Cathode active material and secondary battery having same

Abstract

The present invention provides a cathode active material comprising: a core including a transition metal; and a surface part formed on the surface of the core, wherein the surface part includes: a first coating which is applied to a portion of the surface of the core; and a second coating which is applied to the remaining uncoated portion of the surface of the core and optionally to the outer surface of the first coating, and has relatively better melt spreadability compared to the first coating.

Description

Cathode active material and secondary battery containing the same

[0001] The present invention relates to a positive electrode active material and a secondary battery including the same, and more particularly, to a positive electrode active material including a first coating applied to a portion of a core surface and a second coating applied to the entire remaining uncoated portion of the core surface due to high melting spreadability, and a secondary battery based thereon.

[0002] Lithium secondary batteries are used in various fields such as mobile devices, energy storage systems, and electric vehicles due to their high energy density and voltage, long cycle life, and low self-discharge rate.

[0003] The cathode active materials used in these lithium secondary batteries typically have a secondary particle structure of several micrometers in size, formed by agglomeration of fine primary particles of submicron size. These secondary particle-structured cathode active materials have a problem in that the secondary particles break apart as the agglomerated primary particles separate during repeated charge and discharge, resulting in deterioration of battery performance. Since this problem stems from the structural characteristics of the secondary particles, it is difficult to resolve without modifying the structure. Therefore, a single-body particle with a novel structure has been developed.

[0004] These single particles have a structure of a 'non-agglomerated single particle' rather than a 'structure of agglomerated primary particles', and since there is 'almost' no particle agglomeration, there is no particle separation due to charge and discharge, thereby solving the problem that occurs in secondary particle active materials. Here, the term 'almost' means that some agglomerated lumps that inevitably exist during the manufacturing of the novel single particle / powder are allowed. That is, since it is impossible for all particles to exist in a perfectly separated state due to technical limitations, some unintended agglomerated lumps may occur.

[0005] Unlike conventional secondary particles, the novel single-particle design features individual particles measuring several micrometers in size and a non-agglomerated structure, eliminating particle separation during charge / discharge cycles. This fundamentally addresses the problems inherent in secondary particle active materials. However, challenges associated with the manufacture of these single-particle designs exist.

[0006] Specifically, since the firing for manufacturing polycrystalline NCM or active materials with multiple particle sizes is performed at a relatively low firing temperature, oxygen desorption does not occur. The oxygen desorption phenomenon generates an excessive amount of NiO, which is a rock salt structure, within the layered structure of the positive electrode active material and increases Li byproducts. As NiO gradually increases through repeated charge and discharge, the resistance increases, and as Li byproducts increase, various side reactions occur, resulting in deterioration of battery performance such as capacity reduction.

[0007] On the other hand, for the sintering for the production of single crystal NCM or single particle size active material, the sintering temperature is raised to an extreme degree to implement morphology for primary particle growth, and high temperature sintering is performed. During high temperature sintering, the grain size grows and the grain boundary decreases, and particle growth progresses, but the surface structure collapses due to oversintering, and the problem of difficulty in performance expression occurs due to damaged structural instability caused by the oxygen desorption phenomenon, that is, the increase of NiO, which is a rock salt structure.

[0008] As such, the surface of damaged particles needs to be restored, and surface modification technologies have been proposed as a method for this purpose. Typically, coatings and surface treatments focus more on surface performance than on internal structural stabilization. Coatings and surface treatments can prevent direct contact between the positive active material and the electrolyte, thereby preventing decomposition or oxidation of the electrolyte.

[0009] However, during the coating process, some uncoated areas may be generated, exposing the surface of the active material to the outside. These uncoated areas have the problem of causing a deterioration in the characteristics of the secondary battery in which the active material is used due to a side reaction with the electrolyte.

[0010] To solve these problems, some prior art techniques have proposed multilayer coating techniques, but they not only fail to produce satisfactory results overall, but also do not provide requirements for coating optimization.

[0011] Therefore, there is a high need in the industry for new technologies to solve these problems.

[0012] The present invention aims to solve the problems of the prior art as described above and the technical tasks requested from the past.

[0013] The inventors of the present invention, after repeated in-depth research and various experiments, have confirmed that when the coatings forming the surface portion of a positive electrode active material composed of a core and a surface portion are set to specific conditions, the surface stabilization can be achieved while suppressing the oxygen desorption phenomenon from the active material by complete coating of the core by the surface portion, and side reactions with the electrolyte can be reduced, ultimately improving the characteristics of the positive electrode active material to be used in a secondary battery, thereby completing the present invention.

[0014] Therefore, the positive electrode active material of the present invention to achieve this purpose is

[0015] It comprises a core containing a transition metal and a surface portion formed on the surface of the core, and the surface portion is

[0016] A first coating applied to a portion of the core surface; and

[0017] A second coating is applied to the remaining uncoated portion of the core surface and optionally to the outer surface of the first coating, and has relatively good melt spreadability compared to the first coating;

[0018] It is characterized by including .

[0019] As defined above, the positive electrode active material of the present invention has a surface portion including at least two coatings that can contribute to improving its properties, and has a structure in which a second coating is applied to the remaining surface of the active material not covered by the first coating, and so on, and the second coating is configured to have relatively high melting spreadability to enable this.

[0020] The above melt spreadability can be expressed as the viscosity of the melt when the raw material is melted by firing after applying the raw material to the coating target. A relatively high melt spreadability means having a relatively small contact angle due to low melt viscosity. Melt spreadability can also be expressed as melt wettability.

