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

Abstract

The present invention relates to a positive electrode active material for lithium secondary batteries, which is a single-particle nickel-containing lithium transition metal oxide, wherein the nickel content is 50 to 70 mol% based on the total number of moles of the transition metal, and the lithium transition metal oxide contains Zr and Y as grain growth promoting elements, with the total content of Zr and Y being 2500 to 5200 ppm based on the weight of the lithium transition metal oxide.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same, and more specifically, to a single-particle positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] In a lithium-ion secondary battery, electrical energy is produced by oxidation and reduction reactions that occur when lithium ions are inserted into / deintercalated at the positive and negative electrodes, with an organic or polymer electrolyte filling the space between the positive and negative electrodes, which are made of an active material that allows for the insertion and deintercalation of lithium ions.

[0003] Lithium-ion oxide (LiFePO4), lithium-cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4), and other lithium phosphate compounds have been used as positive electrode active materials for lithium-ion secondary batteries. Of these, lithium-cobalt oxide (LiCoO2) has the advantages of a high operating voltage and excellent capacity characteristics, and is widely used as a positive electrode active material for high voltage applications. However, due to the rising price and unstable supply of cobalt (Co), there are limitations to its large-scale use as a power source in fields such as electric vehicles, and the need for developing alternative positive electrode active materials has emerged.

[0004] Therefore, nickel-cobalt-manganese lithium composite transition metal oxides (hereinafter referred to as "NCM-based lithium composite transition metal oxides") were developed in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). However, conventionally developed NCM-based lithium composite transition metal oxides generally have a secondary particle form in which primary particles are aggregated, resulting in a large specific surface area, low particle strength, and a high lithium by-product content, which leads to a large amount of gas generation during cell operation and reduced stability.

[0005] In response to this, development is underway on single-particle cathode active materials, which are not in the existing secondary particle form. However, in order to manufacture single particles, firing proceeds at a higher temperature than when manufacturing secondary particles, and at this time, over-firing often occurs, causing layered structure crystal defects and degrading electrochemical properties such as capacity and output.

[0006] To address this, lowering the firing temperature resulted in insufficient growth of crystal grains within a single particle, leading to a deterioration of particle strength and lifetime characteristics. Furthermore, insufficient growth of the particle size resulted in a lower rolling density and a deterioration of electrode energy density. [Overview of the project] [Problems that the invention aims to solve]

[0007] One objective of the present invention is to provide a positive electrode active material for lithium secondary batteries, which is a single particle, has few layered structure crystal defects and excellent electrochemical properties, maximizes the size of the crystal grains, and not only has excellent particle strength and lifetime characteristics, but also has a large average particle size and can improve electrode energy density, as well as a method for producing the same and a lithium secondary battery containing the same. [Means for solving the problem]

[0008] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a single-particle nickel-containing lithium transition metal oxide, wherein the nickel content is 50 to 70 mol% based on the total number of moles of the transition metal, and the lithium transition metal oxide contains Zr and Y as grain growth promoting elements, with the total content of Zr and Y being 2500 to 5200 ppm based on the weight of the lithium transition metal oxide.

[0009] The Zr content can be 1300 to 2800 ppm by weight of the lithium transition metal oxide.

[0010] The content of Y can be 1400 to 2400 ppm based on the weight of the lithium transition metal oxide.

[0011] The content of cobalt in the lithium transition metal oxide can be 5 to 20 mol% based on the total number of moles of transition metals.

[0012] The content of manganese in the lithium transition metal oxide can be 10 mol% or more based on the total number of moles of transition metals.

[0013] The positive electrode active material for the lithium secondary battery can have a crystallite size of 200 nm or more.

[0014] The cation mixing ratio of nickel positive ions in the lithium layer of the lithium transition metal oxide can be 3.8% or less.

[0015] The positive electrode active material for the lithium secondary battery can have an average particle size (D50) of 3 μm or more.

[0016] The lithium transition metal oxide can be represented by the following Chemical Formula 1.

[0017] [Chemical Formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2 In Chemical Formula 1, 0.8 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.7, 0.05 ≤ y ≤ 0.2, 0.1 ≤ z ≤ 0.4, 0 < w1 ≤ 0.05, 0 ≤ w2 ≤ 0.1, x + y + z + w1 + w2 = 1, M1 is Zr and Y, and M2 is B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0018] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of preparing a transition metal precursor containing 50 to 70 mol% nickel based on the total molar amount of the transition metal; and firing a mixture containing the transition metal precursor, a lithium raw material substance, a Zr raw material substance, and a Y raw material substance at a temperature of 890 to 950 °C to form a lithium transition metal oxide in a single particle form.

