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

Abstract

To provide a positive electrode active material precursor which allows a coprecipitation reaction to be smoothly carried out even in the absence of ammonia, is environmentally friendly, has high process efficiency, and is excellent in physical property reproducibility, and a method for producing the same.SOLUTION: The present invention relates to a positive electrode active material precursor, a method of preparing the same, a positive electrode active material, and a method of preparing a positive electrode active material, and provides a positive electrode active material precursor including Ni and Mn and including secondary particles formed by agglomeration of a plurality of primary particles, wherein the secondary particles have a ratio of a core area to a total area of the particles (core area / total area) of 28.7% to 34.1% and a porosity represented by Equation 1 below of 11.3% to 11.7%, a method of preparing the same, a positive electrode active material including a reaction product of the positive electrode active material precursor and a lithium raw material, and a method of preparing a positive electrode active material using the same.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0102627 filed on August 17, 2022, and Korean Patent Application No. 10-2022-0125537 filed on September 30, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present 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 technological development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary 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 the lithium-cobalt composite metal oxide LiCoO2 is the most commonly used, due to its high operating voltage and excellent capacity characteristics. However, LiCoO2 has very poor thermal properties due to the destabilization of its crystal structure caused by delithiation, and it is expensive, so there are limitations to its mass use as a power source in fields such as electric vehicles.

[0005] Materials being developed to replace LiCoO2 include lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), and lithium nickel composite metal oxides (such as LiNiO2). Among these, active research and development has focused on lithium nickel composite metal oxides, which have a high reversible capacity of approximately 200 mAh / g and make it easy to create high-capacity batteries. However, LiNiO2 has inferior thermal stability compared to LiCoO2, and if an internal short circuit occurs due to external pressure while the battery is charged, the positive electrode active material itself can decompose, causing the battery to explode or catch fire.

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

[0007] However, due to the recent rise in the price of cobalt (Co), lithium-rich NCM-based positive electrode active materials that contain relatively low cobalt (Co) content and can match high capacity have been developed.

[0008] Typically, precursors for NCM-based cathode active materials are synthesized by coprecipitation, where ammonia (NH4OH) is used as a complexing agent. Ammonia acts as a catalyst to facilitate precursor synthesis by forming complexes with metal salts during precursor synthesis. While ammonia is an essential raw material for precursor synthesis, it has the drawback of increasing the precursor production cost due to its foul odor and environmental restrictions.

[0009] Furthermore, ammonia acts as a catalyst and significantly affects the particle size, morphology, and other physical properties of the precursor produced depending on its concentration (amount). Therefore, in order to produce a positive electrode active material with highly reproducible physical properties, the positive electrode active material precursor must have highly reproducible physical properties. This necessitates careful control of the amount of ammonia used, which has an impact on the reproducibility of the physical properties, and this is inconvenient in the process.

[0010] Therefore, there is a need for the development of a method for producing a positive electrode active material precursor that allows the coprecipitation reaction to be carried out smoothly even in the absence of ammonia, is environmentally friendly, has high process efficiency, and has excellent reproducibility of physical properties. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2016-0063982 (Publication Date: June 7, 2016) Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made to solve the above problems, and has an object to provide a positive electrode active material precursor having excellent particle strength.

[0013] Another object of the present invention is to provide a method for producing the positive electrode active material precursor, which allows the coprecipitation reaction to proceed smoothly even in the absence of ammonia, is environmentally friendly, and has excellent reproducibility of physical properties.

[0014] Another object of the present invention is to provide a positive electrode active material containing a lithium transition metal oxide, which is a reaction product of the positive electrode active material precursor and a lithium source material.

[0015] It is another object of the present invention to provide a method for producing a positive electrode active material using the positive electrode active material precursor. [Means for solving the problem]

[0016] In order 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 cathode active material precursor comprising secondary particles formed by agglomeration of a plurality of primary particles, the secondary particles having a core area ratio to the total particle area (core area / total area) of 28.7% to 34.1% and a porosity of 11.3% to 11.7%, as expressed by the following mathematical formula 1: [Mathematical formula 1] Porosity (%) = (void area of ​​entire particle / area of ​​entire particle) x 100

[0018] (2) The present invention provides a positive electrode active material precursor according to (1) above, wherein the secondary particles have a core porosity of 13.5% to 15.0%.

[0019] (3) In the present invention, in the above (1) or (2), the average particle size of the secondary particles (D 50 ) is 3 μm to 15 μm.

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

[0021] (5) In any one of the above (1) to (4), the present invention provides a positive electrode active material precursor 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であり、M 1 is one or more selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W and Zr.

[0022] (6) The present invention provides any one of the above (1) to (5), wherein the specific surface area is 20 m 2 / g~35m 2 / g and a tap density of 1.4 g / cc to 2.0 g / cc.

[0023] (7) The present invention provides any one of the above (1) to (5), wherein the specific surface area is 15 m 2 / g~30m 2 / g and a tap density of 1.4 g / cc to 2.0 g / cc.

