.

[0054] As a means to address these shortcomings, techniques have been proposed to improve conductivity by forming carbon coatings and to improve Li-N cobalt conductivity by nanoparticleization. + Diffusion technology.

[0055] However, in existing positive electrode active materials, the coated carbon usually exists in an amorphous phase, which may reduce the density of the positive electrode active material.

[0056] Furthermore, existing nanoparticles tend to agglomerate and grow into angular particles during the calcination process.

[0057] As a result, the reduced fluidity caused by amorphous carbon and the reduced density of the positive electrode active material due to angled particles may reduce the energy density of the final product.

[0058] On the other hand, the carbon coating formed by the above method can have a uniform and thin thickness. Furthermore, the carbon raw material can induce the lithium composite compound to grow into a spherical shape.

[0059] On the other hand, the aforementioned carbon raw material can be a compound with a C element ratio in its molecular structure of 30 wt% to 60 wt%, for example, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, or any two of these values.

[0060] By using carbon feedstocks with C ratios within the aforementioned range, products with excellent yields and uniform carbon coating can be prepared even when using compounds with the same content.

[0061] Examples of the aforementioned carbon raw materials 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.

[0062] Furthermore, the properties of the carbon source material can be adjusted to regulate the properties of the resulting carbon coating.

[0063] For example, in positive electrode active materials, minimizing the thickness of the carbon coating and improving its uniformity can minimize the decrease in fluidity caused by amorphous carbon and improve the conductivity of the positive electrode active material.

[0064] In one embodiment, the amount of carbon source material added in step (b) above can be from 0.01 molar ratio to 0.5 molar ratio based on the total molar amount of the lithium complex compound, for example, 0.01 molar, 0.05 molar, 0.1 molar, 0.15 molar, 0.2 molar, 0.25 molar, 0.3 molar, 0.35 molar, 0.4 molar, 0.45 molar, 0.5 molar, or any two of these values.

[0065] In another example, the aforementioned carbon source material may be added such that the ratio (C / Metal) of the number of carbon atoms (C) to the total number of metal atoms (excluding lithium) in the slurry is 0.30 to 0.70, for example, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, or a range between any two of these values.

[0066] In step (b) above, at least one auxiliary raw material may be added to the slurry, including an element selected from the group consisting of 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.

[0067] The aforementioned by-products can be introduced to dope the lithium composite compound with foreign elements. The doped foreign elements can improve the stability of the positive electrode active material or improve its conductivity.

[0068] Furthermore, step (b) above is a step of pulverizing the solid matter in the slurry. The slurry may contain lithium raw materials, metal-phosphorus complexes, carbon source materials, etc.

[0069] When pulverizing or drying slurries containing impurities, these impurities may remain, hindering the carbonization of the carbon source material for coating formation and the growth of olivine crystals. Furthermore, if the slurry containing impurities is washed and used, uniform carbon coating may be difficult to achieve. In contrast, the aforementioned slurry does not contain impurities such as sulfur (S) and nitrogen (N), therefore it can be used directly as a solid without additional washing processes, and the carbon source material can be uniformly coated during calcination.

[0070] In step (b) above, the slurry can be pulverized so that the average particle size of the solids in the slurry is less than 1.0 μm, 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 any two of these values. In another example, the average particle size (D50) of the pulverized particles in step (b) above can be, for example, from 0.5 μm to 0.7 μm, such as 0.5 μm, 0.51 μm, 0.52 μm, 0.53 μm, 0.54 μm, 0.55 μm, 0.56 μm, 0.57 μm, 0.58 μm, 0.59 μm, 0.6 μm, 0.61 μm, 0.62 μm, 0.63 μm, 0.64 μm, 0.65 μm, 0.66 μm, 0.67 μm, 0.68 μm, 0.69 μm, 0.7 μm, or a range between any two of these values.

[0071] The particles pulverized with an average particle size within the aforementioned range may moderately aggregate due to surface energy. As a result, the density characteristics of the aforementioned positive electrode active material can be improved.

[0072] In one example, step (b) above can be performed in a grinding machine containing beads with dimensions ranging from 0.1 mm to 1.5 mm, such as 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1 mm, 1.05 mm, 1.1 mm, 1.15 mm, 1.2 mm, 1.25 mm, 1.3 mm, 1.35 mm, 1.4 mm, 1.45 mm, 1.5 mm, or any two of these values. The dimensions mentioned above may refer to the diameter of the beads. When the beads are non-spherical, the diameter may refer to the diameter of their major axis.

