JP2012099470A - Method for producing positive electrode material precursor for lithium secondary battery and method for producing positive electrode material for lithium secondary battery - Google Patents

Abstract

A method for producing a positive electrode material precursor for a lithium secondary battery capable of obtaining a high-quality positive electrode material is provided.
A slurry production step of obtaining a stock slurry containing a solid content mainly composed of a transition metal hydroxide by bringing a solution containing a transition metal element into contact with an alkali;
A slurry concentration step of concentrating solids in the stock slurry and obtaining a concentrated slurry; and
The concentrated slurry is supplied to an air dryer, and the concentrated slurry is dried with a high-temperature gas of 100 ° C. or higher so that the moisture content becomes a powder having a water content of 40% by weight or less within 60 minutes after being supplied to the air dryer. A drying process;
The manufacturing method of the positive electrode material precursor for lithium secondary batteries which has this.
[Selection figure] None

Description

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

  Lithium secondary batteries have already been put into practical use as power sources for mobile phones, notebook computers, and the like, and are also being applied to medium and large-sized applications such as automobile applications and power storage applications. Lithium secondary batteries use a lithium composite metal oxide as a positive electrode active material contained in the positive electrode.

  As disclosed in Patent Documents 1 and 2, as a method for producing a lithium composite metal oxide, a solution containing a transition metal element such as Ni or Mn is brought into contact with an alkali to contain a transition metal hydroxide as a main component. The resulting slurry is solid-liquid separated by filtration to obtain a transition metal hydroxide wet cake, and the wet cake is dried to form a transition metal hydroxide. A method is known in which a dried product is obtained as a positive electrode material precursor, and the obtained dried product is mixed with a lithium compound and fired.

International Publication No. 09/041722 Pamphlet JP 2010-21125 A

The positive electrode material precursor as a raw material of the lithium secondary battery positive electrode is obtained by obtaining a stock solution slurry containing a solid content mainly composed of a transition metal hydroxide by bringing a solution containing a transition metal element into contact with an alkali. However, this method has been manufactured by forming a wet cake by solid-liquid separation and drying it, but this method is not necessarily suitable for mass production.
In addition, a raw slurry obtained by bringing a solution containing a transition metal element into contact with an alkali or a wet cake obtained by solid-liquid separation of the slurry, when exposed to an oxidizing atmosphere such as air for a long time, The component transition metal hydroxide is oxidized and a part thereof is changed to a transition metal oxide. Since the transition metal oxide is inferior to the transition metal hydroxide in terms of reactivity when changing to a lithium secondary battery positive electrode material, the transition metal oxide remains in the dried product obtained after drying the wet cake. Then, there is a problem that the lithium composite metal oxide obtained by firing the mixture of the dried product and the lithium compound is deteriorated in quality, and as a result, is an obstacle to improving battery performance. This problem is particularly remarkable when Mn is contained in the transition metal hydroxide.
Suppressing the generation of transition metal oxide in the positive electrode material precursor is relatively easy at the laboratory level, but not easy on an industrial scale, and the generation of transition metal oxide is minimized. Thus, there has been a demand for a technique for producing a positive electrode material precursor.

  Therefore, the present invention provides a method for producing a positive electrode material precursor for a lithium secondary battery capable of obtaining a high-quality positive electrode material and a method for producing a positive electrode material for a lithium secondary battery from the precursor obtained by such a method. For the purpose.

  As a result of intensive studies to solve the above problems, the present inventor has found that the following inventions meet the above object, and have reached the present invention.

That is, the present invention relates to the following inventions.
<1> A slurry production step of obtaining a stock slurry containing a solid content mainly composed of a transition metal hydroxide by bringing a solution containing a transition metal element into contact with an alkali;
A slurry concentration step of concentrating solids in the stock slurry and obtaining a concentrated slurry; and
The concentrated slurry is supplied to an air dryer, and the concentrated slurry is dried with a high-temperature gas of 100 ° C. or higher so that the moisture content becomes a powder having a water content of 40% by weight or less within 60 minutes after being supplied to the air dryer. A drying process;
The manufacturing method of the positive electrode material precursor for lithium secondary batteries which has this.
<2> The method for producing a positive electrode material precursor for a lithium secondary battery according to <1>, wherein the transition metal element contains at least Mn.
<3> The method for producing a positive electrode material precursor for a lithium secondary battery according to <1> or <2>, wherein the slurry is concentrated by crossflow filtration in the slurry concentration step.
<4> The fluidized bed drying apparatus according to any one of <1> to <3>, wherein the airflow dryer is a fluidized bed drying device having a medium for attaching the supplied concentrated slurry and drying the attached concentrated slurry. A method for producing a positive electrode material precursor for a lithium secondary battery.
<5> The method for producing a positive electrode material precursor for a lithium secondary battery according to <4>, wherein an inlet temperature of the high-temperature gas in the air dryer is 150 ° C. or higher and 500 ° C. or lower.
<6> The method for producing a positive electrode material precursor for a lithium secondary battery according to <4> or <5>, wherein an outlet temperature of the high-temperature gas in the air dryer is 50 ° C. or higher and 200 ° C. or lower.
<7> The method for producing a positive electrode material precursor for a lithium secondary battery according to any one of <1> to <6>, wherein the high-temperature gas in the air dryer is a gas obtained by burning a combustible gas. .
<8> The method for producing a positive electrode material precursor for a lithium secondary battery according to any one of <1> to <7>, wherein a bag filter is used for a powder recovery part in the air dryer.
<9> A lithium secondary battery, wherein a positive electrode material precursor for a lithium secondary battery obtained by the production method according to any one of <1> to <8> is mixed with a lithium compound and fired. For producing a positive electrode material.

  According to the present invention, since the slurry concentrated before the generation of the transition metal oxide as a by-product can be made into a dry product, a high-quality positive electrode material precursor for a lithium secondary battery even on an industrial scale Can be obtained with high productivity.

