Method for producing cathode active material for non-aqueous electrolyte secondary battery

Abstract

The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, the method comprising at least the following steps, in order: (1) step (1) mixing at least a positive electrode active material precursor compound and a lithium compound to prepare a powdery mixture; and (2) step (2) firing the powdery mixture obtained in step (1) to produce a fired product, wherein the precursor compound is a composite compound containing oxygen (O) and at least one element (Me) other than lithium (Li) and oxygen (O), and in step (2), the fired product is produced while constantly fluidizing the powdery mixture at least from the start to the end of firing, thereby producing a fired product with a coefficient of variation of the ratio (Li / Me) of the amount of Li to the total amount of element Me in the fired products obtained at a predetermined elapsed time of 1.5% or less for all fired products obtained at all predetermined elapsed times.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cathode active material for a non-aqueous electrolyte secondary battery, which can produce a cathode active material that can impart excellent battery characteristics to a non-aqueous electrolyte secondary battery with good production efficiency without degrading the quality. [Background technology]

[0002] Small, lightweight, and high-energy-density non-aqueous electrolyte secondary batteries are known as power sources for mobile phones, laptops, etc. Among these, lithium-ion secondary batteries, which have a large charge / discharge capacity and use lithium nickel oxide as the positive electrode, are widely used.

[0003] A cathode active material having a basic composition of Li(NiM)O2 (wherein M is, for example, an element containing a transition metal) is used, for example, as a positive electrode active material for a lithium ion secondary battery. Such a cathode active material is generally obtained by firing a mixed powder containing a precursor compound containing a transition metal and a lithium compound.

[0004] When firing the mixed powder, as described in Patent Document 1, for example, the mixed powder may be filled into a firing container such as a sagger or a crucible, and fired multiple times as necessary in a firing furnace such as an electric furnace or a roller hearth kiln while appropriately adjusting conditions such as temperature and time. However, the use of an apparatus that can heat-treat the material to be treated while fluidizing it, such as an externally heated rotary kiln, is being promoted because it has higher heat conduction to the material to be treated and is more efficient than the firing furnaces described above.

[0005] A conventional rotary kiln, as described in Patent Document 2, for example, is a device for pyrolyzing or carbonizing waste materials in a waste pyrolysis, gasification, and melting plant or a waste carbonization plant. Here, the waste material (material to be treated) that is constantly supplied to the inner tube of the kiln body is lifted and stirred by a lifter (lifting blade) to fluidize it, and the waste material is thermally treated by indirect heating using hot air supplied from the outside and circulating through a heating flow path. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO 2019 / 194150 A1 [Patent Document 2] JP 4670861 B2 Summary of the Invention [Problem to be solved by the invention]

[0007] As disclosed in Patent Document 2, when a single powder of waste or the like is heat treated using a device such as a conventional rotary kiln, a high thermal conductivity effect is reliably exerted, making it possible to achieve the desired pyrolysis or carbonization of the waste.

[0008] However, as described above, positive electrode active materials for lithium-ion secondary batteries are produced by firing a mixed powder containing a precursor compound and a lithium compound, rather than a single powder. When such mixed powder is supplied to a conventional rotary kiln or similar device for heat treatment, the mixed powder separates when fluidized by simple lifting and stirring using a lifting blade, resulting in insufficient firing of the mixed powder and a deterioration in the quality of the resulting positive electrode active material. Furthermore, when such mixed powder is supplied to a device such as a rotary kiln with a small lifting capacity and no lifting blade, even if the mixed powder is fluidized, heat is not conducted uniformly and efficiently from the inner cylindrical surface (furnace wall) of the kiln body to the entire mixed powder, resulting in an inconsistent firing of the mixed powder and a deterioration in the quality of the positive electrode active material.

[0009] The present invention has been made in consideration of the problems of the conventional art as described above, and an object of the present invention is to provide a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which can produce, with good production efficiency, a positive electrode active material that can impart excellent battery characteristics to a non-aqueous electrolyte secondary battery without degrading the quality. [Means for solving the problem]

[0010] To achieve this object, the method for producing a positive electrode active material of the present invention involves adjusting the ratio of lithium to other elements in the fired products obtained continuously when a mixture of a precursor compound containing a transition metal and a lithium compound is fired while being fluidized, thereby reducing fluctuations in the ratio of lithium to other elements in the fired products.

[0011] The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention (Method A) comprises at least the following steps in order: (1) Step (1) of mixing at least a positive electrode active material precursor compound and a lithium compound to prepare a powdery mixture; and (2) Step (2) of calcining the powdery mixture obtained in Step (1) to produce a calcined product; Including, Here, the precursor compound is a composite compound containing oxygen (O) and at least one element (Me) other than lithium (Li) and oxygen (O), In step (2), the powder mixture is constantly fluidized to produce a fired product at least from the start to the end of firing, and as a result, the coefficient of variation of the ratio (Li / Me) of the amount of lithium (Li) to the total amount of element (Me) in the fired product obtained at a predetermined elapsed time is 1.5% or less for all fired products obtained at the predetermined elapsed time.

[0012] Another embodiment of the present invention relates to a method (Method B) for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, the method comprising at least the following steps in order: (1) Step (1) of mixing at least a positive electrode active material precursor compound and a lithium compound to prepare a powdery mixture; and (2) Step (2) of calcining the powdery mixture obtained in Step (1) to produce a calcined product; Including, Here, the precursor compound is a composite compound containing oxygen (O) and at least one element (Me) other than lithium (Li) and oxygen (O), In step (2), the powder mixture is constantly fluidized from the start of firing to the end of firing to produce a fired product; step (2) is carried out in a rotary kiln provided with one or more lifting blades on the surface portion inside the furnace core tube.

[0013] Advantageously, in Method B, the coefficient of variation of the ratio (Li / Me) of the amount of lithium (Li) to the total amount of element (Me) in the fired product obtained at a predetermined elapsed time is 1.5% or less for all fired products obtained at the predetermined elapsed times.

[0014] Calcination in the sense of the present invention means subjecting a material to a thermal (=heat) treatment (sometimes also called calcination), for example in the temperature range of 350-1000° C. Calcined (calcined) materials are therefore materials that have been subjected to a heat treatment (calcination).

[0015] Fluidization in the context of the present invention means causing a material to flow regardless of its physical state (i.e., whether the material is in a solid state, partially molten, or fully molten).

[0016] Advantages of the Invention The present invention makes it possible to provide a method for producing, with good production efficiency, a positive electrode active material that can impart excellent battery characteristics to a non-aqueous electrolyte secondary battery without degrading the quality. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic radial cross-sectional view showing an example of a furnace tube of a rotary kiln provided with lifting blades on the inner surface portion of the furnace tube, which can be used in one embodiment of the method of the present invention for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view in the radial direction of the furnace core tube of a rotary kiln in which lifting blades are provided on the surface portion of the furnace core tube, illustrating the lifting height of a powder mixture during lifting and stirring using a rotary kiln, as an example of lifting and stirring in a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, where (a) is a schematic cross-sectional view in the radial direction of the furnace core tube in which the installation angle of the lifting blades on the surface portion is 45°, and (b) is a schematic cross-sectional view in the radial direction of the furnace core tube in which the installation angle of the lifting blades on the surface portion is 60°. [Figure 3] Figure 3 is a schematic radial cross-sectional view of the furnace core tube of the rotary kiln used in Examples 1-1 to 1-3 and Examples 2-1 to 2-3, where (a) is a schematic radial cross-sectional view of the furnace core tube in which the lifting blade installation angle on the surface portion is 30°, (b) is a schematic radial cross-sectional view of the furnace core tube in which the lifting blade installation angle on the surface portion is 45°, and (c) is a schematic radial cross-sectional view of the furnace core tube in which the lifting blade installation angle on the surface portion is 60°. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0023] The following describes embodiments of the present invention. The following description of preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its methods of use, or its applications. Unless otherwise specified, the following applies to both Method A and Method B.

[0019] To produce a positive electrode active material for a non-aqueous electrolyte secondary battery with high thermal conductivity and high efficiency, a mixed powder containing at least a precursor compound and a lithium compound is preferably calcined while fluidized rather than left to stand. However, if the mixed powder is calcined while fluidized rather than left to stand, the mixed powder separates due to simple lifting and stirring, and the calcination is insufficient, resulting in a decrease in the quality of the resulting positive electrode active material. Furthermore, if the amount of the mixed powder is reduced, heat is not conducted uniformly and efficiently throughout the mixed powder, resulting in a decrease in the quality of the expected positive electrode active material.

