Positive electrode active material, method for manufacturing the same, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material with improved resistance characteristics and lifespan characteristics, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery, and provides a positive electrode active material comprising polycrystalline particles represented by chemical formula 1 and composed of secondary particles formed by the aggregation of primary particles, wherein the surface porosity (A) defined by mathematical formula 1 is 1% to 30%, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0011790 dated January 30, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material with improved resistance characteristics and lifespan characteristics, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0003] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly rising. 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 use in large quantities as a power source in fields such as electric vehicles.

[0005] As alternative materials to LiCoO2, 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) have been developed. Among these, research and development are actively underway on lithium nickel composite metal oxides, which have a high reversible capacity of approximately 250 mAh / g and are easy to realize in large-capacity batteries. However, LiNiO2 has poorer 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, leading to battery rupture and fire.

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

[0007] However, in recent years, due to rising cobalt (Co) prices, development is underway on lithium-rich (Li-rich) NCM-based cathode active materials that contain relatively low amounts of cobalt (Co) or do not contain any cobalt (Co) but can still handle high capacities.

[0008] On the other hand, cobalt-free, Li and Mn-rich positive electrode active materials require more Li during the calcination process of the precursor and lithium raw material compared to general NCM-based positive electrode active materials. This necessitates a positive electrode active material precursor with a high specific surface area that can come into contact with Li, and if there are no voids, or if voids exist only inside the precursor, there is a problem that the battery characteristics will deteriorate.

[0009] Therefore, there is a need to develop positive electrode active materials that exhibit excellent battery characteristics by having uniformly distributed voids both internally and on the surface. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] CN110112388A (2019.08.09.) [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention aims to solve the above-mentioned problems and to provide a positive electrode active material that is Li and Mn-rich and has a defined surface porosity.

[0012] Moreover, an object of the present invention is to provide a method for manufacturing the positive electrode active material.

[0013] In addition, an object of the present invention is to provide a positive electrode containing the positive electrode active material and a lithium secondary battery.

Means for Solving the Problems

[0014] To solve the above problems, the present invention provides a positive electrode active material, a method for manufacturing the same, and a positive electrode and a lithium secondary battery containing the same.

[0015] (1) The present invention provides a positive electrode active material composed of polycrystalline particles represented by the following Chemical Formula 1 and composed of secondary particles in which primary particles are aggregated, and having a surface void ratio (A) defined by the following Mathematical Formula 1 of 1% to 30%.

[0016] [Chemical Formula 1] x[LiMn , Ni (1-p-q-r) Co q M 1 r O2]·(1 - x)[Li2Mn s M 2 (1-s) O3]

[0017] In the Chemical Formula 1, M 1 and M 2 are each independently one selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, 0.500 < x < 0.800, 0.450 < p < 0.650, 0 ≦ q ≦ 0.025, 0 ≦ r ≦ 0.100, 0.900 ≦ s ≦ 1.000.

[0018] [Mathematical Formula 1] A(%) = [P A / S A × 100

[0019] In the Mathematical Formula 1, P A This is the area ratio of voids within the surface portion of the cross-sectional image of the positive electrode active material. S A This is the area ratio of the surface portion of the cross-sectional image of the positive electrode active material. The inner surface of the cross-sectional image of the positive electrode active material is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material. The surface portion of the cross-sectional image of the positive electrode active material is the region excluding the inner surface portion.

[0020] (2) The present invention provides a positive electrode active material according to (1) above, wherein the surface porosity (A) is 2% to 20%.

[0021] (3) The present invention provides a positive electrode active material according to (1) or (2) above, which does not contain Co.

[0022] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, which is represented by the following chemical formula 1-1.

[0023] [Chemical formula 1-1] x[LiMn p Ni (1-p-r) M 1 r O2]·(1-x)[Li2Mn s M 2 (1-s) O3]

[0024] In the above chemical formula 1-1, M 1 and M 2 Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0.55 <x<0.70、0.52<p<0.58、0≦r≦0.10、0.90≦s≦1.00である。

[0025] (5) The present invention relates to the average particle size (D 50 The present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein the diameter is 3 μm to 12 μm.

[0026] (6) The present invention provides a method for producing a positive electrode active material according to any one of (1) to (5) above, represented by the following chemical formula 1, comprising the steps of mixing a transition metal hydroxide and a lithium raw material and calcining, wherein the transition metal hydroxide is produced by the steps of creating an inert atmosphere with a pH of 12 to 13 inside a reactor (S1), and creating an active atmosphere by introducing nitrogen and air into the reactor in a volume ratio of 99.5:0.5 to 85.0:15.0, and adding a transition metal solution containing Ni and Mn and a basic solution to cause a coprecipitation reaction under conditions of pH 10 to 11 (S2).

[0027] [Chemical formula 1] x[LiMn p Ni (1-p-q-r) Co q M 1 r O2]·(1-x)[Li2Mn s M 2 (1-s) O3]

[0028] In the aforementioned chemical formula 1, M 1 and M 2 Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and is 0.500 <x<0.800、0.450<p<0.650、0≦q≦0.025、0≦r≦0.100、0.900≦s≦1.000である。

[0029] (7) The present invention provides a method for producing a positive electrode active material as described in (6), wherein step (S1) is performed by adding a solvent and a basic solution to a reactor, mixing them to create an atmosphere with a pH of 12 to 13, and then introducing an inert gas.

[0030] (8) The present invention provides a method for producing a positive electrode active material as described in (6) or (7), wherein the coprecipitation reaction in step (S2) is carried out by adding a basic solution to the reactor within 1 to 2 hours after adding a transition metal solution to the reactor so that the pH in the reactor becomes 10 to 11, and then proceeding with the reaction for 20 to 50 hours while maintaining the pH of 10 to 11.

