JP7594850B2 - Hopper and firing device for secondary battery positive electrode active material using same - Google Patents

Description

The present invention relates to a hopper and a firing device for secondary battery positive electrode active material using the same.

In recent years, with the widespread use of mobile devices such as mobile phones and notebook computers, there is a strong demand for the development of small, lightweight secondary batteries with high energy density. In addition, in the field of environmentally friendly automobiles known as xEVs, there is a shift from hybrid electric vehicles (HEVs) to plug-in hybrid electric vehicles (PHEVs) and electric vehicles (BEVs) that require high-capacity secondary batteries. BEVs have a shorter driving distance on a single charge than gasoline-powered vehicles, and there is a demand for high-capacity secondary batteries to improve this.
A lithium-ion secondary battery is one example of a secondary battery that satisfies such requirements. This lithium-ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, etc., and the active materials for the negative electrode and the positive electrode are materials that can extract and insert lithium.

Lithium ion secondary batteries are currently the subject of vigorous research and development. In particular, lithium ion secondary batteries that use layered or spinel-type lithium metal composite oxides as the positive electrode material are capable of achieving a high voltage of about 4 V, and are therefore being put into practical use as batteries with high energy density.
The main materials that have been proposed so far include lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ), lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), and lithium manganese composite oxide (LiMn ₂ O ₄ ) that uses manganese.
Among these, lithium nickel composite oxide (LiNiO ₂ ) has attracted attention due to its high capacity and high output, and is expected to meet the characteristics required for the positive electrode active material of secondary batteries in future environmentally friendly automobiles, and demand for it is rapidly expanding.

Patent Document 1 discloses a positive electrode active material for non-aqueous electrolyte secondary batteries, which is made of a lithium nickel composite oxide represented by the general formula: Li _b Ni _1-x-y Co _x M _y O ₂ (wherein M is at least one element selected from Mg, Al, Ca, Ti, V, Cr, Mn, Nb, Zr, and Mo; b is a value that satisfies 0.95≦b≦1.03, x is a value that satisfies 0<x≦0.15, y is a value that satisfies 0<y≦0.07, and x+y is a value that satisfies ≦0.16).
Furthermore, Patent Document 2 discloses a positive electrode active material for non-aqueous electrolyte secondary batteries, which is composed of particles of a lithium nickel composite oxide represented by the general formula Li _a Ni _1-x-y Co _x Al _y O ₂ (where 0.9≦a≦1.0, 0.10≦x≦0.20, and 0.02≦y≦0.1).

In order to obtain the positive electrode active material of Patent Documents 1 and 2, it is necessary to sinter a mixed powder obtained by mixing nickel composite oxide particles and lithium compound particles. However, since the nickel composite oxide particles and the lithium compound particles have different particle sizes and specific gravities, particle size separation and specific gravity separation are likely to occur. In mass production processes, the mixed powder is generally stored in a large hopper and then supplied to a sintering vessel such as a sagger. Even in this large hopper, particle size separation and specific gravity separation occur, resulting in a variation in the mixing ratio of the nickel composite oxide particles and the lithium compound. As a result, it is difficult to supply the mixed powder to a sintering vessel such as a sagger at a constant mixing ratio.
If the mixing ratio of the nickel composite oxide and the lithium compound is deviated, as described in Patent Document 1, for example, a large decrease in battery capacity during charge/discharge cycles, a large amount of gas generation during charging, and gelation of the slurry during electrode preparation occur.

To prevent this, in Patent Document 1, nickel composite hydroxide is oxidized and roasted to form nickel composite oxide, which is then mixed with a lithium compound. Although gravity separation is less likely to occur in this case than in a mixture of nickel composite hydroxide and lithium compound, as mentioned above, there is a large difference in specific gravity and particle size between the nickel composite oxide and the lithium compound, so gravity separation and particle size separation occur, resulting in a distribution of the mixing ratio in the hopper.

Patent Document 2 also describes that the variation in the mixing ratio can be suppressed by mixing the precursors thoroughly without destroying their shells. When the materials are mixed and fed to the firing vessel immediately without much fluidization, as in research and small-scale production, the variation is small. However, when a large hopper is used as in mass production equipment, gravity separation and particle size separation occur due to fluidization in the hopper, resulting in a distribution in the mixing ratio of the nickel composite oxide and the lithium compound. As a result, mixed powders with different mixing ratios are fired depending on the firing vessel, resulting in the formation of a positive electrode active material that reduces the battery capacity and causes the slurry to gel, as described above.

The present inventors have found that when any mixed powder raw material, including the above-mentioned nickel composite oxide and lithium compound as a positive electrode active material raw material for secondary batteries, is supplied using a hopper, one of the causes of variation in the mixing ratio between the mixed powder raw materials is a solidified layer formed on the cone part of the hopper.
Conventional techniques for preventing the formation of a solidified layer in the cone portion of a conventional hopper include those disclosed in Patent Documents 3 to 5.
Patent Document 3 discloses an apparatus in which a cone-shaped soft container made of a soft material is placed inside a cone-shaped rigid container to form an airtight gap between the rigid container and the soft container, and an air vent pipe is connected to the rigid container to supply compressed fluid from the air vent pipe to the airtight gap to freely expand the soft container inward and break up blocked granules.
Moreover, Patent Document 4 discloses an apparatus including a plate provided on the inner surface in the vicinity of the discharge port and a vibration means for vibrating the plate.
However, in the methods of Patent Documents 3 and 4, since the formed solidified layer is destroyed, the variation in the mixing ratio is improved to some extent, but the formation of the solidified layer cannot be completely prevented, and therefore, sufficient improvement cannot be achieved.

Patent Document 5 discloses a method in which an insertion cone is provided near the top of the bottom opening of a storage tank and vanes are provided on the insertion cone. With this method, no solidified layer is formed and the variation in the mixing ratio of the mixed powder is improved, but the insertion cone restricts the flow of the powder, slowing down the discharge speed of the powder. In addition, because the insertion cone is suspended by a wire, there is a possibility that powder generated by wear of the wire and hanging ring, or powder generated when the insertion cone comes into contact with the hopper wall, may get mixed in due to shaking.

JP 2015-216105 A JP 2017-188211 A JP 2001-039489 A JP 2008-222272 A Japanese Patent Application Publication No. 6-080189

SUMMARY OF THE PRESENT EMBODIMENT In view of the above problems, an object of the present invention is to provide a hopper capable of reducing the variation in the mixing ratio of all kinds of mixed powder raw materials.
Another object of the present invention is to provide an apparatus for sintering a positive electrode active material for a secondary battery, which is capable of producing the positive electrode active material for a secondary battery with reduced variation in the mixing ratio between the raw materials.

The hopper of the first invention is a hopper that supplies a mixed powder raw material containing a nickel composite oxide and a lithium compound having different physical properties, and is characterized in that it comprises a cylindrical hopper section, a conical cone section connected to the lower end of the hopper section, an internal cone inside the hopper section and installed above the cone section, and a discharge section connected to the lower end of the cone section, and the opening angle a of the cone section and the opening angle a of the internal cone are angles represented by formula (1) when the maximum value of the angle of repose of the mixed powder raw material is b, a≦180-2b-10... formula (1), and the distance between the lower end of the cone section and the lower end of the internal cone is the maximum drop distance, which is set to within 1000 mm.
The hopper of the second invention is characterized in that, in the first invention, the internal cones are arranged in multiple tiers in the vertical direction, and the vertical distance between the lower tier of the cone section and the lower end of the internal cone of the lowest tier and the vertical distance between the lower ends of each internal cone are maximum fall distances, which are set to within 1000 mm.
The third invention relates to a firing apparatus for a positive electrode active material for a secondary battery, the firing apparatus comprising: a plurality of setters in which the material to be fired is filled; a supply section for supplying the material to be fired to each setter; a firing furnace for firing the material to be fired supplied to each setter; a conveying section for transporting each setter from the supply section to the firing furnace and transporting each setter containing the material fired in the firing furnace out of the firing furnace; and a discharge section for discharging the material from each setter, the firing apparatus for a positive electrode active material for a secondary battery being characterized in that the hopper described in claim 1 or 2 is used as a device for supplying the material to be fired in the supply section.
A fourth aspect of the present invention is an apparatus for sintering a positive electrode active material for a secondary battery according to the third aspect of the present invention, characterized in that the discharge section includes a crushing mechanism for crushing the sintered material removed from the plurality of setters.
The sintering apparatus for a positive electrode active material for a secondary battery of the fifth invention is characterized in that, in the fourth invention, the crushing mechanism is a roll crusher and is equipped with a cooling mechanism for cooling the roll that comes into contact with the high-temperature sintered material.
The sixth invention relates to an apparatus for sintering a positive electrode active material for a secondary battery, and is characterized in that, in the fourth invention, at least one of the supply unit, the sintering furnace, the discharge unit, and the crushing mechanism is provided with a mechanism for maintaining an oxygen concentration in the working space at 80% or more.
The seventh invention is an apparatus for firing a positive electrode active material for a secondary battery according to any one of the third to sixth inventions, characterized in that the fired product is a lithium-nickel composite oxide containing lithium (Li), nickel (Ni), cobalt (Co), and another element (M), and the atomic ratio of the elements is expressed as Li:Ni:Co:M=s:(1-xy):x:y (where 0.93<s<1.03, 0.00≦x≦0.35, 0.03≦y≦0.35, and M is one or more of a transition metal, an alkaline earth metal, a base metal, or a semimetal).

