Positive electrode active material precursor, method for producing the same, positive electrode active material, and method for producing the positive electrode active material

Abstract

The present invention relates to a cathode active material precursor, a manufacturing method thereof, a cathode active material, and a manufacturing method thereof. The present invention provides a cathode active material precursor that contains Ni and Mn and includes secondary particles formed by aggregation of a plurality of primary particles, the secondary particles having a ratio of a core area to a total area of ​​the particle (core area / total area) of 28.7% to 34.1%, and a porosity represented by the following mathematical formula 1 of 11.3% to 11.7%, a manufacturing method thereof, a cathode active material including a reaction product of the precursor and a lithium raw material, and a manufacturing method of the cathode active material using the precursor.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2022-0102627 dated 17 August 2022 and Korean Patent Application No. 10-2022-0125537 dated 30 September 2022, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] This invention relates to a positive electrode active material precursor, a method for producing the same, a positive electrode active material, and a method for producing a positive electrode active material using the same. [Background technology]

[0003] As the development and demand for mobile device technologies increase, the demand for rechargeable batteries as an energy source is rapidly growing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium transition metal composite oxides are used as the positive electrode active material for lithium secondary batteries, and among them, lithium cobalt composite metal oxide (LiCoO2), which has a high operating voltage and excellent capacity characteristics, is mainly used. However, LiCoO2 has very poor thermal properties due to the destabilization of its crystal structure by delithiation, and it is also expensive, so there are limitations to its large-scale use as a power source in fields such as electric vehicles.

[0005] As alternatives to LiCoO2, materials such as lithium manganese composite metal oxides (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), and lithium nickel composite metal oxides (LiNiO2, etc.) have been developed. Among these, research and development of lithium nickel composite metal oxides are particularly active, as they have a high reversible capacity of approximately 200 mAh / g, making it easy to realize high-capacity batteries. However, LiNiO2 has inferior thermal stability compared to LiCoO2, and if an internal short circuit occurs due to external pressure while charged, the positive electrode active material itself decomposes, causing the battery to rupture and ignite.

[0006] Therefore, in order to maintain the excellent reversible capacity of LiNiO2 while improving its low thermal stability, nickel-cobalt-manganese lithium composite metal oxides (hereinafter simply referred to as "NCM lithium oxides") have been developed in which some of the Ni is replaced with Mn and Co.

[0007] However, due to the recent rise in cobalt (Co) prices, development is underway to create lithium-rich (Li-rich) NCM-based cathode active materials that contain relatively low levels of cobalt (Co) while still meeting high capacity requirements.

[0008] Generally, precursors for NCM-based cathode active materials are synthesized by coprecipitation, where ammonia (NH4OH) is used as a necessary raw material, acting as a complexing agent. Ammonia acts as a catalyst, forming complexes with metal salts during precursor production, thus facilitating precursor synthesis. While it is an essential raw material in precursor synthesis, its malodorous nature and status as an environmentally regulated substance increase the cost of precursor production.

[0009] In addition, ammonia serves as a catalyst and greatly affects physical properties such as the particle size and particle morphology of the precursor produced according to its concentration (amount). Therefore, in order to produce a cathode active material with high physical property reproducibility, the physical property reproducibility of the cathode active material precursor must be high. Thus, fine control of the amount of ammonia used that affects this is necessary, which is inconvenient in the process.

[0010] Therefore, even in the absence of ammonia, it is required to develop a method for producing a cathode active material precursor that can smoothly perform the coprecipitation reaction, is environmentally friendly, has high process efficiency, and has excellent physical property reproducibility.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] The present invention is for solving the above problems and aims to provide a cathode active material precursor having excellent particle strength.

[0013] Also, the present invention aims to provide a method for producing the cathode active material precursor that can smoothly perform the coprecipitation reaction even in the absence of ammonia, is environmentally friendly, and has excellent physical property reproducibility.

[0014] Also, the present invention aims to provide a cathode active material containing a lithium transition metal oxide that is a reaction product of the cathode active material precursor and a lithium raw material substance.

[0015] In addition, the present invention aims to provide a method for producing a cathode active material using the cathode active material precursor.

Means for Solving the Problems

[0016] To solve the above problems, the present invention provides a positive electrode active material precursor, a method for producing the same, a positive electrode active material, and a method for producing a positive electrode active material using the positive electrode active material precursor.

[0017] (1) The present invention provides a positive electrode active material precursor comprising Ni and Mn, and secondary particles formed by the aggregation of a plurality of primary particles, wherein the ratio of the core area to the total surface area of ​​the particles (core area / total surface area) is 28.7% to 34.1%, and the porosity expressed by the following mathematical formula 1 is 11.3% to 11.7%. [Mathematical formula 1] Porosity (%) = (Total void area of ​​the particle / Total surface area of ​​the particle) × 100

[0018] (2) The present invention provides a cathode active material precursor in which the core porosity of the secondary particles is 13.5% to 15.0% as described in (1) above.

[0019] (3) In the present invention, in (1) or (2) above, the average particle size (D 50 The present invention provides a cathode active material precursor having a diameter of 3 μm to 15 μm.

[0020] (4) The present invention provides a positive electrode active material precursor in any one of (1) to (3) above, wherein the primary particles are needle-shaped having a thickness of 40 nm to 100 nm and an aspect ratio of 3 to 10.

[0021] (5) The present invention provides a positive electrode active material precursor represented by the following chemical formula 1 in any one of (1) to (4) above. [Chemical formula 1] [Ni a Mn b M 1 c ](OH)2 In the above chemical formula 1, 0 <a<0.4、0.5≦b<1、0≦c≦0.1であり、M 1 It is one or more elements selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0022] (6) In any one of the above (1) to (5), the present invention provides a positive electrode active material precursor having a specific surface area of 20 m 2 / g to 35 m 2 / g and a tap density of 1.4 g / cc to 2.0 g / c.

[0023] (7) In any one of the above (1) to (5), the present invention provides a positive electrode active material precursor having a specific surface area of 15 m 2 / g to 30 m 2 / g and a tap density of 1.4 g / cc to 2.0 g / c.

[0024] (8) The present invention includes a step of producing a reaction solution containing a transition metal hydroxide by subjecting two or more transition metal raw material substances to a coprecipitation reaction in the presence of a basic aqueous solution under a nitrogen atmosphere. The coprecipitation reaction is carried out by introducing air in the absence of ammonia, and provides a method for producing a positive electrode active material precursor.

