Positive electrode active material and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material which is improved in electrochemical properties and stability.SOLUTION: There is provided a positive electrode active material which includes a lithium composite oxide containing a primary particle containing at least Li, Ni, and B, and a secondary particle in which a plurality of the primary particles are aggregated. A coating layer containing a boron-containing oxide presents on at least part of a surface of the secondary particle. A content of boron (B) in the lithium composite oxide is 0.09 mol% or more and 0.49 mol% or less, and a content of lithium impurities (LiOH) in the lithium composite oxide is 11,661 ppm or less. Weight loss is measured under normal pressure in an Ar atmosphere from 25°C to 350°C at a temperature increase rate of 10°C / min. Here, the onset temperature at which a weight loss (thermal decomposition) peak appears is 231.2°C or above.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material containing a lithium composite oxide with improved electrochemical properties and stability, and a lithium secondary battery containing the same. More specifically, the present invention relates to a positive electrode active material and a lithium secondary battery containing the same in which electrochemical properties and stability are improved by removing at least a portion of the coating layer and lithium-containing impurities present on the surface of the lithium composite oxide. [Background technology]

[0002] Batteries store electrical energy by using electrochemically reactive materials at the positive and negative electrodes. A typical example of such a battery is the lithium-ion secondary battery, which stores electrical energy through the difference in chemical potential that occurs when lithium ions are intercalated / deintercalated at the positive and negative electrodes.

[0003] The lithium secondary battery described above is manufactured by using materials capable of reversible intercalation / deintercalation of lithium ions as the positive electrode and negative electrode active materials, and by filling the space between the positive electrode and the negative electrode with an organic electrolyte or a polymer electrolyte.

[0004] Typical materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. These lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or oxides in which Ni, Co, Mn, or Al are composited, as disclosed in Korean Patent Publication No. 10-2015-0069334 (published June 23, 2015).

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency. However, it has the disadvantage of being expensive due to the resource limitations of cobalt used as a raw material, thus limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but have problems such as small capacity and poor high-temperature characteristics. In addition, LiNiO2-based cathode active materials exhibit battery characteristics with high discharge capacity, but are difficult to synthesize due to the cation mixing problem between Li and transition metals, and thus have significant problems in rate characteristics.

[0007] In addition, a large amount of Li by-products will be generated according to the degree of deepening of such cation mixing. Most of the Li by-products contain LiOH and Li2CO3, which can cause gelation during the manufacture of the cathode paste or cause gas generation by repeated charge and discharge after electrode manufacture. In addition, the residual Li2CO3 among the Li by-products acts as a cause for increasing the swelling phenomenon of the cell and deteriorating the life characteristics.

[0008] In order to compensate for such disadvantages, the demand for High-Ni cathode active materials with a Ni content of 50% or more as the cathode active material of secondary batteries has begun to increase. However, such High-Ni cathode active materials exhibit high-capacity characteristics, but there is a problem that the increase in the Ni content in the cathode active material brings structural instability due to Li / Ni cation mixing. Due to such structural instability of the cathode active material, lithium secondary batteries may deteriorate rapidly not only at high temperatures but also at room temperature.

[0009] Therefore, it is necessary to develop a cathode active material to complement the problems of such High-Ni cathode active materials. Summary of the Invention Problems to be Solved by the Invention

[0010] In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles plays a leading role in the market, the demand for cathode active materials used in lithium secondary batteries is also continuously changing.

[0011] For example, conventionally, lithium secondary batteries using LFPs have been mainly used from the perspective of ensuring safety, but recently, there has been a growing trend to use nickel-based lithium composite oxides, which have a higher energy capacity per unit weight compared to LFPs.

[0012] Thus, the objective of the present invention is to provide a High-Ni cathode active material that can improve the electrochemical properties and stability of lithium secondary batteries.

[0013] Another object of the present invention is to provide a lithium secondary battery that uses a positive electrode containing a lithium composite oxide as defined in this application. [Means for solving the problem]

[0014] Conventionally, a technique has been proposed to improve stability by reducing surface side reactions of the positive electrode active material by ensuring that light elements, such as boron, exist in oxide form within the positive electrode active material (Korean Patent Registration No. 10-1651338, published August 25, 2016).

[0015] However, while forming the light element-containing oxide on the surface of the positive electrode active material can reduce side reactions between the positive electrode active material and the electrolyte, it also presents the problem that the reaction between the positive electrode active material and the light element-containing raw material increases the amount of lithium-containing impurities on the surface of the positive electrode active material.

[0016] This problem arises because, although at least a portion of the lithium-containing impurities present on the surface of the positive electrode active material reacts with the light element-containing raw material to convert them into light element-containing oxides, the amount of lithium-containing impurities converted into light element-containing oxides is extremely small compared to the amount of lithium-containing impurities produced by the reaction between the positive electrode active material and the light element-containing raw material.

[0017] Accordingly, according to one aspect of the present invention, the light element-containing oxide is formed on at least a portion of the surface of primary and / or secondary particles through heat treatment of a mixture of the lithium composite oxide precursor and light element-containing raw material contained in the positive electrode active material, and then the excess light element-containing oxide and lithium-containing impurities are removed from the positive electrode active material to provide a positive electrode active material with improved electrochemical properties and stability.

