Positive electrode active material for lithium secondary battery, and preparing method thereof

Abstract

A positive electrode active material for a lithium secondary battery, according to the present invention, comprises a transition metal oxide precursor, wherein a zeta potential absolute value of the transition metal oxide precursor is a 25 MHz or less, and a zeta potential absolute value of the positive electrode active material is 20 MHz or less. The present invention can provide the positive electrode active material for a lithium secondary battery, and a preparing method thereof, the positive electrode active material having improved zeta potential value, thereby exhibiting excellent electrochemical properties such as lifetime characteristics, increased resistance rate, and thermal stability.

Description

Cathode active material for lithium secondary batteries and method for manufacturing the same

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

[0002] With environmental issues becoming increasingly serious in recent years, the demand for electric vehicles is rising as one of the solutions to overcome them. In response to this explosive demand for electric vehicles and the need for increased driving range, the development of high-capacity, high-energy-density rechargeable batteries is actively underway worldwide.

[0003] To satisfy these requirements, research is being conducted on secondary batteries that utilize NCM cathode active materials with high Ni content, while applying a bimodal cathode active material in which large and small particles are mixed in a certain fraction to improve the density of the electrode plates.

[0004] However, in the case of a cathode active material composed of secondary particles formed by the aggregation of primary particles, the specific surface area of ​​the powder is large, which increases the surface area in contact with the electrolyte. This leads to a problem where the amount of gas generated increases and the lifespan of the battery decreases. In addition, due to the characteristics of High-Ni cathode active materials, there is a disadvantage that the lifespan characteristics are very poor because degradation is severe at high voltages.

[0005] To address these issues, recent research is being conducted using lithium excess oxide to exhibit a capacity similar to that of High-Ni cathode active materials at high voltages.

[0006] However, currently developed lithium excess oxide materials have a problem in that their electrochemical properties, such as lifespan, resistance growth rate, and thermal stability, are generally inferior at high voltages.

[0007] One aspect of the present invention for solving the aforementioned problem is to provide a cathode active material for a lithium secondary battery and a method for manufacturing the same, which has excellent electrochemical properties such as lifespan characteristics, resistance growth rate, and thermal stability by improving the zeta potential value of the cathode active material through the control of the zeta potential value of a transition metal oxide precursor.

[0008] The technical problems intended to be solved in this document are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this invention belongs from the description below.

[0009] To achieve the above objective, a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a transition metal oxide precursor, wherein the transition metal oxide precursor has an absolute zeta potential of 25 mV or less, and the positive electrode active material may have an absolute zeta potential of 20 mV or less.

[0010] In addition, according to one embodiment of the present invention, the absolute value of the zeta potential of the transition metal oxide precursor may be 0.7 mV or more and 23.8 mV or less, and the absolute value of the zeta potential of the positive electrode active material may be 0.2 mV or more and 19.9 mV or less.

[0011] In addition, the transition metal oxide precursor according to one embodiment of the present invention may be represented by the following chemical formula 1.

[0012] [Chemical Formula 1]

[0013] (Ni x Co y Mn z )(OH)2

[0014] (In Chemical Formula 1 above, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.)

[0015] In addition, the average particle size (D50) of the transition metal oxide precursor according to one embodiment of the present invention may be 9㎛ to 13㎛.

[0016] In addition, the positive active material according to one embodiment of the present invention may be represented by the following chemical formula 2.

[0017] [Chemical Formula 2]

[0018] Li a [Ni x Co y Mn z ] 2-a O2

[0019] (In Chemical Formula 2 above, 0.90≤a≤1.5, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.)

[0020] In addition, the method comprises the steps of: preparing a transition metal oxide precursor by co-precipitating a transition metal-containing solution, an ammonium cation-containing complex-forming agent, and a basic compound according to one embodiment of the present invention; and preparing a positive electrode active material by mixing the transition metal oxide precursor and a lithium raw material and then calcining; wherein the transition metal oxide precursor has an absolute zeta potential of 25 mV or less, and the positive electrode active material may have an absolute zeta potential of 20 mV or less.

[0021] In addition, according to one embodiment of the present invention, the absolute value of the zeta potential of the transition metal oxide precursor may be 0.7 mV or more and 23.8 mV or less, and the absolute value of the zeta potential of the positive electrode active material may be 0.2 mV or more and 19.9 mV or less.

[0022] In addition, the ammonium cation-containing complex-forming agent according to one embodiment of the present invention may be included in a molar ratio of 0.10 to 1.0 relative to the transition metal-containing solution.

[0023] In addition, the ammonium cation-containing complex-forming agent according to one embodiment of the present invention may include one or more selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3.

[0024] In addition, the co-precipitation reaction according to one embodiment of the present invention may be carried out for 30 to 60 hours at a temperature of 30 to 60°C under an inert atmosphere such as nitrogen or argon.

[0025] In addition, the transition metal oxide precursor according to one embodiment of the present invention may be represented by the chemical formula 1.

[0026] In addition, the average particle size (D50) of the transition metal oxide precursor according to one embodiment of the present invention may be 9㎛ to 13㎛.

[0027] In addition, the transition metal oxide precursor and the lithium raw material according to one embodiment of the present invention may be mixed in a molar ratio of 1:0.90 to 1:1.50.