It is a conceptual diagram of crossflow filtration. It is a schematic diagram of a cross flow filtration system using a membrane filter. It is a mimetic diagram of a cross flow filtration system provided with a stirring board which generates shearing force compulsorily. It is a schematic diagram of the fluidized bed drying apparatus which concerns on this invention. It is a schematic diagram for demonstrating the drying mechanism in the fluidized-bed drying apparatus which concerns on this invention, (A) is a mode that the slurry adhered to the medium, respectively, (B) is a solvent evaporating from the slurry adhering to the medium, and drying. (C) is a figure which shows a mode that a dried material peels, pulverizes, and is blown up. 2 is an X-ray diffraction pattern of a dried product (positive electrode material precursor) in Example 1. FIG. 3 is an X-ray diffraction pattern of a dried product (positive electrode material precursor) in Comparative Example 1. It is an X-ray diffraction pattern of the dried product (positive electrode material precursor) in Reference Example 1.

In the present invention, first, a slurry production step of obtaining a stock slurry containing a solid content mainly composed of a transition metal hydroxide by bringing a solution containing a transition metal element into contact with an alkali;
A slurry concentration step of concentrating solids in the stock slurry and obtaining a concentrated slurry; and
The concentrated slurry is supplied to an air dryer, and the concentrated slurry is dried with a high-temperature gas of 100 ° C. or higher so that the moisture content becomes a powder having a water content of 40% by weight or less within 60 minutes after being supplied to the air dryer. And a drying step, which relates to a method for producing a positive electrode material precursor for a lithium secondary battery.
Hereinafter, in the production method of the present invention, the slurry production step is referred to as “step (1)”, the slurry concentration step is referred to as “step (2)”, and the drying step is referred to as “step (3)”.

First, step (1) will be described.
In the production method of the present invention, the transition metal element contained in the solution is not limited as long as the hydroxide can be mixed with a lithium compound and fired to become a positive electrode active material of a secondary battery. For example, Ni, Mn, Co, Fe, Cr, Ti, etc. can be mentioned.
Among these, from the viewpoint of obtaining a high-capacity positive electrode for a secondary battery, the solution preferably contains one or more elements selected from the group consisting of Ni and Mn. Furthermore, from the viewpoint of obtaining a positive electrode for a secondary battery having a higher capacity, in addition to one or more elements selected from the group consisting of Ni and Mn, one or more elements selected from the group consisting of Co and Fe are further added. It is preferable to contain.
The production method of the present invention is particularly preferably used when a transition metal element containing at least Mn is used as a raw material. In particular, Mn hydroxide is more easily oxidized in oxidizing atmospheres such as air than other transition metal hydroxides. Therefore, when Mn is contained in the transition metal element as a raw material, manganese oxide, which is a byproduct, is used. (Mn ₃ O ₄ ) is easily generated, but in the production method of the present invention, as described later, the slurry is dried in a short time using an air dryer, thereby generating a transition metal oxide as a by-product. It is suppressed.

Examples of the above solutions include simple metals, oxides, hydroxides, oxyhydroxides, carbonates, sulfates, nitrates, acetates, halides, ammonium salts, oxalates, alkoxides, and the like of the respective transition metal elements. Can be prepared by dissolving it in a solvent such as water or an organic solvent such as an alcohol capable of dissolving these, and water is usually used as the solvent, preferably pure water, ion-exchanged water or the like. Used.
If the transition metal element alone or compound is difficult to dissolve in the solvent, it may be prepared by dissolving them in a solution containing hydrochloric acid, sulfuric acid, nitric acid, acetic acid or the like.
Among these, an aqueous solution obtained by dissolving a sulfate of a transition metal element, for example, a sulfate of Ni, a sulfate of Mn, a sulfate of Co and a sulfate of Fe, in water is preferable. The Fe sulfate is preferably a divalent Fe sulfate.

Examples of the alkali include LiOH (lithium hydroxide), NaOH (sodium hydroxide), KOH (potassium hydroxide), Li ₂ CO ₃ (lithium carbonate), Na ₂ CO ₃ (sodium carbonate), K ₂ CO ₃ ( Mention may be made of one or more anhydrides selected from the group consisting of (potassium carbonate) and (NH ₄ ) ₂ CO ₃ (ammonium carbonate) and one or more hydrates.
Moreover, ammonia can also be used as an alkali.
Alkali is usually used as an aqueous solution. The concentration of alkali in this alkaline aqueous solution is usually about 0.5 to 10 mol / L, preferably about 1 to 8 mol / L. Further, from the viewpoint of production cost, it is preferable to use NaOH and KOH anhydrides and hydrates thereof as the alkali to be used. Two or more of the alkalis described above may be used in combination.

  The water used for the alkaline aqueous solution used as these solvents is preferably pure water and / or ion-exchanged water. Moreover, in the range which does not impair the effect of this invention, organic solvents other than water, such as alcohol, a pH adjuster, etc. may be included.

In this invention, the stock solution slurry containing the transition metal hydroxide produced | generated by contacting the solution containing the said transition metal element with an alkali is obtained. The “stock solution slurry” is a slurry mainly composed of a solid (precipitate) mainly composed of a transition metal hydroxide and a solvent such as water, and the raw material remaining in the course of obtaining the stock slurry. By-product salts such as K ₂ SO ₄ , additives, organic solvents and the like may be contained.
As a method of bringing a solution containing a transition metal element into contact with an alkali, a method of adding an alkaline aqueous solution to a solution containing a transition metal element and mixing, and adding and mixing a solution containing a transition metal element into an alkaline aqueous solution Examples thereof include a method in which a solution containing a transition metal element and an aqueous alkali solution are added to a solvent such as water and mixed. In mixing these, it is preferable to involve stirring. In addition, among the above contact methods, the method of using water as a solvent and adding an aqueous solution containing a transition metal element to an alkaline aqueous solution and mixing is preferably used because it is easy to maintain the pH within a certain range. it can. In this case, as the aqueous solution containing the transition metal element is added to and mixed with the alkaline aqueous solution, the pH of the mixed solution tends to decrease, but this pH is 9 or more, preferably 10 or more. It is good to add the aqueous solution containing a transition metal element, adjusting so that. Further, when one or both of an aqueous solution containing a transition metal element and an alkaline aqueous solution are kept in contact at a temperature of 40 to 80 ° C., a transition metal hydroxide having a more uniform composition is a main component. It is preferable because a slurry containing the solid content can be obtained.