[0018] In one embodiment, the primary particle may be represented by the following chemical formula 1.

[0019] [Chemical formula 1] Li w Ni 1-(x+y+z+z′) Co x B y M1 z M2 z′ O2

[0020] (Here, M1 is at least one selected from Mn and Al, M2 is at least one selected from Mn, Ba, Ce, Hf, Ta, Cr, F, Mg, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, and M1 and M2 are different elements from each other, 0.5≦w≦1.5, 0≦x≦0.50, 0 <y≦0.20、0≦z≦0.20、0≦z′≦0.20である)

[0021] On the other hand, the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl can satisfy the following formula 1.

[0022] [Formula 1] r < (19, 153 × x 1) + x 2

[0023] (Here, x1 is the boron content (mol%) in the lithium composite oxide before washing with water, x2 is the amount of LiOH (ppm) calculated from the amount of HCl consumed corresponding to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing with water, and r is the amount of LiOH eluted from the lithium composite oxide after washing with water (ppm))

[0024] Furthermore, the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl can satisfy the following equation 2.

[0025] [Formula 2] y1≦r≦y1+(y2×(1-y3)×18,429)

[0026] (Here, y1 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing with water; y2 is the boron content (mol%) in the lithium composite oxide before washing with water; y3 is the rate of change in the boron content in the lithium composite oxide before and after washing with water, and has a value greater than 0 and less than or equal to 0.90; and r is the amount of LiOH eluted from the lithium composite oxide after washing with water (ppm).)

[0027] Furthermore, according to another aspect of the present invention, a positive electrode containing the positive electrode active material described above is provided.

[0028] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery using the positive electrode described above is provided. [Effects of the Invention]

[0029] According to the present invention, after forming light element-containing oxides in the positive electrode active material on at least a portion of the surface of primary and / or secondary particles through heat treatment of a mixture of the positive electrode active material precursor and light element-containing raw material, the electrochemical properties and stability can be improved by removing excess light element-containing oxides and lithium-containing impurities from the positive electrode active material.

[0030] In particular, the positive electrode active material according to the present invention can be doped with light elements in the positive electrode active material by mixing the precursor of the positive electrode active material with the light element-containing raw material and heat-treating it during the precursor calcination stage of the positive electrode active material, while at the same time the light element-containing oxide in the positive electrode active material is concentrated on the surface and / or interface of the primary particles.

[0031] Furthermore, by controlling the content of the light element-containing oxide present on the surface of the secondary particles, it is possible to prevent the electrochemical properties of the positive electrode active material from deteriorating due to the light element-containing oxide and / or the lithium-containing impurities. [Brief explanation of the drawing]

[0032] [Figure 1] This is a schematic diagram of a positive electrode active material according to one embodiment of the present invention, illustrating the process by which a coating layer containing a boron-containing oxide and lithium-containing impurities are removed from the surface of secondary particles. [Figure 2] This is a differential graph obtained by neutralization titration before washing with water the lithium composite oxide constituting the positive electrode active material in Example 1, Example 2, and Comparative Example 1. [Modes for carrying out the invention]

[0033] The following describes in more detail the positive electrode active material for lithium secondary batteries with improved electrochemical properties and stability according to the present invention, and the lithium secondary battery containing the same.

[0034] positive electrode active material According to one aspect of the present invention, a positive electrode active material is provided which includes secondary particles formed by the aggregation of multiple primary particles, which are lithium composite oxides capable of lithium intercalation and deintercalation.

[0035] Here, the primary particle refers to a single grain (grain or crystallite), and the secondary particle refers to an aggregate formed by the aggregation of multiple primary particles. The primary particle may have a rod-like, elliptical, and / or amorphous shape. Voids and / or grain boundaries may exist between the primary particles that make up the secondary particle.

[0036] For example, the primary particles can form internal voids by separating themselves from adjacent primary particles within the secondary particles. Alternatively, the primary particles can form surfaces within the secondary particles by contacting the internal voids without forming grain boundaries with adjacent primary particles. On the other hand, the surface of the primary particles on the outermost surface of the secondary particles that is exposed to the outside air forms the surface of the secondary particles.

[0037] Here, the average major axis diameter of the primary particles is within the range of 0.1 μm to 5 μm, preferably 0.1 μm to 2 μm, thereby realizing the optimal density of the positive electrode produced using the positive electrode active material according to various embodiments of the present invention. The average particle size of the secondary particles varies depending on the number of aggregated primary particles, but may be between 1 μm and 30 μm.

[0038] On the other hand, the positive electrode active material may be in a bimodal form containing small particles which are secondary particles with an average particle size of 5 μm or less and large particles which are secondary particles with an average particle size of 12 μm or more.

[0039] In one embodiment, the primary particles may be a lithium composite oxide containing at least Li, Ni, and B. More specifically, the primary particles may be represented by the following chemical formula 1.