According to the first aspect of the present invention, the following effects are achieved.
a) By setting the opening angle a of the cone portion and the inner cone to a value satisfying a value less than or equal to 180°-2b-10°, even if the mixed powder raw material contains a nickel composite oxide and a lithium compound which have different physical properties such as specific gravity and particle size, retention does not occur in a part of the mixed powder raw material (raw material in the region close to the inner wall surface), and variation in the flow of particles during and after falling is suppressed.
b) By providing an internal cone in the hopper, the falling distance of the mixed powder raw material in the hopper can be shortened even if the vertical dimension of the entire hopper is large. Therefore, the variation in the flow of the particles due to differences in specific gravity and particle size during the fall can be suppressed.
c) By setting the maximum falling distance of the mixed powder raw material to 1000 mm or less, the variation in the flow of the particles due to differences in specific gravity and particle size during the fall is suppressed. As a result, the variation in the mixing ratio of the discharged mixed powder raw material can be suppressed to a small extent.
d) As described above, a mixture containing a nickel composite oxide and a lithium compound, which have different physical properties, can be discharged while maintaining an appropriate mixing ratio. This contributes to the secondary battery positive electrode materials obtained by firing the mixture discharged from the hopper all exhibiting the same battery performance.
According to the second invention, even if the inner cone is provided in multiple stages, the falling distance of the powder raw material in the hopper can be shortened. Therefore, the variation in the flow of the particles due to the difference in specific gravity, the difference in particle size, etc. during the fall is suppressed. Furthermore, by setting the maximum falling distance of the mixed powder raw material to 1000 mm or less, the variation in the flow of the particles due to the difference in specific gravity, the difference in particle size, etc. during the fall is also suppressed.
According to the third invention, the mixed powder raw materials are supplied from the hopper to the setter in the supply section with small variation in the mixing ratio, so that the mixing ratio of the mixed powder raw materials in the sintered positive electrode active material also remains small, making it possible to easily produce a high-capacity positive electrode active material for secondary batteries.
According to the fourth aspect of the present invention, the fired product that has hardened due to firing can be pulverized to a particle size suitable for use in a positive electrode active material for a secondary battery. Furthermore, when the pulverized fired product is subjected to a water washing step, the fired product can be washed more uniformly.
According to the fifth invention, the sintered material can be pulverized simply by supplying it between a pair of rolls, and since the rolls are cooled by a cooling mechanism, they do not become excessively hot and the physical properties of the sintered material that comes into contact with the rolls are not changed.
According to the sixth invention, an atmosphere suitable for sintering is maintained from the supply section through the sintering furnace to the discharge section, so that the mixed powder raw material can be reacted sufficiently, and changes in the physical properties of the sintered product after sintering can be suppressed, so that a sintered product with the desired physical properties can be obtained.
According to the seventh aspect of the present invention, it is possible to obtain a fired product of a lithium-nickel composite metal oxide, which is a raw material for a positive electrode active material for a lithium ion secondary battery and has appropriate physical properties.

FIG. 2 is an explanatory diagram of a hopper 50 according to the first embodiment of the present invention. 2 is an explanatory diagram of the operation of the hopper 50 shown in FIG. 1 . FIG. 11 is an explanatory diagram of a hopper 50 according to a second embodiment in which internal cones are provided in multiple stages. FIG. 11 is an explanatory diagram of a hopper 50 according to a third embodiment, which is provided with a partition plate and an internal cone. 1 is a schematic plan view of a baking device 1 according to an embodiment of the present invention. 6 is a schematic cross-sectional view taken along line VI-VI in FIG. 5. FIG. 1 is a diagram showing an example of a method for producing a positive electrode active material for a lithium ion secondary battery. FIG. 1 is a diagram showing an example of a method for producing a nickel composite oxide. FIG. 2 is a diagram showing an example of a treatment process for a lithium nickel composite oxide after calcination. FIG. 2 is a diagram showing an evaluation secondary battery used in the examples. FIG. 2 is an explanatory diagram of the angle of repose.

Hereinafter, the embodiments of the present invention will be described in the following order of (1) to (6) with reference to the drawings. However, the present invention is not limited to the embodiments described below. In the drawings, the embodiments may be represented diagrammatically or at a different scale as appropriate.
(1) Hopper (2) Firing device using the hopper (3) Method for producing positive electrode active material for lithium ion secondary battery (4) Positive electrode active material for lithium ion secondary battery (5) Lithium ion secondary battery (6) Example of lithium ion secondary battery

(1) Hopper The hopper 50 according to one embodiment of the present invention is a hopper that supplies a mixed powder raw material obtained by mixing a plurality of types of powder.
In this specification, the term "multiple types of powders" refers to two or more types of powders having different physical properties such as specific gravity, particle size, composition, etc., and a mixture of these powders is called a mixed powder raw material.
An example of such a mixed powder raw material is a calcined raw material for a positive electrode active material for a secondary battery, such as a lithium compound and a nickel-cobalt composite oxide. Since such multiple types of powder have different specific gravities and particle sizes, even if they are mixed at a constant ratio, the mixing ratio may change partially when flowing through the hopper. If the mixing ratio changes, the properties of the mixed powder will change, so the hopper of the present invention is suitable for supplying a mixed powder raw material whose mixing ratio needs to be kept constant to avoid this.
The multiple types of powder are not limited to two types, but may include three or more types. The present invention can also be applied to supplying multiple types of powder with the same specific gravity.

First Embodiment
1 is composed of a cylindrical hopper portion 51, a cone-shaped cone portion 52 connected to the lower end of the hopper portion 51, and a discharge portion 53 connected to the lower end of the cone portion 52. A valve 54 is provided in the discharge portion 53 to control the discharge of the mixed powder raw material from the hopper.
An internal cone 71 is attached to the hopper portion 51 .

The internal cone 71 is a cone-shaped member whose upper edge is fixed to the inner circumference of the hopper portion 51 and whose lower end is open. The internal cone 71 shown in the figure is a member of approximately the same shape and dimensions as the cone portion 52, but may be of a different size or shape than the cone portion 52.

The height dimension h between the lower end of the internal cone 71 and the lower end of the cone portion 52 (the portion connected to the upper end of the discharge portion 53) is set to 1000 mm or less. This height dimension h is also the maximum falling distance h of the mixed powder raw material referred to in the claims.
In the present invention, by providing the internal cone 71 in the hopper section 51, the falling distance of the mixed powder raw material in the hopper 50 can be shortened even if the vertical dimension of the entire hopper 50 is large. Therefore, the variation in the flow of the particles due to the difference in specific gravity, the difference in particle size, etc. during the fall is suppressed. Furthermore, by setting the falling distance of the mixed powder raw material to 1000 mm or less, the variation in the flow of the particles due to the difference in specific gravity, the difference in particle size, etc. during the fall is also suppressed.

In the present invention, the opening angle a of the cone portion 52 is set to an angle expressed by the formula (1) when the maximum value of the angle of repose of the mixed powder raw material is b, as shown in FIG.
a≦180-2b-10...Formula (1)
The opening angle a is the angle at which opposing inner wall surfaces in a cone intersect with each other.

1, the intersection angle of the inner wall 52a of the cone portion 52 with respect to the horizontal plane is the maximum repose angle b+α of the mixed powder raw material, where α is 5° in the illustrated embodiment.
In this case, the angle between the diagonally opposite inner walls 52, that is, the opening angle a, is (180-2b-10).
The opening angle a is the maximum angle in the above case, and smaller angles are also included. In other words, the present invention also includes an opening angle a in which the cone portion 52 has a sharper taper.
In the embodiment shown in Fig. 1, the opening angle a of the internal cone 71 also satisfies the above formula (1). That is, the intersection angle a of the inner wall 71a constituting the internal cone 71 with respect to the horizontal plane is also the maximum repose angle b + α of the mixed powder raw material. α in the internal cone 71 shown in the figure is 5°. As long as formula (1) is satisfied, the opening angle a of the cone portion 52 and the opening angle a of the internal cone 71 do not necessarily have to be the same angle.

The angle of repose is the angle between the horizontal plane and the slope of the powder peak that forms when the powder pw is dropped from a certain height and remains stable without spontaneously collapsing, as shown in FIG.
This angle of repose c is determined by the size, shape, surface condition, weight, etc. of the particles, and the angle of repose c of powders that flow easily is small, while the angle of repose c of powders that do not flow easily is large. In addition, this angle of repose has a range depending on the properties of the powder, but in the present invention, the maximum value b is used.

In the hopper 50 of this embodiment, the inner walls of the cone portion 52 and the internal cone 71 are inclined at an angle greater than the maximum repose angle b of the mixed powder raw material handled by the hopper, so that the mixed powder raw material pw charged into the hopper 50 flows downward at an angle greater than the maximum repose angle b in the cone portion 52 and the internal cone 71, and a solidified layer is not formed due to the retention of the mixed powder raw material pw. As a result, a portion of the mixed powder raw material pw (raw material in the area close to the inner wall surface) does not stagnate and flows smoothly, making it difficult for the mixing ratio of the mixed powder raw material pw to change. This makes it possible to keep the variation in the mixing ratio small.

As shown in FIG. 2, when the mixed powder raw material pw is charged into the hopper 50 from a flexible container 80 or the like, the mixed powder raw material pw is first stored inside the internal cone 71, and the mixed powder raw material pw flowing out from the lower end opening of the internal cone 71 is stored inside the cone portion 52, collected at the lower end of the cone portion 52, and discharged from the discharge portion 53.
At this time, the falling distance h of the mixed powder raw material pw between the lower end of the internal cone 71 and the lower end of the cone portion 52 is set to 1000 mm or less, so that the variation in the mixture ratio due to the difference in specific gravity or particle size during the fall is suppressed. As a result, the variation in the mixture ratio of the discharged mixed powder raw material can be suppressed to a small value.

Furthermore, the fact that there is little variation in the mixing ratio when the powder is discharged from the hopper 50 means that the mixing ratio when it is put into the hopper 50 is almost maintained, which means that the physical properties of the mixed powder raw material can be maintained as desired and the mixed powder raw material can be supplied to the next process.
For example, when the mixed powder raw material is a raw material for a positive electrode material for a secondary battery, the material to be sintered supplied by the hopper 50 is sintered in a sintering device, and the obtained sintered powder can all contribute to achieving the same battery performance.

Second Embodiment
The hopper 50 of the second embodiment shown in Fig. 3 is provided with multiple stages of internal cones. In the illustrated example, two stages of internal cones 71A and 71B are provided in series above and below. Note that the present invention also includes a hopper using three or more stages of internal cones.
In this embodiment, the distance h between the lower end opening of the upper internal cone 71B and the lower end opening of the lower internal cone 71A is 1000 mm or less. The distance h between the lower end opening of the lower internal cone 71A and the lower end of the cone portion 52 is also 1000 mm or less.
The opening angle a of each internal cone 71A, 71B and the opening angle a of the cone portion 52 are based on the condition of the above formula (1) in which the maximum value b of the angle of repose of the mixed powder raw material is a variable, as in the first embodiment.

In this second embodiment, the hopper section 51 has a larger volume and a larger vertical dimension because it has two internal cones 71A and 71B. However, the falling distance h of the mixed powder raw material in the hopper 50 is 1000 mm or less at both points, so the variation in the mixing ratio due to differences in specific gravity and particle size during the fall is suppressed.

