Method for manufacturing positive electrode active material

Abstract

The present invention relates to a method for producing a positive electrode active material, and more particularly to a method for producing a positive electrode active material comprising: (A) mixing a positive electrode active material precursor and a lithium (Li)-containing raw material, and then firing them to produce a lithium composite transition metal oxide; and (B) mixing the lithium composite transition metal oxide and a coating raw material, and then heat-treating them to form a coating layer on the lithium composite transition metal oxide, wherein the heat treatment includes a heating section in which the temperature is increased and a maintenance section in which the temperature is maintained, and includes a section in which water vapor is introduced only in the heating section.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0107877 filed on August 17, 2023, and all the contents disclosed in the literature of the Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a positive electrode active material.

Background Art

[0003] Recently, with the development of technologies related to mobile devices and electric vehicles and the increasing demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

[0004] As positive electrode active materials of lithium secondary batteries, lithium transition metal oxides such as lithium cobalt oxide such as LiCoO2, lithium nickel oxide such as LiNiO2, lithium manganese oxide such as LiMnO2 or LiMn2O4, and lithium iron phosphate oxide such as LiFePO4 have been developed, and recently, Li[Ni a Co b Mn c O2, Li[Ni a Co b Al c O2, Li[Ni a Co b Mn c Al d O2, such as lithium composite transition metal oxides containing two or more transition metals, have been developed and widely used.

[0005] Particularly, recently, with the development of technologies such as electric vehicles, the demand for high-capacity secondary batteries has been increasing, and accordingly, active research has been conducted on positive electrodes using high-nickel (High-Ni) based positive electrode active materials having excellent capacity characteristics.

[0006] The high-nickel cathode active material is manufactured by mixing a precursor and a lithium raw material substance and then firing them. Here, since the firing is performed at a relatively low temperature, the amount of residual lithium corresponding to a by-product increases on the surface of the cathode active material, and the residual lithium in the form of LiOH and / or Li2CO3 reacts with an electrolyte or the like in the battery to generate gas, causing a problem of swelling.

[0007] When introducing a water washing step to remove such by-products, there are problems that damage occurs on the surface of the cathode active material during water washing, resulting in a decrease in capacity characteristics and rate characteristics, and the process steps become complicated. Also, after water washing, due to the difference in surface energy between the surface of the cathode active material and the surface of the coating raw material substance, it is difficult to form a uniform coating layer, and there is a problem that an excessive amount of the coating raw material is used.

[0008] Therefore, there is a situation where it is necessary to secure a technology for reducing by-products on the surface of the cathode active material and improving coating efficiency.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] In order to solve the above problems, the technical problem of the present invention is to provide a method for manufacturing a cathode active material that can reduce by-products on the surface of a lithium composite transition metal oxide and improve coating efficiency.

Means for Solving the Problems

[0011] In order to solve the above problems, the present invention provides a method for manufacturing a cathode active material.

[0012] (1) The present invention provides a method for producing a positive electrode active material, comprising the steps of (A) mixing a positive electrode active material precursor and a lithium (Li)-containing raw material, and then firing them to produce a lithium composite transition metal oxide, and (B) mixing the lithium composite transition metal oxide and a coating raw material, and then heat-treating them to form a coating layer on the lithium composite transition metal oxide, wherein the heat treatment includes a heating section in which the temperature is increased and a maintenance section in which the temperature is maintained, and includes a section in which water vapor is introduced only in the heating section.

[0013] (2) The present invention provides a method for producing a positive electrode active material having a composition represented by the following chemical formula 1, in accordance with (1) above. [Chemical formula 1] Ni a Mn b Co c M 1 d (OH)2 In the above chemical formula 1, M 1 is one or more elements selected from Al, Zr, W, Mg, Ti, Y, and B, and 0.5 ≤ a < 1, 0 ≤ b < 0.5, 0 ≤ c < 0.5, and 0 ≤ d ≤ 0.1.

[0014] (3) The present invention provides a method for producing a positive electrode active material in which the firing is performed at a temperature of 700°C to 1,000°C in the case of (1) or (2) above.

[0015] (4) The present invention provides a method for producing a positive electrode active material in any one of (1) to (3) above, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 2. [Chemical formula 2] Li 1+x1 Ni a1 Mn b1 Co c1 M 2 d1 O2 In the above chemical formula 2, M 2x1 is one or more elements selected from Al, Zr, W, Mg, Ti, Y, and B, and satisfies the following conditions: 0.0 ≤ x1 ≤ 0.10, 0.5 ≤ a1 < 1, 0 ≤ b1 < 0.5, 0 ≤ c1 < 0.5, and 0 ≤ d1 ≤ 0.1.

