JP2020047534A - Nickel complex compound particle, manufacturing method thereof, and manufacturing method of cathode active material for lithium ion secondary battery - Google Patents

Abstract

To provide a nickel complex compound particle, a manufacturing method thereof, and a manufacturing method of a cathode active material for a lithium ion secondary battery, capable of achieving optimum states of addition amount of aluminum and distribution of aluminum.SOLUTION: The nickel complex compound particle includes at least nickel and aluminum and is a precursor of a cathode active material for a lithium ion secondary battery optionally including cobalt. A mole ratio of each element is Ni:Co:Al=1-x-y:x:y (where, 0≤x≤0.2, 0<y≤0.1). An aluminum high-concentration region with an aluminum concentration higher than the whole average value of the nickel complex compound particle exists in the nickel complex compound particle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nickel composite compound particle, a method for producing the same, and a method for producing a positive electrode active material for a lithium ion secondary battery.

  In recent years, with the spread of portable information terminals such as smartphones and tablet PCs, the development of small and lightweight lithium ion secondary batteries having high energy density has been strongly desired. Also, there is a strong demand for the development of a high-output secondary battery as a battery for electric vehicles such as hybrid vehicles.

  As a secondary battery satisfying such a demand, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution and the like, and a material capable of removing and inserting lithium is used as an active material of the negative electrode and the positive electrode.

  Research and development of lithium ion secondary batteries are currently being actively conducted. Among them, lithium ion secondary batteries using a layered or spinel type lithium metal composite oxide as a positive electrode active material are 4 V class. Since a high voltage can be obtained, the battery has been put to practical use as a battery having a high energy density.

The positive electrode active materials that have been mainly proposed so far include a lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, a lithium nickel composite oxide (LiNiO ₂ ) using nickel that is cheaper than cobalt, A lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), a lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), and the like can be given.

  Among them, lithium nickel composite oxides are attracting attention as materials capable of obtaining high battery capacity. However, when a lithium-ion secondary battery is manufactured using a material synthesized purely with pure Ni as a positive electrode active material, the lithium-nickel composite oxide is inferior to the cobalt-based battery in terms of cycle characteristics, and may be used in a high-temperature environment. However, it has a disadvantage that battery performance is relatively easily impaired when stored.

In order to solve such a drawback, for example, in Patent Document 1, Li _x Ni _a Co _{b Mc} O ₂ (0.8) is used for the purpose of improving the self-discharge characteristics and the cycle characteristics of a lithium ion secondary battery. ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al , V, Mn, at least one element selected from Fe, Cu and Zn). In particular, a material using Al as the M element (hereinafter sometimes referred to as NCA) has been put to practical use as a positive electrode active material having a high battery capacity.

  NCA used as a positive electrode active material of a lithium ion secondary battery is, for example, a nickel-cobalt-aluminum composite hydroxide obtained by mixing and reacting an alkali hydroxide with an aqueous solution containing nickel, cobalt and aluminum in a crystallization step. Is used as a positive electrode active material precursor, mixed with a lithium-containing compound such as lithium hydroxide or lithium carbonate, and fired. The aluminum used here is added in expectation of the effect of stabilizing the crystal lattice of NCA.

  Here, since the obtained NCA contains excessive lithium on the particle surface, there is a problem that the NCA gels when producing the positive electrode mixture paste. Patent Literature 2 discloses, as a means for solving the problem, measuring the pH of a supernatant obtained by stirring and mixing 5 g of the positive electrode active material powder in 100 g of pure water for 120 minutes using a 200 ml beaker, and then allowing the mixture to stand for 30 seconds. In this case, a method for producing a positive electrode active material in which the pH becomes 12.0 or more and 12.7 or less at 25 ° C. is disclosed.

JP-A-8-213015 JP-A-2003-3222

  As described above, aluminum added to NCA is added to stabilize the crystal lattice of NCA, but there is a problem that the residual content is not stable with respect to the amount of aluminum added. In addition, aluminum diffuses to the surface during the manufacturing process, and the concentration of aluminum in the interior is reduced, so that the effect cannot be sufficiently exhibited. In addition, the aluminum concentration on the surface increases, and the characteristics as a battery material are sometimes deteriorated.

  In view of such circumstances, the present invention provides nickel composite compound particles in which the amount of aluminum added and the distribution of aluminum are in an optimal state, a method for producing the same, and a method for producing a positive electrode active material for a lithium ion secondary battery. The purpose is to:

  In order to achieve the above object, the present inventors have conducted intensive studies on the production conditions of the composite hydroxide during the production of the precursor of NCA and the washing conditions in the water washing process. It has been found that the formation of the compound reduces the diffusion of aluminum to the particle surface, and as a result, elution of aluminum can be suppressed when the NCA prepared using the precursor is washed with water.

  That is, one embodiment of the present invention is a nickel composite compound particle which contains at least nickel and aluminum, and optionally contains cobalt, which is a precursor of a positive electrode active material for a lithium ion secondary battery, and has a molar ratio of each element. Is Ni: Co: Al = 1-xy: x: y (where 0 ≦ x ≦ 0.2, 0 <y ≦ 0.1), and the aluminum concentration is the average of the entire nickel composite compound particles. An aluminum high concentration region which is higher than the value exists inside the nickel composite compound particles.