[0021] Therefore, by completely covering the core with the surface, the oxygen desorption phenomenon can be suppressed, and the side reaction with the electrolyte can be reduced, ultimately improving the characteristics of the positive electrode active material. Whether or not the surface is covered can also be confirmed through the degree of gelation of the active material slurry. Since the residual lithium on the surface of the active material particles can gel during the slurry production, which can cause gas generation due to a side reaction with the electrolyte, the side reaction with the electrolyte can be completely blocked by completely covering the core with the surface, and the gelation mitigation can be confirmed.

[0022] The 'crystallization degree' of the coating can be considered as a major factor in determining the above melt spreadability. In the case of a coating material that has low melt spreadability and thus forms an "island-spot" or non-uniform coating on the surface of the positive electrode active material, the coating may contain many crystalline substances and thus have a high crystallinity. On the other hand, if the melt spreadability is high, the coating may form a film on the surface of the positive electrode active material, in which case the coating may contain many amorphous (glassy) substances and thus have a low crystallinity. Therefore, if the coated portion has high crystallinity after coating, it can be predicted that the coating material has low melt spreadability and thus forms an island-spot coating or non-uniform coating. Here, the expression 'high crystallinity' means that the crystalline substances account for at least 50% or more of the entire structure, and the expression 'low crystallinity' means that the crystalline substances account for at least less than 50% of the entire structure.

[0023] The crystallinity as described above can be measured by various methods, and for example, a measurement method using a transmission electron microscope (TEM) can be used. Specifically, it can be calculated by selecting an arbitrary measurement point on the surface of one particle of an arbitrary positive electrode active material. For example, if a positive electrode active material including a coating is measured at 500,000 times with a TEM device, and if crystals are confirmed at 15 of 20 arbitrary points of the first coating selected from the measured image, the crystallinity can be expressed as 75% (= 15 / 20×100), and if crystals are confirmed at 5 of 20 arbitrary points of the second coating selected, the crystallinity can be expressed as 25% (= 5 / 20×100). In this case, the second coating (25%) with relatively low crystallinity has higher melt spreadability than the first coating (75%), and it can be expected that the second coating will be able to cover the surface of the positive electrode active material that the first coating could not coat due to the relatively high melt spreadability of the second coating.

[0024] Therefore, since melt spreadability can be set as a comparative value by crystallinity, crystallinity can be used as a factor to quantitatively determine the degree of melt spreadability for two coatings.

[0025] The application of the core by a specific surface portion as described above can be particularly preferably applied to a positive electrode active material composed of single particles, and for example, the positive electrode active material can be in a form including non-agglomerated primary particles, and in some cases, can be in a form in which such non-agglomerated primary particles are the main component and aggregated secondary particles are the secondary component.

[0026]

[0027] In one specific example, the core may have a composition of the following chemical formula:

[0028] Li[Li x M 1-x-y D y ]O z Q f

[0029] In the above formula,

[0030] M is one or more transition metal elements that are stable in the four- or six-coordinate configuration;

[0031] D is at least one element selected from among alkaline earth metals, transition metals of groups 3 to 12, post-transition metals and metalloids of groups 13 to 15, non-metals of groups 14 to 16, and lanthanide elements as a dopant;

[0032] Q is an anion containing at least one element selected from F, S, and P;

[0033] -0.05≤x≤0.1, 0≤y≤0.1, 0≤x+y<1, 0≤z≤4, 0≤f≤1.

[0034] Specifically, the at least one transition metal element (M) that is stable in the four- or six-coordinate configuration may be, for example, at least one element selected from the group consisting of Ni, Co, and Mn, and preferably may contain at least 70 mol% or more of Ni, more preferably at least 80 mol% or more. When the Ni content is above the above range based on the total transition metal content, the degree of oxygen desorption is large, and therefore, by the surface portion defined above, the oxygen desorption phenomenon and surface stability are improved, and thus the resistance, capacity, efficiency, residual lithium, and life characteristics can be more effectively improved.

[0035] Also, in specific examples, the alkaline earth metal may be, for example, Be, Mg, Ca, Sr, Ba, Ra, etc.

[0036] The above-mentioned group 3 to group 12 transition metals may be, for example, Sc, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, etc., excluding nickel, cobalt, and manganese, and these transition metal elements may include actinide elements.

[0037] The transition metals and metalloids among the above groups 13 to 15 may be, for example, Al, Ga, In, Sn, Tl, Pb, Bi, Po, B, Si, Ge, As, Sb, Te, At, etc.

[0038] Non-metallic elements among the above groups 14 to 16 may be, for example, C, P, S, Se, etc.

[0039] The above lanthanide elements may be, for example, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.

[0040] In a preferred example, D may be one or more selected from the group consisting of Zr, Ti, W, B, P, Al, Si, Mg, Zn and V.

[0041]

[0042] As previously defined, the first coating is applied to only a portion of the core surface, so the resulting uncoated area is covered by the second coating. Here, the size of the core surface to which the first coating is applied is not particularly limited, and may range from 10% to 90% of the total area of ​​the core surface, for example.

[0043] In one specific example, the second coating may be a glass coating. Here, a glass coating refers to a coating that exhibits a relatively high coating coverage and relatively high adhesion to adjacent active material particles due to its high melt viscosity and amorphous nature. Therefore, the glass coating exhibits the characteristic of reducing the tap density due to the agglomeration between particles, as described below.

