Method for producing lithium-metal composite oxide

Abstract

To provide a method for producing a lithium-metal composite oxide that can serve as a positive electrode active material for a nonaqueous electrolyte secondary battery to offer better battery characteristics without any loss of quality.SOLUTION: A method for producing a lithium-metal composite oxide comprises: a firing step in which a powdered mixture comprising a mixture of at least a precursor compound, a lithium compound, and collected powder is fired while continuously fluidized; a collecting step in which the collected powder is obtained by cooling an exhaust gas containing scattered powder that has been produced by the fluidization of the powdered mixture in the firing step, and collecting the scattered powder contained in the exhaust gas; and a mixing step in which the powdered mixture is obtained in the form of a mixture of at least the precursor compound, the lithium compound, and the collected powder.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a lithium metal composite oxide. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries are small, lightweight, and have high energy density, and are used as power sources for mobile phones, notebook computers, etc. Among them, lithium-ion secondary batteries, which use a material such as lithium nickel oxide for the positive electrode and have a large charge / discharge capacity, are widely used.

[0003] Positive electrode active materials for lithium ion secondary batteries include, for example, those represented by the general formula Li(NiM)O 2 (M is, for example, an element including a transition metal) is used. Such lithium metal composite oxides can generally be produced by firing raw material powders of a precursor compound including a transition metal and a lithium compound.

[0004] The raw material powder is fired, for example, by filling a firing vessel such as a sagger or crucible with the raw material powder and appropriately adjusting the conditions such as temperature and time in a firing furnace such as an electric furnace or a roller hearth kiln, and firing multiple times as necessary. However, since this has a higher thermal conductivity to the mixed powder to be treated than such a firing furnace and is more efficient, attempts have been made to use an apparatus that fires the raw material powder while fluidizing it, such as an externally heated rotary kiln.

[0005] When firing raw material powder using a rotary kiln, the mixed powder is usually gradually fed into the furnace, stirred and fluidized, and heated by a heater through the furnace wall. At this time, a gas flow may be introduced from outside the rotary kiln in order to discharge gas containing water vapor and carbon dioxide, which become impurities in the furnace, to the outside of the furnace and to maintain a desired oxidizing atmosphere in the furnace. However, the gas flow introduced into the rotary kiln causes the raw material powder to float in the rotary kiln, and further, some of the raw material powder is swept away by the gas flow in the furnace and discharged outside the rotary kiln system. This phenomenon raises concerns about a decrease in the yield and quality of the final fired product (lithium metal composite oxide).

[0006] The scattered powder discharged from the rotary kiln in the above manner can be collected using a collection device. For example, in the method for producing a lithium metal composite oxide described in Patent Document 1, a rotary kiln is used to sinter raw material powder. This rotary kiln has a dust collector disposed between the raw material powder supply port and the rotating cylinder, which is a sintering furnace. The scattered powder thus discharged is collected by the dust collector using the gas flow introduced from the discharge side of the rotary kiln and the air flow generated by the dust collector, and is then discharged, for example, to the supply port and fed back into the rotating cylinder. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7118187 Summary of the Invention [Problem to be solved by the invention]

[0008] As shown in Patent Document 1, when the scattered powder is collected by a dust collector and then fed back into the rotating drum to be fired together with the raw material powder in the rotating drum, the decrease in the yield of the obtained lithium metal composite oxide can be suppressed to some extent.

[0009] However, the composition of the scattered powder is different from the desired lithium metal composite oxide, i.e., the raw material composition. Specifically, the composition of the scattered powder is different from the desired lithium metal composite oxide, i.e., the raw material composition, as shown in the above general formula Li(NiM)O. 2In the case of lithium metal composite oxides represented by the formula (M is, for example, an element including a transition metal), the amount of Li relative to the total amount of Ni and M (Li / (Ni+M) ratio) tends to be small relative to the raw material powder. Therefore, if such scattered powder is directly charged into a furnace, there will be areas in the furnace system where Li / (Ni+M) is large and areas where it is small, causing unevenness in the composition of the obtained positive electrode active material.

[0010] In addition, in order to perform the firing in the rotary kiln more efficiently and to obtain a positive electrode active material of good quality, it is necessary to increase the temperature inside the furnace. However, the exhaust gas temperature also increases accordingly, and may reach a high temperature of about 400°C. Therefore, when collecting the scattered powder, it is difficult to collect the scattered powder using a collection device unless the exhaust pipe is made of a material that can withstand high temperatures and the pipe length is extended, the exhaust pipe is cooled by heat exchange with cooling water, or the exhaust gas is cooled by spraying a cooling gas on the exhaust gas. In addition, depending on the type of raw material, the scattered powder may become strongly alkaline, causing deterioration such as corrosion of the equipment.

[0011] The cooling method using the above-mentioned cooling gas is more suitable than other cooling methods because it is economical, easy to control, and has excellent productivity. However, when the cooling gas contains carbon dioxide and the lithium compound constituting the mixed powder is lithium hydroxide, the Li content is carbonated during the cooling process, generating lithium carbonate with low reactivity, and the reaction of lithium is suppressed. As a result, the composition of the raw material changes from that corresponding to the target lithium metal composite oxide. In addition, the lithium reaction during the sintering does not proceed sufficiently, and the amount of remaining lithium carbonate in the obtained lithium metal composite oxide increases, and in a lithium ion secondary battery using this as a positive electrode active material, the battery performance deteriorates.

[0012] As described above, simply feeding the scattered powder collected by the dust collector back into the rotating cylinder and continuing the firing process poses problems such as a decrease in the quality of the resulting lithium metal composite oxide and deterioration of the collection equipment.

[0013] The present disclosure has been made in consideration of the above-mentioned circumstances, and has an object to provide a method for producing a lithium metal composite oxide that is free of deterioration in quality and can impart excellent battery characteristics as a positive electrode active material for a non-aqueous electrolyte secondary battery. [Means for solving the problem]

[0014] The present inventors have conducted intensive research to solve the above-mentioned problems. As a result, it has been found that a method for producing a lithium metal composite oxide, which includes a firing step in which a powder mixture obtained by mixing at least a precursor compound, a lithium compound, and a collected powder is fired while being continuously flowed, a collection step in which an exhaust gas containing scattered powder generated by the flow of the powder mixture in the firing step is cooled, and the scattered powder contained in the exhaust gas is collected to obtain a collected powder, and a mixing step in which a powder mixture is obtained as a mixture of at least a precursor compound, a lithium compound, and the collected powder, can provide a method for producing a lithium metal composite oxide that is free of deterioration in quality and can provide excellent battery characteristics as a positive electrode active material for a non-aqueous electrolyte secondary battery. Specifically, the present disclosure provides the following.

[0015] (1) A method for producing a lithium metal composite oxide, comprising the steps of: a firing step of firing a powder mixture obtained by mixing at least the precursor compound, the lithium compound, and the collection powder while continuously flowing the mixture; a collecting step of cooling exhaust gas containing scattered powder generated by the flow of the powder mixture in the firing step, and collecting the scattered powder contained in the exhaust gas to obtain the collected powder; and a mixing step of obtaining the powder mixture as a mixture of at least the precursor compound, the lithium compound, and the collected powder. A method for producing a lithium metal composite oxide.

[0016] (2) The powder mixture is further mixed with a doping source compound and / or a coating source compound; A method for producing the lithium metal composite oxide according to (1).

[0017] (3) The powder mixture is prepared by controlling the mass ratio of either of the following (a) or (b) to be 2:98 to 40:60. A method for producing a lithium metal composite oxide according to (1) or (2). (a) a mass ratio of the amount of the collected powder to the total amount of the precursor compound and the lithium compound; (b) the mass ratio of the amount of the collected powder to the amount of the powder mixture

[0018] (4) In the firing process, a rotary kiln equipped with a scraper on the surface of the furnace core tube is used to scrape and stir the material to be fired in the furnace core tube. A method for producing a lithium metal composite oxide according to (1) or (2).

[0019] (5) The powder mixture prepared in advance is charged into the rotary kiln, and the stirring is performed. (4) A method for producing the lithium metal composite oxide according to (1).

[0020] (6) The lithium compound is lithium hydroxide, and the exhaust gas is cooled in a decarbonation atmosphere while maintaining a temperature above the dew point temperature of a system containing the exhaust gas. A method for producing a lithium metal composite oxide according to (1) or (2).

[0021] (7) The lithium compound is lithium carbonate, the precursor compound is a hydroxide, Cooling the exhaust gas while maintaining a temperature above the dew point temperature of a system containing the exhaust gas. A method for producing a lithium metal composite oxide according to (1) or (2).

[0022] (8) The firing temperature in the firing step is 400° C. or higher and lower than 700° C., After the firing step, the fired product obtained in the firing step is further fired at 700° C. or more and 1000° C. or less in a second firing step. 3. The method for producing the lithium metal composite oxide according to claim 1 or 2. Effect of the Invention

[0023] According to the present disclosure, it is possible to provide a method for producing a lithium metal composite oxide that is free from deterioration in quality and that can impart excellent battery characteristics as a positive electrode active material for a non-aqueous electrolyte secondary battery. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a schematic cross-sectional view in the radial direction of a furnace core tube of a rotary kiln that can be used in a method for producing a lithium metal composite oxide. [Diagram 2] FIG. 2 is a schematic radial cross-sectional view of a furnace core tube of a rotary kiln used in the Examples, Comparative Examples, and Reference Examples. [Diagram 3] FIG. 2 is a flow chart (Flow α) showing a method for producing the positive electrode active material of Example 1-1. [Figure 4] FIG. 1 is a flow chart (Flow β) showing a method for producing the positive electrode active material of Example 1-2. [Diagram 5] FIG. 1 is a flow chart (Flow γ) showing a method for producing a positive electrode active material of Reference Example 1-1. [Figure 6] FIG. 6 is a flow chart (Flow δ) showing a method for producing a positive electrode active material of Comparative Example 1-1. [Figure 7] FIG. 1 is a flow chart (Flow ε) showing a method for producing a positive electrode active material of Comparative Example 1-2. [Figure 8] FIG. 2 is a flow chart (Flow ζ) showing a method for producing the positive electrode active material of Example 2-1. [Figure 9] FIG. 1 is a flow chart (Flow η) showing a method for producing a positive electrode active material of Comparative Example 2-1. [Figure 10] FIG. 1 is a flow chart (flowι) showing a method for producing a positive electrode active material of Comparative Example 2-2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, embodiments of the present disclosure will be described, however, the present disclosure is not limited in any way to the description of the embodiments and can be implemented with appropriate modifications.