[0019] The total content of Zr and Y in the formed lithium transition metal oxide can be 2500 to 5200 ppm based on the weight of the lithium transition metal oxide.

[0020] The content of Zr in the formed lithium transition metal oxide can be 1300 to 2800 ppm based on the weight of the lithium transition metal oxide.

[0021] The content of Y in the formed lithium transition metal oxide can be 1400 to 2400 ppm based on the weight of the lithium transition metal oxide.

[0022] The lithium raw material substance can be Li2CO3.

[0023] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery containing the aforementioned positive electrode active material.

[0024] Another embodiment of the present invention provides a lithium secondary battery containing the aforementioned positive electrode for a lithium secondary battery.

Advantages of the Invention

[0025] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention contains Zr and Y as grain growth promoting elements, and by appropriately adjusting their content, defects in the layered crystal structure can be reduced, improving electrochemical properties. Furthermore, the size of the crystal grains of the positive electrode active material can be maximized, improving particle strength and lifetime characteristics. In addition, the average particle size of the positive electrode active material can be increased, improving electrode energy density. [Brief explanation of the drawing]

[0026] [Figure 1] This is an SEM image of the cathode active material produced by Example 2.

[0027] [Figure 2] This is an SEM image of the cathode active material produced by Comparative Example 1.

[0028] [Figure 3] This is an SEM image of the cathode active material produced by Comparative Example 2.

[0029] [Figure 4] This is an SEM image of the cathode active material produced by Comparative Example 3. [Modes for carrying out the invention]

[0030] The terms "first," "second," and "third," etc., are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section, without departing from the scope of the invention.

[0031] The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular form used herein also includes the plural form unless the context clearly indicates the opposite. The meaning of “includes” as used in this specification is to embody a particular characteristic, area, element, stage, operation, element and / or component, and does not preclude the presence or addition of other characteristics, areas, elements, stages, operations, elements and / or components.

[0032] When a part is described as being "on top of" or "above" another part, it may be directly above or directly above the other part, or the other part may be interposed between them. In contrast, when a part is described as being "directly above" another part, the other part is not interposed between them.

[0033] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are to be interpreted as having the meaning consistent with the relevant technical literature and the present disclosures, and not as ideal or highly formal unless otherwise defined.

[0034] Also, unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent.

[0035] In this specification, the term “their combinations (groups)” as expressed in Markush notation means one or more mixtures or combinations selected from the group of components expressed in Markush notation, and means including one or more selected from the group of components.

[0036] The embodiments of the present invention will be described in detail below so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0037] 1.Cathode active material One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a nickel-containing lithium transition metal oxide in single-particle form, wherein the nickel content is 50 to 70 mol% based on the total number of moles of the transition metal, and the lithium transition metal oxide contains Zr and Y as grain growth promoting elements, with the total content of Zr and Y being 2500 to 5200 ppm based on the weight of the lithium transition metal oxide.

[0038] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is a single-particle positive electrode active material. In this specification, "single particle" is a term used to distinguish it from positive electrode active material particles in the form of secondary particles, which are formed by the aggregation of tens to hundreds of primary particles that have been commonly used in the past. The term includes a single particle consisting of one primary particle and aggregate particles of 30 or fewer primary particles. The "secondary particle" refers to an aggregate, i.e., a secondary structure, in which tens to hundreds of primary particles are aggregated by physical or chemical bonding between primary particles without any intentional aggregation or assembly process for the primary particles. Compared to existing general secondary particles, the single-particle active material has a smaller specific surface area, reducing the amount of gas generated by side reactions with the electrolyte, higher particle strength which can suppress particle breakage during rolling, and can reduce crack formation by repeated charging and discharging. As a result, it has the advantage of superior lifetime and safety compared to secondary particles and can achieve a high energy density of the electrode.

[0039] The positive electrode active material for a lithium secondary battery according to such an embodiment of the present invention has a single-particle form. In this specification, "single particle" means a single particle consisting of only one primary particle, and is a concept that is distinguished from particles consisting of multiple primary particles. From the viewpoint of improving battery life and safety, the above characteristics can be more desirablely realized when the positive electrode active material is in a single-particle form consisting of only one primary particle.