[0016] (5) The present invention provides a method for producing a positive electrode active material in which the lithium composite transition metal oxide is in the form of a single particle, according to any one of (1) to (4) above.

[0017] (6) The present invention provides a method for producing a positive electrode active material in which any one of the above (1) to (5) does not include a water washing step.

[0018] (7) The present invention provides a method for producing a positive electrode active material in any one of (1) to (6) above, wherein the coating raw material is a hydroxide containing one or more selected from Co, Al and Nb.

[0019] (8) The present invention provides a method for producing a positive electrode active material in any one of (1) to (7) above, wherein the coating raw material is cobalt hydroxide.

[0020] (9) The present invention provides a method for producing a positive electrode active material in any one of (1) to (8) above, wherein the coating raw material is mixed in an amount of 0.5 to 5 parts by weight per 100 parts by weight of the lithium composite transition metal oxide.

[0021] (10) The present invention provides a method for producing a positive electrode active material in any one of the above (1) to (9), wherein the heating interval includes an interval in which water vapor is introduced at a temperature of 600°C or lower.

[0022] (11) The present invention provides a method for producing a positive electrode active material in any one of (1) to (10) above, wherein the heating interval has a heating rate of 1°C / min to 10°C / min.

[0023] (12) The present invention provides a method for producing a positive electrode active material in any one of the above (1) to (11), wherein the amount of water vapor introduced is such that the water content (χ) calculated by the following formula 1 is 1% to 10%.

number

[0024] (13) The present invention provides a method for producing a positive electrode active material in any one of the above (1) to (12), wherein the section in which water vapor is introduced is carried out under an oxidizing atmosphere.

[0025] (14) The present invention provides a method for producing a positive electrode active material in any one of (1) to (13) above, wherein the maintenance interval is 500°C to 900°C, and the heat treatment is performed while maintaining the temperature.

[0026] (15) The present invention provides a method for producing a positive electrode active material in any one of (1) to (14) above, wherein the maintenance interval is 1 hour to 12 hours.

[0027] (16) The present invention provides a method for producing a positive electrode active material in any one of the above (1) to (15), wherein the maintenance section does not include a section in which water vapor is introduced. [Effects of the Invention]

[0028] The manufacturing method of the present invention, by including a section in which water vapor is introduced during the heating section for forming the coating layer, can reduce by-products on the surface of the positive electrode active material, can form a thin and uniform coating layer, and can improve coating efficiency. [Brief explanation of the drawing]

[0029] [Figure 1] This is an EPMA (Electron Probe Microanalysis) mapping image of the positive electrode active material produced in Example 1. [Figure 2] This is an EPMA mapping image of the positive electrode active material produced in Example 2. [Figure 3] This is an EPMA mapping image of the positive electrode active material manufactured in Example 3. [Figure 4] This is an EPMA mapping image of the positive electrode active material produced in Comparative Example 1. [Modes for carrying out the invention]

[0030] The present invention will be described in more detail below to facilitate understanding of it.

[0031] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0032] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more different features, figures, steps, components, or combinations thereof.

[0033] In this specification, the term "on top of" means not only when one configuration is formed directly on top of another, but also when a third configuration is interposed between these configurations.

[0034] In this specification, the single particle morphology is a concept contrasted with the spherical secondary particle morphology formed by the aggregation of primary particles having a size of several nm to less than 0.5 μm produced by conventional methods. Instead, it refers to cathode active materials and / or lithium composite transition metal oxides having a non-spherical particle morphology formed by the aggregation of primary particles of 0.5 μm or larger.

[0035] For example, in the present invention, the positive electrode active material in single-particle form may be a single particle consisting of one primary particle of 0.5 μm or larger, or it may be in the form of several primary particles of 0.5 μm or larger aggregated together. On the other hand, "primary particle" refers to the smallest unit of particle that can be recognized when the positive electrode active material is observed with a scanning electron microscope.

[0036] In this specification, "moisture content" may be measured using a heating-type moisture meter (for example, the MX-50 manufactured by AND Corporation). Specifically, after placing approximately 5 g of the sample in the sample dish inside the apparatus, the lid of the apparatus is closed and the temperature of the sample dish is set to 100°C to 150°C, thereby measuring the degree to which the mass decreases while evaporating the moisture contained in the powder sample. Here, the point at which the mass no longer decreases is called the completely dried state. Moisture content may also be expressed as a percentage (%) of the difference between the mass (g) of the sample before and after complete drying, by measuring the mass of the sample before and after complete drying.

[0037] Method for manufacturing positive electrode active material The method for producing a positive electrode active material according to the present invention will be described below.