[0025] (9) In the above (8), the present invention provides a method for producing a positive electrode active material precursor, wherein the air is introduced at more than 0 volume% and less than 10 volume% with respect to 100 volume% of nitrogen.

[0026] (10) In the above (8) or (9), the present invention provides a method for producing a positive electrode active material precursor, wherein the coprecipitation reaction is carried out by continuously introducing air, and the total amount of air introduced during the coprecipitation reaction is more than 0 volume% and 5 volume% or less with respect to the total amount of nitrogen used during the coprecipitation reaction in terms of volume%.

[0027] (11) In any one of the above (8) to (10), the present invention further includes a step of aging the reaction solution. The aging is carried out by allowing the reaction solution to stand for 6 hours to 24 hours under the conditions of pH 12 to 14 in a nitrogen atmosphere, and provides a method for producing a positive electrode active material precursor.

[0028] (12) The present invention provides a method for producing a positive electrode active material precursor in any one of (8) to (11) above, wherein the aging is performed in a temperature range of 30°C to 50°C.

[0029] (13) The present invention provides a method for producing a positive electrode active material precursor, comprising the steps of: producing a reaction solution containing a transition metal hydroxide by coprecipitation of two or more transition metal raw materials in a nitrogen atmosphere and in the presence of a basic aqueous solution, according to any one of (8) to (12) above; aging the reaction solution; and sequentially washing, filtering, and drying.

[0030] (14) The present invention provides a method for producing a positive electrode active material precursor, wherein, in (13) above, the cleaning is carried out in order of primary cleaning and secondary cleaning, the primary cleaning is carried out using an aqueous basic solution, and the secondary cleaning is carried out using distilled water.

[0031] (15) The present invention provides a method for producing a positive electrode active material precursor in any one of (8) to (14) above, wherein the transition metal is two or more selected from Ni, Co, Mn, Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Y, Mo, W, and Zr.

[0032] (16) The present invention provides a positive electrode active material comprising a lithium transition metal oxide which is a reaction product of any one of the positive electrode active material precursors (1) to (7) above and a lithium raw material, and comprising secondary particles formed by the aggregation of a plurality of primary particles, wherein the ratio of the shell thickness to the semi-long axis of the particle is 30% to 60%.

[0033] (17) The present invention provides a positive electrode active material represented by the following chemical formula 2 in (16) above. [Chemical formula 2] Li x [Ni a Mn b M 1 c ]O2 In the above chemical formula 2, 1.1 <a<1.3、0<a<0.4、0.5≦b<1、0≦c≦0.1、x+a+b+c=2であり、M 1 This is one or more elements selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0034] (18) The present invention provides a method for producing a positive electrode active material, comprising the steps of mixing a positive electrode active material precursor described in any one of (1) to (7) above with a lithium raw material, and firing the mixture.

[0035] (19) The present invention provides a method for producing a positive electrode active material, wherein, in (18) above, the positive electrode active material precursor and the lithium raw material are mixed such that the molar ratio of lithium elements in the positive electrode active material precursor and the lithium raw material is 1:1.2 to 1:1.6. [Effects of the Invention]

[0036] The positive electrode active material precursor according to the present invention has thin primary particles and dense secondary particles, so the internal core of the particles has many voids, and the outer shell is dense with uniformly distributed fine voids, and can have the defined area ratio and porosity, thereby improving the charge-discharge capacity performance of the positive electrode active material to which the positive electrode active material precursor is applied.

[0037] Furthermore, the method for producing a positive electrode active material precursor according to the present invention allows for the easy production of the precursor even in the absence of ammonia, by carrying out a coprecipitation reaction under a nitrogen atmosphere with the introduction of air. This method is environmentally friendly and offers excellent reproducibility of the precursor's physical properties. [Brief explanation of the drawing]

[0038] The following drawings attached to this specification illustrate specific embodiments of the present invention and serve to further illustrate the technical concept of the present invention in conjunction with the above-described content of the invention. The present invention should not be construed as being limited only to the matters described in such drawings.

[0039] [Figure 1]The images show the SEM analysis results of the positive electrode active material precursor of Example 1, (a) particle shape at 2K magnification, (b) particle shape at 15K magnification, (c) particle shape at 50K magnification, and (d) cross-sectional image of the particles at 20K magnification. [Figure 2] The images show the SEM analysis results of the positive electrode active material precursor of Comparative Example 1, (a) particle shape at 2K magnification, (b) particle shape at 15K magnification, (c) particle shape at 50K magnification, and (d) cross-sectional image of the particles at 20K magnification. [Figure 3] The SEM analysis results for the positive electrode active material precursor of Comparative Example 2 are shown, with (a) particle shape at 2K magnification, (b) particle shape at 15K magnification, (c) particle shape at 50K magnification, and (d) image of the particle cross-section at 20K magnification. [Figure 4] The images show the SEM analysis results of the positive electrode active material precursor of Comparative Example 3, with (a) an image of the particle shape at 2K magnification and (b) an image of the particle shape at 15K magnification. [Figure 5] The images show the SEM analysis results of the positive electrode active material precursor of Comparative Example 4, with (a) an image of the particle shape at 2K magnification and (b) an image of the particle shape at 15K magnification. [Figure 6] This is a comparative graph of the particle size distribution of the positive electrode active material precursors in Example 1 and Comparative Examples 1 to 4. [Figure 7] The images show the SEM analysis results of the positive electrode active material of Example 1, with (a) the particle shape at 50K magnification and (b) an image of the particle cross-section at 50K magnification. [Figure 8] The images show the SEM analysis results of the positive electrode active material of Comparative Example 1, with (a) the particle shape at 50K magnification and (b) an image of the particle cross-section at 50K magnification. [Figure 9] The images show the SEM analysis results of the positive electrode active material of Comparative Example 2, with (a) the particle shape at 50K magnification and (b) an image of the particle cross-section at 50K magnification. [Figure 10] The images show the SEM analysis results of the positive electrode active material precursor of Example 2, with (a) an image of the particle shape at 15K magnification and (b) an image of the particle shape at 1K magnification. [Figure 11]The images show the SEM separation results of the positive electrode active material precursor of Example 3, with (a) an image of the particle shape at 15K magnification and (b) an image of the particle shape at 1K magnification. [Figure 12] These are XRD graphs of the cathode active material precursors for Examples 2 and 3. [Figure 13] The images show the SEM analysis results of the positive electrode active material of Example 2, with (a) an image of the particle shape at 25K magnification and (b) an image of the particle shape at 1K magnification. [Figure 14] The images show the SEM analysis results of the positive electrode active material of Example 2, with (a) an image of the particle shape at 25K magnification and (b) an image of the particle shape at 1K magnification. [Modes for carrying out the invention]

[0040] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0041] term In this invention, the term "primary particle" refers to a particle unit in which no grain boundaries are visible when observed using a scanning electron microscope (SEM) at a field of view of 5,000 to 20,000 times magnification.