[0040] Furthermore, in the lithium transition metal oxide according to the present invention, the nickel content is 50 to 70 mol% based on the total number of moles of the transition metal. Recently, high-nickel active materials with a nickel molar content of 80 mol% or more have been widely used to increase the capacity of batteries. However, if the nickel content is too high, there is a possibility of thermal propagation issues, i.e., thermal safety problems, which can increase the cost. Therefore, the lithium transition metal oxide according to the present invention has a nickel content of 70 mol% or less, is excellent in thermal safety, and can reduce manufacturing costs. However, if the nickel content is too low, the capacity may be too low.

[0041] However, when manufacturing single-particle cathode active materials, the firing process is carried out at a higher temperature compared to the manufacturing of existing secondary-particle cathode active materials. This can lead to over-firing, causing layered structure crystal defects and degrading electrochemical properties such as capacitance and output.

[0042] In contrast, the lithium transition metal oxide according to the present invention contains Zr and Y as grain growth promoting elements. This makes it possible to lower the firing temperature for single particle formation and prevent crystal defects such as an increase in the positive ion mixing ratio due to high-temperature firing, and to efficiently increase the size of crystal grains within a single particle and the average particle size of a single particle during the firing process. In this specification, "crystal grain" means a segmented region in which atoms within a primary particle form a lattice structure in a certain direction.

[0043] At this time, the total content of Zr and Y is 2500 to 5200 ppm by weight of the lithium transition metal oxide, and more specifically, it can be 3000 to 4100 ppm or 3200 to 3700 ppm. If the content of grain growth promoting elements is too low, the growth of crystal grain size will be minimal, and if the content of grain growth promoting elements is too high, excess grain growth promoting elements will be distributed at the precursor interface during the firing process, which may inhibit the growth of crystal grain size. Therefore, when the total content of Zr and Y satisfies the above range, the crystal grain size can be maximized.

[0044] More specifically, the Zr content can be 1300-2800 ppm, 1300-2200 ppm, or 1300-1600 ppm based on the weight of the lithium transition metal oxide.

[0045] More specifically, the content of Y can be 1400-2400 ppm, 1600-2300 ppm, or 1800-2300 ppm based on the weight of the lithium transition metal oxide.

[0046] The cobalt content in the lithium transition metal oxide can be 5 to 20 mol% based on the total number of moles of the transition metal. If the cobalt content is too low, the growth of crystal grain size may be inhibited, and if the cobalt content is too high, it may result in a high price.

[0047] The manganese content in the lithium transition metal oxide can be 10 mol% or more based on the total number of moles of the transition metal, and more specifically, it can be 15 mol%, 20 mol%, or 25 mol% or more. Manganese is generally unfavorable for layered structure formation and can inhibit grain growth due to its high oxidation state. Therefore, manganese content within the above range may be unfavorable from the viewpoint of maximizing the growth of single grain size. However, the lithium transition metal oxide according to the present invention contains Zr and Y as grain growth promoting elements, and their content is appropriately adjusted. As a result, even with manganese content within the above range, the grain size can grow sufficiently, and the advantages of manganese content, namely the effect of improving lifetime characteristics by improving the structural stability of the active material, can be realized.

[0048] As described above, by adjusting the content of grain growth promoting elements and the like, the positive electrode active material for lithium secondary batteries according to the present invention can have a crystal grain size of 200 nm or more, and more specifically, can be maximized at 230, 250, 270, or 280 nm or more. By satisfying the above range for the crystal grain size of the positive electrode active material, particle strength is improved, particle breakage due to rolling can be suppressed, and life characteristics and stability can be improved. In this specification, "crystal grain size" can be measured using peak broadening of XRD data and can be quantitatively calculated through the Scherr equation.

[0049] Furthermore, the cation mixing ratio of nickel positive ions in the lithium layer within the lithium transition metal oxide can be 3.8% or less, more specifically, 3.6% or 3.3% or less. By having a sufficiently low cation mixing ratio of the positive electrode active material as described above, it is possible to prevent the problem of deterioration of battery life characteristics due to the disintegration of the lithium layer during charging and discharging. In this specification, the cation mixing ratio can be measured by dividing the intensity of the (003) peak in the positive electrode active material XRD (X-ray Diffraction) data by the intensity of the (104) peak.