  According to one embodiment of the present invention, since the diffusion of aluminum to the particle surface can be reduced by forming an aluminum high concentration region inside the particle, the addition amount of aluminum and the distribution of aluminum are in an optimal state. Nickel composite compound particles.

  At this time, in one embodiment of the present invention, the high aluminum concentration region may be present at the center of the particle.

  By forming a high aluminum concentration region in the center of the particle, the diffusion of aluminum to the particle surface can be further reduced.

  In one embodiment of the present invention, the high aluminum concentration region may be present in a layer inside the particle.

  Since the nickel composite compound is formed by a crystallization method, nickel composite compound particles in which a high aluminum concentration region is formed in a layered manner can be easily obtained.

  In one embodiment of the present invention, the nickel composite compound particles may be composed of at least one selected from a nickel composite hydroxide, a nickel composite oxide, and a nickel composite oxyhydroxide.

  The nickel composite compound particles serving as the precursor of the positive electrode active material are composed of one or more selected from these compounds.

  Another embodiment of the present invention is a method for producing nickel composite compound particles that contain at least nickel and aluminum and that optionally contains cobalt, which is a precursor of a positive electrode active material for a lithium ion secondary battery, comprising at least a nickel salt aqueous solution. A crystallization step of crystallizing nickel composite compound particles from a reaction solution mixed with an aqueous alkali solution as an aqueous solution, optionally using an aqueous cobalt salt solution alone or as a mixed aqueous solution obtained by mixing some of the aqueous solution groups, using an aqueous aluminum salt solution In the crystallization step, the crystallization step is adjusted so that a high aluminum concentration region that is higher than the average value of the entire nickel composite compound particles is present inside the nickel composite compound particles.

  According to another aspect of the present invention, a nickel composite in which a high aluminum concentration region is formed inside particles by adjusting the aluminum concentration in the reaction solution, and the added amount of aluminum and the distribution of aluminum are in an optimal state. Compound particles can be produced.

  At this time, in another aspect of the present invention, in the crystallization step, the aluminum concentration is higher than the average value of the entire nickel composite compound particles, a high aluminum concentration mixed solution containing nickel, cobalt and aluminum, and the aluminum concentration is the nickel composite compound. By using a low aluminum concentration mixed solution containing nickel, cobalt, and aluminum lower than the average value of the whole particles, a high aluminum concentration region may be formed inside the particles.

  As described above, by using the mixed solutions having different aluminum concentrations, it is possible to manufacture nickel composite compound particles in which a high aluminum concentration region is formed inside the particles.

  Further, in another aspect of the present invention, in the crystallization step, a mixed solution containing nickel and cobalt and an aqueous solution containing aluminum are used, and the addition rate of the aqueous solution containing aluminum is controlled to form a high aluminum concentration region inside the particles. It may be formed.

  As described above, by changing the mixing ratio between the aqueous solution containing aluminum and the mixed solution containing nickel and cobalt, it is possible to produce nickel composite compound particles in which an aluminum high concentration region having a concentration gradient is formed inside the particles. Can be.

  Another aspect of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery containing at least lithium, nickel and aluminum, and optionally containing cobalt, wherein the nickel compound compound particles described above are mixed with a lithium compound. And a baking step of baking the mixed powder in an oxidizing atmosphere to obtain a baking product, and a washing step of washing the baking product with water.

  By producing a positive electrode active material using the above-described nickel composite compound particles, elution of aluminum in the water washing step can be prevented, and the amount of aluminum added and the distribution of aluminum can be kept in an optimal state.

  According to the present invention, in the production of NCA in which a calcination step is indispensable, in order to solve the problem that the added aluminum is reduced or unevenly distributed due to diffusion or the like, a cathode active material precursor having an aluminum distribution in anticipation of diffusion is prepared. By using it, it becomes possible to secure and stabilize the aluminum concentration in the final product and to optimize the distribution.

FIG. 2 is a schematic diagram for explaining a high aluminum concentration region of the nickel composite compound particles according to one embodiment of the present invention. It is a flowchart showing the outline of the manufacturing method of the cathode active material for lithium ion secondary batteries concerning one embodiment of the present invention.

Hereinafter, the nickel composite compound particles according to the present invention, a method for producing the same, and a method for producing a positive electrode active material for a lithium ion secondary battery will be described in the following order. Note that the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.
1. 1. Nickel composite compound particles 2. Positive electrode active material for lithium ion secondary battery Production method of nickel composite compound particles 3-1. Crystallization step Method for producing positive electrode active material for lithium ion secondary battery 4-1. Mixing step 4-2. Firing step 4-3. Washing process

<1. Nickel composite compound particles>
Nickel composite compound particles according to one embodiment of the present invention contain at least nickel and aluminum, nickel composite compound particles that are precursors of a positive electrode active material for a lithium ion secondary battery optionally containing cobalt, The molar ratio of the elements is Ni: Co: Al = 1-xy: x: y (where 0 ≦ x ≦ 0.2, 0 <y ≦ 0.1) and the aluminum concentration is nickel composite compound particles It is characterized in that a high aluminum concentration region which is higher than the average value of the whole exists inside the particles.

  As described above, in a baking step or the like when manufacturing a positive electrode active material, in order to solve the problem that aluminum is reduced or unevenly distributed due to diffusion to the particle surface, an aluminum high concentration region is formed inside the particle, and By using a positive electrode active material precursor having an aluminum distribution that allows for diffusion, it is possible to secure and stabilize the aluminum concentration of the obtained positive electrode active material.