[0040] [Chemical Formula 1] Li w Ni 1-(x+y+z+z′) Co x B y M1 z M2 z′ O2

[0041] (Here, M1 is at least one selected from Mn and Al, M2 is at least one selected from Mn, Ba, Ce, Hf, Ta, Cr, F, Mg, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, M1 and M2 are different elements from each other, 0.5 ≦ w ≦ 1.5, 0 ≦ x ≦ 0.50, 0 < y ≦ 0.20, 0 ≦ z ≦ 0.20, 0 ≦ z′ ≦ 0.20)

[0042] If the positive electrode active material is in a bimodal form containing small particles and large particles, the concentration of M1 in the small particles may be greater than the concentration of M1 in the large particles.

[0043] Generally, for light elements present in the positive electrode active material, typically light elements such as boron, the content in the positive electrode active material can be predicted based on the content of the boron-containing raw material substance added during the production of the positive electrode active material. There is a problem that it is difficult to specifically confirm how the light elements exist in the positive electrode active material compared to other elements.

[0044] However, according to the present invention, by mixing the precursor (hydroxide precursor or calcined precursor) of the lithium composite oxide with a light element-containing raw material substance at the firing stage and then performing heat treatment, as represented by Chemical Formula 1, the light elements are doped into the primary particles, and at the same time, a coating layer containing a light element-containing oxide in the positive electrode active material can be concentratedly present on the surface and / or interface of the primary particles.

[0045] Furthermore, when the precursor (hydroxide precursor or roasting precursor) of the lithium composite oxide is mixed with a light element-containing raw material during the calcination stage and then heat-treated, a coating layer containing the light element-containing oxide can be formed on at least a portion of the surface of the secondary particles.

[0046] As described above, the coating layer may contain at least one boron-containing oxide represented by the following chemical formula 2.

[0047] [Chemical formula 2] Li a B b O c

[0048] (Here, 0 ≤ a ≤ 8, 0 <b≦8、2≦c≦13である) In other words, the boron-containing oxide is a borate-based compound or an LBO (lithium borate)-based compound, and non-limiting examples of the borate-based compound or LBO (lithium borate)-based compound include B2O3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7, and Li2B8O 13 These are some examples.

[0049] The coating layer is present on at least a portion of the surface of the primary particles and / or the secondary particles, and the coating layer can be defined as the region where the boron-containing oxide represented by chemical formula 2 is present.

[0050] The coating layer can continuously or discontinuously coat at least a portion of the surface of the primary particles and / or the secondary particles, and if the coating layer is discontinuous, it may exist in an island form. The coating layer may also exist in a solid solution form that does not form a boundary with the primary particles and / or the secondary particles, but is not necessarily so.

[0051] The coating layer is not formed by calcining the precursor of the lithium composite oxide (hydroxide precursor or roasting precursor), then mixing the calcined product with a boron-containing raw material and heat-treating it, but rather by mixing the precursor of the lithium composite oxide (hydroxide precursor or roasting precursor) with a boron-containing raw material and heat-treating it.

[0052] On the other hand, after heat treatment of the mixture of the lithium composite oxide precursor (hydroxide precursor or roasting precursor) and the boron-containing raw material, at least a portion of the coating layer present on at least a portion of the surface of the primary particles and / or the secondary particles can be removed by washing with water.

[0053] In particular, by washing the lithium composite oxide on which a coating layer containing a boron-containing oxide is formed with water, the coating layer present on the surface and / or interface of the primary particles, which is located in a region relatively closer to the surface of the secondary particles, can be further removed compared to the coating layer present on the surface and / or interface of the primary particles, which is located in a region relatively closer to the center of the secondary particles.

[0054] Furthermore, by washing the lithium composite oxide on which a coating layer containing boron oxide is formed with water, the coating layer present on the surface of the secondary particles can be further removed compared to the coating layer present on the surface and / or interface of the primary particles, which is present in a region relatively closer to the center of the secondary particles.

[0055] Through the washing described above, some of the light element-containing oxides are removed from the surface of the positive electrode active material, particularly the secondary particles, exposing the surface of the secondary particles. Along with this, lithium-containing impurities present on the surface of the secondary particles can be removed.

[0056] As a result, the boron content in the positive electrode active material after washing can be reduced compared to the boron content in the positive electrode active material before washing, and the rate of change (reduction rate) of the boron content in the positive electrode active material after washing may be greater than 0 and less than or equal to 0.90 (greater than 0% and less than or equal to 95%), preferably 0.10 to 0.90 (10% to 95%), and more preferably 0.20 to 0.90 (20% to 90%).

[0057] The residual boron content in the lithium composite oxide after washing the positive electrode active material is preferably at least 0.3 mol% or less. However, the cases where the residual boron content in the lithium composite oxide is 0.3 mol% or less and the boron content in the lithium composite oxide before washing is 0.3 mol% or less must be distinguished from each other because the distribution of boron-containing oxides and lithium-containing impurities on the surface of the primary and / or secondary particles constituting the lithium composite oxide, as well as the morphology of the coating layer containing boron-containing oxides, are different.

