Positive electrode active material for lithium secondary batteries and method for manufacturing the same

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a method for producing the positive electrode active material.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2021-0185900 dated December 23, 2021, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for lithium secondary batteries and a method for producing the positive electrode active material. [Background technology]

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

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

[0005] As materials to be used in place of the LiCoO2, lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), or lithium nickel composite metal oxides (such as LiNiO2) have been developed. Among them, research and development on lithium nickel composite metal oxides, which have a high reversible capacity of about 200 mAh / g and are easy to realize a large-capacity battery, has been more actively conducted. However, the LiNiO2 has inferior thermal stability compared with LiCoO2. When an internal short circuit occurs due to external pressure or the like in the charged state, there is a problem that the positive electrode active material itself is decomposed, causing battery rupture and ignition. Therefore, as a method for maintaining the excellent reversible capacity of the LiNiO2 and improving its low thermal stability, lithium nickel cobalt metal oxides in which part of Ni is substituted with Co, Mn, or Al have been developed.

[0006] However, in the case of the lithium nickel cobalt metal oxide, the structural stability and capacity are low. In particular, when increasing the nickel content to enhance the capacity characteristics, as the charge-discharge process progresses, the nickel is oxidized from Ni 2+ to Ni 3+ or Ni 4+ and this causes rapid oxygen desorption to progress, resulting in a further decrease in structural stability.

[0007] Therefore, there is a demand for the development of a positive electrode active material that includes a lithium nickel cobalt metal oxide containing a high content of Ni showing high capacity characteristics, and that has excellent structural stability of the lithium nickel cobalt metal oxide and can manufacture a high-capacity and long-life battery.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention aims to produce a positive electrode active material that contains a lithium transition metal oxide with a high nickel content, and in which the surface and crystal grains of the lithium transition metal oxide particles are coated by controlling the temperatures of the primary and secondary heat treatments, thereby improving the lifetime characteristics at high temperatures and suppressing gas generation. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a method for producing a positive electrode active material, comprising the steps of: (S1) preparing a positive electrode active material precursor containing nickel, cobalt, and manganese, with nickel accounting for 60 mol% or more of the total metals other than lithium; (S2) mixing the positive electrode active material precursor with a lithium raw material and performing a primary heat treatment at 660 to 800°C to form a lithium transition metal oxide in the form of secondary particles in which primary particles are aggregated; (S3) mixing the lithium transition metal oxide with a cobalt ion-containing source and performing a secondary heat treatment at 640 to 800°C to form a secondary heat-treated product; (S4) washing the secondary heat-treated product with water; and (S5) dry mixing the washed secondary heat-treated product with a boron coating source and performing a heat treatment.

[0011] Furthermore, the present invention provides a positive electrode active material comprising nickel, cobalt, and manganese, and a lithium transition metal oxide in the form of aggregated primary particles, wherein a coating layer containing cobalt is formed on the surface and at the interface between primary particles located inside the secondary particles of the lithium transition metal oxide, the primary particles have a cobalt content of 7.0 mol% or more relative to the total metal, and the spectrum measured by TEM-EELS, which combines a transmission electron microscope (TEM) with electron energy loss spectroscopy (EELS), includes a first peak in a region corresponding to a depth of 50 nm from the surface of the primary particles located on the surface of the secondary particles, and a second peak in a region corresponding to a depth of 50 nm from the surface of the primary particles located in the core of the secondary particles, the surface of the secondary particles being a region corresponding to a depth of more than 3 μm from the surface of the secondary particles, and the first and second peaks being peaks in the 180-200 eV range in the TEM-EELS spectrum. [Effects of the Invention]

[0012] According to the present invention, a coating effect can be achieved by adjusting the degree of cobalt doping on the surface and crystal grains of lithium transition metal oxide particles containing a high nickel content. Ultimately, a boron- and cobalt composite coating can be formed, thereby producing a cathode active material with improved structural stability.

[0013] When a secondary battery is manufactured using the positive electrode active material produced by the present invention, the high-temperature life characteristics are improved and the amount of gas generated can be reduced. [Brief explanation of the drawing]

[0014] [Figure 1] (a) and (b) are SEM (Scanning electron microscopy) images of the surface of the positive electrode active material produced in Examples 1 and 2, respectively. [Figure 2](a) and (b) are SEM images of the surface of the positive electrode active material produced in Comparative Example 1 and Comparative Example 4, respectively. [Figure 3] (a) and (b) are figures showing the surface and interior TEM data of the positive electrode active material produced in Example 1, respectively. [Figure 4] (a) and (b) are figures showing the surface and interior TEM data of the positive electrode active material manufactured in Example 2, respectively. [Figure 5] This figure shows the TEM data of the surface of the positive electrode active material manufactured in Comparative Example 3. [Figure 6] This graph shows the high-temperature life characteristics of secondary batteries manufactured using the positive electrode active materials described in the examples and comparative examples. [Figure 7] This graph shows the amount of gas generated when secondary batteries manufactured using the positive electrode active materials of the examples and comparative examples are stored at high temperatures. [Figure 8] This figure shows (a) the TEM-EELS measurement location and (B) the TEM-EELS spectrum for the secondary particle surface of Example 1. [Figure 9] This figure shows (a) the TEM-EELS measurement location and (B) the TEM-EELS spectrum for the secondary particle core portion of Example 1. [Figure 10] This figure shows (a) the TEM-EELS measurement location and (B) the TEM-EELS spectrum for the secondary particle surface of Example 2. [Figure 11] This figure shows (a) the TEM-EELS measurement location and (B) the TEM-EELS spectrum for the secondary particle core portion of Example 2. [Figure 12] This figure shows (a) the TEM-EELS measurement location and (B) the TEM-EELS spectrum for the secondary particle surface of Comparative Example 5. [Figure 13] This figure shows (a) the TEM-EELS measurement location and (B) the TEM-EELS spectrum for the secondary particle core portion of Comparative Example 5. [Modes for carrying out the invention]

[0015] The present invention will be described in more detail below to facilitate understanding of it.