[0031] (9) The present invention provides a method for producing a positive electrode active material according to any one of (6) to (8) above, wherein the transition metal hydroxide contains 50 mol% or more of Mn among the transition metals.

[0032] (10) The present invention provides a method for producing a positive electrode active material according to any one of (6) to (9) above, wherein the transition metal hydroxide does not contain Co.

[0033] (11) The present invention provides a method for producing a positive electrode active material according to any one of (6) to (10), wherein the transition metal hydroxide and the lithium raw material are mixed such that the molar ratio of the transition metal hydroxide to the lithium element in the lithium raw material is 1:1.2 to 1:1.6.

[0034] (12) The present invention provides a positive electrode comprising a current collector and a positive electrode active material layer provided on at least one surface of the current collector, wherein the positive electrode active material layer comprises a positive electrode active material described in any one of (1) to (5) above.

[0035] (13) The present invention provides a lithium secondary battery comprising the positive electrode described in (12) above, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0036] The positive electrode active material according to the present invention has voids uniformly distributed not only on the inner surface but also on the surface, which, despite being a Li and Mn-rich positive electrode active material, facilitates the movement of lithium ions during charging and discharging, reduces resistance, and provides excellent capacity characteristics and lifespan characteristics.

[0037] The method for producing a positive electrode active material according to the present invention involves producing a transition metal hydroxide by coprecipitation of a transition metal in an activated atmosphere adjusted to a weak oxygen atmosphere, and then mixing and calcining the transition metal hydroxide with a lithium raw material to produce a positive electrode active material having specific surface void characteristics.

[0038] Furthermore, the positive electrode and lithium secondary battery according to the present invention have the effect of being excellent in capacity characteristics and lifespan characteristics by including the positive electrode active material. [Brief explanation of the drawing]

[0039] The following drawings attached to this specification are for illustrating preferred embodiments of the present invention and, together with the above-described content of the invention, serve to provide a better understanding of the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to what is shown in these drawings. [Figure 1] This is an SEM image (magnification 20K) of the positive electrode active material produced in Example 1. [Figure 2] This is an SEM image (magnification 20K) of the positive electrode active material produced in Example 2. [Figure 3] This is an SEM image (magnification 20K) of the positive electrode active material in Example 3. [Figure 4] This is an SEM image (magnification 20K) of the positive electrode active material of Comparative Example 1. [Figure 5] This is an SEM image (magnification 20K) of the positive electrode active material of Comparative Example 2. [Figure 6] This is an SEM image (magnification 20K) of the positive electrode active material of Comparative Example 3. [Figure 7a] This image shows the process of measuring the surface porosity of a positive electrode active material according to one embodiment of the present invention, and is an image of the process of selecting a particle in a cross-sectional image, separating the outer outline of the particle from the unnecessary background portion, and removing the background portion. [Figure 7b] This image shows the process of measuring the surface porosity of a positive electrode active material according to one embodiment of the present invention, and is an image of the process of separating the inner surface region from the surface region of the particle. [Figure 7c]This image shows the process of measuring the surface porosity of a positive electrode active material according to one embodiment of the present invention, and is an image of the process of obtaining the area ratio of the surface portion excluding voids to the total area of ​​the image (A1) and the area ratio of the surface portion excluding voids to the total area (A2) using Image J. [Figure 7d] This image shows the process of measuring the surface porosity of a positive electrode active material according to one embodiment of the present invention, and is an image of the process of obtaining the area ratio of the surface portion excluding voids to the total area of ​​the image (A1) and the area ratio of the surface portion excluding voids to the total area (A2) using Image J. [Modes for carrying out the invention]

[0040] The terms and words used in this specification 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 appropriately define the concepts of terms in order to best describe their invention.

[0041] Definition of Terms In this specification, the term "polycrystalline grain" means a particle in which the crystalline lattice structure is arranged in irregular orientations throughout the particle, and may consist of secondary particles formed by the aggregation of primary particles. Here, secondary particles are a particle structure usually contrasted with primary particles, in which smaller primary particles are physically and / or chemically aggregated to form a relatively larger particle morphology.

[0042] In this specification, the term "porosity (%)" refers to the proportion of space occupied by voids within a particle, and represents the ratio of the area occupied by voids to the reference area.

[0043] Measurement method In this specification, the surface porosity (A) was measured by obtaining a cross-sectional image of the positive electrode active material using a SEM (Quanta FEG 250, PHILIPS) under the following conditions, selecting particles from the cross-sectional image (Figure 7a), extracting the outline of the particles, removing unnecessary background parts, separating the inner and surface regions (Figure 7b), and measuring using the image processing program ImageJ. In this case, the inner region of the cross-sectional image is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material (see Figure 7b). High impedance: 10,000kV Chamber pressure: 9.0 × X 10 -5 mbar Gun pressure: 6.85 × 10 -10 mbar Emission current: 165μA WD: 10mm Beam spot size: 3.0 Stage bias: 4000V

[0044] Using ImageJ, the area ratio of the surface portion excluding voids to the total area of ​​the image (A1) and the area ratio of the surface portion excluding voids to the total area of ​​the image (A2) are obtained (Figures 7c and 7d). Subtracting the area ratio of the surface portion excluding voids (A2) from the total area (100) (100-A2) gives the area ratio of voids within the surface (P A ) and calculate the surface area ratio (S A ) is the ratio of the area occupied by the surface portion (A1) and the ratio of the area of ​​the voids within the surface portion (P A The calculation was performed by adding ( ).

[0045] Subsequently, the surface porosity was calculated using the following mathematical formula 1.