[0038] The method for producing a positive electrode active material according to the present invention includes the steps of (A) mixing a positive electrode active material precursor and a lithium (Li)-containing raw material, and then firing them to produce a lithium composite transition metal oxide, and (B) mixing the lithium composite transition metal oxide and a coating raw material, and then heat-treating them to form a coating layer on the lithium composite transition metal oxide, wherein the heat treatment includes a heating section in which the temperature is increased and a maintenance section in which the temperature is maintained, and includes a section in which water vapor is introduced only in the heating section.

[0039] The method for producing the positive electrode active material according to the present invention will be described in more detail below.

[0040] (A) Step The process includes the step of mixing a positive electrode active material precursor and a lithium (Li)-containing raw material, followed by calcination to produce a lithium composite transition metal oxide.

[0041] According to one embodiment of the present invention, the positive electrode active material precursor may have a composition represented by the following chemical formula 1.

[0042] [Chemical formula 1] Ni a Mn b Co c M 1 d (OH)2

[0043] In the above chemical formula 1, M 1 is one or more selected from Al, Zr, W, Mg, Ti, Y, and B. 0.5 ≤ a < 1, 0 ≤ b < 0.5, 0 ≤ c < 0.5, and 0 ≤ d ≤ 0.1.

[0044] Said M 1 This is a doping element, specifically, the aforementioned M 1 This may be at least one selected from Al, Zr, W, Mg, Ti, Y, and B.

[0045] The above a is the molar ratio of nickel (Ni) to the total metal in the positive electrode active material precursor, and may be 0.5 or more, 0.7 or more, 0.8 or more, 0.85 or more, or 0.88 or more, and may be 0.9 or less, 0.95 or less, 0.98 or less, or less than 1. When a satisfies the above range, a high energy density is observed and high capacity characteristics can be achieved.

[0046] The above b is the molar ratio of manganese (Mn) among the total metals in the positive electrode active material precursor, and may be 0 or more, 0.03 or more, 0.05 or more, or 0.07 or more, and may be 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, or less than 0.5.

[0047] The aforementioned c is the molar ratio of cobalt (Co) among the total metals in the positive electrode active material precursor, and may be 0 or more, 0.01 or more, 0.02 or more, or 0.03 or more, and may be 0.05 or less, 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, or less than 0.5.

[0048] The above d is M of the total metal in the positive electrode active material precursor. 1 This is the molar ratio, which may be 0 or greater, 0.01 or greater, 0.02 or greater, 0.03 or greater, or 0.04 or greater, and may also be 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, or 0.1 or less.

[0049] When a, b, c, and d satisfy the aforementioned ranges, a positive electrode active material exhibiting excellent energy density and high capacity characteristics can be realized.

[0050] The transition metal hydroxide having the composition represented by the chemical formula 1 can be a commercially available product or can be produced by a method for producing transition metal hydroxides that is well known in the art, such as the coprecipitation method.

[0051] The lithium (Li)-containing raw material may be a lithium-containing sulfate, nitrate, carbonate, or hydroxide. Specifically, the lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiBr, LiI, Li2O, Li2SO4, etc.

[0052] The positive electrode active material precursor and the lithium (Li)-containing raw material may be mixed such that the molar ratio (M:Li) of the transition metal (M) contained in the positive electrode active material precursor to the lithium (Li) contained in the lithium (Li)-containing raw material is 1:1.00 to 1.10. In this case, it is possible to prevent an excess amount of lithium from entering the positive electrode active material structure, and the content of unreacted residual lithium may be low.

[0053] The mixing can be carried out by dry mixing or wet mixing. When the components are mixed by dry mixing, the calcination process can be performed without a separate drying step. When the components are mixed by wet mixing, they may be prepared by adding them to a mixture of water and a solvent, specifically water, or an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.), or a solution containing each raw material, specifically an aqueous solution, may be prepared, mixed, the mixed components may be spray-dried, and then the calcination process may be performed.

[0054] Each raw material and cathode active material precursor can be used in appropriate quantities, taking into account the content of each metal element in the final lithium composite metal oxide.

[0055] According to one embodiment of the present invention, the firing may be carried out at a temperature of 700°C or higher, 750°C or higher, 800°C or higher, or at a temperature of 850°C or lower, 900°C or lower, 950°C or lower, or 1,000°C or lower. Furthermore, the firing may be carried out for 10 hours or more, 15 hours or more, or 20 hours or more, or for a period of 25 hours or less, 30 hours or less, or 40 hours or less, and the firing may be carried out in an oxygen atmosphere. When carried out in the above temperature range, time range, and atmosphere, the lithium (Li)-containing raw material material melts efficiently, the reaction between the positive electrode active material precursor and the lithium (Li)-containing raw material material is promoted, and lithium composite transition metal oxide particles can be grown efficiently.

[0056] According to one embodiment of the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 2.