[0026] <Method for producing lithium metal composite oxide> A method for producing a lithium metal composite oxide according to an embodiment of the present disclosure includes a firing step of firing a powdery mixture obtained by mixing at least a precursor compound, a lithium compound, and a collected powder while continuously flowing, a collection step of cooling exhaust gas containing scattered powder generated by the flow of the powdery mixture in the firing step and collecting the scattered powder contained in the exhaust gas to obtain the collected powder, and a mixing step of obtaining a powdery mixture as a mixture of at least the precursor compound, the lithium compound, and the collected powder.

[0027] In order to efficiently produce a lithium metal composite oxide as a positive electrode active material for a non-aqueous electrolyte secondary battery, it is preferable to sinter at least the raw material powders of the precursor compound and the lithium compound while fluidizing them rather than leaving them still, in order to increase the thermal conductivity from the sintering apparatus. However, when the raw material powders are fluidized, the raw material powders tend to be stirred up by the airflow of the gas introduced from the outside, and some of the raw material powders are carried away by the airflow of the gas in the furnace as scattered powder and are discharged outside the system while scattering. As a result, the yield and quality of the obtained lithium metal composite oxide are reduced.

[0028] In order to suppress the decrease in the yield of the lithium metal composite oxide to some extent, the scattered powder discharged outside the system may be collected and then re-fluidized and fired. However, as described above, the composition of the scattered powder tends to have a smaller amount of lithium than the composition of the fluidized mixed powder. Therefore, even if the collected scattered powder is directly fluidized together with the raw material powder, the composition variation in the system cannot be suppressed. In addition, since the temperature of the exhaust gas containing the scattered powder is high, if the scattered powder is collected at the same temperature, the collection equipment will be corroded. Therefore, it is important to suppress the composition variation between the collected scattered powder and the fluidized mixed powder so that the quality of the target lithium metal composite oxide does not decrease, and to protect the equipment of the collection equipment from corrosion.

[0029] Hereinafter, each step of the method for producing the lithium metal composite oxide of the present disclosure will be described.

[0030] [Firing process] The firing step is a step in which a powder mixture obtained by mixing at least the precursor compound, the lithium compound, and the collection powder is fired while being continuously fluidized.

[0031] The powder mixture used in the firing step is prepared by mixing at least a precursor compound of a lithium metal composite oxide, a lithium compound, and the collection powder.

[0032] Among these, the precursor compound is, for example, a compound consisting of at least one element (M) and oxygen (O). Specific examples of the compound that can be used include hydroxides containing element M, oxides obtained by calcining hydroxides, and carbonate compounds (metal hydroxides, metal oxides, carbonates, etc. when element M is a metal). Since two or more types of element M can be selected, in such cases, hydroxides, oxides, and carbonate compounds of element M can be mixed and used, or composite hydroxides, composite oxides, and composite carbonate compounds (metal hydroxide composite oxides, metal composite oxides, composite carbonates, etc. when element M is a metal) can be used.

[0033] The element M is not particularly limited as long as it is an element other than Li and can constitute a lithium composite metal compound. Specifically, the element M can be selected according to the composition of the desired lithium metal composite oxide, and for example, 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), phosphorus (P), etc. can be used. As the precursor compound, it is preferable to use a composite hydroxide, composite oxide, composite carbonate, etc. containing at least Ni, and it is more preferable to use, for example, a composite hydroxide, composite oxide, composite carbonate, etc. containing at least Ni, Co, and Al and / or Mn.

[0034] The synthesis method of the precursor compound is not particularly limited, but examples thereof include the following synthesis methods. First, at least one aqueous solution of at least one element M or its compound is prepared according to the composition of the desired lithium metal composite oxide, and the mixing ratio is adjusted as necessary. Next, this is dropped into a reaction tank in which one or more alkaline aqueous solutions such as a sodium hydroxide aqueous solution and an ammonia solution are stirred as a mother liquid, and the pH is adjusted to, for example, within the range of 10.5 to 13, and a method of co-precipitating by a crystallization reaction to obtain hydroxides, oxides, carbonates, etc. can be used. The shape of the hydroxides, oxides, carbonates, etc. is not particularly limited, but it is preferable that they are in the shape of secondary particles formed by agglomeration of multiple primary particles.

[0035] The compound of element M is not particularly limited, and for example, one or more compounds selected from the group consisting of nickel compounds, cobalt compounds, manganese compounds, magnesium compounds, aluminum compounds, titanium compounds, zinc compounds, niobium compounds, and tungsten compounds can be used.

[0036] The nickel compound is not particularly limited, but for example, one or more compounds selected from the group consisting of nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel can be used.

[0037] The cobalt compound is not particularly limited, and for example, one or more compounds selected from the group consisting of cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt can be used.

[0038] The manganese compound is not particularly limited, and for example, one or more compounds selected from the group consisting of manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and manganese metal can be used.

[0039] The magnesium compound is not particularly limited, and for example, one or more compounds selected from the group consisting of magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium can be used.

[0040] The aluminum compound is not particularly limited, and for example, one or more compounds selected from the group consisting of aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, metallic aluminum, and the like can be used.

[0041] The titanium compound is not particularly limited, and for example, one or more compounds selected from the group consisting of titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and titanium metal can be used.

[0042] The zinc compound is not particularly limited, and for example, one or more compounds selected from the group consisting of zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and zinc metal can be used.

[0043] The niobium compound is not particularly limited, and for example, one or more compounds selected from the group consisting of niobium oxide, niobium chloride, lithium niobate, niobium iodide, and the like can be used.

[0044] The tungsten compound is not particularly limited, and for example, one or more compounds selected from the group consisting of tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, tungsten sulfide, and the like can be used.

[0045] The type and blending ratio of the compound of element M can be adjusted in consideration of the target composition of the lithium metal composite oxide so that each element is uniformly dispersed within the secondary particles.

[0046] The precursor compound obtained by the wet reaction can be washed and then dried after dehydration. By washing, impurities such as sulfate radicals, carbonate radicals, and Na content that are incorporated into the aggregated particles or attached to the surface during the reaction can be washed away. The drying can be performed in an oxidizing atmosphere at, for example, 50°C to 250°C.

[0047] The precursor compound may also be subjected to an oxidation treatment in an oxidizing atmosphere, for example, at 300°C to 800°C. By carrying out the oxidation treatment, the precursor compound is oxidized, and impurities such as sulfate radicals, carbonate radicals, and sodium are removed from the precursor compound, thereby improving the purity of the precursor compound. In addition, the bulk density of the resulting lithium metal composite oxide may be increased, improving production efficiency.

[0048] Next, the precursor compound thus synthesized and the lithium compound are mixed in a predetermined ratio to prepare a powder mixture. The method for mixing the precursor compound and the lithium compound is not particularly limited, but for example, the precursor compound powder and the lithium compound powder are weighed to a predetermined ratio, and then mixed in a dry state using a mixer or the like. In addition, the blending ratio of the precursor compound and the lithium compound can be adjusted so that the amount of Li and the total amount of element M are in a desired ratio, taking into account the composition of the desired lithium metal composite oxide.

[0049] The lithium compound is not particularly limited, and various lithium salts can be used. As the lithium compound, for example, one or more selected from the group consisting of lithium carbonate, lithium hydroxide hydrate, lithium hydroxide anhydrous, 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, etc. can be used. As the lithium compound, preferably, one or more selected from the group consisting of lithium carbonate, lithium hydroxide hydrate, lithium hydroxide anhydrous, etc. can be used.

[0050] Also, if necessary, a doping source compound or a coating source compound can be added. These compounds can be added when the precursor compound and the lithium compound are mixed. The method of adding these compounds is not particularly limited, but for example, addition in the form of a powder or addition by spraying in the form of a solution can be used. The compound of the element to be the additive is not particularly limited, and for example, a compound of element M can be selected and used.

[0051] [Firing process] The firing step is a step in which a powder mixture obtained by mixing at least the precursor compound, the lithium compound, and the collection powder is fired while being continuously fluidized.

[0052] In this firing process, when firing the powder mixture obtained by the above-mentioned method to produce a fired product, the powder mixture is fired while being continuously flowed in order to conduct heat uniformly throughout the powder mixture.

[0053] In the firing step, the method of firing the powder mixture is not particularly limited. For example, the powder mixture may be simply rotated, but it is preferable to use a method of stirring the powder mixture while stirring it up (hereinafter, sometimes referred to as "stirring up"). In addition, it is preferable to use a rotary kiln equipped with a stirrer on the surface inside the furnace core tube for stirring up. By using such a rotary kiln, the fired product can be produced continuously and easily.