[0046] [Mathematical formula 1] A(%)=[P A / S A ]×100

[0047] In the above mathematical formula 1, P AThis is the area ratio of voids within the surface portion of the cross-sectional image of the positive electrode active material. S A This is the area ratio of the surface portion of the cross-sectional image of the positive electrode active material, wherein the inner surface portion of the cross-sectional image of the positive electrode active material is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material, and the surface portion of the cross-sectional image of the positive electrode active material is the region excluding the inner surface portion.

[0048] As another example, to obtain a more accurate value for the surface porosity (A'), a cross-sectional image of the positive electrode active material is obtained using the aforementioned SEM (Quanta FEG 250, PHILIPS), 30 particles are selected from the cross-sectional image, and the area ratio of the voids within the surface of each of the 30 particles is calculated using the process described above (P Ai (where i is an integer from 1 to 30) and the surface area ratio (S Ai Here, i is an integer from 1 to 30) and the surface porosity (A) of the 30 particles is calculated as shown in the above mathematical formula 1. i Here, after finding i (an integer from 1 to 30), we can then calculate its average value (see formula 2 below).

[0049]

number

[0050] On the other hand, the standard deviation between surface porosity (A) and surface porosity (A') is 2 or less.

[0051] The present invention will be described in more detail below.

[0052] positive electrode active material The present invention provides a Li and Mn-rich cathode active material in which voids are uniformly distributed in the inner and outer surfaces, and in particular, the outer surface has void characteristics under specific conditions, thereby facilitating the movement of lithium ions during charging and discharging.

[0053] A positive electrode active material according to one embodiment of the present invention is a positive electrode active material represented by the following chemical formula 1, consisting of polycrystalline particles composed of secondary particles formed by the aggregation of primary particles, and characterized in that the surface porosity (A) defined by the following mathematical formula 1 is 1% to 30%.

[0054] [Chemical formula 1] x[LiMn p Ni (1-p-q-r) Co q M 1 r O2]·(1-x)[Li2Mn s M 2 (1-s) O3]

[0055] In the aforementioned chemical formula 1, M 1 and M 2 Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and is 0.500 <x<0.800、0.450<p<0.650、0≦q≦0.025、0≦r≦0.100、0.900≦s≦1.000である。

[0056] [Mathematical formula 1] A(%)=[P A / S A ]×100

[0057] In the above mathematical formula 1, P A This is the area of ​​voids within the surface of the cross-sectional image of the positive electrode active material. S A This is the surface area of ​​the cross-sectional image of the positive electrode active material. The inner surface of the cross-sectional image of the positive electrode active material is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material, and the surface of the cross-sectional image of the positive electrode active material is the region excluding the inner surface.

[0058] Specifically, the positive electrode active material according to one embodiment of the present invention may have a surface porosity (A) of 2% to 20%.

[0059] Typical NCM-based cathode active materials are single-phase, manufactured from a rhombohedral lattice precursor, and have a structure in which transition metal layers and Li layers are repeated.

[0060] In contrast, Li and Mn-rich cathode active materials with low cobalt content or that are cobalt-free have two phases: they are manufactured from a Mn-rich precursor with a monoclinic lattice and a rhombohedral lattice crystal structure. In addition to a structure in which transition metal layers and Li layers are repeated, they also have a structure in which Li atoms are additionally included in the transition metal layer. Therefore, compared to general NCM-based cathode active materials, a large amount of Li is required when mixing the precursor and lithium raw material and firing to obtain the cathode active material. This necessitates a cathode active material precursor with a high specific surface area that can contact Li. In this case, if voids are not uniformly distributed in the inner and outer surfaces of the precursor and are only present in the inner surface, the surface of the manufactured cathode active material will lack voids. This leads to problems such as poor lithium ion movement during charging and discharging, resulting in inferior battery performance.

[0061] However, the positive electrode active material according to the present invention, while being a Li and Mn-rich (perlithium and manganese-based) positive electrode active material, has a porosity on its surface that is specified under specific conditions, which facilitates the movement of lithium ions during charging and discharging, and allows it to have excellent capacity characteristics and lifespan characteristics.

[0062] On the other hand, the surface porosity (A) is either the average value of all or some of the polycrystalline particles constituting the positive electrode active material, or a value satisfied by 70% or more of the polycrystalline particles constituting the positive electrode active material.

[0063] For example, 30 polycrystalline particles constituting the positive electrode active material may be randomly selected, the surface porosity may be obtained from the cross-sectional image of each particle, and the range of the surface porosity (A) may be defined by the average value of these values.

[0064] As another example, the range of the surface porosity (A) may be defined by obtaining the surface porosity of each polycrystalline particle constituting the positive electrode active material, and specifying that it is within the range that satisfies 70% or more of the polycrystalline particles.

[0065] The positive electrode active material according to one embodiment of the present invention is a lithium composite transition metal oxide containing Ni and Mn, and may contain 50 mol% or more of Mn among the transition metals excluding lithium. In this case, it is easy to secure a high volume of positive electrode active material.

[0066] As another example, in terms of having a well-balanced and excellent initial charge-discharge capacity, the Mn content among the transition metals may be 55 mol% to 80 mol%, specifically 60 mol% to 80 mol%.

[0067] As another example, the positive electrode active material does not need to contain Co.

[0068] More specifically, the positive electrode active material according to one embodiment of the present invention may be represented by the following chemical formula 1.