[0028] In addition, the firing according to one embodiment of the present invention may be performed in the step of first firing at a temperature of 300°C to 600°C for 1 to 15 hours and second firing at a temperature of 800°C to 950°C for 10 to 15 hours.

[0029] In addition, the positive active material according to one embodiment of the present invention may be represented by the chemical formula 2.

[0030] [Chemical Formula 2]

[0031] Li a [Ni x Co y Mn z ] 2-a O2

[0032] (In Chemical Formula 2 above, 0.90≤a≤1.5, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.)

[0033] A positive electrode according to one embodiment of the present invention may include the positive electrode active material for a lithium secondary battery.

[0034] A lithium secondary battery according to one embodiment of the present invention may include the positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0035] It is possible to provide a positive electrode active material for a lithium secondary battery with excellent electrochemical properties such as resistance growth rate and thermal stability, and a method for manufacturing the same.

[0036] The effects obtainable from the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0037] Figure 1 is the result of SEM analysis of the surface of the transition metal oxide precursor prepared in Comparative Example 2.

[0038] Figure 2 is the result of SEM analysis of the surface of a transition metal oxide precursor prepared in Example 2 according to one embodiment of the present invention.

[0039] Figure 3 shows the results of SEM analysis of the surface of the transition metal oxide precursor prepared in Comparative Example 3.

[0040] Figure 4 is the result of SEM analysis of the surface of a transition metal oxide precursor prepared in Example 11 according to one embodiment of the present invention.

[0041] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0042] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0043] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense. For instance, singular expressions in this specification include plural expressions unless the context clearly indicates an exception.

[0044] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0045] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described in detail below.

[0046] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a transition metal oxide precursor, wherein the transition metal oxide precursor has an absolute zeta potential of 25 mV or less, and the positive electrode active material may have an absolute zeta potential of 20 mV or less.

[0047] As mentioned above, currently developed cathode active materials have a problem in that their electrochemical characteristics deteriorate at high voltages. One of the reasons for this degradation is that the currently developed cathode active materials fail to satisfy an appropriate zeta potential value.

[0048] In the present invention, the zeta potential is a very important parameter. In the present invention, by controlling the absolute value of the zeta potential of the transition metal oxide precursor to sufficiently ensure the stability and dispersibility of the precursor and to distribute it uniformly among the lithium particles, the absolute value of the zeta potential of the cathode active material can finally be controlled to a target value.

[0049] The above transition metal oxide precursor preferably has an absolute zeta potential of 25 mV or less, and more preferably 0.7 mV or more and 23.8 mV or less.

[0050] If the absolute value of the zeta potential of the above transition metal oxide precursor exceeds 25mV, the stability and cohesiveness of the precursor are reduced, so it cannot be uniformly distributed in the lithium particles. Consequently, the absolute value of the zeta potential of the target cathode active material cannot be satisfied, which leads to a decrease in electrochemical characteristics and a decrease in lifespan characteristics due to side reactions with the electrolyte.

[0051] In addition, the cathode active material containing the above transition metal oxide precursor preferably has an absolute zeta potential of 20 mV or less, and more preferably 0.2 mV or more and 19.9 mV or less.

[0052] If the absolute value of the zeta potential of the above-mentioned positive electrode active material exceeds 20mV, electrochemical properties such as resistance increase rate and thermal stability at high voltage may be degraded due to reduced aggregation with the transition metal oxide precursor, and lifespan characteristics may also be degraded due to side reactions with the electrolyte.

[0053] That is, in the present invention, the absolute value of the zeta potential of a transition metal oxide precursor is controlled to obtain the absolute value of the zeta potential of the target cathode active material, and by manufacturing the cathode active material using the transition metal oxide precursor with the controlled absolute value of the zeta potential, the absolute value of the zeta potential of the cathode active material can be finally satisfied, and accordingly, the electrochemical characteristics at high voltage targeted in the present invention can be satisfied.

[0054] The above transition metal oxide precursor can be represented by the following chemical formula 1.

[0055] [Chemical Formula 1]

[0056] (Ni x Co y Mn z )(OH)2

[0057] (In Chemical Formula 1 above, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.)

[0058] Among the elements excluding hydroxyl groups in the transition metal oxide precursor of Chemical Formula 1 above, Mn may be included in the largest amount (molar ratio or atomic %). For example, the content of Mn in Chemical Formula 1 above may be 0.58 or more and 0.65 or less. In addition, the transition metal oxide precursor may include nickel, cobalt, and manganese, or may include nickel and manganese.

[0059] The above transition metal oxide precursor may have a secondary particle form in which a plurality of primary particles are aggregated. In this case, the primary particle refers to a primary structure of a single particle, and the secondary particle refers to an aggregate, i.e., a secondary structure, in which primary particles are aggregated by physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles (or primary structures) constituting the secondary particle.

[0060] In addition, the above transition metal oxide precursor may be doped with one or more doping elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, M, and Mo.

[0061] The above transition metal oxide precursor may have an average particle size (D50) of 9 μm to 13 μm, preferably 9 μm to 10 μm. When the average particle size is within the above range, the stability of the cathode active material manufactured using the transition metal oxide precursor is improved, and the charge / discharge efficiency of the cathode active material and the capacity and output of the lithium secondary battery can be improved.

[0062] In addition, the cathode active material containing the above transition metal oxide precursor can be represented by the following chemical formula 2.