[0020] From these findings, it is understood that when firing a mixed powder containing a precursor compound and a lithium compound, it is important to fluidize the mixed powder so as to achieve high thermal conductivity while suppressing separation of the mixed powder. Here, suppressing separation of the mixed powder means suppressing fluctuations in the composition of the fired product due to separation of the mixed powder, i.e., suppressing fluctuations in the ratio (Li / Me) of lithium (Li) to elements other than lithium and oxygen (Me) in the fired product.

[0021] The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention comprises at least the following steps in order: (1) Step (1) of mixing at least a positive electrode active material precursor compound and a lithium compound to prepare a powdery mixture; and (2) Step (2) of calcining the powdery mixture obtained in Step (1) to produce a calcined product; These steps will be explained below in order.

[0022] <Process (1)> The positive electrode active material precursor compound used in preparing the powdered mixture in step (1) is a composite compound containing oxygen (O) and at least one element (Me) other than lithium (Li) and O. Examples of the composite compound include composite hydroxides, composite oxides obtained by calcining composite hydroxides, and composite carbonates. These composite compounds contain the element Me and are synthesized by a conventional method.

[0023] The element Me is not particularly limited, but is an element that can constitute a positive electrode active material and should be appropriately selected depending on the composition of the desired positive electrode active material. Examples of the element Me include, but are not particularly limited to, nickel (Ni), cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), boron (B), and phosphorus (P). Preferably, Me comprises at least one of nickel (Ni), cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), boron (B) and / or phosphorus (P); more preferably, Me comprises at least one of nickel (Ni), cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), niobium (Nb), or tungsten (W). Even more preferably, Me comprises at least Ni, in particular Ni and at least one of Co, Al and Mn, and particularly Me comprises Ni, Co and one or both of Al and Mn.

[0024] Preferably, the precursor compound comprising oxygen (O) and at least one element (Me) is a complex hydroxide, complex oxide, complex carbonate, or a mixed form thereof. By "mixed form" it is meant that the precursor compound comprises two or more of hydroxide, oxide, and carbonate. For example, when an oxide is prepared from the corresponding hydroxide and the conversion is not complete, a mixed form of hydroxide / oxide may result from the preparation process. When the precursor compound is a complex hydroxide, complex oxide, complex carbonate, or a mixed form thereof, Me preferably (additionally) comprises one or more of the above-mentioned metals or metalloids. In particular, the precursor compound is a hydroxide, oxide, or a mixed form thereof.

[0025] The precursor compound is preferably a composite hydroxide, composite oxide, or composite carbonate containing at least Ni, and more preferably, for example, a composite hydroxide, composite oxide, or composite carbonate containing at least Ni, Co, and Al and / or Mn.

[0026] The method for synthesizing the precursor compound is not particularly limited, and it is possible to employ a method in which, depending on the composition of the target positive electrode active material, an aqueous solution of at least one element Me or at least one compound thereof is prepared, the compounding ratio is adjusted as necessary, and one or more aqueous alkali solutions (mother liquors) such as an aqueous sodium hydroxide solution and an aqueous ammonia solution are added dropwise to a stirring reaction tank, and sodium hydroxide or the like is simultaneously added dropwise so that the pH is in an appropriate range of, for example, about 11 to 13, to cause co-precipitation by a controlled crystallization reaction, thereby obtaining hydroxides, oxides, carbonates, or the like having a shape in which primary particles are aggregated to form secondary particles.

[0027] The compound of Me element is not particularly limited, but examples thereof include nickel compounds, cobalt compounds, manganese compounds, magnesium compounds, aluminum compounds, titanium compounds, zinc compounds, niobium compounds, and tungsten compounds.

[0028] The nickel compound is not particularly limited, but examples include nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel.

[0029] The cobalt compound is not particularly limited, but examples thereof include cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt.

[0030] The manganese compound is not particularly limited, but examples include manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and manganese metal.

[0031] The magnesium compound is not particularly limited, but examples thereof include magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium.

[0032] The aluminum compound is not particularly limited, but examples thereof include aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum.

[0033] The titanium compound is not particularly limited, but examples thereof include titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium.

[0034] The zinc compound is not particularly limited, but examples thereof include zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc.

[0035] The niobium compound is not particularly limited, but examples include niobium oxide, niobium chloride, lithium niobate, and niobium iodide.

[0036] The tungsten compound is not particularly limited, but examples include tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, and tungsten sulfide.

[0037] The types and compounding ratios of the compounds of element Me are appropriately adjusted so that the desired types and ratios of each element are obtained, taking into consideration the desired composition of the positive electrode active material.

[0038] Furthermore, the precursor compound obtained by the above-described wet reaction is subjected to a washing treatment, dehydration, and subsequent drying treatment. By performing the washing treatment, it is possible to wash away impurities in the form of sulfate radicals and carbonate radicals that have been incorporated into the aggregated particles during the reaction and that have adhered to the surface, as well as Na moieties. Furthermore, the drying treatment can be performed, for example, in an oxidizing atmosphere at about 50°C to about 250°C.

[0039] Furthermore, the precursor compound may be subjected to an oxidation treatment in an oxidizing atmosphere at, for example, about 300°C to about 800°C. The oxidation treatment not only oxidizes the precursor compound but also separates impurities from the precursor compound, thereby improving the purity of the precursor compound. Furthermore, the bulk density is also improved, leading to improved production efficiency.

[0040] The particle size of the precursor compound is not critical. However, in certain embodiments, it is in the range of 1 to 30 μm. Within this range, particle size can be determined by conventional means, for example, using scanning electron microscope (SEM) photographs; in particular, SEM photographs as defined below. For spherical particles, particle size refers to the diameter, and for non-spherical particles, it refers to the largest dimension.

[0041] The precursor compound and the lithium compound synthesized as described above are mixed in a predetermined ratio to prepare a powder mixture. For example, the precursor compound and the lithium compound can be mixed by weighing the precursor compound powder and the lithium compound powder in a predetermined ratio and dry-mixing them using a mixer or the like. Furthermore, it is preferable that the blending ratio of the precursor compound and the lithium compound be appropriately adjusted so that the amount of Li and the total amount of element Me are in the desired ratio, taking into account the composition of the desired positive electrode active material.

[0042] The lithium compound to be mixed with the precursor compound is not particularly limited, and various lithium salts can be used. Examples of the lithium compound include lithium carbonate, lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium nitrate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide. As the lithium compound, lithium carbonate, lithium hydroxide monohydrate, and anhydrous lithium hydroxide can be preferably used.

[0043] The particle size of the lithium compound is not critical. For example, in certain embodiments, it can be in the range of 1 μm to 10 mm. In this range, particle size can be determined by conventional means, for example, using scanning electron microscope (SEM) photographs; in particular, SEM photographs, as defined below, are in the μm range, and visual inspection or optical microscopy are in the range of 500 μm to 10 mm.

[0044] Furthermore, compounds of elements to be used as additives can be added as needed. Such compounds can be added when mixing the precursor compound and the lithium compound, and examples of the addition method include adding them in powder form or adding them by spraying them in solution form. The compounds of elements to be used as additives are not particularly limited, and for example, compounds of the element Me to be used can be appropriately selected and used.

[0045] <Process (2)> In step (2), the powdery mixture obtained in step (1) is fired to produce a fired product, and in order to obtain a high-quality positive electrode active material, it is important to uniformly increase the thermal conductivity of the entire powdery mixture while suppressing separation of the powdery mixture during firing. Therefore, an important feature of the production method according to the present invention is that in step (2), the powdery mixture is constantly fluidized from at least the start to the end of firing, in other words, the powdery mixture is constantly fluidized while being fired to produce a fired product.

[0046] The fired product obtained in step (2) may contain unreacted compounds. Considering that firing may be performed again at a high temperature after step (2), unreacted compounds may also remain, and the amount of unreacted compounds may depend on the amount of unreacted compounds added and the firing temperature at which these compounds can react.