Third Embodiment
A hopper 50 according to a third embodiment shown in Fig. 4 is provided with a partition plate 61 and an internal cone 71 inside a hopper section 51. An upper section of the hopper section 51 is divided into a plurality of spaces by the partition plate 61. An internal cone 71 is provided in a lower section of the hopper section 51.

The partition plate 61 is attached vertically to prevent lateral movement of powder inside the hopper section 51. The area to which the partition plate 61 is attached does not need to be the entire vertical area of the hopper section 51, but it is preferable that it be most of the area. The lower end of the partition plate 61 may extend to near the upper end of the internal cone section 71.

The number of divisions into the hopper section 51 by the partition plates 61 is preferably 4 to 8. If the number of divisions in the hopper section 51 is 4 to 8, it is possible to effectively suppress irregular lateral movement while ensuring sufficient space for the powder to fall, so that the mixture ratio of multiple types of powder is kept uniform while it falls inside the hopper 50. In contrast, if the number of divisions is 3 or less, the effect of suppressing irregular lateral movement of the powder is reduced, and if the number of divisions is 9 or more, the flow resistance due to friction between the powder and the partition plates 61 becomes large, so neither is preferable.

In the hopper 50 of this embodiment shown in Fig. 4, the flow of the charged mixed powder raw material in the lateral outward direction and in the circumferential direction is suppressed by the partition plate 61. This also prevents the mixed powder raw material from flying up.
As a result, the mixed powder raw material that is added flows straight down and within the hopper 50 while maintaining the mixing ratio that was present before it was added to the hopper 50. This makes it difficult for the mixing ratio of the mixed powder raw material to change, and as a result, the mixing ratio can be maintained uniform.

Furthermore, since the inclination angle a of the inner cone 71 and the inner wall of the cone section 52 is greater than the maximum repose angle b of the mixed powder raw material being supplied, the entire amount of the mixed powder raw material slides down the inner wall of the cone section 52 at the mixing ratio. As a result, a solidified layer of the mixed powder raw material does not form on the inner wall surface of the cone section 52, and part of the mixed powder raw material (raw material in the area close to the inner wall surface) does not stagnate and flows smoothly, making it difficult for the mixing ratio of the mixed powder raw material to change. This further reduces the variation in the mixing ratio.

In the third embodiment of the hopper 50, (A) the hopper section 51 is separated by a partition plate 61, (B) the opening angle a of the internal cone 71 and the cone section 52 satisfies the above formula (1) based on the maximum repose angle b of the mixed powder raw material, and (C) the falling distance h of the powder inside the hopper 50 is set to 1000 mm or less. Therefore, the synergistic effect of these requirements (A), (B), and (C) works, and even if the vertical dimension of the hopper 50 is increased, the effect of suppressing the variation in the mixing ratio is increased.

As described above, the fact that there is little variation in the mixing ratio when the powder is discharged from the hopper 50 means that the mixing ratio when it is charged into the hopper 50 is almost maintained, which means that the physical properties of the mixed powder raw material can be maintained as desired and the mixed powder raw material can be supplied to the next process.
For example, when the mixed powder raw material is a raw material for a positive electrode material for a secondary battery, the material to be sintered supplied by the hopper 50 is sintered in a sintering device, and the obtained sintered powder can all contribute to achieving the same battery performance.

(2) Baking Apparatus A baking apparatus 1 according to one embodiment of the present invention will be described with reference to Figs.
This baking apparatus 1 is a baking apparatus that uses the hopper 50 in FIG. 1 as a component of the supply section 10 to supply the material to be baked (the mixed powder raw material is referred to as the material to be baked at the stage of being baked in the baking apparatus).
5 and 6, the baking device 1 includes a baking furnace 2 that bakes the baked object from the object to be baked, a plurality of setters S on which the object to be baked is placed, a supply section 10 that supplies the object to be baked to the setter S, a discharge section 20 that discharges the object baked in the baking furnace 2 from the setter S (the object to be baked after baking is completed is called the baked object), and a conveying section 5 that conveys the setter S. The plurality of setters S are moved by the conveying section 5 in the order of the supply section 10, the baking furnace 2, and the discharge section 20, so that the objects to be baked can be baked continuously.
Each part of the baking device 1 will be described in detail below.

(Supply Unit 10)
5 and 6, the supply unit 10 is provided so as to be located above a path along which the setter S moves in the supply and conveyance unit 5a described below. The supply unit 10 includes a hopper 50 that supplies the mixed powder raw material. The hopper 50 is supplied with the mixed powder raw material that has been mixed at a predetermined ratio from a flexible container 80 or the like.
A known filling machine 15 may be placed between the hopper 50 and the setter S located above the conveying and supplying section 5a. The filling machine 15 is provided when it is necessary to improve the filling of the material to be fired into the setter 5, but it does not have to be provided when this is not necessary. When the filling machine 15 is not provided, the hopper 50 may be placed at a lower position than the vertical position shown in the figure.

When the setter S moves below the hopper 50, the supply section 10 opens and closes the valve 54 to discharge a predetermined amount of mixed powder raw material, thereby supplying the mixed powder raw material into the setter S as the material to be sintered.
It is desirable that the opening and closing of the valve 54 of the hopper 50 is controlled so as to be linked to the operation of the supply and conveyance unit 5a. For example, when the setter S is placed below the hopper 50, the supply and conveyance unit 5a temporarily stops conveying the setter S, and upon receiving the stop signal, the valve 54 of the hopper 50 opens and the material to be baked is supplied to the setter S. Then, when a predetermined amount of material to be baked is supplied to the supplier 12, the valve 54 of the hopper 50 closes, but the supply and conveyance unit 5a can be made to move upon receiving a signal that the valve is closed.
Alternatively, the supply and transport section 5a may supply the object to be sintered from the supply section 10 to the setter S while moving the setter S, without temporarily stopping the transport of the setter S.

(Setter S)
5 and 6, the symbol S indicates a setter. This setter S is formed in a box shape with an opening Sa at the top and a hollow space Sh inside, and is also called a sagger. With the object to be fired housed in the space Sh of this setter S, the object to be fired is fired from the object to be fired in the firing furnace 2 described later.

The setter S is made of a material that can maintain its shape even at the temperature at which the object to be sintered is sintered and does not react with the substances in the object to be sintered. For example, when a lithium composite metal oxide is sintered, the setter S is made of a material that has corrosion resistance against lithium even at 600 to 900°C, which is the sintering temperature range of the lithium composite metal oxide. Specifically, alumina (Al ₂ O ₃ ), mullite (3Al _{2 O} 3.2SiO ₂ ), cordierite (2MgO.2Al _{2 O} 3.5SiO ₂ ), silicon nitride (Si ₃ N ₄ ), sialon (Si ₃ N _{4.Al 2} O ₃ ), magnesia (MgO), zirconia (ZrO ₂ ), or beryllia (BeO) can be used as the material for the setter S. In particular, high-purity alumina or alumina containing ZrO ₂ is preferable because it has excellent corrosion resistance against lithium. Furthermore, mullite and cordierite are inexpensive and have relatively good corrosion resistance, and are therefore suitable as materials for the setter S when mass-producing fired products, due to their overall low cost.

The setter S does not have to be entirely made of the above-mentioned materials. At least the surface of the setter S that comes into contact with the object to be sintered (i.e., the inner surface of the setter S) needs to be made of a material that does not react with the substances in the object to be sintered. For example, when sintering a lithium composite metal oxide, the inner surface of the setter S made of a metal or the like may be covered with alumina, mullite, or the like. Even in this case, the material that forms the main body of the setter S needs to be a material that can maintain its shape at the temperature at which the object to be sintered is sintered into the sintered product.

(Transportation unit 5)
5 and 6, the firing device 1 is provided with a conveying section 5 that conveys the plurality of setters S. The conveying section 5 is composed of a supply conveying section 5a, a firing furnace conveying section 5b, a discharge conveying section 5c, and a return conveying section 5d.
The supply and transport section 5 a continuously carries a plurality of setters S, to which the objects to be fired have been supplied in the supply section 10 , into the firing furnace 2 .
The firing furnace transport section 5 b moves a plurality of setters S within the firing furnace 2 .
The discharge/transport section 5 c continuously carries out a plurality of setters S containing the fired products from the firing furnace 2 and supplies them to the discharge section 20 .
The return transport section 5d transports the plurality of setters S from which the fired products have been discharged in the discharge section 20 to the supply section 10. Note that equipment for cleaning the setters S (e.g., a suction device, etc.) may be provided midway along the return transport section 5d.

The conveying section 5 may be configured such that the supply conveying section 5a, the firing furnace conveying section 5b, the discharge conveying section 5c, and the return conveying section 5d (hereinafter sometimes simply referred to as each conveying section 5a to 5d) move multiple setters S at the same speed, or the speeds at which the multiple setters S move may be different from each other. Of course, each conveying section 5a to 5d may also be configured such that the multiple setters S can be moved at different speeds.

As described above, each of the transport units 5a to 5d may transport multiple setters S, and the transport mechanism is not particularly limited. For example, a belt conveyor, a chain conveyor, a roller conveyor, etc. may be used as the transport mechanism. The transport mechanisms of the transport units 5a to 5d may all be the same mechanism, or different transport mechanisms may be used.

5 and 6 show an example in which each of the transport sections 5a to 5d is formed by a roller conveyor.
Furthermore, although there are no particular limitations on the materials that constitute the components of each of the transport sections 5a to 5d, it is preferable to use materials that are resistant to corrosion by lithium, such as alumina or mullite, etc. If such materials are used for the surfaces of the components, damage caused by lithium hydroxide or the like can be prevented in the event that lithium hydroxide or the like scatters from the sintered object.

(Firing furnace 2)
In Fig. 5 and Fig. 6, the reference numeral 2 denotes the firing furnace of the firing device 1 of this embodiment. This firing furnace 2 is a continuous firing furnace in which the object to be fired is fired while moving. The firing furnace 2 is provided with the firing furnace conveying section 5b described above, and the object to be fired can be fired while moving a plurality of setters S containing the object to be fired. For example, a known continuous firing furnace such as a roller hearth kiln, a pusher furnace, or a conveyor furnace can be used as the firing furnace 2 of the firing device 1 of this embodiment.
In addition, in the case where the firing furnace 2 itself has a transport mechanism for transporting the setter S, the object to be fired, etc., this transport mechanism may be used as the firing furnace transport section 5b.