  Here, the high aluminum concentration region refers to a region where the aluminum concentration is higher than the average value of the entire nickel composite compound particles. As described later, in the nickel composite compound particles according to one embodiment of the present invention, an aluminum high concentration region is intentionally formed inside the particles during production, but an aluminum high concentration region is accidentally formed inside the particles. Is not excluded from the scope of the present invention. The concentration of the high aluminum concentration region is, for example, preferably 1.1 times or more, more preferably 1.9 times or more, the average value of the aluminum concentration of the whole particles. On the other hand, when the concentration in the aluminum high concentration region is high, the distribution of aluminum of the positive electrode active material obtained after the firing is unevenly distributed, and desired characteristics may not be obtained in some cases. Therefore, the concentration of the aluminum high concentration region is preferably 17.1 times or less, more preferably 5.7 times or less, of the average value of the aluminum concentration of the whole particles.

  FIG. 1 is a schematic diagram for explaining a high aluminum concentration region of a nickel composite compound particle according to one embodiment of the present invention. The shape of the aluminum high-concentration region is not particularly limited. For example, as shown in FIG. 1 (A), a substantially spherical aluminum high-concentration region 11a is formed at the central part of the nickel composite compound particles 10A. Alternatively, as shown in FIG. 1B, a high aluminum concentration region 11b is formed in a layered manner inside the nickel composite compound particles 10B. Alternatively, as shown in FIG. 1C, the high aluminum concentration region 11c may be formed such that the aluminum concentration gradually increases from the surface side of the nickel composite compound particles 10C toward the center. As will be described later, since the nickel composite compound particles are formed by a crystallization method, those having these shapes can be easily produced.

  In the present invention, “inside the particle” means a portion other than the surface of the particle. Since the aluminum high-concentration region only needs to be at least partially present inside the particles, a part thereof may be present on the particle surface, but it is preferable that the whole aluminum concentration region be present inside the particle. In FIG. 1, the nickel composite compound particles are shown in a spherical shape, and the high aluminum concentration region is shown in a symmetrical spherical or annular shape. However, the nickel composite compound particles according to one embodiment of the present invention are limited to these shapes. It is not something to be done. For example, the nickel composite compound particles may have an elliptical shape, a plate shape, an acicular or asymmetric irregular shape, and the aluminum high concentration region may also have an elliptical shape, a plate shape, a rod shape or an asymmetric irregular shape. There may be. The nickel composite compound particles are composed of secondary particles formed by aggregating a plurality of primary particles. In this case, it is determined whether or not the aluminum high concentration region exists in the secondary particles in the secondary particles. .

  The formation of the high aluminum concentration region is confirmed by elemental analysis of the cross section of the obtained nickel composite compound particles. Specifically, the element distribution of the cross section can be measured by EDX.

  The nickel composite compound particles according to one embodiment of the present invention include at least one selected from a nickel composite hydroxide, a nickel composite oxide, and a nickel composite oxyhydroxide. According to the method for producing nickel composite compound particles described below, nickel composite hydroxide is mainly produced. For example, before or at the stage of producing the positive electrode active material, the nickel composite hydroxide is subjected to heat treatment or oxidation treatment. Part or all may be a nickel composite oxide or a nickel composite oxyhydroxide, or may be a mixed particle thereof.

  Further, the nickel composite compound of the present invention may contain an element other than Ni, Co and Al in order to improve various properties. For example, Mn, Ti, W, B, Mo, V, Nb, Ca, Cr, Zr, Mg and the like can be mentioned. These additional elements may be contained inside the particles, or may be coated on the surfaces of the particles.

<2. Positive active material for lithium ion secondary battery>
The positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention is obtained by mixing the above-described nickel composite compound particles as a precursor of the positive electrode active material with a lithium compound, firing and washing with water.

  The positive electrode active material of the present invention contains lithium, nickel, cobalt (optional) and aluminum, and has an aluminum residual ratio of 90% or more before and after the water washing treatment. By using the above-described positive electrode active material precursor, diffusion of aluminum to the particle surface is suppressed, and as a result, reduction of aluminum due to water washing can be suppressed. It is not clear why aluminum elutes, but it is speculated that aluminum diffused on the surface of the positive electrode active material reacts with excess Li to form a water-soluble lithium aluminum compound. Therefore, by using the nickel composite compound particles according to one embodiment of the present invention as a precursor, it is possible to obtain a positive electrode active material in which the addition amount of aluminum and the distribution of aluminum are optimal.

The aluminum residual ratio is calculated by the following equation 1. The aluminum content of the positive electrode active material before and after water washing can be measured by, for example, a method such as ICP emission spectroscopy.
Aluminum residual ratio (%) = (aluminum amount of positive electrode active material after water washing / aluminum amount of positive electrode active material before water washing) × 100 (formula 1)

<3. Method for producing nickel composite compound particles>
Next, a method for producing the above-described nickel composite compound particles will be described. One embodiment of the present invention is a method for producing nickel composite compound particles that contains at least nickel and aluminum and that is a precursor of a positive electrode active material for a lithium ion secondary battery that optionally contains cobalt, comprising at least a nickel salt aqueous solution. A crystallization step of crystallizing nickel composite compound particles from a reaction solution mixed with an aqueous alkali solution as an aqueous solution using an aqueous aluminum salt solution, or an aqueous solution group optionally using a cobalt salt aqueous solution alone or as a mixed aqueous solution obtained by mixing some of the aqueous solution groups; In the crystallization step, the crystallization step is adjusted so that a high aluminum concentration region which is higher than the average value of the entire nickel composite compound particles exists inside the nickel composite compound particles.