[0016] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0017] Method for manufacturing positive electrode active material The present invention provides a method for producing a positive electrode active material, comprising the steps of: (S1) preparing a positive electrode active material precursor containing nickel, cobalt, and manganese, and containing 60 mol% or more of nickel among the total metals other than lithium; (S2) mixing the positive electrode active material precursor with a lithium raw material and performing a primary heat treatment at 660 to 800°C to form a lithium transition metal oxide in the form of secondary particles in which primary particles are aggregated; (S3) mixing the lithium transition metal oxide with a cobalt ion-containing source and performing a secondary heat treatment at 640 to 800°C to form a secondary heat-treated product; (S4) washing the secondary heat-treated product with water; and (S5) dry mixing the water-washed secondary heat-treated product with a boron coating source and performing a heat treatment.

[0018] Step (S1) A cathode active material precursor is prepared containing nickel, cobalt, and manganese, with nickel making up 60 mol% or more of the total metals excluding lithium.

[0019] The positive electrode active material precursor can be purchased and used from a commercially available positive electrode active material precursor, or it can be manufactured by a method for manufacturing positive electrode active material precursors that is well known in the art.

[0020] For example, the precursor can be produced by adding an ammonium cation-containing complex-forming agent and a basic compound to a transition metal solution containing a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material, and then causing a coprecipitation reaction.

[0021] The nickel-containing raw material can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically can be, but are not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0022] The cobalt-containing raw material can be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically can be, but is not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or combinations thereof.

[0023] The manganese-containing raw material can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof. Specifically, it can be, but is not limited to, manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate salts, manganese citrate, manganese fatty acid salts; manganese oxyhydroxide, manganese chloride, or combinations thereof.

[0024] The transition metal solution can be produced by adding a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material to a solvent, specifically, water, or a mixed solvent of an organic solvent (e.g., alcohol) that can be homogeneously mixed with water, or by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and a manganese-containing raw material.

[0025] The ammonium cation-containing complex-forming agent may be, but is not limited to, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. On the other hand, the ammonium cation-containing complex-forming agent may also be used in the form of an aqueous solution, where the solvent may be water or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol).

[0026] The basic compound may be an alkali metal or alkaline earth metal hydroxide such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, where the solvent may be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0027] The basic compound is added to adjust the pH of the reaction solution, and can be added in an amount that brings the pH of the metal solution to 11-13.

[0028] On the other hand, the coprecipitation reaction can be carried out at a temperature of 40-70°C under an inert atmosphere such as nitrogen or argon. Through the above process, nickel-cobalt-manganese hydroxide particles are produced and precipitate in the reaction solution. By adjusting the concentrations of the nickel-containing raw material, cobalt-containing raw material, and manganese-containing raw material, a precursor can be produced in which the nickel content of the total metal content is 60 mol% or more. The precipitated nickel-cobalt-manganese hydroxide particles can be separated by conventional methods and dried to obtain a nickel-cobalt-manganese precursor. The precursor may be secondary particles formed by the aggregation of primary particles.

[0029] Step (S2) The positive electrode active material precursor and the lithium raw material are mixed and subjected to primary heat treatment at 660-800°C to form a lithium transition metal oxide in the form of secondary particles in which primary particles have aggregated.

[0030] In the present invention, "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross-section of the positive electrode active material is observed using a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains.

[0031] In this invention, "secondary particle" means a secondary structure formed by the aggregation of multiple primary particles.

[0032] The lithium raw material can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and one or more of these can be used as a mixture.

[0033] The lithium transition metal oxide is a high-concentration nickel (Ni-rich) lithium transition metal oxide containing 60 mol% or more of nickel among the total metals other than lithium, more preferably containing 70 mol% or more, or 80 mol% or more of nickel, and even more preferably 85 mol% or more of nickel (Ni). By satisfying the requirement that the nickel (Ni) content of the total metals other than lithium in the lithium transition metal oxide be 60 mol% or more, it is possible to secure a high capacity.

[0034] More specifically, the lithium transition metal oxide can be represented by the following chemical formula 1.

[0035] [Chemical formula 1] Li a Ni 1-(b+c+d) Co b Mn c Q d O2

[0036] In the above formula, Q is Al, Si, V, Nb, Mo, Ta, Y 、S n, Zr, B, W, Mg, Ce, Hf 、T One or more elements selected from the group consisting of i, Sr, Ba, F, P, S, and La.

[0037] 0.9≦a≦1.1, 0≦b≦0.2, 0≦c≦0.2, 0≦d≦0.1, 0 <b+c+d≦0.4である。

[0038] In the lithium transition metal oxide of chemical formula 1, Li can be present in an amount corresponding to a, i.e., 0.9 ≤ a ≤ 1.1. If a is less than 0.9, the capacity may decrease, and if it is greater than 1.1, the particles may sinter during the firing process, making it difficult to manufacture the positive electrode active material. Considering the balance between the remarkable effect of controlling the Li content on improving the capacity characteristics of the positive electrode active material and the sinterability during the manufacture of the active material, the Li can more preferably be present in an amount of 1.0 ≤ a ≤ 1.05.