[0069] [Chemical formula 1] x[LiMn p Ni (1-p-q-r) Co q M 1 r O2]·(1-x)[Li2Mn s M 2 (1-s) O3]

[0070] In the aforementioned chemical formula 1, M 1 and M 2 Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and is 0.500 <x<0.800、0.450<p<0.650、0≦q≦0.025、0≦r≦0.100、0.900≦s≦1.000である。

[0071] Specifically, in the positive electrode active material, Li may be included in a content corresponding to (2-x), and specifically, (2-x) may be 1.10 to 1.30 or 1.13 to 1.21. When (2-x) is within the above range, excellent initial capacity characteristics can be obtained without the risk of difficulty in forming a per-lithium manganese phase structure due to the generation of a secondary phase and the resulting decrease in capacity, as well as an increase in the amount of gas generated due to an increase in lithium byproducts and the resulting decrease in discharge capacity.

[0072] Furthermore, in the positive electrode active material, Mn may be included in a content corresponding to [xp + (1-x)s], and when [xp + (1-x)s] is within the above range, it can have excellent charging capacity.

[0073] Furthermore, in the positive electrode active material, Ni may be included in a content corresponding to x(1-pqr), and when x(1-pqr) is within the above range, it can have excellent charging capacity.

[0074] Furthermore, in the positive electrode active material, M 1 and M 2 These are doping elements contained in the crystal structure of the positive electrode active material, and may be present in a content corresponding to xr+(1-x)(1-s), M 1 and M 2 They may be the same or different.

[0075] More specifically, the positive electrode active material may be represented by the following chemical formula 1-1.

[0076] [Chemical formula 1-1] x[LiMn p Ni (1-p-r) M 1 r O2]·(1-x)[Li2Mn s M 2 (1-s) O3]

[0077] In the above chemical formula 1-1, M 1 and M 2Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. 0.55 <x<0.70、0.52<p<0.58、0≦r≦0.10、0.90≦s≦1.00である。

[0078] As another example, the positive electrode active material has an average particle size (D 50 The size of the saturation is 3 μm to 12 μm, and specifically it may be 5 μm to 10 μm or 6 μm to 8 μm.

[0079] Furthermore, the positive electrode active material has a total porosity of 1% to 30%, and the difference between the inner porosity and the surface porosity is 1% to 30%. Specifically, the total porosity may be 5% to 20%, and the difference between the inner porosity and the surface porosity may be 7% to 20%, with the inner porosity being higher than the surface porosity. In this case, since the voids are uniformly distributed throughout the positive electrode active material, lithium can move more smoothly during charging and discharging, resulting in superior battery characteristics.

[0080] Method for manufacturing positive electrode active material The present invention provides a method for producing a positive electrode active material, which can produce the positive electrode active material.

[0081] A method for producing a positive electrode active material represented by chemical formula 1 according to one embodiment of the present invention includes the step of mixing a transition metal hydroxide and a lithium raw material and calcining, wherein the transition metal hydroxide is produced by the steps of creating an inert atmosphere with a pH of 12 to 13 inside a reactor (S1), and creating an active atmosphere by introducing nitrogen and air into the reactor in a volume ratio of 99.5:0.5 to 85.0:15.0, and adding a transition metal solution containing Ni and Mn and a basic solution to carry out a coprecipitation reaction under conditions of pH 10 to 11 (S2).

[0082] Examples of lithium raw materials include 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)), and chlorides (e.g., lithium chloride (LiCl)). One of these may be used alone, or a mixture of two or more.

[0083] The mixing of the transition metal hydroxide and the lithium raw material may be carried out by solid-phase mixing such as a jet mill, and the mixing ratio of the transition metal hydroxide, which is the positive electrode active material precursor, and the lithium raw material may be determined within a range that satisfies the mole fraction of each component in the final positive electrode active material. More specifically, the transition metal hydroxide and the lithium raw material may be mixed such that the molar ratio of the transition metal hydroxide to the lithium element in the lithium raw material is 1:1.2 to 1:1.6.

[0084] Furthermore, although not essential, the mixing may include, in addition to the transition metal hydroxide 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-containing raw material or the X-containing raw material described later may be further mixed in during the mixing process. Examples of the X-containing raw material include, but are not limited to, Na3PO4, K3PO4, Mg3(PO4)2, AlF3, NH4F, and LiF. When a portion of the oxygen is replaced with element X as described above, the effect of suppressing oxygen desorption and reaction with the electrolyte during charging and discharging of the secondary battery can be obtained.

[0085] Furthermore, the firing may be carried out at 750°C to 1,050°C, specifically at 850°C to 950°C, and the firing time may be 5 hours to 30 hours, specifically at 8 hours to 15 hours, but is not limited to these.

[0086] On the other hand, the transition metal hydroxide can be produced by a method comprising the steps of creating an inert atmosphere with a pH of 12 to 13 inside a reactor (S1), and creating an active atmosphere by adding nitrogen and air to the reactor in a volume ratio of 99.5:0.5 to 85.0:15.0, and then adding a transition metal solution containing Ni and Mn and a basic solution to carry out a coprecipitation reaction under conditions of pH 10 to 11 (S2).

[0087] The method for producing the transition metal hydroxide according to the present invention will be described in detail step by step below.

[0088] (S1) Step Step (S1) described above is a step of creating an inert atmosphere and specific pH conditions inside the reactor before the coprecipitation reaction. This may be done by adding and mixing a solvent and a basic solution into the reactor to create an atmosphere with a pH of 12-13, and then introducing an inert gas.

[0089] The solvent may be a polar solvent commonly used in the industry, and may, for example, be water, an alcohol, or a mixture thereof.

[0090] The aforementioned inert gas is not particularly limited and can be any inert gas commonly used in the industry, and may be one or more selected from nitrogen, argon, helium, and neon, and specifically may be nitrogen.

[0091] The basic solution is a precipitating agent and serves to adjust the pH in the reactor, and may be a hydroxide of an alkali metal or alkaline earth metal such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof.

