Precursor for positive electrode active material and method for preparing the same

Abstract

The present invention relates to a method for producing a precursor for a positive electrode active material, the method comprising: a seed formation step of forming a precursor for a positive electrode active material seed by performing a coprecipitation reaction while supplying a transition metal aqueous solution, an ammonium cation complexing agent, and an alkaline compound to a reactor; and a particle growth step of growing a precursor for a positive electrode active material particle by performing a coprecipitation reaction while supplying a transition metal aqueous solution, an ammonium cation complexing agent, and an alkaline compound to a reaction solution in which the precursor for a positive electrode active material seed has been formed, wherein the supply rate of the transition metal aqueous solution and the supply rate of the ammonium cation complexing agent in the particle growth step are each more than twice the supply rate of the transition metal aqueous solution and the supply rate of the ammonium cation complexing agent in the seed formation step.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2021-0020103, filed on February 15, 2021, the disclosure of which is incorporated herein by reference.

[0002] This invention relates to a precursor for a positive electrode active material used in secondary batteries and a method for preparing the same, and more particularly, to a precursor for a positive electrode active material and a method for preparing the same, wherein the precursor for the positive electrode active material exhibits excellent reactivity with lithium during sintering. Background Technology

[0003] With the technological development and increasing demands of mobile devices, the demand for secondary batteries as an energy source has increased significantly. Among these secondary batteries, lithium-ion batteries, which have high energy density, high voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium composite transition metal oxides containing two or more transition metals, such as nickel, cobalt, manganese and aluminum, have been used as positive electrode active materials for lithium secondary batteries.

[0005] Lithium complex transition metal oxides are typically prepared by adding a metal solution containing a transition metal element, an ammonium cation complexing agent, and an alkaline aqueous solution as raw materials to a continuous stirred tank reactor (CSTR) or a batch reactor for co-precipitation reaction to prepare a precursor in the form of hydroxides. The precursor is then mixed with lithium raw materials, and the mixture is sintered.

[0006] In a continuous stirred tank reactor (CSTR), the precursor composed of particles is discharged while the feed is added and co-precipitated. In contrast, in a batch reactor, the feed is added according to the volume of the reactor. When the reactor is full, the addition of feed is stopped and the reaction proceeds. The precursor is then discharged after the reaction is complete.

[0007] When preparing precursors using a continuous stirred tank reactor (CSTR), the high productivity is advantageous because the precursor is discharged simultaneously with the addition of reactants and co-precipitation. However, since the addition of reactants and the discharge of products occur continuously, the residence time and reaction time of the precursors used to form the positive electrode active material in the reactor may vary. Therefore, a limitation exists: the resulting precursor particles exhibit inhomogeneity in size and particle size distribution. Thus, to ensure the uniformity of precursor quality, batch reactors are primarily used for precursor preparation.

[0008] However, regarding the method of preparing precursors for cathode active materials using a batch reactor, as the co-precipitation reaction time increases, the growth rate of precursor particles decreases while the surface density of the precursor particles increases and the size of the primary particles increases, resulting in a decrease in the surface energy of the precursor particles. Consequently, a problem arises: the reactivity with the lithium feedstock decreases during sintering, and the penetration of lithium and dopant elements into the precursor particles is inhibited, making uniform sintering difficult. Furthermore, using a batch reactor to prepare precursors for cathode active materials also results in reduced productivity.

[0009] Therefore, there is a need to develop a precursor for positive electrode active materials that exhibits excellent reactivity with lithium feedstock during sintering. Summary of the Invention

[0010] Technical issues

[0011] One aspect of the present invention provides a method for preparing a precursor for a positive electrode active material, the method controlling the surface density of the precursor particles by adjusting the supply flow rate of the raw material during the preparation of the precursor, so that the precursor has excellent reactivity with lithium raw material during sintering.

[0012] Technical solution

[0013] According to one aspect of the present invention, a method for preparing a precursor for a positive electrode active material is provided, the method comprising:

[0014] Seed formation steps: Precursor seeds for the positive electrode active material are formed by co-precipitation reaction simultaneously with the supply of an aqueous transition metal solution, an ammonium cation complexing agent, and an alkaline compound to the reactor; and

[0015] Particle growth steps: Precursor particles for the positive electrode active material are grown by simultaneously supplying a transition metal aqueous solution, an ammonium cation complexing agent, and an alkaline compound to a reaction solution in which precursor seeds for the positive electrode active material have already formed.

[0016] In the particle growth step, the supply rates of the transition metal aqueous solution and the ammonium cation complexing agent are more than twice the supply rates of the transition metal aqueous solution and the ammonium cation complexing agent in the seed formation step.

[0017] According to another aspect of the present invention, a precursor for a positive electrode active material prepared by the above preparation method is provided, and a positive electrode active material prepared by using the precursor for a positive electrode active material is provided.

[0018] Beneficial effects

[0019] The method for preparing precursors for cathode active materials according to the present invention increases the reaction rate by rapidly increasing the supply rate of the transition metal aqueous solution, which serves as the reactant, by more than double during the precursor particle growth step, thereby preparing precursor particles with low surface density and small primary particle size. If the surface density and primary particle size of the precursor particles decrease, the specific surface area increases, resulting in improved reactivity with the lithium feedstock during the sintering step, thereby improving sintering uniformity and promoting better crystal structure development. Therefore, when cathode active materials prepared using the precursors prepared according to the method of the present invention are used in secondary batteries, improved capacity characteristics and high-temperature cycling characteristics can be obtained.