[0039] In the lithium transition metal oxide of Chemical Formula 1, Ni can be contained in a content corresponding to 1-(b + c + d), for example, 0.6 ≦ 1-(b + c + d) < 1. When the content of Ni in the lithium transition metal oxide of Chemical Formula 1 is 0.6 or more, a sufficient amount of Ni for contributing to charge and discharge is ensured, and high capacity can be achieved. More preferably, Ni can be contained in a content of 0.80 ≦ 1-(b + c + d) ≦ 0.99.

[0040] In the lithium transition metal oxide of Chemical Formula 1, Co can be contained in a content corresponding to b, that is, 0 ≦ b ≦ 0.2. When the content of Co in the lithium transition metal oxide of Chemical Formula 1 exceeds 0.2, there is a risk of cost increase. Considering the remarkable effect of improving the capacity characteristics by including Co, more specifically, Co can be contained in a content of 0.05 ≦ b ≦ 0.2.

[0041] In the lithium transition metal oxide of Chemical Formula 1, Mn can be contained in a content corresponding to c, that is, a content of 0 < c ≦ 0.2. When c in the lithium transition metal oxide of Chemical Formula 1 exceeds 0.2, rather, the output characteristics and capacity characteristics of the battery may decrease, and more specifically, Mn can be contained in a content of 0.05 ≦ c ≦ 0.2.

[0042] In the lithium transition metal oxide of Chemical Formula 1, Q is one or more selected from the group consisting of Al, Si, V, Nb, Mo, Ta, Y 、S n, Zr, B, W, Mg, Ce, Hf 、T i, Sr, Ba, F, P, S and La, and such metal elements can improve the stability of the active material, and as a result, improve the stability of the battery. Considering the effect of improving the life characteristics, Q can be contained in a content corresponding to d, that is, a content of 0 ≦ d ≦ 0.2. When Q in the lithium transition metal oxide of Chemical Formula 1 exceeds 0.2, rather, the output characteristics and capacity characteristics of the battery may decrease, and more specifically, Q can be contained in a content of 0.05 ≦ d ≦ 0.2.

[0043] Furthermore, when the positive electrode active material precursor and the lithium raw material are mixed, the mixture can be adjusted so that the molar ratio of Li to metal (Li / metal ratio) is 1 to 1.3, preferably 1.05 to 1.1, and more preferably 1.04 to 1.09. When the nickel-containing transition metal hydroxide precursor and the lithium raw material are mixed within the above range, a positive electrode active material exhibiting excellent capacitance characteristics can be produced.

[0044] The primary heat treatment is carried out at a temperature of 660 to 800°C, more preferably at 660°C or higher, or 680°C or higher, 800°C or lower, or 790°C or lower, for example, 660 to 790°C.

[0045] Performing primary heat treatment within the aforementioned range offers the advantages of ensuring a regular atomic arrangement and volume based on the nickel composition of the lithium transition metal oxide, as well as enabling appropriate control of grain size.

[0046] The primary heat treatment can be carried out in an oxidizing atmosphere. When the primary heat treatment is carried out in an oxidizing atmosphere, sufficient residual lithium impurities can be obtained to form a coating material, and a positive electrode nickel-containing lithium transition metal oxide with excellent crystal grain development can be obtained. For example, if the primary heat treatment is carried out in an inert atmosphere such as a nitrogen atmosphere, the amount of residual lithium impurities will be large, preventing the synthesis of metal oxides and potentially making it difficult to form a coating material.

[0047] The aforementioned primary heat treatment can be carried out in an oxidizing atmosphere at a temperature of 660-800°C for 4-10 hours, or 4-7 hours.

[0048] Step (S3) The lithium transition metal oxide and the cobalt ion-containing source are mixed and subjected to secondary heat treatment at 640-800°C to form a secondary heat-treated product.

[0049] In step (S3), a coating layer containing cobalt can be formed at the interface between primary particles that make up secondary particles of lithium transition metal oxide by secondary heat treatment.

[0050] In the manufacturing method of the present invention, as described above, a coating layer containing cobalt is formed on the surface of the secondary particles and at the interface between primary particles located inside them, thereby strengthening the surface before the water washing process, and ultimately forming a composite coating layer containing cobalt, as described later. With such a coating, the problem of reduced structural and chemical stability of the positive electrode active material can be improved, and it can be used in secondary batteries that exhibit excellent high-temperature life characteristics.

[0051] In the present invention, the cobalt ion-containing source may include one or more selected from the group consisting of Co(OH)2, Co2O3, CoCO3, Co5(CO3)2(OH)6, Co3(PO4)2, CoF3, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co3O4, Co(SO4)2·7H2O, and CoC2O4, and more preferably Co(OH)2 or Co3O4.

[0052] The cobalt ion-containing source can be 0.4 to 4 parts by weight, or 0.8 to 3 parts by weight, per 100 parts by weight of lithium transition metal oxide. By mixing the cobalt ion-containing source within the above range, advantages such as improved capacity, high-temperature lifetime, and increased resistance can be achieved in a solid solution formed with an appropriate coating thickness and equivalent composition.