[0047] Suppressing separation of the powder mixture containing a precursor compound and a lithium compound means suppressing fluctuations in the composition of the fired product due to separation of the powder mixture, i.e., suppressing fluctuations in the ratio (Li / Me) of the amount of lithium (Li) to the total amount of elements other than lithium and oxygen (Me) in the fired product.

[0048] In step (2), the powder mixture is constantly fluidized from the start of firing until the end of firing to produce the fired product, so that the coefficient of variation of Li / Me (hereinafter also referred to as Li / Me variation coefficient) of the fired product obtained at a predetermined elapsed time is 1.5% or less, preferably 1.3% or less, more preferably 1.2% or less, and particularly 1.0% or less, relative to all fired products obtained at the predetermined elapsed times.

[0049] Furthermore, the greater the degree to which separation of the powdery mixture during firing is appropriately suppressed, the greater the similarity in the compositions of the N (e.g., N≧10) fired products obtained over a given time period, and the Li / Me coefficient of variation gradually approaches 0%. In other words, a small Li / Me coefficient of variation is preferable; an excessively large Li / Me coefficient is indicated by the separation of the powdery mixture during firing, resulting in variations in the compositions of the fired products obtained over a given time period. In step (2), the powdery mixture is fired while constantly flowing at least from the start to the end of firing. Therefore, for fired products obtained over all given time periods, such as 1 hour, 2 hours, 3 hours, and 4 hours, the Li / Me coefficient of variation is 1.5% or less, preferably 1.3% or less, more preferably 1.2% or less, and particularly 1.0% or less. Therefore, variation in the composition of all fired products produced is appropriately suppressed.

[0050] In this specification, the Li / Me variation coefficient is a value calculated based on the standard deviation and average value of Li / Me for N (N=10) samples randomly taken from the fired product obtained at a predetermined elapsed time, using the following formula: Furthermore, the Li / Me ratio in the fired product is obtained by heating and dissolving a 0.2 g sample of the fired product in 25 mL of 20% aqueous hydrochloric acid solution, cooling, transferring it to a 100 mL measuring flask, and adding pure water (100 mL) to prepare a solution. The elements in the solution are quantitatively determined using a suitable analytical method, such as AES (atomic emission spectroscopy), particularly ICP-AES (inductively coupled plasma atomic emission spectroscopy; synonymous with inductively coupled plasma atomic emission spectroscopy, abbreviated as ICP-OES) (e.g., using an Optima 8300 manufactured by PerkinElmer, Inc.). Li / Me variation coefficient (%) = (standard deviation / average value) × 100 The standard deviation applied here is the standard deviation of the sample with Bessel correction applied:

number

number

[0051] In step (2), the means for constantly fluidizing the powdered mixture from the start to the end of firing so that the Li / Me variation coefficient is equal to or less than the upper limit value of the fired product obtained at all specified elapsed times is not particularly limited, but lifting stirring, in which the powdered mixture is stirred while being lifted, can be used.

[0052] Although fluidization of the powdered mixture can be achieved, for example, by simply rotating the powdered mixture, lifting and stirring can also be performed to ensure that the powdered mixture is fired in a state of high thermal conductivity. Lifting and stirring is performed so that the height of the top of the powdered mixture is preferably 1.0 to 1.6 times, and more preferably 1.0 to 1.5 times, the height of the top of the powdered mixture without lifting and stirring, thereby more appropriately maintaining a state of high thermal conductivity. If the height of the top of the powdered mixture exceeds 1.6 times the height of the top of the powdered mixture without lifting and stirring, separation may occur due to differences in specific gravity of the components of the powdered mixture when the lifted powdered mixture falls. Furthermore, the force of falling may cause components with lower specific gravity to scatter, potentially resulting in separation.

[0053] The particularly important point about lifting and stirring is as follows: If the powdered mixture is simply fired while fluidized, some areas will be formed in the powdered mixture that are particularly susceptible to heat from the oven walls, while others will not, which is thought to lead to a decline in quality. However, when the powdered mixture is lifted and stirred, fluidization also occurs, and the powdered mixture that is not fluidized near the oven walls moves to the oven walls, where it is effectively replaced by the oven walls. This prevents the formation of areas in the powdered mixture that are susceptible to heat from the oven walls and areas that are not, and allows for uniform firing.

[0054] In order to most effectively fire the powdered mixture under conditions of high thermal conductivity and to suppress fluctuations in the composition of the fired product, it is important that when the powdered mixture is fluidized by the lifting and stirring means, the powdered mixture is not lifted excessively high relative to the height of the top of the powdered mixture when no lifting and stirring is performed, although this depends on the ease with which the powdered mixture separates when it falls.

[0055] Furthermore, as described above, the height of the top of the powdery mixture achieved by lifting and stirring is thought to be related to the properties of the powdery mixture, i.e., at least the particle size of the precursor compound and the particle size of the lithium compound, the particle size ratio of both components, the angle of repose of the powdery mixture, etc., and the lifting height can be set depending on the properties of the powdery mixture supplied for lifting and stirring.

[0056] For lifting and stirring, it is preferable to use a rotary kiln provided with one or more lifting blades on the surface portion inside the furnace core tube, which makes it easy to produce fired products continuously.

[0057] When improving the thermal conductivity of a powdered mixture by lifting and stirring, the area in which the entire powdered mixture can receive heat is important. For example, when using a rotary kiln with one or more lifting blades installed on the surface of the furnace core tube, the area in which the entire powdered mixture can come into contact with the surface of the furnace core tube (hereinafter also referred to as the furnace wall) is important. This improvement can be achieved, for example, by appropriately adjusting the rotation speed of the rotary kiln and the filling rate of the powdered mixture in the rotary kiln.

[0058] On the other hand, when fluidizing the powder mixture by lifting and stirring, care must be taken to prevent the powder mixture from separating. For example, when using a rotary kiln with one or more lifting blades installed on the surface of the furnace core tube, it is considered preferable to appropriately adjust the installation angle of the lifting blades and also appropriately adjust the angle of repose of the mixed powder while taking into account the relationship between the degree of lifting of the powder mixture in the furnace and the dead space created by the lifting blades.

[0059] When a certain amount of powdered mixture is lifted and stirred using a rotary kiln equipped with one or more lifting blades on the surface inside the furnace tube, the powdered mixture can be brought into contact with the furnace wall most efficiently by installing the lifting blades in a direction parallel to the axial direction of the furnace tube. However, as mentioned above, considering the need to improve the thermal conductivity of the powdered mixture while suppressing separation of the powdered mixture, it is not desirable to determine the installation angle of the lifting blades solely with an eye on bringing the powdered mixture into efficient contact with the furnace wall.

[0060] If the installation angle of the lifting blade(s) is too large, in other words, if the lifting blade(s) are too close to the direction parallel to the axial direction of the furnace core tube, the powder mixture may separate and scatter as it rises and falls, resulting in large fluctuations in the Li / Me content of the fired product. If the installation angle of the lifting blade(s) is too small, in other words, if the lifting blade(s) are too close to the direction perpendicular to the axial direction of the furnace core tube, dead space may be formed between the lifting blade(s) and the furnace wall, reducing the frequency of contact between the powder mixture and the furnace wall and potentially preventing optimal heat conduction. Furthermore, considering the angle of repose of the powder mixture, a large lifting force may not be obtained, preventing the improvement in heat conduction due to lifting and stirring.

[0061] Therefore, when a rotary kiln having one or more lifting blades provided on the surface inside the furnace tube is used to lift and constantly fluidize the powder mixture by stirring, the installation angle of the lifting blade(s) relative to the direction perpendicular to the axial direction of the furnace tube is preferably 15° or more, more preferably 20° or more, and 85° or less, more preferably 80° or less. Preferably, the installation angle relative to the direction perpendicular to the axial direction of the furnace tube is 15° to 85°, more preferably 20° to 80°, even more preferably 25° to 70°, particularly preferably 25° to 65°, and especially 30° to 60°.

[0062] 1 is a schematic radial cross-sectional view showing an example of a rotary kiln core tube provided with lifting blades on its inner surface, which can be used in one embodiment of the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention. In FIG. 1, a rotary kiln core tube 1 has a plurality of lifting blades 3 provided on its surface 2, and rotates in the direction of arrow A. The installation angle θ of the lifting blades 3 is the angle with respect to a direction perpendicular to the direction of the axis 4 of the core tube 1, and as mentioned above, the installation angle θ is preferably adjusted to 15° to 85°.