[0042] In this invention, the term "secondary particle" refers to a particle formed by the aggregation of multiple primary particles.

[0043] In this invention, the term "average particle size (D 50 )" refers to the particle size at the 50% point of the volume cumulative distribution by particle size.

[0044] Measurement method In this invention, the porosity of the precursor, the ratio of the core area to the total area of ​​the precursor, and the porosity of the core were measured using a particle cross-sectional image obtained with a scanning electron microscope (SEM) and an image analysis program.

[0045] Specifically, cross-sectional images (50K magnification) of each precursor were acquired using a SEM (Hitachi Corporation), and the porosity of the precursor, the porosity of the core, and the ratio of the core area to the total area were analyzed. Carbon black Super-P was used as the precursor and conductive material, and poly(vinylidene fluoride) was used as the binder in a weight ratio of 54:4:43 (based on 1g of precursor). A slurry was prepared by uniformly mixing this with 1.8g of N-methylpyrrolidone. The prepared slurry was thinly coated onto aluminum foil to a thickness of 0.25mm and dried at 100°C to prepare electrodes for cross-sectional measurement. An ion milling instrument was used to irradiate the cross-section of the electrode coated with the precursor with an ion beam to prepare test specimens for SEM measurement. Using the aforementioned SEM measurement specimen, a cross-sectional image of the precursor was acquired. Particles were selected from the cross-sectional image, and using an image processing program (Pore analysis), the cross-section of one particle was extracted using the watershed image processing technique, and then the core region was separated using the erosion image processing technique. Subsequently, the image was converted to binary using the threshold image processing technique, and the porosity of the precursor, the porosity of the core, and the ratio of the core area to the total area were analyzed. Here, the core region was defined as the area inside the particle where pores are densely concentrated. In this case, the program was used to define the core region as the region formed by connecting the pores located at the outermost edge of the internal pores. Furthermore, in the cross-sectional image, 10 particles with particle diameters of 2 to 8 μm were selected, and for each particle, the porosity of the precursor, the porosity of the core, and the ratio of the core area to the total area were measured using the above method, and the results are shown as the average of these measured values.

[0046] In this invention, the average particle size was measured using a particle size analyzer (S-3500, manufactured by Microtrac) with the particle size characteristics of the precursor set to a refractive index of 1.55.

[0047] In this invention, the tap density was measured by placing 50 g of precursor in a 50 ml graduated cylinder and performing 3000 strokes using a TAPDENSER (KYT-4000K, SEISHIN ENTERPRISE Co., Ltd.).

[0048] In this invention, the specific surface area was measured using a Tristar II 3020 (manufactured by micromeritics) after pretreatment of the precursor at 150°C for 3 hours, with a P / Po (relative pressure) of 0.05-0.2.

[0049] The present invention provides a positive electrode active material precursor, a method for producing the same, a positive electrode active material containing a reaction product of the same and a lithium raw material, and a method for producing a positive electrode active material using the positive electrode active material precursor.

[0050] The present invention will be described in more detail below.

[0051] Cathode active material precursor The present invention provides a positive electrode active material precursor that has a particle morphology with many voids in the core portion and a dense shell portion, and which contains voids, thereby improving the charge and discharge capacity.

[0052] The positive electrode active material precursor according to one embodiment of the present invention contains Ni and Mn, and includes secondary particles formed by the aggregation of a plurality of primary particles, wherein the ratio of the core area to the total surface area of ​​the particles (core area / total surface area) is 28.7% to 34.1%, and the porosity expressed by the following mathematical formula 1 is 11.3% to 11.7%.

[0053] [Mathematical formula 1] Porosity (%) = (Total void area of ​​the particle / Total surface area of ​​the particle) × 100

[0054] Furthermore, the core porosity of the secondary particles can be 13.50% to 15.00%, and the average particle size (D) of the secondary particles. 50 The particle size can be between 3 μm and 15 μm.

[0055] Furthermore, the primary particles can be needle-shaped, having a thickness of 40 nm to 100 nm and an aspect ratio of 3 to 10.

[0056] As another example, the positive electrode active material precursor can be represented by the following chemical formula 1.

[0057] [Chemical formula 1] [Ni a Mn b M 1 c ](OH)2

[0058] In the above chemical formula 1, 0 <a<0.4、0.5≦b<1、0≦c≦0.1であり、M 1 This is one or more elements selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0059] Furthermore, the positive electrode active material precursor has a specific surface area of ​​20 m². 2 / g~35m 2 The value is / g, and the tap density can be 1.4g / cc to 2.0g / cc.

[0060] As another example, the positive electrode active material precursor has a specific surface area of ​​15 m². 2 / g~30m 2 The value is / g, and the tap density can be 1.4g / cc to 2.0g / cc.

[0061] As yet another example, the positive electrode active material precursor has an average particle size (D 50 The surface area is 3 μm to 6 μm and the specific surface area is 20 m². 2 / g~35m 2 The value is / g, and the tap density can be 1.4g / cc to 2.0g / cc.

[0062] As yet another example, the positive electrode active material precursor has an average particle size (D 50 The surface area is 7 μm to 15 μm, and the specific surface area is 15 m². 2 / g~30m 2The value is / g, and the tap density can be 1.4g / cc to 2.0g / cc.

[0063] Method for manufacturing a positive electrode active material precursor The present invention provides a method for producing a positive electrode active material precursor that is environmentally friendly and has high reproducibility of physical properties.

[0064] A method for producing the positive electrode active material precursor according to one embodiment of the present invention includes the step of producing a reaction solution containing a transition metal hydroxide by coprecipitation of two or more transition metal raw materials in a nitrogen atmosphere and in the presence of a basic aqueous solution, wherein the coprecipitation reaction can be carried out in the absence of ammonia and by introducing air.