The firing furnace 2 is capable of maintaining the temperature of the internal space 2h at a predetermined temperature. There are no particular limitations on the method for maintaining the temperature of the internal space 2h of the firing furnace 2 at a predetermined temperature. For example, the temperature of the space 2h in the firing furnace 2 can be maintained at or above the predetermined temperature by an electric heater, a gas heater, a heat medium heater, etc.

When the firing furnace 2 has a soaking zone 2a, a temperature increasing zone 2b, and a temperature decreasing zone 2c, the temperature in each zone is adjusted as follows. Also, the movement time of the fired product in each zone, that is, the speed at which the conveying unit 5 conveys the setter S, is adjusted as follows.
First, the soaking zone 2a is an area where the material to be sintered is sintered. In this soaking zone 2a, the temperature of the space is maintained at a temperature at which the material to be sintered can be sintered. The time for each setter S to move through the soaking zone 2a is adjusted so that the material to be sintered in each setter S can be sintered into a sintered product. As described above, oxygen gas is introduced into the soaking zone 2a to create an atmosphere in which the physical properties of the material to be sintered or the sintered product do not change.
The temperature rise zone 2b is a region where the temperature of the material to be sintered is raised to a predetermined temperature so that the material to be sintered in the soaking zone 2a is sintered appropriately. In the temperature rise zone 2b, the temperature of the space and the movement time of the material to be sintered are adjusted so that the temperature of the material to be sintered rises to a predetermined temperature. Specifically, the temperature of the space and the movement time of the material to be sintered are adjusted in the temperature rise zone 2b so that the material to be sintered gradually approaches the temperature of the soaking zone 2a. In other words, the temperature of the temperature rise zone 2b is adjusted so that the temperature gradually rises from the entrance to the exit so that a sudden temperature rise does not cause abnormal reactions of the substances in the material to be sintered. As described above, oxygen gas is also introduced into the temperature rise zone 2b so that the atmosphere does not change the physical properties of the material to be sintered.
The temperature-reducing zone 2c is an area where the temperature of the material to be sintered is reduced to a predetermined temperature, in contrast to the temperature-raising zone 2b. If the material sintered in the soaking zone 2a is exposed to room temperature air as it is, the temperature of the material may change suddenly, causing problems such as deterioration of the material and changes in physical properties such as specific surface area due to contact with air at high temperatures. Therefore, in the temperature-reducing zone 2c, the temperature of the space and the movement time of the material are adjusted so that the temperature of the material gradually decreases, so that the temperature of the material does not deteriorate even if it comes into contact with room temperature air at the stage when it is discharged from the sintering furnace 2, and the atmosphere of the temperature-reducing zone 2c is made equivalent to that of the soaking zone 2a.

For example, consider the _case where lithium composite _metal oxide ₍ LiNi0.91Co0.04Al0.05O2) is sintered from _a mixture of lithium hydroxide (LiOH) from which water of hydration has been removed and nickel composite hydroxide ( _{Ni0.91Co0.04Al0.05} (OH) ₂ ). In this case, since the temperature at which _the lithium composite metal oxide is sintered is about 730 to 770°C, the soaking zone _2a of the sintering furnace 2 is set so that the space is about 730 to 770°C, and the operation of the conveying unit 5 is adjusted so that the time it takes for each setter S to move within the soaking zone 2a is about 2 to 5 hours. Moreover, since the temperature in the heating zone 2b is preferably at the calcination temperature (about 730 to 770°C) at the stage when the mixture enters the soaking zone 2a, the temperature is set to about 300°C at the entrance side of the heating zone 2b and the space at the exit side is set to the calcination temperature, and the operation of the conveying unit 5 is adjusted to adjust the time for each setter S to move within the heating zone 2b so that the lithium composite oxide reaches the calcination temperature at the exit of the heating zone 2b.

(Discharge section 20)
5 and 6, the discharge section 20 is disposed between the discharge conveying section 5c and the return conveying section 5d. The discharge section 20 includes a crushing mechanism 21 that crushes the baked object (the object to be baked after baking) in the setter S into small lumps or powder, and a baked object supplier (not shown) that supplies the baked object in the setter S to the crushing mechanism 21.

The baked product supplying device inverts the setter S transported on the discharge conveying section 5c and supplies the baked product in the setter S to the crushing mechanism 21. This baked product supplying device is not particularly limited as long as it can invert the setter S. For example, a device equipped with an arm that holds the setter S and inverts it can be used. It is preferable that the baked product supplying device has a function of transferring the setter S from the discharge conveying section 5c to the return conveying section 5d after inverting the setter S.

The crushing mechanism 21 is not particularly limited as long as it has the function of crushing the baked material supplied from the baked material supply device. For example, as shown in Figures 2 and 3, if it has a pair of rolls 22, 22 arranged at a predetermined distance, the baked material can be sandwiched between the pair of rolls 22, 22 and crushed. In other words, if a roll crusher is used as the crushing mechanism 21, the baked material can be crushed by supplying it between the pair of rolls.

It is preferable to provide a cooling mechanism for the rolls 22, 22 of the roll crusher, such as a mechanism for supplying and discharging cooling water inside the roll. If the roll 22 can be cooled by a cooling mechanism, the roll surface will not become excessively hot, and the physical properties of the fired material that comes into contact with the roll will not change.

In addition to the roll crusher, a jaw crusher or the like can be used. In addition, when crushing to a particle size of a few millimeters or less, a pin mill, a hammer mill, a jet mill, or the like can be used in combination with the roll crusher or jaw crusher.
Furthermore, the crushing mechanism 21 may have a function of transporting the lumps or powder formed by crushing the fired material to the next process, or may be configured to discharge the lumps or powder onto a conveyor or the like that transports them to the next process.

The grinding mechanism 21 allows the fired material that has hardened due to firing to be ground, making it suitable for use as a positive electrode active material for secondary batteries. In addition, the ground fired material can be subjected to a water washing process, allowing the fired material to be washed more uniformly.

(Firing atmosphere maintaining mechanism)
The baking apparatus 1 of the present invention is preferably provided with a mechanism for maintaining the oxygen concentration in the working space of each portion at 80% or more.
1) It is desirable that the supply unit 10 has a function of maintaining a predetermined atmosphere inside the valve 54 of the hopper 50. For example, if the supply unit 10 has a function of introducing oxygen into the valve 54 of the hopper 50, the atmosphere around the material to be sintered inside the valve 54 of the hopper 50 can have an oxygen concentration of 80% or more. In other words, the atmosphere inside the valve 54 of the hopper 50 can be made to be one in which the physical properties of the material to be sintered do not change.
The supply section 10 may also have a hood or the like that covers the setter S (the setter S arranged below the supply device 12) to which the material to be sintered is supplied from the valve 54. In that case, the material to be sintered that is supplied to the setter S from the valve 54 and the material to be sintered inside the setter S can also be maintained in a predetermined atmosphere.

2) The firing furnace 2 has a function of maintaining the space 2h inside, that is, the object to be fired and the surroundings of the object to be fired, in a predetermined atmosphere. The predetermined atmosphere means an atmosphere suitable for firing the object to be fired into a fired object. For example, in the case of firing a lithium composite metal oxide, the oxygen atmosphere in which the space 2h in the firing furnace 2 is maintained at a predetermined oxygen concentration (e.g., 80% or more) corresponds to the predetermined atmosphere. There is no limitation on the method of maintaining the space 2h in the firing furnace 2 in the above-mentioned oxygen atmosphere. For example, an oxygen introduction device that introduces oxygen into the space 2h in the firing furnace 2 is provided, and oxygen gas is introduced into the space 2h by this oxygen introduction device. Then, the space 2h in the firing furnace 2 can be maintained in an oxygen atmosphere maintained at a predetermined oxygen concentration (e.g., 80% or more).
Oxygen gas is introduced into the soaking zone 2a so as to obtain an oxygen concentration necessary for the firing reaction.
Oxygen gas is also introduced into the temperature decreasing zone 2c so as to create an atmosphere in which the physical properties of the fired product do not change.

3) It is desirable that the interior of the discharge section 20, and in particular the crushing mechanism 21, has a function of maintaining a predetermined atmosphere in the space in which the baked material is crushed or the space to which the baked material is supplied. For example, if the crushing mechanism 21 has a function of introducing oxygen into the interior, it is possible to make the atmosphere surrounding the baked material supplied to the crushing mechanism 21 have an oxygen concentration of 80% or more. In other words, it is possible to prevent the physical properties of the baked material from changing while it is being crushed in the crushing mechanism 21.

4) If a hood or the like is provided to cover the area from the supply section 10 to the entrance of the firing furnace 2, a predetermined atmosphere can be maintained around the material to be fired while it is being moved from the supply section 10 to the firing furnace 2.
This makes it possible to suppress changes in the physical properties of the material to be fired while it is moving from the supply section 10 to the firing furnace 2.
Furthermore, if there is a hood or the like that covers the area from the firing furnace 2 to the discharge section 20, the atmosphere around the fired material can be maintained at a predetermined level while the fired material is moving from the firing furnace 2 to the discharge section 20. This makes it possible to prevent the physical properties of the fired material from changing while it is moving from the firing furnace 2 to the discharge section 20.

The "work space" in the claims refers to the space in the supply section 10, the sintering furnace 2, and the discharge section 20 (including the crushing mechanism 21) through which the material to be sintered moves and undergoes the necessary processing.

(3) Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery The hopper and the sintering device of the present invention can be suitably used for supplying raw materials and sintering the positive electrode active material for secondary batteries.
The positive electrode active material for a secondary battery to which the present invention is applied is not particularly limited, but an example thereof is a lithium nickel composite oxide .
The lithium nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and other elements (M), and the atomic ratio of the elements is expressed as Li:Ni:Co:M=s:(1-xy):x:y (where 0.93<s<1.03, 0.00≦x≦0.35, 0.03≦y≦0.35, and M is one or more transition metals, alkaline earth metals, base metals, or semimetals). The lithium nickel composite oxide (hereinafter also simply referred to as "composite oxide") has a layered crystal structure, and may include a form of secondary particles formed by aggregation of primary particles.

Fig. 7 is a diagram showing an example of a method for producing a positive electrode active material for a lithium ion secondary battery. As shown in Fig. 7, the method for producing a positive electrode active material includes obtaining a lithium mixture containing a nickel composite oxide, which is a raw material for the positive electrode active material , and a lithium compound (mixing step: step S10), and calcining the lithium mixture (calcining step: step S30). Each step will be described below.