[0044]

[0045] In another specific example, the first coating may include at least one element selected from the group consisting of alkaline earth metals, transition metals, post-transition metals, and lanthanides, and the second coating may include at least one element selected from the group consisting of transition metals, metalloids, and non-metals in a different element range from the first coating. The examples described above may be applied to the alkaline earth metals, transition metals, transition metals, lanthanides, metalloids, and non-metals.

[0046] Preferably, the first coating may be configured to include at least one element selected from among Al, Ti, Zr, Co, Mn, V, Cr, Ni, Cu, Y, Mg, and Nb, and the second coating may be configured to include at least one element selected from among W, B, P, and Si, and more preferably, the first coating may be configured to include Al and Zr, and the second coating may be configured to include B.

[0047] In particular, in the case of B, it was confirmed that the stability difference due to the limited surface coverage caused by the first coating was resolved by excellent melting spreadability and wettability, thereby improving surface uniformity and suppressing side reactions with the electrolyte, resulting in significantly improved cycle characteristics of the secondary battery. In addition, it was confirmed that B plays a role in increasing the Li ion diffusion between grain boundaries by forming an LBO (Li-B oxide) layer and acting as a CEI (cathode electrolyte interface), thereby improving the rate characteristics and increasing the capacity. Since B has a relatively small ion size (0.098 nm) and freely diffuses near the surface bulk, it is highly likely to diffuse near the surface bulk when the temperature is above an appropriate level.

[0048] However, as the inventors of the present application have confirmed through various experiments and in-depth discussions, the above effect is highly dependent on the content of B in the second coating. If the content of B is too excessive, the surface bulk Li, i.e., Li in the core near the surface, may be consumed as the content increases, increasing the resistance. On the other hand, if the content of B is too small, the effect of coating formation is greatly reduced. In addition, since an appropriate amount of residual lithium can react with the coating raw material to form an LBO layer, the relationship between the content of B and the residual amount of lithium compounds on the surface of the active material particles was confirmed.

[0049] Therefore, based on the above facts, it was possible to establish conditions for forming an optimal surface through various experiments.

[0050]

[0051] In the first setting example, the positive electrode active material of the present invention may have a value of A1 wt%, a tap density of T g / cc, and A1 / T defined as C according to the following appropriate conditions in the calculation formula 1, where C may be in the range of 0.05 to 0.12.

[0052] [Appropriate conditions]

[0053] ① Sample pretreatment: Stir the sample and distilled water for 5 minutes.

[0054] - Sample: 5±0.01 g

[0055] - Distilled water: 100 g

[0056] ② Appropriate method

[0057] - Appropriate equipment: Metrohm (Model: 814 Sample Processor)

[0058] - Titration solution: 0.1N HCl

[0059] - Titration solution dispensing method: DET (Dynamic equivalence point titrations)

[0060] - Auto-completion conditions: pH 2.5

[0061] - Titration rate: Greatest

[0062] [Calculation Formula 1]

[0063]

[0064] In the above formula,

[0065] EP1 is the volume of titrant added to the first endpoint in the neutralization titration graph.

[0066] EP2 is the volume of titrant added to the second endpoint in the titration graph,

[0067] C ais the titrant concentration,

[0068] M1 is the molecular weight of LiOH.

[0069]

[0070] For example, as the B content in the second coating increases, the value of A1 tends to increase, and in the above, A1 can be preferably set to a range of 0.23 or less, and its lower limit can be set to, for example, 0.1 or more.

[0071] The above tap density can predict the sphericity of the particles, the uniformity or non-uniformity of the powder, etc., and if it is too low or high, there is a possibility of cycle deterioration due to side reactions caused by cracks or fine particles in the charge / discharge active material, and when the B content increases in the second coating, the tap density decreases due to coagulation between particles, so by comprehensively considering the above, the T can be set to a range of 2.2 or less, and its lower limit can be set to, for example, 1.5 or more, preferably 1.7 or more.

[0072]

[0073] In the second setting example, the positive electrode active material of the present invention may have a value of A2wt% in the calculation formula 2 according to the above-described appropriate conditions, and when A1 / A2 is defined as D, the D may be in the range of 0.6 or less.

[0074] [Calculation Formula 2]

[0075]

[0076] In the above formula,

[0077] EP1 is the volume of titrant added to the first endpoint in the neutralization titration graph,

[0078] EP2 is the volume of titrant added to the second endpoint in the neutralization titration graph.

[0079] C a is the titrant concentration,

[0080] M2 is the molecular weight of Li2CO3

[0081] As the B content in the second coating increases, the value of A2 tends to be somewhat constant, D is 0.6 or less as defined above, and its lower limit may be set to, for example, 0.2 or more, preferably 0.25 or more.

[0082] When A1 / A2×T is defined as E above, E can be set to a range of 0.45 or more, and its upper limit can be set to, for example, 1.5 or less, preferably 1.25 or less.

[0083]

[0084] In consideration of the first and second setting examples above, as a preferred example, the positive electrode active material of the present invention may be set to satisfy at least two conditions among the following characteristics 1 to 5, and more preferably, to satisfy all of the conditions of characteristics 1 to 5, when the value of the calculation formula 1 according to the above-described appropriate conditions is defined as A1 wt%, the value of the calculation formula 2 as A2 wt%, and the tap density is defined as T g / cc.