[0020] Furthermore, the method for preparing precursors for positive electrode active materials according to the present invention can produce precursor particles with excellent particle size uniformity, and because the reaction time required to form precursor particles with the desired particle size is reduced, the productivity can be improved. While increasing the supply of reactants can increase the growth rate of precursor particles and shorten the reaction time, adding a large amount of reactants from the initial stage of the reaction can lead to uneven particle size in the precursor particles. Conversely, the present invention improves productivity while preventing uneven particle size in the final prepared precursor particles by supplying reactants at a low rate in the initial stage of seed formation and increasing the supply rate after sufficient seed formation. Attached Figure Description

[0021] Figure 1 These are scanning electron microscope (SEM) images showing the surface features and particle size distribution of the precursor prepared in Example 1;

[0022] Figure 2 These are scanning electron microscope (SEM) images showing the surface features and particle size distribution of the precursor prepared in Comparative Example 1;

[0023] Figure 3 These are scanning electron microscope (SEM) images showing the surface features and particle size distribution of the precursor prepared in Comparative Example 2;

[0024] Figure 4 These are scanning electron microscope (SEM) images showing the particle size distribution of the precursors collected during the precursor preparation process in Examples 1, 2, 3, and 4.

[0025] Figure 5 It is a graph showing the specific capacity-voltage curves obtained by charging / discharging secondary batteries using the positive electrode active materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 at 0.1C / 0.1C;

[0026] Figure 6This is a graph showing the high-temperature lifetime characteristics of secondary batteries using the positive electrode active materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0027] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meanings defined in common dictionaries, and it should also be understood that the words or terms should be interpreted as having meanings consistent with their meanings in the context of the relevant field and technical ideas of the invention, based on the principle that the inventors can appropriately define the meanings of the words or terms to best interpret the invention.

[0028] Methods for preparing precursors for positive electrode active materials

[0029] As a result of extensive research conducted to develop precursors for cathode active materials that exhibit excellent reactivity with lithium during sintering, the inventors have discovered that precursor particles with low surface density and high specific surface area can be prepared by rapidly increasing the supply rate of reactants at specific points during precursor preparation, and that the reactivity with lithium during sintering can be improved when using the precursor, thus completing the present invention.

[0030] Specifically, the method for preparing precursors for positive electrode active materials according to the present invention is characterized in that the method comprises the following steps:

[0031] (1) Seed formation step: Precursor seeds for the positive electrode active material are formed by co-precipitation reaction simultaneously with the supply of a transition metal aqueous solution, an ammonium cation complexing agent, and an alkaline compound to the reactor; and

[0032] (2) Particle growth step: The precursor particles for the positive electrode active material are grown by simultaneously supplying a transition metal aqueous solution, an ammonium cation complexing agent, and an alkaline compound to a reaction solution in which precursor seeds for the positive electrode active material have already been formed.

[0033] In the particle growth step (2), the supply rate of the transition metal aqueous solution and the ammonium cation complexing agent is more than twice the supply rate of the transition metal aqueous solution and the ammonium cation complexing agent in the seed formation step (1).

[0034] The method for preparing precursors for positive electrode active materials according to the present invention will be described in more detail below.

[0035] (1) Seed formation steps

[0036] First, an aqueous solution of a transition metal, an ammonium cation complexing agent, and an alkaline compound are supplied to the reactor, and a co-precipitation reaction is carried out while stirring to form precursor seeds.

[0037] Ideally, the reactor should be a batch reactor. This is because it is difficult to control the particle size of the precursor particles when using a continuous stirred tank reactor (CSTR) to prepare the precursor.

[0038] The reactor may contain a mother liquor. Specifically, before supplying the aqueous transition metal solution, ammonium cation complexing agent, and basic compound as reaction raw materials, the ammonium cation complexing agent, basic compound, and water can be added to the reactor to form a mother liquor.

[0039] In this case, the ammonium cation complexing agent can be at least one selected from the following: NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3, and can be added to the reactor in the form of a solution obtained by dissolving the above compounds in a solvent. In this case, water or a mixture of water and an organic solvent (specifically an alcohol, etc.) that can be uniformly mixed with water can be used as the solvent.

[0040] Next, the basic compound can be at least one selected from NaOH, KOH, and Ca(OH)₂, and can be added to the reactor in the form of a solution obtained by dissolving the above compound in a solvent. In this case, water or a mixture of water and an organic solvent (specifically an alcohol, etc.) that can be uniformly mixed with water can be used as the solvent.

[0041] The reaction mother liquor can be prepared with a pH of 11.0 to 13.0, for example, 11.5 to 12.5. When the pH of the reaction mother liquor meets the above range, seed formation can proceed smoothly.

[0042] After forming the reaction mother liquor by adding an ammonium cation complexing agent, an alkaline compound, and water to the reactor, oxygen in the reaction mother liquor is preferably removed by purging with nitrogen.