[0053] The aforementioned secondary heat treatment is carried out at a temperature of 640 to 800°C, more preferably at 640°C or higher, 660°C or higher, or 670°C or higher, 800°C or lower, 780°C or lower, or 750°C or lower, for example, at 660 to 780°C.

[0054] By performing secondary heat treatment within the aforementioned range, a coating layer containing cobalt is formed not only on the surface of the lithium transition metal oxide secondary particles but also at the interfaces between primary particles located inside, thereby enabling the advantages of solid diffusion to manifest on the surface and core of the secondary particles as a whole.

[0055] The aforementioned secondary heat treatment can be carried out at 640-800°C for 4-10 hours, or 4-8 hours.

[0056] Step (S4) In the step of washing the secondary heat-treated product with water, lithium by-products present on the surface of the lithium transition metal oxide particles can be removed.

[0057] In the case of high-nickel (High-Ni) lithium transition metal oxides, the structural instability compared to lithium transition metal oxides with low nickel content leads to the generation of even more unreacted lithium by-products such as lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) during the manufacturing process. For example, in the case of lithium composite metal oxides with a nickel fraction of less than 80 mol%, the amount of lithium by-products after synthesis is about 0.5-0.6% by weight, whereas in the case of lithium composite metal oxides with a nickel fraction of 80 mol% or more, the amount of lithium by-products after synthesis is significantly higher, at about 1% by weight. On the other hand, if a large amount of lithium by-products is present in the positive electrode active material, the lithium by-products react with the electrolyte, generating gas and causing a swelling phenomenon, which significantly reduces high-temperature stability. Therefore, a water washing process to remove lithium by-products from lithium transition metal oxides containing high concentrations of nickel is essential.

[0058] The washing step can be carried out, for example, by adding lithium transition metal oxide to a washing solution such as distilled water or tap water and stirring.

[0059] The temperature of the washing liquid used during the washing can be 1 to 80°C, or 5 to 80°C. Also, the washing time can be 3 to 60 minutes, more preferably 5 to 40 minutes. When the washing temperature and the washing time satisfy the above ranges, lithium by-products can be effectively removed.

[0060] The washing step can be carried out by mixing the washing liquid and the lithium transition metal oxide in a weight ratio of 100:20 to 100:300, more preferably in a weight ratio of 100:50 to 100:200, and even more preferably in a weight ratio of 100:60 to 100:180. When the mixing ratio of the washing liquid and the lithium transition metal oxide satisfies the above range, lithium by-products can be effectively removed, and surface defects of the lithium transition metal oxide can be reduced as much as possible.

[0061] Step (S5) The washed secondary heat-treated product and the boron coating source are dry-mixed and heat-treated.

[0062] By the heat treatment, a boron coating part can be formed on the surface of the particles of the lithium transition metal oxide. In the present invention, by performing a coating treatment on the surface of the lithium transition metal oxide particles, stability and gas generation phenomena are improved.

[0063] The boron coating source can contain at least one selected from the group consisting of H3BO3, B4C, B2O3, BF3, (C3H7O)3B, (C6H5O)3B, [CH3(CH2)3O]3B, C 13 H 19 O3, C6H5B(OH)2, and B2F4, and more preferably can be H3BO3. In the case of H3BO3, the melting point is relatively low, and not only the surface but also a part of the inside of the secondary particle core can be coated, which is useful for improving long-term life. The boron coating source can be mixed in an amount of 0.01 to 0.90 parts by weight with respect to 100 parts by weight of the lithium transition metal oxide, and more preferably can be mixed in an amount of 0.30 to 0.60 parts by weight.

[0064] Within the aforementioned range, a cobalt-containing boron coating layer can be formed with an appropriate thickness on the surface of the secondary particles of the lithium transition metal oxide and at the interface between primary particles located within it.

[0065] The water-washed secondary heat-treated material and the boron coating source are dry-mixed, and then the composite coating portion can be formed by heat treatment at 200 to 750°C. The heat treatment can be more preferably carried out at 200 to 500°C.

[0066] Within the aforementioned range, no unreacted cobalt by-products are formed, and the amount of lithium by-products due to boron does not increase, while the composite coating layer can be formed smoothly.

[0067] Furthermore, before dry-mixing the washed secondary heat-treated material with the boron coating source, a drying step can be performed first. For example, after washing the secondary heat-treated material with water, it can be dried at 80-140°C, then dry-mixed with the boron coating source and heat-treated.

[0068] positive electrode active material The positive electrode active material of the present invention contains nickel, cobalt, and manganese, and also contains a lithium transition metal oxide in the form of secondary particles in which primary particles are aggregated, wherein a coating layer containing cobalt is formed on the surface and at the interface between primary particles located inside the secondary particles of the lithium transition metal oxide, the primary particles have a cobalt content of 7.0 mol% or more relative to the total metal, and the spectrum measured by TEM-EELS, which combines a transmission electron microscope (TEM) with electron energy loss spectroscopy (EELS), includes a first peak in a region located on the surface of the secondary particles at a depth of 50 nm from the surface of the primary particles, and a second peak located in a region located in the core of the secondary particles at a depth of 50 nm from the surface of the primary particles, wherein the surface of the secondary particles is the region located at a depth of 50 nm from the surface of the secondary particles, and the core of the secondary particles is the region located at a depth of more than 3 μm from the surface of the secondary particles, and the first and second peaks are peaks in the range of 180 to 200 eV in the TEM-EELS spectrum.