[0085] [Calculation Formula 1]

[0086]

[0087] [Calculation Formula 2]

[0088]

[0089] [Feature 1]

[0090] When A1 / T is defined as C, C is between 0.05 and 0.12.

[0091] [Feature 2]

[0092] When A1 / A2 is defined as D, D is less than or equal to 0.6.

[0093] [Feature 3]

[0094] A1 is less than or equal to 0.23

[0095] [Feature 4]

[0096] When A1 / A2×T is defined as E, E is greater than or equal to 0.45.

[0097] [Feature 5]

[0098] T is less than or equal to 2.2

[0099] The range of conditions within which excellent characteristics can be exhibited in relation to the above conditions can be confirmed through the experimental examples described below.

[0100]

[0101] In the active material of the present invention, the amount of the first coating may be in the range of 1 to 15% based on the total weight of the core, the amount of the second coating may be in the range of 2 to 15%, and it is preferable that the total amount of the first coating and the second coating does not exceed 20%.

[0102] The first coating and the second coating can be formed sequentially after the core is manufactured, and each raw material is applied and then fired at a respective appropriate temperature. Preferred examples can be specifically confirmed in the following examples.

[0103] Some of the elements forming the coating may be introduced into the core during the firing process to form doping. That is, some of the elements of the coating may be introduced into the core during the firing process for forming the coating to form dopants, so that at least one or more of the elements of the coating may be doped into the core and a structure may be formed in which the content is higher at the core surface than at the core center.

[0104] These coating elements may be elements of the first coating, elements of the second coating, or elements of both the first coating and the second coating, and the amount of doping may range from 0% to 15% based on the coating elements, for example.

[0105] In general, doping to improve the properties of the positive electrode active material is performed at the core manufacturing stage, and although it may vary depending on the type of elements, in the case of some dopants, it may be desirable to form them in a region adjacent to the surface of the core.

[0106] In the case of the present invention, doping is performed in such a way that elements move from a position on the surface toward the inside of the core during the sintering process, and therefore, as described above, a structure is created in which the dopant content is higher at the surface of the core than at the center of the core.

[0107] Therefore, when introduced in the direction of the core interior during the coating formation process as in the present invention and acts as a dopant, compared to the prior art, it is possible to reduce the cost of manufacturing the active material and exhibit higher doping performance under the same or similar conditions.

[0108]

[0109] The present invention also provides a secondary battery including the positive electrode active material. Since the overall configuration and manufacturing method of the secondary battery are known in the art, a detailed description thereof is omitted herein.

[0110] As described above, the positive electrode active material according to the present invention can ultimately improve the properties of the positive electrode active material to be used in a secondary battery, i.e., resistance, capacity, efficiency, lifespan characteristics, etc., by achieving surface stabilization and reducing side reactions with the electrolyte while suppressing oxygen desorption from the active material through complete coating of the core by the surface portion, and alleviating gelation of the active material slurry during the manufacturing process.

[0111] Figure 1 is a neutralization titration graph;

[0112] Figures 2a and 2b are FE-TEM cross-sectional images of the positive electrode active material of Example 4;

[0113] Figures 3a to 3c are EDS images of FE-TEM cross-sections, in which (a) is an FE-TEM cross-section image, (b) is an Al element image, and (c) is a Zr element image of the positive electrode active material of Example 5;

[0114] Figure 4 is an SEM image of the positive electrode active material of Comparative Example 7;

[0115] Figure 5 is an SEM image of the positive electrode active material of Example 5.

[0116] Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention, but the scope of the present invention is not limited thereto.

[0117]

[0118] [Example 1]

[0119] Ni based on NCM composition 0.75 Co 0.15 Mn 0.10 To manufacture the cathode active material, first, a nickel precursor, NiSO4, a cobalt precursor, CoSO4, and a manganese precursor, MnSO4, were added to water at a molar ratio of 0.75:0.15:0.10 to manufacture a nickel-cobalt-manganese hydroxide precursor aqueous solution.

[0120] By slowly adding sodium hydroxide aqueous solution dropwise while stirring the aqueous solution so that the raw materials are uniformly mixed and stirring the reaction mixture for 5 hours, the precursor aqueous solution is neutralized to obtain nickel-cobalt-manganese hydroxide, Ni. 0.75 Co 0.15 Mn 0.10 (OH)2 was precipitated.

[0121] The above-mentioned precursor (nickel-cobalt-manganese hydroxide) powder and LiOH·H2O (SQM) were weighed at a Li / Metal = 1.01 ratio and placed in a Henschel 10L device, and stirred at 3000 rpm for 30 min to prepare a mixture.

[0122] By heat-treating the mixture in an alumina crucible and firing it at 900°C for 10 hours under an O2 atmosphere, a cathode active material with high crystallinity and a developed layered structure was obtained during the firing. The cathode active material exhibits a single morphology during NCM production.

[0123] The manufactured positive electrode active material has the characteristic of being easily crushed by an external physical force, so it was possible to obtain a positive electrode active material in the form of single particles with an average particle size of 2 to 4 μm by crushing at high speed in an ACM crushing equipment.

[0124] For the positive electrode active material on the single particle manufactured above, Al(OH)3 equivalent to 0.1 mol of Al and ZrO2 equivalent to 0.15 mol of Zr were mixed, and secondary firing was performed at 600°C for 7 hours under an O2 atmosphere to manufacture a positive electrode active material having a surface layer formed.