(Mixing process: step S10)
First, a nickel composite oxide and a lithium compound are mixed to obtain a lithium mixture (step S10). In the manufacturing method, a lithium nickel composite oxide having high crystallinity can be obtained with high productivity by firing in a very short time by using a nickel composite oxide as a raw material. Each raw material used in the mixing step (step S10) will be described below.

(Nickel composite oxide)
The nickel composite oxide is a composite oxide containing nickel and other transition metals, alkaline earth metals, base metals, semimetals, etc. In the following description, an oxide containing nickel and cobalt (hereinafter also referred to as "nickel-cobalt composite oxide") will be described as an example of the nickel composite oxide.

The nickel-cobalt composite oxide may contain, in addition to nickel and cobalt, another element M. The element M is at least one element selected from nickel, transition metals other than cobalt, alkaline earth metals, base metals, and semimetals, such as manganese, molybdenum, tungsten, aluminum, silicon, boron, niobium, vanadium, and titanium.

Nickel-cobalt composite oxide may contain, for example, nickel (Ni), cobalt (Co), and element M, and the atomic ratio (molar ratio) of each element may be expressed as Ni:Co:M = (1-x-y):x:y (0.00≦x≦0.35, 0.03≦y≦0.35). The ratio of each element contained in the nickel-cobalt composite oxide is inherited to the lithium-nickel composite oxide. Therefore, the composition of the entire nickel-cobalt composite oxide can be the same as the composition of the metals other than lithium in the lithium-nickel composite oxide to be obtained.

Nickel-cobalt composite oxide can be obtained, for example, by oxidizing nickel-cobalt composite hydroxide, which is used as a precursor of the positive electrode active material. When nickel-cobalt composite oxide is used, the amount of water vapor generated during the firing of the lithium mixture is reduced, the reaction proceeds much more easily, and the firing time can be significantly shortened. An example of a method for producing nickel-cobalt composite oxide is described below. Note that nickel-cobalt composite oxide may also be obtained by other production methods.

Figure 8 shows an example of a method for producing nickel-cobalt composite oxide. For example, nickel-cobalt composite oxide can be obtained by a method including oxidizing and roasting (step S2) nickel-cobalt composite hydroxide obtained by crystallization (step S1). The nickel-cobalt composite hydroxide obtained by crystallization has a uniform composition throughout the particles, and the composition of the final positive electrode active material is also uniform. Note that nickel-cobalt composite oxide may be obtained by a method other than crystallization. Each step of producing nickel-cobalt composite oxide will be described below.

(Crystallization step; step S1)
The nickel-cobalt composite hydroxide is obtained by supplying a neutralizing agent or the like to an aqueous solution containing a salt containing nickel (Ni salt), a salt containing cobalt (Co salt), and a salt containing element M, and crystallizing (step S1). As a specific example, the nickel-cobalt composite hydroxide can be produced by neutralizing an aqueous solution containing a nickel salt, a cobalt salt, and a salt of element M in the presence of a complexing agent such as an ammonium ion donor while stirring the aqueous solution, and performing a crystallization reaction. The nickel-cobalt composite hydroxide obtained by the crystallization method is composed of secondary particles in which primary particles are aggregated, and the positive electrode active material obtained by using this nickel-cobalt composite hydroxide particle as a precursor is also composed of secondary particles in which primary particles are aggregated.
As the metal salt used in preparing the aqueous solution containing the metal salt, for example, sulfates, nitrates, and chlorides of Ni, Co, and element M can be used.

The nickel-cobalt composite hydroxide can contain nickel (Ni), cobalt (Co), and optionally other metals (M), and the molar ratio of each element is preferably expressed as Ni:Co:M = 1-x-y:x:y (0.00≦x≦0.35, 0.03≦y≦0.35). The ratio of each element contained in the nickel-cobalt composite hydroxide is inherited to the nickel-cobalt composite oxide and the lithium-nickel composite oxide. Therefore, the composition of the nickel-cobalt composite hydroxide as a whole can be made the same as the composition of the metals other than lithium in the lithium-nickel composite oxide to be obtained.

The crystallization method is not particularly limited, and for example, a continuous crystallization method, a batch method, etc. can be used. The continuous crystallization method is, for example, a method of continuously recovering nickel-cobalt composite hydroxide overflowing from a reaction vessel, and can easily produce a large amount of nickel-cobalt composite hydroxide having the same composition. In addition, since the nickel-cobalt composite oxide obtained by the continuous crystallization method has a wide particle size distribution, it is possible to improve the packing density of the mixed powder raw material when it is packed into a setter. The particle size of the nickel-cobalt composite hydroxide is, for example, 1 μm or more and 50 μm or less.
The batch method can obtain nickel-cobalt composite hydroxide having a more uniform particle size and a narrow particle size distribution. The nickel-cobalt composite hydroxide obtained by the batch method can react more uniformly with a lithium compound during firing. In addition, the nickel-cobalt composite hydroxide obtained by the batch method can reduce the inclusion of fine powder, which is one of the causes of deterioration of cycle characteristics and output characteristics when used in a secondary battery.

(Oxidation roasting: step S2)
Next, the nickel-cobalt composite hydroxide is subjected to oxidative roasting (heat treatment) to obtain a nickel-cobalt composite oxide (step S2). The conditions of the oxidative roasting are not particularly limited as long as most of the nickel-cobalt composite hydroxide is converted to the nickel-cobalt composite oxide, but for example, the temperature of the oxidative roasting is preferably 600°C or more and 800°C or less. If the temperature of the oxidative roasting is less than 600°C, moisture may remain in the nickel-cobalt composite hydroxide (precursor) and oxidation may not proceed sufficiently. On the other hand, if the temperature of the oxidative roasting exceeds 800°C, the composite oxides may be bonded together to form coarse particles. In addition, if the temperature of the oxidative roasting is too high, a lot of energy is used, so productivity decreases from the viewpoint of cost, and it is not industrially suitable.

The time for oxidizing roasting is preferably, for example, 0.5 hours or more and 3.0 hours or less. If the time for oxidizing roasting is less than 0.5 hours, the oxidation of the nickel-cobalt composite hydroxide may not proceed sufficiently. On the other hand, if the time for oxidizing roasting exceeds 3.0 hours, the energy cost increases, the productivity decreases, and it is not industrially suitable.

(Lithium compounds)
Returning to Fig. 7, the lithium compound to be mixed with the nickel composite oxide (nickel-cobalt composite oxide shown in Fig. 8) will be described. The lithium compound is not particularly limited, and any known lithium compound can be used, such as lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate, or a mixture thereof. Of these, lithium hydroxide and lithium carbonate are preferably used.

In addition, lithium hydroxide is preferred as the lithium compound from the viewpoint of increasing reactivity during sintering and shortening the firing time.

As the lithium hydroxide, a hydrate such as lithium hydroxide monohydrate ( _LiOH.H2O ) or an anhydrous such as anhydrous lithium hydroxide (LiOH) can be used. Among them, anhydrous lithium hydroxide is preferred, and lithium hydroxide having a moisture content of 1.5% or less and a total carbon content of 1.0% or less is more preferred.
Lithium hydroxide having a moisture content of 1.5% or less and a total carbon content of 1.0% or less can be obtained, for example, by heat treating lithium hydroxide hydrate (LiOH.H ₂ O). When such lithium hydroxide is used, the generation of moisture in the firing step (step S30) is suppressed, thereby accelerating the synthesis reaction of the lithium nickel composite oxide and shortening the firing time.

(Lithium mixture)
The mixing ratio of the nickel composite oxide and the lithium compound shown in the process diagram of FIG. 7 is such that the ratio (Li/Me ratio) of the total number of atoms (Me) of nickel, cobalt, and aluminum in the nickel composite oxide to the number of atoms (Li) of lithium is in the range of more than 0.93 and less than 1.03. If the Li/Me ratio is 0.93 or less, some of the nickel composite oxide may remain unreacted in the firing step (step S30), and sufficient battery performance may not be obtained. On the other hand, if the Li/Me ratio is 1.03 or more, sintering may be promoted in the firing step (step S30), the fired product may become hard and difficult to crush, or the particle size and crystallite size of the lithium nickel composite oxide obtained may become too large, and sufficient battery performance may not be obtained. The role of the hopper (FIG. 1) of the present invention is to keep this mixing ratio (Li/Me ratio) unchanged before and after supplying it to the firing device 1 (FIGS. 2-3) of the present invention.

The required Li/Me ratio value varies depending on the configuration of the secondary battery, and the Li/Me ratio value can be set appropriately within the above range according to the requirements. The Li/Me ratio value may be, for example, 0.95 or more and less than 1.03, 1.0 or more and less than 1.03, or more than 1.0 and less than 1.03.

In addition, since the Li/Me ratio does not change much before and after the calcination process (step S30), the Li/Me ratio in the lithium mixture is almost maintained in the lithium nickel composite oxide. Therefore, the mixing ratio of the nickel composite oxide and the lithium compound can be appropriately adjusted so that it is the same as the Li/Me ratio in the lithium nickel composite oxide to be obtained.

A common mixer can be used to mix the nickel composite oxide and the lithium compound, such as a shaker mixer, a Loedige mixer, a Julia mixer, or a V blender. This mixing should be sufficient so long as the nickel composite oxide is not destroyed. If the mixing is not sufficient, the Li/Me ratio may vary between individual particles, resulting in problems such as insufficient battery characteristics.

When the Li/Me ratio is appropriately mixed as described above, the mixture is filled into a flexible container (reference numeral 80 in FIG. 3) or the like. Then, the mixed powder raw material is supplied from the flexible container 80 to the hopper 50 in the supply unit 10 of the firing device 1 shown in FIG. 5 before the firing process.
Furthermore, the mixed powder raw material is charged from the hopper 50 to the setter S of the firing device 1 as the material to be fired, and the process from firing to discharge is carried out.

(Baking: Step S30)
In the firing step (S30) shown in the process diagram of Fig. 7, the obtained sintered material is fired in an oxygen atmosphere at 650°C to 1100°C (sintering step, step S30). By firing the sintered material, the nickel-cobalt composite oxide reacts with the lithium compound to produce a lithium-nickel composite oxide. By firing the above-mentioned sintered material at the above temperature, a lithium-nickel composite oxide (positive electrode active material) having high crystallinity equal to or higher than that of the conventional material can be obtained in a much shorter time than the conventional firing time.