[0057] [Chemical formula 2] Li 1+x1 Ni a1 Mn b1 Co c1 M 2 d1 O2

[0058] In the aforementioned chemical formula 2, M 2 is one or more selected from Al, Zr, W, Mg, Ti, Y, and B. 0.0≦x1≦0.10, 0.5≦a1<1, 0≦b1<0.5, 0≦c1<0.5, 0.0≦d1≦0.1.

[0059] Said M 2 This is a doping element, specifically, the aforementioned M 2 The M may be at least one selected from Al, Zr, W, Mg, Ti, Y, and B. 2 Although it is not an essential component, when included in appropriate amounts, it can improve the particle shape of the positive electrode active material and enhance the stability of its crystal structure.

[0060] The aforementioned x1 may be 0 or greater, 0.01 or greater, 0.02 or greater, 0.03 or greater, or 0.04 or greater, and may also be 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, or 0.1 or less.

[0061] The a1 is the molar ratio of nickel (Ni) to the total metals other than lithium in the lithium composite transition metal oxide, and may be 0.5 or more, 0.7 or more, 0.8 or more, 0.85 or more, or 0.88 or more, and may be 0.9 or less, 0.95 or less, 0.98 or less, or less than 1. When a1 satisfies the above range, it exhibits high energy density and high capacity characteristics can be achieved.

[0062] The b1 is the molar ratio of manganese (Mn) among all metals other than lithium in the lithium composite transition metal oxide, and may be 0 or more, 0.03 or more, 0.05 or more, or 0.07 or more, and may be 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, or less than 0.5.

[0063] The aforementioned c1 is the molar ratio of cobalt (Co) among all metals other than lithium in the lithium composite transition metal oxide, and may be 0 or more, 0.01 or more, 0.02 or more, or 0.03 or more, and may be 0.05 or less, 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, or less than 0.5.

[0064] The aforementioned d1 is M, which is the total amount of metal other than lithium in the lithium composite transition metal oxide. 2 The molar ratio is 0 or greater, 0.01 or greater, 0.02 or greater, 0.03 or greater, or 0.04 or greater, and may be 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, or 0.1 or less. When d1 satisfies the above range, the stability of the crystal structure of the positive electrode active material can be improved, and the output characteristics, capacity characteristics, and lifetime characteristics can be improved.

[0065] When x1, a1, b1, c1, and d1 satisfy the above ranges, a positive electrode active material exhibiting excellent energy density and high capacity characteristics can be obtained.

[0066] According to one embodiment of the present invention, the lithium composite transition metal oxide may be in the form of a single particle. When the lithium composite transition metal oxide is in the form of a single particle, the structural stability of the positive electrode active material containing the lithium composite transition metal oxide can be increased. In connection with this, when rolling for electrode manufacturing or driving the cell, particle cracking (micro / macro-crack) due to grain boundaries can be suppressed, the area of ​​grain boundaries in contact with the electrolyte is reduced, the generation of gas due to side reactions with the electrolyte is reduced, and the life characteristics of the secondary battery can be improved.

[0067] (B) Step The process includes mixing the lithium composite transition metal oxide and the coating raw material, followed by heat treatment to form a coating layer on the lithium composite transition metal oxide, wherein the heat treatment includes a heating section in which the temperature is increased and a maintenance section in which the temperature is maintained, and includes a section in which water vapor is introduced only in the heating section.

[0068] Conventionally, when forming a coating layer on lithium composite transition metal oxides, either an excessive amount of coating raw material was used or a water washing treatment was performed to reduce by-products on the surface of the lithium composite transition metal oxide. However, when an excessive amount of coating raw material was used, by-products still remained, resulting in a decrease in efficiency. When water washing treatment was performed, the surface of the positive electrode active material was damaged, the process steps became complicated, and it was not economically viable.

[0069] The inventors have discovered that when forming a coating layer on a lithium composite transition metal oxide, after mixing the lithium composite transition metal oxide and the coating raw material, by introducing steam at a specific point during the heating process, it is possible to reduce by-products on the surface of the lithium composite transition metal oxide, thereby enabling the formation of a thin and uniform coating layer and improving coating efficiency. This led to the completion of the present invention.

[0070] On the other hand, when steam is introduced during the heat treatment process to maintain the temperature, the steam promotes the reduction reaction between Li2O and H2O, which increases the amount of residual lithium, a by-product on the surface of the lithium composite transition metal oxide, leading to a decrease in coating efficiency.

[0071] According to one embodiment of the present invention, the coating layer may be in a discontinuous or continuous form.

[0072] According to one embodiment of the present invention, the rinsing step may be omitted. As a result, damage to the surface of the positive electrode active material is prevented, the process is simplified, and there are economic benefits.