[0024] (8) The present invention provides a method for producing a cathode active material precursor, comprising the step of co-precipitation of two or more transition metal source materials in the presence of a basic aqueous solution under a nitrogen atmosphere to produce a reaction solution containing a transition metal hydroxide, wherein the co-precipitation reaction is carried out in the absence of ammonia by introducing air.

[0025] (9) The present invention provides the method for producing a positive electrode active material precursor according to (8), wherein the air is added in an amount of more than 0% by volume and less than 10% by volume with respect to 100% by volume of nitrogen.

[0026] (10) The present invention provides the method for producing a positive electrode active material precursor according to (8) or (9), 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% by volume and not more than 5% by volume, relative to 100% by volume of the total amount of nitrogen used during the coprecipitation reaction.

[0027] (11) The present invention provides a method for producing a positive electrode active material precursor according to any one of (8) to (10), further comprising a step of aging the reaction solution, wherein the aging is performed by leaving the reaction solution to stand in a nitrogen atmosphere under conditions of pH 12 to 14 for 6 to 24 hours.

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

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

[0030] (14) The present invention provides the method for producing a cathode active material precursor according to (13), wherein the washing is performed in order as a primary washing and a secondary washing, the primary washing being performed using a basic aqueous solution, and the secondary washing being performed using distilled water.

[0031] (15) The present invention provides the method for producing a positive electrode active material precursor according to 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 cathode active material comprising a lithium transition metal oxide that is a reaction product of a cathode active material precursor according to any one of (1) to (7) above and a lithium raw material, and secondary particles formed by aggregation of a plurality of primary particles, wherein the ratio of the shell thickness to the semi-major axis of the secondary particles is 30% to 60%.

[0033] (17) The present invention provides a positive electrode active material represented by the following chemical formula 2 in the above (16). [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 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 the positive electrode active material precursor according to any one of (1) to (7) above with a lithium source material, and firing the mixture.

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

[0036] The cathode active material precursor according to the present invention has thin primary particles and dense secondary particles, and therefore the inner core of the particle has many voids, and the outer shell is dense and has uniformly distributed microvoids, thereby achieving a defined area ratio and porosity. As a result, the charge / discharge capacity performance of a cathode active material using the cathode active material precursor can be improved.

[0037] Furthermore, the method for producing a cathode active material precursor according to the present invention involves conducting a coprecipitation reaction under a nitrogen atmosphere with the introduction of air, thereby easily producing the precursor even in the absence of ammonia, which is environmentally friendly and provides excellent reproducibility of the precursor properties. [Brief explanation of the drawings]

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

[0039] [Figure 1]1 shows the results of SEM analysis of the positive electrode active material precursor of Example 1, including (a) particle shape at 2K magnification, (b) particle shape at 15K magnification, (c) particle shape at 50K magnification, and (d) particle cross-section image at 20K magnification. [Figure 2] 1 shows the results of SEM analysis of the positive electrode active material precursor of Comparative Example 1, including (a) particle shape at 2K magnification, (b) particle shape at 15K magnification, (c) particle shape at 50K magnification, and (d) particle cross-section image at 20K magnification. [Figure 3] 1 shows the results of SEM analysis of the positive electrode active material precursor of Comparative Example 2, including (a) particle shape at 2K magnification, (b) particle shape at 15K magnification, (c) particle shape at 50K magnification, and (d) particle cross-section image at 20K magnification. [Figure 4] 1 shows the results of SEM analysis of the positive electrode active material precursor of Comparative Example 3, including (a) an image of particle shape at 2K magnification and (b) an image of particle shape at 15K magnification. [Figure 5] 1 shows the results of SEM analysis of the positive electrode active material precursor of Comparative Example 4, including (a) an image of particle shape at 2K magnification and (b) an image of particle shape at 15K magnification. [Figure 6] 1 is a graph comparing the particle size distribution of the positive electrode active material precursors of Example 1 and Comparative Examples 1 to 4. [Figure 7] 1 shows the results of SEM analysis of the positive electrode active material of Example 1, where (a) is an image of the particle shape at 50K magnification and (b) is an image of the particle cross section at 50K magnification. [Figure 8] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1, where (a) is an image of the particle shape at 50K magnification and (b) is an image of the particle cross section at 50K magnification. [Figure 9] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 2, where (a) is an image of the particle shape at 50K magnification and (b) is an image of the particle cross section at 50K magnification. [Figure 10] 1 shows the results of SEM analysis of the positive electrode active material precursor of Example 2, including (a) an image of particle shape at 15K magnification and (b) an image of particle shape at 1K magnification. [Figure 11]1 shows the results of SEM analysis of the positive electrode active material precursor of Example 3, where (a) is an image of particle shape at 15K magnification and (b) is an image of particle shape at 1K magnification. [Figure 12] 1 is an XRD graph of the positive electrode active material precursors of Examples 2 and 3. [Figure 13] 1 shows the results of SEM analysis of the positive electrode active material of Example 2, including (a) an image of particle shape at 25K magnification and (b) an image of particle shape at 1K magnification. [Figure 14] 1 shows the results of SEM analysis of the positive electrode active material of Example 2, including (a) an image of particle shape at 25K magnification and (b) an image of particle shape at 1K magnification. DETAILED DESCRIPTION OF THE INVENTION

[0040] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0041] term In the present invention, the term "primary particle" means a particle unit that does not appear to have grain boundaries when observed at a magnification of 5000 to 20000 times using a scanning electron microscope (SEM).