[0058] If the rate of reduction in the boron content in the positive electrode active material due to water washing exceeds 95%, the content of boron-containing oxides in the positive electrode active material, particularly on the surface of the secondary particles, becomes excessively low, making it difficult to realize the effect of suppressing surface side reactions by the boron-containing oxides.

[0059] On the other hand, if the lithium composite oxide is not washed with water after forming a boron-containing oxide on its surface, or if the boron content in the positive electrode active material is hardly reduced as a result of washing the positive electrode active material with water, there is a risk that the electrochemical properties of the positive electrode active material may actually deteriorate due to the excessive presence of boron-containing oxide or lithium-containing impurities on the surface of the secondary particles.

[0060] In one embodiment, the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl can satisfy the following formula 1.

[0061] [Formula 1] r < (19, 153 × x 1) + x 2

[0062] (Here, x1 is the boron content (mol%) in the lithium composite oxide before washing with water. x2 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing with water. r is the amount of LiOH eluted from the lithium composite oxide after washing with water (ppm).

[0063] In this case, the neutralization titration method may be performed using 0.1N HCl per 5g of the positive electrode active material, and the amount of LiOH eluted can be measured by a differential graph of the change in pH due to the amount of HCl added, obtained through the neutralization titration method.

[0064] In Equation 1, the constant "19,153" is used to calculate the increase in LiOH due to the boron content in the lithium composite oxide before washing.

[0065] As described above, the higher the blending ratio of the light element-containing raw material reacting with the lithium composite oxide precursor, the higher the boron content in the lithium composite oxide and the boron-containing oxide content in the lithium composite oxide. The higher the boron-containing oxide content in the lithium composite oxide, the greater the amount of LiOH eluted during neutralization titration according to the following reaction equation 1.

[0066] [Reaction Equation 1] Li3BO3 + H2O → LiOH + H3BO3

[0067] On the other hand, x2 is the amount of LiOH (ppm) calculated from the amount of HCl consumed corresponding to the x-axis value of the first peak that appears at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing with water. The amount of HCl consumed corresponding to the x-axis value of the first peak that appears at the smallest x-axis value is determined not by the LiOH converted from Li3BO3 by reaction equation 1, but by the amount of LiOH present in the lithium composite oxide before washing with water.

[0068] For example, referring to the differential graph corresponding to Example 1 in Figure 2, the amount of HCl consumed corresponding to the x-axis value of the first peak appearing at the minimum x-axis value can be converted to the amount of LiOH present in the lithium composite oxide. The amount of HCl consumed corresponding to the difference between the x-axis value of the first peak appearing at the minimum x-axis value and the x-axis value of the second peak that appears next can be converted to the amount of LiOH converted from Li3BO3 by reaction equation 1. Furthermore, the amount of HCl consumed corresponding to the difference between the x-axis value of the second peak and the x-axis value of the third peak that appears next can be converted to the amount of Li2CO3 in the lithium-containing impurities.

[0069] Therefore, if the boron content (mol%) in the lithium composite oxide before washing is 1.0 mol%, and the amount of LiOH (ppm) calculated from the HCl consumption corresponding to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing is 8,638 ppm, then the amount of LiOH calculated from the right-hand side of Equation 1 may be 27,791 ppm.

[0070] In this case, the amount of LiOH eluted from the positive electrode active material containing the lithium composite oxide after washing with water, as measured by a neutralization titration method using HCl, is preferably less than 27,791 ppm.

[0071] If the boron content (mol%) in the lithium composite oxide before washing is 1.0 mol%, and the amount of LiOH (ppm) calculated from the HCl consumption corresponding to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing is 8,638 ppm, then if the amount of LiOH eluted by the neutralization titration method using HCl from the positive electrode active material containing the washed lithium composite oxide is 27,791 ppm or more, then there is a risk that the electrochemical properties of the positive electrode active material may actually deteriorate due to the excessive presence of the boron-containing oxide and / or the lithium-containing impurities on the surface of the secondary particles.

[0072] More specifically, the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl can satisfy the following equation 2.

[0073] [Formula 2] y1≦r≦y1+(y2×(1-y3)×18,429)

[0074] (Here, y1 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the smallest x-axis value in the differential graph showing the differential of the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing with water. y2 is the boron content (mol%) in the lithium composite oxide before washing with water. y3 is the rate of change in the boron content in the lithium composite oxide before and after washing with water, and has a value greater than 0 and less than or equal to 0.90. r is the amount of LiOH eluted from the lithium composite oxide after washing with water (ppm).

[0075] In equation 2 above, the constant "18,429" is used to calculate the increase in LiOH due to the boron content in the lithium composite oxide after washing with water.

[0076] y1 corresponds to x2 in equation 1, and is the amount of LiOH (ppm) calculated from the amount of HCl consumed corresponding to the x-axis value of the first peak that appears at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing with water. The amount of HCl consumed corresponding to the x-axis value of the first peak that appears at the smallest x-axis value is determined not by the LiOH converted from Li3BO3 by reaction equation 1, but by the amount of LiOH present in the lithium composite oxide after washing with water.