[0125] Additionally, B2O3 in an amount of 0.06 mol B was mixed into the positive electrode active material on which the surface layer was formed, and calcined a third time at 300°C for 7 hours under an O2 atmosphere to obtain a single particle positive electrode active material including uniform coatings.

[0126]

[0127] [Example 2]

[0128] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of the Ni, Co, and Mn compound aqueous solution being 0.88:0.04:0.08. The difference from Example 1 is that the sintering condition during the heat treatment of the mixture is 900°C for 7 hours.

[0129]

[0130] [Example 3]

[0131] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering conditions for the heat treatment of the mixture are 850°C for 10 hours, and B2O3 in an amount equivalent to 0.01 mol of B is mixed during the third sintering.

[0132]

[0133] [Example 4]

[0134] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering conditions for the heat treatment of the mixture are 850°C for 10 hours, and B2O3 in an amount equivalent to 0.04 mol of B is mixed during the third sintering.

[0135]

[0136] [Example 5]

[0137] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering conditions for the heat treatment of the mixture are 850°C for 10 hours, and B2O3 in an amount equivalent to 0.06 mol of B is mixed during the third sintering.

[0138]

[0139] [Example 6]

[0140] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering conditions for the heat treatment of the mixture are 850°C for 10 hours, and B2O3 in an amount equivalent to 0.1 mol of B is mixed during the third sintering.

[0141]

[0142] [Example 7]

[0143] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering conditions for the heat treatment of the mixture are 850°C for 10 hours, and B2O3 in an amount equivalent to 0.15 mol of B is mixed during the third sintering.

[0144]

[0145] [Comparative Example 1]

[0146] A positive electrode active material was manufactured using the same manufacturing method as in Example 1. The difference from Example 1 is that no additional firing process was performed after manufacturing the positive electrode active material.

[0147]

[0148] [Comparative Example 2]

[0149] A positive electrode active material precursor was prepared in the same manner as the positive electrode active material precursor preparation method of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.88:0.04:0.08. The difference from Example 1 is that no separate additional calcination process was performed after preparation of the positive electrode active material.

[0150]

[0151] [Comparative Example 3]

[0152] A positive electrode active material precursor was prepared in the same manner as the method for preparing a positive electrode active material precursor of Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering condition for the heat treatment of the mixture was 850°C for 7 hours, and no separate additional sintering process was performed after preparing the positive electrode active material.

[0153]

[0154] [Comparative Example 4]

[0155] In the same manner as the method for producing a positive electrode active material precursor of Example 1, a positive electrode active material precursor was produced so that the ratio of the Ni, Co, and Mn compound aqueous solution was 0.93:0.05:0.02. The difference from Example 1 is that the firing condition during the heat treatment of the mixture was 850°C for 10 hours, and after producing the positive electrode active material, 0.15 mol of Al was mixed in the second firing, and then fired at 600°C for 7 hours in an O2 atmosphere to produce an active material having an Al coating layer, and no separate additional firing process was performed thereafter.

[0156]

[0157] [Comparative Example 5]

[0158] In the same manner as the method for preparing the positive electrode active material precursor of Example 1, the positive electrode active material precursor was prepared so that the ratio of the Ni, Co, and Mn compound aqueous solution was 0.93:0.05:0.02. The difference from Example 1 is that the firing condition during the heat treatment of the mixture was 850°C for 10 hours, and after preparing the positive electrode active material, 0.15 mol of Zr was mixed in the second firing, and then fired at 600°C for 7 hours in an O2 atmosphere to prepare an active material having a Zr coating layer, and no separate additional firing process was performed thereafter.

[0159]

[0160] [Comparative Example 6]

[0161] In the same manner as the method for producing a positive electrode active material precursor of Example 1, a positive electrode active material precursor was produced so that the ratio of the Ni, Co, and Mn compound aqueous solution was 0.93:0.05:0.02. The difference from Example 1 is that the firing condition during the heat treatment of the mixture was 850°C for 10 hours, and after producing the positive electrode active material, 0.1 mol of B was mixed with B2O3 during the second firing, and then fired at 300°C for 7 hours in an O2 atmosphere to produce an active material having a B coating layer formed thereon, and no separate additional firing process was performed thereafter.

[0162]

[0163] [Comparative Example 7]

[0164] A positive electrode active material precursor was prepared using the same method as in Example 1, with the ratio of Ni, Co, and Mn compound aqueous solutions being 0.93:0.05:0.02. The difference from Example 1 is that the sintering conditions for the heat treatment of the mixture were 850°C for 10 hours, and no additional sintering process was performed after the second sintering.

[0165]

[0166] [Experimental Example 1]

[0167] The particle size and BET of the positive electrode active materials manufactured in Examples 1 to 7 and Comparative Examples 1 to 7 were specified, and neutralization titration was performed under the following conditions. Based on the obtained values ​​(A1, A2, T), A1 / T (=C), A1 / A2 (=D), and A1 / A2×T (=E) was calculated and shown in Table 1 below. An example of a neutralization titration graph is presented in Fig. 1.

[0168]

[0169] ① Sample pretreatment

[0170] - Place 5±0.01 g of sample and 100 g of distilled water in a conical beaker containing a magnetic bar and stir for 5 minutes.

[0171] - Natural filtration is performed on the sample stirred in the filter paper.

[0172] - Place the filtered solution in a beaker and titrate.