[0063] [Chemical Formula 2]

[0064] Li a [Ni x Co y Mn z ] 2-a O2

[0065] (In Chemical Formula 2 above, 0.90≤a≤1.5, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.)

[0066] In the above chemical formula 2, the lithium content (a) is preferably 0.90 or more and 1.5 or less, and more preferably 1.30 or more and 1.35 or less. When the lithium content satisfies the above range, the charge / discharge efficiency of the cathode active material and the capacity and output of the lithium secondary battery can be improved.

[0067] The above-mentioned cathode active material may be an active material of a high-manganese (High-Mn) system in which the manganese content among the total transition metals is 58% or more and 65% or less.

[0068] The average particle size of the above-mentioned positive electrode active material is not particularly limited as long as it is within a conventional range where it can be used as an active material. For example, it may be in the range of 9㎛ to 13㎛.

[0069] Hereinafter, a method for manufacturing a positive electrode active material according to one embodiment of the present invention will be described.

[0070] A method for manufacturing a positive electrode active material according to one embodiment of the present invention may include: a step of preparing a transition metal oxide precursor by co-precipitating a transition metal-containing solution, an ammonium cation-containing complex-forming agent, and a basic compound; and a step of preparing a positive electrode active material by mixing the transition metal oxide precursor and a lithium raw material and then calcining.

[0071] Each step is explained in detail below.

[0072] In a method for manufacturing a positive electrode active material according to one embodiment of the present invention, step 1 is a step of manufacturing a transition metal oxide precursor.

[0073] In order to control the absolute zeta potential of the cathode active material in the present invention, it is essential to control the absolute zeta potential of the transition metal oxide precursor. Accordingly, in the present invention, the absolute zeta potential of the transition metal oxide precursor is controlled to the target absolute zeta potential of the present invention by adjusting the concentration of the ammonium cation-containing complex-forming agent added during the preparation of the transition metal oxide precursor and the reaction conditions during the co-precipitation reaction, thereby enabling the achievement of the target absolute zeta potential of the cathode active material.

[0074] Specifically, the transition metal oxide precursor can be prepared by co-precipitating a transition metal-containing solution containing nickel raw materials and manganese raw materials and, if necessary, cobalt raw materials, an ammonium cation-containing complex-forming agent, and a basic compound.

[0075] The above transition metal oxide precursor may be a manganese-rich transition metal precursor, for example, a nickel-cobalt-manganese precursor or a nickel-manganese precursor, but is not necessarily limited to these, and any manganese-rich transition metal precursor that can be used in the relevant technical field may be used.

[0076] The above nickel raw material may be nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, may be Ni(OH)2, NiO, NiOOH, NiCO3ㆍ2Ni(OH)2ㆍ4H2O, NiC2O2ㆍ2H2O, Ni(NO3)2ㆍ6H2O, NiSO4, NiSO4ㆍ6H2O, nickel fatty acid salts, nickel halides, or combinations thereof, but are not limited thereto.

[0077] The above cobalt-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, Co(SO4)2ㆍ7H2O or a combination thereof, but is not limited thereto.

[0078] The above manganese-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically, manganese oxides such as Mn2O3, MnO2, Mn3O4, etc.; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid, manganese fatty acid; manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0079] When preparing the above transition metal-containing solution, the amount of raw materials such as nickel, manganese, and cobalt used may be appropriately determined according to the composition of the metal hydroxide in the final precursor.

[0080] The above transition metal-containing solution may be prepared by adding a raw material to a solvent, specifically water, or a mixed solvent of an organic solvent that can be uniformly mixed with water (e.g., alcohol, etc.), or by mixing an aqueous solution of a nickel raw material, an aqueous solution of a cobalt raw material, an aqueous solution of a manganese raw material, etc.

[0081] The ammonium cation-containing complex-forming agent may be NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, (NH4)2CO3, or a combination thereof, but is not limited thereto. Meanwhile, the ammonium cation-containing complex-forming agent may be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) may be used as the solvent.

[0082] The above ammonium cation-containing complex-forming agent is preferably included in a molar ratio of 0.10 to 1.0 relative to the transition metal-containing solution, more preferably in a molar ratio of 0.15 to 0.8, and most preferably in a molar ratio of 0.2 to 0.8.

[0083] If the molar ratio of the ammonium cation-containing complex-forming agent is less than 0.10, the stability and dispersibility of the transition metal oxide precursor are insufficient, making it impossible to form a uniform coating on the lithium raw material during the manufacture of the cathode active material, and it may be difficult to achieve the absolute zeta potential of the cathode active material targeted in the present invention. In addition, if the molar ratio of the ammonium cation-containing complex-forming agent exceeds 1.0, it is difficult to control the absolute zeta potential of the transition metal oxide precursor targeted in the present invention, making it impossible to form a uniform coating on the lithium raw material during the manufacture of the cathode active material; consequently, the electrochemical characteristics of the cathode active material are degraded, and the lifespan characteristics may be degraded due to side reactions with the electrolyte.

[0084] The basic compound may be a hydroxide of an alkali metal or alkaline earth metal such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) may be used as the solvent. The basic compound may be added in an amount that satisfies the pH conditions during the co-precipitation reaction, and specifically, it may be added in a molar ratio of 1 to 10 moles of the basic compound per 1 mole of the ammonium cation-containing complex-forming agent.