[0077] Therefore, if the rate of change in the boron content in the lithium composite oxide after washing is 0.88 (88%), and the amount of LiOH (ppm) calculated from the amount of HCl consumed corresponding to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing is 2.34 ppm, then the range of the amount of LiOH calculated from Equation 2 may be 2,734 ppm or more and 4,945 ppm or less.

[0078] In this case, the amount of LiOH eluted from the positive electrode active material containing the lithium composite oxide after washing with water, measured by a neutralization titration method using HCl, is preferably 2,734 ppm or more and 4,945 ppm or less, more preferably greater than 2,734 ppm and 4,945 ppm or less.

[0079] If the boron content (mol%) in the lithium composite oxide before washing is 1.0 mol%, and the rate of change in the boron content in the lithium composite oxide after washing is 0.88 (88%), and the amount of LiOH (ppm) calculated from the HCl consumption corresponding to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing is 2.34 ppm, then if the washing process for the positive electrode active material is carried out excessively, the amount of LiOH eluted from the positive electrode active material containing the washed lithium composite oxide by the neutralization titration method using HCl may be less than 2.34 ppm.

[0080] In this case, while the amount of lithium-containing impurities present on the surface of the lithium composite oxide can be reduced, there is a risk of damaging the surface of the lithium composite oxide and reducing its electrochemical properties and stability. Furthermore, since most of the boron-containing oxide is removed from the surface of the lithium composite oxide, it may be difficult to realize the effect of suppressing surface side reactions.

[0081] On the other hand, if the amount of LiOH eluted from the positive electrode active material containing a lithium composite oxide, after being washed with water under the same conditions, exceeds 4,945 ppm by a neutralization titration method using HCl, there is a risk that the boron-containing oxide and / or the lithium-containing impurities will remain in excess on the surface of the secondary particles, which may actually degrade the electrochemical properties of the positive electrode active material.

[0082] In other embodiments, the coating layer may further contain at least one metal oxide represented by the following chemical formula 3.

[0083] [Chemical formula 3] Li d M3 e O f

[0084] (Here, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd. 0 ≤ d ≤ 8, 0 <e≦8、2≦f≦13である。)

[0085] The metal oxide can improve the electrochemical properties of the positive electrode active material by reducing lithium-containing impurities present on the surface of the positive electrode active material and by acting as a diffusion path for lithium ions.

[0086] The metal oxide may be formed by further mixing the M3-containing raw material before heat-treating the mixture of the lithium composite oxide precursor (hydroxide precursor or roasting precursor) and the B-containing raw material. Alternatively, the metal oxide may be formed by heat-treating the mixture with the lithium composite oxide, which has a boron-containing oxide formed on its surface, either before or after washing.

[0087] The metal oxide may be present on at least a portion of the surface of the primary and / or secondary particles of the lithium composite oxide, and may be present in the same or a different layer as the boron-containing oxide.

[0088] The aforementioned metal oxide is an oxide in which lithium and an element represented by M3 are composited, or an oxide of M3, and the aforementioned metal oxide is, for example, Li a W b O c Li a Zr b O c Li a Ti b O c Li a Ni b O c Li a Co b O c Li a Al b O c Co b O c , Al b O c , W b O c , Zr b O c or action b O c Other examples are also acceptable, but the examples described above are merely for convenience to aid understanding, and the metal oxides defined in this application are not limited to the examples described above.

[0089] Furthermore, the metal oxide may be an oxide in which lithium and at least two elements represented by M3 are combined, or it may further contain an oxide in which lithium and at least two elements represented by M3 are combined. An oxide in which lithium and at least two elements represented by M3 is, for example, Li a (W / Ti) b O c Li a (W / Zr) b O c Li a (W / Ti / Zr) b O c Li a (W / Ti / B) b O c Other options are also acceptable, but they are not necessarily limited to these.

[0090] The positive electrode active material according to the present invention is characterized by being composed of a lithium composite oxide comprising primary particles containing at least Li, Ni, and B, and secondary particles formed by aggregation of the primary particles, wherein a coating layer containing a boron-containing oxide is present on at least a portion of the surface of the secondary particles, and at least a portion of the coating layer is removed from the surface of the secondary particles.

[0091] The coating layer can be formed by heat treatment of a mixture of the lithium composite oxide precursor and a boron-containing raw material, and at least a portion of the lithium composite oxide can be removed from the surface of the secondary particles by washing the lithium composite oxide with water.

[0092] In this case, the ratio of the porosity of the secondary particles after washing with water to the porosity of the secondary particles before washing with water, relative to the lithium composite oxide, may be 1.7 or more.

[0093] In other words, as a result of washing the lithium composite oxide with water, some of the boron-containing oxide on the surface of the secondary particles is removed, and at the same time, some of the boron-containing oxide present inside the secondary particles is also removed. The boron-containing oxide present inside the secondary particles may also be present as a coating layer on the surface of the primary particles.

[0094] The porosity within the secondary particles can be increased by removing a portion of the boron-containing oxide present inside the secondary particles through the washing of the lithium composite oxide with water.

[0095] In this case, if the ratio of the porosity of the secondary particles after washing with water to the porosity of the secondary particles before washing with water is less than 1.7 for the lithium composite oxide, there is a risk that the electrochemical properties of the positive electrode active material will deteriorate due to the excessive retention of the boron-containing oxide and / or the lithium-containing impurities inside the secondary particles.