[0065] The aforementioned coprecipitation reaction is carried out to produce transition metal hydroxides from transition metal raw materials, under a nitrogen atmosphere, in the presence of a basic aqueous solution, and with the addition of air, and can be carried out in the absence of ammonia. Here, "in the presence of a basic aqueous solution" means that a basic aqueous solution is included as a reactant during the coprecipitation reaction.

[0066] Generally, precursors for NCM-based cathode active materials are synthesized by forming complexes with transition metal salts using ammonia as a complexing agent. However, ammonia is an olfactory and environmentally regulated substance, making the construction of a treatment system essential. This results in treatment system costs that are excessively high relative to the production scale, leading to poor process efficiency when applied to industry. Furthermore, ammonia acts as a catalyst in precursor synthesis, and its concentration greatly affects the properties of the resulting precursor. Controlling the primary particles and fine voids of the precursor is not easy, and as a result, when applied as a cathode active material, controlling the diffusion rate of Li is difficult, limiting capacity and power characteristics, and making it difficult to reproduce consistent properties of the cathode active material.

[0067] However, the method for producing a positive electrode active material according to the present invention involves carrying out the coprecipitation reaction in the absence of ammonia and introducing air under a nitrogen atmosphere. In this method, the air takes over the role of ammonia, allowing the coprecipitation reaction to proceed smoothly, and it is also environmentally friendly and highly reproducible.

[0068] Specifically, in one embodiment of the present invention, the coprecipitation reaction can be carried out under a nitrogen atmosphere by introducing air, where the air can be introduced in an amount greater than 0% by volume and less than 10% by volume, more specifically, greater than 0% by volume and 5% by volume or less, relative to 100% by volume of nitrogen.

[0069] More specifically, the coprecipitation reaction is carried out under a nitrogen atmosphere by continuously introducing air, where the total amount of air introduced during the coprecipitation reaction can be greater than 0% and less than 10% by volume, or greater than 0% and 5% by volume, relative to 100% by volume of the total amount of nitrogen used during the coprecipitation reaction. For example, if the amount of air introduced is 10% or more by volume relative to the nitrogen, aggregation of the precursor particles produced will occur, which may necessitate an additional grinding step, or the deformation of particle size and particle state may make it difficult to produce a positive electrode active material precursor that satisfies the above-mentioned physical properties.

[0070] The transition metal raw material can be a sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide of a transition metal, and the transition metal can be two or more selected from Ni, Mn, Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0071] As another example, the transition metal raw material may include nickel and manganese raw materials.

[0072] Specifically, the nickel raw material can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides. More specifically, it can be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0073] Furthermore, the manganese raw material can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides. Specific examples include, but are not limited to, manganese oxides such as Mn2O3, MnO2, and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylates, manganese citrate, and manganese fatty acid salts; manganese oxyhydroxide, manganese chloride, or combinations thereof.

[0074] As yet another example, if necessary, the metal solution may contain M 1 Contains raw materials and / or M 2 Further raw material substances may be included.

[0075] Said M 1 In the raw materials contained, M 1 The element can be one or more selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr, M 1 The raw material contained is the above-mentioned M 1 These can be elemental acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides.

[0076] Furthermore, for a more uniform coprecipitation reaction, the transition metal raw material can be used in the form of a metal solution in which the transition metal raw material is dissolved in a solvent, where the metal solution can be prepared by adding the transition metal raw material to a solvent, specifically, a mixed solvent of water or an organic solvent that can be homogeneously mixed with water (e.g., alcohol), or by mixing an aqueous solution of the transition metal raw material.

[0077] Here, the transition metal raw materials can be mixed in a stoichiometric ratio that satisfies the molar ratio of each element within the transition metal hydroxide particles formed by the coprecipitation reaction. That is, in the present invention, the transition metal raw materials can be mixed in an amount that satisfies the mole fractions of a, b, and c in [Chemical Formula 1] described later.

[0078] The aforementioned basic aqueous solution can be prepared by dissolving a strong basic compound in distilled water as a precipitating agent.

[0079] Furthermore, the basic aqueous solution may contain 15 wt% to 35 wt% of a strong basic compound, or have a pH of 9 to 13.

[0080] Here, the strong base compound may be an alkali metal hydroxide or hydrate, an alkaline earth metal hydroxide or hydrate, or a combination thereof. More specifically, the strong base compound may be sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, or a combination thereof.

[0081] As another example, the basic aqueous solution may be one or more selected from aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous calcium hydroxide solution, and aqueous lithium hydroxide solution.

[0082] Furthermore, the basic aqueous solution may be added during the coprecipitation reaction to adjust the pH, and in an amount such that the pH in the reaction system where the coprecipitation reaction is taking place becomes 9 to 13.

[0083] On the other hand, the coprecipitation reaction can be carried out at a temperature of 40°C to 70°C. Furthermore, to increase the reaction rate of the coprecipitation reaction, a stirring step can be selectively performed, where the stirring speed can be 100 rpm to 2000 rpm.

[0084] As another example, a method for producing the positive electrode active material precursor according to one embodiment of the present invention may further include a step of aging the reaction solution after the coprecipitation reaction, wherein the aging can be carried out by letting the reaction solution stand for 6 to 24 hours under a nitrogen atmosphere and pH 12 to 14.

[0085] As another example, the aging process can be carried out in a temperature range of 30°C to 50°C.

[0086] The NCM-based cathode active material precursor used in the production of lithium-rich NCM-based cathode active materials is synthesized by coprecipitation. Recently, methods to improve the density of the precursor have been studied to maximize the energy density of batteries, and one such method is coprecipitation in the presence of a basic solution (e.g., sodium hydroxide). In this case, metal oxides (e.g., manganese oxide) are generated in the reaction system separately from the target precursor material. When these are washed and dried, they cause aggregation of the precursor particles, leading to problems in the classification process. Furthermore, even after being applied as a raw material for cathode active materials and calcined, they remain as impurities in the cathode active material, causing a decrease in the capacity and lifespan of the cathode active material.