  The specific method for producing the nickel composite compound particles of this embodiment is not particularly limited, and the particles can be produced by any method so as to have the above-described structure. Here, one configuration example of the method for producing the positive electrode active material precursor of the present embodiment will be described.

(3-1. Crystallization Step)
In the crystallization step, at least a nickel salt aqueous solution and an aluminum salt aqueous solution are used, and an aqueous solution group optionally using a cobalt salt aqueous solution alone or as a mixed aqueous solution obtained by mixing some of the aqueous solution groups is mixed with an alkaline aqueous solution to form a nickel composite solution. The compound particles are crystallized. That is, a nickel salt aqueous solution, an aluminum salt aqueous solution, and a cobalt salt aqueous solution (optional) may be independently mixed with an alkaline aqueous solution to form a reaction aqueous solution. For example, a mixed aqueous solution obtained by mixing a nickel salt aqueous solution and a cobalt salt aqueous solution is prepared. Alternatively, the mixed aqueous solution and the aluminum salt aqueous solution may be mixed with an alkaline aqueous solution to form a reaction aqueous solution. Hereinafter, as one mode of the present invention, a mixed solution having a high aluminum concentration in which the aluminum concentration is higher than the average value of the entire nickel composite compound particles, and a mixed solution in which the aluminum concentration is lower than the average value of the entire nickel composite compound particles, An example in which crystallization is performed using a solution will be described.

  First, a high aluminum concentration mixed solution having an aluminum concentration higher than the average value of the entire nickel composite compound particles and a low aluminum concentration mixed solution having an aluminum concentration lower than the average value of the entire nickel composite compound particles are prepared. Crystallization using a high aluminum concentration mixed solution forms an aluminum high concentration region inside the particles. The low aluminum concentration mixed solution is prepared in consideration of the composition of the high aluminum concentration mixed solution so as to satisfy the composition of the positive electrode active material finally obtained.

  Here, as the mixed solution, a sulfate solution, a nitrate solution, a chloride solution, or the like of nickel, cobalt, and aluminum can be used. The sum of the composition of the metal elements contained in the mixed solution and the composition of the metal elements contained in the obtained nickel-containing compound coincide. Therefore, the composition of the metal element in the mixed solution can be adjusted to be the same as the composition of the target nickel-containing compound. For example, when trying to obtain nickel composite compound particles as described above, the ratio of the metal element in the raw material aqueous solution is set to Ni: Co: Al = 1-xy: x: y (where 0 ≦ x ≤ 0.2, 0 <y ≤ 0.1).

  Next, water is poured into the reaction tank, and while stirring, a high-aluminum-concentration mixed solution and an alkali solution are first added while controlling the pH, and the mixture is switched to a low-aluminum-concentration mixed solution on the way to coprecipitate nickel compound particles. To be analyzed. By such crystallization, a high aluminum concentration region can be formed at the center of the nickel compound particles (FIG. 1A).

  In another embodiment, a low aluminum concentration mixed solution is used in the early stage of the reaction, a high aluminum concentration mixed solution is switched in the middle, and then a low aluminum concentration mixed solution is used. Can be formed (FIG. 1B). The number of layers may be plural, and the position and concentration of each layer can be appropriately adjusted.

  As the aqueous alkali solution used in the crystallization step, for example, sodium hydroxide, potassium hydroxide, or the like can be used.

  Further, a complexing agent can be added to the reaction solution together with the aqueous alkali solution. The complexing agent is not particularly limited as long as it is capable of forming a complex by combining with nickel ions or other metal ions in an aqueous solution, and examples thereof include an ammonium ion donor. The ammonium ion donor is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, and the like can be used.

  In the crystallization step, when no complexing agent is used, the temperature of the reaction aqueous solution is preferably in the range of more than 60 ° C. and 80 ° C. or less, and the pH at the temperature of the reaction aqueous solution is 10 to 12 (25 (Based on ° C.).

  When the pH of the reaction vessel exceeds 12 and crystallizes, the nickel composite hydroxide becomes fine particles, the filterability deteriorates, and spherical particles may not be obtained. On the other hand, if the pH is less than 10, the generation rate of the nickel composite hydroxide particles becomes extremely slow, Ni remains in the filtrate, the precipitated amount of Ni deviates from the target composition, and the desired ratio of the mixed hydroxide is reduced. May not be obtained.

  Further, when the temperature of the reaction aqueous solution is higher than 60 ° C., the solubility of Ni is increased, and the phenomenon that the amount of precipitated Ni deviates from the target composition to prevent coprecipitation can be avoided. On the other hand, when the temperature of the reaction aqueous solution exceeds 80 ° C., the slurry concentration increases due to the large amount of water evaporation, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration decreases. For example, there is a possibility that the charge / discharge capacity of the positive electrode active material is reduced, for example, it is increased.

  On the other hand, when an ammonium ion donor such as ammonia is used as a complexing agent, the solubility of Ni increases, so that the pH of the reaction aqueous solution is preferably 10 to 13 and the temperature is preferably 30 to 60 ° C. preferable.