[0063] The number of lifting blades installed on the surface portion inside the furnace core tube is not particularly limited, and is adjusted appropriately depending on the retort diameter, etc., so as to ensure sufficient lifting and stirring. For example, it is preferable to install 3 to 6 lifting blades when the retort diameter is approximately 200 mm to 700 mm, and 4 to 10 lifting blades when the retort diameter is approximately 1000 mm to 2000 mm.

[0064] The angle of repose of the powdered mixture is related to the particle size of the powdered mixture, but it is important that the angle of repose is large enough to allow the powdered mixture to be lifted to a predetermined height by a lifting blade installed at a predetermined angle on the surface inside the furnace core tube, and that the powdered mixture does not separate when raised and lowered.

[0065] If the angle of repose of the powder mixture is too large, the fluidity of the powder mixture during lifting and lowering may be poor, and the powder mixture supplied to the lifting and stirring process may not be smoothly replaced. Furthermore, if the angle of repose of the powder mixture is too small, the powder mixture may become fluidized during lifting and lowering, reducing the effectiveness of the lifting and stirring process. Therefore, the angle of repose of the powder mixture measured by the injection method (in accordance with ISO 902:1976) is preferably 20° to 80°. Furthermore, the angle of repose can be determined using the particle size of the precursor compound and the particle size of the lithium compound that make up the powder mixture. In particular, by appropriately adjusting the particle size of the lithium compound, a powder mixture with the desired angle of repose can be achieved. In the context of the present invention, the angle of repose refers to the static angle of repose.

[0066] Here, the lifting height of the powdered mixture will be explained using the example of lifting and stirring the powdered mixture using a rotary kiln equipped with a lifting blade on the surface layer inside the furnace core tube.

[0067] 2A and 2B are schematic cross-sectional views of the furnace core tube in the radial direction of a rotary kiln equipped with lifting blades on the surface of the furnace core tube, illustrating the lifting height of the powder mixture during lifting and stirring using a rotary kiln, which is an example of lifting and stirring in the production method of the present invention. (a) is a schematic cross-sectional view of the furnace core tube in the radial direction when the lifting blades on the surface are installed at an angle of 45°, and (b) is a schematic cross-sectional view of the furnace core tube in the radial direction when the lifting blades on the surface are installed at an angle of 60°. When lifting and stirring is performed using such a rotary kiln, the lifting height of the powder mixture can be set according to the installation angle of the lifting blades.

[0068] As shown in Figures 2(a) and (b), when the powder mixture is fluidized by stirring with the lifting blade, gas is entrained in the powder mixture, which reduces the angle of repose of the powder mixture compared to when there is no lifting blade. This reduces the height to which the powder mixture rises due to the rotation of the furnace core tube (= the height of the powder mixture independent of the lifting blade, arrow α). During this process, the powder mixture above the lifting blade is further lifted, and when the angle exceeds its own angle of repose (arrow β), it falls from the lifting blade.

[0069] At this time, the height of the powder mixture not affected by the lifting blade (arrow α) is defined as the height of the top of the powder mixture without lifting and stirring, and the maximum height of the powder mixture lifted by the lifting blade (arrow γ) is defined as the height of the top of the powder mixture being lifted and stirred. Also, the value calculated as the multiplication factor (arrow γ / arrow α) of the height of the top of the powder mixture without lifting and stirring is defined as the lifting height of the powder mixture.

[0070] For example, in Examples 1-2 and 1-3 described below, the angle of repose of the powdered mixture 1 is 43.7°, and in Example 1-2 (lifting blade installation angle: 45°, corresponding to Figure 2(a)), the lifting height of the powdered mixture 1 is approximately 1.3 times, and in Example 1-3 (lifting blade installation angle: 60°, corresponding to Figure 2(b)), the lifting height of the powdered mixture 1 is approximately 1.6 times.

[0071] In a rotary kiln that does not have a lifting blade on the surface inside the furnace core tube, the lifting height of the powdered mixture depends solely on the angle of repose of the powdered mixture and is higher than the arrow α shown in Figures 2(a) and (b).

[0072] There are no particular restrictions on the conditions for lifting and stirring the powdery mixture using a rotary kiln equipped with one or more lifting blades on the surface portion inside the furnace core tube, but for example, the following conditions are preferably considered.

[0073] (retort rotation speed) To further improve the thermal conductivity of the powdered mixture, it is necessary to increase the retort rotation speed while ensuring the residence time of the powdered mixture in the rotary kiln core tube. However, if the retort rotation speed is too fast, the conversion of lithium during firing may not proceed sufficiently, potentially resulting in a deterioration in the quality of the target positive electrode active material. Furthermore, if the retort rotation speed is too low, Li may selectively adhere to the furnace wall, potentially resulting in variations in the composition of the mixed powder. Therefore, it is preferable to appropriately adjust the optimal retort rotation speed depending on the furnace diameter (retort diameter), etc. Those skilled in the art will know how to adjust the rotation speed to optimize heat transfer in a particular furnace, or can perform simple preliminary tests. For example, if the retort diameter is approximately 200 mm to 1500 mm, the retort rotation speed can be adjusted to approximately 0.3 rpm to 4.0 rpm.

[0074] (Powder mixture packing rate) The filling rate of the powder mixture in the rotary kiln (the ratio of the volume of the powder mixture to the internal volume of the rotary kiln) can be adjusted by changing the gas input rate and the residence time of the powder mixture depending on the type of rotary kiln. The residence time can also be adjusted by changing the inclination angle and rotation speed of the retort. However, if the filling rate is too high, the quality of the fired product may be reduced, and if the filling rate is too low, sufficient productivity may not be achieved. Therefore, the filling rate of the powder mixture is preferably about 3% to 30%, more preferably about 5% to 20%.

[0075] (Furnace air speed and dew point) Both the in-furnace air velocity and dew point can be adjusted by changing the gas input rate. If the gas input rate is low and the dew point is excessively high, condensation will occur, especially near the retort inlet where the powdered mixture is introduced. This will lead to the elution of Li from the lithium compounds in the powdered mixture, resulting in irregular aggregation / sintering of primary and secondary particles, which may result in a deterioration in the quality of the fired product. If the gas input rate is high and the in-furnace air velocity is excessively high, the powdered mixture may be selectively dispersed (separated). Those skilled in the art will know how to select an appropriate gas input rate. Preferably, the input gas rate (IGR) corresponds to the output gas rate (OGR) from the raw material multiplied by a coefficient a = 1 to 2.5: IGR = OGR × a; a = 1 to 2.5.

[0076] (heating rate) The heating rate for the powder mixture to be fired can be adjusted by adjusting the temperature setting of the rotary kiln. If the heating rate is too low, productivity may be insufficient, while if the heating rate is too high, the lithium conversion reaction may be insufficient, resulting in localized lithium conversion reactions, resulting in a lack of uniformity and a decrease in the quality of the fired product. Those skilled in the art will know how to select a heating rate appropriate for a particular system. However, a preferred range is between 200°C / h and 2000°C / h.

[0077] (surface temperature of the furnace tube) When firing a powdered mixture in a rotary kiln equipped with one or more lifting blades on the surface of the furnace core tube, the powdered mixture is lifted and stirred, and the powdered mixture is constantly flowing. If the maximum temperature of the powdered mixture is too low, the quality of the fired product may be reduced. On the other hand, if the maximum temperature is too high, crystal growth may proceed in parallel with the lithium conversion reaction, which may also reduce the quality of the fired product. In this case, the firing temperature will also differ depending on the type of lithium compound that makes up the powdered mixture, as their melting points differ. For example, when the lithium compound is lithium hydroxide, the set temperature inside the rotary kiln is appropriately adjusted taking into consideration the packing rate of the powdered mixture so that the maximum temperature of the powdered mixture is preferably about 500°C to 650°C, more preferably about 530°C to 630°C, and the surface temperature of the furnace core tube heated by the heater is set to 400°C or higher or 500°C or higher, and 1000°C or lower or 850°C or lower, i.e., preferably 400°C to 1000°C, particularly 500 to 850°C, more particularly 500 to 700°C, and particularly 550 to 700°C, and the powdered mixture is fired. More generally, the maximum temperature of the powdered mixture is preferably from about 500°C to a maximum of 250°C higher than the melting point of the lithium compound used in step (1), or from about 500°C to a maximum of 200°C higher than the melting point of the lithium compound used in step (1), particularly from about 530°C to a maximum of 170°C higher than the melting point of the lithium compound used in step (1). The powdered mixture is preferably fired by setting the surface temperature of the furnace tube heated by the heater to 400°C or higher, or 500°C or higher, and 1000°C or lower, or 850°C or lower, i.e., preferably 400°C to 1000°C, particularly 500°C to 850°C, more particularly 500°C to 700°C, and particularly 550°C to 700°C.