Next, step (2) will be described.
In step (2), the solid content in the stock slurry obtained in step (1) above is concentrated to obtain a concentrated slurry. The “concentrated slurry” refers to a slurry having a solid content higher than that of the stock solution slurry obtained in step (1) by removing a part of the solvent component.

  The solid content concentration in the concentrated slurry is preferably 3% by weight or more, and more preferably 10% by weight or more from the viewpoint of improving the efficiency of the drying step, which is a subsequent step.

  In the present invention, the concentration of the slurry may be performed by any method, but cross-flow filtration that can be easily washed and obtain a transition metal hydroxide with less impurities is preferably used. In addition, “cross flow filtration” means that a stock solution slurry containing a solid content is supplied to a filter medium as a liquid to be filtered, and the filtrate that has permeated the filter medium is recovered to remove a solvent component from the stock solution slurry. This is a filtration method for concentrating the solid content.

FIG. 1 shows a conceptual diagram of cross flow filtration in a cylindrical membrane filter.
As the liquid to be filtered, a stock solution slurry containing a solid content is supplied to the inside of the membrane filter, and the filtrate that has permeated the membrane filter is collected from the outer surface of the membrane filter, and the solid content in the stock solution slurry is concentrated. Here, the membrane filter is fixedly used.

  In cross-flow filtration, filtration is performed while flowing the stock solution slurry in parallel with the inner wall of the filter, and it is difficult to deposit the cake layer by the shearing force of the slurry flowing in parallel with the filter inner wall. There is an advantage that clogging is less likely to occur even when solid content is included. In addition, stable filtration can be performed for a long time even if the solid content concentration of the stock solution slurry varies.

FIG. 2 shows an example of a cross flow filtration system according to the production method of the present invention.
A cross-flow filtration system 10 shown in FIG. 2 includes a slurry storage tank 11 for storing a stock solution slurry, and a cylindrical membrane filter that filters the stock solution slurry from the slurry storage tank 11 and separates it into a filtrate and a concentrated slurry (see FIG. 1). The filter 12 is provided.
The cross-flow filtration system 10 is designed so as to avoid contact between the slurry and the outside air as much as possible in order to suppress oxidation of the transition metal hydroxide in the slurry by air, and the slurry storage tank 11 is a hermetically sealed type. It is a tank, and its internal atmosphere can be replaced with an inert gas.
When the slurry is concentrated in the cross flow filtration system 10, the stock solution slurry obtained in the above step (1) is used as the liquid to be filtered, and the stock solution slurry is supplied from the slurry storage tank 11 into the membrane filter 12. By discharging the solvent contained in the slurry as a filtrate to the outside of the membrane filter 12, the solid content is concentrated while removing impurities other than the solid content (mainly transition metal hydroxide) in the stock slurry together with the solvent component. Thus, a concentrated slurry is obtained. As will be described in detail later, in order to reduce the concentration of impurities in the concentrated slurry, a part of the concentrated slurry is circulated to the slurry storage tank 11 again, and water for dilution is added to wash the solid content of the concentrated slurry. Preferably it is done.
Examples of impurities contained in the stock slurry include raw materials and by-product salts such as K ₂ SO ₄ , additives, and organic solvents that remain in the course of obtaining the stock slurry.

  In addition, when obtaining a concentrated slurry of high concentration, cross flow filtration is performed by forcibly generating shearing force near the surface of the filter medium and peeling off the solid content layer formed on the filter medium surface. A filtration system may be used. In the cross-flow filtration system, it is possible to avoid the cake layer from being deposited to a certain thickness or more on the surface of the filter medium, and it is difficult to cause clogging, so that high filtration efficiency can be maintained. An example is shown in FIG.

The crossflow filtration system 30 shown in FIG. 3 includes a crossflow filtration device 20, a slurry storage tank 31, a liquid feed pump 32, and a washing water supply facility 33 as main parts.
The cross flow filtration system 30 is designed to avoid contact between the slurry and the outside air as much as possible in order to suppress oxidation of the transition metal hydroxide in the slurry by the air. Both storage tanks 31 are of a sealed type, and the internal atmosphere can be replaced with an inert gas.

The cross-flow filtration device 20 includes a filtration chamber 22, a plurality of filtration plates 23 arranged at predetermined intervals in the filtration chamber 22, a plurality of stirring plates 24 arranged adjacent to the filtration plate, and the plurality of filtration plates An electric motor 25 that is a drive mechanism for rotating the stirring plate 24 is provided.
In addition, the filter plate 23 has a filter cloth pasted on both surfaces of a plate provided with a filtrate discharge groove, and functions as a filter medium.

An operation method of the cross flow filtration system 30 having the above-described configuration will be described.
First, the stock solution slurry is stored in the slurry storage tank 31, and the stock solution slurry is pressurized and supplied to the filtration chamber 22 of the cross flow filtration device 20 by the feed pump 32. The stock slurry supplied under pressure moves from one end side (slurry supply port 26 side) of the filtration chamber 22 toward the other end side (slurry discharge port 27 side), and passes through the space separated by the filter plate 23. pass. The stock slurry is filtered and dehydrated by the filter plate 23 when passing through the space partitioned by the filter plate 23, and the solid content concentration in the slurry gradually increases toward the other end side.
The agitation plate 24 between the filtration plates 23 is always rotating during filtration, agitates the supplied slurry, forcibly generates a shearing force near the surface of the filtration plate 23, and the surface of the filtration plate 23. The cake layer formed in the step is peeled off. In addition, by controlling the rotational speed of the stirring plate 24, by controlling the deposition rate of solid content in the slurry and the removal rate, the thickness of the cake layer generated on the surface of the filter plate 23 is made constant, The filtration rate can be kept constant.
The slurry (concentrated slurry) having reached the other end side and having a high solid content concentration is discharged from the slurry discharge port 27 and collected in the slurry storage tank 31. The solid content concentration of the concentrated slurry can be arbitrarily adjusted as long as the fluidity of the concentrated slurry is maintained.