[0096] On the other hand, if the ratio of the porosity within the secondary particles after washing to the porosity within the secondary particles before washing exceeds 2.0, it may actually damage the surface and interior of the lithium composite oxide, reducing its electrochemical properties and stability. Furthermore, because most of the boron-containing oxide is removed from the interior of the lithium composite oxide, it may be difficult to realize the effect of suppressing side reactions at the interface of the primary particles present within the secondary particles.

[0097] Lithium-ion battery According to another aspect of the present invention, a positive electrode can be provided comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may contain a lithium composite oxide according to the various embodiments of the present invention described above as the positive electrode active material. Therefore, a detailed explanation of the lithium composite oxide will be omitted, and only the remaining components not mentioned above will be described below. Also, for convenience, the lithium composite oxide mentioned above will be referred to as the positive electrode active material below.

[0098] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes 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 may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0099] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0100] In this case, the positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When included in this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0101] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0102] The binder plays a role in improving adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0103] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0104] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0105] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0106] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0107] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0108] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing the battery container.

[0109] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0110] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0111] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and, if necessary, a selective binder, to the negative electrode current collector.

[0112] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0113] The aforementioned negative electrode active material may be present in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0114] The binder may be added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0115] The conductive material may be added as a component to further improve the conductivity of the negative electrode active material, in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskey such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0116] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0117] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0118] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may 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, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0119] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0120] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0121] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 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 may 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, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0122] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. 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.

[0123] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0124] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0125] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0126] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0127] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0128] Manufacturing Example 1. Manufacturing of positive electrode active material Example 1 Spherical Ni 0.80 Co 0.12 Mn 0.08 (OH)2 hydroxide precursor was synthesized. Specifically, in a 90L reactor, 25 wt% NaOH and 30 wt% NH4OH were added to a 1.5M aqueous solution of complex transition metal sulfuric acid, which was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 80:12:8. The pH in the reactor was maintained at 11.5, the reactor temperature was maintained at 60°C, and an inert gas, N2, was added to the reactor to prevent oxidation of the produced precursor. After the synthesis and stirring were completed, the solution was filtered through a filter press (F / P) and Ni 0.80 Co 0.12 Mn 0.08 (OH)2 hydroxide precursor (nickel composite precursor) was obtained.

[0129] Next, the nickel composite precursor was mixed with LiOH (Li / (Ni+Co+Mn)mol ratio=1.01) as a lithium compound and 1.0 mol% H3BO3 relative to the nickel composite precursor. Then, the mixture was heat-treated in a calcination furnace for 12 hours at a rate of 2°C per minute up to 700°C while maintaining an O2 atmosphere, and then crushed to obtain a lithium composite oxide.

[0130] Next, the lithium composite oxide was washed with distilled water, filtered, and then dried.

[0131] Specifically, the washing of the lithium composite oxide was carried out as follows. ·Primary water washing First, the lithium composite oxide and distilled water were mixed in a 1:1 weight ratio, and then stirred at 25°C for 30 minutes to produce a mixture. Next, the mixture was added to the aqueous solution of the composite transition metal sulfuric acid used in the precursor synthesis, and at the same time, NaOH and NH4OH were added and stirred for 30 minutes.

[0132] • Secondary rinsing and filtration After the initial washing was completed, the lithium composite oxide was washed with distilled water of the same weight as the total weight of the lithium composite oxide, filtered through F / P equipment, and then dried to finally obtain the positive electrode active material.

[0133] Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that H3BO3 was mixed with the nickel composite precursor to a concentration of 0.5 mol%.

[0134] Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that H3BO3 was mixed with the nickel composite precursor to a concentration of 2.0 mol%.

[0135] Example 4 The positive electrode active material was manufactured in the same manner as in Example 1, except that during the secondary washing, the lithium composite oxide was washed with distilled water at a weight twice that of the total weight of the lithium composite oxide.

[0136] Example 5 The positive electrode active material was manufactured in the same manner as in Example 1, except that during the secondary washing, the lithium composite oxide was washed with distilled water at a weight of 0.5 times the total weight of the lithium composite oxide.

[0137] Example 6 A positive electrode active material was produced in the same manner as in Example 1, except that after washing with water and drying the lithium composite oxide, 0.15 mol% Al2O3 and 0.3 mol% TiO2 were mixed with the lithium composite oxide, and then the mixture was further heat-treated in a firing furnace for 8 hours at a rate of 2°C per minute up to 680°C while maintaining an O2 atmosphere.

[0138] Comparative Example 1 A positive electrode active material was produced in the same manner as in Example 1, except that the lithium composite oxide obtained as a result of heat treatment of the nickel composite precursor and lithium compound mixture without mixing H3BO3 was not washed with water.

[0139] Comparative Example 2 The positive electrode active material was manufactured in the same manner as in Example 1, except that H3BO3 was not mixed before the heat treatment of the nickel composite precursor.