[0085] Meanwhile, the co-precipitation reaction can be carried out for 30 to 60 hours at a temperature of 30°C or higher and 60°C or lower, preferably at a temperature of more than 30°C and less than 60°C, under an inert atmosphere such as nitrogen or argon.

[0086] If the temperature during the above co-precipitation reaction is below 30°C, the stability and dispersibility of the transition metal oxide precursor are insufficient, making it impossible to form a uniform coating on the lithium raw material during the manufacture of the cathode active material, and it may be difficult to achieve the absolute zeta potential value of the cathode active material targeted in the present invention. In addition, if the temperature exceeds 60°C, it is difficult to control the absolute zeta potential value of the transition metal oxide precursor targeted in the present invention, making it impossible to form a uniform coating on the lithium raw material during the manufacture of the cathode active material, which degrades the electrochemical characteristics of the cathode active material and may lead to a decrease in lifespan characteristics due to side reactions with the electrolyte.

[0087] By the above process, particles of nickel-manganese-cobalt hydroxide or nickel-manganese hydroxide are generated and precipitated in the reaction solution. The precipitated hydroxide particles can be separated by a conventional method and dried to obtain a transition metal oxide precursor. At this time, the drying process can be carried out at 110°C to 400°C for 15 to 30 hours.

[0088] In addition, when the above transition metal oxide precursor is doped, a raw material of the doping element can be added when preparing the above transition metal-containing solution.

[0089] At this time, the doping element may be one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and sulfates, nitrates, acetates, halides, hydroxides, or oxyhydroxides containing one or more of the doping elements may be used as raw materials. For example, when the doping element is tungsten, tungsten sulfate (W(SO4)2), etc. may be used as raw materials.

[0090] The raw material of the above-mentioned doping element can be appropriately determined according to the content of the doping element in the transition metal oxide precursor.

[0091] In addition, the distribution of doping elements in transition metal oxide precursors can be determined by controlling the mixing ratio when mixing transition metal-containing solutions, and if the doping elements are uniformly distributed within the transition metal oxide precursor, the structural stability of the precursor and the cathode active material prepared using it can be further improved.

[0092] Next, Step 2 is a step of manufacturing a cathode active material by mixing the transition metal oxide precursor and lithium raw material prepared in Step 1.

[0093] Specifically, the step of manufacturing the above-mentioned cathode active material can be performed by mixing the prepared transition metal oxide precursor with a lithium raw material and then calcining it.

[0094] The above lithium raw material may be any of the various lithium raw materials known in the relevant technical field without limitation, and examples include lithium-containing carbonates (e.g., lithium carbonate, etc.), lithium-containing hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O), etc.), lithium-containing hydroxides (e.g., lithium hydroxide, etc.), lithium-containing nitrates (e.g., lithium nitrate (LiNO3), etc.), lithium-containing chlorides (e.g., lithium chloride (LiCl), etc.).

[0095] It is preferable that the above transition metal oxide precursor and lithium raw material be included in a molar ratio of 1:0.90 to 1:1.50, and more preferably in a molar ratio of 1:1.30 to 1:1.35. If the content of the lithium raw material relative to the above transition metal oxide precursor falls outside the above range, it may be difficult to manufacture an anode active material having the absolute zeta potential value intended in the present invention.

[0096] In addition, although the precursor prepared according to the above method for preparing the transition metal oxide precursor is not doped, if the final cathode active material is doped, the raw material of the doping element can be selectively added when mixing the transition metal oxide precursor and the lithium raw material.

[0097] The raw material of the above-mentioned doping element is as described above, and the raw material of the doping element can be determined according to the content of the doping element in the lithium transition metal oxide in the finally manufactured cathode active material.

[0098] When the raw material of the above-mentioned doping element is added during the mixing stage between the transition metal oxide precursor and the lithium raw material, the surface stability of the finally manufactured cathode active material can be improved, thereby suppressing the occurrence of side reactions with the electrolyte.

[0099] In addition, when mixing the above transition metal oxide precursor and the lithium raw material, a sintering agent may be further added. Specifically, the sintering agent may be a compound containing ammonium ions such as NH4F, NH4NO3, (NH4)2SO4, etc.; a metal oxide such as B2O3 or Bi2O3, etc.; or a metal halide such as NiCl2 or CaCl2, etc. The sintering agent may be added in an amount of 0.01 to 0.2 moles per 1 mole of the transition metal oxide precursor.

[0100] In addition, when mixing the transition metal oxide precursor and the lithium raw material, a moisture remover may be further added. Specifically, the moisture remover may be citric acid, tartaric acid, glycolic acid, or maleic acid. The moisture remover may be added in an amount of 0.01 to 0.2 moles per 1 mole of the transition metal oxide precursor.

[0101] In addition, the mixing process of the transition metal oxide precursor, the lithium raw material, and, if necessary, the raw material of the doping element and other additives can be carried out by a dry mixing method, and more specifically, by a mechanical mixing method such as a ball mill.

[0102] The mixture of the above transition metal oxide precursor, the lithium raw material, and, if necessary, the raw material of the above doping element and other additives subsequently undergoes a calcination step.

[0103] The above firing may be performed in a first firing step at a temperature of 300°C to 600°C and a second firing step at a temperature of 800°C to 950°C.