[0073] According to one embodiment of the present invention, the coating raw material may be a hydroxide containing one or more selected from Co, Al, and Nb. In particular, in the case of cobalt hydroxide, the resistance characteristics of the lithium transition metal oxide can be improved, and the output characteristics and capacitance characteristics can be improved.

[0074] According to one embodiment of the present invention, the coating raw material may be 0.5 parts by weight or more, 1 part by weight or more, 1.5 parts by weight or more, or 2 parts by weight or more, or 3 parts by weight or less, 4 parts by weight or less, or 5 parts by weight or less, per 100 parts by weight of the lithium composite transition metal oxide. When the amount of the coating raw material is within the above range, the coating layer is thin and uniform, coating efficiency is improved, and there is an economic effect.

[0075] On the other hand, the heat treatment includes a heating section in which the temperature is increased and a maintenance section in which the temperature is maintained, and includes a section in which steam is introduced only in the heating section. That is, the section in which steam is introduced exists only in the heating section, and other sections other than the heating section do not include a section in which steam is introduced. Specifically, the maintenance section does not have to include a section in which steam is introduced. Including a section in which steam is introduced in the heating section promotes the reaction between the coating raw material and residual lithium, eliminating the need for a further washing step to remove surface by-products, thus reducing by-products on the surface of the lithium composite transition metal oxide compared to conventional methods and simplifying the process steps. On the other hand, if a section in which steam is introduced is included in other sections other than the heating section, specifically in the maintenance section, the steam promotes the reduction reaction between Li2O and H2O, which increases the amount of residual lithium, a by-product on the surface of the lithium composite transition metal oxide, and reduces the coating efficiency.

[0076] According to one embodiment of the present invention, the heating section may include a section in which steam is introduced at a temperature of 600°C or lower. Specifically, it may include a section in which steam is introduced at a temperature of 0°C to 250°C, a section in which steam is introduced at a temperature of 250°C to 500°C, or a section in which steam is introduced at a temperature of 0°C to 500°C. When the section in which steam is introduced is within the temperature range, the reaction between the coating raw material and residual lithium can be efficiently controlled and the amount of heat required for the reaction can be sufficiently supplied.

[0077] According to one embodiment of the present invention, the heating interval may have a heating rate of 1°C / min or more, 2°C / min or more, 3°C / min or more, or 4°C / min or more, and may also be 6°C / min or less, 7°C / min or less, 8°C / min or less, 9°C / min or less, or 10°C / min or less. When the heating rate in the heating interval is within the above range, the production volume is excellent, the temperatures of the reactor, lithium composite transition metal oxide and coating raw material are similar, and all the heat required for the set maintenance temperature can be received. In particular, when the heating rate is 5°C / min, the heat required for the reaction can be supplied efficiently.

[0078] According to one embodiment of the present invention, the water vapor may have a water content (χ) of 1% or more, 2% or more, 3% or more, 4% or more, or 5% or more according to the following formula 1, and may be introduced in an amount such that the water content is 6% or less, 7% or less, 8% or less, 9% or less, or 10% or less.

[0079]

number

[0080] In the above formula 1, α is the mass (g) of the lithium composite transition metal oxide and coating raw material immediately after passing through the section where water vapor is introduced, and β is the mass (g) of the lithium composite transition metal oxide and coating raw material after completely drying immediately after passing through the section where water vapor is introduced.

[0081] According to one embodiment of the present invention, the section in which water vapor is introduced may be carried out under an oxidizing atmosphere. In this case, the atmosphere necessary for the reaction can be provided, and the reaction between the coating raw material and residual lithium can be efficiently controlled.

[0082] According to one embodiment of the present invention, the maintenance interval may be 500°C or higher, 600°C or higher, or 700°C or higher, and the temperature may be maintained at 800°C or lower, 850°C or lower, or 900°C or lower while performing heat treatment. When the temperature of the maintenance interval is within the above range, the coating raw material melts, and there is a stabilization effect on the surface of the positive electrode active material by recrystallization of the lithium composite transition metal oxide surface.

[0083] According to the present invention, the maintenance period may be 1 hour or more, 2 hours or more, or 3 hours or less, 5 hours or less, or 12 hours or less. When the duration of the maintenance period is within the above range, sufficient thermal energy is supplied to the lithium composite transition metal oxide and the coating raw material, resulting in a more uniform coating overall.

[0084] positive electrode active material Furthermore, the present invention provides a positive electrode active material manufactured by the manufacturing method described above.

[0085] The positive electrode active material according to the present invention is manufactured by the manufacturing method described above and is a positive electrode active material having a uniform coating layer on a lithium composite transition metal oxide. The coating layer may have a small concentration deviation of the coating elements.