[0042] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of a plurality of primary particles.

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

[0044] Measurement method In the present 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 an image of the particle cross section using an SEM and an image analysis program.

[0045] Specifically, cross-sectional images (50K magnification) of each precursor were taken using a SEM (Hitachi Corporation), and the precursor porosity, core porosity, and core-to-total area ratio were analyzed. The precursor, carbon black Super-P as a conductive material, and poly(vinylidene fluoride) as a binder were used in a weight ratio of 54:4:43 (based on 1 g of precursor). These materials were uniformly mixed with 1.8 g of N-methylpyrrolidone to prepare a slurry. The resulting slurry was thinly coated onto aluminum foil to a thickness of 0.25 mm and dried at 100°C to prepare electrodes for cross-sectional measurement. The resulting electrodes were then irradiated with an ion beam using an ion milling machine to prepare test specimens for SEM measurement. Cross-sectional images of the precursor were obtained using the SEM specimen. Particles were selected from the cross-sectional image, and the cross section of a particle was extracted using the watershed image processing technique with an image processing program (Pore Analysis). The core area was then identified using the erosion image processing technique. The image was then converted to binary data using threshold image processing, and the precursor porosity, core porosity, and core area to total area ratio were analyzed. The core area was defined as the area where pores were densely concentrated inside the particle, and the program defined the area formed by connecting the outermost pores among the internal pores as the core area. Ten particles with diameters between 2 and 8 μm were selected from the cross-sectional image, and the precursor porosity, core porosity, and core area to total area ratio were measured for each particle using the same method. The results were expressed as the average of these measurements.

[0046] In the present 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 the present invention, the tap density was measured by placing 50 g of the precursor in a 50 ml measuring cylinder and performing 3,000 strokes using a TAPDENSER (KYT-4000K, SEISHIN ENTERPRISE Co., Ltd.).

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

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

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

[0051] Positive electrode active material precursor The present invention provides a positive electrode active material precursor that can improve charge / discharge capacity by having a particle morphology in which the core portion is porous and the shell portion is dense and porous.

[0052] According to one embodiment of the present invention, the cathode active material precursor includes secondary particles formed by agglomeration of a plurality of primary particles, which contain Ni and Mn. The secondary particles have a core area ratio to a total particle area (core area / total area) of 28.7% to 34.1% and a porosity of 11.3% to 11.7%, as expressed by the following mathematical formula 1:

[0053] [Mathematical formula 1] Porosity (%) = (void area of ​​entire particle / area of ​​entire particle) x 100

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

[0055] The primary particles may be needle-shaped with a thickness of 40 nm to 100 nm and an aspect ratio of 3 to 10.

[0056] In another example, the positive electrode active material precursor may 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 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] The positive electrode active material precursor has a specific surface area of ​​20 m 2 / g~35m 2 / g, and the tap density can be 1.4 g / cc to 2.0 g / cc.

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

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

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

[0063] Method for producing a positive electrode active material precursor The present invention provides a method for producing a cathode active material precursor, which can produce the cathode active material precursor with high reproducibility of physical properties in an environmentally friendly manner.

[0064] According to an embodiment of the present invention, a method for preparing a cathode active material precursor includes a step of co-precipitating two or more transition metal source materials in the presence of a basic aqueous solution under a nitrogen atmosphere to prepare a reaction solution containing a transition metal hydroxide, and the co-precipitation reaction can be performed by introducing air in the absence of ammonia.

[0065] The coprecipitation reaction is carried out to produce a transition metal hydroxide from a transition metal source material, and is carried out in a nitrogen atmosphere in the presence of a basic aqueous solution with air introduced, but in the absence of ammonia. Here, "in the presence of a basic aqueous solution" means that the basic aqueous solution is included as a reactant during the coprecipitation reaction.

[0066] Typically, precursors for NCM-based cathode active materials are synthesized by forming complexes with transition metal salts using ammonia, a complexing agent. However, ammonia is a malodorous and environmentally regulated substance, necessitating the establishment of a processing system. The processing system costs increase depending on the production scale, resulting in poor process efficiency when applied industrially. Furthermore, ammonia acts as a catalyst in the synthesis of the precursor, and the physical properties of the precursor are significantly affected by its concentration. Furthermore, it is difficult to control the primary particles and micropores of the precursor. As a result, when used as a cathode active material, it is difficult to control the Li diffusion rate, limiting capacity and output characteristics, and making it difficult to reproduce consistent physical properties of the cathode active material.

[0067] However, in the method for producing a positive electrode active material according to the present invention, the co-precipitation reaction is carried out in the absence of ammonia, and air is introduced into a nitrogen atmosphere, whereby the air plays the role of ammonia, resulting in a smooth co-precipitation reaction, environmental friendliness, and high reproducibility.