[0069] Furthermore, the intensities of the first and second peaks can be in a ratio of 1:0.5 to 1:20, specifically, 1:0.7 to 1:15, or 1:1 to 1:10.

[0070] Also, the aforementioned first peak is 1*10 3 ~30*10 3 The strength, specifically, 2*10 3 ~30*10 3 , 2*10 3 ~28*10 3 , or 5*10 3 ~16*10 3 It can demonstrate the strength of the substance.

[0071] Furthermore, the second peak is 20*10 3 ~60*10 3 , or 30*10 3 ~50*10 3 It can demonstrate the strength of the substance.

[0072] The TEM-EELS measurement described above can be performed by a method that includes the steps of preparing a TEM specimen using a focused ion beam (FIB), defining an analysis region on the specimen, and obtaining an EELS spectrum within the analysis region. The EELS measurement conditions can be an acceleration voltage of 200 kV and a dispersion of 0.05 eV / channel.

[0073] The peaks appearing in the TEM-EELS spectrum in the 180-200 eV range, i.e., the first and second peaks, indicate the presence of boron contained on the surface of the primary particles forming the lithium transition metal oxide.

[0074] In other words, when TEM-EELS measurements are performed on primary particles located on the surface and core of secondary particles, the lithium transition metal oxide contained in the positive electrode active material of the present invention shows a boron peak in the region corresponding to a depth of 50 nm from the surface, and the primary particles located on the surface of secondary particles show a higher boron content than the primary particles located in the core.

[0075] As described above, by including boron, the BET surface area, which has increased due to water washing, can be effectively reduced, ensuring the stability of the positive electrode active material, and achieving a reduction in the resistance increase rate and excellent life characteristics.

[0076] Furthermore, the primary particles may have a cobalt content of 10.0 mol% or more, 12.0 mol% or more, or 15.0 mol% or more relative to the total metal.

[0077] As described above, primary particles are aggregated on the surface and inside the lithium transition metal oxide of the present invention, and a cobalt-containing coating layer is formed at the interface between the primary particles. As a result, the cobalt content is higher on both the surface and inside the secondary particles compared to lithium transition metal oxides in which a cobalt-containing coating layer is not formed at the interface between primary particles.

[0078] Thus, because a coating layer is formed at the interface between primary particles, the stability of secondary particles is improved, the lifetime characteristics at high temperatures are enhanced, and problems such as gas generation are suppressed.

[0079] The "surface portion" of the secondary particle may refer to the region from the surface of the secondary particle to a depth of 50 nm, that is, the region from the outermost surface of the secondary particle to one depth between 0 and 50 nm. More specifically, it may refer to the region from the surface of the secondary particle to a depth of 10 nm, or the region from the surface of the secondary particle to a depth of 7 nm.

[0080] The "core portion" of the secondary particle may refer to the region extending more than 3 μm from the surface of the secondary particle.

[0081] The positive electrode active material can be manufactured by the manufacturing method of the present invention described above, and can be represented by [Chemical Formula 1] as described above.

[0082] As described above, the lithium transition metal oxide of the present invention can have a concentration gradient in which cobalt gradually decreases from the surface layer to the center of the primary particles constituting the lithium transition metal oxide.

[0083] In the present invention, "exhibiting a concentration gradient in which the concentration of the transition metal gradually changes (increases or decreases)" means that the concentration of the transition metal exists in a concentration distribution that gradually changes throughout the particles. Specifically, the concentration distribution can have a difference of 0.1 to 5 mol%, more specifically 0.1 to 3 mol%, and even more specifically 1 to 2 mol%, in the change of the transition metal concentration per 1 μm within the particles, relative to the total number of moles of the metal contained in the positive electrode active material.

[0084] The positive electrode active material according to the present invention may further include a coating layer on the surface of a lithium transition metal oxide.

[0085] The coating layer is formed on the surface of secondary particles of lithium transition metal oxide and may contain one or more coating elements (M) selected from the group consisting of B, Li, Al, F, W, Mo, Ti, Mn, Ca, Sr, Zr, Zn, Mg, Ca, Si, Sn, and Nb.

[0086] The coating element can be included in an amount of 50 to 5,000 ppm, preferably 50 to 2,000 ppm, relative to the total weight of the positive electrode active material. If the content of the coating element is too high, the coating layer may be formed to be excessively thick, potentially adversely affecting capacitance characteristics and resistance characteristics, while if the content of the coating element is too low, the electrolyte barrier effect will be insufficient.

[0087] As described above, when the surface of the lithium transition metal oxide includes a coating layer containing one or more coating elements selected from the group consisting of B, Li, Al, F, W, Mo, Ti, Mn, Ca, Sr, Zr, Zn, Mg, Ca, Si, Sn, and Nb, the coating layer suppresses contact between the electrolyte and the lithium transition metal oxide, thereby suppressing the leaching of transition metals and the generation of gases.

[0088] positive electrode Furthermore, the present invention provides a positive electrode for a lithium secondary battery containing a positive electrode active material manufactured by the method described above.

[0089] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and containing the positive electrode active material described above.

[0090] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0091] The positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0092] In this case, the positive electrode active material can be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight, relative to the total weight of the positive electrode active material layer. When included within the above content range, excellent capacity characteristics can be observed.

[0093] In this case, the conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. The conductive material may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0094] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0095] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, it can be manufactured by coating a positive electrode composite material, prepared by dissolving or dispersing the positive electrode active material and, selectively, a binder and a conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0096] The solvent can 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 can be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the positive electrode active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0097] Alternatively, the positive electrode can also be manufactured by casting the positive electrode composite onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0098] Lithium-ion battery Furthermore, the present invention can be used to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element can be a battery, a capacitor, and more specifically, a lithium secondary battery.