[0140] Comparative Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that the lithium composite oxide obtained as a result of heat treatment of the nickel composite precursor, the lithium compound, and the mixture of H3BO3 was not washed with water.

[0141] Comparative Example 4 The positive electrode active material was manufactured in the same manner as in Example 1, except that during the secondary washing, the lithium composite oxide was washed with distilled water at a weight three times the total weight of the lithium composite oxide.

[0142] Comparative Example 5 The positive electrode active material was manufactured in the same manner as in Example 1, except that during the secondary washing, the lithium composite oxide was washed with distilled water at a weight of 0.2 times the total weight of the lithium composite oxide.

[0143] Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries A cathode slurry was prepared by dispersing 92 wt% each of the cathode active materials produced according to Production Example 1, 4 wt% of artificial graphite, and 4 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0144] A coin cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and an electrolyte containing ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 with LiPF6 present at a concentration of 1.15 M.

[0145] Experimental Example 1. Component Analysis of Cathode Active Material (1) Measurement of boron content in lithium composite oxide before and after washing ICP analysis was performed on the positive electrode active material to measure the boron (B) content in the lithium composite oxide before and after washing.

[0146] Specifically, 0.05 g each of the positive electrode active material before and after washing, produced according to Production Example 1, were weighed and added to a mixed solvent of 2 mL of nitric acid, 6 mL of hydrochloric acid, and 20 mL of ultrapure water to produce a mixture, and the positive electrode active material was completely dissolved in the mixture. Next, ultrapure water was added to the mixture to dilute it to a total volume of 100 mL, and the content of boron (B) in the lithium composite oxide contained in the positive electrode active material was measured using ICP-OES (Perkin Elmer, Avio 500).

[0147] The measurement results for the boron (B) content in lithium composite oxides before and after washing are shown in Table 1 below. In Table 1, the percentage change before and after washing indicates the decrease in the boron (B) content in lithium composite oxides after washing compared to the boron (B) content before washing, and the values ​​in parentheses are expressed as percentages.

[0148] [Table 1] *nd:not detected

[0149] (2) Measurement of the content of lithium-containing impurities (LiOH) in lithium composite oxide before and after washing with water. pH titration analysis was performed to measure the content of lithium-containing impurities (LiOH) in lithium composite oxides before and after washing.

[0150] Specifically, 5g each of the lithium composite oxide before and after washing, produced according to Production Example 1, was placed in 100ml of DIW, stirred for 10 minutes (300rpm), and then filtered. Next, 0.1N HCl was added to 50ml of the filtered solution, and the amount of HCl consumed due to the change in the solution's pH was measured (using a pH meter and Ag / AgCl metal wire). A differential graph was obtained by differentiating the pH value with respect to the amount of HCl added.

[0151] The measurement results of the lithium impurity content (LiOH) in the lithium composite oxide before and after washing are shown in Table 2 below. For reference, in the case of Comparative Example 1 and Comparative Example 3, since the lithium composite oxide was not washed with water, only the lithium impurity content (LiOH) in the lithium composite oxide before washing is listed.

[0152] [Table 2] *nc: not changed

[0153] Furthermore, based on the results in Tables 1 and 2, we confirmed whether the lithium composite oxide before and after washing satisfies the following equations 1 and 2, and the results are shown in Table 3 below.

[0154] [Formula 1] r < (19, 153 × x 1) + x 2

[0155] (Here, x1 is the boron content (mol%) in the lithium composite oxide before washing with water, x2 is the amount of LiOH (ppm) calculated from the amount of HCl consumed corresponding to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing with water, and r is the amount of LiOH eluted from the lithium composite oxide after washing with water (ppm).)

[0156] [Formula 2] y1≦r≦y1+(y2×(1-y3)×18,429)

[0157] (Here, y1 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing with water; y2 is the boron content (mol%) in the lithium composite oxide before washing with water; y3 is the rate of change in the boron content in the lithium composite oxide before and after washing with water, and has a value greater than 0 and less than or equal to 0.90; and r is the amount of LiOH eluted from the lithium composite oxide after washing with water (ppm).)

[0158] [Table 3] *In the case of Comparative Example 1 and Comparative Example 3, since the water washing process was not performed, the LiOH content after water washing is indicated as the LiOH content in the final product, the positive electrode active material.

[0159] Experimental Example 2. Evaluation of the electrochemical properties of lithium secondary batteries. Charge and discharge experiments were conducted on the lithium secondary battery (coin cell) manufactured in Manufacturing Example 2 using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 3.0V to 4.3V and a discharge rate of 0.1C, to measure the charge and discharge capacity.

[0160] Furthermore, the same lithium secondary battery underwent 50 charge-discharge cycles at 25°C and a drive voltage range of 3.0V to 4.4V under 1C / 1C conditions. The ratio of the discharged capacity at the 50th cycle to the initial capacity (cycle capacity retention) was then measured.

[0161] The measurement results are shown in Table 4 below.