[0078] Regardless of the apparatus used in step (2), the powdered mixture obtained in step (1) is preferably heated in step (2) to a powdered mixture temperature of 350 to 950°C, for example a powdered mixture temperature of 450 to 800°C, or a temperature of 350 to a maximum of 250°C higher than the melting point of the lithium compound used in step (1), or a temperature of 350 to a maximum of 200°C higher than the melting point of the lithium compound used in step (1), or a temperature of 450 to a maximum of 200°C higher than the melting point of the lithium compound used in step (1), or a temperature of 500 to a maximum of 200°C higher than the melting point of the lithium compound used in step (1), or a temperature of 530 to a maximum of 170°C higher than the melting point of the lithium compound used in step (1).

[0079] In step (2), the firing atmosphere is not particularly limited as long as it allows the lithium conversion reaction and crystal growth to proceed reliably and uniformly. Examples of atmospheres that can be used include a decarbonating oxidizing gas atmosphere having a carbon dioxide concentration of 30 ppm or less, and an oxygen atmosphere having an oxygen concentration of preferably 80 vol % or more, more preferably 90 vol % or more.

[0080] The calcination time is not particularly limited as long as the lithium conversion reaction and crystal growth proceed reliably and uniformly, and is preferably, for example, about 1 to 12 hours, or about 2 to 10 hours.

[0081] <Process (3)> The target positive electrode active material for a nonaqueous electrolyte secondary battery can be produced by successively carrying out steps (1) and (2) as described above, but the production method of the present invention can also include step (3), in which the fired product obtained in step (2) is further fired. By carrying out step (3), more reliable and uniform crystal growth is achieved, further improving the quality of the resulting positive electrode active material.

[0082] Furthermore, in the manufacturing method of the present invention, the above-mentioned step (3) can also be performed after adding an additive to the fired product obtained in step (2). When an additive is added to the fired product obtained in step (2) in this way, an effect different from that when the additive is added when the precursor compound and the lithium compound are mixed in step (1) is exhibited, and an improvement in the quality of the resulting positive electrode active material can be expected. The additive is not particularly limited, and an appropriate compound of Me element or a lithium compound can be selected and used. Examples of the addition method that can be used include addition in powder form or addition by spraying in solution form.

[0083] When performing the firing in step (3), the fired material can be filled into a firing vessel such as a sagger or crucible, or into an apparatus such as a roller hearth kiln, or a rotary kiln can be used as in the firing in step (2).It is also preferable to select an appropriate apparatus for the firing in step (3) that can be finely adjusted to obtain conditions suitable for crystallization.

[0084] In step (3), the firing atmosphere is not particularly limited as long as it allows crystal growth to proceed more reliably and uniformly. Examples of atmospheres that can be used include a decarbonated oxidizing gas atmosphere having a carbon dioxide concentration of 30 ppm or less, and an oxygen atmosphere having an oxygen concentration of preferably 80% by volume or more, more preferably 90% by volume or more.

[0085] The product of step (2) is generally cooled before being subjected to step (3), but cooling between these steps may be omitted to avoid or reduce heat loss and energy consumption. When no additive is added before or during step (3), when step (3) is carried out in the same reaction vessel as step (2), and when the firing atmosphere is not changed, step (3) means extending the reaction time under optional temperature changes.

[0086] The firing temperature needs to be adjusted appropriately depending on the maximum temperature of the powder mixture during firing in step (2) and the composition of the desired positive electrode active material, but is preferably adjusted so that the maximum temperature of the fired product from step (2) is approximately 700°C to 1000°C.

[0087] The baking time is not particularly limited as long as it is long enough to obtain a positive electrode active material having a desired crystal structure, and is preferably, for example, about 1 to 12 hours, or about 2 to 10 hours.

[0088] When the positive electrode active material obtained through a series of steps (1), (2), and, if necessary, (3) is a high-Ni positive electrode active material containing Ni as elemental Ni and having a Ni content of 80 mmol or more, the amount of lithium compounds remaining in the particle surface layer (hereinafter referred to as "residual Li compounds") may be larger than that of a low-Ni positive electrode active material having a lower Ni content. The amount of residual Li compounds is the sum of unreacted lithium compounds and the amount of lithium compounds that are released from the crystalline structure relative to the particle surface layer during the firing step. The amount of residual Li compounds can be reduced by subjecting the positive electrode active material to a water washing treatment or by surface treating the surfaces of the primary particles and / or secondary particles of the positive electrode active material.

[0089] Furthermore, even if the cathode active material obtained by the series of steps (1) and (2) has a low Ni content, if the secondary particles contain small primary particles, they may be subjected to surface treatment, for example, because their specific surface area is large and there is a risk of metal elution by hydrogen fluoride. Furthermore, even if the secondary particles contain large primary particles, a sintering accelerator such as KOH may be used before firing to achieve the shape of the primary particles, and a water washing process may be performed to wash away this sintering accelerator.

[0090] The surface treatment method is not particularly limited, and examples thereof include a dry method in which aluminum oxide fine particles are attached to the particle surface of the positive electrode active material while applying shear force, followed by heat treatment at approximately 300°C to 700°C, and a method in which a predetermined amount of the positive electrode active material is introduced into an aqueous solution in which a predetermined amount of sodium sulfate has been dissolved, stirred for approximately 5 to 10 minutes, dehydrated and dried, and then heat treated at approximately 250°C to 700°C to coat the particle surface with an aluminum compound. Furthermore, in addition to aluminum compounds, boron compounds or tungsten compounds can also be used for the surface treatment, and the compound can be selected depending on the application. Furthermore, two or more compounds may be used simultaneously.

[0091] The positive electrode active material for a non-aqueous electrolyte secondary battery produced by the production method according to the present invention may contain a lithium composite oxide containing Li and at least one element Me, and although there are no particular limitations on its composition, it preferably has a composition represented by the following formula (I): Li a MeO2(I) (wherein Me is an element other than Li and O, and 0.95≦a≦1.40).

[0092] In the positive electrode active material having the composition represented by formula (I), the amount a of Li, in other words, the ratio a of the amount of Li to the total amount of element Me (Li / Me), is preferably 0.95≦a≦1.40, more preferably 0.95≦a≦1.25, and particularly preferably 0.96≦a≦1.15. Furthermore, independently of formula (I), in the positive electrode active material, the ratio of the amount of Li to the total amount of element Me (Li / Me) is preferably 0.95≦a≦1.40, more preferably 0.95≦a≦1.25, and particularly preferably 0.96≦a≦1.15.

[0093] In the positive electrode active material having the composition represented by the above formula (I), Me is preferably at least Ni, more preferably at least Ni, Co, Al and / or Mn. When Me is at least Ni, the amount of Ni, in other words, the ratio of the amount of Ni to the total amount of element Me (Ni / Me) is preferably 0.3 < b ≦ 1, more preferably 0.5 < b < 1, particularly preferably 0.8 < b < 1. Further, independently of the formula (I), when the positive electrode active material contains Ni, the ratio of the amount of Ni to the total amount of other element Me (Ni / Me) is preferably 0.3 < b ≦ 1, more preferably 0.5 < b < 1, particularly preferably 0.8 < b < 1.

[0094] Since the characteristics of the positive electrode active material for a non-aqueous electrolyte secondary battery produced by the production method according to the present invention mainly differ depending on its composition, it cannot be strictly defined, but the average particle size (average secondary particle size) and the average crystallite size of the secondary particles are preferably values in the ranges shown below, for example.