[0068] Specifically, the coprecipitation reaction according to one embodiment of the present invention may be carried out under a nitrogen atmosphere by introducing air, and the air may be introduced at more than 0% by volume and less than 10% by volume, more specifically, more than 0% by volume and less than 5% by volume, relative to 100% by volume of nitrogen.

[0069] More specifically, the coprecipitation reaction is carried out under a nitrogen atmosphere with continuous introduction of air, and the total amount of air introduced during the coprecipitation reaction may be greater than 0% by volume and less than 10% by volume, or greater than 0% by volume and less than 5% by volume, based on 100% by volume of the total amount of nitrogen used during the coprecipitation reaction. For example, if the air is introduced at 10% by volume or more relative to the nitrogen, aggregation of the produced precursor particles may occur, requiring an additional subsequent milling process, or deformation of the particle size and particle state may make it difficult to produce a cathode active material precursor satisfying the above-mentioned physical properties.

[0070] The transition metal source material may be a sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide of a transition metal, and the transition metal may 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 source material may include a nickel source material and a manganese source material.

[0072] Specifically, the nickel source material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and more specific examples include, but are not limited to, Ni(OH), NiO, NiOOH, NiCO·2Ni(OH)·4H2O, NiCO·2H2O, Ni(NO)·6H2O, NiSO, NiSO·6H2O, fatty acid nickel salts, nickel halides, and combinations thereof.

[0073] Furthermore, the manganese source material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide. Specific examples include, but are not limited to, manganese oxides such as MnO, MnO, and MnO; manganese salts such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or a combination thereof.

[0074] As a further example, the metal solution may optionally contain M 1 Contains raw materials and / or M 2 Ingredients may further be included.

[0075] Said M 1 In the raw material containing 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, and M 1 The raw material contained is the M 1 It can be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing the element.

[0076] In addition, the transition metal source material may be used in the form of a metal solution in which the transition metal source material is dissolved in a solvent for a more uniform co-precipitation reaction. Here, the metal solution may be prepared by adding the transition metal source material to a solvent, specifically, water or a mixed solvent of an organic solvent (e.g., alcohol) that is uniformly miscible with water, or by mixing an aqueous solution of the transition metal source material.

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

[0078] The basic aqueous solution may be prepared by dissolving a strong basic compound as a precipitant in distilled water.

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

[0080] Here, the strong basic compound may be a hydroxide or hydrate of an alkali metal, a hydroxide or hydrate of an alkaline earth metal, or a combination thereof. More specifically, the strong basic 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 at least one selected from the group consisting of an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, and an aqueous lithium hydroxide solution.

[0082] The basic aqueous solution is added to adjust the pH during the coprecipitation reaction, and may be added in an amount that allows the pH to be 9 to 13 in the reaction system where the coprecipitation reaction is carried out.

[0083] Meanwhile, the co-precipitation reaction may be carried out at a temperature of 40° C. to 70° C. In addition, in order to increase the reaction rate of the co-precipitation reaction, a stirring process may be optionally carried out, and the stirring speed may be 100 rpm to 2000 rpm.

[0084] As another example, the 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 co-precipitation reaction, and the aging may be performed by leaving the reaction solution to stand for 6 to 24 hours under a nitrogen atmosphere at a pH of 12 to 14.

[0085] As another example, the aging 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 (Li-rich) NCM-based cathode active materials is synthesized by coprecipitation. Recently, methods for increasing the density of the precursor have been studied to maximize the energy density of batteries. 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 in addition to the target precursor material. This can cause aggregation of precursor particles during washing and drying, creating problems during the classification process. Even after application as a cathode active material raw material and calcination, these remain as impurities in the cathode active material, reducing the capacity and lifespan of the cathode active material.

[0087] In the method for preparing a cathode active material precursor according to the present invention, when the aging step is further included after the co-precipitation reaction, oxidation of transition metal hydroxides in the reaction solution is prevented and the generation of metal oxides, particularly manganese oxide, is suppressed, thereby eliminating problems associated with the aggregation and classification process caused by the metal oxides during drying. This has the effect of eliminating or significantly reducing the amount of metal oxide impurities in the finally prepared cathode active material precursor 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 a nitrogen atmosphere, at a pH of 13 to 14, and at a temperature of 40°C to 50°C, in order to more easily achieve the intended effect.

[0089] On the other hand, in the aging step, the pH condition can be adjusted by adding a strong basic compound to the reaction solution. Here, the strong basic compound can be added as it is or in the form of an aqueous solution obtained by dissolving it in distilled water. The strong basic compound is not particularly limited as long as it is generally known as a strong basic compound, and can be, for example, sodium hydroxide, potassium hydroxide, calcium hydroxide, or lithium hydroxide.

[0090] As yet another example, a method for preparing a cathode active material precursor according to an embodiment of the present invention may include the steps of co-precipitating two or more transition metal source materials in the presence of a basic aqueous solution under a nitrogen atmosphere to prepare a reaction solution containing a transition metal hydroxide, aging the reaction solution, and sequentially washing, filtering, and drying the reaction solution.