  In the reaction tank, the ammonia concentration in the reaction aqueous solution is preferably maintained at a constant value within the range of 3 to 25 g / L. When the ammonia concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, so that plate-like hydroxide primary particles having a uniform shape and particle size are not formed, and gel-like nuclei are formed. Because it is easy to produce, the particle size distribution is also easy to spread. On the other hand, if the ammonia concentration exceeds 25 g / L, the solubility of metal ions becomes too large, the amount of metal ions remaining in the reaction aqueous solution increases, and the composition is likely to shift.

  Further, when the ammonia concentration fluctuates, the solubility of metal ions fluctuates and uniform hydroxide particles are not formed. Therefore, it is preferable to maintain the hydroxide ion at a constant value. For example, it is preferable that the ammonia concentration is maintained at a desired concentration by setting the range between the upper limit and the lower limit to about 5 g / L.

  Further, as another embodiment, there is a method in which a mixed solution containing nickel and cobalt and an aqueous solution containing aluminum are prepared, and each is introduced into a reaction tank in a separate system to perform crystallization. In this method, by controlling the addition amounts of the mixed solution containing nickel and cobalt and the aqueous solution containing aluminum, a high aluminum concentration region can be formed in the nickel compound particles. In this production method, since the addition amount of aluminum can be arbitrarily controlled during crystallization, for example, it is necessary to produce nickel composite compound particles having a concentration gradient such that the aluminum concentration gradually decreases from the particle center toward the surface. (FIG. 1 (C)).

<4. Method for producing positive electrode active material for lithium ion secondary battery>
Finally, a method for producing a positive electrode active material for a lithium ion secondary battery will be described. FIG. 2 is a process diagram schematically showing a method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention. One embodiment of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery containing at least lithium, nickel, and aluminum, and optionally containing cobalt, wherein the above-described nickel composite compound particles and a lithium compound are mixed. The method includes a mixing step S1 of obtaining a mixed powder by firing, a firing step S2 of firing the mixed powder in an oxidizing atmosphere to obtain a fired product, and a washing step S3 of washing the fired product with water. The specific conditions of the method for producing a positive electrode active material according to the present embodiment are not particularly limited. Hereinafter, an example of each step will be described.

(4-1. Mixing step)
In the mixing step S1, the above-described nickel composite compound particles (positive electrode active material precursor) and a lithium compound are mixed to obtain a mixture (mixed powder).

  The ratio when mixing the nickel composite compound particles (positive electrode active material precursor) and the lithium compound is not particularly limited, and can be selected according to the composition of the positive electrode active material to be manufactured. Since Li / Me does not change before and after the sintering step S2 described later, Li / Me in the mixture supplied to the sintering step S2 becomes the same as Li / Me in the obtained positive electrode active material. For this reason, it is preferable to mix so that Li / Me in the mixture prepared in the mixing step S1 is the same as Li / Me in the cathode active material to be obtained.

  For example, in the mixing step S1, the ratio (Li / Me) of the number of atoms of metal other than lithium (Me) to the number of atoms of lithium (Li) in the mixture is 1.00 or more and 1.08 or less. It is preferable to mix as follows. In particular, it is more preferable to mix the mixture so that the ratio (Li / Me) of the number of atoms of lithium in the mixture to the number of atoms of a metal other than lithium is 1.025 or more and 1.045 or less.

  The lithium compound to be subjected to the mixing step S1 is not particularly limited, but for example, one or more selected from lithium hydroxide, lithium carbonate and the like can be preferably used.

  In the mixing step S1, as a mixing means for mixing the nickel composite compound particles and the lithium compound, a general mixer can be used, for example, a shaker mixer, a redige mixer, a julia mixer, a V blender, and the like. May be used.

  The roasting step is performed before the mixing step S1. In the mixing step S1, a mixing step S1 is performed in which a mixture of a nickel composite compound in which some or all of the composite metal oxide is a composite metal oxide and a lithium compound is prepared. It can also be. In addition, a mixing step S1 of preparing a mixture of a lithium compound and a nickel composite oxyhydroxide in which part or all of the nickel composite compound has been subjected to an oxidation step in advance can also be used.

  For this reason, the mixing step S1 includes the above-described nickel composite hydroxide as the positive electrode active material precursor, the nickel composite metal oxide obtained by roasting the positive electrode active material precursor, and the nickel obtained by oxidizing the positive electrode active material precursor. It can also be said that a step of preparing a mixture of at least one selected from composite oxyhydroxides and a lithium compound.

(4-2. Firing step)
The firing step S2 is a step of firing the mixture obtained in the mixing step S1 to obtain a positive electrode active material. When the mixture is fired in the firing step, lithium in the lithium compound is diffused into the nickel composite compound particles (positive electrode active material precursor) to form a positive electrode active material.

  In the firing step S2, the firing temperature at which the mixture is fired is not particularly limited, but is preferably, for example, 600 ° C to 950 ° C, more preferably 700 ° C to 900 ° C.

  By setting the firing temperature at 600 ° C. or higher, lithium can be sufficiently diffused into the nickel composite compound particles, and the crystal structure of the obtained positive electrode active material can be made uniform. For this reason, when the product is used as the positive electrode active material, the battery characteristics can be particularly improved, which is preferable. Further, because the reaction can proceed sufficiently, it is possible to suppress the residual lithium and the residual unreacted particles from remaining.