[0092] As another example, the basic solution may be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (for example, alcohol) may be used as the solvent.

[0093] (S2) Step Step (S2) is a step for producing a transition metal hydroxide by coprecipitation of a transition metal, and may be carried out by creating an active atmosphere inside the reactor, adding the transition metal solution and a basic solution, and performing a coprecipitation reaction at pH 10-11.

[0094] Specifically, the activated atmosphere can be created by introducing an inert gas and air into the reactor in a volume ratio of 99.5:0.5 to 85.0:15.0 to form a weak oxygen atmosphere. Here, the inert gas is as described above, and may specifically be nitrogen.

[0095] The manufacturing method according to the present invention allows for the formation and growth of narrow, short, needle-shaped primary particles by changing the reactor environment from an inert atmosphere to a weak oxygen active atmosphere during the coprecipitation reaction. This results in the uniform formation of voids to the surface, yielding a transition metal hydroxide with a large specific surface area. Furthermore, by mixing and calcining the transition metal hydroxide having the above characteristics with a lithium raw material, a positive electrode active material can be obtained in which voids are distributed to the surface. Despite being a perlithium nickel manganese-based positive electrode active material, lithium ion movement during charging and discharging is facilitated, resistance is reduced, and it exhibits excellent capacity characteristics and lifespan characteristics.

[0096] Alternatively, the coprecipitation reaction may be carried out by adding a basic solution to the reactor within 1 to 2 hours after adding the transition metal solution, so that the pH in the reactor becomes 10 to 11, and then allowing the reaction to proceed for 20 to 50 hours while maintaining the pH of 10 to 11.

[0097] Furthermore, the coprecipitation reaction may be carried out at a temperature of 40°C to 60°C while stirring. The stirring speed is not particularly limited, but it may be stirred at 100 rpm to 1,000 rpm because it is easy to increase the reaction rate.

[0098] The transition metal solution may be prepared by adding a transition metal raw material to a solvent, specifically a mixed solvent of water or an organic solvent that can be homogeneously mixed with water (for example, alcohol), and mixing, or by mixing an aqueous solution of the transition metal raw material.

[0099] The transition metal raw material may be a sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide of a transition metal.

[0100] As a specific example, the Ni raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide. More specific examples include, but are not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4·6H2O, fatty acid nickel salt, nickel halide, or combinations thereof.

[0101] Furthermore, the Mn raw material may be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides. More specific examples include manganese oxides such as Mn2O3, MnO2, and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate salts, manganese citrate, and manganese fatty acid salts; manganese oxyhydroxide, manganese chloride, or combinations thereof, but is not limited to these.

[0102] As yet another example, the transition metal solution may further contain one or more selected from Zr, Al, Re, V, Co, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. In this case, the transition metal solution may further contain a raw material containing Zr, Al, Re, V, Co, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, or Pt, and the raw material may be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing each of the metals.

[0103] Furthermore, the transition metal solution may contain 50 mol% or more of Mn among the transition metals in the solution.

[0104] As another example, the transition metal solution mentioned above does not contain Co.

[0105] A method for producing a positive electrode active material according to one embodiment of the present invention may further involve a washing step and a drying step to remove lithium by-products after the calcination. The washing step may be carried out, for example, by immersing the produced positive electrode active material in ultrapure water and stirring it. In this case, the washing temperature may be 20°C or lower, specifically 10°C to 20°C, and the washing time may be about 10 minutes to 1 hour. When the washing temperature and washing time meet the above ranges, lithium by-products can be effectively removed.

[0106] Positive electrode and secondary battery The present invention provides a positive electrode containing the positive electrode active material, and a lithium secondary battery containing the positive electrode.

[0107] The positive electrode according to one embodiment of 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.

[0108] 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 may 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 the positive electrode composite material may be cast onto another support, peeled off this support, and the resulting film laminated onto the positive electrode current collector.

[0109] In this case, 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 a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector usually has a thickness of 3 μm to 500 μm, and the adhesion strength of the positive electrode active material may be increased by forming fine irregularities on the surface of the current collector. For example, various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric are possible.

[0110] A positive electrode active material layer containing the positive electrode active material according to the present invention, and optionally further selectively containing at least one of a conductive material and a binder, is located on at least one surface of the current collector.

[0111] The positive electrode active material may be present in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight, relative to the total weight of the positive electrode active material layer. When present within the above content range, excellent capacity characteristics can be observed.

[0112] The conductive material is used to impart conductivity to the electrodes and is not particularly limited as long as it does not cause chemical changes in the battery it is used in. Specific examples include graphite such as natural graphite and 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; and conductive polymers such as polyphenylene derivatives. One of these may be used alone, or a mixture of two or more. 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.

[0113] 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, and one of these may be used alone or a mixture of two or more. The binder may be included in an amount of 1% to 30% by weight relative to the total weight of the positive electrode active material layer.

[0114] On the other hand, the solvent used in the production of the positive electrode composite material may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, either alone or in mixtures thereof. The amount of solvent used may be adjusted as appropriate, taking into consideration the slurry coating thickness, production yield, viscosity, etc.

[0115] Furthermore, the lithium 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 described above.

[0116] On the other hand, the lithium 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.

[0117] In the lithium 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.

[0118] The negative electrode can be manufactured by a conventional negative electrode manufacturing method that is generally known in the art. For example, the negative electrode may be manufactured by dissolving or dispersing the components constituting the negative electrode active material layer, i.e., the negative electrode active material and a conductive material and / or binder, etc., in a solvent to produce a negative electrode composite, applying the negative electrode composite to at least one surface of the negative electrode current collector, and then drying and rolling it; or the negative electrode composite may be cast onto another support, peeled off this support, and the resulting film laminated onto the negative electrode current collector.