[0104] In this case, the above 'same temperature' should be interpreted as the same temperature if it is maintained within a temperature deviation range of ±10℃ from a specific temperature. Preferably, the 'same temperature' is a temperature maintained within a temperature deviation range of ±5℃ from a specific temperature, and most preferably, a temperature at which almost no temperature deviation appears from a specific temperature.

[0105] The above first firing can be performed by raising the temperature to 300°C to 600°C and maintaining the same temperature for 1 to 15 hours.

[0106] If the temperature during the first calcination above is less than 300℃, the transition metal oxide precursor coated on the surface of the lithium particles may not be sufficient, or the manufacturing of the cathode active material may not be smooth, and if it exceeds 600℃, cracks or fissures may occur in the cathode active material, and the electrochemical properties may deteriorate.

[0107] Next, after the first firing, the temperature is raised to 800°C to 950°C, and then a second firing is performed for 10 to 15 hours while maintaining the same temperature.

[0108] If the temperature during the second calcination above does not satisfy the above range, the cathode active material targeted in the present invention may not achieve the absolute value of the zeta potential. Therefore, if the second calcination is performed at a temperature of 800°C to 950°C, the absolute value of the zeta potential of the cathode active material satisfies 20mV or less, so there may be no concern regarding a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage due to the residue of unreacted raw materials and the generation of by-products. Accordingly, it is preferable that the second calcination be performed at 800°C to 950°C.

[0109] In addition, the above secondary calcination can be performed for 10 to 15 hours in an oxidizing atmosphere such as air or oxygen, or in a non-oxidizing atmosphere containing nitrogen. Through secondary calcination under these conditions, the diffusion reaction between particles can be sufficiently carried out, and accordingly, an anode active material having the absolute value of the zeta potential desired in the present invention can be manufactured.

[0110] In addition, an annealing process at 700°C to 900°C for 10 to 20 hours may be further performed after the first and second firing.

[0111] The cathode active material of the present invention manufactured as described above may have an absolute zeta potential of 20 mV or less, and the average particle size (D50) of the cathode active material may be in the range of 9 μm to 13 μm.

[0112] In addition, the anode according to one embodiment of the present invention may include the anode active material.

[0113] Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and comprising the anode active material described above.

[0114] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0115] At least one surface of the above-mentioned current collector comprises a positive active material layer comprising a positive active material and, if necessary, one or more of a conductive material and a binder.

[0116] At this time, the above-mentioned positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98% by weight, based on the total weight of the positive active material layer, and when included within the above content range, it may exhibit excellent capacity characteristics.

[0117] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specifically, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives may be used. The above conductive material may be included in an amount of 0.5% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0118] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specifically, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof may be used. The above binder may be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive active material layer.

[0119] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the anode active material described above. For example, the above-described anode may be manufactured by preparing an anode slurry by dissolving or dispersing the above-described anode active material and optionally at least one of a binder and a conductive material in a solvent, applying the anode slurry to at least one surface of an anode current collector, and then drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0120] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the cathode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for cathode manufacturing.

[0121] Alternatively, the anode may be manufactured by casting the anode slurry onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0122] In addition, a lithium secondary battery according to one embodiment of the present invention may include the above-mentioned positive electrode, negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. The lithium secondary battery may optionally further include a battery container housing an electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member sealing the battery container.

[0123] The above cathode includes a cathode current collector and a cathode active material layer located on at least one surface of the cathode current collector.

[0124] The above-mentioned negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0125] The above-mentioned cathode active material layer includes a cathode active material and, if necessary, may further include one or more of a binder and a conductive material.

[0126] For example, the above-mentioned negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry that includes a negative electrode active material on a negative electrode current collector and, if necessary, further includes one or more of a binder and a conductive material, or by casting the negative electrode slurry onto a separate support and then laminating the film obtained by peeling off from the support onto the negative electrode current collector.

[0127] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ β Metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, may be used.

[0128] In addition, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as carbon materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0129] In addition, the binder and conductive material mentioned above may be the same as those previously described in the anode.

[0130] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in lithium secondary batteries may be used without special restrictions, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0131] In addition, the electrolyte used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0132] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0133] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent is an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; or an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to 1:9 can result in excellent performance of the electrolyte.

[0134] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1M to 5.0M, more preferably 0.1M to 3.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0135] In addition to the electrolyte components, the above electrolyte may further include additives for the purpose of improving the lifespan characteristics of the battery, suppressing the reduction of battery capacity, and improving the discharge capacity of the battery. For example, the above additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate; pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1% to 10.0% by weight, preferably 0.1% to 5.0% by weight, based on the total weight of the electrolyte.

[0136] The present invention will be explained in more detail below through the following examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

[0137] Example 1

[0138] (Preparation of transition metal oxide precursors)

[0139] (Ni x Co y Mn z A transition metal oxide precursor having the composition of )(OH)2(0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, x+y+z=1) was prepared by the co-precipitation method as follows.

[0140] Specifically, NiSO4·6H2O was used as the nickel raw material, CoSO4·7H2O as the cobalt raw material, and MnSO4·H2O as the manganese raw material. These raw materials were dissolved in distilled water to prepare a transition metal-containing solution.