[0087] In the method for producing a positive electrode active material precursor according to the present invention, if the aging step is further included after the coprecipitation reaction, the oxidation of transition metal hydroxides in the reaction solution is prevented, thereby suppressing the formation of metal oxides, particularly manganese oxides. This eliminates the problems of aggregation and classification processes caused by the metal oxides during drying, and ultimately results in the production of a positive electrode active material precursor that is free of metal oxide impurities or significantly reduced compared to conventional methods.

[0088] As yet another example, in a manufacturing method according to one embodiment of the present invention, the aging can be carried out for 12 to 24 hours under conditions of a nitrogen atmosphere, pH 13 to 14, and a temperature of 40°C to 50°C, in order to more easily achieve its intended effect.

[0089] On the other hand, in the aging step, the pH conditions can be set by adding a strong base compound to the reaction solution, where the strong base compound can be added either on its own or in an aqueous solution in distilled water, and the strong base compound is not particularly limited as long as it is commonly known as a strong base compound, for example it can be sodium hydroxide, potassium hydroxide, calcium hydroxide or lithium hydroxide.

[0090] As yet another example, a method for producing a positive electrode active material precursor according to one embodiment of the present invention may include the steps of: producing a reaction solution containing a transition metal hydroxide by coprecipitation of two or more transition metal raw materials in a nitrogen atmosphere and in the presence of a basic aqueous solution; aging the reaction solution; and sequentially washing, filtering, and drying.

[0091] The coprecipitation and aging steps are as described above. The washing, filtering, and drying can be carried out by conventional means in the industry.

[0092] The cleaning can be carried out in the order of a primary cleaning and a secondary cleaning, the primary cleaning can be carried out using an alkaline aqueous solution, and the secondary cleaning can be carried out using distilled water.

[0093] Here, the basic aqueous solution used in the primary wash can have a pH of 12 to 14, and, as an example, the basic aqueous solution may contain 2 wt% to 5 wt% of a strong basic compound.

[0094] In the method for producing a positive electrode active material precursor according to the present invention, when the washing is performed by primary washing with a basic aqueous solution and secondary washing with distilled water, oxidation of transition metal hydroxides that may occur during the washing process can be prevented, and impurities can be further removed.

[0095] The drying process can be carried out at 110°C to 400°C for 15 to 30 hours.

[0096] positive electrode active material The present invention provides a positive electrode active material comprising a lithium transition metal oxide, which is a reaction product of a positive electrode active material precursor and a lithium raw material.

[0097] The positive electrode active material according to one embodiment of the present invention comprises a lithium transition metal oxide which is a reaction product of the positive electrode active material precursor and a lithium raw material, and comprises secondary particles formed by the aggregation of a plurality of primary particles, wherein the ratio of the shell thickness to the semi-long axis of the particle is 30% to 60%.

[0098] As another example, the positive electrode active material can be represented by the following chemical formula 2.

[0099] [Chemical formula 2] Li x [Ni a Mn b M 1 c ]O2

[0100] In the above chemical formula 2, 1.1 <a<1.3、0<a<0.4、0.5≦b<1、0≦c≦0.1、x+a+b+c=2であり、M 1 This is one or more elements selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0101] Method for manufacturing positive electrode active material The present invention provides a method for producing a positive electrode active material using the positive electrode active material precursor.

[0102] A method for producing a positive electrode active material according to one embodiment of the present invention may include the steps of mixing the positive electrode active material precursor with a lithium raw material and firing the mixture.

[0103] Specifically, the method for producing a positive electrode active material according to the present invention can be carried out by a method for producing a positive electrode active material that is well known in the art, except that a positive electrode active material precursor according to the present invention is used, and the method is not particularly limited.

[0104] The aforementioned lithium raw material includes lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), chlorides (e.g., lithium chloride (LiCl)), and others. One of these may be used alone or a mixture of two or more.

[0105] On the other hand, the mixing of the positive electrode active material precursor and the lithium raw material can be carried out by solid-phase mixing such as jet milling, and the mixing ratio of the positive electrode active material precursor and the lithium raw material can be determined to satisfy the mole fraction of each component in the final positive electrode active material. More specifically, the positive electrode active material precursor and the lithium raw material can be mixed such that the molar ratio of lithium elements in the positive electrode active material precursor and the lithium raw material is 1:1.2 to 1:1.6.

[0106] Furthermore, although not essential, the mixing may include, in addition to the positive electrode active material precursor and lithium raw material, a raw material for doping a portion of the transition metal and / or oxygen of the positive electrode active material. For example, the above-mentioned M 1The included raw materials, or the X-containing raw materials described later, can be further mixed in. Here, the X-containing raw materials can be, but are not limited to, Na3PO4, K3PO4, Mg3(PO4)2, AlF3, NH4F, LiF, etc. As described above, when a portion of the oxygen is replaced by element X, the effect of suppressing oxygen desorption and reaction with the electrolyte during charging and discharging of the secondary battery can be obtained.

[0107] On the other hand, the firing can be carried out at 700°C to 900°C, specifically at 750°C to 850°C, and the firing time can be 5 hours to 30 hours, specifically at 8 hours to 15 hours, but is not limited to these.

[0108] On the other hand, a washing step and a drying step can be further performed after the calcination to remove lithium by-products. The washing step can be carried out, for example, by adding the manufactured positive electrode active material to ultrapure water and stirring. Here, the washing temperature can be 20°C or lower, specifically 10°C to 20°C, and the washing time can be about 10 minutes to 1 hour. When the washing temperature and washing time meet the above range, lithium by-products can be effectively removed.

[0109] Positive electrode and secondary battery The positive electrode active material produced by the method for producing the positive electrode active material according to the present invention can be usefully used in the manufacture of positive electrodes for secondary batteries.

[0110] Specifically, the positive electrode for a secondary battery according to the present invention includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material.

[0111] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material is used. For example, the positive electrode can be manufactured by dissolving or dispersing the components constituting the positive electrode active material layer, i.e., the positive electrode active material and a conductive material and / or binder, etc., in a solvent to produce a positive electrode composite material, applying the positive electrode composite material to at least one surface of a positive electrode current collector, and then drying and rolling it; or by casting the positive electrode composite material onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0112] Here, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0113] A positive electrode active material layer containing the positive electrode active material according to the present invention is located on at least one surface of the current collector, and optionally further selectively containing at least one of a conductive material and a binder.

[0114] The positive electrode active material can be included in an amount of 80-99% by weight, more specifically 85-98% by weight, relative to the total weight of the positive electrode active material layer. When included within the above content range, excellent capacity characteristics can be observed.