[0119] 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 may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics are possible.

[0120] 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, and lithium vanadium oxides that can be doped and undoped with lithium; or composites containing the metallic compound and a carbonaceous material, such as Si-C composites or Sn-C composites, etc. may be mentioned, and mixtures of any one or two or more of these may be used. Further, a thin film of metallic lithium may 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 low-crystalline carbons are soft carbon and hard carbon, and representative high-crystalline carbons 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 carbons such as petroleum or coal tar pitch-derived cokes.

[0121] Further, the binder and the conductive material are the same as those described above for the positive electrode.

[0122] 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. Any separator commonly used in secondary batteries can be used without particular limitations, and those with low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be used selectively as single-layer or multi-layer structures.

[0123] On the other hand, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte, which are usable in the manufacture of secondary batteries, but is not limited to these.

[0124] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0125] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, and is not particularly limited. 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); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as Ra-CN (where Ra is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may 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, by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to 9, excellent electrolyte performance can be achieved.

[0126] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, and is not particularly limited. 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 concentration of the lithium salt is preferably 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, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0127] In addition to the components of the electrolyte, the electrolyte may further 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 such as difluoroethylene carbonate; or pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, 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.

[0128] 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, making it usefully applicable in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0129] Furthermore, the secondary battery according to the present invention may be used as a unit cell of a battery module, and the battery module is applicable to a battery pack. The battery module or battery pack can be used as a power source for one or more medium- and large-sized devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0130] Examples Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0131] Example 1 (1) Production of transition metal hydroxides NiSO4 and MnSO4 were mixed in deionized water in amounts resulting in a Ni:Mn molar ratio of 35:65 to produce a 2.4 M transition metal aqueous solution.

[0132] 2.6 L of deionized water and 3.5 ml of a 25 wt% NaOH aqueous solution were added to a 10 L continuous stirring tank reactor, and the mixture was stirred at 150 rpm while maintaining a temperature of 50°C to adjust the pH inside the reactor to 12. In addition, nitrogen gas was flowed at 2 L / min to remove dissolved oxygen and create a non-oxidizing atmosphere inside the reactor.

[0133] Thereafter, while stirring at 1000 rpm, nitrogen and air were introduced into the reactor at a volume ratio of 90:10 to create a weakly oxygen atmosphere, and the transition metal aqueous solution was continuously introduced into the reactor at 0.85 L / hr. At this time, an NaOH aqueous solution was introduced together with the transition metal aqueous solution so that the pH in the reactor became 10 within 2 hours to initiate a coprecipitation reaction, and then the coprecipitation reaction was continued for 50 hours while maintaining pH 10. After completion of the coprecipitation reaction, the produced transition metal hydroxide was separated and washed, and then dried at 100 °C for 12 hours to produce the transition metal hydroxide [Mn 0.65 Ni 0.35 (OH)2] which is the precursor of the positive electrode active material.

[0134] (2) Production of positive electrode active material 50 g of the produced transition metal hydroxide was mixed with 31.1 g of LiOH using a mechanical homogenizer for 20 minutes, and heat-treated at 900 °C for 10 hours to produce the positive electrode active material [0.63(LiMn 0.57 Ni<00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​(1) Production of transition metal hydroxides NiSO4 and MnSO4 were mixed in deionized water in amounts resulting in a Ni:Mn molar ratio of 35:65 to produce a 2.4 M transition metal aqueous solution.

[0138] 2.6 L of deionized water and 3.5 ml of a 25 wt% NaOH aqueous solution were added to a 10 L continuous stirring tank reactor, and the mixture was stirred at 150 rpm while maintaining a temperature of 50°C to adjust the pH inside the reactor to 12. In addition, nitrogen gas was flowed at 2 L / min to remove dissolved oxygen and create a non-oxidizing atmosphere inside the reactor.

[0139] Subsequently, the transition metal aqueous solution was continuously added to the reactor at a rate of 0.85 L / hr. At this time, NaOH aqueous solution was added along with the transition metal aqueous solution to bring the pH of the reactor to 10 within 2 hours to start the coprecipitation reaction, and the coprecipitation reaction was continued for 50 hours while maintaining the pH at 10. After the completion of the coprecipitation reaction, the generated transition metal hydroxide was separated and washed, and then dried at 100°C for 12 hours to obtain the transition metal hydroxide [Mn], which is the cathode active material precursor. 0.65 Ni 0.35 (OH)2] was produced.

[0140] (2) Manufacturing of positive electrode active material 50 g of the aforementioned manufactured transition metal hydroxide was mixed with 31.1 g of LiOH using a mechanical homogenizer for 20 minutes, and then heat-treated at 900°C for 10 hours to obtain a positive electrode active material [0.63(LiMn 0.57 Ni 0.43 We manufactured O2)·0.37(Li2MnO3).

[0141] Comparative Example 2 (1) Production of transition metal hydroxides NiSO4 and MnSO4 were mixed in deionized water in amounts resulting in a Ni:Mn molar ratio of 35:65 to produce a 2.4 M transition metal aqueous solution.

[0142] 2.6 L of deionized water and 3.5 ml of a 25 wt% NaOH aqueous solution were added to a 10 L continuous stirring tank reactor, and the mixture was stirred at 150 rpm while maintaining a temperature of 50°C to adjust the pH inside the reactor to 12. In addition, nitrogen gas was flowed at 2 L / min to remove dissolved oxygen and create a non-oxidizing atmosphere inside the reactor.