[0054] The significance of stirring is as follows: If the powder mixture is simply fluidized while firing, the powder mixture will not flow easily near the oven walls, resulting in some areas that are easily exposed to heat from the oven walls and others that are not, which may result in a decrease in quality. On the other hand, if the powder mixture is fired while being stirred, the powder mixture will flow easily even near the oven walls, allowing firing to proceed uniformly.

[0055] Depending on whether or not the powder mixture is likely to separate due to falling, in order to more efficiently bake the material under high thermal conductivity and suppress variation in the composition of the baked product, it is preferable not to stir the powder mixture too high relative to the height of the top of the material that is not stirred by stirring when fluidizing the powder mixture by stirring.

[0056] The height of the top of the powder mixture produced by stirring up and stirring is thought to be related to the particle size of the precursor compound and the particle size of the lithium compound, the particle size ratio of both components, the particle size of any added compounds, the angle of repose of the powder mixture, etc., and the height of stirring up can be set taking these factors into consideration.

[0057] When improving the heat transfer to the powder mixture by stirring, it is preferable to consider how much heat the entire powder mixture can obtain. For example, when using a rotary kiln equipped with a stirring blade on the surface of the furnace core tube, it is preferable to consider to what extent the entire powder mixture can be brought into contact with the surface of the furnace core tube (hereinafter also referred to as the furnace wall). For example, the heat transfer to the powder mixture can be improved by appropriately adjusting the rotation speed of the rotary kiln and the filling rate of the powder mixture in the rotary kiln.

[0058] On the other hand, when the powder mixture is fluidized by stirring, it is preferable to pay attention not to separate the powder mixture. For example, when using a rotary kiln equipped with a stirring blade on the surface of the furnace core tube, it is preferable to appropriately adjust the installation angle of the stirring blade and also appropriately adjust the repose angle of the powder mixture, taking into consideration the relationship between the stirring degree of the powder mixture in the furnace and the dead space caused by the stirring blade.

[0059] When stirring is performed by a rotary kiln equipped with a stirring blade on the surface inside the furnace core tube, it is preferable to install the stirring blade in a direction parallel to the axial direction of the furnace core tube. This allows the stirring blade to come into contact with the furnace wall more efficiently. However, as described above, in consideration of improving the thermal conductivity of the fired material while suppressing the separation of the powder mixture, it is not preferable to determine the installation angle of the stirring blade only by focusing on the efficient contact of the fired material with the furnace wall.

[0060] If the installation angle of the agitation blade is too large, the agitation blade approaches a direction parallel to the axial direction of the furnace core tube. In such a case, the amount of scattered powder increases when the powder mixture is agitated and falls. As a result, the amount of lithium metal composite oxide obtained relative to the amount of powder mixture input may decrease, leading to a decrease in productivity and a large variation in Li / M of the obtained lithium metal composite oxide. On the other hand, if the installation angle of the agitation blade is too small, the agitation blade approaches a direction perpendicular to the axial direction of the furnace core tube. In such a case, a dead space is generated between the agitation blade and the furnace wall, reducing the frequency of contact between the powder mixture and the furnace wall, which may reduce the efficiency of heat conduction. Furthermore, when the repose angle of the powder mixture is taken into consideration, it may not be possible to agitate the powder mixture to a large extent, and the effect of improving heat conduction by agitation may not be obtained.

[0061] Therefore, when stirring a powder mixture by using a rotary kiln equipped with a scraper on the surface inside the furnace tube, the installation angle of the scraper (θ in FIG. 1) is preferably, for example, 15 degrees or more, 20 degrees or more with respect to the direction perpendicular to the axial direction of the furnace tube, while the installation angle of the scraper is preferably 85 degrees or less, 80 degrees or less.

[0062] Fig. 1 is a schematic cross-sectional view in the radial direction of a furnace core tube of a rotary kiln that can be used in a method for producing a lithium metal composite oxide. In Fig. 1, a furnace core tube 1 of the rotary kiln is provided with a plurality of scraping blades 3 on its surface portion 2, and rotates in the direction of arrow A. The installation angle θ of the scraping blades 3 is the angle with respect to the direction of the axis 4 of the furnace core tube 1 and the direction perpendicular to the axis 4.

[0063] The number of blades to be installed on the surface of the furnace core tube is not particularly limited, and it is preferable to provide sufficient stirring depending on the retort diameter, etc. For example, when the retort diameter is 200 to 700 mm, it is preferable to install 3 to 6 blades. On the other hand, when the retort diameter is 1000 to 2000 mm, it is preferable to install 4 to 10 blades.

[0064] The angle of repose of the powder mixture is preferably such that the powder mixture can be stirred up to an expected height by the stirring blades and does not separate when stirred up and dropped.

[0065] If the repose angle of the powder mixture is too large, the powder mixture may have low fluidity when it is stirred up and falls, and the heat transfer efficiency of the powder mixture subjected to stirring may be low. If the repose angle of the powder mixture or mixture is too small, the powder mixture may flow and fall while being stirred up, and the effect of stirring may be reduced. Therefore, the repose angle of the powder mixture is preferably 20° or more and 80° or less. The repose angle of the powder mixture is measured by the injection method.

[0066] The angle of repose of the powder mixture can be determined by at least the particle size of the precursor compound contained therein, the particle size of the lithium compound, and the particle size of the collected powder.

[0067] The conditions for stirring the mixture are not particularly limited, but it is preferable to take into consideration the following conditions, for example.

[0068] (Retort rotation speed) In order to improve the thermal conductivity of the powder mixture, the retort rotation speed may be increased while maintaining the residence time in the furnace core tube of the rotary kiln. However, if the retort rotation speed is too high, the mixture is discharged from the rotary kiln in a short time, and the lithium conversion by firing does not proceed sufficiently, which may result in a deterioration in the quality of the obtained lithium metal composite oxide. On the other hand, if the retort rotation speed is too low, lithium may adhere to the furnace wall, which may cause variation in the composition of the obtained powder mixture. Therefore, it is preferable to appropriately adjust the retort rotation speed according to, for example, the diameter of the furnace (retort diameter). For example, when the retort diameter is 200 to 1500 mm, it is preferable to adjust the retort rotation speed to 0.3 to 6.0 rpm.

[0069] (Filling rate of firing material) The filling rate of the powder mixture in the rotary kiln (percentage expressed as the volume of the fired material / volume of the rotary kiln) can be adjusted by changing the gas input rate and residence time of the powder mixture according to the type of rotary kiln. Among these, the residence time can be adjusted by changing the retort tilt angle and the retort rotation speed. However, if the filling rate is too high, the retort cross-sectional area is reduced and the wind speed is increased, which increases the amount of scattered powder, leading to a decrease in productivity and a risk of a decrease in the quality of the obtained lithium metal composite oxide. On the other hand, if the filling rate is too low, there is a possibility that sufficient productivity cannot be obtained. Therefore, the filling rate of the powder mixture is preferably 2 to 30%, more preferably 3 to 20%.

[0070] (Furnace air speed and dew point) Both the air velocity and the dew point in the furnace can be adjusted by changing the gas input rate. If the gas input rate is low and the dew point is too high, condensation occurs near the retort inlet where the powder mixture is fed. This causes lithium to dissolve in the water generated from the lithium compounds in the powder mixture, which can lead to irregular aggregation / sintering of primary and secondary particles, and the quality of the resulting lithium metal composite oxide can be reduced. On the other hand, if the gas input rate is high and the air velocity in the furnace is too high, selective scattering (separation) of the powder mixture can occur. For the inflow of gas into the furnace, separate exhaust ports can be used at different positions from the inlet of the furnace.

[0071] (heating rate) The heating rate can be adjusted by adjusting the temperature setting of the rotary kiln. If the heating rate is too low, sufficient productivity may not be obtained. On the other hand, if the heating rate is too high, localized lithiation reactions may occur, resulting in a decrease in the uniformity of the resulting lithium metal composite oxide, which may result in a decrease in quality.

[0072] (surface temperature of furnace tube) When the powder mixture is fired while being stirred, if the maximum temperature of the powder mixture is too low, the quality of the fired product may be reduced. On the other hand, if the maximum temperature of the powder mixture is too high, crystal growth may proceed in parallel with the lithiation reaction, and the quality of the resulting lithium metal composite oxide may be reduced. In this case, since the melting point differs depending on the type of lithium compound constituting the powder mixture, the surface temperature of the furnace tube may be determined accordingly. Specifically, the firing temperature is preferably 400°C or higher, 410°C or higher, 420°C or higher, 430°C or higher, 440°C or higher, 450°C or higher, 460°C or higher, 470°C or higher, 480°C or higher, 490°C or higher, or 500°C or higher. On the other hand, the firing temperature may be less than 700°C, 690°C or less, 680°C or less, 670°C or less, 660°C or less, 650°C or less, 640°C or less, 630°C or less, 620°C or less, 610°C or less, or 600°C or less. For example, when lithium hydroxide is used as the lithium compound, the maximum temperature of the powder mixture is preferably 500 to 650°C, 530 to 630°C. In addition, when the lithium compound is lithium carbonate, the maximum temperature of the powder mixture is preferably 600 to 770°C, 630 to 770°C, or 690 to 760°C. During firing, it is preferable to adjust the temperature setting of the rotary kiln while taking into consideration the filling rate of the powder mixture. Specifically, it is preferable to sinter the powder mixture so that the surface temperature of the furnace core tube heated by the heater is 400°C or more, 450°C or more, 500°C or more, and 1000°C or less, 950°C or less, 900°C or less, 850°C or less.

[0073] In the firing step, the firing atmosphere is not particularly limited as long as the lithiation reaction and crystal growth proceed reliably and uniformly. For example, it is preferable to use a decarbonated oxidizing gas atmosphere with a carbon dioxide gas concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of 80 vol% or more, preferably 90 vol% or more.