[0043] Next, an aqueous solution of a transition metal, an ammonium cation complexing agent, and an alkaline compound are supplied to the reactor, and a co-precipitation reaction is carried out while stirring to form precursor seeds.

[0044] If an aqueous solution of a transition metal, an ammonium cation complexing agent, and an alkaline compound are supplied to a reactor containing a reaction mother liquor and stirred, precursor nuclei in the form of primary particles (nucleation) are formed as the coprecipitation reaction proceeds, and seeds in the form of secondary particles are formed as the primary particle nuclei aggregate.

[0045] In this case, the transition metal aqueous solution can contain nickel, cobalt and manganese elements, and can be formed by mixing nickel raw materials, cobalt raw materials and manganese raw materials with water.

[0046] The nickel raw materials can be Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts or nickel halides, and any one of them or a mixture of two or more of them can be used.

[0047] The cobalt raw materials can be Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O or CoSO4·7H2O, and any one of them or a mixture of two or more of them can be used.

[0048] Manganese raw materials can be: manganese oxides such as Mn2O3, MnO2 and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate and fatty acid manganese salts; hydroxy oxides; and manganese chloride, and any one of them or a mixture of two or more thereof can be used.

[0049] Depending on the requirements, aqueous solutions of transition metals may contain doping elements (M) in addition to nickel, cobalt, and manganese. 1 In this case, M 1 It may contain at least one of the following: aluminum (Al), tungsten (W), molybdenum (Mo), chromium (Cr), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), and niobium (Nb). When the transition metal aqueous solution also contains dopant elements, improved lifetime characteristics, discharge characteristics, and / or stability can be achieved.

[0050] The transition metal aqueous solution also contains the dopant element M. 1 In this case, a dopant element M may be optionally added further during the preparation of the transition metal aqueous solution. 1 The raw materials.

[0051] M, as a doping element 1 The raw materials may be selected from at least one of the following: doped element M 1 Acetates, sulfates, sulfides, hydroxides, oxides, or hydroxyoxides.

[0052] The nickel content in the transition metal aqueous solution is such that, based on the total moles of the transition metal, the nickel content is 30 mol% or more, preferably 80 mol% or more, more preferably 85 mol% or more, and for example, 90 mol% or more. When the nickel content in the transition metal aqueous solution is 80 mol% or more, the capacity characteristics can be further improved.

[0053] The ammonium cation complexing agent and basic compound can be the same as those used during the formation of the reaction mother liquor.

[0054] The seed formation step can take anywhere from 1 to 8 hours, for example, 1 to 5 hours. If the seed formation time is too short, productivity may decrease and the particle size distribution of precursor particles may become uneven because the seeds may not form sufficiently. Conversely, if the seed formation time is too long, productivity may decrease because the reaction time required for the precursor particles to grow to the desired particle size may increase excessively, and the particle size distribution may become uneven due to the potential growth of some particles during the seed formation process.

[0055] Furthermore, the pH of the reaction solution in the seed formation step can be in the range of 11.0 to 12.5, for example, 11.0 to 12.2, and the temperature of the reaction solution can be in the range of 40°C to 65°C, preferably 50°C to 65°C, more preferably 50°C to 60°C. When the pH and temperature of the reaction solution meet the above ranges, nuclei for the precursor of the positive electrode active material are formed in the reaction solution, and the process of seed formation by the aggregation of nuclei can proceed smoothly. The pH of the reaction solution can be controlled by adjusting the amount of alkaline compound added using a pH sensor or similar method.

[0056] (2) Particle growth steps

[0057] When the seeds are fully formed through the process described above, the positive electrode active material is grown using precursor particles by co-precipitation reaction, which is carried out while supplying a transition metal aqueous solution, an ammonium cation complexing agent and an alkaline compound to the reaction solution in which the precursor seeds have been formed.

[0058] In this case, the supply rate of the transition metal aqueous solution and the ammonium cation complexing agent is increased to more than twice the supply rate in the seed formation step, preferably 2 to 10 times, more preferably 2 to 5 times, for example 3 to 5 times. If the supply rate of the transition metal aqueous solution and the ammonium cation complexing agent in the precursor particle growth step is rapidly increased to more than twice, the surface density and primary particle size of the formed precursor particles decrease while the reaction rate increases due to the increase in reactants, resulting in the preparation of precursor particles with a large specific surface area. If a precursor with a large specific surface area is used in the preparation of the cathode active material, the reactivity between the precursor and the lithium raw material is improved in the sintering step, thereby improving sintering uniformity and well-developed crystal structure. To obtain the above effects, the supply rate of the raw materials must be rapidly increased, and the effect of increasing the specific surface area is not significant when the supply rate of the raw materials in the particle growth step is less than twice the supply rate in the seed formation step.