[0073] On the other hand, the aforementioned grinding machine can include beads ranging from 30% to 50% in volume, for example, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, or any two of these values.

[0074] Furthermore, the solid content of the slurry fed into the aforementioned grinding mill can be 20% to 50%, for example, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, 47.5%, 50%, or any two of these values.

[0075] To pulverize the aforementioned particles, dry or wet dispersing mills such as ball mills, bead mills (which can use beads commonly used for pulverizing metallic materials such as aluminum beads, iron beads, or zirconium beads), vibratory mills, attritor mills, air jet mills, disc mills, or air classifier mills can be used.

[0076] In one example, the aforementioned grinding mill could be a nanomill containing zirconium beads.

[0077] On the other hand, in step (b) above, the slurry can be dried after pulverization to obtain a powder form. For example, the slurry can be dried by spray drying. That is, the powder in step (c) above can be the powder obtained by spray drying the slurry pulverized in step (b).

[0078] Spray drying, as an example of the above-mentioned drying process, can be carried out in a spray dryer. As for the spray dryer, there are no particular limitations as long as it is a spray drying apparatus that can prepare near-spherical dry particles by spray drying the above-mentioned slurry containing pulverized particles. For example, ultrasonic sprayers, single-fluid nozzle sprayers, two-fluid nozzle sprayers, ultrasonic nozzle sprayers, filter expansion droplet generators (FEAG), or disc droplet generators can be used.

[0079] The spray dryer described above may include a spray nozzle and a drying chamber, wherein the slurry is atomized into droplets of a predetermined size through the spray nozzle and sprayed into the drying chamber into which a relatively high-temperature gas flows.

[0080] The raw material in the droplets sprayed into the drying chamber can be dried into near-spherical particles under the temperature conditions inside the drying chamber.

[0081] On the other hand, if the slurry contains specific carbonaceous raw materials, unnecessary agglomeration of the particles during spray drying can be suppressed. As a result, near-spherical particles can be obtained.

[0082] In one example, moisture loss during drying reduces particle density, creating pores. As a result, particle strength may decrease, leading to insufficient stability of the positive electrode active material.

[0083] Here, when adjusting the viscosity of the slurry after pulverizing in step (b) above, the condensation time during drying can be shortened, and the decrease in density due to moisture loss during drying can be minimized.

[0084] On the other hand, if the viscosity of the slurry is too high, its fluidity will decrease during drying, resulting in insufficient process efficiency and difficulty in obtaining spherical particles.

[0085] One method for adjusting the viscosity of the above-mentioned slurry is to add a binder.

[0086] Subsequently, step (c) above may be a step of heat-treating the powder dried in step (b) above to form a lithium composite compound.

[0087] During the heat treatment in step (c) above, the carbon raw material can be carbonized to form a carbon coating. Therefore, the carbon raw material needs to be carbonized within the heat treatment temperature of step (c). If uncarbonized carbon compounds remain in the positive electrode active material, the improvement in conductivity may be minimal, or unpredictable side effects may occur.

[0088] The heat treatment in step (c) above can be carried out in an inert atmosphere at a maximum temperature of 700°C to 950°C for 5 to 15 hours. The maximum temperature can vary depending on the composition of the target positive electrode active material.

[0089] For example, the heat treatment described above can be performed at 700°C, 725°C, 750°C, 775°C, 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, or any two of these values. For example, this heat treatment can be performed by maintaining the highest temperature for 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, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours, 15 hours, or any two of these values, but is not limited to these.

[0090] When heat treatment is performed at temperatures within the range described above, the density of lithium composite compounds can be excellent.

[0091] On the other hand, if the heat treatment temperature in step (c) is insufficient, the calcination of the precursor may not be complete, resulting in insufficient crystal growth of the lithium composite compound or difficulty in forming a carbon coating. Consequently, the density of the lithium composite compound may decrease.

[0092] On the other hand, when the heat treatment temperature in step (c) is too high, the lithium composite compound may undergo thermal decomposition, resulting in reduced particle strength or particle collapse.

[0093] On the other hand, the above-mentioned heat treatment can be carried out by heating at a rate of 1°C to 10°C per minute, for example, at a rate of 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 per minute or a range between any two of these values.

[0094] Here, for example, the aforementioned inert atmosphere can be composed of at least one inert gas selected from the group consisting of N2, Ar, He, Rn, Ne and Xe, replacing air, but is not limited thereto.