[0086] positive electrode Furthermore, the present invention provides a positive electrode for a lithium secondary battery containing the above-mentioned positive electrode active material.

[0087] 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.

[0088] 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 usually 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.

[0089] The positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0090] Here, 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 this content range, excellent capacity characteristics can be observed.

[0091] Here, 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. Of these, one 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.

[0092] 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, 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.

[0093] 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 the entire positive electrode assembly with a positive electrode composite material prepared by dissolving or dispersing the positive electrode active material, a binder, and a conductive material selectively in a solvent, 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.

[0094] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone or in a mixture of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have 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.

[0095] 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.

[0096] 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.

[0097] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes. 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0102] 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 thereof can be used. A metallic lithium thin film can 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. Examples of low-crystalline carbon include soft carbon and hard carbon, while 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.

[0103] 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.

[0104] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and can usually be added in an amount of 0.1% to 10% by weight relative to 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.

[0105] 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.

[0106] 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.

[0107] 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. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability 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. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0108] 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.

[0109] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0110] 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); alcoholic 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.

[0111] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 4.0 M, more preferably 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.

[0112] 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.

[0113] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent and stable cycle characteristics, making it 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).

[0114] Accordingly, 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] The present invention will be described in detail below with reference to examples. However, the examples of the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0119] Examples and Comparative Examples Example 1 Ni 0.885 Co 0.035 Mn 0.08 (OH)2 and LiOH are mixed so that the molar ratio of (Ni+Co+Mn):Li is 1:1.03, and then fired at 800°C for 22 hours under an oxidizing atmosphere to produce LiNi. 0.885 Co 0.035 Mn 0.08A lithium composite transition metal oxide in single-particle form having a composition represented by O2 was prepared.

[0120] After mixing 100 parts by weight of lithium composite transition metal oxide with 2.5 parts by weight of Co(OH)2, steam was introduced into the firing furnace at a rate of 2.0 kg / hour, and the temperature was raised from 0°C to 500°C at a rate of 5°C / min under an oxidizing atmosphere. Then, the steam was stopped, and the temperature was raised from 500°C to 700°C at a rate of 5°C / min under an oxidizing atmosphere. Finally, the mixture was heat-treated while maintaining the temperature at 700°C for 2 hours under an oxidizing atmosphere to produce a positive electrode active material in which a coating layer containing Co was formed on the lithium composite transition metal oxide.

[0121] Example 2 In Example 1, 100 parts by weight of lithium composite transition metal oxide was mixed with 2.5 parts by weight of Co(OH)2. Then, steam was introduced into the firing furnace at a rate of 2.0 kg / hour, and the temperature was raised from 0°C to 250°C at a rate of 5°C / min under an oxidizing atmosphere. After that, the steam was stopped, and the temperature was raised from 250°C to 700°C at a rate of 5°C / min under an oxidizing atmosphere. Finally, the mixture was heat-treated while maintaining the temperature at 700°C for 2 hours under an oxidizing atmosphere to produce a positive electrode active material in which a coating layer containing Co was formed on the lithium composite transition metal oxide.

[0122] Example 3 In Example 1, 100 parts by weight of lithium composite transition metal oxide were mixed with 2.5 parts by weight of Co(OH)2. The mixture was then heated from 0°C to 250°C at a rate of 5°C / min, steam was introduced into the furnace at a rate of 2.0 kg / hour, and the temperature was raised from 250°C to 500°C at a rate of 5°C / min under an oxidizing atmosphere. After that, the steam was stopped, and the temperature was raised from 250°C to 700°C at a rate of 5°C / min under an oxidizing atmosphere. Finally, the mixture was heat-treated at 700°C for 2 hours under an oxidizing atmosphere to produce a positive electrode active material in which a coating layer containing Co was formed on the lithium composite transition metal oxide.

[0123] Comparative Example 1 To produce a positive electrode active material, 2.5 parts by weight of Co(OH)2 was mixed with 100 parts by weight of the lithium composite transition metal oxide produced in Example 1. The mixture was then heated in an oxidizing atmosphere from 0°C to 700°C at a rate of 5°C / min, and then heat-treated while maintaining the temperature at 700°C for 2 hours in an oxidizing atmosphere. A coating layer containing Co was formed on the lithium composite transition metal oxide.

[0124] Comparative Example 2 In Example 1, 100 parts by weight of lithium composite transition metal oxide was mixed with 2.5 parts by weight of Co(OH)2. The mixture was then heated from 0°C to 700°C at a rate of 5°C / min under an oxidizing atmosphere, and then steam was introduced into the furnace at a rate of 2.0 kg / hour. The mixture was then heat-treated at 700°C for 2 hours under an oxidizing atmosphere to produce a positive electrode active material in which a coating layer containing Co was formed on the lithium composite transition metal oxide.