[0173]

[0174] ② Appropriate method

[0175] - Appropriate equipment: Metrohm (Model: 814 Sample Processor)

[0176] - After filling the titrant with the titrant solution (0.1N HCl), remove air bubbles from the cylinder.

[0177] - Titration solution: 0.1N HCl

[0178] - Titration solution dispensing method: DET

[0179] - Auto-completion conditions: pH 2.5

[0180] - Titration rate: Greatest

[0181]

[0182] [Calculation Formula 1]

[0183]

[0184] [Calculation Formula 2]

[0185]

[0186] In the above formulas,

[0187] EP1 is the volume of titrant added to the first endpoint in the neutralization titration graph,

[0188] EP2 is the volume of titrant added to the second endpoint in the neutralization titration graph.

[0189] C a is the titrant concentration,

[0190] M1 is the molecular weight of LiOH (23.94 g / mole),

[0191] M2 is the molecular weight of Li2CO3 (73.89 g / mole).

[0192]

[0193]

[0194] As shown in Table 1 above, it can be confirmed that the positive electrode active materials of Examples 1 to 7 according to the present invention all satisfy the conditions that A1 is 0.23 or less, T is 2.2 or less, A1 / T (=C) is 0.05 to 0.12, A1 / A2 (=D) is 0.6 or less, and A1 / A2×T (=E) is 0.45 or more.

[0195] On the other hand, it can be confirmed that the positive electrode active materials of Comparative Examples 1 to 7 only satisfy the T-related conditions and do not satisfy most of the conditions.

[0196] The above figures are closely related to the coating content of B.

[0197] Specifically, when comparing Comparative Example 7 and Example 6, it can be confirmed that A2 of Example 6 is lower (0.447<0.525) than A2 of Comparative Example 7. This can be understood as a decrease in value as residual lithium on the surface is consumed by the additional B coating.

[0198] On the other hand, in the case of A1, it can be confirmed that Example 6 is higher than Comparative Example 7 (0.166>0.1). This is a tendency resulting from a unique phenomenon that occurs in the measurement method using titration. The present inventors studied this phenomenon and concluded that when B is coated, an LBO (Li-BO) phase is formed, and when calculated through Calculation Formula 1, it is affected by the LBO phase, and it was confirmed that even if residual lithium is consumed by B coating due to this phenomenon, A1 tends to increase. This tendency can be confirmed that A1 increases even when the B coating content is increased as in Examples 3 to 7.

[0199] In the case of A2, when comparing Comparative Example 7 with Examples 1 to 7, it was shown that the residual lithium on the surface of the positive electrode active material was consumed and reduced by the B coating, but no specific tendency was shown as the B coating content increased as in Examples 3 to 7.

[0200] In this way, specific conditions can be set by expressing them in a formula by the characteristics of A1 showing a tendency for B content and A2 showing no tendency.

[0201] Additionally, the B coating content is closely related to TD. Specifically, as the B coating content increases, the degree of cohesion between positive electrode active material particles increases, resulting in a decrease in TD. This trend can be confirmed in cases where the B coating content increases, as in Examples 4 to 7.

[0202] As seen above, since A1, A2, and TD are values ​​that change depending on the B coating content, when these are expressed in a specific formula, conditions that can set a certain range could be found. When the conditions that A1 / T (=C) is 0.05 to 0.12, A1 / A2 (=D) is 0.6 or less, and A1 / A2×T (=E) is 0.45 or more are each satisfied, the battery characteristics can be improved, but when these conditions are satisfied at the same time, the battery characteristics can be further improved.

[0203] In conclusion, the B coating has the advantage of improving battery characteristics by allowing the LBO layer to act as a CEI and cover the exposed non-coated area of ​​the positive electrode active material, thereby reducing side reactions with the electrolyte, and increasing the diffusion of Li ions between grain boundaries of B. However, if excessive B is added, there is a possibility that Li on the surface of the positive electrode active material will be consumed due to the increase in the B coating content, which will cause an increase in resistance, and therefore, there is a need to select an appropriate coating content.

[0204] Therefore, appropriate setting conditions can be derived through a correlation equation calculated using the above figures, and the coating content can be controlled to satisfy the conditions, thereby providing a cathode active material with optimized battery characteristics.

[0205] Whether these setting conditions are satisfied or not causes a large difference in the electrochemical characteristics in Experimental Example 4 described later.

[0206]

[0207] [Experimental Example 2]

[0208] When manufacturing slurry, the positive active material, conductive agent (Super-C), binder, and NMP were measured in a set ratio, and then mixed using a paste mixer (PM-300) at 750 rpm for 20 min to manufacture a slurry. The manufactured slurry was placed in the equipment, and measurement was performed after the spindle was fastened. Here, the spindle is the main axis of the equipment, the rotation axis, and the measured viscosity range differs depending on the type of spindle. Using spindle LV-4 (64), a viscosity range (cP) of 1K to 2M can be measured. The viscosity range means K=1,000, M=1,000,000 (LV model; manufacturer: Brookfield; for low viscosity meter, low torque value).

[0209] To measure the change over time of the slurry, approximately 80 ml of slurry was stored in a plastic container and viscosity measurements were performed at regular intervals. The change over time at room temperature was measured after leaving it for 60 minutes, and then after leaving it for 1, 2, 3, 5, and 7 days. To accelerate the change over time at high temperatures, the viscosity was also measured in a 40℃ oven. Unlike at room temperature, the viscosity was measured after leaving it for 60 minutes, and then after leaving it for 1 hour, 3 hours, and 24 hours. When measuring the change over time at high temperatures, the slurry must be sufficiently cooled before measurement. When measuring the change over time, the slurry must be stirred approximately 10 times before being mounted on the spindle, and viscosity measurements are performed after mounting. The measurement results are shown in Table 2 below.