[0115] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include 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, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used. The conductive material may be included in an amount of 1% to 30% by weight relative to the total weight of the positive electrode active material layer.

[0116] Furthermore, the binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 1% to 30% by weight relative to the total weight of the positive electrode active material layer.

[0117] On the other hand, the solvent used in the production of the positive electrode composite material can be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, which can be used individually or in combination. The amount of solvent used can be appropriately adjusted considering the slurry coating thickness, production yield, viscosity, etc.

[0118] Furthermore, the secondary battery according to the present invention includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the present invention as described above.

[0119] On the other hand, the secondary battery may optionally further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0120] In the secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector.

[0121] The anode can be manufactured by a conventional method for manufacturing anodes that is generally known in the art. For example, the anode can be manufactured by dissolving or dispersing the components constituting the anode active material layer, i.e., the anode active material and a conductive material and / or binder, etc., in a solvent to produce a anode composite material, coating the anode composite material onto at least one surface of the anode current collector, and then drying and rolling it; or by casting the anode composite material onto another support, peeling it off the support, and laminating the resulting film onto the anode current collector.

[0122] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0123] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can 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. v(0 < v < 2), metal oxides such as SnO2, vanadium oxides, lithium vanadium oxides that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. may be mentioned, and any one or a mixture of two or more of these can be used. Further, a thin film of metallic lithium can also be used as the negative electrode active material. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and high-temperature calcined carbons such as petroleum or coal tar pitch derived cokes.

[0124] Also, the binder and the conductive material are as described above for the positive electrode.

[0125] On the other hand, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, 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 can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0126] On the other hand, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of secondary batteries.

[0127] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0128] The organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include 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 hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropyl alcohol; nitriles such as Ra-CN (where Ra is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 can produce an electrolyte with excellent performance.

[0129] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0130] In addition to the electrolyte components, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate; or pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, 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 additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0131] As described above, the secondary battery containing the positive electrode active material according to the present invention has excellent capacity characteristics and high-temperature stability, and can be usefully applied to portable devices such as mobile phones, notebook computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0132] Furthermore, the secondary battery according to the present invention can be used as a unit cell of a battery module, and the battery module can be applied to a battery pack. The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0133] Examples Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention may be realized in various different forms and is not limited to the embodiments described herein.

[0134] Experimental Material I Example 1 Nickel sulfate and manganese sulfate were dissolved in deionized water in a molar ratio of 0.35:0.65 to prepare a 2.4M metal solution, and a separate 25% sodium hydroxide aqueous solution was prepared.

[0135] A nitrogen atmosphere was created in a coprecipitation reactor set to 50°C by introducing nitrogen gas at a rate of 300 L / hr. The metal solution was then added at a rate of 0.5 L / hr, followed by an aqueous sodium hydroxide solution at a rate of 0.3 L / hr, and the coprecipitation reaction was carried out for 24 hours. During this coprecipitation reaction, air was introduced at a rate of 15 L / hr (5 vol%) relative to 100 vol% nitrogen.

[0136] Afterward, the material was washed with water, filtered, and then dried at 120°C for 12 hours to produce a cathode active material precursor.

[0137] Comparative Example 1 Nickel sulfate and manganese sulfate were dissolved in deionized water in a molar ratio of 0.35:0.65 to prepare a 2.4M metal solution, and a separate 25% sodium hydroxide aqueous solution was prepared.

[0138] A nitrogen atmosphere was created in a coprecipitation reactor set to 50°C by introducing nitrogen gas at a rate of 300 L / hr. The metal solution was then added at a rate of 0.5 L / hr, a sodium hydroxide aqueous solution at 0.3 L / hr, and a 9% ammonia aqueous solution at 0.12 L / hr to carry out the coprecipitation reaction.

[0139] Afterward, the material was washed with water, filtered, and then dried at 120°C for 12 hours to produce a cathode active material precursor.

[0140] Comparative Example 2 A cathode active material precursor was produced in the same manner as in Example 1, except that the coprecipitation reaction was carried out while adding air at a rate of 10% by volume relative to 100% by volume of nitrogen.

[0141] Comparative Example 3 A cathode active material precursor was produced in the same manner as in Example 1, except that the coprecipitation reaction was carried out while adding air at a rate of 50% by volume relative to 100% by volume of nitrogen.

[0142] Comparative Example 4 In Example 1, the cathode active material precursor was produced in the same manner as in Example 1, except that the coprecipitation reaction was carried out with 100% by volume of air added instead of nitrogen during the reaction.

[0143] Experimental Example 1 The particle properties of each cathode active material precursor produced in the examples and comparative examples were compared and analyzed.

[0144] (1) SEM measurement The particle shape of each precursor was confirmed using a SEM (Hitachi Corporation), and the results are shown in Figures 1 to 5.

[0145] (2) Particle size analysis The particle size characteristics of each precursor were measured using a particle size analyzer (S-3500, Microtrac) with the refractive index set to 1.55. In the measuring device, the diameter (D) corresponding to 50% of the maximum value in the cumulative particle number distribution by particle size was used. 50 ), diameter corresponding to 5% (D5), diameter corresponding to 95% (D 95 ), maximum diameter (D max ), minimum diameter (D min The following values ​​were calculated and the results are shown in Table 1 and Figure 6 below.

[0146] (3) Tap density analysis 50g of each precursor was placed in a 50ml graduated cylinder, and the tap density was measured by performing 3000 strokes using a TAPDENSER (KYT-4000K, SEISHIN ENTERPRISE Co.,Ltd.). The results are shown in Table 1 below.

[0147] (4) Specific surface area Each precursor was pretreated using a Tristar II 3020 (micromeritics) at 150°C for 3 hours, and then the specific surface area was measured at a P / Po (relative pressure) of 0.05-0.2. The results are shown in Table 1 below.

[0148] (5) Particle structure analysis Using a SEM (Hitachi Corporation), cross-sectional images (50K magnification) of each precursor were acquired, and from these, the porosity of the precursor, the porosity of the core, and the ratio of the core area to the total area were analyzed.