[0095] The average secondary particle size varies depending on the intended use of the positive electrode active material, but is determined in consideration of characteristics such as high capacity due to high packing density and high cycle characteristics. For example, the average secondary particle size is preferably about 1 μm to 30 μm, more preferably about 2 μm to 25 μm.

[0096] The crystallite size can be adjusted according to the desired composition, primary particle size and secondary particle size, and is preferably about 50 nm to 600 nm, more preferably about 60 nm to 500 nm.

[0097] In this specification, the secondary particle size is a value determined based on a scanning electron microscope photograph (SEM photograph) of the secondary particles of the positive electrode active material image, particularly a SEM photograph taken at an acceleration voltage of 10 kV using a scanning electron microscope SEM-EDS [field emission scanning electron microscope JSM-7100F: manufactured by JEOL Ltd.]. Here, the scale shown in the electron microscope photograph is used as the reference scale.

[0098] In this specification, the crystallite size is a value determined by obtaining XRD diffraction data of the positive electrode active material, particularly by obtaining XRD diffraction data by the following method, and then performing Rietveld analysis.

[0099] XRD diffraction data of the positive electrode active material was obtained using an X-ray diffractometer [SmartLab, manufactured by Rigaku Corp.] under the following X-ray diffraction conditions, and then Rietveld analysis was performed using this XRD diffraction data (see R.A. Young, ed., "The Rietveld Method," Oxford University Press (1992)): (X-ray diffraction conditions) Radiation source: Cu-Kα Accelerating voltage and current: 45 kV and 200 mA Sampling width: 0.02 deg. Scan width: 15°~122° Scan speed: 1.0 steps / second Divergence slit: 2 / 3 deg. Receiving slit width: 0.15 mm Scattering slit: 2 / 3deg.

[0100] The positive electrode active material for a non-aqueous electrolyte secondary battery produced by the production method according to the present invention may be contained in the positive electrode of a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery includes this positive electrode, a negative electrode, and an electrolytic solution containing an electrolyte.

[0101] To prepare a positive electrode, a conductive agent and a binder are mixed with the positive electrode active material by a conventional method. Examples of the conductive agent include acetylene black, carbon black, and graphite. Examples of the binder include polytetrafluoroethylene and polyvinylidene fluoride.

[0102] For the negative electrode, for example, not only negative electrode active materials such as lithium metal, graphite, and low-crystalline carbon materials, but also at least one non-metal or metal element selected from the group consisting of Si, Al, Sn, Pb, Zn, Bi, and Cd, or an alloy containing these, or a chalcogen compound containing these can also be used.

[0103] Examples of solvents for the usable electrolytic solution include an organic solvent containing at least one carbonate such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, or at least one ether such as dimethoxyethane.

[0104] In addition to lithium hexafluorophosphate (LiPF6), for example, at least one lithium salt such as lithium perchlorate or lithium tetrafluoroborate may be dissolved in a solvent and used.

[0105] <Function> By the production method of the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery that can impart excellent battery characteristics to the non-aqueous electrolyte secondary battery without degrading the quality can be produced with good production efficiency.

Examples

[0106] Hereinafter, the present invention will be specifically described with reference to typical examples and comparative examples of the present invention, but the present invention is not limited to these examples. The characteristics and the methods for obtaining these characteristics are as shown below.

[0107] <X-ray diffraction> The XRD diffraction data of the positive electrode active material was obtained under the following X-ray diffraction conditions using an X-ray diffractometer [SmartLab, manufactured by Rigaku Corp.], and then Rietveld analysis was performed using this XRD diffraction data (refer to "The Rietveld Method" edited by R.A. Young, Oxford University Press (1992)): (X-ray diffraction conditions) Radiation source: Cu-Kα Accelerating voltage and current: 45 kV and 200 mA Sampling width: 0.02 deg. Scan width: 15°~122° Scan speed: 1.0 steps / second Divergence slit: 2 / 3 deg. Receiving slit width: 0.15 mm Scattering slit: 2 / 3deg.

[0108] <Composition of precursor compound and fired product (positive electrode active material)> A 0.2 g sample of the precursor compound and a 0.2 g sample of the fired body (positive electrode active material) were each dissolved in 25 mL of 20% aqueous hydrochloric acid solution by heating, cooled, and then transferred to a 100 mL measuring flask. Pure water (100 mL) was added to prepare a liquid solution, and elemental quantification was performed using ICP-AES (Optima 8300, manufactured by PerkinElmer, Inc.).

[0109] <Coin cell using positive electrode active material> The 2032-type coin cells using the positive electrode active material were fabricated using the positive electrode, negative electrode, and electrolyte prepared by the following methods.

[0110] (positive electrode) Acetylene black and graphite were used as the conductive agent in a mass ratio of 1:1, and polyvinylidene fluoride was used as the binder. The positive electrode active material, conductive agent, and binder were mixed together in a mass ratio of 90:6:4 (positive electrode active material:conductive agent:binder). These materials were mixed with N-methylpyrrolidone to obtain a slurry, which was then coated onto aluminum foil. The coated aluminum foil was dried at 110°C to produce a sheet, which was then punched out to a diameter of 15 mm. The density of the composite material was 3.0 g / cm. 3 This was used as a positive electrode.

[0111] (Negative electrode) A lithium foil with a thickness of 500 μm and punched to a diameter of 16 mm was used as the negative electrode.

[0112] (electrolyte) A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared at a volume ratio of EC:DMC=1:2, and a solution obtained by mixing this with 1M LiPF6 electrolyte was used as the electrolyte.

[0113] <Battery characteristics of non-aqueous electrolyte secondary batteries> (Initial charge capacity and initial charge / discharge efficiency) The coin cell prepared by the above method was charged at a constant current of 18 mA / g at 25°C up to 4.30 V (maximum voltage), and then charged at a constant voltage until the current reached 2 mA / g. The capacity at this time was defined as the initial charge capacity (mAh / g).

[0114] After a 5-minute rest, the battery was discharged at a constant current density of 18 mA / g up to 3.00 V under the same conditions, and after a 5-minute rest, the initial discharge capacity (mAh / g) was measured. The series of steps up to the measurement of the initial discharge capacity was defined as the charge-discharge cycle under condition A.

[0115] The initial charge / discharge efficiency was calculated based on the following formula using the measured values ​​of the initial charge capacity and the initial discharge capacity.

[0116] Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) x 100 <Synthesis Example 1: Synthesis of precursor compound 1> A mixed aqueous solution was obtained by mixing a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and an aluminum sulfate aqueous solution so that the molar ratio of Ni, Co, and Al was Ni:Co:Al = 89:7:4. A mother liquor was prepared in advance in a reaction tank by adding 300 g of sodium hydroxide aqueous solution and 500 g of ammonia water to 10 L of pure water. A nitrogen atmosphere was established in the reaction tank by supplying nitrogen gas at a flow rate of 0.7 L / min, and the reaction was also carried out under a nitrogen atmosphere.

[0117] After this, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously added dropwise at a predetermined rate, and the amount of alkaline aqueous solution added was adjusted so that the pH became 11.8. Through a crystallization reaction, Ni, Co, and Al crystallized and co-precipitated to form aggregated particles, and a coprecipitate was obtained.

[0118] Thereafter, the slurry in the reactor was subjected to solid-liquid separation and further washed with pure water to reduce residual impurities, and then the solidified coprecipitate was dried in air at 110°C for 12 hours to obtain precursor compound 1. At this time, D50 in the volume-based particle size distribution of precursor compound 1 was 11.2 μm.

[0119] <Synthesis Example 2: Synthesis of precursor compound 2> A mixed aqueous solution was obtained by mixing an aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, and an aqueous manganese sulfate solution so that the molar ratio of Ni, Co, and Mn was Ni:Co:Mn=5:2:3. A mother liquor was prepared in advance in a reaction tank by adding 300 g of aqueous sodium hydroxide and 500 g of aqueous ammonia to 10 L of pure water. A nitrogen atmosphere was established in the reaction tank by supplying nitrogen gas at a flow rate of 0.7 L / min, and the reaction was also carried out under a nitrogen atmosphere.

[0120] After this, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously added dropwise at a predetermined rate, and the amount of alkaline aqueous solution added was adjusted so that the pH became 12. Through this crystallization reaction, Ni, Co, and Mn crystallized and co-precipitated to form aggregated particles, and a coprecipitate was obtained.