As the membrane filter or filter cloth used in the cross flow filtration systems 20 and 30 described above, a membrane filter or filter cloth having a pore size smaller than the particle size of the solid content contained in the stock slurry is used.
As the membrane filter, either a ceramic membrane filter or an organic membrane filter can be used, and a ceramic membrane filter excellent in corrosion resistance, heat resistance and durability is preferably used. As the ceramic membrane filter, a ceramic raw material powder such as alumina, silica, alumina, zirconia, etc., and those manufactured by applying known molding and sintering techniques can be used.
The filter cloth has an air permeability that prevents particles from leaking through the filter cloth depending on the particle size of the solid content in the slurry, specifically 1 mL / cm ² / min or less, preferably 0.3 mL. A filter cloth having an air permeability of not more than / cm ² / min is used.

  In addition, the conditions at the time of performing crossflow filtration are suitably determined on the conditions which can obtain the target concentrated slurry, and are not specifically limited.

Moreover, in order to reduce the impurities in the concentrated slurry, it is preferable to wash the solid content (transition metal hydroxide) in the slurry.
The solid content is washed by crossflow filtration to remove a part of the solvent component from the stock slurry to form a concentrated slurry, and then adding the washing liquid to the concentrated slurry and performing crossflow filtration again. be able to. In order to further reduce the concentration of impurities in the concentrated slurry, the washing is preferably performed repeatedly.
The degree of progress of washing can be managed, for example, by measuring the conductivity of the filtrate and measuring the concentration of the electrolyte. When the desired degree of washing progress is reached, the water washing is terminated and concentrated again to obtain a concentrated slurry having the desired impurity concentration.
As the cleaning liquid, the same solvent as that used when forming the stock solution slurry is usually used, but the cleaning liquid is not limited to this, and any cleaning liquid can be used as long as it can be removed in a subsequent drying step. Specific examples include water and alcohols such as ethanol.

Next, step (3) will be described.
In the step (3), the concentrated slurry is supplied to the air dryer, and the water content is 40% by weight or less within 60 minutes after the concentrated slurry is supplied to the air dryer while flowing the hot gas to the air dryer. It is a process of drying so that it may become powder. The air dryer used in this drying step is a device that performs heat exchange between the object to be dried and the supplied high-temperature gas to dry the object to be dried. Note that the high temperature gas means a gas of 100 ° C. or higher, preferably 200 ° C. or higher.
As the gas species supplied as the high-temperature gas, air or an inert gas such as nitrogen or argon is usually used. These are heated to the target temperature outside the air dryer and then supplied to the air dryer.

From the viewpoint of reducing the heating cost, a gas obtained by burning a combustible gas is preferable. Examples of the combustible gas include hydrogen, methane, ethane, propane, butane, acetylene, and a mixed gas thereof. Also, liquefied petroleum gas (LPG) or natural gas can be used. Among these gas species, LPG is preferably used because it has a large amount of heat during combustion and is relatively inexpensive.
The combustible gas is usually burned with a gas containing oxygen (O ₂ ), for example, oxygen gas or air. As the gas containing oxygen, the exhaust gas after combustion may be recycled and used.
When a gas obtained by burning a combustible gas with air as a high-temperature gas is used, the oxygen (O ₂ ) concentration becomes lower than when the air is used as it is, and the transition metal hydroxide This is preferable because oxidation can be suppressed.

In step (3), the concentrated slurry containing the transition metal hydroxide is supplied to the air dryer while flowing a high-temperature gas, and within 60 minutes, the water content is 40% by weight or less, preferably 15% by weight or less. It is possible to suppress the oxidation of the transition metal hydroxide and to suppress the generation of the transition metal oxide, and to obtain a high-quality positive electrode material precursor it can. Moreover, since a large amount of concentrated slurry can be processed by rapidly drying the concentrated slurry sequentially, the positive electrode material precursor can be obtained with high productivity.
“Within 60 minutes after being supplied to the air dryer” means that the concentrated slurry is supplied to the air dryer and the dried powder (positive electrode material precursor) is discharged from the air dryer. It means that the residence time is within 60 minutes.
Moreover, it is preferable to use a bag filter as a powder collection part in an air dryer. Note that the bag filter is made of a heat-resistant material so as not to be deteriorated by the discharged high-temperature gas.

  As the air flow dryer, a fluidized bed drying apparatus having a medium for attaching the supplied concentrated slurry and drying the attached concentrated slurry is suitable. The fluidized bed drying apparatus is to supply a high temperature gas from below to a spherical medium in a drying chamber to form a fluidized bed, and drop concentrated slurry into the fluidized bed to obtain a dried product, which is heated. The material to be dried can be dried by heat conduction from the medium and convection heat transfer from the high-temperature gas, and since the fluidized bed is completely mixed, there is an advantage that drying with less unevenness is possible. As the fluidized bed drying device, for example, Okawara Manufacturing Co., Ltd. slurry dryer SFD series can be used.

Hereinafter, as a preferred embodiment of the step (3), an example in which a fluidized bed drying apparatus is used as an air flow dryer will be described with reference to the drawings.
The air flow dryer (fluidized bed drying device) 40 shown in FIG. 4 includes a raw material storage tank 41 in which the concentrated slurry obtained in the step (2) is stored and a water storage tank 42 in which cleaning water is stored in a slurry supply pipe 43. Is connected to the body portion of the apparatus main body 45 with a slurry supply pump 44 interposed therebetween.
In the lower part of the apparatus main body 45, an intake pipe 47 provided with an intake filter 46 at the intake port has an intake fan 48 for taking in the gas and a heat exchanger 49 with a filter unit as a heat source for heating the gas. And are connected with each other.
A discharge pipe 51 connected to the body of the bag filter 50 is connected to the upper part of the apparatus main body 45. An exhaust pipe 53 exhausted by an exhaust fan 52 is connected to the upper portion of the bag filter 50.