[0095] Most of the metal-phosphorus complexes formed in step (a) above may be in hydrated form. The hydrated form of the metal-phosphorus complex can be recrystallized by removing the water of crystallization during calcination in step (c). This recrystallization process generates moisture and consumes heat energy. As a result, carbonization of the carbon raw material can be achieved at higher temperatures, resulting in a more uniform carbon coating and thus improved electrical conductivity.

[0096] Furthermore, after the heat treatment in step (c) above, cooling can be performed while maintaining an inert atmosphere at a temperature of 150°C or lower. For example, the heat-treated lithium composite compound can be obtained by furnace cooling.

[0097] In addition, before or after step (c) above, the lithium composite compound may be subjected to disintegration, distribution and / or washing processes.

[0098] Positive electrode active material for lithium secondary batteries

[0099] According to another aspect of this specification, the positive electrode active material for a lithium secondary battery is a positive electrode active material prepared by the above method, comprising a lithium composite compound capable of lithium intercalation / deintercalation, wherein the lithium composite compound comprises a plurality of particulate materials, and at least a portion of the particulate materials has an amorphous carbon coating with a thickness of 1 nm to 500 nm formed on its surface, and the lithium composite compound is represented by the following chemical formula 1:

[0100] [Chemical Formula 1]

[0101] Li p Fe 1-x-y M x A y A' z P 1-z O w

[0102] In the above formula, M is at least one selected from the group consisting of Mn, Ni, and Co; A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr; A' is at least one selected from the group consisting of C, Si, S, N, B, F, Cl, and I; 0.5 ≤ p ≤ 1.5, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 <w≤4。

[0103] The aforementioned positive electrode active material may include particulate material composed of lithium composite compounds capable of lithium intercalation / deintercalation.

[0104] In one embodiment, the aforementioned particulate material can exist without forming any aggregates. In this case, the particulate material can have a spherical shape. Furthermore, since the aforementioned lithium composite compound is a particulate material with a smooth surface, the aforementioned positive electrode active material can have excellent compressibility.

[0105] The average particle size of the aforementioned particulate material (here, the average particle size of the aforementioned particulate material can be the average major axis length of the aforementioned particulate material) is in the range of 0.01 μm to 5 μm, thus enabling the achievement of optimal density of the positive electrode prepared using the positive electrode active material according to various embodiments.

[0106] Meanwhile, in another example, the aforementioned particulate matter exists in the form of primary particles, which can aggregate into multiple particles to form secondary particles. Here, a primary particle refers to a single grain (or grain crystallite), and a secondary particle refers to an aggregate formed by the condensation of multiple primary particles. In this case, the primary particles can have a spherical shape. As described above, since the aforementioned lithium composite compound consists of particles with smooth surfaces, the aforementioned positive electrode active material can possess excellent compressibility.

[0107] Pores and / or grain boundaries may exist between the primary particles constituting the secondary particles. The primary particles may be spaced apart from adjacent primary particles within the secondary particles to form internal pores. Furthermore, the primary particles may form surfaces existing within the secondary particles by contacting internal pores, rather than forming grain boundaries by contacting adjacent primary particles. On the other hand, the surface of the primary particles existing on the outermost surface of the secondary particles, exposed to external air, forms the surface of the secondary particles.

[0108] The average particle size of the primary particles (here, the average particle size of the primary particles can be the average major axis length of the primary particles) is in the range of 0.1 μm to 5 μm, thus achieving the optimal density of the positive electrode prepared using the positive electrode active material according to various embodiments. The average particle size of the secondary particles formed by the aggregation of multiple primary particles can vary depending on the number of primary particles aggregated, but is typically 30.0 μm to 40.0 μm.

[0109] In another embodiment, the above-mentioned positive electrode active material may include a lithium composite compound existing in single crystal form with an average particle size of 0.1 μm or more.

[0110] On the other hand, the positive electrode active material may include a coating covering at least a portion of the surface of the particulate material (e.g., the interface between the particulate materials) and / or the aggregate formed by agglomerating the particulate material.

[0111] Here, the coating may include a carbon layer and / or an oxide layer to improve the stability of the particulate material or improve its electrical conductivity.

[0112] For example, the coating may be present in a manner that covers at least a portion of the exposed surface of the particulate material. On the other hand, when the particulate material agglomerates to form secondary particles, the coating may be present in a manner that covers at least a portion of the exposed surface of the primary particles present on the outermost periphery of the secondary particles.