[0050] Furthermore, the positive electrode active material for the lithium secondary battery may have an average particle size (D50) of 3 μm, 3.5 μm, or 4.0 μm or larger. More specifically, the lithium transition metal oxide according to the present invention contains Zr and Y grain growth promoting elements, which allows for efficient increase in the particle size of individual particles during the firing process. By satisfying the above range for the average particle size of the positive electrode active material, the rolling density can be improved, and the electrode energy density can be improved. In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve. The average particle size (D50) can be measured, for example, using the laser diffraction method.

[0051] Such a lithium transition metal oxide according to the present invention can be more specifically represented by the following Chemical Formula 1.

[0052] [Chemical Formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2 In Chemical Formula 1, 0.8 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.7, 0.05 ≤ y ≤ 0.2, 0.1 ≤ z ≤ 0.4, 0 < w1 ≤ 0.05, 0 ≤ w2 ≤ 0.1, x + y + z + w1 + w2 = 1, M1 is Zr and Y, and M2 is B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0053] In the lithium transition metal oxide of Chemical Formula 1, lithium can be contained in a content corresponding to a, that is, 0.8 ≤ a ≤ 1.2. If a is too small, the capacity may decrease. If a is too large, the strength of the fired cathode active material may increase, making it difficult to pulverize, and the amount of gas generation may increase due to an increase in lithium by-products. Considering the effect of improving the capacity characteristics of the cathode active material by controlling the lithium content and the balance of sinterability during the production of the active material, the lithium can be more preferably contained in a content of 0.9 ≤ a ≤ 1.1.

[0054] In the lithium transition metal oxide of Chemical Formula 1, nickel can be contained in a content corresponding to x, that is, 0.5 ≤ x ≤ 0.7. If the nickel content is too low, it may be difficult to plan for a high-capacity battery. If the nickel content is too high, the battery life and thermal safety may decrease due to a decrease in the stability of the active material structure, and the production cost may also increase.

[0055] In the lithium transition metal oxide of Chemical Formula 1, cobalt can be contained in a content corresponding to y, that is, 0.05 ≤ y ≤ 0.2. If the cobalt content is too low, the growth of the crystal grain size may be inhibited, and the output characteristics may decrease. If the cobalt content is too high, the manufacturing cost may increase and the reversible capacity may decrease.

[0056] In the lithium transition metal oxide of Chemical Formula 1, manganese can be contained in a content corresponding to z, that is, 0.1 ≤ z ≤ 0.4. If the manganese content is too low, the production unit price may become high, and the active material stability may decrease. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0057] In the lithium transition metal oxide of Chemical Formula 1, M1 can be contained in a content corresponding to w1, that is, 0 < w1 ≤ 0.05. At this time, M1 is Zr and Y which are grain growth promoting elements. In the lithium transition metal oxide of Chemical Formula 1, M2 can be contained in a content corresponding to w2, that is, 0 ≤ w2 ≤ 0.1. At this time, M2 is other doping elements except for grain growth promoting elements, and can be appropriately added within the range where the battery performance does not deteriorate, and can be B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

[0058] On the other hand, the optimal contents of Zr and Y for realizing the effects of the present invention described above are more appropriate when the composition of the lithium transition metal oxide satisfies the above range, and are inappropriate when the composition of the lithium transition metal oxide exceeds the above range.

[0059] 2. Method for manufacturing a positive electrode active material Another embodiment of the present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a transition metal precursor containing 50 to 70 mol% nickel based on the total moles of the transition metal; and forming a mixture containing the transition metal precursor, a lithium raw material, a Zr raw material, and a Y raw material, and then firing it at a temperature of 890 to 950°C to form a lithium transition metal oxide in single-particle form.

[0060] The following describes, step by step, a method for producing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0061] First, prepare a transition metal precursor containing 50-70 mol% nickel based on the total moles of the transition metal.

[0062] The nickel-containing transition metal precursor is not particularly limited and can be, for example, a transition metal hydroxide.

[0063] The transition metal hydroxide can also be produced, for example, by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution containing a nickel raw material and selectively a cobalt raw material or a manganese raw material, and then causing a coprecipitation reaction.

[0064] The nickel raw material is not particularly limited as long as it is used in the production of cathode active material precursors in this industry. For example, the nickel raw material may be nickel-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides or oxyhydroxides, and may specifically be, but not limited to, NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salts, nickel halides or combinations thereof.