[0074] The baking time is not particularly limited as long as the lithium addition reaction and crystal growth proceed reliably and uniformly, and is preferably, for example, 1 to 12 hours, and more preferably 2 to 10 hours.

[0075] [Second firing step] Although the calcination step described above (hereinafter sometimes referred to as the "first calcination step") can produce a lithium metal composite oxide of the desired composition, a second calcination step can be provided in which the lithium metal composite oxide obtained in the first calcination step is further calcined. By carrying out multiple calcinations, including this second calcination step, crystal growth becomes more reliable and uniform, and the quality of the obtained lithium metal composite oxide can be further improved.

[0076] When carrying out the second firing, the obtained lithium metal composite oxide can be filled into a firing vessel such as a sagger or crucible, and fired using equipment such as a stationary furnace such as an electric furnace, a roller hearth kiln, etc. Also, a rotary kiln can be used as in the firing in the firing step. For the further firing, it is preferable to select and use equipment that can finely adjust the conditions suitable for crystallization.

[0077] The atmosphere in the second firing step is not particularly limited as long as it allows the crystal growth to proceed more reliably and uniformly. Specifically, it is preferable to use, for example, a decarbonated oxidizing gas atmosphere with a carbon dioxide gas concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of 80 vol% or more, preferably 90 vol% or more.

[0078] The heating temperature in the second firing step may be adjusted taking into consideration the maximum temperature of the powder mixture in the first firing step and the desired composition of the lithium metal composite oxide. For example, it is preferable to adjust the heating temperature to 700°C or higher and 1050°C or lower.

[0079] The calcination time is not particularly limited as long as it is a time sufficient to obtain a lithium metal composite oxide having a desired crystal structure, and is, for example, preferably 1 to 12 hours, and more preferably 2 to 10 hours.

[0080] In addition, the doping source compound and / or the coating source compound may be added to the lithium metal composite oxide obtained in the first baking step, and the second baking step may be performed. In this way, the doping source compound and / or the coating source compound is added to the lithium metal composite oxide obtained in the baking step, and the function derived from the compound itself or the element contained in the compound may be expressed. When the doping source compound and / or the coating source compound is added in this way, it may be added in the form of a powder or sprayed in the form of a solution.

[0081] Specifically, as the doping source compound, at least one selected from the group consisting of cobalt oxide, cobalt hydroxide, manganese oxide, manganese hydroxide, manganese carbonate, magnesium oxide, magnesium hydroxide, aluminum oxide, aluminum hydroxide, aluminum chloride, aluminum fluoride, titanium oxide, titanium hydroxide, titanium chloride, zinc oxide, niobium oxide, niobium hydroxide, niobium chloride, tungsten oxide, tungsten chloride, molybdenum oxide, vanadium oxide, chromium oxide, iron oxide, iron hydroxide, and zirconium oxide can be used.

[0082] As the coating source compound, one or more compounds selected from the group consisting of gallium oxide, potassium oxide, potassium hydroxide, barium oxide, barium hydroxide, barium chloride, calcium oxide, calcium hydroxide, gallium oxide hydroxide, strontium oxide, strontium hydroxide, yttrium oxide, ruthenium oxide, indium oxide, tin oxide, tantalum oxide, bismuth oxide, boric acid, boron oxide, boron carbide, phosphoric acid, and ammonium hydrogen phosphate can be used.

[0083] The lithium metal composite oxide obtained through the first firing step and the second firing step contains nickel as element M, and the high-nickel lithium metal composite oxide has a nickel content of, for example, 80 mol% or more. Compared with a low-nickel lithium metal composite oxide, the amount of unreacted lithium compounds and the amount of lithium compounds that come out of the crystal structure to the particle surface during the firing process (hereinafter, sometimes referred to as "residual lithium compounds") may be larger. The amount of residual lithium compounds can be reduced, for example, by subjecting the lithium metal composite oxide to a water washing treatment or by subjecting the surfaces of the primary particles and / or secondary particles of the lithium metal composite oxide to a surface treatment.

[0084] In addition, even if the lithium metal composite oxide obtained through the first and second firing steps has a low nickel content, if the primary particles are generally small in shape, the specific surface area is large and there is a risk that the metal will be eluted by hydrogen fluoride that may come into contact with the lithium metal composite oxide as a non-aqueous electrolyte when the lithium metal composite oxide is used as a positive electrode active material. Therefore, the lithium metal composite oxide may be subjected to a surface treatment.

[0085] The surface treatment method is not particularly limited, and for example, a method can be used in which fine particles of aluminum oxide are applied to the surface layer of lithium metal composite oxide particles in a dry manner while applying a shearing force, and then heat treatment is performed at about 300 to 700°C. In addition, a method can be used in which a predetermined amount of lithium metal composite oxide is mixed into an aqueous solution in which a predetermined amount of aluminum sulfate is dissolved, and the mixture is stirred for about 5 to 10 minutes, dehydrated, dried, and then heat treatment is performed at about 250°C to 700°C to coat the surface layer of the particles with an aluminum compound. In addition to the aluminum compound, for example, one or more compounds selected from boron compounds and tungsten compounds can be used for surface treatment.

[0086] Even when the lithium metal composite oxide is in the form of secondary particles composed of large primary particles, a sintering accelerator such as potassium hydroxide may be used before firing in order to obtain the primary particle shape. In order to wash off such a sintering accelerator, the lithium metal composite oxide may be subjected to a water washing treatment.

[0087] [Collection process] The collection step is a step of cooling the exhaust gas containing the scattered powder generated by the flow of the powder mixture in the firing step, and collecting the scattered powder contained in the exhaust gas to obtain the collected powder.

[0088] As described above, when firing while continuously flowing the powder mixture, the powder mixture is stirred up by the gas flow introduced into the system, and some of it is entrained in the gas flow as scattered powder and discharged to the outside of the system in the exhaust gas state. In the collection step, the scattered powder discharged to the outside of the system in the exhaust gas state is collected to obtain collected powder.

[0089] On the other hand, exhaust gas containing scattered powder is alkaline due to at least lithium in the lithium compound. In addition, since exhaust gas containing scattered powder is generated when the powder mixture is sintered, it is heated to a high temperature of 200°C to 400°C when the sintering temperature is 400°C to 600°C. Therefore, metal materials of the equipment related to the collection may be damaged by corrosion. Therefore, the exhaust gas containing scattered powder is cooled to prevent the equipment related to the collection from corroding.

[0090] The temperature of the exhaust gas after cooling is not particularly limited and may be set depending on the type of metal material of the equipment related to the capture, and is preferably, for example, 200°C or less, 195°C or less, 190°C or less, 185°C or less, 180°C or less, 175°C or less, 170°C or less, 165°C or less, 160°C or less, 155°C or less, 150°C or less, 145°C or less, 140°C or less, 135°C or less, 130°C or less, 125°C or less, 120°C or less, 115°C or less, or 110°C or less.

[0091] As a method for cooling the exhaust gas, for example, a method of cooling by using a material that can withstand high temperatures for the exhaust piping through which the exhaust gas passes and extending the piping length is conceivable, but extending the piping length may cause scattered powder to accumulate in the exhaust piping, reducing the yield. In addition, a method of cooling the exhaust piping by using a heat exchanger and exchanging heat with cooling water or the like is conceivable, but there is a risk that local condensation may occur in the heat exchanger, leading to blockage due to accumulation of scattered powder. Therefore, it is preferable to use a method of contacting the exhaust gas containing scattered powder by blowing a cooling gas such as air against it. According to such a method, the exhaust gas can be cooled in a relatively short time, which is economical and has excellent productivity. In addition, such a method is easy to control.

[0092] The exhaust gas may be cooled naturally. If the temperature of the exhaust gas drops too much, the exhaust gas or the cooling gas may be heated.

[0093] Here, when a hydroxide is used as the precursor compound and / or lithium hydroxide is used as the lithium compound, water is generated by the calcination, and the exhaust gas contains water vapor. In such a case, it is preferable to cool the exhaust gas while maintaining a temperature above the dew point temperature of the system including the exhaust gas.

[0094] It is preferred to cool the exhaust gas whilst maintaining the temperature of the exhaust gas at above 100°C, 102°C or greater, 105°C or greater, 107°C or greater, 110°C or greater at atmospheric pressure.

[0095] In addition, when lithium hydroxide is used as the lithium compound or when a hydroxide is used as the precursor compound, if the refrigerant gas (atmosphere of the cooling mechanism) contains carbon dioxide, the carbonation of lithium hydroxide proceeds and lithium carbonate is easily generated. Here, since lithium carbonate has a lower reactivity than other lithium compounds such as lithium hydroxide, even if the scattered powder containing lithium carbonate is fired, the lithium carbonate is less likely to react with the precursor compound. Therefore, depending on the heating temperature, the lithiation reaction of the precursor compound may not proceed sufficiently, and lithium carbonate may remain in the fired product. In such a case, it is preferable to cool the exhaust gas in a decarbonation atmosphere. In this way, by suppressing the generation of lithium carbonate, the amount of lithium carbonate remaining in the target lithium metal composite oxide can be reduced, and the deterioration of the quality of the lithium metal composite oxide can be suppressed.

[0096] In addition, when lithium carbonate is used as the lithium compound and a hydroxide is used as the precursor compound, or when lithium carbonate and lithium hydroxide are used as the lithium compounds, the atmosphere in the system does not need to be a decarbonation atmosphere because lithium carbonate is already present, and the exhaust gas may be cooled while maintaining a temperature above the dew point temperature of the system including the exhaust gas. After preparing the lithium metal composite oxide, the lithium carbonate may be removed.