The firing conditions are not particularly limited as long as the nickel composite oxide and the lithium compound in the fired material react to form a lithium nickel composite oxide. For example, it is preferable to gradually increase the temperature from room temperature and maintain it at a temperature range of 650°C to 1100°C for 3 hours or less. If the firing temperature is less than 650°C, lithium diffusion may not be sufficient, unreacted lithium compound particles may remain, or the crystal structure of the lithium nickel composite oxide may not be fully aligned, so that a secondary battery using the obtained positive electrode active material may not have sufficient battery characteristics. On the other hand, if the firing temperature is more than 1100°C, intense sintering may occur between the lithium nickel composite oxide particles and abnormal grain growth may occur, resulting in a decrease in the specific surface area. In addition, the specific surface area of the positive electrode active material may decrease, increasing the resistance of the positive electrode in the secondary battery and decreasing the battery capacity.

The firing temperature can be adjusted as appropriate depending on the composition and shape of the material to be fired. For example, when the other element M of the nickel composite oxide is aluminum (Al) and the lithium compound is lithium hydroxide, the firing temperature may be in the range of 700°C to 800°C, and is preferably in the range of 730°C to 770°C, and this temperature can be maintained for about 2 to 5 hours. When the other element is manganese and the lithium compound is lithium carbonate, the firing temperature is in the range of about 850 to 1050°C, and this temperature can be maintained for about 6 to 15 hours.

The time for which the material to be fired is held at the firing temperature (hereinafter also referred to as the "holding time") is not particularly limited as long as a lithium nickel composite oxide having high crystallinity is formed, but may be, for example, 5 hours or less, and preferably 3 hours or less. The shorter the firing time, the higher the productivity. The lower limit of the firing time may be, for example, 2.5 hours or more.

The atmosphere during firing is preferably an oxidizing atmosphere having an oxygen concentration equal to or higher than that of the air atmosphere, more preferably an atmosphere having an oxygen concentration of 80% by volume or more, and may be 100% by volume. In other words, the atmosphere during firing is preferably an oxygen stream. If the oxygen concentration is less than 80% by volume, it may be impossible to supply the amount of oxygen necessary for the reaction between the nickel composite oxide and the lithium compound, and the lithium nickel composite oxide may not be sufficiently formed.

There are no particular limitations on the firing furnace, and any furnace capable of heating in an oxygen stream may be used, including vertical furnaces, rotary hearth furnaces, and roller hearth kilns. Of these, it is preferable to use a roller hearth kiln from the standpoint of capital investment and running costs.

(Lithium nickel composite oxide treatment steps S40 to S60)
FIG. 9 is a diagram showing an example of a process for treating the lithium nickel composite oxide obtained after calcination. As shown in the figure, the method for producing a positive electrode active material according to this embodiment includes crushing the lithium nickel composite oxide (calcined product) obtained after the calcination process (step S30) to obtain a crushed product (lithium nickel composite oxide powder) (crushing process: step S40), washing the crushed product with water and filtering it (water washing process: step S50), and drying the washed lithium nickel composite oxide (drying process: step S60). The method for producing a positive electrode active material according to this embodiment does not need to include the above-mentioned crushing (step S40), water washing (step S50), and drying process (step S60), or may include at least one of these three processes. Each process will be described below.

(Crushing process: step S40)
The lithium nickel composite oxide (calcined product) obtained after the calcination (step S30) may be further crushed (step S40). By crushing, secondary particles of the lithium nickel composite oxide in which aggregation or slight sintering has occurred can be separated from each other, and the average particle size and particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range. In addition, since the obtained calcined product generates bonds between particles during the calcination reaction, it is preferable to crush it (step S40). Note that, the crushing refers to an operation of inputting mechanical energy into an aggregate consisting of a plurality of secondary particles generated by sintering necking between secondary particles during calcination, separating the secondary particles themselves almost without destroying them, and loosening the aggregates.

As a method of crushing, known means can be used, such as a pin mill, a hammer mill, or a crusher with a classification function. In this case, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

(Water washing process: step S50)
Next, the crushed material obtained may be washed with water (step S50). By washing the lithium nickel composite oxide (crushed material) with water, excess lithium and impurities on the surface of the lithium nickel composite oxide particles are removed, and a positive electrode active material for a lithium ion secondary battery having a higher capacity and higher thermal stability can be obtained. Here, the washing method is not particularly limited, and a known technique can be used.

As a method of washing with water, for example, it is preferable to add the lithium nickel composite oxide (crushed material) to water to make a slurry, and stir the slurry so that excess lithium on the surface of the lithium nickel composite oxide particles is sufficiently removed. After stirring, the mixture is separated into solid and liquid, and dried (step S60) as described below to obtain the lithium nickel composite oxide.

As for the slurry concentration, it is preferable to add 0.5 to 2 parts by mass of the lithium nickel composite oxide (crushed material) per 1 part by mass of water. If the amount of crushed material added per 1 part by mass of water exceeds 2 parts by mass as the slurry concentration, the viscosity becomes very high and stirring becomes difficult, and the alkalinity in the liquid is high, so that the dissolution rate of the attached matter slows down due to the equilibrium relationship, and even if peeling occurs, separation from the powder may become difficult. On the other hand, if the amount of crushed material added per 1 part by mass of water as the slurry concentration is less than 0.5 parts by mass, the slurry is too dilute, so the amount of lithium eluted is large, and lithium is also released from the crystal lattice of the lithium nickel composite oxide (crushed material), making the crystals more likely to collapse, and the high pH aqueous solution (slurry) absorbs carbon dioxide gas in the air, causing lithium carbonate to be reprecipitated on the surface of the lithium nickel composite oxide.

The cleaning liquid used in the water washing step (step S50) is not particularly limited, and may be, for example, water. When water is used, for example, water with an electrical conductivity measurement of less than 10 μS/cm is preferred, and water with an electrical conductivity measurement of 1 μS/cm or less is more preferred. When water with an electrical conductivity measurement of less than 10 μS/cm is used, it is possible to further suppress the deterioration of battery performance due to the adhesion of impurities to the positive electrode active material.

When subjecting the above slurry to solid-liquid separation, it is preferable that there is little water remaining on the surface of the lithium nickel composite oxide particles. If there is a lot of water remaining, lithium dissolved in the liquid (slurry) may be reprecipitated, and the amount of lithium present on the surface of the lithium nickel composite oxide after drying (step S60) may increase. For solid-liquid separation, a commonly used centrifuge, filter press, etc. may be used.

(Drying process: step S60)
After washing with water (step S50), the lithium nickel composite oxide (positive electrode active material) may be obtained by drying (step S60). The drying conditions are not particularly limited as long as at least a part of the moisture in the lithium nickel composite oxide is removed. The drying step (step S60) is preferably performed at a predetermined temperature using a dryer that can control the lithium nickel composite oxide (powder) after filtration (solid-liquid separation) under a gas atmosphere that does not contain compound components containing carbon and sulfur, or under a vacuum atmosphere.

The drying temperature is preferably 80°C or higher and 550°C or lower, more preferably 120°C or higher and 350°C or lower. When the drying temperature is 80°C or higher, the positive electrode active material after washing with water (step S50) can be quickly dried, and the occurrence of a gradient of lithium concentration between the particle surface and the inside of the particle can be suppressed. On the other hand, when the drying temperature exceeds 550°C, it is expected that some lithium is desorbed and the state is close to the charged state. Therefore, the crystal structure near the surface of the lithium nickel composite oxide collapses from the site where lithium is desorbed, which may cause a decrease in the battery characteristics in the secondary battery.
Moreover, the drying temperature is more preferably 120° C. or higher and 350° C. or lower from the viewpoints of productivity and heat energy costs.

(4) Positive electrode active material The above-mentioned method for producing a positive electrode active material can produce a lithium nickel composite oxide (positive electrode active material) with excellent crystallinity with high productivity by firing in a very short time. The characteristics of the lithium nickel composite oxide (positive electrode active material) obtained by this production method will be described below.

(composition)
The lithium nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and an arbitrary element (M), and the molar ratio of each metal element is expressed as Li:Ni:Co:M=s:(1-xy):x:y (where 0.93<s<1.03, 0.00≦x≦0.35, 0.03≦y≦0.35, and M is one or more of a transition metal, an alkaline earth metal, a base metal, or a semimetal).

(Lithium seat occupancy rate)
The lithium nickel composite oxide has a lithium site occupancy rate of 95% or more, preferably 96% or more, and more preferably 97% or more, of the 3a site, which is a lithium-dominated layer obtained by Rietveld analysis of an X-ray diffraction pattern. When the lithium site occupancy rate is within the above range, the sintering reaction between the precursor and the lithium compound is sufficiently carried out in the firing step (step S30), and the lithium nickel composite oxide has high crystallinity. When a lithium nickel composite oxide with high crystallinity is used as a positive electrode active material for a secondary battery, it shows excellent battery characteristics (high battery capacity, etc.).

(amount of dissolved lithium)
The lithium nickel composite oxide has an amount of lithium eluted into water when the lithium nickel composite oxide is dispersed in water (amount of eluted lithium) of, for example, 0.11% by mass or less, preferably 0.10% by mass or less, and more preferably 0.05% by mass or less, based on the total amount of the lithium nickel composite oxide. The amount of eluted lithium can be measured by neutralization titration. When the water washing step (step S50) is performed, the amount of eluted lithium is a value measured using the lithium nickel composite oxide obtained after the water washing (step S50) and drying (step S60).

The eluted lithium is thought to originate from unreacted lithium compounds present on the particle surface of the lithium nickel composite oxide (positive electrode active material) and from excess lithium present in the crystals. In other words, the amount of eluted lithium can be used as an indicator of the remaining amount of unreacted lithium compounds originating from the raw materials, and it can be said that the smaller the amount of eluted lithium, the smaller the amount of unreacted lithium compounds remaining, and the more the sintering reaction between the precursor and the lithium compounds has progressed. In addition, the smaller the amount of eluted lithium, the more it is possible to suppress gelling of the positive electrode composite paste.

The amount of eluted lithium is calculated by dispersing 15 g of lithium nickel composite oxide in 75 ml of pure water, leaving it to stand for 10 minutes, diluting 10 ml of the supernatant with 50 ml of pure water, and measuring the amount of lithium eluted in the water (amount of eluted lithium) by neutralization titration with the addition of 1 mol/L hydrochloric acid.