In the apparatus main body 45, a plurality of spherical media M (balls) are stored. The medium M may be any medium that can efficiently exchange heat with the slurry to be supplied, and ceramics such as alumina and zirconia, and heat-resistant resin materials such as polytetrafluoroethylene are appropriately used. The average diameter of the medium M is usually 1 mm to 5 mm, preferably 2 mm to 3 mm. In the present embodiment, the medium M is an alumina ball having an average diameter of 2 mm to 3 mm.
By using such a medium in an air dryer, the concentrated slurry is attached to the medium, and the solvent is evaporated from the concentrated slurry attached to the medium by flowing a high-temperature gas, thereby increasing the heat conduction from the medium and the high temperature. The drying process can be performed in a short time by convective heat transfer of the gas.

Here, the operation of the air dryer 40 in the step (3) and the method for producing the positive electrode material precursor of the present invention will be described in detail with reference to FIG. 5 together with FIG.
The air sucked by the suction fan 48 is supplied into the apparatus main body 45 from the lower part of the apparatus main body 45 after being heated by the heat exchanger 49. The supplied air blows up the medium M to form a fluidized bed F.
Next, the concentrated slurry stored in the raw material storage tank 41 by the slurry supply pump 44 is dropped into the fluidized bed F formed in the apparatus main body 45 through the raw material supply pipe 43.
The concentrated slurry dropped is attached to the surface of the medium M constituting the fluidized bed F in the form of a thin film (see FIG. 5A). The concentrated slurry adhering to the surface of the medium M is dried by the evaporation of the solvent (water) by heat conduction from the heated medium M and convection heat transfer of the hot gas blown (FIG. 5B). )reference). When the media M collide with each other in the fluidized bed F, the dried material on the surface of the media M is peeled off and pulverized and blown upward together with high-temperature air (see FIG. 5C).
The dried material blown up is sent to the bag filter 50 which is a powder recovery portion via the discharge pipe 51.
In the bag filter 50, a dry substance, which is a positive electrode material precursor in powder form, is stored in a container 54 provided at the lower end, and high-temperature air is discharged to the outside through an exhaust pipe 53.
As a fluidized bed drying device, the powder can be dried when it reaches the bag filter 50 by selecting appropriate operating conditions.
In addition, in the case of using the slurry dryer SFD series having the configuration of the air dryer 40, “within 60 minutes from being supplied to the air dryer” in the step (3) means that the concentrated slurry is in the apparatus main body 45. It means that the time from the supply to the bag filter 50 as a powder is within 60 minutes.

In the method for producing a positive electrode material precursor of the present invention, the concentrated slurry stored in the raw material storage tank 41 is dropped into the apparatus main body 45, and the gas temperature at the outlet of the apparatus main body 45 is 50 ° C. or higher and 200 ° C. or lower, preferably 110 ° C. or higher. The input amount of the concentrated slurry is adjusted so as to be 150 ° C. or lower. The flow rate of the high-temperature gas may be arbitrarily set, but the lower limit of the flow rate is a condition that the medium M flows in the apparatus main body 45, and the upper limit is a condition that the medium M does not scatter from the apparatus main body 45. .
Here, it is desirable that the set temperature of the heat exchanger 49 as a heating device is 150 ° C. or more and 500 ° C. or less, preferably 180 ° C. or more and 350 ° C. or less at the inlet of the airflow dryer before contact with the concentrated slurry. The temperature of the hot gas prior to contact with the concentrated slurry can be increased as the temperature within the capacity of the heating device (heat exchanger 49) increases, so that the slurry supply rate can be increased, and thus the drying rate can be increased. If it is too high, the transition metal hydroxide contained in the concentrated slurry may be altered.
Further, after contact with the slurry, it is desirably 50 ° C. or higher and 200 ° C. or lower, preferably 110 ° C. or higher and 150 ° C. or lower. This is because the lower the temperature after contact with the slurry, the higher the drying speed, but the temperature needs to be higher than the temperature having a vapor pressure that sufficiently evaporates the solvent of the slurry. When water is used as the solvent, the temperature is particularly preferably 100 ° C. or higher, and more preferably 110 ° C. or higher for stable operation. The temperature after contact with the slurry should not exceed the upper limit of the heat resistance of the bag filter 50 that collects the dry powder, and particularly when water is used as the solvent of the slurry, the temperature should be 150 ° C. or lower. Provides a suitable drying rate.

In the method for producing a positive electrode material for a lithium secondary battery of the present invention, a method of firing a mixture obtained by mixing a dried transition metal hydroxide (positive electrode material precursor) obtained in step (3) with a lithium compound. Thus, a lithium composite metal oxide is obtained.
Examples of the lithium compound include one or more anhydrides selected from the group consisting of lithium hydroxide, lithium chloride, lithium nitrate, and lithium carbonate, and one or more hydrates thereof. The mixing may be either dry mixing or wet mixing, but from the viewpoint of simplicity, dry mixing is preferable. Examples of the mixing device include stirring and mixing, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a ball mill, and the like.

  The holding temperature in the firing is preferably in the range of 650 ° C. or higher and 900 ° C. or lower. The holding time at the holding temperature is usually 0.1 to 20 hours, preferably 0.5 to 8 hours. The rate of temperature rise to the holding temperature is usually 50 ° C. to 400 ° C./hour, and the rate of temperature drop from the holding temperature to room temperature is usually 10 ° C. to 400 ° C./hour. As the firing atmosphere, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used, but an air atmosphere is preferable.