[0143] Subsequently, while stirring at 1000 rpm, air was introduced into the reactor to create an oxygen atmosphere, and the transition metal aqueous solution was continuously added to the reactor at a rate of 0.85 L / hr. At this time, NaOH aqueous solution was added along with the transition metal aqueous solution to bring the pH of the reactor to 10 within 2 hours to start the coprecipitation reaction, and the coprecipitation reaction was continued for 50 hours while maintaining a pH of 10. After the completion of the coprecipitation reaction, the generated transition metal hydroxide was separated and washed, and then dried at 100°C for 12 hours to obtain the transition metal hydroxide [Mn 0.65 Ni 0.35 (OH)2] was produced.

[0144] (2) Manufacturing of positive electrode active material 50 g of the aforementioned manufactured transition metal hydroxide was mixed with 31.1 g of LiOH using a mechanical homogenizer for 20 minutes, and then heat-treated at 900°C for 10 hours to obtain a positive electrode active material [0.63(LiMn 0.57 Ni 0.43 We manufactured O2)·0.37(Li2MnO3).

[0145] Comparative Example 3 In Example 1, the same procedure was followed except that nitrogen and air were introduced in a volume ratio of 80:20 to create a weak oxygen atmosphere, and transition metal hydroxide [Mn 0.65 Ni 0.35 (OH)2] and positive electrode active material [0.63(LiMn 0.57 Ni 0.43 We manufactured O2)·0.37(Li2MnO3).

[0146] Experimental Example 1 The surface porosity of each positive electrode active material produced in the examples and comparative examples was analyzed, and the results are shown in Figures 1 to 6 and Table 1.

[0147] The void shape of the cross-sectional images of each cathode active material was observed using a SEM (Quanta FEG 250, PHILIPS) under the following conditions. High impedance: 10,000kV Chamber pressure: 9.0 × 10 -5 mbar Gun pressure: 6.85 × 10 -10 mbar Emission current: 165μA WD: 10mm Beam spot size: 3.0 Stage bias: 4000V

[0148] Furthermore, the porosity of the surface was measured as shown in the schematic diagram in Figure 7.

[0149] Specifically, particles were selected in each cross-sectional image (Figure 7a), the outer shell lines of the particles were extracted, unnecessary background areas were removed, and the inner and outer regions were separated (Figure 7b). The surface porosity was then measured using the image processing program ImageJ. In this process, the inner region of the cross-sectional image is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material (see Figure 7b).

[0150] First, using ImageJ, we obtained the area ratio of the surface portion excluding voids to the total area of ​​the image (A1), and the area ratio of the surface portion excluding voids to the total area of ​​the image (A2) (Figures 7c and 7d). Then, subtracting the area ratio of the surface portion excluding voids (A2) from the total area (100) (100-A2) gives the area ratio of voids within the surface portion (P A The surface area ratio (S) was calculated. A ) is the ratio of the area occupied by the surface portion (A1) and the ratio of the area of ​​the voids within the surface portion (P A The calculation was performed by adding ( ).

[0151] Subsequently, the surface porosity was calculated using the following mathematical formula 1.

[0152] [Mathematical formula 1] A(%)=[P A / S A ]×100

[0153] In the above mathematical formula 1, P A This is the area ratio of voids within the surface portion of the cross-sectional image of the positive electrode active material. S A This is the area ratio of the surface portion of the cross-sectional image of the positive electrode active material. The inner surface of the cross-sectional image of the positive electrode active material is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material. The surface portion of the cross-sectional image of the positive electrode active material is the region excluding the inner surface portion.

[0154] Furthermore, after obtaining a cross-sectional image of the positive electrode active material using the aforementioned SEM (Quanta FEG 250, PHILIPS), 30 particles were selected from the cross-sectional image, and the area ratio of the voids within the surface of each of the 30 particles was determined by the process described above (P Ai (where i is an integer from 1 to 30) and the surface area ratio (S Ai Here, i is an integer from 1 to 30) and the surface porosity (A) of the 30 particles is calculated as shown in the above mathematical formula 1. i Here, i is an integer from 1 to 30. After determining the value, the average value was used to show the surface porosity (A') of each positive electrode active material (see mathematical formula 2 below). In this case, Comparative Example 3 was performed on 20 particles.

[0155]

number

[0156] [Table 1]

[0157] From Figures 1 to 6, it can be confirmed that the positive electrode active materials of Examples 1 to 3 have uniformly distributed voids on their surfaces, and from Table 1, it can be confirmed that the positive electrode active materials of Examples 1 to 3 have a surface void ratio of 1% or more and 30% or less. In contrast, it was confirmed that the positive electrode active materials of Comparative Examples 1 and 2 have a surface void ratio of less than 1%. Furthermore, for Examples 1 to 3, the standard deviation between the surface void ratio (A) and the surface void ratio (A'), which is the average value of 30 particles, is 2 or less, and it was confirmed that there is almost no deviation between the particles constituting each positive electrode active material, indicating that they have a uniform void ratio.

[0158] On the other hand, in Comparative Example 3, the surface porosity exceeded 30%, and particle fracture was severe, making it impossible to manufacture the positive electrode and evaluate the battery characteristics as described later. Furthermore, when the surface porosity (A') of 20 particles in Comparative Example 3 was calculated, the deviation in surface porosity from particle to particle exceeded 10, indicating that the surface porosity was not consistent for each particle.

[0159] Experimental Example 2 After manufacturing positive electrodes and batteries using the positive electrode active materials produced in the examples and comparative examples, the battery performance was evaluated.

[0160] (1) 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 92.5:3.0:4.5 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.

[0161] (3) Battery manufacturing Lithium metal was used as the negative electrode.

[0162] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes produced as described above. After positioning the electrode assembly inside a case, an electrolyte was injected into the case to produce a lithium secondary battery. The electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixed volume ratio = 3 / 7), and adding 3% by weight of fluoroethylene carbonate (FEC) and 0.5% by weight of LiBF4 as additives.