  By setting the firing temperature to 950 ° C. or lower, it is possible to suppress the progress of sintering between the particles of the generated positive electrode active material. Further, it is possible to suppress the occurrence of abnormal grain growth and to suppress the particles of the obtained positive electrode active material from becoming coarse.

  In the process of raising the temperature to the sintering temperature, it is preferable to maintain the temperature near the melting point of the lithium compound for about 1 hour to 5 hours so that the reaction can be performed more uniformly.

  Among the firing times in the firing step S2, the holding time at a predetermined temperature, that is, the above-described firing temperature is not particularly limited, but is preferably 2 hours or more, and more preferably 4 hours or more. This is because by setting the holding time at the firing temperature to 2 hours or more, the generation of the positive electrode active material can be sufficiently promoted, and the unreacted material can be more reliably prevented from remaining. The upper limit of the holding time at the firing temperature is not particularly limited, but is preferably 24 hours or less in consideration of productivity and the like.

  The atmosphere during firing is not particularly limited, but is preferably an oxidizing atmosphere. As the oxidizing atmosphere, an oxygen-containing gas atmosphere can be preferably used. For example, an atmosphere having an oxygen concentration of 18% by volume or more and 100% by volume or less is more preferable. This is because the crystallinity of the positive electrode active material can be particularly increased by setting the oxygen concentration in the atmosphere at the time of firing to 18% by volume or more.

  In the case of using an oxygen-containing gas atmosphere, as the gas constituting the atmosphere, for example, air, oxygen, a mixed gas of oxygen and an inert gas, or the like can be used. When a mixed gas of oxygen and an inert gas is used as the gas constituting the oxygen-containing gas atmosphere, for example, as described above, the oxygen concentration in the mixed gas preferably satisfies the above range. In particular, the firing step is preferably performed in an oxygen-containing gas stream, more preferably in the air or in an oxygen stream. In consideration of battery characteristics, it is preferable to carry out in an oxygen stream.

  The furnace used for firing is not particularly limited, as long as the mixture can be fired in an oxygen-containing gas atmosphere. From the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is used. Preferably, a batch-type or continuous-type furnace can be used.

  The positive electrode active material obtained in the firing step S2 may have agglomeration or slight sintering. In this case, it may be crushed. Here, crushing means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles generated by sintering necking between the secondary particles during firing, and the secondary particles themselves are almost destroyed. Is an operation to separate secondary particles and to loosen aggregates.

  Further, it is preferable to perform a preliminary firing before the firing step S2. When performing the preliminary firing, the temporary firing temperature is not particularly limited, but may be lower than the firing temperature in the firing step S2. The calcination temperature is, for example, preferably from 250 ° C. to 600 ° C., more preferably from 350 ° C. to 550 ° C. The calcination time, that is, the holding time at the calcination temperature is, for example, preferably about 1 hour to 10 hours, more preferably 3 hours to 6 hours. After the calcination, the calcination may be once cooled and then applied to the calcination step S2. However, the calcination temperature may be increased from the calcination temperature to the calcination temperature, and the calcination step S2 may be continuously performed. Note that the atmosphere for performing the preliminary firing is not particularly limited, but may be, for example, the same atmosphere as in the firing step S2. By performing the calcination, lithium is sufficiently diffused into the positive electrode active material precursor, and a particularly uniform positive electrode active material can be obtained.

(4-3. Rinse step)
In the water washing step S3, the excess lithium compound attached to the surface of the positive electrode active material obtained in the firing step S2 is washed and removed. In the water washing step S3, for example, the positive electrode active material obtained in the firing step S2 can be put into pure water to form a slurry, stirred for a predetermined time, separated from water, filtered, and dried.

  According to the method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention, since the above-described nickel composite compound particles (positive electrode active material precursor) are used, the positive electrode in the firing step S2 is used. Diffusion of aluminum to the surface of the active material is suppressed, and the amount of elution of aluminum in the water washing step S3 is reduced, so that a positive electrode active material having a desired composition can be stably manufactured.

  The condition of the water washing treatment S3 is not particularly limited as long as the surplus lithium compound attached to the surface of the positive electrode active material can be appropriately removed, but the concentration of the slurry is about 500 to 2000 g / L, and the water washing time is about 10 to 60 minutes. Preferably, there is. After washing with water, the resultant is filtered by a known method, and dried at 80 to 200 ° C. in an inert gas or vacuum to obtain a positive electrode active material.

  The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited by these Examples and Comparative Examples.

(Example 1)
(Production of positive electrode active material precursor)
In Example 1, a crystallization process was performed according to the following procedure to produce a nickel composite hydroxide having an overall metal ratio of Ni: Co: Al = 88: 9: 3 as a positive electrode active material precursor.

  First, pure water was placed in a 600 L reaction tank up to a volume of 6.5 L, and the temperature in the tank was set to 49 ° C. The temperature of the reaction solution was maintained at 49 ° C. until the crystallization step was completed. Next, 25% by mass aqueous ammonia was added to the water in the reaction tank as an aqueous solution containing an ammonium ion supplier so that the initial aqueous solution had an ammonium ion concentration of 15.5 g / L. Further, as an alkaline aqueous solution, a 24% by mass aqueous solution of sodium hydroxide was added to the water in the reaction tank, and the pH was adjusted to 11.4.