[0149] For each precursor, carbon black Super-P was used as the conductive material and poly(vinylidene fluoride) as the binder in a weight ratio of 54:4:43 (based on 1g of precursor). This mixture was then uniformly mixed with 1.8g of N-methylpyrrolidone to produce a slurry. The prepared slurry was thinly coated onto aluminum foil to a thickness of 0.25mm and dried at 100°C to produce an electrode for cross-sectional measurement. An ion milling device was used to irradiate the electrode cross-section coated with the precursor with an ion beam to produce a test specimen for SEM measurement.

[0150] Subsequently, cross-sectional images were acquired from the specimen using a scanning electron microscope (SEM). Particles were selected from the cross-sectional images, and using an image processing program (Pore analysis), the cross-section of a single particle was extracted using the watershed image processing technique, followed by the separation of the core region using the erosion image processing technique. Then, the images were converted to binary using the threshold image processing technique, and the porosity of the precursor, the core porosity, and the ratio of the core area to the total area were analyzed. Here, the core region was defined as the area inside the particle where pores are densely concentrated, and the program was used to define the core region as the region formed by connecting the pores located at the outermost edge of the internal pores.

[0151] Furthermore, ten particles with a particle diameter of 2 to 8 μm were selected from each cross-sectional image, and the porosity of the precursor, the porosity of the core, and the ratio of the core area to the total area were measured for each particle using the method described above. The results were then presented as the average value of these measured values.

[0152] [Table 1]

[0153] As shown in Table 1 above, the positive electrode active material precursor of Example 1 was found to have similar particle size characteristics and equivalent tap density to the positive electrode active material precursor of Comparative Example 1. Furthermore, although the overall porosity of the positive electrode active material precursor of Example 1 is similar to that of the positive electrode active material precursor of Comparative Example 1, it has a lower core area ratio and a higher core porosity, satisfying the porosity and core area ratio presented in the present invention.

[0154] Furthermore, while the cathode active material precursor of Example 1 exhibited particle characteristics in which the core had many voids and the shell (outer) was dense with coexisting fine voids, it was confirmed that the cathode active material precursor of Comparative Example 1 had voids only in the core and a thick shell (see Figure 2(b) and Figure 4(b)).

[0155] In the case of the positive electrode active material precursor of Comparative Example 2, the tap density was significantly reduced compared to Example 1 and Comparative Example 1, and the particle exhibited characteristics in which there were many voids both inside and outside the particle, and the core and shell were not clearly separated (see Figure 5(b)).

[0156] Experimental Example 2 The cathode active materials were manufactured using the cathode active material precursors produced in the examples and comparative examples, and their particle properties were compared and analyzed.

[0157] Each positive electrode active material precursor was mixed with LiOH such that the molar ratio of the transition metals (Ni and Mn) in the precursor to the Li in the LiOH was 1:1.35. The mixture was then fired at 700°C for 15 hours under an atmospheric environment to produce each positive electrode active material.

[0158] The particle shape of each manufactured cathode active material was confirmed at a magnification of 50K using a SEM (Hitachi Corporation), and the results are shown in Figures 7 to 9.

[0159] Furthermore, the ratio of shell thickness to particle radius of the positive electrode active material was analyzed, and the results are shown in Table 2 below.

[0160] The ratio of shell thickness to particle semi-major axis was calculated using the same method as in Experimental Example 1, except that the active material was used instead of the precursor. A cross-sectional measurement electrode was manufactured from this electrode, and a test specimen for SEM measurement was prepared. A cross-sectional image was obtained at 50K magnification using SEM, the semi-major axis of the particle was measured, and the shell thickness was calculated using the distance from the outer edge of the core to the outer surface of the particle along the semi-major axis as the shell thickness, and the ratio was calculated as [shell thickness / particle semi-major axis] × 100. Here, the outer edge of the core was defined as the part of the particle where pores are densely concentrated, with the outermost pores among the internal pores being the boundary between the core and the shell. Furthermore, 10 particles with particle diameters of 2 to 8 μm were selected from each cross-sectional image, and the ratio of shell thickness to particle semi-major axis was determined for each particle using the method described above. The average value of these values ​​was used to show the results.

[0161] [Table 2]

[0162] As shown in Table 2 above, it was confirmed that the positive electrode active material of Example 1 satisfies the range indicated by the ratio of the shell thickness to the semi-long axis of the particles.

[0163] Experimental Example 3 Using the positive electrode active material precursors produced in the examples and comparative examples, positive electrode active materials were manufactured, and batteries were then manufactured using these materials. After the batteries were manufactured, their performance was evaluated.

[0164] (1) Manufacturing of positive electrode active material Each positive electrode active material precursor was mixed with LiOH such that the molar ratio of the transition metals (Ni and Mn) in the precursor to the Li in the LiOH was 1:1.35. The mixture was then fired at 700°C for 15 hours under an atmospheric environment to produce each positive electrode active material.

[0165] (2) Manufacturing of the positive electrode The manufactured positive electrode active materials, carbon black conductive material, and PVdF binder were mixed in N-methylpyrrolidone solvent in a weight ratio of 96.5:1.5:2.0 to produce a positive electrode composite material (viscosity: 5000 mPa·S). This composite material was then applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0166] (3) Battery manufacturing The negative electrode used lithium metal. An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and negative electrode manufactured as described above. After positioning the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / diethyl carbonate / ethyl methyl carbonate (EC / DEC / EMC mixed volume ratio = 3 / 2 / 5).

[0167] For each lithium secondary battery half-cell manufactured as described above, the initial charge / discharge capacity and efficiency were measured by charging to 0.33C and 4.4V in CCCV mode at 25°C, and then discharging to 2.5V at a constant current of 0.33C. The results are shown in Table 3 below.

[0168] [Table 3]

[0169] As shown in Table 3 above, it can be confirmed that the positive electrode active material of Example 1 has superior initial charge / discharge capacity and efficiency compared to the positive electrode active materials of Comparative Examples 1 and 2.

[0170] Experimental Material II Example 2 A reaction solution was prepared by carrying out a coprecipitation reaction in the same manner as in Example 1.

[0171] Subsequently, the reaction solution was aged for 6 hours under conditions of pH 13 and a temperature of 50°C while maintaining a nitrogen atmosphere. After that, it was washed with water, filtered, and dried at 120°C for 12 hours to produce a cathode active material precursor.

[0172] Example 3 In Example 2, a cathode active material precursor was produced in the same manner as in Example 2, except that after aging, the washing step consisted of primary washing with a 2 wt% sodium hydroxide aqueous solution followed by secondary washing with distilled water.