[0097] Cooling of the exhaust gas in a decarbonation atmosphere can be performed by contacting the exhaust gas with a decarbonation cooling gas. The decarbonation cooling gas preferably has a carbon dioxide gas concentration of 200 ppm or less, 170 ppm or less, 150 ppm or less, 120 ppm or less, 100 ppm or less, 70 ppm or less, 50 ppm or less, 30 ppm or less, 20 ppm or less, 15 ppm or less, or 10 ppm or less. For example, one or more cooling gases selected from the group consisting of low dew point decarbonation air, gas with an oxygen concentration of 90 vol% or more, nitrogen gas, argon gas, etc. can be used.

[0098] When lithium hydroxide is used as the lithium compound, the production of lithium carbonate can be suppressed by cooling in a decarbonation atmosphere while maintaining a temperature above the dew point temperature. In addition, condensation of water vapor can be suppressed in the pipe during contact with the decarbonated gas. Furthermore, the lithium content in the scattered powder can be suppressed from precipitating and adhering to the inner wall of the pipe. As a result, the fluidity of the scattered powder can be maintained and the powder can be efficiently collected, and corrosion of the inner wall of the pipe due to the lithium content can also be suppressed.

[0099] In addition, when lithium carbonate is used as the lithium compound, by performing cooling while maintaining a temperature above the dew point temperature, the lithium carbonate can be partially dissolved due to condensation of water vapor, thereby eliminating the cause of adhesion.

[0100] As described above, the amount of remaining lithium carbonate in the lithium metal composite oxide produced can be reduced by suppressing the formation of lithium carbonate when cooling the exhaust gas, but the amount of remaining lithium carbonate can also be reduced by other methods. Specifically, when firing in the firing step or when firing further thereafter, firing is performed at a temperature that is, for example, about 100° C. higher than the melting point of lithium carbonate. This makes it possible to reduce the amount of remaining lithium carbonate in the lithium metal composite oxide produced.

[0101] The remaining amount of lithium carbonate is, for example, 0.60% by weight or less, and preferably 0.55% by weight or less.

[0102] The remaining amount of lithium carbonate is a value obtained by using the Walder method. Specifically, 20 g of a lithium metal composite oxide sample is added to 100 mL of water, and the mixture is stirred at room temperature for 20 minutes. The solid content is then filtered and removed to obtain a supernatant, which is then titrated with 0.2 N hydrochloric acid. On a pH curve plotted with the titration amount (mL) on the horizontal axis and the pH of the supernatant on the vertical axis, the two points with the largest slope are designated as the first titration point and the second titration point, starting from the point with the smallest titration amount. The amounts of each are calculated from the titration amounts at these points using the following formula, and are regarded as the remaining amount of lithium carbonate. The abbreviations in the formula are as follows: T 1 : Titration volume up to the first titration point (mL) T 2 : Titration volume up to the second titration point (mL) C HCl : Concentration of hydrochloric acid used in titration (mol / L) F HCl : Factor of hydrochloric acid used in titration M: Molecular weight of lithium carbonate W: Weight of the lithium metal composite oxide sample (g) Residual amount of lithium carbonate (wt%) =(T 2 -T 1 )×C HCl ×F HCl ×M×2×100 / (W×1000)

[0103] After the exhaust gas has been cooled in the above manner, the scattered powder contained in the exhaust gas is collected using a collection facility or the like.

[0104] Specifically, the collecting equipment for collecting the scattered powder is not particularly limited, and for example, a bag filter, a cyclone, etc. can be used.

[0105] [Mixing process] In the mixing step, the scattered powder is collected and the collected powder is subjected to the firing step again, so that a powder mixture is obtained as a mixture of at least the precursor compound, the lithium compound, and the collected powder.

[0106] The composition of the scattered powder and collected powder generated by the flow of the powder mixture may be different from the metal composition of the precursor compound and the lithium compound. Specifically, the ratio of the amount of Li to the total amount of element M in the scattered powder and collected powder (hereinafter referred to as Li / M) may be smaller than the Li / M in the powder mixture (which is also equivalent to the intended lithium metal composite oxide). Therefore, in order to produce a lithium metal composite oxide using the collected powder, it is preferable to suppress the variation in the composition by considering the balance between the Li / M of the collected powder and the Li / M of the powder mixture in the system. Note that when the amount of scattered powder discharged per hour is constant and the amount of scattered powder discharged outside the system is approximately the same as the amount of collected powder added and mixed, no large variation occurs when such a system is operated steadily.

[0107] The order and place of addition and mixing of the precursor compound, lithium compound, and collected powder, and the device used for addition and mixing are not particularly limited. For example, when each is added at one location, any of the mixing methods 1 to 4 shown below can be used. However, the addition of the precursor compound, lithium compound, and collected powder is not limited to one location.

[0108] Mixing method 1: The collected powder is mixed with a precursor compound and a lithium compound to prepare a powder mixture. Mixing method 2: The collected powder is mixed with a mixture of the precursor compound and the lithium compound that has been previously mixed to prepare a powder mixture. Mixing method 3: The collected scattered powder is mixed with a precursor compound, and then further mixed with a lithium compound to prepare a powder mixture. Mixing method 4: The collected scattered powder is mixed with a lithium compound, and then further mixed with a precursor compound to prepare a powder mixture.

[0109] (Mixing method 1) More specific examples of the mixing method 1 include the following mixing method 1-1 and mixing method 1-2. Mixing method 1-1: The precursor compound, the lithium compound, and the collected powder are precisely mixed using a mixer or the like capable of uniformly mixing the precursor compound, the lithium compound, and the collected powder without unevenness (hereinafter referred to as precision mixing). Mixing method 1-2: After precisely mixing the precursor compound and lithium compound, The obtained precision mixture is rotated by a rotating means such as a screw, and the collected powder is added to a conveying path that conveys the mixture to a mixture storage tank or the like equipped with a rotating means such as a screw or ribbon blender, and / or The collected powder is added to the transported precision mixture in a mixture storage tank or the like and mixed.

[0110] (Mixing method 2) More specific examples of the mixing method 2 include the following mixing method 2-1 and mixing method 2-2. Mixing method 2-1: The powder mixture and scattered powder are precisely mixed, for example, using a mixer capable of precise mixing. Mixing method 2-2: The powder mixture is rotated by a rotating means such as a screw, and the collected powder is added to a conveying path that conveys the mixture to a mixture storage tank or the like equipped with a rotating means such as a screw or ribbon blender, and / or The collected powder is added to the transported powder mixture in a mixture storage tank or the like and mixed.

[0111] In mixing methods 3 and 4, similarly to mixing methods 1 and 2, the respective mixing operations may be carried out in a mixer capable of precision mixing, a conveying path for conveying the materials to a mixture storage tank or the like, and a mixture storage tank or the like.

[0112] As described above, by mixing the precursor compound, lithium compound, and collected powder before subjecting them to the firing step and homogenizing the mixture to be subjected to firing, the lithiation of unreacted element M in the collected powder is facilitated. As a result, the Li / M in the collected powder approaches the Li / M in the target lithium metal composite oxide, stabilizing the Li / M of the mixture to be subjected to the firing step, and more uniform crystal growth and particle growth can be achieved.

[0113] In addition to the precursor compound, the lithium compound, and the collected scattered powder, a doping source compound and / or a coating source compound may also be mixed together to prepare a powder mixture. In this case, the powder mixture is a mixture with a doping source compound and / or a coating source compound. The order and place of addition and mixing of the doping source compound and / or the coating source compound, and the device used for addition and mixing are not particularly limited.

[0114] As the doping source compound and the coating source compound, the same compounds as those mentioned above can be used.

[0115] As exemplified in the mixing methods 1 to 4, the collected powder may be preliminarily prepared as a powder mixture together with the precursor compound and the lithium compound before firing. For example, when firing while fluidizing the mixture by stirring using the rotary kiln described above, the powder mixture is preliminarily prepared before firing in the rotary kiln begins, and is then charged into the rotary kiln and stirred. The time of preparation of the mixture is not particularly limited.

[0116] In the mixing step, it is preferable that the entire amount of the collected powder is mixed into the powder mixture. In this case, the mixing ratio of the precursor compound, the lithium compound, and the collected powder may be determined so as to be constant based on the particle size of the precursor compound, the particle size of the lithium compound, the difference between the two, etc., and it is preferable to mix them while taking into consideration the Li / M of the powder mixture.

[0117] Specifically, it is preferable to prepare the powder mixture by controlling the mass ratio of either one of the following (a) or (b) to 2:98 to 40:60, 5:95 to 40:60, or 7:93 to 37:63. (a) Mass ratio of the amount of collected powder to the total amount of precursor compound and lithium compound (b) Mass ratio of the amount of collected powder to the amount of powder mixture Within this range, it is preferable to make the amount of the scattered powder per hour equal to the amount of the collected powder added again to the mixing step. In addition, when there is no mixture storage tank or batch mixer downstream of the addition of the collected powder, and the collected powder is added and continuously mixed and then fired, it is necessary to control the addition of the collected powder so that it is added continuously. In addition, even when the powder mixture contains the above-mentioned doping source compound and / or coating source compound, it is preferable to control the amount of the collected powder in the same range.

[0118] If the mass ratio of (a) or (b) varies with time, the quality of the resulting lithium metal composite oxide may deteriorate, and therefore it is necessary to reset the flow conditions.

[0119] In this manner, by preparing a powder mixture while controlling the amount of the collection powder added, the lithium metal composite oxide obtained by firing this powder mixture will have the desired Li / M ratio.