[0141] Next, after preparing the co-precipitation reactor, N2 was purged to prevent oxidation of metal ions during the co-precipitation reaction, and the reactor temperature was maintained at 48°C. The transition metal-containing solution was introduced into the co-precipitation reactor, and 0.1 mol of NH4(OH) was added as an ammonium cation-containing complex-forming agent, and 1.0 mol of NaOH was added as a basic compound to adjust the pH. During the co-precipitation reaction, the pH was in the range of 11.0 to 12.0, and the reaction was carried out for a total of 48 hours at the temperatures shown in Table 1 below.

[0142] The precipitate obtained from the above co-precipitation reaction was filtered, washed with distilled water, and dried in a 100°C oven for 24 hours to produce a transition metal oxide precursor with an average particle size (D50) of 9 to 13 μm.

[0143] (Manufacturing of cathode active material)

[0144] The transition metal oxide precursor prepared above and LiOH·H2O (Samjeon Chemical, battery grade) were uniformly mixed in a molar ratio of 1:1.30 to 1.35. Subsequently, the mixture was subjected to a first calcination for 5 hours at a rate of 2.5°C / min to 480°C in a box-shaped kiln with an oxygen inflow of 40 mL / min. Then, a second calcination was performed by maintaining the temperature at 800–950°C at a rate of 2.5°C / min for 10–15 hours, thereby [releasing] Li a [Ni x Co y Mn z ] 2-a A positive electrode active material having the composition of O2 (0.90≤a≤1.5, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, x+y+z=1) was prepared.

[0145] Examples 2–15 and Comparative Examples 1–5

[0146] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a transition metal oxide precursor was prepared by varying the co-precipitation reaction temperature and the concentration of the ammonium cation-containing complex forming agent as shown in Table 1 below, and a cathode active material was prepared by varying the secondary calcination temperature.

[0147] Classification Transition metal oxide precursor Cathode active material Reaction temperature (°C) Ammonium cation-containing complex forming agent (molar ratio) Secondary calcination temperature (°C) Example 1 Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O250~600.15800~950 Example 2Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O250~600.15800~950 Example 3Ni 0.40 Co 0.02 Mn0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O250~600.2800~950 Example 4Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O240~500.2800~950 Example 5Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O240~500.2800~950 Example 6Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O240~500.4800~950 Example 7Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O230~400.6800~950 Example 8Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O230~400.8800~950 Example 9Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O250~600.15800~950 Example 10Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn0.65 ] 0.7 O250~600.15800~950 Example 11Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O250~600.2800~950 Example 12Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O240~500.2800~950 Example 13Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O240~500.2800~950 Example 14Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O230~400.6850~950 Example 15Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O230~400.8850~950 Comparative Example 1Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O250~600.05800~950 Comparative Example 2Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn 0.58 ] 0.7 O220~301.0800~950 Comparative Example 3Ni 0.40 Co 0.02 Mn 0.58 Li 1.30 [Ni 0.40 Co 0.02 Mn0.58 ] 0.7 O260~700.15950~1100 Comparative Example 4Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O250~600.05800~950 Comparative Example 5Ni 0.35 Mn 0.65 Li 1.30 [Ni 0.35 Mn 0.65 ] 0.7 O220~301.0800~950

[0148] The zeta potential values ​​of the transition metal oxide precursors and cathode active materials prepared in Examples 1 to 15 and Comparative Examples 1 to 5 are shown in Table 2 below.

[0149] The zeta potential value was calculated by using the Otsuka Electronics ELSZ-1000 instrument to disperse the transition metal oxide precursor and the cathode active material in N-methyl-2-pyrrolidone (NMP) solvent at a concentration of 1 mg / ml, and measuring the value 50 times at 25°C to obtain the average value.

[0150] Classification Transition Metal Oxide Precursor Zeta Potential Value (mV) Anode Active Material Zeta Potential Value (mV) Example 1-15.7-18.7 Example 2-22.7-19.9 Example 3-10.5-15.8 Example 4-3.8-5.6 Example 5-0.7-1.2 Example 65.84.2 Example 712.713.5 Example 823.819.2 Example 9-16.5-19.7 Example 10-15. 3-17.1 Example 11-12.5-13.9 Example 12-1.5-1.6 Example 130.80.2 Example 1413.511.8 Example 1522.118.7 Comparative Example 1-26.7-26.2 Comparative Example 225.822.1 Comparative Example 3-15.6-23.1 Comparative Example 4-25.3-23.2 Comparative Example 526.120.7

[0151] As shown in Table 2 above, in the case of Examples 1 to 15, in which an ammonium cation-containing complex-forming agent was added in a molar ratio of 0.10 to 1.0 according to the present invention and a transition metal oxide precursor was prepared by co-precipitating at 30°C to 60°C, and a cathode active material was prepared by mixing the transition metal oxide precursor with a lithium raw material and then performing a first calcination followed by a second calcination at 800°C to 950°C, it was confirmed that the absolute value of the zeta potential of the transition metal oxide precursor was 25 mV or less and the absolute value of the zeta potential of the cathode active material was 20 mV or less. On the other hand, in Comparative Examples 1 to 5, in which an ammonium cation-containing complex-forming agent was included at a concentration outside the range of 0.10 molar ratio to 1.0 molar ratio, a transition metal oxide precursor was prepared by co-precipitation at a temperature outside the range of 30°C to 60°C, and a cathode active material was prepared by secondary calcination at a temperature outside the range of 800°C to 950°C, it was confirmed that neither the absolute zeta potential of the transition metal oxide precursor was 25 mV or less nor the absolute zeta potential of the cathode active material was 20 mV or less. Meanwhile, in Comparative Example 3, in which the absolute zeta potential of the transition metal oxide precursor was 25 mV or less but the cathode active material was calcined at a temperature of 950°C to 1100°C during secondary calcination, it was confirmed that the absolute zeta potential of the cathode active material was not 20 mV or less.