[0099] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte. As the positive electrode is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0100] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0101] In the lithium secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0102] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0103] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0104] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metallic oxides that can be doped and dedoped with lithium, 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, and any one or more mixtures of these can be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can 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.

[0105] The anode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the anode active material layer.

[0106] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and is usually added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0107] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, specifically 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause chemical changes in the battery and is conductive, 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 whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0108] For example, the negative electrode active material layer can be manufactured by coating a negative electrode composite material, 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 composite material onto another support, peeling it off this support, and then laminating the resulting film onto the negative electrode current collector.

[0109] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent moisture-absorbing capacity for the electrolyte are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0110] 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.

[0111] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0112] The organic solvent can be used without particular limitations as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcohol solvents such as 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 can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 allows the electrolyte to exhibit excellent performance.

[0113] The lithium salt can be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0114] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. These additives may include, for example, 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 parts by weight per 100 parts by weight of the total weight of the electrolyte.

[0115] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention exhibit excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making them useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0116] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0117] The aforementioned 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.

[0118] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0119] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells. [Examples]

[0120] Examples The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

[0121] Example 1 Ni 0.96 Co 0.02 Mn 0.02 (OH)2, LiOH·H2O, ZrO2, and Al(OH)3 are mixed so that the Li / Metal(Ni, Co, Mn) molar ratio is 1.05:1, and then subjected to primary heat treatment at 710°C for 5 hours to obtain LiNi 0.94 Co 0.03 Mn 0.02 Al 0.02We manufactured lithium transition metal oxides of O2.

[0122] Subsequently, Co(OH)2 was mixed with Ni:Co:Mn:Al in a molar ratio of 92:4:2:2, and then subjected to a secondary heat treatment at 720°C for 5 hours to form a cobalt coating layer on the surface of the LiNi particles. 0.92 Co 0.04 Mn 0.02 Al 0.02 We manufactured a lithium transition metal oxide with an O2 composition.

[0123] Subsequently, 200g and 240g (weight ratio 1:1.2) of the lithium transition metal oxide with the cobalt coating layer were mixed with water, and the mixture was stirred for 5 minutes and washed with water. After that, the washed lithium transition metal oxide was processed using a filter press to reduce its water content to 3-15%, and then dried at 130°C.

[0124] Next, H3BO3 was mixed with the dried lithium transition metal oxide so that the weight ratio of H3BO3 to H3BO3 was 100:0.57, and the mixture was heat-treated at 300°C for 4 hours to produce the positive electrode active material.

[0125] Example 2 The positive electrode active material was manufactured in the same manner as in Example 1, except that the temperature of the primary heat treatment was changed to 720°C and the temperature of the secondary heat treatment was changed to 680°C.

[0126] Comparative Example 1 The positive electrode active material was manufactured in the same manner as in Example 1, except that the temperature of the primary heat treatment was changed to 740°C and the temperature of the secondary heat treatment was changed to 600°C.

[0127] Comparative Example 2 The positive electrode active material was manufactured in the same manner as in Example 1, except that the temperature of the primary heat treatment was changed to 640°C and the temperature of the secondary heat treatment was changed to 720°C.

[0128] Comparative Example 3 Except for not mixing Co(OH)2, the same method as in Example 1 was used to prepare LiNi 0.92 Co 0.04 Mn 0.02 Al0.02 We manufactured a lithium transition metal oxide with an O2 composition.

[0129] Comparative Example 4 Ni 0.96 Co 0.02 Mn 0.02 (OH)2, LiOH·H2O, ZrO2, and Al(OH)3 are mixed so that the Li / Metal(Ni, Co, Mn) molar ratio is 1.05:1, and then subjected to primary heat treatment at 720°C for 5 hours to obtain LiNi 0.94 Co 0.02 Mn 0.02 Al 0.02 We manufactured lithium transition metal oxides of O2.

[0130] Subsequently, the weight ratio of lithium transition metal oxide to H3BO3 was adjusted to 100:0.57, and Co(OH)2 was mixed in such a molar ratio of Ni:Co:Mn:Al as 92:4:2:2. After this, a secondary heat treatment was performed at 690°C for 5 hours, resulting in a cobalt + boron coating layer being formed on the surface of the LiNi particles. 0.92 Co 0.04 Mn 0.02 Al 0.02 We manufactured a lithium transition metal oxide with an O2 composition.

[0131] Comparative Example 5 Ni 0.96 Co 0.02 Mn 0.02 (OH)2, LiOH·H2O, ZrO2, and Al(OH)3 are mixed so that the Li / Metal(Ni, Co, Mn) molar ratio is 1.05:1, and subjected to primary heat treatment at 720°C for 5 hours. 0.94 Co 0.02 Mn 0.02 Al 0.02 We manufactured lithium transition metal oxides of O2.

[0132] Subsequently, lithium acetate was mixed with 100 mL of ethanol (ethanol:lithium acetate weight ratio 100:1), and cobalt acetate was added to prepare a transition metal-containing solution by mixing in Ni:Co:Mn:Al in a molar ratio of 92:4:2:2.