[0121] Thereafter, the slurry in the reactor was subjected to solid-liquid separation and further washed with pure water to reduce residual impurities, and then the solidified coprecipitate was dried in air at 110°C for 12 hours to obtain precursor compound 2. At this time, D50 in the volume-based particle size distribution of precursor compound 2 was 5.1 μm.

[0122] <Example 1-1: Production of positive electrode active material> Precursor compound 1 and anhydrous lithium hydroxide were weighed out so that the molar ratio of Li to the total amount of Ni, Co, and Al was Li / (Ni + Co + Al) = 1.02, and mixed using a mixer to prepare powdered mixture 1. The angle of repose of powdered mixture 1, measured by the injection method, was 43.7°.

[0123] As shown in Figure 3(a), a rotary kiln with a retort diameter of 300 mm and four lifting blades installed circumferentially at a 30° angle on the surface inside the furnace core tube was used. Powdered mixture 1 was fired under an oxygen atmosphere (oxygen concentration: 97% by volume) for 13 hours under the following conditions while constantly lifting and stirring to fluidize it (powdered mixture 1 flowed as indicated by arrow B). Powdered fired products were continuously produced. The firing time from when powdered mixture 1 was introduced into the rotary kiln to when the powdered mixture was continuously discharged stably was 4 hours, and the firing time at the maximum temperature (approximately 600 °C shown below) was approximately 4 hours.

[0124] Furthermore, lifting and stirring using the lifting blade was performed so that the height of the top of the powdery mixture 1 was approximately 1.0 times the height of the top when lifting and stirring was not performed. Furthermore, the size of the lifting blade was set so that 50% of the total amount of powdery mixture 1 could be stirred at a filling rate of 20% in one rotation.

[0125] (Rotary kiln conditions) Retort rotation speed: 0.9 rpm Filling rate: 20% Furnace air velocity and dew point: Adjust the gas input to 47L / min. Heating rate: The surface temperature of the furnace tube is set as shown below. Maximum furnace tube surface temperature: 640℃ Maximum temperature of powder mixture 1: approximately 600°C.

[0126] When powder mixture 1 was fired for 13 hours, the time 4 hours after the start of firing after stable discharge was reached was defined as the initial time. Ten samples were randomly extracted from the fired product obtained at each time point from the initial time, and the Li / Me ratio of each sample was identified. The coefficient of variation of Li / Me at each elapsed time was calculated from the standard deviation and average value according to the method described above.

[0127] 8 kg of the obtained powdered sintered material was packed into a box with a width of 300 mm and a depth of 100 mm, and sintered using a rotary hearth kiln in an oxygen atmosphere (oxygen concentration: 97% by volume) for 4 hours so that the maximum temperature of the powdered sintered material reached approximately 740°C, thereby obtaining a positive electrode active material.

[0128] The average secondary particle size and crystallite size of the obtained positive electrode active material were determined according to the above-mentioned methods.

[0129] <Example 1-2: Production of positive electrode active material> A positive electrode active material was obtained in the same manner as in Example 1-1, except that the rotary kiln used in Example 1-1 was changed to a rotary kiln equipped with four lifting blades circumferentially at an installation angle of 45° on the surface of the furnace core tube, as shown in Figure 3(b) (powdered mixture 1 flowed as shown by arrow B), and lifting stirring was performed using the lifting blades so that the height of the top of the powdered mixture 1 was about 1.3 times the height of the top in a state without lifting stirring. Furthermore, the Li / Me variation coefficient, the average secondary particle size and the crystallite size of the positive electrode active material were determined at each elapsed time in the same manner as in Example 1-1.

[0130] <Example 1-3: Production of positive electrode active material> A positive electrode active material was obtained in the same manner as in Example 1-1, except that the rotary kiln used in Example 1-1 was changed to a rotary kiln equipped with four lifting blades circumferentially at an installation angle of 60° on the surface of the furnace core tube, as shown in Figure 3(c) (powdered mixture 1 flowed as indicated by arrow B), and lifting stirring was performed using the lifting blades so that the height of the top of the powdered mixture 1 was about 1.6 times the height of the top in a state without lifting stirring. Furthermore, the Li / Me variation coefficient, the average secondary particle size and the crystallite size of the positive electrode active material were determined at each elapsed time in the same manner as in Example 1-1.

[0131] <Comparative Example 1-1: Production of Positive Electrode Active Material> Ten sheaths were prepared by filling 8 kg of powdered mixture 1 prepared in the same manner as in Example 1-1 into boxes 300 mm wide and 100 mm deep, and the sheaths were fired in an oxygen atmosphere (oxygen concentration: 97% by volume) using a rotary hearth kiln for 4 hours so that the maximum temperature of powdered mixture 1 reached approximately 740°C to obtain positive electrode active materials. The positive electrode active material obtained from each sheath was pulverized, and 10 samples were randomly taken. The Li / Me coefficient of variation, the average secondary particle size, and the crystallite size of the positive electrode active material were determined in the same manner as in Example 1-1.

[0132] <Example 2-1: Production of positive electrode active material> Precursor compound 2 and anhydrous lithium hydroxide were weighed out so that the ratio (molar ratio) of Li to the total amount of Ni, Co, and Mn was Li / (Ni + Co + Mn) = 1.125, and mixed using a mixer to prepare powdered mixture 2. The angle of repose of powdered mixture 2, measured by the injection method, was 56.3°.

[0133] As shown in Figure 3(a), a rotary kiln with a retort diameter of 300 mm and four lifting blades installed circumferentially at a 30° angle on the surface inside the furnace core tube was used. Powdered mixture 2 was fired under an oxygen atmosphere (oxygen concentration: 97% by volume) for 13 hours under the following conditions while constantly lifting and stirring to fluidize it (powdered mixture 1 flowed as indicated by arrow B). Powdered fired products were continuously produced. The firing time from when powdered mixture 2 was introduced into the rotary kiln to when the powdered mixture was continuously discharged stably was set to 4 hours, and the time for firing powdered mixture 2 at the maximum temperature (approximately 560°C shown below) was approximately 4 hours.

[0134] Furthermore, lifting and stirring using the lifting blade was performed so that the height of the top of the powdery mixture 2 was approximately 1.0 times the height of the top when lifting and stirring was not performed. Furthermore, the size of the lifting blade was set so that 50% of the total amount of the powdery mixture 2 could be stirred at a filling rate of 20% in one rotation.

[0135] (Rotary kiln conditions) Retort rotation speed: 1.1 rpm Filling rate: 20% Furnace air velocity and dew point: Adjust the gas input rate to 54 L / min. Heating rate: The surface temperature of the furnace tube is set as shown below. Maximum furnace tube surface temperature: 630℃ Maximum temperature of powder mixture 2: approximately 560°C.

[0136] When powder mixture 2 was fired for 13 hours, the time 4 hours after the start of firing after stable discharge was reached was defined as the initial time. Ten samples were randomly extracted from the fired product obtained at each time point from the initial time, and the Li / Me ratio of each sample was identified. The Li / Me coefficient of variation at each elapsed time was calculated from the standard deviation and average value according to the method described above.

[0137] 8 kg of the obtained powdered sintered material was packed into a box with a width of 300 mm and a depth of 100 mm, and sintered using a rotary hearth kiln in an oxygen atmosphere (oxygen concentration: 97% by volume) for 4 hours so that the maximum temperature of the powdered sintered material reached approximately 940°C, thereby obtaining a positive electrode active material.

[0138] The average secondary particle size and crystallite size of the obtained positive electrode active material were determined according to the above-mentioned methods.

[0139] <Example 2-2: Production of positive electrode active material> A positive electrode active material was obtained in the same manner as in Example 2-1, except that the rotary kiln used in Example 2-1 was changed to a rotary kiln equipped with four lifting blades circumferentially at an installation angle of 45° on the surface of the furnace core tube, as shown in Figure 3(b) (powdered mixture 2 flowed as shown by arrow B), and lifting stirring was performed using the lifting blades so that the height of the top of powdered mixture 2 was about 1.4 times the height of the top in a state without lifting stirring. Furthermore, the Li / Me variation coefficient, the average secondary particle size, and the crystallite size of the positive electrode active material were determined at each elapsed time in the same manner as in Example 2-1.