[0125] Comparative Example 3 In Example 1, 2.5 parts by weight of Co(OH)2 were mixed with 100 parts by weight of lithium composite transition metal oxide. Then, steam was introduced into the firing furnace at a rate of 2.0 kg / hour, and the temperature was raised from 0°C to 500°C at a rate of 5°C / min under an oxidizing atmosphere. After that, the steam was stopped, and the temperature was raised from 500°C to 700°C at a rate of 5°C / min under an oxidizing atmosphere. Finally, steam was introduced into the firing furnace at a rate of 2.0 kg / hour, and the material was heat-treated while maintaining the temperature at 700°C for 2 hours under an oxidizing atmosphere to produce a positive electrode active material in which a coating layer containing Co was formed on the lithium composite transition metal oxide.

[0126] Experimental example Experimental Example 1: Evaluation of Residual Lithium To confirm the quality of the positive electrode active materials produced in Examples 1-3 and Comparative Examples 1-3, the residual lithium content present on the surface of the positive electrode active materials was measured.

[0127] Specifically, pH titration was performed to measure the residual lithium content present on the surface of the positive electrode active materials produced in Examples 1-3 and Comparative Examples 1-3. A Metrohm pH meter was used, and the pH was recorded after titrating 1 mL at a time. Specifically, 5 g of the positive electrode active material powder produced in Examples 1-3 and Comparative Examples 1-3 was mixed with 100 mL of distilled water. The pH was titrated while adding a 1 N HCl solution to the solution, and the Li2CO3 and LiOH content was derived. The results are shown in Table 1 below.

[0128] [Table 1]

[0129] Referring to Table 1, it can be confirmed that the amount of by-products present in the form of Li2Co3 and LiOH on the surface of the positive electrode active material produced in Examples 1 to 3, which include a section in which water vapor is introduced only during the heating section, is lower than the amount of by-products (total residual lithium) present on the surface of the positive electrode active material produced in Comparative Example 1, which does not include a section in which water vapor is introduced during the heating and maintenance sections, the positive electrode active material produced in Comparative Example 2, which includes a section in which water vapor is introduced during the maintenance section, and Comparative Example 3, which includes a section in which water vapor is introduced during both the heating and maintenance sections.

[0130] Experimental Example 2: Evaluation of Coating Efficiency The EPMA mapping images of the cathode active materials produced in Examples 1-3 and Comparative Example 1 are shown in order in Figures 1-4 below.

[0131] Specifically, EPMA is a technique for determining the concentration and distribution of elements in a solid sample by analyzing emitted X-rays using EDS after impacting the sample particles with an electron beam. The Co distribution within the positive electrode active material was shown using EPMA (JXA-8350F, -15kV, 20nA stage mapping conditions) of the positive electrode active material produced in Examples 1 to 3 and Comparative Example 1. Figure 1 is an EPMA (Electron Probe Microanalysis) mapping image of the positive electrode active material produced in Example 1, Figure 2 is an EPMA mapping image of the positive electrode active material produced in Example 2, Figure 3 is an EPMA mapping image of the positive electrode active material produced in Example 3, and Figure 4 is an EPMA mapping image of the positive electrode active material produced in Comparative Example 1.

[0132] In Figures 1 to 4 below, the areas indicated by arrows represent regions where the Co-containing coating layer exists in an aggregated form. In Comparative Example 1, which does not include a section in which water vapor is introduced during the heating phase, it can be confirmed that a larger number of Co-containing coating layers have aggregated compared to Examples 1 to 3.

[0133] In other words, if the heating process includes a section where water vapor is introduced only during the heating phase, it can be confirmed that the coating layer is formed thinly and uniformly, the concentration deviation of the coating elements on the positive electrode active material is reduced, and the coating efficiency is improved.

[0134] Experimental Example 3: Evaluation of Moisture Content To measure the moisture content of the powders produced in Examples 1-3 and Comparative Examples 1-3, a heating-type moisture meter (MX-50, manufactured by AND Corporation) was used to measure the moisture content of each powder produced in Examples 1-3 and Comparative Examples 1-3. The results are shown in Table 2 below.

[0135] Specifically, lithium composite transition metal oxides and coating raw materials were obtained immediately after passing through the section in which water vapor was introduced in Examples 1-3 and Comparative Examples 1-3. Approximately 5 g of each sample was placed in a sample dish in the apparatus, and then the lid of the apparatus was closed and the temperature of the sample dish was set to 130°C. The degree to which the mass decreased while evaporating the water contained in the lithium composite transition metal oxides and coating raw materials was measured. Here, the point at which the mass no longer decreases was defined as the completely dried state.