[0162] [Table 4]

[0163] Experimental Example 3. Evaluation of the stability of the positive electrode active material and lithium secondary battery. (1) Evaluation of the thermal stability of the positive electrode active material To evaluate the thermal stability of the positive electrode active material produced by Production Example 1, weight loss was measured using a thermogravimetric analyzer (TA Instruments, Q20) under atmospheric pressure and an Ar atmosphere, from 25°C to 350°C at a heating rate of 10°C / min. The onset temperature at which the weight loss (thermal decomposition) peak appeared for each positive electrode active material is shown in Table 5 below.

[0164] [Table 5]

[0165] Referring to the results in Table 5, it can be confirmed that the thermal decomposition initiation temperature of the positive electrode active materials in Examples 1 to 6 is higher than that of the positive electrode active materials in Comparative Examples 1 to 5.

[0166] In particular, as shown in Table 4, the lithium secondary batteries using the positive electrode active materials of Comparative Examples 3 and 5 appear to be at a similar level to the lithium secondary batteries using the positive electrode active materials of Examples 1 to 6 in some indicators of electrochemical properties. However, as shown in Table 5, it can be confirmed that the thermal stability of the positive electrode active materials is insufficient (in the case of Comparative Example 3, it is at a similar level to Example 4, which was subjected to the most severe water washing conditions among the examples).

[0167] (2) Measurement of gas generation amount of lithium secondary battery The lithium secondary battery manufactured according to Manufacturing Example 2 was charged to 4.25V with a constant current of 0.2C, and then stored at 60°C for 14 days. The volume change of the lithium secondary battery due to gas generation inside the battery was measured. The measurement results of the volume change are shown in Table 6 below.

[0168] [Table 6]

[0169] Referring to the results in Table 6 above, it can be confirmed that the volume change rate during high-temperature storage of lithium secondary batteries manufactured by Manufacturing Example 2, using the positive electrode active materials of Examples 1 to 6, is smaller than that of lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 to 5.

[0170] In particular, as shown in Table 4, the lithium secondary batteries using the positive electrode active materials of Comparative Examples 3 and 5 appear to be at a similar level to the lithium secondary batteries using the positive electrode active materials of Examples 1 to 6 in some indicators of electrochemical properties. However, as shown in Table 6, it can be confirmed that their high-temperature storage stability is insufficient.

[0171] Although embodiments of the present invention have been described above, any person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A positive electrode active material composed of a lithium composite oxide comprising primary particles containing at least Li, Ni, and B, and secondary particles formed by aggregation of the primary particles, A coating layer containing a boron-containing oxide is present on at least a portion of the surface of the secondary particles. The content of boron (B) in the lithium composite oxide is 0.09 mol% or more and 0.49 mol% or less. The lithium impurity (LiOH) content in the lithium composite oxide is 11,661 ppm or less. Weight loss was measured under an Ar atmosphere at normal pressure from 25°C to 350°C at a heating rate of 10°C / min, and the starting temperature at which the weight loss (thermal decomposition) peak appeared was 231.2°C or higher. The primary particles are a positive electrode active material represented by the following chemical formula 1. [Chemical formula 1] Li ｗ Ni １－（ｘ＋ｙ＋ｚ＋ｚ′） Co ｘ B ｙ M1 ｚ M2 ｚ′ O ２ (Here, M1 is at least one selected from Mn and Al. M2 is at least one selected from Mn, Ba, Ce, Hf, Ta, Cr, F, Mg, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu. M1 and M2 are different elements. (0.5 ≤ w ≤ 1.5, 0 ≤ x ≤ 0.50, 0 < y ≤ 0.20, 0 ≤ z ≤ 0.20, 0 ≤ z' ≤ 0.20, 0 < x + y + z + z' ≤ 0.50)

2. The positive electrode active material according to claim 1, wherein the coating layer further comprises at least one metal oxide represented by the following chemical formula 3. [Chemical formula 3] Li ｄ M3 ｅ O ｆ (Here, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd. (0 ≤ d ≤ 8, 0 < e ≤ 8, 2 ≤ f ≤ 13)

3. The positive electrode active material according to claim 1, wherein the coating layer is removed from the surface of the secondary particles by washing the lithium composite oxide with water.

4. The positive electrode active material according to claim 3, wherein the content of residual boron in the lithium composite oxide after washing with water is 0.3 mol% or less.

5. The positive electrode active material according to claim 1, wherein the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl satisfies the following formula 1. [Formula 1] r<(19,153×x1)+x2 (Here, x1 is the boron content (mol%) in the lithium composite oxide before washing with water. x2 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing with water. r is the amount of LiOH leached from the lithium composite oxide after washing with water (ppm).

6. The positive electrode active material according to claim 1, wherein the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl satisfies the following formula 2. [Formula 2] y1≦r≦y1+(y2×(1-y3)×18,429) (Here, y1 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing with water. y2 is the boron content (mol%) in the lithium composite oxide before washing with water. y3 is the rate of change in the boron content in the lithium composite oxide before and after washing with water, and has a value greater than 0 and less than or equal to 0.

90. r is the amount of LiOH leached from the lithium composite oxide after washing with water (ppm).

7. The positive electrode active material according to claim 3, wherein the ratio of the porosity of the secondary particles after washing with water to the porosity of the secondary particles before washing with water for the lithium composite oxide is 1.7 or more.

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