[0120] The lithium metal composite oxide produced by the production method according to the present disclosure is not particularly limited in composition as long as it is made of a lithium metal composite oxide containing Li and at least one element M. For example, the lithium metal composite oxide may be represented by the formula (I): Li a MO 2 (I) (In the formula, M is an element other than Li and O, and 0.95≦a≦1.40.) It is preferable that the composition is represented by the following formula:

[0121] In the lithium metal composite oxide having the composition represented by formula (I), the stoichiometric ratio a of Li, i.e., the ratio of the number of moles of Li to the total number of moles of element M (Li / M), is preferably 0.95≦a≦1.40, 0.95≦a≦1.25, or 0.96≦a≦1.15.

[0122] In the lithium metal composite oxide having the composition represented by the formula (I), the element M is preferably at least Ni, and more preferably at least Ni, Co, and Al and / or Mn. When M is at least Ni, the stoichiometric ratio b of Ni, that is, the ratio (Ni / M) of the number of moles of Ni to the total number of moles of the element M, is preferably 0.3 < b ≦ 1, 0.5 < b < 1, or 0.8 < b < 1. When lithium carbonate is used as the lithium compound, the ratio of Ni / M is more preferably 0.3 < b ≦ 0.8.

[0123] The characteristics of the lithium metal composite oxide produced by the production method according to the present disclosure are preferably, for example, that the average particle diameter (average secondary particle diameter) and the crystallite size of the secondary particles are each in the ranges shown below.

[0124] The average secondary particle diameter is preferably, for example, 1 μm to 30 μm, and more preferably 2 μm to 25 μm.

[0125] The average secondary particle diameter is D50 measured on a volume basis by the wet laser method using a laser particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0126] The crystallite size is preferably, for example, 50 nm to 600 nm, and more preferably 60 nm to 500 nm.

[0127] The crystallite size is a value obtained by performing Rietveld analysis after obtaining the XRD diffraction data of the lithium metal composite oxide by the following method.

[0128] Using an X-ray diffractometer [SmartLab, manufactured by Rigaku Corporation], after obtaining the XRD diffraction data of the lithium metal composite oxide under the following X-ray diffraction conditions, Rietveld analysis was performed with reference to "R.A. Young, ed., 'The Rietveld Method', Oxford University Press (1992)" using the XRD diffraction data. (X-ray diffraction conditions) Source: Cu-Kα Acceleration voltage and current: 45kV and 200mA Sampling width: 0.02 deg. Scanning width: 15deg.~122deg. Scan speed: 1.0 step / sec Divergence slit: 2 / 3deg. Receiving slit width: 0.15 mm Scattering slit: 2 / 3deg.

[0129] In the manufacturing method of the present disclosure, as described above, the scattered powder generated during firing while continuously flowing the powder mixture is collected, and the collected powder is not fired as it is, but is mixed with at least a precursor compound and a lithium compound before firing, thereby suppressing the variation in the composition of the resulting lithium metal composite oxide, and a lithium metal composite oxide having a desired composition can be obtained.

[0130] As an index of the variation of Li / M, the coefficient of variation of Li / M of multiple fired product samples taken from different parts of the fired product obtained at a predetermined time after the start of firing (hereinafter, sometimes referred to as "Li / M variation coefficient") can be mentioned. A small coefficient of variation of Li / M for fired products obtained at any predetermined time means that the variation of Li / M is small.

[0131] The Li / M coefficient of variation approaches 0% as the compositions of N (e.g., N≧10) sintered samples taken from different parts of the sintered product obtained at a predetermined time are closer to the same. In other words, the smaller the Li / M coefficient of variation, the more preferable it is. If the Li / M coefficient of variation is too large, it indicates that there is variation in the composition of the sintered product samples obtained at a predetermined time. According to the manufacturing method of the present disclosure, the composition variation of the sintered product samples obtained at any predetermined time, such as 1 hour, 2 hours, 3 hours, 4 hours, etc., is sufficiently suppressed. The Li / M coefficient of variation is measured every hour (10 times in total) for 10 consecutive hours. The Li / M coefficient of variation is not particularly limited, but is preferably 0.7% or less, 0.6% or less, or 0.5% or less at any time.

[0132] The Li / M variation coefficient is a value calculated based on the following formula using the standard deviation and average value of Li / M of N (N=10) fired samples obtained at a specified time. The Li / M of each fired sample is calculated by dissolving 0.2 g of the fired sample in 25 mL of 20% hydrochloric acid solution by heating, transferring it to a 100 mL measuring flask after cooling, and adding pure water to prepare a liquid, and quantifying each element using ICP-AES [Optima8300, PerkinElmer Co., Ltd.]. Li / M coefficient of variation (%) = (standard deviation / average value) x 100

[0133] The lithium metal composite oxide produced by the production method according to the present disclosure can be used as a positive electrode active material for a non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte-containing electrolytic solution, and the positive electrode active material for a non-aqueous electrolyte secondary battery can be contained in the positive electrode.

[0134] When manufacturing a positive electrode, a conductive agent and a binder are added to and mixed with a positive electrode active material. As the conductive agent, for example, acetylene black, carbon black, graphite, etc. are preferable. As the binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, etc. are preferable.

[0135] The negative electrode may be, for example, a negative electrode active material such as lithium metal, graphite, or a low-crystalline carbon material, or one or more nonmetallic or metallic elements selected from the group consisting of Si, Al, Sn, Pb, Zn, Bi, and Cd, or an alloy or chalcogen compound containing the same.

[0136] As the solvent for the electrolytic solution, for example, an organic solvent containing at least one selected from the group consisting of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and ethers such as dimethoxyethane can be used.

[0137] The electrolyte is lithium hexafluorophosphate (LiPF 6 In addition to the above, for example, one or more selected from the group consisting of lithium salts such as lithium perchlorate and lithium tetrafluoroborate can be used. The electrolyte is used by dissolving it in the above-mentioned solvent.

[0138] <effect> According to the manufacturing method of the present disclosure, it is possible to manufacture a lithium metal composite oxide that is free from deterioration in quality and that can impart excellent battery characteristics as a positive electrode active material for a non-aqueous electrolyte secondary battery. EXAMPLES

[0139] The present disclosure will be specifically described below using examples of the present disclosure, but the present disclosure is not limited to these examples in any way.

[0140] [Sample Analysis] The samples of the examples and comparative examples were analyzed using the following methods.

[0141] [XRD Diffraction] Using an X-ray diffractometer [SmartLab, manufactured by Rigaku Corporation], XRD diffraction data of the lithium metal composite oxide sample was obtained under the following X-ray diffraction conditions. Then, using the XRD diffraction data, Rietveld analysis was performed with reference to "RA Young, ed., "The Rietveld Method", Oxford University Press (1992)". (X-ray diffraction conditions) Source: Cu-Kα Acceleration voltage and current: 45kV and 200mA Sampling width: 0.02 deg. Scanning width: 15deg.~122deg. Scan speed: 1.0 step / sec Divergence slit: 2 / 3deg. Receiving slit width: 0.15 mm Scattering slit: 2 / 3deg.

[0142] [Composition of precursor compound and lithium metal composite oxide sample] 0.2 g of a precursor compound or lithium metal composite oxide sample was dissolved by heating in 25 mL of 20% hydrochloric acid solution, cooled, and then transferred to a 100 mL measuring flask. Pure water was added to prepare a liquid, and each element in the liquid was quantified using ICP-AES [Optima 8300, PerkinElmer Co., Ltd.].

[0143] [Coin cell using lithium metal composite oxide sample] A 2032 type coin cell using the lithium metal composite oxide sample as the positive electrode active material was manufactured using a positive electrode, a negative electrode and an electrolyte prepared by the following method.

[0144] (positive electrode) Acetylene black and graphite were used as conductive agents in a ratio of 1:1 (weight ratio), and polyvinylidene fluoride was used as a binder. The positive electrode active material, conductive agent, and binder were mixed in a ratio of 90:6:4 (weight ratio) of positive electrode active material:conductive agent:binder, and these were mixed in N-methylpyrrolidone to form a slurry, which was then applied onto an aluminum foil. This was dried at 110°C to produce a sheet, which was then punched out to a diameter of 15 mm, after which the density of the composite was 3.0 g / cm. 3 The resultant was rolled to obtain a positive electrode.

[0145] (Negative electrode) A lithium foil having a thickness of 500 μm and punched to 16 mmφ was used as the negative electrode.

[0146] (electrolyte) A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared so that the volume ratio of EC:DMC was 1:2, and 1M LiPF 6 The mixed solution was used as the electrolyte.

[0147] [Battery characteristics of non-aqueous electrolyte secondary batteries] (Initial charge capacity and initial charge / discharge efficiency) Using the coin cell manufactured by the method shown in the section "Coin cell using lithium metal composite oxide sample", a constant current charge was performed at a current density of 18 mA / g up to 4.30 V (upper limit voltage) in an environment of 25° C., followed by constant voltage charge until the current density reached 2 mA / g. The capacity at this time was taken as the initial charge capacity (mAh / g).

[0148] Next, after a 5-minute pause, constant-current discharge was performed at a current density of 18 mA / g up to 3.00 V under the same environment, and after a 5-minute pause, the initial discharge capacity (mAh / g) was measured.

[0149] The initial charge / discharge efficiency was calculated based on the measured initial charge capacity and the measured initial discharge capacity according to the following formula. Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) x 100

[0150] [Sample preparation] Lithium metal composite oxide samples of the examples and comparative examples were prepared by the methods described below.