[0140] <Example 2-3: Production of positive electrode active material> A positive electrode active material was obtained in the same manner as in Example 2-1, except that the rotary kiln used in Example 2-1 was changed to a rotary kiln equipped with four lifting blades circumferentially at an installation angle of 60° on the surface of the furnace core tube, as shown in Figure 3(c) (powdered mixture 2 flowed as shown by arrow B), and lifting stirring was performed using the lifting blades so that the height of the top of powdered mixture 2 was about 1.7 times the height of the top in a state without lifting stirring. Furthermore, the Li / Me variation coefficient, the average secondary particle size, and the crystallite size of the positive electrode active material were determined at each elapsed time in the same manner as in Example 2-1.

[0141] <Comparative Example 2-1: Production of Positive Electrode Active Material> Ten sheaths were prepared by filling 8 kg of powdered mixture 2 prepared in the same manner as in Example 2-1 into boxes 300 mm wide and 100 mm deep, and the sheaths were fired in an oxygen atmosphere (oxygen concentration: 97% by volume) using a rotary hearth kiln for 4 hours so that the maximum temperature of powdered mixture 2 reached approximately 940°C to obtain positive electrode active materials. The positive electrode active material obtained from each sheath was pulverized, and 10 samples were randomly taken. The Li / Me coefficient of variation, the average secondary particle size, and the crystallite size of the positive electrode active material were determined in the same manner as in Example 2-1.

[0142] Table 1 shows the Li / Me variation coefficients at each elapsed time obtained for the positive electrode active materials obtained in Examples 1-1 to 1-3 and Comparative Example 1-1, and Examples 2-1 to 2-3 and Comparative Example 2-1, and Table 2 shows the average secondary particle diameters and crystallite diameters of the positive electrode active materials.

[0143] Furthermore, according to the above-mentioned method, the initial charge capacity and the initial charge / discharge efficiency were measured as the battery characteristics of the nonaqueous electrolyte secondary batteries using the positive electrode active materials obtained in Examples 1-1 to 1-3 and Comparative Example 1-1, and Examples 2-1 to 2-3 and Comparative Example 2-1. The results are shown in Table 2.

[0144] [Table 1]

[0145] [Table 2]

[0146] In Examples 1-1 to 1-3 and 2-1 to 2-3 produced by the production method of the present invention, there was no separation of the powder mixture containing the precursor compound and the lithium compound, thermal conductivity was sufficiently enhanced, and the powder mixture was continuously fired while constantly flowing from start to finish, so that the Li / Me coefficient of variation of the fired products obtained at a predetermined elapsed time (fired products obtained after each elapsed time) was 1.5% or less. Therefore, it is clear that the nonaqueous electrolyte secondary batteries using the positive electrode active materials produced in these Examples have good initial charge capacities and initial charge-discharge efficiencies.

[0147] On the other hand, in Comparative Examples 1-1 and 2-1, the powder mixture was not sintered while being constantly fluidized from start to finish so that the Li / Me coefficient of variation of the resulting sintered product would be 1.5% or less. As a result, the shapes of the primary particles and the secondary particles formed by aggregation of the primary particles were not uniform, causing fluctuations in crystallinity and resulting in a non-uniform distribution of the aggregates of secondary particles in the formed powder. Therefore, it is clear that the non-aqueous electrolyte secondary batteries using the positive electrode active materials obtained in these Comparative Examples exhibited reduced battery characteristics.

[0148] [Industrial Applicability] The positive electrode active material obtained by the manufacturing method according to the present invention can impart excellent battery characteristics to a non-aqueous electrolyte secondary battery without deteriorating its quality. [Explanation of symbols]

[0149] 1. Furnace tube 2 Surface area 3 Lifting Blades 4 axis center θ Installation angle

Claims

1. At least the following steps in sequence: (1) Step (1) of mixing at least a positive electrode active material precursor compound and a lithium compound to prepare a powdery mixture; and (2) Step (2) of firing the powdery mixture obtained in Step (1) to produce a fired product; A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: the precursor compound is a composite compound containing oxygen (O) and at least one element (Me) other than lithium (Li) and oxygen (O), In step (2), a calcined product is produced while constantly fluidizing the powdery mixture at least from the start of calcination to the end of calcination, and thereby the coefficient of variation of the ratio (Li / Me) of the amount of lithium (Li) to the total amount of elements (Me) in the calcined products obtained at a predetermined elapsed time is 1.5% or less for all calcined products obtained at all predetermined elapsed times.

2. 2. The method according to claim 1, wherein the means for constantly fluidizing the powdered mixture at least from the start of firing to the end of firing is lifting stirring for stirring the powdered mixture while lifting it.

3. The composition according to claim 2, wherein the height of the top of the powdery mixture by the lifting and stirring is 1.0 to 1.6 times the height of the top of the powdery mixture without lifting and stirring.

4. 3. The method according to claim 2, wherein the fired product is continuously produced by using a rotary kiln having one or more lifting blades provided on the surface portion of the furnace core tube for the lifting and stirring.

5. At least the following steps in sequence: (1) Step (1) of mixing at least a positive electrode active material precursor compound and a lithium compound to prepare a powdery mixture; and (2) Step (2) of firing the powdery mixture obtained in Step (1) to produce a fired product; A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: the precursor compound is a composite compound containing oxygen (O) and at least one element (Me) other than lithium (Li) and oxygen (O), In step (2), a fired product is produced while constantly fluidizing the powdery mixture at least from the start of firing to the end of firing; and step (2) is carried out in a rotary kiln provided with one or more lifting blades on the surface portion inside a furnace core tube.

6. The method according to claim 4 or 5, wherein the installation angle of the one or more lifting blades in the rotary kiln is 15° to 85°, preferably 20° to 80° with respect to a direction perpendicular to the axial direction of the furnace tube.

7. 7. The method according to claim 6, wherein the angle of the one or more lifting blades in the rotary kiln is 25° to 70°, preferably 25° to 65°, relative to a direction perpendicular to the axial direction of the furnace tube.

8. 8. The method according to claim 7, wherein the installation angle of the one or more lifting blades in the rotary kiln is 30° to 60° with respect to a direction perpendicular to the axial direction of the furnace tube.

9. 6. The method according to claim 1 or 5, wherein in step (2), the powder mixture obtained in step (1) is heated to a temperature of the powder mixture between 350 and 1000°C, preferably to a temperature of 350°C to a maximum of 250°C higher than the melting point of the lithium compound used in step (1).

10. 6. The method according to claim 4, wherein the powder mixture is fired while the surface temperature of the furnace tube is set to 400°C to 1000°C.

11. 6. The method of claim 1, wherein the precursor compound comprising oxygen (O) and at least one element (Me) comprises at least one of nickel (Ni), cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), boron (B) and / or phosphorus (P); preferably, Me comprises at least one of nickel (Ni), cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), niobium (Nb), or tungsten (W).

12. 6. The method of claim 1 or 5, wherein the precursor compound comprising oxygen (O) and at least one element (Me) is a complex hydroxide, a complex oxide, a complex carbonate, or a mixture thereof.

13. 12. The method of claim 11, wherein Me comprises Ni; preferably, Me comprises Ni, Co, and one or both of Al and Mn.

14. 14. The method according to claim 13, wherein the molar ratio b of Ni to the total amount of other elements Me is in the range of 0.3<b≦1, preferably 0.5<b<1.

15. 6. The method of claim 1 or 5, wherein the lithium compound is selected from the group consisting of lithium carbonate, lithium hydroxide (e.g., in the form of anhydrous LiOH or in the form of LiOH monohydrate), lithium nitrate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide, and mixtures thereof.

16. 16. The method of claim 15, wherein the lithium compound is selected from the group consisting of lithium carbonate, lithium hydroxide (e.g., in the form of anhydrous LiOH or LiOH monohydrate), and mixtures thereof.

17. 6. The method according to claim 1 or 5, wherein the precursor compound and the lithium compound are used in amounts such that the ratio a of the amount of Li to the total amount of element Me (Li / Me) is in the range of 0.95≦a≦1.40, preferably in the range of 0.95≦a≦1.25, more preferably in the range of 0.96≦a≦1.15.

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