[0210]

[0211] As shown in Table 2 above, the positive electrode active material of Comparative Example 7 gelled in 24 hours under conditions of RH 35% and 40°C, and showed an increase in viscosity of at least 6 times over time compared to Examples 5 and 6 under conditions of RH 20% and 20°C. Since Comparative Example 7 did not perform an additional B coating, it can be understood that gelling occurred due to the large amount of residual lithium present on the surface of the positive electrode active material.

[0212]

[0213] [Experimental Example 3]

[0214] For FE-TEM analysis of the positive electrode active materials manufactured in Examples 4 and 5, cross-sections were processed using a focused ion beam (FIB), and FE-TEM analysis was performed under the following measurement conditions. The results are shown in Figs. 2a to 2b and Figs. 3a to 3c.

[0215]

[0216] [FE-TEM measurement conditions]

[0217] - Model: Themis Z

[0218] - Accelerating voltage: 300 kV

[0219] - Probe current @ 1nm (nA*) : 0.6

[0220] - System evergy resolution: 0.7 eV

[0221] -STEM resolution (nm): 0.136

[0222] - EDS-Scan rate: medium (30s / scan), 5min

[0223]

[0224] Referring to the FE-TEM cross-sectional images of FIGS. 2a and 2b, the presence of an uneven and thick coating layer on the outer surface of the core in the positive electrode active material of Example 4 can be confirmed.

[0225] In addition, referring to the EDS images of the FE-TEM cross-sections of FIGS. 3a to 3c, in the positive electrode active material of Example 5, (a) shows the FE-TEM cross-section image, (b) shows the Al element, and (c) shows the Zr element image, and a coating in the form of a layer or dot can be confirmed on the particle surface.

[0226]

[0227] In addition, SEM images were obtained for the positive electrode active materials manufactured in Comparative Example 7 and Example 5, respectively, and these are disclosed in FIGS. 4 and 5, respectively. Since B cannot be measured through EDS, the presence of a coating can be indirectly confirmed through changes in surface morphology in the SEM images.

[0228] Referring to Fig. 4, some dot-shaped small particles can be seen on the surface of the active material particles, which means that some of the materials forming the first coating do not provide uniformity in the coating and form small aggregates.

[0229] On the other hand, referring to Fig. 5, it can be confirmed that such small particles have completely disappeared, which shows that the surface of the active material particles has been completely coated by the second coating having excellent melting spreadability and wettability.

[0230]

[0231] [Experimental Example 4]

[0232] The positive electrode active material was mixed with the conductive agent Super-P and the binder PVdF in a solvent N-methylpyrrolidone at a weight ratio of 93:5:2 to prepare a positive electrode active material slurry, which was then applied onto an aluminum current collector. After drying at 120°C and rolling, an electrode was manufactured. An electrode assembly was manufactured by using lithium metal as an anode together with the positive electrode manufactured above and interposing a porous polyethylene film as a separator therebetween, and the electrode assembly was placed inside a battery case, and an electrolyte was injected into the battery case to manufacture a lithium secondary battery. At this time, the electrolyte used was 1.0 M lithium hexafluorophosphate (LiPF6) dissolved in an organic solvent consisting of ethylene carbonate / dimethyl carbonate (EC / DMC mixing volume ratio = 1 / 1).

[0233]

[0234] ① Resistance measurement

[0235] For each lithium secondary battery manufactured in this way, charge and discharge were performed under the conditions of 0.2C, 4.25 V (charge) and 0.2C, 2.5 V (discharge), and the resistance was calculated by dividing the applied current by the voltage change between 0 and 65 seconds from the start of discharge (V / I=R). The results are shown in Table 3 below.

[0236]

[0237] ② Measurement of lifespan and resistance increase rate

[0238] Lithium secondary batteries were manufactured based on the positive electrode active materials manufactured in the comparative examples and examples above, and the cycle life and resistance increase rate were confirmed by repeating the cycle 50 times at 45°C under the conditions of 0.2C, 4.25 V (charge) and 0.2C, 2.5 V (discharge). The results are shown in Table 3 below.

[0239]

[0240]

[0241] As shown in Table 3 above, the positive electrode active materials of Examples 1 to 7 according to the present invention have generally superior efficiency of charge-to-discharge compared to the corresponding positive electrode active materials of Comparative Examples 1 to 7, and in particular, it can be confirmed that the cycle characteristics (lifespan) are superior and the resistance increase rate is low.

[0242] Among them, it can be seen that the positive electrode active materials of Examples 4 to 6 are excellent, and in particular, the positive electrode active material of Example 5 is excellent.

[0243]

[0244] When the battery evaluation results are examined together with the above conditions, in Examples 3 to 5, A1, C, D, and E tend to increase, and T tends to decrease, showing that the lifespan and resistance characteristics are improved as the residual lithium is reduced and the aggregation between the positive electrode active material particles increases due to the B coating. However, in Examples 5 to 7, the lifespan and resistance characteristics seem to deteriorate, and it can be expected that this is because the Li on the surface of the positive electrode active material is consumed due to the excessive B coating content, as seen in the continuous increase in A1. Therefore, it can be seen that it is important to set the above conditions within an appropriate range in order to optimize the battery characteristics.