[0059] Ideally, the rate of increase in the supply rate of the transition metal aqueous solution and the rate of increase in the supply rate of the ammonium cation complexing agent should be equal. Here, the rate of increase in supply rate refers to the ratio of the supply rate in the particle growth step to the supply rate in the seed formation step. That is, the ratio of the supply rate of the transition metal aqueous solution in the particle growth step to the supply rate of the transition metal aqueous solution in the seed formation step and the ratio of the supply rate of the ammonium cation complexing agent in the particle growth step to the supply rate of the ammonium cation complexing agent in the seed formation step can be the same. If the rate of increase in the supply rate of the transition metal aqueous solution and the rate of increase in the supply rate of the ammonium cation complexing agent are different, the specific surface area may decrease due to the increase in particle density, or the sphericity of the particles may decrease because the shape of the primary particles may change due to variations in crystal growth conditions.

[0060] The aqueous solution of transition metals, ammonium cation complexing agents, and basic compounds added in the particle growth step are the same as those used in the seed formation step.

[0061] The pH of the reaction solution in the particle growth step can be in the range of 10.5 to 12.0, for example, 10.7 to 11.8, and the temperature of the reaction solution can be in the range of 40°C to 65°C, preferably 50°C to 65°C, more preferably 50°C to 60°C. When the pH and temperature of the reaction solution meet the above ranges, particle growth can proceed smoothly. The pH of the reaction solution can be controlled by adjusting the amount of alkaline compound added using a pH sensor or similar method.

[0062] When the reactor is full during the particle growth step, after stopping the feed supply and agitation to allow the precursor particles in the reaction solution to settle, the supernatant is removed, and then the feed supply is resumed for the reaction. By performing the supernatant removal process described above, sufficient reaction time required for precursor particle growth can be ensured, and the precursor yield can be increased. The above process can be repeated more than twice.

[0063] When the precursor particles are fully grown through the above process, the precursor particles can be separated from the reaction solution, washed, and then dried to obtain precursor particles for positive electrode active materials.

[0064] Precursors for positive electrode active materials

[0065] Next, the precursor for the positive electrode active material according to the present invention will be described.

[0066] The precursor for positive electrode active material according to the present invention is a precursor for positive electrode active material prepared by the above-described preparation method of the present invention.

[0067] The precursor for positive electrode active materials prepared according to the preparation method of the present invention has a lower surface density and a higher specific surface area compared with conventional precursors for positive electrode active materials, and has a uniform particle size distribution.

[0068] Specifically, the Brunauer-Emmett-Teller (BET) precursor for the positive electrode active material according to the present invention has a specific surface area of ​​10 m². 2 / g to 20m 2 / g, preferably 10m 2 / g to 18m 2 / g, more preferably 10m 2 / g to 15m 2 / g. Furthermore, the tap density of the precursor for the positive electrode active material according to the present invention can be from 1.8 g / cc to 2.2 g / cc, preferably from 1.8 g / cc to 2.1 g / cc, and more preferably from 1.9 g / cc to 2.1 g / cc. Furthermore, the (D90-D10) / D50 of the precursor for the positive electrode active material according to the present invention can be from 0.5 to 0.8, for example from 0.5 to 0.75.

[0069] If the BET specific surface area, tap density, and particle size distribution of the precursor meet the above ranges, the reactivity with lithium or doping elements during sintering is improved, thereby improving the sintering quality. As a result, positive electrode active materials with excellent capacity characteristics and structural stability can be prepared.

[0070] Specifically, the precursor for the positive electrode active material can be a hydroxide or hydroxy oxide containing nickel, cobalt and manganese, for example, a compound having a composition represented by [Formula 1] or [Formula 2] below.

[0071] [Formula 1]

[0072] [Ni a Co b Mn c M 1 d ](OH)2

[0073] [Equation 2]

[0074] [Ni a Co b Mn c M 1 d O·OH

[0075] In equations 1 and 2, M 1is at least one selected from Al, W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb, and 0.8 ≤ a < 1, 0 < b < 0.2, 0 < c < 0.2, and 0 ≤ d < 0.1. Preferably, 0.85 ≤ a < 1, 0 < b < 0.15, 0 < c < 0.15, and 0 ≤ d < 0.1, and more preferably 0.9 ≤ a < 1, 0 < b < 0.1, 0 < c < 0.1, and 0 ≤ d < 0.1.

[0076] Positive electrode active material

[0077] The precursor of the positive electrode active material according to the present invention prepared as described above is mixed with a lithium raw material and then sintered to prepare a positive electrode active material.

[0078] The lithium raw material can be used without particular limitation as long as it is a compound containing a lithium source, but preferably at least one selected from the following can be used: lithium carbonate (Li2CO3), lithium hydroxide (LiOH·H2O), LiNO3, CH3COOLi, and Li2(COO)2.

[0079] The precursor and the lithium raw material can be mixed in an amount such that the molar ratio of transition metal (Me) to lithium (Li) in the precursor is in the range of 1:1 to 1:1.2, for example, 1:1 to 1:1.1. When the lithium raw material is mixed in a ratio less than the above range, the capacity of the prepared positive electrode active material may decrease, and when the lithium raw material is mixed in a ratio greater than the above range, since the particles are sintered during the sintering process, it may be difficult to prepare the positive electrode active material, the capacity may decrease, and separation of the positive electrode active material particles may occur after sintering.

[0080] In addition, if necessary, a material containing a doping element M 2 can be additionally mixed during sintering. For example, the doping element M 2 can be at least one selected from Al, W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb, and the material containing the doping element M 2 can be at least one selected from acetates, sulfates, sulfides, hydroxides, oxides, or hydroxyoxides containing the doping element M 2 .