[0091] Here, the co-precipitation and aging steps are as described above, and the washing, filtering and drying steps can be carried out by means commonly used in the art.

[0092] The washing may be performed in the order of a primary washing and a secondary washing, in which the primary washing is performed using a basic aqueous solution and the secondary washing is performed using distilled water.

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

[0094] In the method for preparing a cathode active material precursor according to the present invention, when the washing is performed by first washing with a basic aqueous solution and then second washing with distilled water, oxidation of the transition metal hydroxide that may occur during the washing process can be prevented and impurities can be further removed.

[0095] The drying 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 the positive electrode active material precursor and a lithium source material.

[0097] The cathode active material according to one embodiment of the present invention includes a lithium transition metal oxide, which is a reaction product of the cathode active material precursor and a lithium source material, and includes secondary particles formed by agglomeration of a plurality of primary particles, wherein the ratio of the shell thickness to the semi-major axis of the secondary particles is 30% to 60%.

[0098] In another example, the positive electrode active material may 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 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 producing positive electrode active material The present invention provides a method for producing the positive electrode active material using the positive electrode active material precursor.

[0102] A method for preparing a positive electrode active material according to an embodiment of the present invention may include mixing the positive electrode active material precursor and a lithium source material, and calcining 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 well known in the art, except for using the positive electrode active material precursor according to the present invention, and the method is not particularly limited.

[0104] Examples of the lithium source material include lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3), etc.), and chlorides (e.g., lithium chloride (LiCl)), and any of these may be used alone or in combination.

[0105] Meanwhile, the positive electrode active material precursor and the lithium source material may be mixed by solid-phase mixing such as jet milling, and the mixing ratio of the positive electrode active material precursor and the lithium source material may be determined within a range that satisfies the molar fraction of each component in the final positive electrode active material. More specifically, the positive electrode active material precursor and the lithium source material may be mixed such that the molar ratio of lithium element in the positive electrode active material precursor and the lithium source material is 1:1.2 to 1:1.6.

[0106] Although not essential, a source material for doping a portion of the transition metal and / or oxygen of the positive electrode active material may be further included in addition to the positive electrode active material precursor and the lithium source material during the mixing. 1The X-containing raw material or the X-containing raw material described later can be further mixed. Here, the X-containing raw material can be, for example, Na3PO4, K3PO4, Mg3(PO4)2, AlF3, NH4F, LiF, etc., but is not limited thereto. As described above, when a portion of oxygen is substituted by the X element, it is possible to obtain the effect of suppressing oxygen desorption and reaction with the electrolyte during charge and discharge of the secondary battery.

[0107] Meanwhile, the firing may be performed at 700°C to 900°C, specifically 750°C to 850°C, and the firing time may be 5 hours to 30 hours, specifically 8 hours to 15 hours, but is not limited thereto.

[0108] Meanwhile, after the calcination, a water-washing step and a drying step may be further performed to remove lithium by-products. The water-washing step may be performed, for example, by adding the prepared cathode active material to ultrapure water and stirring the mixture. Here, the water-washing temperature may be 20°C or less, specifically, 10°C to 20°C, and the water-washing time may be about 10 minutes to 1 hour. When the water-washing temperature and water-washing time satisfy the above ranges, lithium by-products can be effectively removed.

[0109] Positive electrodes and secondary batteries The cathode active material prepared by the method for preparing the cathode active material according to the present invention can be usefully used in the manufacture of a cathode for a secondary battery.

[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 may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. For example, the positive electrode may be manufactured by dissolving or dispersing components constituting the positive electrode active material layer, i.e., the positive electrode active material, a conductive material, and / or a binder, in a solvent to prepare a positive electrode composite, applying the positive electrode composite to at least one surface of a positive electrode current collector, drying, and rolling the applied positive electrode composite, or by casting the positive electrode composite on a separate support, peeling it from the support, and laminating the resulting film on the positive electrode current collector.

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

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

[0114] The positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when contained in the above amount range.

[0115] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the battery and has electronic conductivity can be used without particular limitations. 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 powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode active material layer.

[0116] The binder also serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0117] Meanwhile, the solvent used in preparing the cathode composite may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, which may be used alone or in combination. The amount of the solvent used may be appropriately adjusted in consideration of the coating thickness, production yield, viscosity, etc. of the slurry.

[0118] In addition, the secondary battery according to the present invention includes a positive electrode, a negative electrode facing 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 described above.

[0119] Meanwhile, the secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0120] In the secondary battery, 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 negative electrode may be manufactured by a conventional method commonly known in the art. For example, the negative electrode may be manufactured by dissolving or dispersing components constituting the negative electrode active material layer, i.e., the negative electrode active material, and a conductive material and / or binder, in a solvent to prepare a negative electrode composite, applying the negative electrode composite to at least one surface of a negative electrode current collector, drying, and rolling the negative electrode composite, or by casting the negative electrode composite on a separate support, peeling it from the support, and laminating the resulting film on the negative electrode current collector.