[0245]

[0246] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A core including a transition metal and a surface portion formed on the surface of the core, wherein the surface portion comprises: A first coating applied to a portion of the core surface; and A second coating, which is applied to the remaining uncoated portion of the core surface and optionally to the outer surface of the first coating and has relatively good melting spreadability compared to the first coating; A cathode active material characterized by containing:

2. In the first paragraph, the cathode active material is characterized in that it includes non-agglomerated primary particles and optionally includes aggregated secondary particles.

3. In the first paragraph, the core is a cathode active material characterized by having a composition of the following chemical formula: Li[Li x M 1-x-y D y ]O z Q f In the above formula, M is one or more transition metal elements stable in four- or six-coordinate configurations; D is a dopant, at least one element selected from alkaline earth metals, transition metals of groups 3 to 12, post-transition metals and metalloids of groups 13 to 15, nonmetals of groups 14 to 16, and lanthanide elements; Q is an anion containing one or more elements among F, S, and P; -0.05≤x≤0.1, 0≤y≤0.1, 0≤x+y<1, 0≤z≤4, 0≤f≤1.

4. A cathode active material according to claim 1, characterized in that the second coating is a glassy coating.

5. In paragraph 1, The first coating comprises at least one element selected from the group consisting of an alkaline earth metal, a transition metal, a post-transition metal, and a lanthanide; A cathode active material, characterized in that the second coating comprises at least one element selected from the group consisting of a transition metal, a metalloid, and a non-metal.

6. In paragraph 1, The above first coating contains one or more elements selected from the group consisting of Al, Ti, Zr, Co, Mn, V, Cr, Ni, Cu, Y, Mg, and Nb; A cathode active material, characterized in that the second coating comprises at least one element selected from the group consisting of W, B, P, and Si.

7. A cathode active material according to claim 6, characterized in that the first coating includes Al and Zr, and the second coating includes B.

8. In paragraph 1, A cathode active material characterized in that when the value of the calculation formula 1 according to the following appropriate conditions is defined as A1 wt%, the tap density as T g / cc, and A1 / T as C, C is in the range of 0.05 to 0.12: [Appropriate conditions] ① Sample pretreatment: Stir the sample and distilled water for 5 minutes. - Sample: 5±0.01 g - Distilled water: 100 g ② Appropriate method - Appropriate equipment: Metrohm (Model name: 814 Sample Processor) - Titration solution: 0.1N HCl - Titration solution dispensing method: DET (Dynamic equivalence point titrations) - Optimum auto-completion conditions: pH 2.5 - Titration rate: Greatest [Calculation formula 1] In the above formula, EP1 is the volume of titrant added to the first endpoint in the neutralization titration graph, EP2 is the volume of titrant added to the second endpoint in the titration graph. C a is the titrant concentration, M1 is the molecular weight of LiOH.

9. In clause 8, a cathode active material characterized in that A1 is 0.23 or less 10. In the 8th paragraph, a cathode active material characterized in that when the value of the calculation formula 2 according to the above appropriate conditions is defined as A2wt% and A1 / A2 as D, D is 0.6 or less: [Calculation formula 2] In the above formula, EP1 is the volume of titrant added to the first endpoint in the neutralization titration graph, EP2 is the volume of titrant added to the second endpoint in the titration graph. C a is the titrant concentration, M2 is the molecular weight of Li2CO3.

11. A positive electrode active material, characterized in that in clause 10, when A1 / A2×T is defined as E, E is 0.45 or more.

12. A cathode active material, characterized in that in clause 8, T is 2.2 or less.

13. In paragraph 1, A cathode active material characterized by satisfying at least two conditions among the following characteristics 1 to 5, when the value of the calculation formula 1 according to the following appropriate conditions is defined as A1 wt%, the value of the calculation formula 2 as A2 wt%, and the tap density as T g / cc: [Appropriate conditions] ① Sample pretreatment: Stir the sample and distilled water for 5 minutes. - Sample: 5±0.01 g - Distilled water: 100 g ② Appropriate method - Appropriate equipment: Metrohm (Model name: 814 Sample Processor) - Titration solution: 0.1N HCl - Titration solution dispensing method: DET (Dynamic equivalence point titrations) - Optimum auto-completion conditions: pH 2.5 - Titration rate: Greatest [Calculation formula 1] [Calculation formula 2] In the above formulas, EP1 is the volume of titrant added to the first endpoint in the neutralization titration graph, EP2 is the volume of titrant added to the second endpoint in the titration graph. C a is the titrant concentration, M1 is the molecular weight of LiOH, M2 is the molecular weight of Li2CO3. [Feature 1] When A1 / T is defined as C, C is between 0.05 and 0.

12. [Feature 2] When A1 / A2 is defined as D, D is less than or equal to 0.6 [Feature 3] A1 is less than or equal to 0.23 [Feature 4] When A1 / A2×T is defined as E, E is greater than or equal to 0.

45. [Feature 5] T is less than or equal to 2.2 14. A cathode active material according to claim 13, characterized in that it satisfies all of the conditions of features 1 to 5.

15. A cathode active material characterized in that, in the first paragraph, at least one of the elements of the coating is doped into the core and has a higher content at the core surface than at the core center.

16. A secondary battery characterized by containing a positive electrode active material according to Article 1.

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