  In the crystallization step, a mixed aqueous solution (a) (a high aluminum concentration mixed solution) in which the composition ratio of nickel, cobalt and aluminum is Ni: Co: Al = 88: 9: 6, and Ni: Co: Al = 88: 9: A mixed aqueous solution (b) (low aluminum concentration mixed solution) was prepared. Sulfate was used as a salt of each metal used. Then, the metal salt concentration of each mixed solution was adjusted to be 2.1 mol / L.

  Then, while stirring the initial aqueous solution by the stirring blade, the mixed aqueous solution (a), the aqueous solution (c) containing the ammonium ion donor, and the alkaline aqueous solution (d) are continuously supplied into the initial aqueous solution. To form a reaction solution, and the positive electrode active material was crystallized. When the mixed aqueous solution (a) was added for 120 minutes, the solution was switched to the mixed solution (b), and the crystallization reaction was further performed for 120 minutes. As the aqueous solution (c) containing the ammonium ion donor and the alkaline aqueous solution (d), the same aqueous solutions as those used in preparing the above-mentioned initial aqueous solution were used.

  During the crystallization step, the mixed aqueous solution (a) and the mixed aqueous solution (b) containing the nickel salt and the cobalt salt were supplied at a supply rate of 1.13 L / min, and the aqueous solution (c) containing the ammonium ion donor was added at a rate of 0.1%. At a supply rate of 16 L / min, the aqueous caustic solution (d) was supplied to the initial aqueous solution and the reaction solution at a supply rate of 0.74 L / min. During the crystallization step, the reaction solution is maintained at a liquid temperature of 49 ° C., a pH of 11.1 to 11.7 based on 50 ° C., and an ammonia concentration of 15.5 g / L. It could be confirmed.

  The collected crystallized product was washed with water, filtered, and dried to obtain a nickel composite hydroxide as a positive electrode active material precursor. After dissolving the obtained nickel composite hydroxide with nitric acid, the composition ratio of the whole particles was measured with an ICP emission spectrophotometer (ICPS-8100, manufactured by Shimadzu Corporation). Ni: Co: Al = 88 : 9: 3.

  When a cross section of the nickel composite hydroxide was subjected to surface analysis with an EDX (AMETEK Co. Ltd., model number: Genesis) using a scanning electron microscope (manufactured by Hitachi High-Tech Fielding, model number: S-4700), A high aluminum concentration region was confirmed in the center of the particles, and the composition ratio was 88: 9: 6, which was the same as in the mixed solution (a).

(Manufacture of positive electrode active material)
Further, a mixture of the lithium compound and the obtained nickel composite hydroxide was prepared by the following procedure (mixing step). As the lithium compound, anhydrous lithium hydroxide was used.

  In the mixing step, the lithium compound and the obtained nickel composite hydroxide were weighed and mixed such that the ratio of the number of atoms in the mixture was Li / Me 1.035, to prepare a mixture. Here, Me means the total number of atoms of metals other than Li, and is the total number of atoms of Ni, Co, and Al.

  The mixture obtained in the mixing step is charged into a firing container having an inner size of 280 mm (L) × 280 mm (W) × 90 mm (H), and the mixture is subjected to oxygen oxidation using a roller hearth kiln which is a continuous firing furnace. The baking was performed under an air current at a maximum temperature of 770 ° C. (baking step). Further, the obtained fired product was put into pure water to make a slurry in a mass ratio of 1.5 with respect to 1 to water, stirred for 30 minutes, filtered, and dried to obtain a positive electrode active material ( Washing step).

  After dissolving the positive electrode active material before and after water washing with nitric acid, each Al concentration was measured by ICP emission spectroscopy, and the Al residual ratio after water washing (Al concentration of positive electrode active material after water washing / positive electrode active material before water washing) Was calculated to be 94%.

(Example 2)
In Example 2, mixed solution (b) was added for 48 minutes from the start of the reaction, then switched to mixed solution (a), added for 120 minutes, and switched again to mixed solution (b) for 72 minutes. A nickel composite hydroxide according to Example 2 was obtained in the same manner as in Example 1 except that the mixture was added for 1 minute.

  With respect to the obtained nickel composite hydroxide, the metal composition ratio of the entire particles was Ni: Co: Al = 88: 9: 3.

  Further, when a cross-sectional analysis of the cross section of the nickel composite hydroxide was performed, a layered aluminum high concentration region was confirmed inside the particles, and the composition ratio was 88: 9: 6, which is the same as the mixed solution (a). .

  Next, a positive electrode active material was prepared from the nickel composite hydroxide according to Example 2 in the same manner as in Example 1. The Al residual ratio of the obtained positive electrode active material was 92%.

(Example 3)
In Example 3, a mixed aqueous solution (e) in which the composition ratio of nickel, cobalt and aluminum was Ni: Co: Al = 88: 9: 0 was prepared such that the metal salt concentration was 2.10 mol / L. Further, an aqueous solution of aluminum was prepared to be 2.10 mol / L.

  At the start of the reaction, the addition of the aqueous mixed solution (e) was started at 1.03 L / min and the aqueous solution of aluminum was started at 0.07 L / min, and the amount of the aqueous mixed solution (e) was gradually increased. Reduced. The total addition rate was constant at 1.13 L / min. A nickel composite hydroxide according to Example 3 was obtained in the same manner as Example 1 except for the above.

  With respect to the obtained nickel composite hydroxide, the metal composition ratio of the entire particles was Ni: Co: Al = 88: 9: 3.