[0152] Through these results, it was found that when a transition metal oxide precursor having a specific absolute zeta potential is prepared by including an ammonium cation-containing complex-forming agent in a ratio of 0.1 molar to 1.0 molar as in the present invention and co-precipitating it at a temperature of 30°C to 60°C, and then preparing an anode active material by performing a first calcination and then a second calcination at 800°C to 950°C using the transition metal oxide precursor, the absolute zeta potential of the anode active material targeted in the present invention can be secured.

[0153] Experimental Example. Measurement of Electrochemical Properties

[0154] (Coin cell manufacturing)

[0155] CR2032 coin cells were manufactured as follows using the cathode active materials prepared in Examples 1 to 15 and Comparative Examples 1 to 5, and then electrochemical evaluations were performed.

[0156] Specifically, the cathode active material, conductive material (Denka Black), and polyvinylidene fluoride binder (product name: KF1100) prepared in Examples 1 to 15 and Comparative Examples 1 to 5 were mixed in a weight ratio of 92.5:3.5:4, respectively, and the mixture was added to an N-methyl-2-pyrrolidone solvent to produce a cathode active material slurry such that the solid content was about 30% by weight.

[0157] The above-mentioned positive active material slurry was coated onto an aluminum foil (Al foil, thickness: 15㎛) serving as a positive current collector using a doctor blade, dried, and then rolled to produce a positive electrode. The loading amount of the positive electrode was approximately 14.5 mg / cm², and the rolling density was approximately 2.75 g / cc.

[0158] A 2032 coin-type half-cell was manufactured using the above-mentioned positive electrode, lithium metal negative electrode (thickness 300 μm, MTI), electrolyte, and polypropylene separator in a conventional manner. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mixing ratio EC:EMC = 3:7 volume%) to prepare a mixed solution.

[0159] (Charge / Discharge Characteristics Evaluation)

[0160] After aging the above-manufactured coin-type half-cell at room temperature (25℃) for 10 hours, a charge / discharge test was performed.

[0161] The capacity evaluation was based on a reference capacity of 200 mAh / g, and the charge / discharge conditions applied were a constant current (CC) / constant voltage (CV) of 2.5 V to 4.45 V and a 1 / 20 C cut-off. The initial capacity was measured by performing a 0.1 C charge / 0.1 C discharge followed by a 0.2 C charge / 0.2 C discharge.

[0162] (Evaluation of Room Temperature Cycle Life Characteristics)

[0163] The room temperature cycle life characteristics were measured 30 times under 1.0C charge / 1.0C discharge conditions at 25℃, and the average value was presented.

[0164] The results of the above charge / discharge characteristics and cycle life characteristics are shown in Table 3 below.

[0165] Classification 0.1C Charge Capacity (mAh / g) 0.1C Discharge Capacity (mAh / g) Cathode Material Rate (0.33C / 0.1C) Room Temperature Life (%) Example 1 27 2.3 25 1.1 9 2.8 9 4.5 Example 2 27 1.6 24 8.8 9 3.5 9 3.7 Example 3 27 2.9 25 0.8 9 4.3 9 4.0 Example 4 27 7.5 25 2.3 9 3.6 9 5.2 Example 5 27 7.1 25 3.6 9 4.1 9 4.2 Example 6 27 7.7 25 2.4 9 4.6 9 4.8 Example 7 27 0.6 24 9.5 9 3.8 9 2.8 Example 8 26 8.6 24 5.6 9 2.5 9 1.4 Example 9289.4269.393.092.3 Example 10294.9274.694.093.0 Example 11296.3276.093.693.1 Example 12299.7277.193.592.9 Example 13295.1274.693.893.8 Example 14297.2276.094.192.1 Example 15289.6267.693.192.6 Comparative Example 1257.9230.191.288.7 Comparative Example 2244.2205.688.172.5 Comparative Example 3263.7237.689.582.5 Comparative Example 4281.8259.091.888.1 Comparative Example 5268.3247.190.988.1

[0166] As shown in Table 3 above, in the case of Examples 1 to 15 containing a cathode active material satisfying both the absolute zeta potential value of the transition metal oxide precursor being 25 mV or less and the absolute zeta potential value of the cathode active material being 20 mV or less, it can be confirmed that the overall initial capacity and room temperature lifetime characteristics are improved compared to Comparative Examples 1 to 5.

[0167] Experimental Example 2. SEM analysis of the surface of the cathode active material

[0168] The surfaces of the transition metal oxide precursors prepared in Example 2 and Comparative Example 2 and Example 11 and Comparative Example 3 were analyzed using a Scanning electron microscope (SEM, JEOL JSM-6610), and the results are shown in Figures 1 to 4.