[0173] Experimental Example 4 The particle properties of the positive electrode active material precursors from Examples 2 and 3 were analyzed.

[0174] (1) SEM measurement Using a SEM (Hitachi), the particle shapes of each precursor were confirmed by analysis at magnifications of 1K and 15K, and the results are shown in Figures 10 and 11.

[0175] (2)XRD measurement Using an XRD (manufactured by Rigaku), the crystallinity of each precursor was analyzed with a start angle of 10°, an end angle of 70°, and a scan speed of 4° / min. The results are shown in Figure 12.

[0176] (3) Particle size analysis The particle size characteristics of each precursor were measured using a particle size analyzer (S-3500, Microtrac) with the refractive index set to 1.55. In the measuring device, the diameter (D) corresponding to 50% of the maximum value in the cumulative particle number distribution by particle size was used. 50 ), diameter corresponding to 5% (D5), diameter corresponding to 95% (D 95 ), maximum diameter (D max ), minimum diameter (D min The result was calculated and is shown in Table 4 below.

[0177] (4) Tap density analysis 50g of each precursor was placed in a 50ml graduated cylinder, and the tap density was measured by performing 3000 strokes using a TAPDENSER (KYT-4000K, SEISHIN ENTERPRISE Co.,Ltd.). The results are shown in Table 4 below.

[0178] (5) Specific surface area Each precursor was pretreated using Tristar II 3020 (micromeritics) at 150°C for 3 hours, and then the specific surface area was measured at a P / Po (relative pressure) of 0.05-0.2. The results are shown in Table 4 below.

[0179] (6) Classification rate (%) The classification rate is the actual amount of each precursor obtained after drying, and was calculated using the following mathematical formula 2.

[0180] [Mathematical formula 2] Classification rate (%) = [Weight of precursor after classification (kg) / Weight of precursor before classification (kg)] × 100

[0181] [Table 4]

[0182] Figures 10 and 11 confirm that the cathode active material precursors of Examples 2 and 3 exhibited similar particle shapes to the cathode active material precursor of Example 1, and also demonstrated superior classification efficiency, lower specific surface area, and higher tap density. Furthermore, referring to Figure 12, it was confirmed that no manganese oxide (Mn3O4) peaks were observed in the cathode active material precursors produced in Examples 2 and 3.

[0183] The results above indicate that when the positive electrode active material precursor of the present invention is produced by a manufacturing method further comprising an aging step and a washing step, the properties of the precursor particles are not altered, and oxidation of transition metal hydroxides is prevented, thereby suppressing the formation of metal oxides. This results in no aggregation or classification problems during drying, a remarkably excellent classification rate, and the absence or significant reduction of impurities in the precursor.

[0184] Experimental Example 5 A positive electrode active material was manufactured using the positive electrode active material precursors produced in Example 2 and Example 3. A battery was then manufactured using this active material, and the battery performance was evaluated. The results are shown in Table 5.

[0185] Here, the production of the positive electrode active material, initial charge / discharge capacity, and initial efficiency were carried out in the same manner as in Experimental Example 3. Furthermore, the C-rate was measured, and after 30 cycles of charging at 0.1C and discharging at 0.1C, the capacity retention rate was confirmed.

[0186] Furthermore, each manufactured cathode active material was analyzed using a SEM (Hitachi Corporation) at magnifications of 1K and 25K to confirm the particle shape of each precursor, and the results are shown in Figures 13 and 14.

[0187] [Table 5]

[0188] Table 5 above confirms that the positive electrode active materials of Examples 2 and 3 have superior charge / discharge capacity compared to the positive electrode active material of Example 1.

Claims

1. Including Ni and Mn, It contains secondary particles formed by the aggregation of multiple primary particles, The aforementioned secondary particles have an average particle size (D 50) of 3 μm to 6 μm, a ratio of core area to total particle area (core area / total area) measured using a cross-sectional image of the particles with an SEM and an image analysis program, and a porosity expressed by the following mathematical formula 1 of 11.3% to 11.7%. A cathode active material precursor having a core porosity of 13.5% to 15.0% for the secondary particles. [Mathematical formula 1] Porosity (%) = (Total void area of ​​the particle / Total surface area of ​​the particle) × 100 In the above mathematical formula 1, the total void area of ​​the particle and the total area of ​​the particle were measured using a particle cross-sectional image obtained with a SEM and an image analysis program.

2. The positive electrode active material precursor according to claim 1, wherein the primary particles are needle-shaped with a thickness of 40 nm to 100 nm and an aspect ratio of 3 to 10.

3. A cathode active material precursor according to claim 1, represented by the following chemical formula 1. [Chemical formula 1] [Ni ａ Mn ｂ M １ ｃ ](OH) ２ In the above chemical formula 1, 0 < a < 0.4, 0.5 ≤ b < 1, 0 ≤ c ≤ 0.1, and M １ This is one or more elements selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

4. Specific surface area is 20 m² ２ / g ~ 35m ２ The positive electrode active material precursor according to claim 1, wherein the value is / g and the tap density is 1.4 g / cc to 2.0 g / cc.

5. The specific surface area is 15 m ２ / g to 30 m ２ / g, and the tap density is 1.4 g / cc to 2.0 g / c. The positive electrode active material precursor according to claim 1.

6. The lithium transition metal oxide is a reaction product of the positive electrode active material precursor and lithium raw material described in claim 1, It contains secondary particles formed by the aggregation of multiple primary particles, The aforementioned secondary particles are a positive electrode active material in which the ratio of the shell thickness to the semi-long axis of the particles is 30% to 60%.

7. The positive electrode active material according to claim 6, represented by the following chemical formula 2. [Chemical formula 2] Li ｘ [Ni ａ Mn ｂ M １ ｃ ]O ２ In the above chemical formula 2, 1.1 < x < 1.3, 0 < a < 0.4, 0.5 ≤ b < 1, 0 ≤ c ≤ 0.1, and x + a + b + c = 2, M １ This is one or more elements selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

8. A step of mixing the positive electrode active material precursor and lithium raw material according to claim 1, A method for producing a positive electrode active material, comprising the step of firing.

9. The method for producing a positive electrode active material according to claim 8, wherein the positive electrode active material precursor and the lithium raw material are mixed such that the molar ratio of lithium elements in the positive electrode active material precursor and the lithium raw material is 1:1.2 to 1:1.6.

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