During the firing, the mixture may contain a reaction accelerator.
Specific examples of the reaction accelerator include chlorides such as NaCl, KCl, RbCl, CsCl, CaCl ₂ , MgCl ₂ , SrCl ₂ , BaCl ₂ and NH ₄ Cl, Na ₂ CO ₃ , K ₂ CO ₃ , Rb _2. Carbonates such as CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , MgCO ₃ , SrCO ₃ and BaCO ₃ ; sulfates such as K ₂ SO ₄ and Na ₂ SO ₄ ; fluorides such as NaF, KF and NH ₄ F; Is mentioned. Among these, the chloride, carbonate or sulfate of one or more elements selected from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba can be mentioned, more preferably KCl. , K ₂ CO ₃ , K ₂ SO ₄ . Two or more reaction accelerators can be used in combination.
In order to contain the reaction accelerator in the mixture, for example, the reaction accelerator may be added when the transition metal hydroxide is mixed with the lithium compound.
Further, the reaction accelerator may remain in the fired lithium composite metal oxide or may be removed by washing, evaporation or the like.
The mixing ratio of the mixture and the reaction accelerator is preferably from 0.1 to 100 parts by weight, more preferably from 1.0 to 25 parts by weight, in 100 parts by weight of the mixture.

  Moreover, although lithium composite metal oxide is obtained by the said baking, you may grind | pulverize this lithium composite metal oxide using a ball mill, a jet mill, etc. Moreover, you may repeat a grinding | pulverization and baking twice or more. Further, the lithium composite metal oxide can be washed or classified as necessary.

  The lithium composite metal oxide obtained by the above method is usually composed of primary particles having an average particle diameter of 0.05 μm or more and 1 μm or less, and is formed by agglomeration of primary particles and primary particles of 0.1 μm or more and 100 μm. It consists of a mixture with secondary particles of the following average particle size. The average particle diameters of the primary particles and the secondary particles can be measured by observing with an SEM (scanning electron microscope).

The lithium composite metal oxide obtained by the above method has an α-NaFeO ₂ type crystal structure, that is, a crystal structure belonging to the R-3m space group. The crystal structure can be identified for a lithium composite metal oxide from a powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα as a radiation source.

As the composition of Li in the lithium composite metal oxide obtained by the above method, the amount of Li (mol) relative to the total amount (mol) of transition metal elements M such as Ni, Mn, Fe, Co, etc. It is preferably 0.5 or more and 1.5 or less, and preferably 0.95 or more and 1.5 or less, more preferably 1.0 or more and 1.4 or less in the sense of further increasing the capacity retention rate. When expressed as the following formula (A), y is usually 0.5 or more and 1.5 or less, preferably 0.95 or more and 1.5 or less, more preferably 1.0 or more and 1.4 or less. is there.
Li _y (Ni _1-x M _x ) O ₂ (A)
(Here, M represents one or more transition metal elements, and x is 0 <x <1.)

  In addition, in the lithium composite metal oxide of the present invention obtained by the above method, a part of the transition metal element may be substituted with another element within a range not impairing the effects of the present invention. Here, as other elements, B, Al, Ga, In, Si, Ge, Sn, Mg, Sc, Y, Zr, Hf, Nb, Ta, Mo, W, Tc, Ru, Rh, Ir, Pd, Examples of the element include Cu, Ag, and Zn.

  A compound different from the lithium composite metal oxide may be attached to the surface of the particles constituting the lithium composite metal oxide obtained by the above method. As such a compound, for example, a compound containing one or more elements selected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Mg and a transition metal element, preferably B, Al, A compound containing one or more elements selected from the group consisting of Mg, Ga, In, and Sn, more preferably, a compound of Al can be mentioned. Compounds, oxyhydroxides, carbonates, nitrates, and organic acid salts. Preferred are oxides, hydroxides, and oxyhydroxides. Moreover, you may use these compounds in mixture. Among these compounds, a particularly preferred compound is alumina. Moreover, you may heat after adhesion.

  The lithium composite metal oxide obtained by the above method is useful as a positive electrode active material, and is suitable for a positive electrode of a secondary battery, particularly a nonaqueous electrolyte secondary battery, and particularly suitable as a positive electrode material for a lithium secondary battery. used.

  The positive electrode for the secondary battery is produced by a known method, for example, the method described in International Publication No. 09/041722, using the lithium composite metal oxide obtained by the above method as the positive electrode active material. be able to.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is changed.

The sample evaluation method is shown below.
<Powder X-ray diffraction measurement>
The powder X-ray diffraction measurement (XRD) was performed using Ultima IVASC-10 manufactured by Rigaku Corporation. The measurement was carried out by filling a powder sample on a dedicated substrate and using a CuKα radiation source under the conditions of a voltage of 40 kV and a current of 40 mA in a diffraction angle range of 2θ = 10 ° to 90 °.
<Moisture content measurement>
The moisture content was measured using a heat and dry moisture meter MX-50 manufactured by A & D Co., Ltd. After leaving about 5 g of the powder sample in the sample pan in the device, the lid of the device is closed and the sample pan temperature is set to 130 ° C. to evaporate the water contained in the powder sample and reduce the weight. The point at which no more water is recognized is considered to be completely dry, that is, the water content is zero. The ratio of the reduced weight with respect to the weight of the powder sample placed on the sample dish was taken as the moisture content of the powder sample.

Example 1
"Production of cathode material precursor for lithium secondary battery"
Process (1)
In a stirring tank, 100 parts by weight of potassium hydroxide was added to 535 parts by weight of distilled water, and potassium hydroxide was completely dissolved by stirring to prepare an aqueous potassium hydroxide solution (alkali aqueous solution).
Further, in another stirring tank, 255 parts by weight of distilled water, 98.4 parts by weight of nickel (II) sulfate hexahydrate, 64.6 parts by weight of manganese (II) sulfate monohydrate, and iron sulfate (II ) 11.1 parts by weight of heptahydrate was added and dissolved by stirring to obtain a nickel-manganese-iron mixed aqueous solution.
Next, after adding 936 parts by weight of distilled water and 15.8 parts by weight of the potassium hydroxide aqueous solution to another stirring tank, the solution was stirred at a liquid temperature of 30 ° C. By dropping 95.1 parts by weight of a nickel-manganese-iron mixed aqueous solution, a precipitate composed of a transition metal hydroxide was generated, and a stock solution slurry was obtained. When the pH at the end of the reaction was measured, the pH was 13.