[0065] The aforementioned cobalt raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the cobalt raw material may be cobalt-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides, or oxyhydroxides, and may specifically be, but not limited to, CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or combinations thereof.

[0066] The manganese raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the manganese raw material may be manganese-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof. Specifically, it may be, but is not limited to, manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate salts, manganese citrate, and manganese fatty acid salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxides, manganese chloride, or combinations thereof.

[0067] The transition metal-containing solution may be prepared by adding a nickel raw material and, selectively, a cobalt raw material or a manganese raw material to a solvent, specifically, water, or a mixture of water and an organic solvent (e.g., alcohol) that can be homogeneously mixed with water.

[0068] The complexing agent-containing solution plays a role in complex formation, and the complexing agent may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof. On the other hand, the complexing agent-containing solution can be used in aqueous solution form, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (e.g., alcohol) can be used as the solvent.

[0069] At this time, the concentrations of nickel, cobalt, and manganese raw materials can be adjusted to control the molar ratio of nickel, cobalt, and manganese in the precursor.

[0070] As a result, the nickel content in the transition metal precursor can be 50 to 70 mol% based on the total number of moles of the transition metal.

[0071] Furthermore, the cobalt content in the transition metal precursor can be 5 to 20 mol% based on the total number of moles of the transition metal.

[0072] Furthermore, the manganese content in the transition metal precursor can be 10 mol% or more based on the total number of moles of the transition metal, and more specifically, it can be 15 mol%, 20 mol%, or 25 mol% or more.

[0073] The technical significance of adjusting the nickel, cobalt, and manganese content in transition metal precursors is the same as described above and will therefore be omitted.

[0074] Next, a mixture containing the transition metal precursor, lithium raw material, Zr raw material, and Y raw material is formed, and then calcined at a temperature of 890-950°C to form a lithium transition metal oxide in single-particle form.

[0075] The aforementioned lithium raw material is not particularly limited as long as it is commonly used in this industry, but more specifically, it can be, for example, Li2CO3. By using the lower-cost Li2CO3 instead of LiOH, which is commonly used as a lithium raw material, cost savings can be achieved.

[0076] The aforementioned Zr raw material may be Zr(SO4)2, ZrS2, ZrO2, Zr(NO3)4, or a combination thereof, but is not necessarily limited to these.

[0077] The aforementioned Y raw material can be Y(SO4)2, Y2(SO4)3, Y2O3, Y(NO3)3, or combinations thereof, but is not necessarily limited to these.

[0078] At this time, the firing is carried out at a temperature of 890 to 950°C. If the firing temperature is too low, the growth of the crystal grain size within a single particle and the average particle size of a single particle will be inhibited, and if the firing temperature is too high, crystal defects may occur due to over-firing, such as an increase in the positive ion mixing ratio.

[0079] Furthermore, the firing process can be carried out for 5 to 20 hours, or more specifically, 7 to 15 hours.

[0080] Furthermore, the firing can be carried out in an oxygen or air atmosphere. When firing is performed in the aforementioned atmosphere, the local oxygen partial pressure increases, which can improve the crystallinity of the positive electrode active material.

[0081] The total content of Zr and Y in the formed lithium transition metal oxide may be 2500 to 5200 ppm by weight of the lithium transition metal oxide, and more specifically, it can be 3000 to 4100 ppm or 3200 to 3700 ppm.

[0082] The Zr content in the formed lithium transition metal oxide may be 1300 to 2800 ppm by weight of the lithium transition metal oxide, and more specifically, it can be 1300 to 2200 ppm or 1300 to 1600 ppm.

[0083] The Y content in the formed lithium transition metal oxide may be 1400 to 2400 ppm by weight of the lithium transition metal oxide, and more specifically, it may be 1600 to 2300 ppm or 1800 to 2300 ppm.

[0084] The technical significance of adjusting the Zr and Y content in lithium transition metal oxides is the same as described above and will therefore be omitted.

[0085] On the other hand, when further doping with other doping elements excluding grain growth promoting elements, the lithium transition metal oxide can be further doped with other doping raw materials by adding them during the formation of the mixture and firing.

[0086] Next, the lithium transition metal oxide can be selectively crushed as needed.

[0087] This makes it easier to form lithium transition metal oxides in single-particle form. The crushing can be carried out using methods commonly used in this industry. For example, it can be crushed using a jet mill, but is not necessarily limited to this method.

[0088] 3. Lithium-ion batteries Another embodiment of the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material described above.