[0136] Table 2 below shows the moisture content (χ), that is, the percentage difference (moisture content (%)) between the mass (g) of the lithium composite transition metal oxide and coating raw material immediately after passing through the section in which water vapor is introduced and the mass (g) of the lithium composite transition metal oxide and coating raw material after completely drying immediately after passing through the section in which water vapor is introduced.

[0137] On the other hand, in the case of Comparative Example 1, which does not include a section in which water vapor is introduced, the percentage difference (moisture content (%)) between the mass (g) of the lithium composite transition metal oxide and the coating raw material and the mass (g) of the lithium composite transition metal oxide and the coating raw material after they have been completely dried is shown in Table 2 below.

[0138] [Table 2]

[0139] Table 2 confirms that in Examples 1-3, which include a section where steam is introduced only during the heating phase, the moisture content ranged from 1.7% to 5.2%.

[0140] In other words, by introducing water vapor to satisfy the aforementioned moisture content, the by-products present on the surface of the positive electrode active material reacted appropriately with the coating raw material, resulting in a uniform coating overall.

Claims

1. (A) A step of mixing a positive electrode active material precursor and a lithium (Li)-containing raw material, and then firing them to produce a lithium composite transition metal oxide, (B) The process includes the step of mixing the lithium composite transition metal oxide and the coating raw material, and then heat-treating the mixture to form a coating layer on the lithium composite transition metal oxide, The heat treatment includes a heating section in which the temperature is increased and a maintenance section in which the temperature is maintained. A method for producing a positive electrode active material, comprising a section in which water vapor is introduced only into the aforementioned heating section.

2. The method for producing a positive electrode active material according to claim 1, wherein the positive electrode active material precursor has a composition represented by the following chemical formula 1. [Chemical formula 1] Ni ａ Mn ｂ Co ｃ M １ ｄ (OH) ２ In the aforementioned chemical formula 1, M １ is one or more selected from Al, Zr, W, Mg, Ti, Y, and B. 0.5 ≤ a < 1, 0 ≤ b < 0.5, 0 ≤ c < 0.5, and 0 ≤ d ≤ 0.

1.

3. The method for producing a positive electrode active material according to claim 1, wherein the firing is carried out at a temperature of 700°C to 1,000°C.

4. The method for producing a positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 2. [Chemical formula 2] Li １＋ｘ１ Ni ａ１ Mn ｂ１ Co ｃ１ M ２ ｄ１ O ２ In the above chemical formula 2, M ２ is one or more selected from Al, Zr, W, Mg, Ti, Y, and B. 0.0 ≤ x1 ≤ 0.10, 0.5 ≤ a1 < 1, 0 ≤ b1 < 0.5, 0 ≤ c1 < 0.5, 0 ≤ d1 ≤ 0.

1.

5. The method for producing a positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide is in the form of a single particle.

6. A method for producing a positive electrode active material according to claim 1, which does not include a water washing step.

7. The method for producing a positive electrode active material according to claim 1, wherein the coating raw material is a hydroxide containing one or more selected from Co, Al, and Nb.

8. The method for producing a positive electrode active material according to claim 1, wherein the coating raw material is cobalt hydroxide.

9. The method for producing a positive electrode active material according to claim 1, wherein the coating raw material is mixed in an amount of 0.5 to 5 parts by weight per 100 parts by weight of the lithium composite transition metal oxide.

10. The method for producing a positive electrode active material according to claim 1, wherein the heating section includes a section in which steam is introduced at a temperature of 600°C or lower.

11. The method for producing a positive electrode active material according to claim 1, wherein the heating rate in the heating interval is 1°C / min to 10°C / min.

12. The method for producing a positive electrode active material according to claim 1, wherein the water vapor is introduced in an amount such that the water content (χ) calculated by the following formula 1 becomes 1% to 10%. [Math 1] In the above formula 1, α is the mass (g) of the lithium composite transition metal oxide and coating raw material immediately after passing through the section in which water vapor is introduced, and β is the mass (g) of the lithium composite transition metal oxide and coating raw material after completely drying immediately after passing through the section in which water vapor is introduced.

13. The method for producing a positive electrode active material according to claim 1, wherein the section in which the water vapor is introduced is carried out under an oxidizing atmosphere.

14. The method for producing a positive electrode active material according to claim 1, wherein the aforementioned maintenance interval is 500°C to 900°C, and heat treatment is performed while maintaining the temperature.

15. The method for producing a positive electrode active material according to claim 1, wherein the maintenance interval is performed for 1 to 12 hours.

16. The method for producing a positive electrode active material according to claim 1, wherein the maintenance section does not include a section for introducing water vapor.

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