[0151] [Synthesis Example 1: Synthesis of Precursor Compound 1] A mixed aqueous solution was obtained by mixing an aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, and an aqueous aluminum sulfate solution so that the ratio (molar ratio) of Ni, Co, and Al was Ni:Co:Al = 89:7:4. 10 L of pure water to which 300 g of an aqueous sodium hydroxide solution and 500 g of an aqueous ammonia solution had been added was prepared in advance in the reaction tank as a mother liquid, and the reaction tank was filled with nitrogen gas at a flow rate of 0.7 L / min to create a nitrogen atmosphere, and the reaction was also carried out in a nitrogen atmosphere.

[0152] Thereafter, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously dropped at a predetermined speed, and the amount of the alkaline solution dropped was adjusted so that the pH became 11.8. Through a crystallization reaction, Ni, Co, and Al were crystallized and coprecipitated to form agglomerated particles, thereby obtaining a coprecipitate.

[0153] Thereafter, the slurry in the reactor was subjected to solid-liquid separation, and further washed with pure water to reduce remaining impurities, and the coprecipitate in a cake state was dried at 110°C for 12 hours in an air environment to obtain precursor compound 1. At this time, D50 in the volume-based particle size distribution of precursor compound 1 was 11.2 μm. In addition, the angle of repose of precursor compound 1 measured by the injection method was 34.2°.

[0154] [Example 1-1: Production of lithium metal composite oxide sample] 3 is a flow chart (Flow α) showing a method for producing a positive electrode active material of Example 1-1. In Example 1-1, a lithium metal composite oxide sample was produced according to Flow α.

[0155] Precursor compound 1 and anhydrous lithium hydroxide (angle of repose measured by injection method: 52.2°) were weighed out so that the ratio (molar ratio) of Li to the total amount of Ni, Co and Al was Li / (Ni+Co+Al)=1.02, and then, as described below, they were charged into a mixer so as to control the mass ratio (scattered powder: total amount) of the amount of collected powder to the total amount of precursor compound 1 and anhydrous lithium hydroxide, and mixed precisely to prepare mixture 1. The obtained mixture 1 was further continuously mixed while being conveyed by a screw, and further continuously mixed in a mixture storage tank equipped with a mixing function by a screw (rotation speed: 104 rpm) and stored. The angle of repose of mixture 1 measured by injection method was 43.7°.

[0156] Next, mixture 1 was put from the mixture storage tank into a rotary kiln and fired. Firing was carried out using a rotary kiln with a retort diameter of 300 mm and four agitating blades on the circumference at an installation angle of 30 degrees on the surface inside the furnace core tube as shown in Figure 2, in an oxygen atmosphere (oxygen concentration: 97 vol%) under the rotary kiln conditions described below for 13 hours while agitating and continuously flowing mixture 1 (mixture 1 flows as indicated by arrow B).

[0157] The exhaust gas (about 280℃) containing the scattered powder generated during this firing was discharged outside the system from the inlet side of the rotary kiln, and the exhaust gas containing the scattered powder was cooled in the decarbonation atmosphere by introducing a decarbonation cooling gas (ultra-low dew point dry air, carbon dioxide concentration: 10ppm or less) into the exhaust gas and bringing it into contact with it. The temperature of the exhaust gas at this time was about 180℃ at a slight negative pressure of about 101.2kPa.

[0158] Next, while the temperature of the exhaust gas was maintained at about 180° C. under a slight negative pressure of about 101.2 kPa, as in the cooling process, the scattered powder contained in the exhaust gas was collected using a filter cloth bag filter, and this was used as the collected powder.

[0159] The collected powder was fed into a mixer in which precursor compound 1 and anhydrous lithium hydroxide were mixed to prepare mixture 1, and precursor compound 1, anhydrous lithium hydroxide, and scattered powder were precisely mixed to prepare a powder mixture. The amount of collected powder fed at this time was controlled so that the mass ratio of the amount of collected powder to the total amount of precursor compound 1 and anhydrous lithium hydroxide (scattered powder: precursor compound 1 and anhydrous lithium hydroxide) was about 13:87. The obtained powder mixture was continuously mixed while being conveyed by a screw, and further continuously mixed in a mixture storage tank and stored.

[0160] The powder mixture was then fed from the mixture tank into a rotary kiln and continuously fired to continuously obtain a lithium metal composite oxide. The yield of the obtained lithium metal composite oxide was about 82% based on the total amount (mass) of the precursor compound 1 and anhydrous lithium hydroxide fed.

[0161] In this calcination, the powder mixture was loaded into the rotary kiln and the time for which the powder mixture was calcined was set to 3 hours when it was steadily and continuously discharged, and the time for which the powder mixture was calcined at the maximum temperature (approximately 600°C) was approximately 1.5 hours.

[0162] The stirring with the stirrer was performed so that the height of the top of the powder mixture was about 1.0 times the height of the top of the powder mixture without stirring. The size of the stirrer was set so that a mixture with a filling rate of 20% could be stirred by 50% of the total amount in one rotation.

[0163] (Rotary kiln conditions) Retort rotation speed: 0.9 rpm Filling rate: 20% Furnace air velocity and dew point: Gas input rate adjusted to 47L / min Heating rate: Set the surface temperature of the furnace core tube as follows: Maximum furnace tube surface temperature: 640℃ Maximum temperature of mixture: approx. 600℃

[0164] During the 13-hour calcination of the powder mixture, the point at which stable discharge was achieved (4 hours after the start of calcination) was counted as the first time, and thereafter, 10 calcined product samples were taken from different parts of the resulting calcined product every hour. The Li / M of each sample was then measured, and the Li / M coefficient of variation at each time point was calculated from the standard deviation and average value according to the method described above.

[0165] The obtained lithium metal composite oxide was randomly sampled, packed into a sagger measuring 300 mm in width and 100 mm in depth, and further fired in a static furnace under an oxygen atmosphere (oxygen concentration: 98 vol%) at 750°C for 5 hours to obtain a lithium metal composite oxide sample.

[0166] The amount of remaining lithium carbonate in the obtained lithium metal composite oxide sample was determined according to the method described above and was found to be 0.49% by weight.

[0167] [Example 1-2: Production of lithium metal composite oxide sample] 4 is a flow chart (Flow β) showing a method for producing a positive electrode active material of Example 1-2. In Example 1-2, a lithium metal composite oxide sample was produced according to this Flow β.

[0168] The collected powder was not put into the mixer in which the precursor compound 1 and anhydrous lithium hydroxide were mixed to prepare the mixture 1, but the prepared mixture 1 and the scattered powder were continuously mixed while being conveyed by a screw to prepare a powdery mixture, and the mixture was continuously mixed and stored in a mixture storage tank, and then the mixture was put from the mixture storage tank into a rotary kiln to be continuously fired, and a fired product was continuously obtained. A lithium metal composite oxide sample was produced in the same manner as in Example 1-1. The yield of the obtained lithium metal composite oxide sample was 82% based on the total amount (mass) of the precursor compound 1 and anhydrous lithium hydroxide put in. The remaining amount of lithium carbonate was 0.51 mass%.

[0169] [Reference Example 1-1: Production of lithium metal composite oxide sample] 5 is a flow chart (Flow γ) showing a method for producing a positive electrode active material of Reference Example 1-1. In Reference Example 1-1, a lithium metal composite oxide sample was produced according to this Flow γ.

[0170] A lithium metal composite oxide sample was produced in the same manner as in Example 1-1, except that the exhaust gas containing the scattered powder was not cooled in a decarbonation atmosphere (a cooling gas other than a decarbonation gas (dry air, carbon dioxide concentration: about 400 ppm) was introduced into the exhaust gas), and the scattered powder contained in the exhaust gas was collected. The yield of the obtained lithium metal composite oxide was 81% based on the total amount (mass) of the precursor compound 1 and anhydrous lithium hydroxide introduced. The remaining amount of lithium carbonate was 0.69 mass%.

[0171] <Comparative Example 1-1: Production of Lithium Metal Composite Oxide Sample> 6 is a flow chart (Flow δ) showing a method for producing a positive electrode active material of Comparative Example 1-1. In Comparative Example 1-1, a lithium metal composite oxide sample was produced according to this Flow δ.

[0172] A lithium metal composite oxide sample was produced in the same manner as in Example 1-1, except that the exhaust gas containing the scattered powder was cooled by extending the piping length to the outside to protect the equipment, and then the scattered powder was treated with a scrubber to collect the scattered powder contained in the exhaust gas, and only the powder mixture 1 was fired. The yield of the obtained lithium metal composite oxide sample was 72% based on the total amount (mass) of the precursor compound 1 and anhydrous lithium hydroxide added. In addition, the remaining amount of lithium carbonate was 0.53 wt%.

[0173] [Comparative Example 1-2: Production of Lithium Metal Composite Oxide Sample] 7 is a flow chart (Flow ε) showing a method for producing a positive electrode active material of Comparative Example 1-2. In Comparative Example 1-2, a lithium metal composite oxide sample was produced according to Flow ε.

[0174] A lithium metal composite oxide sample was produced in the same manner as in Example 1-1, except that the mixture 1 and the collected powder were separately charged into the rotary kiln. The yield of the obtained lithium metal composite oxide sample was 82% based on the total amount (mass) of the charged precursor compound 1 and anhydrous lithium hydroxide. The remaining amount of lithium carbonate was 0.53 mass%.

[0175] Table 1 shows the Li / M variation coefficients at each time point for the lithium metal composite oxide samples of Examples 1-1 to 1-2, Reference Example 1-1, and Comparative Examples 1-1 to 1-2. Table 2 shows the yields and remaining amounts of lithium carbonate for the lithium metal composite oxide samples of Examples 1-1 to 1-2, Reference Example 1-1, and Comparative Examples 1-1 to 1-2, as well as the initial charge capacities and initial charge / discharge efficiencies of the nonaqueous electrolyte secondary batteries used as the positive electrode active materials.