[0081] The sintering can be carried out at a temperature range of 700°C to 800°C for 5 hours to 20 hours, for example, at a temperature range of 700°C to 780°C for 5 hours to 15 hours, but the present invention is not limited thereto.

[0082] The positive electrode active material can be, for example, a lithium nickel cobalt manganese oxide represented by the following formula 3.

[0083] [Formula 3]

[0084] Li 1+p Ni x Co y Mn z M 2 w O2

[0085] In Formula 3, M 2 may be at least one selected from Al, W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb.

[0086] 1 + p represents the molar ratio of lithium in the lithium transition metal oxide, where p may satisfy 0 ≤ p ≤ 0.3, for example, 0 ≤ p ≤ 0.2.

[0087] x represents the molar ratio of nickel in all transition metals, where x may satisfy 0.80 ≤ x < 1.0, 0.85 ≤ x < 1, or 0.90 ≤ x < 1. When the nickel content satisfies the above range, excellent capacity characteristics can be achieved.

[0088] y represents the molar ratio of cobalt in all transition metals, where y may satisfy 0 < y < 0.20, 0 < y < 0.15, or 0 < y < 0.10.

[0089] z represents the molar ratio of manganese in all transition metals, where z may satisfy 0 < z < 0.20, 0 < z < 0.15, or 0.01 < z < 0.10.

[0090] w represents M 2 in the molar ratio of all transition metals, where w may satisfy 0 ≤ w ≤ 0.1 or 0 ≤ w ≤ 0.05.

[0091] positive electrode

[0092] In addition, the present invention provides a positive electrode for a lithium secondary battery, and the positive electrode includes a positive electrode active material prepared by the above method.

[0093] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector and includes the above positive electrode active material.

[0094] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery. Materials used include, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Furthermore, the positive electrode current collector can typically have a thickness of 3μm to 500μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0095] In addition to the positive electrode active material, the positive electrode active material layer may also include conductive materials and adhesives.

[0096] In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80% to 99% by weight, for example, 85% to 98% by weight. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be obtained.

[0097] In this context, a conductive material is used to provide conductivity to the electrode. Any conductive material can be used without particular limitation, provided it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of conductive materials can include: graphite such as natural or artificial graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material is typically from 1% to 30% by weight.

[0098] The adhesive improves the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the adhesive can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% to 30% by weight.

[0099] In addition to using the aforementioned positive electrode active materials, positive electrodes can be prepared according to typical methods for preparing positive electrodes. For example, a mixture of positive electrode materials prepared by dissolving or dispersing the aforementioned positive electrode active materials, along with optional binders and conductive materials, in a solvent can be coated onto a positive electrode current collector, and then the positive electrode can be prepared by drying and calendering the coated positive electrode current collector; or the positive electrode can be prepared by casting the positive electrode material mixture onto a separate carrier, and then pressing the film layer separated from the carrier onto the positive electrode current collector.

[0100] The solvent used to prepare the cathode material mixture can be a solvent commonly used in the art. The solvent may contain dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one or a mixture of two or more thereof may be used. If, taking into account the coating thickness and manufacturing yield of the slurry, the solvent can dissolve or disperse the cathode active material, conductive material, and binder, and can produce a viscosity that provides excellent thickness uniformity during subsequent coating for cathode preparation, then the amount of solvent used can be sufficient.

[0101] Lithium secondary batteries

[0102] Furthermore, in this invention, an electrochemical device comprising the positive electrode can be prepared. Specifically, the electrochemical device can be a battery or a capacitor, such as a lithium secondary battery.

[0103] A lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining structures will be described in detail below.

[0104] In addition, the lithium secondary battery may optionally include a battery container that houses an electrode assembly of a positive electrode, a negative electrode and a separator, and a sealing member that seals the battery container.

[0105] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0106] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause adverse chemical changes in the battery. Materials used include, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys. Furthermore, the negative electrode current collector can typically have a thickness of 3μm to 500μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0107] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0108] Compounds capable of reversibly inserting and de-intercalating lithium can be used as anode active materials. Specific examples of anode active materials include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-)metallic materials capable of forming alloys with lithium, such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxides capable of doping and de-doping lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or composite materials containing (semi-)metallic materials and carbonaceous materials such as Si-C composite materials or Sn-C composite materials, and any one or a mixture of two or more thereof may be used. Alternatively, a thin film of metallic lithium may be used as the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be from 80% to 99% by weight.

[0109] Adhesives are components that facilitate bonding between conductive materials, active materials, and current collectors. The adhesive content is typically between 0.1% and 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0110] Conductive materials are components used to further improve the conductivity of the negative electrode active material. The content of the conductive material can be less than 10% by weight, for example, less than 5% by weight, based on the total weight of the negative electrode active material layer. There are no particular limitations on the conductive material, as long as it is conductive and will not cause adverse chemical changes in the battery. Examples of conductive materials that can be used include: graphite such as natural or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxides; or polyphenylene derivatives.