  Further, when a cross-sectional analysis of the cross section of the nickel composite hydroxide was performed, it was confirmed that the Al content gradually decreased from the center of the particle toward the outside.

  Next, a positive electrode active material was prepared from the nickel composite hydroxide according to Example 3 in the same manner as in Example 1. The residual ratio of Al in the obtained positive electrode active material was 91%.

(Comparative Example 1)
In Comparative Example 1, a mixed aqueous solution (f) in which the composition ratio of nickel, cobalt and aluminum was Ni: Co: Al = 88: 9: 3 was prepared such that the metal salt concentration was 2.10 mol / L. During the crystallization, the mixed aqueous solution (f) was supplied at 1.13 L / min. The other conditions were the same as in Example 1 to obtain a nickel composite hydroxide according to Comparative Example 1.

  With respect to the obtained nickel composite hydroxide, the metal composition ratio of the entire particles was Ni: Co: Al = 88: 9: 3.

  Further, when a cross-sectional analysis of the cross section of the nickel composite hydroxide was performed, it was confirmed that Al was almost uniformly distributed in the particles.

  Next, a positive electrode active material was produced from the nickel composite hydroxide according to Comparative Example 1 in the same manner as in Example 1. The residual ratio of Al in the obtained positive electrode active material was 85%.

  Table 1 shows the results according to Examples 1 to 3 and Comparative Example 1.

  In Examples 1 to 3 to which one embodiment of the present invention was applied, the residual ratio of aluminum exceeded 90%, and it was found that there was an effect of stabilizing the residual amount of aluminum. On the other hand, in the conventional comparative example 1 to which the present invention was not applied, the residual ratio of aluminum was 85%, and 10% or more of aluminum was eluted. As described above, by applying the present invention, a cathode active material precursor having an optimal aluminum distribution can be obtained, and it is possible to secure, stabilize, and optimize the distribution of aluminum in the cathode active material. become.

  Although each embodiment and each example of the present invention have been described in detail as described above, it is obvious to those skilled in the art that many modifications that do not substantially depart from the novel matter and effects of the present invention are possible. , Will be easy to understand. Therefore, such modified examples are all included in the scope of the present invention.

  For example, in the description or drawings, a term described at least once together with a broader or synonymous different term can be replaced with the different term in any part of the description or drawing. Further, the configuration and operation of the nickel composite compound particles, the method for producing the same, and the method for producing the positive electrode active material for a lithium ion secondary battery are not limited to those described in each embodiment and each example of the present invention, and various modifications may be made. Implementation is possible.

10A, 10B, 10C Nickel composite compound particles, 11a, 11b, 11c High aluminum concentration region

Claims (8)

Nickel composite compound particles containing at least nickel and aluminum, which is a precursor of a positive electrode active material for a lithium ion secondary battery optionally containing cobalt,
The molar ratio of each element is Ni: Co: Al = 1-xy: x: y (where 0 ≦ x ≦ 0.2, 0 <y ≦ 0.1), and the aluminum concentration is A nickel composite compound particle characterized in that a high aluminum concentration region which is higher than the average value of the entire composite compound particle exists inside the nickel composite compound particle.   The nickel composite compound particles according to claim 1, wherein the high aluminum concentration region is present at a particle center.   The nickel composite compound particles according to claim 1, wherein the high aluminum concentration region exists in a layer inside the particles.   The nickel composite compound particles are composed of at least one selected from a nickel composite hydroxide, a nickel composite oxide, and a nickel composite oxyhydroxide. 2. The nickel composite compound particles according to item 1. A method for producing nickel composite compound particles that is a precursor of a positive electrode active material for a lithium ion secondary battery containing at least nickel and aluminum and optionally containing cobalt,
Using at least a nickel salt aqueous solution and an aluminum salt aqueous solution, crystallization of nickel composite compound particles from a reaction solution obtained by mixing an aqueous solution group optionally using a cobalt salt aqueous solution alone or a mixed aqueous solution obtained by mixing some of the aqueous solution groups with an alkaline aqueous solution. Having a crystallization step,
In the crystallization step, the crystallization step is adjusted so that an aluminum high concentration region deeper than the average value of the entire nickel composite compound particles exists inside the nickel composite compound particles. Manufacturing method.   In the crystallization step, a high aluminum concentration mixed solution containing nickel, cobalt, and aluminum having an aluminum concentration higher than the average value of the entire nickel composite compound particles, and an aluminum concentration lower than the average value of the entire nickel composite compound particles The method for producing nickel composite compound particles according to claim 5, wherein a high aluminum concentration region is formed inside the particles by using a low aluminum concentration mixed solution containing nickel, cobalt and aluminum.   The crystallization step, wherein a mixed solution containing nickel and cobalt and an aqueous solution containing aluminum are used, and the addition rate of the aqueous solution containing aluminum is controlled to form an aluminum high concentration region inside the particles. 6. The method for producing nickel composite compound particles according to 5. A method for producing a positive electrode active material for a lithium ion secondary battery containing at least lithium, nickel and aluminum, and optionally containing cobalt,
A mixing step of mixing the nickel compound compound particles according to any one of claims 1 to 4 and a lithium compound to obtain a mixed powder;
A firing step of firing the mixed powder in an oxidizing atmosphere to obtain a fired product,
A water washing step of washing the fired product with water.

Images