[0169] Figure 1 shows the SEM analysis (×30,000x) results for the transition metal oxide precursor prepared in Comparative Example 2, Figure 2 shows the transition metal oxide precursor prepared in Example 2, Figure 3 shows the transition metal oxide precursor prepared in Comparative Example 3, and Figure 4 shows the transition metal oxide precursor prepared in Example 11.

[0170] Referring to Figures 1 and 2, it can be seen that compared to the precursor prepared according to Comparative Example 2, the precursor of Example 2 has more primary particles aggregated to form a seamless precursor. In addition, it was confirmed that the primary particles of Example 2 were uniformly distributed even after the preparation of the cathode active material.

[0171] In addition, referring to Figures 3 and 4, it can be seen that compared to the precursor prepared according to Comparative Example 3, the precursor of Example 11 has more primary particles aggregated to form a seamless precursor. Furthermore, it was confirmed that the primary particles of Example 11 were uniformly distributed even after the preparation of the cathode active material.

[0172] These results indicate that the degree of particle aggregation of the precursor is altered by controlling the absolute value of the zeta potential of the transition metal oxide precursor. It was found that in the case of a cathode active material prepared using a transition metal oxide precursor satisfying an absolute value of 25 mV or less according to the present invention, the electrochemical characteristics are improved, and side reactions with the electrolyte are reduced, resulting in improved lifespan characteristics.

[0173] Although embodiments of the invention disclosed above have been illustrated and described, the disclosed invention is not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the disclosed invention belongs without departing from the essence claimed in the claims.

Claims

1. A positive electrode active material for a lithium secondary battery comprising a transition metal oxide precursor, The above transition metal oxide precursor has an absolute zeta potential of 25mV or less, and The above-mentioned positive electrode active material is a positive electrode active material for a lithium secondary battery having an absolute zeta potential of 20 mV or less.

2. In Paragraph 1, A cathode active material for a lithium secondary battery, wherein the absolute zeta potential of the transition metal oxide precursor is 0.7 mV or more and 23.8 mV or less, and the absolute zeta potential of the cathode active material is 0.2 mV or more and 19.9 mV or less.

3. In Paragraph 1, The above transition metal oxide precursor is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1. [Chemical Formula 1] (Ni x What y Mn z )(OH)2 (In the above Chemical Formula 1, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.) 4. In Paragraph 1, A positive electrode active material for a lithium secondary battery having an average particle size (D50) of the above transition metal oxide precursor of 9㎛ to 13㎛.

5. In Paragraph 1, The above-mentioned positive electrode active material is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 2. [Chemical Formula 2] Li a [Ni x Co y Mr z ] 2-a O2 (In Chemical Formula 2 above, 0.90≤a≤1.5, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.) 6. A step of preparing a transition metal oxide precursor by co-precipitating a transition metal-containing solution, an ammonium cation-containing complex-forming agent, and a basic compound; and The method comprises the step of preparing an anode active material by mixing the above-mentioned transition metal oxide precursor and lithium raw material and then calcining; The above transition metal oxide precursor has an absolute zeta potential of 25 mV or less, and A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above positive electrode active material has an absolute zeta potential of 20 mV or less.

7. In Paragraph 6, A method for manufacturing a cathode active material for a lithium secondary battery, wherein the absolute zeta potential of the transition metal oxide precursor is 0.7 mV or more and 23.8 mV or less, and the absolute zeta potential of the cathode active material is 0.2 mV or more and 19.9 mV or less.

8. In Paragraph 6, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above-mentioned ammonium cation-containing complex-forming agent is included in a ratio of 0.10 molar to 1.0 molar relative to a transition metal-containing solution.

9. In Paragraph 6, A method for manufacturing a positive electrode active material for a lithium secondary battery comprising one or more selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4 and (NH4)2CO3, wherein the above ammonium cation-containing complex forming agent.

10. In Paragraph 6, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above co-precipitation reaction is performed for 30 to 60 hours at a temperature of 30 to 60°C under an inert atmosphere such as nitrogen or argon.

11. In Paragraph 6, The above transition metal oxide precursor is a method for manufacturing a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1. [Chemical Formula 1] (Ni x What y Mn z )(OH)2 (In the above Chemical Formula 1, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.) 12. In Paragraph 6, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the average particle size (D50) of the above transition metal oxide precursor is 9㎛ to 13㎛.

13. In Paragraph 6, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above transition metal oxide precursor and lithium raw material are mixed in a molar ratio of 1:0.90 to 1:1.

50.

14. In Paragraph 6, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above calcination is performed in the step of first calcining at a temperature of 300℃ to 600℃ for 1 to 15 hours and second calcining at a temperature of 800℃ to 950℃ for 10 to 15 hours.

15. In Paragraph 6, The above-mentioned positive active material is a method for manufacturing a positive active material for a lithium secondary battery represented by the following chemical formula 2. [Chemical Formula 2] Li a [Ni x Co y Mr z ] 2-a O2 (In Chemical Formula 2 above, 0.90≤a≤1.5, 0.35≤x≤0.40, 0≤y≤0.02, 0.58≤z≤0.65, and x+y+z=1.) 16. A cathode comprising a cathode active material for a lithium secondary battery according to paragraph 1.

17. Anode pursuant to Paragraph 16, cathode, A separator interposed between the anode and the cathode, and A lithium secondary battery containing an electrolyte.

Images