[0111] For example, the negative electrode active material layer can be prepared by coating a mixture of optional adhesives and conductive materials, prepared by dissolving or dispersing the negative electrode active material together with a solvent, onto a negative electrode current collector and drying the coated negative electrode current collector; or the negative electrode active material layer can be prepared by casting the negative electrode material mixture onto a separate carrier and then pressing the film layer separated from the carrier onto the negative electrode current collector.

[0112] In lithium-ion secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium-ion secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer can be used. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminated structures of two or more layers thereof. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0113] Furthermore, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries, but this invention is not limited thereto.

[0114] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0115] Any organic solvent can be used without particular limitation, as long as it serves as a medium through which ions participating in the battery electrochemical reaction can move. Specifically, the following substances can be used as the organic solvent: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents can be used, such as a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charging / discharging performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate).

[0116] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the following substances can be used as lithium salts: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Lithium salts can be used in concentration ranges from 0.1M to 4.0M. When the concentration of the lithium salt is included in the above range, excellent electrolyte performance can be obtained because the electrolyte can have appropriate conductivity and viscosity, and lithium ions can move efficiently.

[0117] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, electrolytes may also contain additives.

[0118] The lithium secondary batteries described above can be suitably used in: portable devices such as mobile phones, laptops and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs).

[0119] Preferred implementation scheme

[0120] In the following description, embodiments of the invention will be described in detail in a manner readily practiced by those skilled in the art. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0121] Example 1

[0122] (S-1) NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water in amounts such that the molar ratio of nickel:cobalt:manganese was 92:4:4 to prepare a 2.28 M transition metal aqueous solution. Distilled water, 15 wt% ammonia, and 40 wt% sodium hydroxide aqueous solution were added to a 20 L batch reactor, and the reactor temperature was increased while stirring at 600 rpm and purging with N2 gas.

[0123] (S-2) When the temperature of the solution in the reactor reaches 58°C, a transition metal aqueous solution and ammonia solution with a concentration of 15% by weight are added quantitatively over 3 hours at supply rates of 1200 ml / h and 108 ml / h, respectively. Sodium hydroxide aqueous solution is added by using a pH adjustment pump to maintain the pH of the reaction solution at 11.1.

[0124] (S-3) After 3 hours, the supply rates of the transition metal aqueous solution and ammonia solution were increased to 3600 ml / h and 324 ml / h, respectively, and the coprecipitation reaction was carried out while adding sodium hydroxide aqueous solution using a pH adjusting pump to maintain the pH of the reaction solution at 11.1.

[0125] (S-4) When the volume of the reaction solution reaches 20 L, stop supplying reactants, stop stirring to allow the precursor intermediate to settle, and then remove the supernatant to restart the reaction. Repeat this operation approximately 5 times, and adjust the average particle size D of the precursor particles. 50 The reaction was terminated when the particle size reached 15 μm. The total reaction time was 15 hours.

[0126] (S-5) After separating the precursor particles from the reaction solution, impurities are removed by washing, and the washed precursor particles are dried in a drying oven at 110°C for 12 hours and then sieved to prepare a precursor for positive electrode active material.

[0127] (S-6) After mixing the precursor prepared above, LiOH, Al2O3 and ZrO2 in an amount such that the molar ratio of (Ni+Co+Mn):Li:Al:Zr is 1:1.03:0.02:0.004, the mixture is sintered at 740°C for 10 hours to prepare the positive electrode active material.

[0128] Example 2

[0129] Except that in (S-3) the supply rates of the transition metal aqueous solution and ammonia solution were increased to 6000 ml / h and 540 ml / h respectively, and the total reaction time was 10 hours, the positive electrode active material was prepared in the same manner as in Example 1.

[0130] Comparative Example 1

[0131] (S-1) NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water in amounts such that the molar ratio of nickel:cobalt:manganese was 92:4:4 to prepare a 2.28 M transition metal aqueous solution. Distilled water, 15 wt% ammonia, and 40 wt% sodium hydroxide aqueous solution were filled into a 20 L batch reactor, and the reactor temperature was increased while stirring at 600 rpm and purging with N2 gas.

[0132] (S-2) When the temperature of the solution in the reactor reaches 58°C, a transition metal aqueous solution and ammonia solution with a concentration of 15% by weight are added quantitatively at supply rates of 1200 ml / h and 108 ml / h, respectively, and a coprecipitation reaction is carried out while adding sodium hydroxide aqueous solution by using a pH adjustment pump to keep the pH of the reaction solution at 11.1.

[0133] (S-3) When the volume of the reaction solution reaches 20 L, stop supplying reactants, stop stirring to allow the precursor intermediates to settle, and then remove the supernatant to restart the reaction. Repeat this operation approximately 5 times, and adjust the average particle size D of the precursor particles. 50 The reaction was terminated when the particle size reached 15 μm. The total reaction time was 40 hours.

[0134] (S-4) After separating the precursor particles from the reaction solution, impurities are removed by washing, and the washed precursor particles are dried in a drying oven at 110°C for 12 hours and then sieved.

[0135] (S-5) After mixing the precursor prepared above, LiOH, Al2O3 and ZrO2 in an amount such that the molar ratio of (Ni+Co+Mn):Li:Al:Zr is 1:1.03:0.02:0.004, the mixture is sintered at 740°C for 10 hours to prepare the positive electrode active material.