[0122] The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and examples of such materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0123] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. vMetal oxides that can be doped and undoped with lithium, such as (0 < v < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and a 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, scaly, 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 carbon such as petroleum or coal tar pitch derived cokes.

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

[0125] Meanwhile, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity are preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Separators coated with ceramic components or polymeric materials to ensure heat resistance or mechanical strength can also be used, and they can be used in either a single-layer or multi-layer structure.

[0126] On the other hand, examples of the electrolyte include 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 manufacturing secondary batteries, but are not limited to these.

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

[0128] The organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethanol and isopropyl alcohol, nitriles such as Ra-CN (Ra is a hydrocarbon group having 2 to 20 carbon atoms, linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries. In this case, a mixture of the cyclic carbonate and the linear carbonate at a volume ratio of about 1:1 to about 1:9 can provide excellent electrolyte performance.

[0129] The lithium salt can be any compound capable of providing lithium ions used 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. The lithium salt is preferably used at a concentration in the range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0130] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, or pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0131] As described above, the secondary battery including the cathode 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, and electric vehicles such as hybrid electric vehicles (HEVs).

[0132] 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 the battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0133] Example While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the embodiments set forth herein, and that the invention may be embodied in various different forms, without departing from the spirit or scope of the present invention.

[0134] Experimental Material I Example 1 Nickel sulfate and manganese sulfate were dissolved in ion-exchanged water so that the molar ratio of nickel to manganese was 0.35:0.65 to prepare a 2.4 M metal solution, and separately, a 25% aqueous solution of sodium hydroxide was prepared.

[0135] Nitrogen gas was introduced into a coprecipitation reactor set at 50°C at 300 L / hr to create a nitrogen atmosphere, and the metal solution and sodium hydroxide aqueous solution were introduced at rates of 0.5 L / hr and 0.3 L / hr, respectively, to carry out the coprecipitation reaction for 24 hours. The coprecipitation reaction was carried out while introducing air at 15 L / hr (5% by volume relative to 100% by volume of nitrogen).

[0136] Thereafter, the mixture was washed with water, filtered, and then dried at 120° C. for 12 hours to prepare a positive electrode active material precursor.

[0137] Comparative Example 1 Nickel sulfate and manganese sulfate were dissolved in ion-exchanged water so that the molar ratio of nickel to manganese was 0.35:0.65 to prepare a 2.4 M metal solution, and separately, a 25% aqueous solution of sodium hydroxide was prepared.

[0138] Nitrogen gas was introduced into a coprecipitation reactor set at 50°C at a rate of 300 L / hr to create a nitrogen atmosphere, and the metal solution, sodium hydroxide aqueous solution, and 9% ammonia aqueous solution were introduced at rates of 0.5 L / hr, 0.3 L / hr, and 0.12 L / hr, respectively, to carry out the coprecipitation reaction.

[0139] Then, the mixture was washed with water, filtered, and dried at 120° C. for 12 hours to prepare a positive electrode active material precursor.

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

[0141] Comparative Example 3 A positive electrode active material precursor was produced in the same manner as in Example 1, except that the coprecipitation reaction was carried out while introducing air in an amount of 50% by volume relative to 100% by volume of nitrogen.

[0142] Comparative Example 4 A positive electrode active material precursor was produced in the same manner as in Example 1, except that the coprecipitation reaction was carried out while introducing 100% by volume of air instead of introducing nitrogen during the coprecipitation reaction.

[0143] Experimental Example 1 The particle characteristics of the positive electrode active material precursors prepared in the Examples and Comparative Examples were compared and analyzed.

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

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

[0146] (3) Tap density analysis 50 g of each precursor was placed in a 50 ml measuring cylinder, and the tap density was measured by 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 (manufactured by 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 Cross-sectional images (50K magnification) of each precursor were obtained using an SEM (Hitachi), and the porosity, core porosity, and ratio of core area to total area of ​​the precursor were analyzed.

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

[0150] Next, cross-sectional images of each specimen were obtained using an SEM. Particles were selected from the cross-sectional images, and the cross section of each particle was extracted using the watershed image processing technique with an image processing program (Pore Analysis). The core region was then identified using the erosion image processing technique. The images were then converted to binary using threshold image processing, and the precursor porosity, core porosity, and the ratio of core area to total area were analyzed. Here, the core region was defined as the area inside the particle where pores were densely packed, and the program defined the region formed by connecting the pores located at the outermost edge of the internal pores as the core region.

[0151] In addition, 10 particles with particle diameters of 2 to 8 μm were selected from each cross-sectional image, and the precursor porosity, core porosity, and ratio of core area to total area were measured for each particle using the above-mentioned method, and the results were expressed as the average values ​​of these measurements.