Process (2)
Next, the slurry was concentrated using the cross flow filtration system having the configuration shown in FIG. A rotary filter RF-02 type (manufactured by Kotobuki Industries Co., Ltd.) was used as the cross flow filtration device 20.
First, at room temperature, 100 parts by weight of the stock solution slurry is charged into the slurry storage tank 31, and the pump circulation in which the slurry charged with the stock solution is circulated to the slurry storage tank 31 via the cross-flow filtration device 20 is filtered. The slurry was concentrated until 50 parts by weight was extracted. In addition, the slurry supply inlet pressure of the crossflow filtration apparatus 20 is 0.4 MPaG, and P2560C (made by Shikishima canvas) was used for the filter cloth.
Next, 50 parts by weight of distilled water was added to the slurry storage tank 31 to dilute the concentrated slurry, and then filtration was performed under the same conditions as described above. Similarly, the operation of adding distilled water and filtering was repeated. After the washing, the filtrate was extracted under the same conditions as the previous concentration, and the slurry was concentrated. At this time, the solid content concentration in the concentrated slurry obtained in the slurry storage tank 31 was 12% by weight.

Process (3)
Next, the concentrated slurry obtained in the step (2) was dried with an air flow dryer (fluidized bed drying device) ("Slurry dryer SFD", Okawara Seisakusho Co., Ltd.) having the configuration shown in FIG.
Air is used as the high-temperature gas, and the heat exchanger 49 is adjusted so that the inlet temperature of the apparatus main body 45 in FIG. 4 is 250 ° C., and the slurry supply pump is adjusted so that the outlet temperature of the apparatus main body 45 is 143 ° C. 44, the slurry supply amount was adjusted to 2.4 kg / h. The flow rate of the high temperature gas was 3.3 m / s. The drying time (the residence time from when the concentrated slurry was supplied into the apparatus main body 45 until reaching the bag filter 50 as powder) was within 1 minute on average.
Under the above conditions, and drying the slurry to obtain a powdery dried product P _1. The water content of the dried product P ₁ was 3.5% by weight.
FIG. 6 shows an X-ray diffraction pattern of the dried product P ₁ . As can be seen from FIG. 6, a signal (2θ = 36.08 ° (Miller index 350)) indicating Mn oxide (Mn ₃ O ₄ ) was not confirmed.

"Manufacture of cathode materials for lithium secondary batteries"
Mix 100 parts by weight of the dried product P _{1 with} 52.2 parts by weight of lithium carbonate and 18.0 parts by weight of potassium sulfate in a rocking mill containing alumina balls for 4 hours and hold at 870 ° C. for 6 hours with a roller hearth kiln. Then, it was fired and cooled to room temperature to obtain a fired product. Pulverizing the calcination product, subjected to filtration and washed with distilled water, after drying for 6 hours at 0.99 ° C., by performing the annealing treatment for 6 hours at 300 ° C., to obtain a powder B _1.
The powder X-ray diffraction pattern was measured, and it was found that the crystal structure of the powder B _{1 was} a crystal structure belonging to the R-3m space group.

(Comparative Example 1)
"Production of cathode material precursor for lithium secondary battery"
In step (3), the concentrated slurry was charged into a drying vat instead of a flash dryer, and the concentrated slurry was dried using a shelf dryer (general-purpose dryer AT-20 (manufacturer: Asahi Kagaku Co., Ltd.)). Gave a dried product R ₁ in the same manner as in Example 1. Drying conditions by the shelf dryer are 120 ° C. and 8 hours. The water content of the obtained dried product R ₁ was 8% by weight.
An X-ray diffraction pattern of the dried product R ₁ is shown in FIG. As apparent from FIG. 7, a signal of 36.08 ° (Miller index 350) indicating Mn oxide (Mn ₃ O ₄ ) was confirmed.

"Manufacture of cathode materials for lithium secondary batteries"
A powder B ₂ was obtained in the same manner as in Example 1 except that the dried product R ₁ was used instead of the dried product P ₁ . The powder X-ray diffraction pattern was measured, and it was found that the crystal structure of the powder B _{2 was} a crystal structure belonging to the R-3m space group.

(Reference Example 1)
As Reference Example 1, a positive electrode material precursor for a lithium secondary battery was manufactured by a conventional method of solid-liquid separation of a stock solution slurry to form a wet cake and drying the wet cake.
First, a stock solution slurry having a solid content concentration of 3.5% by weight was obtained under the same conditions as in step (1) in Example 1.
Subsequently, solid-liquid separation of the slurry obtained by the filter press was performed. For the filter press, a “roll fit filter press dryer” (distributor: Eurotech Co., Ltd.) was used. 100 parts by weight of the slurry was supplied to a filter press and filtered under conditions of room temperature at a filtration pressure of 0.4 MPaG and a filtration time of 50 minutes. Next, distilled water was supplied at a washing pressure of 0.4 to 0.6 MPaG at room temperature to perform washing with water. After washing with water, pressing and dewatering was performed at a pressing pressure of 0.7 MPaG for 15 minutes. Next, the pressure inside the filtration chamber of the vacuum filter press was set to 10 kPa, and 90 ° C. hot water was passed through the fluid supply path of each filtration chamber of the filter press, and preliminary drying was performed for 170 minutes. After preliminary drying, 4.62 parts by weight of the wet cake discharged from the filter press was recovered. The water content of the wet cake at this time was 29.5% by weight on a wet basis.
The obtained wet cake is charged into a drying vat, dried using a shelf dryer (general-purpose dryer AT-20 (manufacturer: Asahi Kagaku Co., Ltd.)) at 120 ° C. for 8 hours, and then milled with a feather mill. It was carried out to obtain a powdery dried product X _1. The water content of the obtained dried product X ₁ was 3% by weight.
An X-ray diffraction pattern of the dried product X ₁ is shown in FIG. As can be seen from FIG. 8, a slight signal of 2θ = 36.08 ° (Miller index 350) indicating Mn oxide (Mn ₃ O ₄ ) was confirmed.