[0133] Subsequently, a sol-gel reaction was carried out at 70°C, followed by vacuum drying at 150°C, and then a secondary heat treatment at 690°C for 5 hours, resulting in LiNi having a cobalt coating layer formed on the surfaces of the secondary and primary particles. 0.92 Co 0.04 Mn 0.02 Al 0.02 We manufactured a lithium transition metal oxide with an O2 composition.

[0134] Experimental Example 1 The surfaces of the positive electrode active material secondary particles produced in Examples 1 and 2, and Comparative Examples 1 and 4, were observed using a scanning electron microscope.

[0135] Figures 1(a) and 1(b) are SEM images of the surface of the positive electrode active materials produced in Examples 1 and 2, respectively, while Figure 2 is an SEM image of the surface of the positive electrode active materials produced in Comparative Examples 1 and 4.

[0136] Similar to Figures 1(a) and 1(b), in the case of the positive electrode active material according to Examples 1 and 2, no residual Co source was shown, confirming that the coating extended to the interior of the secondary particles through the primary particle interface. On the other hand, in Figure 2, unreacted Co and B solid solutions were observed, indicating that the thickness of the surface layer of the secondary particles was thick, causing a decrease in capacity. This is understood to be because the coating layer was formed by using both a cobalt ion-containing source and a boron coating source simultaneously, or because the reaction of Co was inhibited.

[0137] Experimental Example 2 The metallic element distribution and content of the cathode active materials of Examples 1 and 2 and Comparative Examples 1 to 4 were analyzed using a TEM (instrument name: Titan G2 80-200 ChemiSTEM w / Gatan Continuum S EELS system, FEI). Prior to the analysis, TEM samples with a thickness of 70 nm or less were prepared using a FIB (instrument name: Helios G4 UX, FEI) equipped with target sampling capabilities for cathode material particles.

[0138] Specifically, the content (mol%) of each metal was calculated for primary particles located at a depth of 20 nm from the outermost layer of the lithium transition metal oxide secondary particles, and the results are shown in Table 1 below.

[0139] [Table 1]

[0140] Furthermore, the content (mol%) of each metal was calculated for primary particles located within the secondary particles of lithium transition metal oxides, specifically at a depth of 5-6 μm from the outermost layer, and is shown in Table 2 below.

[0141] [Table 2]

[0142] TEM data for Examples 1 and 2 and Comparative Example 3 are also shown in Figures 3 to 5.

[0143] As shown in Tables 1 and 2 above, the positive electrode active material of the examples produced by the present invention showed a higher cobalt content compared to the comparative example, both in the primary particles located on the surface of the secondary particles and in the primary particles located inside the secondary particles. This confirmed that a cobalt-containing coating layer was formed at the interface between primary particles in a general area both on the surface and inside the secondary particles.

[0144] Experimental Example 3 Lithium secondary batteries were manufactured using the positive electrode active materials produced in the above examples and comparative examples, and their resistance characteristics were evaluated.

[0145] Specifically, the respective positive electrode active materials, carbon black conductive material, and polyvinylidene fluoride binder produced in the examples or comparative examples were mixed in an N-methylpyrrolidone solvent in a weight ratio of 97.5:1.0:1.5 to produce a positive electrode slurry. After applying the positive electrode slurry to one surface of an aluminum current collector, it was dried at 130°C and then rolled to produce a positive electrode.

[0146] Next, a negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (SBR+CMC) were mixed in water in a weight ratio of 95:1.5:3.5 to produce a negative electrode forming composition. The negative electrode forming composition was applied to a copper current collector, dried, and then rolled to produce a negative electrode.

[0147] After manufacturing an electrode assembly by interposing a porous polyethylene separator between the positive and negative electrodes manufactured as described above, this assembly was placed inside a battery case, and then an electrolyte was injected into the case to manufacture a lithium secondary battery. Here, as the electrolyte, an electrolyte solution in which 1M LiPF6 was dissolved in an organic solvent mixture of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) in a ratio of 3:4:3 was injected to manufacture lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 to 4.

[0148] Coin-type half cells were fabricated using the positive electrode manufactured as described above and lithium metal as the negative electrode. Each half cell was charged to 4.25V at 25°C with a constant current / voltage of 0.1C / 0.05C, and then discharged to 2.5V with a constant current of 0.1C. The initial charge capacity and initial discharge capacity were then measured.

[0149] [Table 3]

[0150] Each of the manufactured lithium secondary batteries (3cm x 4cm Full Cell) was charged to 4.25V at 25°C with a constant current of 0.33C, and then initially charged and discharged to 2.5V at a constant current of 0.33C. For each of these batteries, one cycle was performed by charging to 4.25V at 45°C with a constant current of 0.33C / 0.05C / constant voltage, and then discharging to 2.5V at a constant current of 0.33C. This cycle was repeated 100 times.

[0151] The capacity retention rate is expressed as a percentage of the degree to which the capacity at the 100th cycle is maintained relative to the capacity at the first cycle, and the resistance increase rate is expressed as a percentage of the degree to which the resistance at the 30th cycle increased relative to the resistance at the first cycle. The results are shown in Figure 6.

[0152] [Table 4]

[0153] As described above, when the positive electrode active material manufactured by the present invention is used in a secondary battery, it has been confirmed that it is possible to achieve the capacity without a decrease in initial capacity, and that a secondary battery with excellent capacity retention rate, low resistance increase rate, and improved life characteristics can be manufactured.

[0154] Experimental Example 4 The amount of gas generated was observed while the secondary batteries manufactured in Experimental Example 1 were stored at 60°C for a maximum of 6 weeks. The volume increase rate (%) relative to the initial volume was calculated and the amount of gas generated was compared. The results are shown in Figure 7.