[0136] Comparative Example 2

[0137] Except that in Example 1 (S-3), the supply rates of the transition metal aqueous solution and ammonia solution were increased to 1800 ml / h and 162 ml / h respectively, and the total reaction time was 30 hours, the precursor and positive electrode active material were prepared in the same manner as in Example 1.

[0138] Comparative Example 3

[0139] Except that in Comparative Example 1 (S-2), the transition metal aqueous solution and ammonia solution with a concentration of 15% by weight were quantitatively added at supply rates of 3600 ml / h and 324 ml / h respectively, and the total reaction time was 13 hours, the precursor for the positive electrode active material and the positive electrode active material were prepared in the same manner as in Comparative Example 1.

[0140] Comparative Example 4

[0141] Except that in Comparative Example 1 (S-2), the transition metal aqueous solution and ammonia solution with a concentration of 15% by weight were quantitatively added at supply rates of 6000 ml / h and 540 ml / h respectively, and the total reaction time was 8 hours, the precursor for the positive electrode active material and the positive electrode active material were prepared in the same manner as in Comparative Example 1.

[0142] Experimental Example 1 - Evaluation of Precursor Powder Properties

[0143] The average particle size (D50), BET specific surface area, and tap density of the precursors for positive electrode active materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 were measured using the following method.

[0144] The measurement results are shown in Table 1 below.

[0145] (1) Average particle size D50: The volume-based cumulative particle size distribution was measured using a particle size distribution measuring instrument (Microtrac S3500, Microtrac).

[0146] (2) BET specific surface area: The specific surface area is measured by the BET method, in which the specific surface area is calculated by the amount of nitrogen adsorbed at liquid nitrogen temperature (77K) using Bell Japan's BELSORP-mini II.

[0147] (3) Tap density: After weighing 50g of the positive electrode active material precursor and placing it in a special container, the volume was measured by tapping 3000 times, and then the tap density was calculated by dividing the weight by the volume. The SEISHIN KYT-4000 was used as the measuring device.

[0148] [Table 1]

[0149] D50 [Unit: μm] <![CDATA[BET [Unit: m 2 / g]]]> Tap density [unit: g / cc] Example 1 14.9 12.66 1.98 Comparative Example 1 15.1 8.41 2.08 Comparative Example 2 15.2 9.23 2.04

[0150] Furthermore, the surface of the precursor particles and the precursor powder of the positive electrode active material prepared in Example 1, Comparative Example 1, and Comparative Example 2 were measured by scanning electron microscopy (SEM). SEM images of the positive electrode active material precursors prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown below. Figure 1 , Figure 2 and Figure 3 middle.

[0151] refer to Figures 1 to 3 It can be confirmed that, compared with the precursors for positive electrode active materials prepared in Comparative Examples 2 and 3, the surface density and primary particle size of the precursor for positive electrode active materials prepared in Example 1 are reduced.

[0152] Experimental Example 2 - Precursor Particle Size Analysis

[0153] During the preparation of precursors for positive electrode active materials in Examples 1 and 2 and Comparative Examples 3 and 4, after 20% of the total reaction time had elapsed, samples were collected from the reaction solution, and the volume-based cumulative particle size distribution of the precursor particles formed in the reaction solution was measured using a particle size distribution meter (Microtrac S3500, Microtrac Corporation).

[0154] The measurement results are shown in Table 2 below and Figure 4 The SEM images showing the particle size distribution of the precursor particles collected in Examples 1 and 2 and Comparative Examples 3 and 4 are presented below. Figure 4 middle.

[0155] [Table 2]

[0156] D10[μm] D50[μm] D90[μm] Span (D90-D10) / D50 Example 1 6.48 8.71 12.67 0.71 Example 2 7.35 9.92 14.48 0.72 Comparative Example 3 5.04 7.14 10.85 0.81 Comparative Example 4 6.62 10.09 16.17 0.95

[0157] Refer to [Table 2] and Figure 4 It can be confirmed that the precursors for positive electrode active materials prepared by the methods of Examples 1 and 2 have a more uniform particle size compared to the precursors for positive electrode active materials prepared by the methods of Comparative Examples 3 and 4. This indicates that when the reactant supply rate is high from the beginning of the reaction, as in Comparative Examples 3 and 4, the particle size of the formed precursor particles is not uniform.

[0158] Experimental Example 3 - Capacity Characteristic Evaluation

[0159] A positive electrode slurry was prepared by mixing various positive electrode active materials, conductive materials, and PVDF binders prepared in Example 1 and Comparative Examples 1 and 2 in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.5:1:1.5. The slurry was then coated onto an aluminum current collector using a doctor blade, dried, and rolled to prepare the positive electrode.

[0160] An electrode assembly was fabricated by stacking a polyethylene separator and a lithium metal anode on the positive electrode prepared as described above, and an electrolyte was injected to fabricate a coin cell. As the electrolyte, a solution in which 1M LiPF6 was dissolved in an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) were mixed at a volume ratio of 3:3:4.