[0113] Therefore, the coating can exist as a layer that continuously or discontinuously coats the surface of the particulate material and / or forms the surface of the secondary particles by agglomeration of the particulate material. When the coating exists discontinuously, it can exist in the form of islands.

[0114] Furthermore, when the aforementioned particulate matter forms an aggregate, the coating can exist not only at the interface between the aforementioned particulate matter and at least a portion of the surface of the aforementioned secondary particles, but also in the internal voids formed within the aforementioned secondary particles.

[0115] Coatings in this manner can help improve the electrochemical properties and stability of the positive electrode active material.

[0116] At this time, the coating may exist in the form of a solid solution that does not form a boundary with the particulate matter and / or the secondary particles formed by the aggregation of the particulate matter, but is not necessarily limited to this.

[0117] On the other hand, the thickness of the amorphous carbon coating formed on at least a portion of the surface of the aforementioned particulate matter can be from 1 nm to 500 nm, for example, it can be 1 nm, 2.5 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or a range between any two of these values.

[0118] The thickness of the carbon coating can be adjusted based on the balance between the fluidity and conductivity of the aforementioned lithium composite compound.

[0119] In particular, the aforementioned carbon coating has a small thickness deviation, thus the aforementioned positive electrode active material has an excellent balance in terms of complementary fluidity and conductivity.

[0120] The thickness of a carbon coating can be measured using a variety of known methods. For example, it can be measured by TEM or SEM images, or confirmed by EDX analysis results or line scanning of the carbon in a specific direction. The thickness, as described above, can be the average of at least three measurements.

[0121] Furthermore, the aforementioned carbon coating can be uniformly formed on the surface of the lithium composite compound, which is a particulate material, thereby giving it a smooth surface texture. As a result, the compressive density of the aforementioned positive electrode active material can be increased.

[0122] As is well known, olivine-based cathode materials have PO4 content that... 3- The strong covalent bonds in the Li crystal result in low electrical conductivity. Furthermore, due to the presence of Li in the crystal structure... + Diffusion occurs in a one-dimensional manner, resulting in low ionic conductivity. To address this issue, the formation of carbon coatings and the preparation of nano-sized positive electrode active materials have been proposed.

[0123] However, amorphous carbon coatings can lead to a decrease in the density of the positive electrode active material. Nanoparticles, due to aggregation, can grow into angular shapes during calcination, reducing fluidity and also causing a decrease in the density of the positive electrode active material. Therefore, a decrease in energy density per unit volume occurs.

[0124] On the other hand, the particulate material containing the lithium composite compound according to this specification has a uniform carbon coating. Furthermore, under the conditions for forming the aforementioned carbon coating, the lithium composite compound can be grown into spherical particulate material, thereby minimizing density loss.

[0125] Furthermore, the aforementioned lithium composite compound can be represented by the following chemical formula 1.

[0126] [Chemical Formula 1]

[0127] Li p Fe 1-x-y M x A y A' z P 1-z O w

[0128] In the above formula, M is at least one selected from the group consisting of Mn, Ni, and Co; A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr; A' is at least one selected from the group consisting of C, Si, S, N, B, F, Cl, and I; 0.5 ≤ p ≤ 1.5, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 <w≤4。

[0129] The above chemical formula 1 represents a lithium complex compound capable of lithium insertion / extraction, which may include lithium, metals and phosphates.

[0130] For example, p can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or a range between any two of these values, but is not limited thereto.

[0131] Furthermore, x, y, and z can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.99, or any two of these values, but are not limited to these.

[0132] Furthermore, the value of w can be 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, or a range between any two of these values, but is not limited thereto.

[0133] In other words, LiFePO4, LiFe 0.8 Mn0.2 PO4, LiFe 0.5 Mn 0.5 PO4 can be represented by the above chemical formula 1. On the other hand, the above lithium composite compound may also contain dopants. Here, the dopants may be represented as A and / or A'.

[0134] On the other hand, at least a portion of the surface of the particle-like material may contain a compound represented by the following chemical formula 2:

[0135] [Chemical Formula 2]

[0136] Li a M' b O c

[0137] In the above chemical 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, Fe, Ga, Hf, In, K, La, Mg, Mn, Mo, Na, Nb, Nd, Ni, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr, where 0 ≤ a ≤ 10, 0 <b≤8,2≤c≤13。

[0138] The compound represented by Chemical Formula 2 above can exist independently of the amorphous carbon coating, or it can exist as a discontinuous phase within the continuous phase of the amorphous carbon coating. In one example, the compound represented by Chemical Formula 2 above can form a coating. The coating can continuously or discontinuously cover at least a portion of the surface of the particulate material, and when the coating is discontinuous, it can exist in the form of islands. Furthermore, the coating can exist as a solid solution that does not form a boundary with the particulate material, but is not limited thereto.