"Manufacture of cathode materials for lithium secondary batteries"
A powder B ₃ was obtained in the same manner as in Example 1 except that the dried product X ₁ was used instead of the dried product P ₁ . The powder X-ray diffraction pattern was measured, and it was found that the crystal structure of the powder B _{3 was} a crystal structure belonging to the R-3m space group.

<Preparation of nonaqueous electrolyte secondary battery>
A coin-type non-aqueous electrolyte secondary battery using the produced powders B _{1 to} B ₃ as a positive electrode active material was produced, and a charge / discharge test was performed.
A mixture of a positive electrode active material (powder B _{1 to} B ₃ ) and a conductive material (a mixture of acetylene black and graphite at a ratio of 9: 1 (weight ratio)), PVdF N-methyl-2-pyrrolidone (hereinafter referred to as “binder”) NMP.) The solution is added to the composition of active material: conductive material: binder = 87: 10: 3 (weight ratio) and kneaded to obtain a paste, and the thickness is 40 μm to be a current collector. The paste was applied to an Al foil and vacuum dried at 150 ° C. for 8 hours to obtain a positive electrode.
To the obtained positive electrode, 30 of ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC) and ethyl methyl carbonate (hereinafter sometimes referred to as EMC) as electrolytes. : 35:35 (volume ratio) LiPF ₆ dissolved in a mixed solution to 1 mol / liter (hereinafter sometimes referred to as LiPF ₆ / EC + DMC + EMC), a laminated film as a separator, and a negative electrode A coin-type battery (R2032) was manufactured by combining metallic lithium.
Using the above coin-type battery, a charge / discharge test was performed under the conditions shown below while maintaining at 25 ° C. The results are shown in Table 1.

<Charge / discharge test>
Charging maximum voltage 4.3V, charging time 8 hours, charging current 0.18 mA / cm ²
During discharge, the minimum discharge voltage was kept constant at 2.5 V, and the discharge current in each cycle was changed as follows to perform discharge. Higher discharge capacity due to discharge in each cycle means higher output.
First cycle discharge (0.2 C): discharge current 0.18 mA / cm ²
Second cycle discharge (1C): discharge current 0.88 mA / cm ²

When the discharge capacities of Example 1 and Comparative Example 1 were compared, Example 1 was larger than Comparative Example 1 at both discharge rates of 0.2 and 1C.
In addition, Example 1 showed a discharge capacity equal to or higher than that of Reference Example 1 using a positive electrode material derived from a conventional wet cake.
As described above, according to the production method of the present invention, it was confirmed that a high-quality positive electrode material can be obtained even on an industrial scale.

  The production method of the present invention can be suitably used when a precursor of a positive electrode material for a lithium secondary battery is produced, or when a positive electrode material is produced from this precursor.

DESCRIPTION OF SYMBOLS 10 Crossflow filtration system 11 Slurry storage tank 12 Filter 20 Crossflow filtration apparatus 22 Filtration chamber 23 Filtration plate 24 Stirring plate 25 Motor 26 Slurry supply port 27 Slurry discharge port 28 Slurry discharge valve 30 Crossflow filtration system 31 Slurry storage tank 31a Stirring device 32 Liquid feed pump 33 Washing water supply equipment P ₁ and P ₂ piping 40 Air dryer 41 Slurry storage tank 42 Water storage tank 43 Slurry supply pipe 44 Slurry supply pump 45 Main body 46 Intake filter 47 Intake pipe 48 Suction fan 49 Heat exchanger 50 Bug Filter 51 Discharge pipe 52 Exhaust fan 53 Exhaust pipe 54 Container M Medium F Fluidized bed

Claims (9)

A slurry production step of obtaining a stock slurry containing a solid content mainly composed of a transition metal hydroxide by contacting a solution containing a transition metal element with an alkali; and
A slurry concentration step of concentrating solids in the stock slurry and obtaining a concentrated slurry; and
The concentrated slurry is supplied to an air dryer, and the concentrated slurry is dried with a high-temperature gas of 100 ° C. or higher so that the moisture content becomes a powder having a water content of 40% by weight or less within 60 minutes after being supplied to the air dryer. A drying process;
The manufacturing method of the positive electrode material precursor for lithium secondary batteries characterized by having.   The method for producing a positive electrode material precursor for a lithium secondary battery according to claim 1, wherein the transition metal element contains at least Mn.   The manufacturing method of the positive electrode material precursor for lithium secondary batteries of Claim 1 or 2 which performs slurry concentration by crossflow filtration in the said slurry concentration process.   The positive electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the air flow dryer is a fluidized bed drying device having a medium for allowing the supplied concentrated slurry to adhere and drying the adhered concentrated slurry. A method for producing a material precursor.   The method for producing a positive electrode material precursor for a lithium secondary battery according to claim 4, wherein an inlet temperature of the high-temperature gas in the air dryer is 150 ° C. or more and 500 ° C. or less.   The method for producing a positive electrode material precursor for a lithium secondary battery according to claim 4 or 5, wherein an outlet temperature of the high-temperature gas in the air dryer is 50 ° C or higher and 200 ° C or lower.   The method for producing a positive electrode material precursor for a lithium secondary battery according to any one of claims 1 to 6, wherein the high-temperature gas in the air dryer is a gas obtained by burning a combustible gas.   The manufacturing method of the positive electrode material precursor for lithium secondary batteries in any one of Claim 1 to 7 which uses a bag filter for the powder collection | recovery part in the said air dryer.   A method for producing a positive electrode material for a lithium secondary battery, comprising mixing the lithium compound positive electrode material precursor obtained by the production method according to any one of claims 1 to 8 with a lithium compound and firing the mixture. .

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