[0161] At 25°C, each coin cell prepared as described above was charged at a constant current of 0.1C until the voltage reached 4.25V. Then, each coin cell was discharged at a constant current of 0.1C until the voltage reached 2.5V. The charging capacity and discharging capacity were then measured.

[0162] Furthermore, at 25°C, each coin cell prepared as described above was charged at a constant current of 0.2C until the voltage reached 4.25V, and then discharged at a constant current of 0.2C until the voltage reached 2.5V. The charging capacity and discharging capacity were measured.

[0163] The measurement results are shown in Table 3 below. Figure 5 middle. Figure 5 It is a graph showing the specific capacity-voltage curve during 0.1C charging / 0.1C discharging.

[0164] [Table 3]

[0165]

[0166] Refer to [Table 3] and Figure 5 The secondary battery prepared using the positive electrode active material of Example 1 has a better charge / discharge capacity than the secondary batteries prepared using the positive electrode active materials of Comparative Examples 1 and 2. It can be confirmed that the higher the charge / discharge rate, the better the capacity improvement effect.

[0167] Experimental Example 4 - High Temperature Cycling Characteristics

[0168] The coin cells prepared in Experimental Example 3 were charged to 4.25V at a constant current of 0.33C at 45°C. Subsequently, each coin cell was discharged to 2.5V at a constant current of 0.33C. This charging and discharging cycle was defined as one cycle, and after repeating this cycle 30 times, the initial charge and discharge efficiencies and capacity retention rates after 30 cycles of the lithium secondary batteries of Example 1 and Comparative Examples 1 and 2 were measured. In this case, the initial charge and discharge efficiency is the percentage of the discharge capacity to the charge capacity after the first cycle, and the capacity retention rate after 30 cycles is the percentage of the discharge capacity to the discharge capacity after the first cycle.

[0169] The measurement results are shown in Table 4 below and Figure 6 middle.

[0170] [Table 4]

[0171] Initial charge and discharge efficiency [%) Capacity retention rate after 30 cycles [%) Example 1 94.5 95.4 Comparative Example 1 92.4 94.0 Comparative Example 2 93.1 94.2

[0172] Refer to Table 4 and Figure 6It can be confirmed that, compared with the secondary batteries using the positive electrode active materials of Comparative Examples 1 and 2 respectively, the secondary battery using the positive electrode active material of Example 1 has higher initial charge and discharge efficiency and capacity retention after 30 cycles.

Claims

1. A method for preparing a precursor for a positive electrode active material, the method comprising: A seed formation step: forming seeds of a precursor for a positive electrode active material by performing a coprecipitation reaction while supplying an aqueous transition metal solution, an ammonium cation complexing agent, and an alkaline compound to a reactor; and A particle growth step: growing precursor particles for a positive electrode active material by performing a coprecipitation reaction while supplying an aqueous transition metal solution, an ammonium cation complexing agent, and an alkaline compound to a reaction solution in which the seeds of the precursor for a positive electrode active material have already been formed, wherein in the particle growth step, the supply rates of the aqueous transition metal solution and the ammonium cation complexing agent are 3 to 5 times the supply rates of the aqueous transition metal solution and the ammonium cation complexing agent in the seed formation step, respectively.

2. The method according to claim 1, wherein the ratio of the supply rate of the aqueous transition metal solution in the particle growth step to the supply rate of the aqueous transition metal solution in the seed formation step is the same as the ratio of the supply rate of the ammonium cation complexing agent in the particle growth step to the supply rate of the ammonium cation complexing agent in the seed formation step.

3. The method according to claim 1, wherein the seed formation step is carried out for 1 hour to 8 hours.

4. The method according to claim 1, wherein the aqueous transition metal solution contains nickel, cobalt, and manganese elements, and contains 30 mol% or more of nickel among all transition metal elements.

5. The method according to claim 4, wherein the aqueous transition metal solution contains 80 mol% or more of nickel among all transition metal elements.

6. The method according to claim 1, wherein in the seed formation step, the alkaline compound is added in an amount such that the pH of the reaction solution is maintained at 11.0 to 12.

5.

7. The method according to claim 1, wherein in the particle growth step, the alkaline compound is added in an amount such that the pH of the reaction solution is maintained at 10.5 to 12.

0.

8. The method according to claim 1, wherein in the seed formation step and the particle growth step, the temperature of the reaction solution is in the range of 40°C to 65°C.

9. A precursor for a positive electrode active material, the precursor being prepared by the method according to any one of claims 1 to 8, and having a tapped density of 1.8 g / cc to 2.2 g / cc and a (D90 - D10) / D50 of 0.5 to 0.8, and having a composition represented by [Formula 1] or [Formula 2], [Formula 1] [Ni a What b Mn c M 1 d ](OH)2 [Formula 2] [Ni a Co b Mr c M 1 d ]O·OH wherein in Formulas 1 and 2, M 1 It is selected from at least one of Al, W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb. 0.8 ≤ a < 1, 0 < b < 0.2, 0 < c < 0.2, and 0 ≤ d < 0.

1.

10. The precursor for a positive electrode active material according to claim 9, wherein the precursor for a positive electrode active material has a 10m... 2 / g to 20m 2 / g of Brueer-Emmett-Teller (BET) specific surface area.

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