[0163] The half-cells of each lithium secondary battery manufactured as described above were charged at 25°C in CCCV mode at 0.1C until they reached 4.7V, and then discharged at a constant current of 0.1C until they reached 2.0V. The initial charge / discharge capacity was then measured. In addition, the capacity retention rate was checked after repeating the charging and discharging cycle at 0.1C 30 times. The results are shown in Table 2 below.

[0164] Furthermore, the initial resistance and resistance increase rate were measured from the voltage change during the discharge period of the first 60 seconds of each cycle for each half-cell.

[0165] [Table 2]

[0166] As shown in Table 2 above, Examples 1 to 3 demonstrated significantly superior initial charge / discharge capacity and capacity retention compared to Comparative Examples 1 and 2, and also showed a significant improvement in initial resistance and resistance increase rate. On the other hand, the positive electrode active material of Comparative Example 3 had too high a surface porosity, resulting in low particle density. As a result, most of the particles were crushed during electrode manufacturing, making battery production impossible.

Claims

1. A positive electrode active material consisting of polycrystalline particles represented by the following chemical formula 1, which are composed of secondary particles formed by the aggregation of primary particles, A positive electrode active material having a surface porosity (A) defined by the following mathematical formula 1, which is between 1% and 30%. [Chemical formula 1] 8[LiMn ｐ Ni （１－ｐ－ｑ－ｒ） Co ｑ M １ ｒ O ２ ]・(1-x)[- ２ Mn ｓ M ２ （１－ｓ） O ３ ] (In the above chemical formula 1, M １ and M ２ Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. (0.500 < x < 0.800, 0.450 < p < 0.650, 0 ≤ q ≤ 0.025, 0 ≤ r ≤ 0.100, 0.900 ≤ s ≤ 1.000.) [Mathematical formula 1] A(%)=[P Ａ / S Ａ ]×100 (In the above mathematical formula 1, P Ａ This is the area ratio of voids within the surface portion of the cross-sectional image of the positive electrode active material. S Ａ This is the area ratio of the surface portion of the cross-sectional image of the positive electrode active material. The inner surface of the cross-sectional image of the positive electrode active material is a region formed by connecting points that are half the distance from the center of the cross-sectional image of the positive electrode active material to the outermost shell surface of the cross-sectional image of the positive electrode active material. The surface portion of the cross-sectional image of the positive electrode active material is the region excluding the inner surface portion.

2. The positive electrode active material according to claim 1, wherein the surface porosity (A) is 2% to 20%.

3. The positive electrode active material according to claim 1, which does not contain Co.

4. The positive electrode active material according to claim 1, which is represented by the following chemical formula 1-1. [Chemical formula 1-1] 8[LiMn ｐ Ni （１－ｐ－ｒ） M １ ｒ O ２ ]・(1-x)[- ２ Mn ｓ M ２ （１－ｓ） O ３ ] (In the above chemical formula 1-1, M １ and M ２ Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. (0.55 < x < 0.70, 0.52 < p < 0.58, 0 ≤ r ≤ 0.10, 0.90 ≤ s ≤ 1.00.)

5. Average particle size (D ５０ The positive electrode active material according to claim 1, wherein the diameter is 3 μm to 12 μm.

6. The process includes the step of mixing a transition metal hydroxide and a lithium raw material and firing them, The transition metal hydroxide is used in the step (S1) of creating a pH of 12-13 and an inert atmosphere inside the reactor. A method for producing a positive electrode active material represented by the following chemical formula 1, comprising the steps of: (S2) creating an activated atmosphere by introducing nitrogen and air into the reactor in a volume ratio of 99.5:0.5 to 85.0:15.0, and then adding a transition metal solution containing Ni and Mn and a basic solution to carry out a coprecipitation reaction under pH conditions of 10 to 11. [Chemical formula 1] 8[LiMn ｐ Ni （１－ｐ－ｑ－ｒ） Co ｑ M ２ ｒ O ２ ]・(1-x)[- ２ Mn ｓ M １ （１－ｓ） O ３ ] (In the above chemical formula 1, M １ and M ２ Each is independently selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. (0.500 < x < 0.800, 0.450 < p < 0.650, 0 ≤ q ≤ 0.025, 0 ≤ r ≤ 0.100, 0.900 ≤ s ≤ 1.000.)

7. The method for producing a positive electrode active material according to claim 6, wherein step (S1) is performed by adding a solvent and a basic solution to a reactor, mixing them to create an atmosphere with a pH of 12 to 13, and then introducing an inert gas.

8. The method for producing a positive electrode active material according to claim 6, wherein the coprecipitation reaction in step (S2) is carried out by adding a basic solution to the reactor within 1 to 2 hours after adding a transition metal solution to the reactor so that the pH in the reactor becomes 10 to 11, and then proceeding with the reaction for 20 to 50 hours while maintaining the pH of 10 to 11.

9. The method for producing a positive electrode active material according to claim 6, wherein the transition metal hydroxide contains 50 mol% or more of Mn among the transition metals.

10. The method for producing a positive electrode active material according to claim 6, wherein the transition metal hydroxide does not contain Co.

11. The method for producing a positive electrode active material according to claim 6, wherein the transition metal hydroxide and the lithium raw material are mixed such that the molar ratio of the transition metal hydroxide to the lithium element in the lithium raw material is 1:1.2 to 1:1.

6.

12. Current collector and, The current collector includes a positive electrode active material layer provided on at least one surface of the current collector, The positive electrode comprises the positive electrode active material layer according to any one of claims 1 to 5.

13. The positive electrode according to claim 12, The negative electrode and, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery containing an electrolyte.

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