[0139] On the other hand, preferably, even if at least a portion of the surface of the particulate material is coated with the compound, the particulate material retains its spherical shape.

[0140] Lithium secondary batteries

[0141] From another perspective, a positive electrode can be provided, comprising a positive current collector and a positive active material layer formed on the positive current collector. The positive active material layer may include a positive active material prepared according to the preparation methods of various embodiments as the positive active material.

[0142] There are no particular limitations on the aforementioned positive electrode current collector, as long as it does not induce chemical changes in the battery and has electrical conductivity. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or surface treatments of aluminum or stainless steel using carbon, nickel, titanium, silver, etc., can be used. Furthermore, the aforementioned positive electrode current collector typically has a thickness of 3μm to 500μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0143] The aforementioned positive electrode active material layer can be prepared by coating the aforementioned positive electrode current collector with a positive electrode slurry composition comprising the aforementioned positive electrode active material, a conductive material, and, if desired, a binder.

[0144] In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight. When the positive electrode active material is included in the above content range, excellent capacity performance can be shown, but it is not limited thereto.

[0145] The aforementioned conductive materials are used to impart conductivity to the electrodes. In the constructed battery, they can be used without restriction as long as they do not cause chemical changes and possess electronic conductivity. Specific examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One or more mixtures of these materials may be used. The total weight of the positive electrode active material layer may range from 0.1% to 15% by weight of the aforementioned conductive materials.

[0146] The aforementioned binder enhances the adhesion between multiple positive electrode active material particles and the bonding force 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 monomer (EPDM), sulfonated ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof; one or more mixtures thereof may be used. The binder may comprise 0.1% to 15% by weight of the aforementioned binder relative to the total weight of the positive electrode active material layer.

[0147] In addition to utilizing the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, it can be prepared by coating a positive electrode slurry composition onto a positive electrode current collector and then drying and calendering it. The positive electrode slurry composition is prepared by dissolving or dispersing the aforementioned positive electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent.

[0148] The solvents mentioned above can be those commonly used in this technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or a mixture of two or more of them can be used. Considering the coating thickness and preparation yield of the slurry, the amount of the solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that exhibits excellent thickness uniformity when coated for the preparation of the positive electrode.

[0149] Furthermore, in another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then laminating the thin film obtained by peeling off the support onto the positive electrode current collector.

[0150] Furthermore, according to another aspect of the present invention, an electrochemical device including the aforementioned positive electrode can be provided. Specifically, the aforementioned electrochemical device can be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0151] Specifically, the aforementioned lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separation membrane and electrolyte between the positive electrode and the negative electrode.

[0152] Furthermore, the aforementioned lithium secondary battery can be provided as an anode-free secondary battery. The positive electrode described above is the same as previously explained; therefore, for convenience, detailed descriptions are omitted, and only the remaining components not previously described will be explained below. Additionally, descriptions related to the negative electrode described below should be understood as assuming the presence of a negative electrode in the aforementioned lithium secondary battery.

[0153] On the other hand, the aforementioned lithium secondary battery can be a lithium secondary battery in which a solid electrolyte replaces the separator. In this case, an electrode slurry composition with an added solid electrolyte can be used when preparing the positive and negative electrodes.

[0154] The aforementioned lithium secondary battery may optionally include: a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separation membrane; and a sealing component for sealing the battery container.

[0155] The aforementioned negative electrode may include a negative current collector and a layer of negative active material located on the aforementioned negative current collector.

[0156] There are no particular limitations on the aforementioned negative electrode current collector, as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the aforementioned negative electrode current collector can typically have a thickness of 3μm to 500μm. Similar to the positive electrode current collector, the bonding force of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0157] The aforementioned negative electrode active material layer can be prepared by coating the aforementioned negative electrode current collector with a negative electrode slurry composition comprising the aforementioned negative electrode active material and conductive material, and selectively including a binder as needed.