[0152] [Table 1]

[0153] As shown in Table 1, it was confirmed that the cathode active material precursor of Example 1 had similar particle size characteristics and a similar level of tap density as the cathode active material precursor of Comparative Example 1. In addition, the cathode active material precursor of Example 1 had a similar overall porosity to the cathode active material precursor of Comparative Example 1, but a lower core area ratio and a higher core porosity, satisfying the porosity and core area ratio proposed in the present invention.

[0154] Furthermore, it was confirmed that the positive electrode active material precursor of Example 1 exhibited particle characteristics in which the core had many voids and the shell (outside) was dense and contained fine voids, whereas the positive electrode 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 particles had many voids throughout both the inside and outside of the particles, exhibiting particle characteristics in which the core and shell were not separated (see FIG. 5(b)).

[0156] Experimental Example 2 Positive electrode active materials were prepared using the positive electrode active material precursors prepared in the examples and comparative examples, and the particle characteristics of the positive electrode active materials were compared and analyzed.

[0157] Each positive electrode active material precursor and LiOH were mixed so that the transition metals (Ni and Mn) in the precursor and Li in the LiOH were in a molar ratio of 1:1.35, and then calcined at 700°C for 15 hours in an air atmosphere to produce each positive electrode active material.

[0158] The particle shape of each of the produced positive electrode active materials was confirmed at a magnification of 50K using an SEM (manufactured by Hitachi Corporation), and the results are shown in FIGS.

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

[0160] The ratio of shell thickness to particle semimajor axis was determined by preparing electrodes for cross-section measurement in the same manner as in Experimental Example 1, except that an active material was used instead of a precursor. Test specimens for SEM measurement were then prepared from these electrodes, and cross-sectional images were taken using an SEM at 50K magnification. The particle semimajor axis was measured, and the distance from the outer edge of the core to the outer surface of the particle on the semimajor axis was used as the shell thickness, which was calculated as [shell thickness / particle semimajor axis] x 100. Here, the outer edge of the core was defined as the part of the particle where pores were densely concentrated, and the outermost pores among the internal pores were defined as the core-shell boundary. Ten particles with diameters between 2 and 8 μm were selected from each cross-sectional image, and the ratio of shell thickness to particle semimajor axis was calculated for each particle using the method described above. The results were expressed as the average of these values.

[0161] [Table 2]

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

[0163] Experimental Example 3 Positive electrode active materials were produced using the positive electrode active material precursors produced in the examples and comparative examples, and batteries were produced using the positive electrode active materials, and then the battery performance was evaluated.

[0164] (1) Manufacturing of positive electrode active material Each positive electrode active material precursor and LiOH were mixed so that the transition metals (Ni and Mn) in the precursor and Li in the LiOH were in a molar ratio of 1:1.35, and then calcined at 700°C for 15 hours in an air atmosphere to produce each positive electrode active material.

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

[0166] (3) Battery manufacturing The negative electrode used was lithium metal. An electrode assembly was fabricated by interposing a porous polyethylene separator between the fabricated positive and negative electrodes, and the electrode assembly was placed inside a case. An electrolyte solution was then injected into the case to fabricate a lithium secondary battery. The electrolyte solution 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 in a volume ratio of 3 / 2 / 5).

[0167] Each lithium secondary battery half cell prepared as described above was charged at 0.33 C in CCCV mode at 25° C. to 4.4 V, and then discharged at a constant current of 0.33 C to 2.5 V to measure the initial charge / discharge capacity and efficiency. The results are shown in Table 3 below.

[0168] [Table 3]

[0169] From Table 3, it can be seen that the positive electrode active material of Example 1 is superior to the positive electrode active materials of Comparative Examples 1 and 2 in initial charge / discharge capacity and efficiency.

[0170] Experimental Materials II Example 2 A coprecipitation reaction was carried out in the same manner as in Example 1 to prepare a reaction solution.

[0171] Thereafter, the reaction solution was aged by being left to stand at a temperature of 50°C for 6 hours under a nitrogen atmosphere and a pH of 13. Thereafter, the reaction solution was washed with water, filtered, and dried at 120°C for 12 hours to prepare a cathode active material precursor.

[0172] Example 3 A positive electrode active material precursor was produced in the same manner as in Example 2, except that after aging, the washing step was performed by first washing with a 2 wt % sodium hydroxide aqueous solution and then by second washing with distilled water.

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

[0174] (1) SEM measurement The particle shape of each precursor was confirmed by analysis at magnifications of 1K and 15K using an SEM (Hitachi Corporation), and the results are shown in FIGS.

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

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

[0177] (4) Tap density analysis 50 g of each precursor was placed in a 50 ml measuring cylinder, and the tap density was measured by performing 3,000 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 at 150° C. for 3 hours using a Tristar II 3020 (manufactured by Micromeritics), 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] 10 and 11, it was confirmed that the positive electrode active material precursors of Examples 2 and 3 exhibited particle shapes similar to those of the positive electrode active material precursor of Example 1, had excellent classification rates, lower specific surface areas, and higher tap densities. Furthermore, referring to FIG. 12, it was confirmed that no manganese oxide (Mn3O4) peaks were observed in the positive electrode active material precursors prepared in Examples 2 and 3.