(Initial charge/discharge efficiency)
The initial charge-discharge efficiency (initial discharge capacity/initial charge capacity) of the 2032-type coin battery CBA (see FIG. 9) for evaluation, which is produced using lithium nickel composite oxide as a positive electrode active material, is, for example, 85% or more, preferably 89% or more, and more preferably 89.5% or more. When the initial charge-discharge efficiency is within the above range, the sintering reaction between the precursor and the lithium compound is sufficiently carried out in the firing step (step S30), and the lithium nickel composite oxide has high crystallinity. The initial discharge capacity efficiency is a value measured by leaving the coin battery CBA used in the examples for about 24 hours after production, charging it to a cutoff voltage of 4.3 V with a current density of 0.1 mA/cm ² to the positive electrode after the open circuit voltage OCV (Open Circuit Voltage) has stabilized, and discharging it to a cutoff voltage of 3.0 V after a 1-hour pause.

(5) Lithium-ion secondary battery The lithium-ion secondary battery described below is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode is obtained by using the positive electrode active material obtained by the above-mentioned manufacturing method. Note that secondary batteries other than the above may include, for example, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, or may include a positive electrode, a negative electrode, and a solid electrolyte. In addition, the secondary battery may be composed of the same components as known lithium-ion secondary batteries.
Hereinafter, each of the constituent materials of a secondary battery using a non-aqueous electrolyte solution and a method for producing the same will be described.

(Positive electrode)
The positive electrode is formed using the positive electrode active material described above.
First, the positive electrode active material, conductive material, and binder are mixed, and activated carbon and a solvent for viscosity adjustment, etc. are added as necessary, and the mixture is kneaded to prepare a positive electrode composite paste. Note that the constituent materials of the positive electrode composite paste are not particularly limited, and materials equivalent to known positive electrode composite pastes may be used.
The mixing ratio of each material in the positive electrode composite paste is not particularly limited and is appropriately adjusted according to the required performance of the secondary battery. The mixing ratio of the materials can be in the same range as that of the positive electrode composite paste of a known secondary battery. For example, when the total mass of the solid content of the positive electrode composite excluding the solvent is 100 parts by mass, the content of the positive electrode active material may be 60 parts by mass or more and 95 parts by mass or less, the content of the conductive material may be 1 part by mass or more and 20 parts by mass or less, and the content of the binder may be 1 part by mass or more and 20 parts by mass or less.
As the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, Ketjen black, and other carbon black-based materials can be used.
The binder serves to bind the active material particles together, and examples of the binder that can be used include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, and polyacrylic acid.
If necessary, a solvent for dispersing the positive electrode active material, conductive material, and activated carbon and dissolving the binder may be added to the positive electrode mixture paste. Specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) may be used as the solvent. Activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.
Next, the obtained positive electrode composite paste is applied to the surface of a current collector made of, for example, aluminum foil, dried, and the solvent is removed to prepare a sheet-shaped positive electrode. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. The sheet-shaped positive electrode can be cut to an appropriate size according to the desired battery and used to prepare the battery.

(Negative electrode)
The negative electrode may be made of metallic lithium, a lithium alloy, etc. The negative electrode may be made by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, adding an appropriate solvent to the negative electrode mixture to make a paste, applying the paste to the surface of a metal foil current collector such as copper, drying the paste, and compressing the paste to increase the electrode density as necessary.
As the negative electrode active material, for example, natural graphite, artificial graphite, a calcined organic compound such as phenolic resin, or a powder of a carbon material such as coke can be used. As the negative electrode binder, a fluorine-containing resin such as PVDF can be used, as in the positive electrode. As the solvent for dispersing these active materials and binders, an organic solvent such as N-methyl-2-pyrrolidone can be used.

(Separator)
A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte. A thin membrane made of polyethylene, polypropylene, or the like and having many minute pores can be used as the separator.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, for example, a non-aqueous electrolytic solution can be used.
As the non-aqueous electrolyte, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Alternatively, as the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an ionic liquid can be used. Note that the ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and is liquid even at room temperature.
The organic solvent may be one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. Two or more of these organic solvents may be used alone or in combination.
The supporting salt may be LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , or a composite salt thereof. Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.
The non-aqueous electrolyte may be a solid electrolyte. The solid electrolyte has a property of being able to withstand high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.
Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.
The oxide-based solid electrolyte is not particularly limited, and for example, one that contains oxygen (O) and has lithium ion conductivity and electronic insulation properties can be suitably used. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO ₄ , Li ₄ SiO ₄ -Li ₃ VO ₄ , Li ₂ O-B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O ₃ -ZnO, Li _1+X Al _X Ti _2-X (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦ _X ≦ ₁ ), _LiTi2 ( _PO4 ) _{3 , Li3XLa2 /3-XTiO3 ( 0 ≦ X} ≦ ₂ / _{3 )} , _Li5La3Ta2O12 , _{Li7La3Zr2O12 ,} Li6BaLa2Ta2O12, _{Li3.6Si0.6P0.4O4} , _{and the like} can be used.
The sulfide-based solid electrolyte is not particularly limited, and for example, one that contains sulfur (S) and has lithium ion conductivity and electronic insulation properties can be suitably used. As the sulfide-based solid electrolyte, for example, one or more types selected from Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ S ₅ , LiI-Li ₂ S-B ₂ S ₃ , Li ₃ PO ₄ -Li ₂ S-Si ₂ S, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , LiPO ₄ -Li ₂ S-SiS, LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ and the like can be used.
The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity, and examples of the organic solid electrolyte that can be used include polyethylene oxide, polypropylene oxide, copolymers thereof, etc. The organic solid electrolyte may also contain a supporting salt (lithium salt).

(Battery shape and configuration)
The shape of the lithium ion secondary battery composed of the above positive electrode, negative electrode, and non-aqueous electrolyte can be various, such as a cylindrical type, a laminated type, etc. Regardless of the shape, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte solution, the positive electrode current collector and the positive electrode terminal connected to the outside, and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collector lead or the like, and the battery is sealed in a battery case to complete the lithium ion secondary battery. In addition, when a solid electrolyte is used, the solid electrolyte may also serve as a separator.

(6) Example of Lithium Ion Secondary Battery Hereinafter, an example of a lithium ion secondary battery using a positive electrode active material obtained using the illustrated hopper 50 and sintering device 1 will be described.
The performance (stability of paste, initial discharge capacity, positive electrode resistance, discharge capacity retention rate) of the positive electrode active material of (4) and the lithium ion secondary battery using this positive electrode active material was measured. In this example, each sample of special grade reagents manufactured by Wako Pure Chemical Industries, Ltd. was used for the production of the composite hydroxide, the positive electrode active material, and the secondary battery.

(Production and Evaluation of Evaluation Secondary Batteries)
A 2032-type coin-type battery CBA (see FIG. 10) was produced by the following method, and the battery characteristics of the positive electrode active material were evaluated.

(Preparation of coin cell battery)
52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and pressed at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to prepare a positive electrode PE (electrode for evaluation). The prepared positive electrode PE was dried in a vacuum dryer at 120 ° C. for 12 hours. Using the dried positive electrode D1, negative electrode D3, separator D2, and electrolyte, a coin-type battery CBA shown in FIG. 8 was prepared in a glove box in an Ar atmosphere with a dew point controlled at −80 ° C.
For the negative electrode D3, a negative electrode sheet was used in which graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride were applied to copper foil, punched into a disk shape with a diameter of 14 mm, and an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiPF ₆ as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. For the separator D2, a polyethylene porous film with a film thickness of 25 μm was used. In addition, the coin-type battery CBA had a gasket D4 and a wave washer, and was assembled into a coin-shaped battery with a positive electrode can D5 and a negative electrode can D6.

(Initial discharge capacity)
The initial discharge capacity was determined by leaving the coin-type battery CBA for about 24 hours after production, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, charging the battery with a current density of 0.1 mA/cm2 to ^a cut-off voltage of 4.3 V to the positive electrode, resting for 1 hour, and discharging the battery to a cut-off voltage of 3.0 V. The capacity was defined as the initial discharge capacity.

(Lithium dissolution titration)
15 g of the obtained lithium nickel composite oxide (positive electrode active material) was dispersed in 75 ml of pure water, and then the dispersion was left to stand for 10 minutes. 10 ml of the supernatant was diluted with 50 ml of pure water, and the amount of lithium dissolved in the water (amount of dissolved lithium) was measured by neutralization titration by adding 1 mol/L of hydrochloric acid.

(Lithium content)
The lithium content was determined by analyzing each metal element and calculating the ratio of lithium to other metals (Li/Me ratio).
The analysis of each metal element was carried out using ICP, and the analytical samples were prepared by dissolving the fired products of each of the Examples and Comparative Examples.

Example 1
A nickel composite oxide obtained by oxidizing and roasting a nickel composite hydroxide having a composition ratio of Ni:Co:Al=88:9:3 in a rotary kiln was mixed with lithium hydroxide having a moisture content of 1.5% or less and a total carbon content of 1.0% or less so that the Li/Me ratio was 1.03 to prepare a lithium mixture (which becomes the material to be fired). The maximum angle of repose of the prepared lithium mixture was 65°.
This lithium mixture was sintered using a sintering device 1 (FIGS. 5 and 6) to obtain a sintered product. The hopper 50 used was the one shown in FIG. 1, in which the drop distance h between the lower end of the internal cone 71 and the lower end of the cone portion 52 was 1000 mm, the opening angle a of the internal cone 71 and the opening angle a of the cone portion 52 were 40°, and the hopper was made of SUS304. 48 kg of the lithium mixture was filled into a box-shaped setter S by using a filling machine from the hopper 50, and sintered at 760°C using a sintering furnace 2 (roller hearth kiln), to obtain 12 sintered products.
In this Example 1, a small solidified layer having a thickness of about 20 mm was formed on the inner surface of the cone portion 52, but the solidified layer was broken by vibration using a bridge breaker installed in the hopper 50, and the entire amount of the lithium mixture was discharged. Table 1 shows an evaluation of the occurrence of a solidified layer and the variation in the mixture ratio.
The twelve pieces of the fired material were crushed to 1 mm or less, and the lithium content of each of the twelve pieces was analyzed. The twelve pieces of the obtained positive electrode active material and the twelve pieces were mixed and homogenized to prepare a coin-type battery, and the initial discharge capacity was measured. The Li/Me ratio and the initial discharge capacity of the fired material are shown in Table 2.