[0158] As the aforementioned negative electrode active material, compounds capable of reversible lithium insertion and extraction can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; and metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; such as SiO₂. β Metal oxides capable of being doped and dedoped with lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above-mentioned metal compounds and carbon materials, such as Si-C composites or Sn-C composites, may be used, and one or more mixtures thereof may be used. Furthermore, lithium metal films may also be used as the above-mentioned negative electrode active material. Moreover, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, while representative high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitch, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0159] Based on the total weight of the negative electrode active material layer, it may contain 80% to 99% of the aforementioned negative electrode active material.

[0160] The aforementioned binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector. Typically, 0.1% to 10% by weight of the binder can be added based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0161] The aforementioned conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, up to 10% by weight of the aforementioned conductive material can be added, preferably up to 5% by weight. There are no particular limitations on this conductive material as long as it does not induce chemical changes in the corresponding battery and has conductivity. For example, graphite such as natural graphite or artificial graphite can be used; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0162] In one embodiment, the aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent. Alternatively, the negative electrode slurry composition can be cast onto a separate support, and then a thin film layer obtained by peeling off the support can be pressed onto the negative electrode current collector.

[0163] Furthermore, in another embodiment, the aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent. Alternatively, the negative electrode slurry composition can be cast onto a separate support, and then a thin film layer obtained by peeling off the support can be pressed onto the negative electrode current collector.

[0164] On the other hand, in the aforementioned lithium secondary battery, the separator membrane is used to separate the negative electrode and the positive electrode and provide a channel for the movement of lithium ions. Any separator membrane commonly used in lithium secondary batteries can be used without limitation. In particular, it is preferable to have low impedance and excellent electrolyte moisture-holding capacity for electrolyte ion movement. Specifically, porous polymer films can be used, for example, porous polymer films prepared using polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or their two- or more-layered stacked structures. Furthermore, conventional porous nonwoven fabrics can also be used, for example, nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, to ensure heat resistance or mechanical strength, separator membranes coated with ceramic components and polymeric substances can also be used, selectively in single-layer or multi-layer structures.

[0165] Furthermore, examples of electrolytes used in this invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, but they are not limited to these.

[0166] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0167] As the aforementioned organic solvents, organic solvents that can act as a medium for the movement of ions participating in the electrochemical reactions of the battery can be used without limitation. Specifically, as the aforementioned organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate can be used. Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where r is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxanes such as 1,3-dioxane; or sulfolane, etc. Among these, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) that can improve the charge-discharge performance of the battery. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be observed.

[0168] The lithium salts described above can be any compound capable of providing lithium ions for use in lithium secondary batteries, without limitation. Specifically, the lithium salts can 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. Preferably, the concentration of the lithium salts is used in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance and enabling efficient movement of lithium ions.

[0169] In addition to the electrolyte components described above, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity, the electrolyte may also contain one or more additives such as halogenated alkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the electrolyte may contain 0.1% to 5% by weight of the aforementioned additives relative to its total weight.

[0170] On the other hand, the electrolytes mentioned above may include solid electrolytes such as solid polymer electrolytes, gel polymer electrolytes, or solid inorganic electrolytes.

[0171] Lithium secondary batteries containing solid electrolytes can omit the aforementioned separation membrane. However, since the electrolyte is difficult to penetrate into the positive and negative electrodes, the electrodes can be formed by mixing solid electrolytes during electrode manufacturing.

[0172] On the other hand, solid polymer electrolytes or gel-type polymer electrolytes can be composed of salts of Group 1 or Group 2 metal ions from the periodic table combined with polymer resins. For example, it can be formed by adding polymer resins to solvated lithium salts.

[0173] The salts of the aforementioned metal ions can 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.

[0174] Examples of the aforementioned polymer resins include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkyl oxide derivatives of polyethylene glycol, phosphate polymers, agitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociative groups, branched copolymers in which amorphous polymers such as PMMA, polycarbonate, polysiloxane (PDMS), or phosphazene are copolymerized as comonomers in the PEO (polyethylene glycol) backbone, comb-like polymer resins, and crosslinked polymer resins.

[0175] As solid inorganic electrolytes, sulfide-based solid electrolytes and oxide-based solid electrolytes can be used in general.

[0176] Sulfide-based solid electrolytes can be materials containing sulfur (S) and having the conductivity of Group 1 or Group 2 metal ions used in secondary batteries. For example, they can be Li-PS-based glasses or Li-PS-based glass ceramics with lithium-ion conductivity.

[0177] Examples of the above-mentioned sulfide-based solid electrolytes 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.