[0176] [Table 1]

[0177] [Table 2]

[0178] [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 ratio (molar ratio) of Ni, Co, and Mn was Ni:Co:Mn=4:3:3. 10 L of pure water to which 300 g of an aqueous sodium hydroxide solution and 500 g of an aqueous ammonia solution had been added was prepared in advance in the reaction tank as a mother liquid, and a nitrogen atmosphere was created in the reaction tank by adding nitrogen gas at a flow rate of 0.7 L / min, and the reaction was also carried out in a nitrogen atmosphere.

[0179] Thereafter, while rotating the stirring blade at 1100 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously dropped at a predetermined rate, and the amount of the alkaline solution dropped was adjusted so that the pH was 12.2. Through a crystallization reaction, Ni, Co, and Mn were crystallized and co-precipitated to form agglomerated particles, thereby obtaining a coprecipitate.

[0180] Thereafter, the slurry in the reactor was subjected to solid-liquid separation, and further washed with pure water to reduce remaining impurities, and the coprecipitate in a cake state was dried at 110°C for 12 hours in an air environment to obtain precursor compound 2. At this time, D50 in the volume-based particle size distribution of precursor compound 2 was 5.8 μm. In addition, the angle of repose of precursor compound 2 measured by the injection method was 46.1°.

[0181] [Example 2-1: Production of lithium metal composite oxide sample] 8 is a flow chart (Flow ζ) showing a method for producing a positive electrode active material of Example 2-1. In Example 2-1, a lithium metal composite oxide sample was produced according to this Flow ζ.

[0182] The precursor compound 2 and lithium carbonate (angle of repose measured by the injection method: 60.1°) 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)=1.10, and then, as described below, they were charged into a mixer so as to control the weight ratio (amount of scattered powder: total amount) of the amount of collected powder to the total amount of precursor compound 2 and lithium carbonate, and mixed precisely to prepare mixture 2. The obtained mixture 2 was further continuously mixed while being conveyed by a screw, and further continuously mixed in a mixture storage tank equipped with a screw (rotation speed: 104 rpm) and stored. The angle of repose of the powder mixture 2 measured by the injection method was 51.2°.

[0183] Next, mixture 2 was put from the mixture storage tank into a rotary kiln and fired. Firing was performed using a rotary kiln with a retort diameter of 300 mm and four agitating blades on the circumference at an installation angle of 30 degrees on the surface inside the furnace core tube as shown in Figure 2, in an oxidizing atmosphere with low dew point dry air (oxygen concentration: 21 vol%) for 13 hours under the rotary kiln conditions described below, while agitating and continuously flowing mixture 2 (mixture 2 flows as indicated by arrow B).

[0184] The exhaust gas (about 270℃) containing the scattered powder generated during the calcination was discharged from the inlet side of the rotary kiln, and a cooling gas (low dew point dry air) was introduced and brought into contact with the exhaust gas to cool the exhaust gas containing the scattered powder. The temperature of the exhaust gas at this time was about 160℃ at a slight negative pressure of about 101.2kPa.

[0185] Next, while the temperature of the exhaust gas was maintained at about 160°C with a slight negative pressure of about 101.2 kPa, as in the cooling process, the scattered powder contained in the exhaust gas was collected with a bag filter (made of ceramics) and this was used as the collected powder.

[0186] The collected powder was fed into a mixer in which precursor compound 2 and lithium carbonate were mixed to prepare mixture 2, and precursor compound 2, lithium carbonate, and scattered powder were precisely mixed to prepare a powdery mixture. The amount of collected powder fed at this time was controlled so that the mass ratio of the amount of collected powder to the total amount of precursor compound 2 and lithium carbonate (scattered powder: precursor compound 2 and lithium carbonate) was approximately 12:88. The obtained powdery mixture was continuously mixed while being conveyed by a screw, and further mixed in a mixture storage tank and stored.

[0187] The powder mixture was then fed from the mixture tank into a rotary kiln and continuously fired to continuously obtain a lithium metal composite oxide. The yield of the obtained lithium metal composite oxide was 80% based on the total amount (mass) of the precursor compound 2 and lithium carbonate fed.

[0188] In this calcination, the powder mixture was loaded into the rotary kiln and the time for which the powder mixture was calcined was set to 3 hours when it was steadily and continuously discharged, and the time for which the powder mixture was calcined at the maximum temperature (approximately 600°C) was approximately 1.5 hours.

[0189] The stirring with the stirrer was performed so that the height of the top of the powder mixture was about 1.0 times the height of the top of the powder mixture without stirring. The size of the stirrer was set so that a mixture with a filling rate of 20% could be stirred by 50% of the total amount in one rotation.

[0190] (Rotary kiln conditions) Retort rotation speed: 1.25 rpm Filling rate: 20% Furnace air velocity and dew point: Gas input rate adjusted to 52L / min Heating rate: Set the surface temperature of the furnace core tube as follows: Maximum surface temperature of furnace core tube: 640℃ Maximum temperature of mixture: approx. 600℃

[0191] During the 13-hour calcination of the powder mixture, the first measurement was taken 4 hours after the start of calcination when the discharge became stable. After that, 10 calcined product samples were randomly taken from different parts of the calcined product every hour. The Li / M of each sample was measured, and the coefficient of variation of Li / M at each time point was calculated from the standard deviation and average value according to the method described above.

[0192] The obtained lithium metal composite oxide was randomly sampled, packed into a sagger measuring 300 mm in width and 100 mm in depth, and further calcined in a static furnace under an oxidizing atmosphere of low-dew-point dry air (oxygen concentration: 21 vol%) at 980°C for 5 hours to obtain a lithium metal composite oxide sample.

[0193] <Comparative Example 2-1: Production of Lithium Metal Composite Oxide Sample> 9 is a flow chart (Flow η) showing a method for producing a positive electrode active material of Comparative Example 2-1. In Comparative Example 2-1, a lithium metal composite oxide sample was produced according to this Flow η.

[0194] A lithium metal composite oxide sample was produced in the same manner as in Example 2-1, except that the exhaust gas containing the scattered powder was cooled by extending the piping length to the outside to protect the equipment, and then the scattered powder was treated with a scrubber, without collecting the scattered powder contained in the exhaust gas, and only the powder mixture 2 was fired. The yield of the obtained lithium metal composite oxide sample was 69% based on the total amount (mass) of the precursor compound 2 and lithium carbonate charged.

[0195] <Comparative Example 2-2: Production of Lithium Metal Composite Oxide Sample> 10 is a flow chart (Flowι) showing a method for producing a positive electrode active material of Comparative Example 2-2. In Comparative Example 2-2, a lithium metal composite oxide sample was produced according to Flowι.

[0196] A lithium metal composite oxide sample was produced in the same manner as in Example 2-1, except that the mixture 2 and the collected powder were separately charged into the rotary kiln. The yield of the obtained lithium metal composite oxide sample was 79% based on the total amount (mass) of the precursor compound 2 and lithium carbonate charged.

[0197] Table 3 shows the Li / M variation coefficients at each time point for the lithium metal composite oxide samples of Example 2-1 and Comparative Examples 2-1 to 2-2. Table 4 shows the yields and remaining amounts of lithium carbonate for the fired lithium metal composite oxide samples of Example 2-1 and Comparative Examples 2-1 to 2-2, as well as the initial charge capacities and initial charge / discharge efficiencies of the nonaqueous electrolyte secondary batteries used as the positive electrode active materials.

[0198] [Table 3]

[0199] [Table 4] [Explanation of symbols]

[0200] 1 Furnace tube 2 Surface part 3. Kakiage wings 4 axis center θ Installation angle

Claims

1. A method for producing a lithium metal composite oxide, comprising the steps of: a firing step of firing a powder mixture obtained by mixing at least the precursor compound, the lithium compound, and the collection powder while continuously flowing the mixture; a collecting step of cooling exhaust gas containing scattered powder generated by the flow of the powder mixture in the firing step, and collecting the scattered powder contained in the exhaust gas to obtain the collected powder; and a mixing step of obtaining the powder mixture as a mixture of at least the precursor compound, the lithium compound, and the collected powder. A method for producing a lithium metal composite oxide.

2. The method according to claim 1, wherein the powder mixture is further mixed with a doping source compound and / or a coating source compound.

3. The method according to claim 1 or 2, wherein the powder mixture is prepared by controlling the mass ratio of any one of the following (a) or (b) to be 2:98 to 40:

60. (a) a mass ratio of the amount of the collected powder to the total amount of the precursor compound and the lithium compound; (b) the mass ratio of the amount of the collected powder to the amount of the powder mixture

4. 3. The method according to claim 1, wherein in the firing step, a rotary kiln having a scraping blade on the surface inside the furnace core tube is used to scrape and stir the material to be fired inside the furnace core tube.

5. The powder mixture prepared in advance is charged into the rotary kiln, and the stirring is performed. The method for producing a lithium metal composite oxide according to claim 4.

6. the lithium compound is lithium hydroxide, 3. The process of claim 1, wherein the exhaust gas is cooled in a decarbonation atmosphere while maintaining a temperature above the dew point temperature of a system containing the exhaust gas.

7. the lithium compound is lithium carbonate, the precursor compound is a hydroxide, Cooling the exhaust gas while maintaining a temperature above the dew point temperature of a system containing the exhaust gas. The method for producing a lithium metal composite oxide according to claim 1 or 2.

8. The firing temperature in the firing step is 400° C. or more and less than 700° C., After the firing step, the fired product obtained in the firing step is further fired at 700° C. or more and 1000° C. or less in a second firing step. The method for producing the lithium metal composite oxide according to claim 1 or 2.

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