Example 2
The same procedure was followed as in Example 1, except that the opening angle a of the cone portion 52 and the internal cone 71 of the hopper 50 was set to 30°. No solidified layer was observed inside the hopper 50, and the entire amount of the lithium mixture could be discharged. The evaluation of the occurrence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

Example 3
The same procedure was followed as in Example 2, except that the distance between the bottom end of the internal cone 71 and the bottom end of the cone portion 52 was set to 700 mm. No solidified layer was observed in the hopper 50, and the entire amount of the lithium mixture could be discharged naturally. Evaluations regarding the presence or absence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

Example 4
The composition ratio of the nickel composite oxide was Ni:Co:Al=91:4:5, the Li/Me ratio was 1.02, and the sintering temperature was 745°C, but the same as in Example 1. The maximum angle of repose of the lithium mixture produced was 63°. A solidified layer with a thickness of about 15 mm was formed on the inner surface of the cone part 52, and the solidified layer was finally broken by vibration using a bridge breaker installed in the hopper, and the entire amount of the lithium mixture was discharged. Table 1 shows the evaluation of the occurrence of a solidified layer and the variation in the mixing ratio. Table 2 shows the Li/Me ratio and initial discharge capacity of the sintered product.

Example 5
The same procedure was followed as in Example 4, except that the opening angle of the cone portion 52 and the internal cone 71 of the hopper 50 was set to 30°. No solidified layer was observed in the cone portion 52, and the entire amount of the lithium mixture could be discharged naturally. The evaluation of the occurrence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

Example 6
The same procedure was followed as in Example 5, except that the distance between the bottom end of the internal cone 71 and the bottom end of the cone portion 52 was set to 700 mm. No solidified layer was observed in the cone portion 52, and the entire amount of the lithium mixture could be discharged naturally. The evaluation of the occurrence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

(Comparative Example 1)
The same procedure was followed as in Example 1, except that the opening angle of the cone portion 52 installed in the hopper 50 was set to 50°. A solidified layer of about 150 mm thickness was formed on the upper part of the cone portion 52, and the solidified layer was finally broken by the bridge breaker, allowing the entire amount of the lithium mixture to be discharged. Evaluations regarding the occurrence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

(Comparative Example 2)
The same procedure was followed as in Example 4, except that the opening angle of the cone portion 52 and the internal cone 71 installed in the hopper 50 was set to 50°. A solidified layer with a thickness of about 140 mm was formed on the top of the cone portion 52, and the solidified layer was finally broken by the bridge breaker, allowing the entire amount of the lithium mixture to be discharged. Evaluations regarding the occurrence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

(Comparative Example 3)
The same procedure was followed as in Example 1, except that the internal cone 71 was not installed in the hopper 50. The charge drop of the lithium mixture in the hopper 50 was 1960 mm, which was the total height of the hopper. A solidified layer of about 20 mm in thickness was formed on the inner surface of the hopper 50, and the solidified layer was finally broken by vibration using a bridge breaker installed in the hopper, and the entire amount of the lithium mixture was discharged. Table 1 shows the evaluation of the occurrence of a solidified layer and the variation in the mixture ratio. Table 2 shows the Li/Me ratio and initial discharge capacity of the fired product.

(Comparative Example 4)
The same procedure was followed as in Example 4, except that the internal cone 71 was not installed in the hopper 50. The charge height of the lithium mixture in the hopper 50 was 1960 mm, which was the total height of the hopper. A solidified layer of about 15 mm in thickness was formed on the inner surface of the hopper 50, and the solidified layer was finally broken by vibration using a bridge breaker installed in the hopper, and the entire amount of the lithium mixture was discharged. Table 1 shows the evaluation of the occurrence of a solidified layer and the variation in the mixture ratio. Table 2 shows the Li/Me ratio and initial discharge capacity of the fired product.

(Comparative Example 5)
The same procedure was followed as in Example 1, except that the distance between the bottom end of the internal cone 71 and the bottom end of the cone portion 52 was set to 1100 mm. No solidified layer was observed inside the hopper, and the entire amount of the lithium mixture could be discharged naturally. Evaluations regarding the presence or absence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

(Comparative Example 6)
The same procedure was followed as in Example 4, except that the distance between the bottom end of the internal cone 71 and the bottom end of the cone portion 52 was set to 1100 mm. No solidified layer was observed inside the hopper, and the entire amount of the lithium mixture could be discharged naturally. The evaluation of the occurrence of a solidified layer and the variation in the mixture ratio are shown in Table 1. The Li/Me ratio and initial discharge capacity of the fired product are shown in Table 2.

(Evaluation Results)
(1) Variation in Li/Me ratio of the fired product In Examples 1 to 6, the opening angle a of the cone portion 52 and the internal cone 71 of the hopper 50 is an angle of a≦180-2b-10, which makes it difficult for a solidified layer to form. In addition, the drop distance h within the hopper is 1000 mm or less, which reduces the drop when the lithium mixture is added, thereby reducing the variation in the Li/Me ratio of the fired product. As a result, a homogeneous positive electrode active material with high battery characteristics is obtained.
On the other hand, in Comparative Examples 1 and 2, the opening angle a of the cone portion 52 is large, so a thick solidified layer is formed, and as a result, the Li/Me ratio of the fired product varies widely. In Comparative Examples 3 and 4, the internal cone 71 is not installed in the hopper 50, so the drop of the lithium mixture when it is poured into the hopper 50 is large, and as a result, the Li/Me ratio varies widely. In Comparative Examples 5 and 6, the distance between the lower end of the internal cone 71 and the lower end of the cone portion 52 exceeds 1000 mm, so the drop of the fired product to the cone portion 52 is large, and as a result, the Li/Me ratio of the fired product varies widely.

(2) Initial Discharge Capacity A comparison is made between an example and a comparative example having a common composition ratio.
Examples 1 to 3 in which Ni:Co:Al is 88:9:3 are compared with Comparative Examples 1, 3, and 5.
In Examples 1 to 3, the variation in the Li/Me ratio of the fired product was reduced, and therefore the initial discharge capacity was 210.4 to 211.2. In contrast, in Comparative Example 1, the variation in the Li/Me ratio was increased, and therefore the initial discharge capacity was 205.8. In Comparative Example 3, the difference in the lithium mixture was increased, and therefore the variation in the Li/Me ratio was increased, and therefore the initial discharge capacity was 209.8. In Comparative Example 5, the difference in the Li/Me ratio from the inner cone 71 to the cone portion 52 was increased, and therefore the variation in the Li/Me ratio was increased, and therefore the initial discharge capacity was 209.9. Thus, Examples 1 to 3 achieved higher initial discharge capacities.

Examples 4 to 7 in which the Ni:Co:Al ratio is 91:4:5 are compared with Comparative Examples 2, 4, and 6.
In Examples 4 to 7, the variation in the Li/Me ratio of the fired product was reduced, and therefore the initial discharge capacity was 213.5 to 214.0. In contrast, in Comparative Example 2, the variation in the Li/Me ratio was increased, and therefore the initial discharge capacity was 209.3. In Comparative Example 4, the difference in the lithium mixture was increased, and therefore the variation in the Li/Me ratio was increased, and therefore the initial discharge capacity was 212.6. In Comparative Example 6, the difference in the Li/Me ratio from the inner cone 71 to the cone portion 52 was increased, and therefore the variation in the Li/Me ratio was increased, and therefore the initial discharge capacity was 213.0. Thus, Examples 4 to 7 achieved higher initial discharge capacities.

The hopper of the present invention can be used for any mixed powder raw material as long as it supplies a mixed powder raw material containing a plurality of powders. Therefore, the hopper of the present invention can be used not only for raw materials for positive electrode active materials for secondary batteries, but also for raw materials for positive electrode active materials for lithium ion secondary batteries.
The firing apparatus of the present invention can be used for firing any object to be fired. Therefore, the firing apparatus of the present invention can be used not only for raw materials for positive electrode active materials for secondary batteries, but also for raw materials for positive electrode active materials for lithium ion secondary batteries.

REFERENCE SIGNS LIST 1 Firing device 2 Firing furnace 5 Conveying section 10 Supply section 20 Discharge section 21 Crushing mechanism S Setter 50 Hopper 51 Hopper section 52 Cone section 53 Discharge section 61 Partition plate 71 Inner cone

Claims (7)

A hopper for supplying a mixed powder raw material containing a nickel composite oxide and a lithium compound having different physical properties,
A cylindrical hopper portion,
A cone-shaped portion connected to a lower end of the hopper portion;
An internal cone disposed inside the hopper section and above the cone section;
A discharge portion connected to a lower end of the cone portion,
The opening angle a of the cone portion and the opening angle a of the inner cone are angles expressed by the formula (1) when the maximum value of the angle of repose of the mixed powder raw material is b,
a≦180-2b-10...Formula (1),
A hopper characterized in that the distance between the lower end of the cone portion and the lower end of the internal cone is a maximum drop distance, which is set to within 1000 mm. The inner cone is arranged in a vertical direction in multiple stages,
2. A hopper as described in claim 1, characterized in that the vertical distance between the lower end of the cone section and the lower end of the lowest internal cone and the vertical distance between the lower ends of each internal cone are maximum fall distances, which are set to within 1000 mm. A plurality of setters in which objects to be fired are filled;
A supply unit that supplies an object to be sintered to each setter;
a firing furnace for firing the objects to be fired supplied to each setter;
a conveying section that conveys each setter from the supply section to the firing furnace and conveys each setter containing the fired product fired in the firing furnace out of the firing furnace;
a discharge section for discharging the fired material from each of the setters,
3. An apparatus for sintering a positive electrode active material for a secondary battery, comprising: a hopper according to claim 1 or 2, which is used as a device for supplying a material to be sintered in said supply section. The discharge section is
4. The apparatus for sintering a positive electrode active material for a secondary battery according to claim 3, further comprising a crushing mechanism for crushing the sintered products removed from said plurality of setters. The crushing mechanism is a roll crusher,
5. The apparatus for baking a positive electrode active material for a secondary battery according to claim 4 , further comprising a cooling mechanism for cooling the roll which comes into contact with the high-temperature baked material. At least one of the supply unit, the sintering furnace, the discharge unit, or the crushing mechanism,
5. The apparatus for baking a positive electrode active material for a secondary battery according to claim 4 , further comprising a mechanism for maintaining an oxygen concentration in the working space at 80% or more. The fired product is
The firing apparatus for a positive electrode active material for a secondary battery according to any one of claims 3 to 6, characterized in that the lithium nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and another element (M), and the atomic ratio of each element is expressed as Li:Ni:Co:M=s:(1-x-y):x:y (where 0.93<s<1.03, 0.00≦x≦0.35, 0.03≦y≦0.35, and M is one or more transition metals, alkaline earth metals, base metals, or semimetals).

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