[0089] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, which includes 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 surfaces treated with carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector usually has a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode 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, net, porous material, foam, nonwoven fabric, etc.

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

[0092] At this time, 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 positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used, but are not limited to these. 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 conductive material is used to impart conductivity to the electrodes and can be used in the battery without any special restrictions as long as it does not cause chemical changes 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 can be used alone or in mixtures of two or more, but this is not limited to these examples. The conductive material can usually be contained in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0094] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used.

[0095] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which includes the positive electrode active material described above and optionally a binder, binder, conductive material, or solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0096] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into consideration the coating thickness and production yield of the slurry, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for cathode manufacturing.

[0097] Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0098] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for lithium secondary batteries described above.

[0099] The lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

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

[0101] The negative electrode may include 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 surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector usually has a thickness of 3 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, net, porous material, foam, and nonwoven fabric.

[0103] The negative electrode active material layer may selectively contain a binder and a conductive material along with the negative electrode active material. For example, the negative electrode active material layer can be manufactured by applying a negative electrode active material layer forming composition, which includes the negative electrode active material and selectively a binder and a conductive material, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[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; metallic oxides capable of doping and dedoping with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more of these can be used in combination. Furthermore, a metallic lithium thin film can also be used as the negative electrode active material. In addition, all types of carbon materials, including low-crystalline carbon and high-crystalline carbon, can be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, 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 binder and conductive material can be the same as those described earlier for the positive electrode.

[0106] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It can be used without special limitations as long as it is a separator typically used in lithium secondary batteries, and is particularly preferred if it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from 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.

[0107] The aforementioned electrolytes can 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.

[0108] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0109] The organic solvent can be used without special limitations as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; or dibutyl ether. A variety of solvents can be used, including ether solvents such as ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene 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 of C2-C20, which may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based 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, which 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 desirable. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9 can result in superior electrolyte performance.

[0110] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any special 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 has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0111] In addition to the electrolyte components, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0112] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0113] Thus, yet another embodiment of the present invention provides a battery module and a battery pack containing the lithium secondary battery as a unit cell.

[0114] 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.

[0115] The following examples illustrate the realization of the present invention in more detail. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to these examples.

[0116] Example 1 (1) Manufacture of positive electrode active material (Mixed)Ni 0.6 Co 0.1 Mn 0.3 A precursor with an (OH)2 composition was prepared. Subsequently, Li2CO3 was added to the precursor so that the molar ratio of lithium to the transition metal (Li / M) was 1.05, ZrO2 was added so that the weight ratio of Zr to the lithium transition metal oxide (wt%) was 2700 ppm, and Y2O3 was added so that the weight ratio of Y to the lithium transition metal oxide (wt%) was 2100 ppm. These were then mechanically mixed in a mixer to form a mixture.

[0117] (Casturing) The mixture was then calcined at 940°C for 13 hours under an oxygen atmosphere, and then allowed to cool naturally. Subsequently, the calcined material was crushed to produce single-particle lithium transition metal oxides.

[0118] (2) Manufacturing of lithium secondary batteries The slurry for manufacturing the electrode plate was prepared by mixing the manufactured positive electrode active material, conductive material (carbon black, denkablack), and binder (PVDF, KF9700) in a ratio of 95.0:2.0:3.0 wt%, and adjusting the viscosity by adding NMP (N-Methyl-2-pyrrolidone) so that the solid content was approximately 60%. The manufactured slurry was coated onto 20 μm thick aluminum foil using Doctor, Blade, and then dry-rolled. The electrode loading amount was 16.0 mg / cm². 2 The rolling density (25°C, 20kN) is 3.5g / cm³. 3 That was it.

[0119] The electrolyte used was 1M LiPF6in EC:DMC:DEC=1:2:1 (vol%) with 2.0 vol% VC added relative to the total electrolyte volume. Coin cells were fabricated using a PP separation membrane and a lithium anode (400 μm, NEBAmetal).

[0120] Comparative Examples, Other Examples, and Reference Examples The cathode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the amounts of ZrO2 and Y2O3 added were adjusted so that the doped Zr and Y content was adjusted as shown in Table 1 below.

[0121] [Table 1]

[0122] Experimental Example 1: SEM Image Observation of Cathode Active Material The SEM (scanning electron microscope) images of the positive electrode active materials produced by Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were evaluated and are shown in Figures 1 to 4.