[0178] On the other hand, oxide-based solid electrolytes can be materials containing oxygen (O) and having the conductivity of Group 1 or Group 2 metal ions used in secondary batteries. For example, examples of the aforementioned oxide-based solid electrolytes could be LLTO-based compounds, such as Li6La2CaTa2O. 12 Li6La2ACaNb2O 12 Li6La2ASrNb2O 12 Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 It is at least one of the following groups: Li9SiAlO8, LAGP-based compounds, LATP-based compounds, LISICON-based compounds, LIPON-based compounds, perovskite-based compounds, NASICO-based compounds, and LLZO-based compounds.

[0179] As described above, lithium secondary batteries containing the aforementioned positive electrode active materials consistently exhibit excellent discharge capacity, output characteristics, and lifespan characteristics. Therefore, they can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs).

[0180] The shape of the aforementioned lithium secondary battery is not particularly limited and can be cylindrical, prismatic, pouch-shaped, or coin-shaped, etc. Furthermore, preferably, the lithium secondary battery can be used not only as a single battery cell for powering small devices, but also as a unit battery in medium or large battery modules comprising multiple battery cells.

[0181] According to another aspect, a battery module comprising the aforementioned lithium secondary battery as a single unit and / or a battery pack comprising therein can be provided.

[0182] The aforementioned battery module or battery pack can be used as a power tool; an electric vehicle, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or a power source for one or more medium or large-sized devices in an energy storage system.

[0183] The invention will be described in more detail below by way of examples. However, these examples are merely illustrative and the scope of the invention should not be construed as being limited by these examples.

[0184] Preparation Example 1. Preparation of Positive Electrode Active Material

[0185] (1) Example 1

[0186] FeOOH and 85% by weight H3PO4 were mixed in a reactor to achieve a Fe to P molar ratio of 1:1.05. Distilled water was then added to bring the solid content of the reactants in the slurry to 40% by weight. The mixture was then stirred at 80°C for 24 hours to obtain a slurry containing the Fe-P complex.

[0187] Li₂CO₃, a lithium feedstock, was added to the slurry to achieve a Fe to Li molar ratio of 1:1.01. Sucrose, a carbon feedstock, was then added to achieve a Fe to C molar ratio of 1:0.7. Zirconia beads with a particle size of 0.5 mm were packed into a nanomill, filling 40% of the mill's internal volume. The slurry was then pulverized to achieve a D50 of 0.5 μm to 0.7 μm. Finally, the slurry was dried using a spray dryer (Dongjin Tech-Tech Co., Ltd., DJE003R).

[0188] The mixture was heat-treated for 8 hours in a N2 atmosphere furnace, heated to 850°C at a rate of 2°C / min and held at that temperature. Afterwards, furnace cooling and grading were performed to obtain a positive electrode active material containing lithium iron phosphate.

[0189] (2) Comparison Example 1

[0190] FeOOH, 85% by weight H3PO4, and Li2CO3 were mixed in a reactor to achieve a molar ratio of Fe, P, and Li of 1:1.05:1.01. The mixture was then stirred at 80°C for 24 hours to obtain a slurry.

[0191] Sucrose, a carbon feedstock, was added to the slurry to achieve an atomic ratio of Fe to C of 1:0.7. Zirconia beads with a particle size of 0.5 mm were then packed into a nano-grinding mill, filling 40% of the mill's internal volume. The slurry was then pulverized to achieve a D50 of 0.5 μm to 0.7 μm. Finally, the slurry was dried using a spray dryer.

[0192] The mixture was heat-treated for 8 hours in a calcining furnace under N2 atmosphere, with the temperature increased to 850°C at a rate of 2°C / min and maintained at that temperature. Subsequently, furnace cooling and grading were performed to obtain a positive electrode active material containing lithium iron phosphate.

[0193] (3) Comparison Example 2

[0194] Except for the use of oxalic acid as a carbon raw material in the preparation of the slurry, the positive electrode active material was prepared in the same manner as in Comparative Example 1 above.

[0195] (4) Comparative Example 3

[0196] Except that Li2CO3, which is used as a carbon raw material, was dissolved in distilled water and added dropwise during the preparation of the slurry, the positive electrode active material was prepared in the same way as in Comparative Example 1 above.

[0197] Preparation Example 2. Preparation of Lithium Secondary Batteries

[0198] A positive electrode slurry was prepared by dispersing 94% by weight of each of the positive electrode active materials prepared according to Preparation Example 1, 3% by weight of artificial graphite, and 3% by weight of PVDF binder in 3.5 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on an aluminum film with a thickness of 20 μm as the positive electrode current collector and dried, and then rolled to prepare the positive electrode.