[0155] [Table 5]

[0156] As shown in the results above, when the positive electrode active material of the example was used, it was confirmed that gas generation was significantly reduced and the degree of volume increase was reduced.

[0157] Experimental Example 5 Figures 8 to 13 show the distribution and content of boron in the cathode active material, analyzed using a TEM (instrument name: Titan G2 80-200 ChemiSTEM w / Gatan Continuum EELS system, FEI).

[0158] Specifically, before analysis, TEM samples with a thickness of 70 nm or less were prepared using a FIB (instrument name: Helios G4 UX, FEI) equipped with target sampling capabilities for cathode active material particles. The measurement conditions were an acceleration voltage of 200 kV and a dispersion of 0.05 eV / channel.

[0159] Furthermore, the first and second peaks were measured using the TEM-EELS spectrum, and their values ​​were compiled.

[0160] [Table 6]

[0161] As shown in Table 6 above, the positive electrode active materials of Examples 1 and 2 according to the present invention were confirmed to show a first peak and a second peak, thereby indicating the presence of boron.

Claims

1. (S1) A step of preparing a positive electrode active material precursor containing nickel, cobalt, and manganese, and containing 60 mol% or more of nickel among the total metals other than lithium, (S2) A step of mixing the positive electrode active material precursor and lithium raw material and performing a primary heat treatment at 710 to 720°C to form a lithium transition metal oxide in the form of secondary particles in which primary particles are aggregated, (S3) The step of mixing the lithium transition metal oxide and the cobalt ion-containing source and performing a secondary heat treatment at 680 to 720°C to form a secondary heat-treated product. (S4) A step of washing the secondary heat-treated product with water, (S5) A method for producing a positive electrode active material, comprising the step of dry mixing the water-washed secondary heat-treated material and the boron coating source and heat-treating them.

2. The method for producing a positive electrode active material according to claim 1, wherein step (S3) is to form a coating layer containing cobalt at the interface between primary particles that make up secondary particles of lithium transition metal oxide.

3. The method for producing a positive electrode active material according to claim 1, wherein the lithium transition metal oxide is a compound represented by the following chemical formula 1. [Chemical formula 1] Li ａ Ni １－（ｂ＋ｃ＋ｄ） Co ｂ Mn ｃ Q ｄ O ２ In the above formula, Q is one or more elements selected from the group consisting of Al, Si, V, Nb, Mo, Y, Sn, Zr, B, W, Mg, Ce, Hf, Ta, Ti, Sr, Ba, F, P, S, and La. 0.9 ≤ a ≤ 1.1, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.1, and 0 < b + c + d ≤ 0.

4.

4. The method for producing a positive electrode active material according to claim 1, wherein step (S4) is performed for 3 to 60 minutes using a water washing solution at 1 to 90°C.

5. The cobalt ion-containing source is Co(OH) ２ , Co ２ O ３ , CoCO ３ , Co ５ (CO ３ ) ２ (OH) ６ , Co ３ (PO ４ ) ２ , CoF ３ , CoOOH, Co(OCOCH ３ ) ２ ·4H ２ O, Co(NO ３ )·6H ２ O, Co ３ O ４ , Co(SO ４ ) ２ ·7H ２ O and CoC ２ O ４ The method for producing a positive electrode active material according to claim 1, which is one or more selected from the group consisting of

6. The boron-coated source is H ３ BO ３ , B ４ C, B ２ O ３ BF ３ , (C ３ H ７ O) ３ B, (C ６ H ５ O) ３ B [da ３ (CH ２ ) ３ O] ３ B, C １３ H １９ O ３ , C ６ H ５ B (OH) ２ and B ２ F ４ A method for producing a positive electrode active material according to claim 1, wherein the active material is one or more selected from the group consisting of the following:

7. A lithium transition metal oxide comprising nickel, cobalt, and manganese, and having a secondary particle form in which primary particles are aggregated, The aforementioned lithium transition metal oxide contains 60 mol% or more of nickel among the total metals other than lithium. A coating layer containing cobalt is formed on the surface of the secondary particles of the lithium transition metal oxide and at the interface between primary particles located inside them, and the primary particles have a cobalt content of 7.0 mol% or more relative to the total metal. The spectrum measured for the aforementioned lithium transition metal oxide using TEM-EELS, which combines a transmission electron microscope (TEM) with electron energy loss spectroscopy (EELS), is as follows: The waveform includes a first peak in the region corresponding to a depth of 50 nm from the surface of the primary particle located on the surface of the secondary particle, and a second peak in the region corresponding to a depth of 50 nm from the surface of the primary particle located in the core of the secondary particle. The surface portion of the secondary particle is a region corresponding to a depth of 50 nm from the surface of the secondary particle. The core portion of the secondary particle is a region that extends more than 3 μm from the surface of the secondary particle. The first and second peaks are positive electrode active materials, with the peaks in the TEM-EELS spectrum being in the 180-200 eV range.

8. The positive electrode active material according to claim 7, wherein the intensities of the first and second peaks are 1:0.5 to 1:

20.

9. The positive electrode active material according to claim 7, wherein the primary particles have a cobalt content of 10.0 mol% or more relative to the total metal.

10. The positive electrode active material according to claim 7, wherein the lithium transition metal oxide has a concentration gradient in which cobalt gradually decreases from the surface to the center of the primary particle.

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