[0123] Referring to Figures 1 to 4, it was confirmed that the positive electrode active materials in the examples and comparative examples were in single-particle form.

[0124] Experimental Example 2: Evaluation of the physical properties of the positive electrode active material The physical properties of the positive electrode active materials produced according to the examples, comparative examples, and reference examples were evaluated, and the results are shown in Table 2 below.

[0125] (1) Evaluation of average particle size (D50) For the positive electrode active materials produced according to the examples and comparative examples, the particle size corresponding to 50% of the cumulative volume was measured using the laser diffraction method.

[0126] (2) Evaluation of crystal grain size For the cathode active materials produced according to the examples and comparative examples, the grain size was measured quantitatively using peak broadening of XRD data and the Scherr equation.

[0127] (3) Evaluation of the ratio of positive ion mixing For the positive electrode active materials produced according to the examples and comparative examples, the positive ion mixing ratio was measured by dividing the intensity of the (003) peak in the positive electrode active material XRD data by the intensity of the (104) peak.

[0128] [Table 2]

[0129] Referring to Table 2, in Examples 1-4, where Zr and Y were doped and their content was appropriately adjusted, it was confirmed that the average particle size was generally sufficiently large, the positive ion mixing ratio was small, and the crystal grain size was large. On the other hand, in Comparative Example 1, where Zr and Y were not doped, and in Comparative Examples 2, 3, and 5, where only one of Zr or Y was doped, it was confirmed that the average particle size was generally inferior, the positive ion mixing ratio was large, and the crystal grain size was small.

[0130] Furthermore, in Comparative Example 4, which was doped with Zr and Y but had too little Y doping, we were able to confirm that the average particle size was inferior, the positive ion mixing ratio was large, and the crystal grain size was small.

[0131] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. Various modifications can be made within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention.

[0132] Therefore, the substantial scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A single-particle nickel-containing lithium transition metal oxide, The nickel content is 50 to 70 mol% based on the total number of moles of transition metals. The lithium transition metal oxide contains Zr and Y as grain growth promoting elements. The positive electrode active material for lithium secondary batteries has a total content of Zr and Y of 2,500 to 5,200 ppm by weight of the lithium transition metal oxide.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the Zr content is 1300 to 2800 ppm by weight of the lithium transition metal oxide.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of Y is 1400 to 2400 ppm by weight of the lithium transition metal oxide.

4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the cobalt content in the lithium transition metal oxide is 5 to 20 mol% based on the total number of moles of the transition metal.

5. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the manganese content in the lithium transition metal oxide is 10 mol% or more based on the total number of moles of the transition metal.

6. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the crystal grain size is 200 nm or larger.

7. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive ion mixing ratio of nickel positive ions in the lithium layer within the lithium transition metal oxide is 3.8% or less.

8. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size (D50) is 3 μm or more.

9. The lithium transition metal oxide is represented by the following chemical formula 1 and is the positive electrode active material for a lithium secondary battery according to claim 1: [Chemical formula 1] Li ａ [Ni ｘ Co ｙ Mn ｚ M1 ｗ１ M2 ｗ２ ]O ２ In the above chemical formula 1, 0.8 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.7, 0.05 ≤ y ≤ 0.2, 0.1 ≤ z ≤ 0.4, 0 < w1 ≤ 0.05, 0 ≤ w2 ≤ 0.1, x + y + z + w1 + w2 = 1, M1 is Zr and Y, and M2 is B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

10. A step of preparing a transition metal precursor containing 50 to 70 mol% nickel based on the total moles of the transition metal; and The process includes forming a mixture containing the transition metal precursor, lithium raw material, Zr raw material, and Y raw material, and then calcining it at a temperature of 890 to 950°C to form a lithium transition metal oxide in single-particle form. A method for producing positive electrode active material for lithium secondary batteries.

11. A method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the total content of Zr and Y in the formed lithium transition metal oxide is 2,500 to 5,200 ppm by weight of the lithium transition metal oxide.

12. The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the Zr content in the formed lithium transition metal oxide is 1300 to 2800 ppm by weight of the lithium transition metal oxide.

13. The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the content of Y in the formed lithium transition metal oxide is 1400 to 2400 ppm by weight of the lithium transition metal oxide.

14. The lithium raw material substance is Li ２ CO ３ The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the method is as described above.

15. A positive electrode for a lithium secondary battery comprising the positive electrode active material described in any one of claims 1 to 9.

16. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 15.

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