[0183] The above results indicate that when the cathode active material precursor of the present invention is prepared by a preparation method further including an aging step and a washing step, the characteristics of the precursor particles are not changed, and oxidation of the transition metal hydroxide is prevented, thereby suppressing the generation of metal oxides. As a result, there are no problems with aggregation and classification during drying, and the classification rate is significantly improved, and impurities in the precursor are eliminated or significantly reduced.

[0184] Experimental Example 5 Positive electrode active materials were produced using the positive electrode active material precursors produced in Examples 2 and 3, and batteries were produced using the positive electrode active materials. Battery performance was then evaluated. The results are shown in Table 5.

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

[0186] Each of the produced positive electrode active materials was analyzed using an SEM (manufactured by Hitachi) at magnifications of 1K and 25K to confirm the particle shape of each precursor, and the results are shown in FIGS.

[0187] [Table 5]

[0188] From Table 5, it was confirmed that the positive electrode active materials of Examples 2 and 3 were superior to the positive electrode active material of Example 1 in charge / discharge capacity.

Claims

1. Contains Ni and Mn, The secondary particles are formed by agglomeration of a plurality of primary particles, The secondary particles have a ratio of a core area to a total area of ​​the particles (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%. [Mathematical formula 1] Porosity (%) = (void area of ​​entire particle / area of ​​entire particle) x 100

2. 2. The positive electrode active material precursor according to claim 1, wherein the secondary particles have a core porosity of 13.5% to 15.0%.

3. The average particle size of the secondary particles (D ５０ 2. The positive electrode active material precursor according to claim 1, wherein the average particle diameter is 3 μm to 15 μm.

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

5. The positive electrode 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 formula 1, 0<a<0.4, 0.5≦b<1, 0≦c≦0.1, and M １ is one or more selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W and Zr.

6. Specific surface area is 20m ２ / g~35m ２ 2. The positive electrode active material precursor according to claim 1, wherein the positive electrode active material precursor has a tap density of 1.4 g / cc to 2.0 g / cc.

7. Specific surface area is 15m ２ / g to 30m ２ 2. The positive electrode active material precursor according to claim 1, wherein the positive electrode active material precursor has a tap density of 1.4 g / cc to 2.0 g / cc.

8. The method includes a step of co-precipitating two or more transition metal source materials in the presence of a basic aqueous solution under a nitrogen atmosphere to produce a reaction solution containing a transition metal hydroxide, The method for producing a positive electrode active material precursor, wherein the coprecipitation reaction is carried out in the absence of ammonia by introducing air.

9. The method for producing a positive electrode active material precursor according to claim 8 , wherein the air is introduced in an amount of more than 0 vol % and less than 10 vol % relative to 100 vol % of nitrogen.

10. The coprecipitation reaction is carried out by continuously introducing air, 9. The method for producing a cathode active material precursor according to claim 8, wherein the total amount of air introduced during the coprecipitation reaction is more than 0% by volume and 5% by volume or less, based on 100% by volume of the total amount of nitrogen used during the coprecipitation reaction.

11. further comprising a step of aging the reaction solution; 9. The method for producing a positive electrode active material precursor according to claim 8, wherein the aging is performed by leaving the reaction solution to stand in a nitrogen atmosphere at a pH of 12 to 14 for 6 to 24 hours.

12. The method for producing a positive electrode active material precursor according to claim 8, wherein the aging is carried out at a temperature in the range of 30°C to 50°C.

13. a step of co-precipitating two or more transition metal source materials in the presence of a basic aqueous solution under a nitrogen atmosphere to produce a reaction solution containing a transition metal hydroxide; Aging the reaction solution; and sequentially carrying out washing, filtering, and drying.

14. The cleaning is performed in the order of primary cleaning and secondary cleaning, The method for producing a positive electrode active material precursor according to claim 13 , wherein the primary cleaning is performed using a basic aqueous solution, and the secondary cleaning is performed using distilled water.

15. 9. The method for producing a positive electrode active material precursor according to claim 8, 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.

16. The cathode active material precursor according to claim 1 comprises a lithium transition metal oxide, which is a reaction product of the cathode active material precursor and a lithium source material, The secondary particles are formed by agglomeration of a plurality of primary particles, The secondary particles have a shell thickness ratio of 30% to 60% relative to the semi-major axis of the particle.

17. The positive electrode active material according to claim 16 , represented by the following chemical formula 2: [Chemical formula 2] Li ｘ [Ni ａ Mn ｂ M １ ｃ ]O ２ In the formula 2, 1.1<a<1.3, 0<a<0.4, 0.5≦b<1, 0≦c≦0.1, and x+a+b+c=2; M １ is one or more selected from the group consisting of Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W and Zr.

18. mixing the cathode active material precursor of claim 1 with a lithium source material; and firing the resulting mixture.

19. 19. The method for producing a cathode active material according to claim 18, wherein the cathode active material precursor and the lithium source material are mixed so that a molar ratio of lithium element in the cathode active material precursor to the lithium source material is 1:1.2 to 1:1.6.

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