[0199] In contrast to the aforementioned positive electrode, lithium foil was used as the counter electrode, and a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as the separation membrane. The button cell was manufactured using a conventional manufacturing process with a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 and an electrolyte containing LiPF6 at a concentration of 1.15 M.

[0200] Experimental Example 1. Characteristic Evaluation of Positive Electrode Active Material

[0201] In Preparation Example 2, coin cells were subjected to charge-discharge experiments using an electrochemical analysis apparatus (Toyo, Toscat 3100) at 25°C, a voltage range of 2.0V to 3.65V, and a discharge rate of 0.1C to 5.0C. The initial charge capacity and initial discharge capacity were measured. Following XRD measurements, the FeP₂O₇ and LiFePO₄ contents were confirmed by Rietveld analysis. The analytical results are shown in Table 1 below.

[0202] Table 1

[0203]

[0204] Referring to Table 1, the crystal structure and chemical formula of the resulting Fe-P complex may change depending on the order in which the raw materials are added. As a result, the content of FeP2O7 impurities in the prepared positive electrode active material varies.

[0205] Although the underlying mechanism is not yet clear, it may be due to the different crystal structures of the Fe-P complex, which leads to changes in its reactivity with lithium, thereby generating FeP2O7 impurities that do not react with lithium.

[0206] On the other hand, when oxalic acid is used as a carbon raw material, the amount of carbon forming the coating after carbonization is relatively small, resulting in insufficient performance.

[0207] While the embodiments of this specification have been described above, those skilled in the art will understand that various modifications and alterations can be made to this specification by adding, modifying, deleting, or supplementing the constituent elements without departing from the spirit of this specification as set forth in the claims, and these modifications and alterations also fall within the scope of the claims of this specification.

Claims

1. A method for preparing a positive electrode active material for lithium secondary batteries, characterized in that, include: Step (a) involves reacting a transition metal raw material with a phosphoric acid raw material to prepare a slurry containing a metal-phosphorus complex. Step (b) involves adding lithium and carbon raw materials to the slurry, followed by pulverization and drying to obtain powder; and Step (c) involves heat-treating the powder to obtain a lithium composite compound.

2. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, The aforementioned transition metal is Fe, or includes Fe and at least one selected from the group consisting of Mn, Ni and Co.

3. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, The reaction in step (a) above is carried out at a temperature of 60°C to 150°C.

4. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, In step (b) above, the lithium raw material is added such that the ratio of the number of lithium atoms (Li) to the total number of metal atoms other than lithium (Metal) in the slurry (Li / Metal) is 0.90 to 1.

10.

5. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, The amount of carbon raw material added in step (b) above is based on a molar ratio of 0.01 to 0.5 of the total molar of the lithium composite compound.

6. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, In step (b) above, at least one auxiliary raw material is further added to the slurry, including an element selected from the group consisting of 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.

7. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, In step (b) above, the material is pulverized so that the average particle size of the solids in the slurry is less than 1.0 μm.

8. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, characterized in that, The heat treatment in step (c) above is carried out at 750°C to 950°C.

9. A positive electrode active material, which is a positive electrode active material prepared according to any one of claims 1 to 8, characterized in that, Including lithium composite compounds capable of lithium intercalation / deintercalation, The aforementioned lithium composite compound contains multiple particulate substances. At least a portion of the aforementioned particulate matter has an amorphous carbon coating with a thickness of 1 nm to 500 nm formed on its surface. The above-mentioned lithium complex compound is represented by the following chemical formula 1: [Chemical Formula 1] Li p Feb 1-x-y M x A y A' z Q 1-z O w In the above formula, M is selected from at least one of the group consisting of Mn, Ni, and Co. A is at least one selected from the group consisting of Ag, Al, As, Au, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cu, Ga, Hf, In, K, La, Mg, Mo, Na, Nb, Nd, Os, Pd, Pr, Pt, Rh, Ru, Sm, Sn, Sr, Ta, Ti, V, W, Y, Zn, and Zr. A' is selected from at least one of the groups consisting of C, Si, S, N, B, F, Cl, and I, where 0.5 ≤ p ≤ 1.5, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, and 0 ≤ p ≤ 1.

5. <w≤4。 10. A positive electrode, characterized in that, Includes the positive electrode active material according to claim 9.

11. A lithium secondary battery, characterized in that, Use the positive electrode as described in claim 10.

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