JP2020035693A - Transition metal composite hydroxide, manufacturing method thereof, lithium transition metal composite oxide active material, and lithium ion secondary battery - Google Patents

Abstract

To provide a transition metal composite hydroxide that has higher oil absorption than a conventional art and can exhibit excellent output characteristics, a manufacturing method thereof, a lithium transition metal composite oxide active material, and a lithium ion secondary battery.SOLUTION: A transition metal composite hydroxide as a precursor of a positive electrode active material for a lithium ion secondary battery includes a two-layer structure including a central portion and an outer peripheral portion having different crystal structures, and the central portion is made of an alpha-type transition metal hydroxide in which water molecules are inserted between crystal layers of the transition metal hydroxide, and the outer peripheral portion is made of a beta-type transition metal hydroxide containing no water molecules between crystal layers of the transition metal composite hydroxide.SELECTED DRAWING: None

Description

  The present invention relates to a transition metal composite hydroxide that is a precursor of a positive electrode active material for a lithium ion secondary battery, a method for producing the transition metal composite hydroxide, a lithium transition metal composite oxide active material, and a lithium ion secondary battery. .

  In recent years, with the spread of small information terminals such as smartphones and tablet PCs, development of small and lightweight 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 a motor drive power supply, particularly for a power supply for transportation equipment.

  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 an active 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 lithium metal composite oxide having a layered or spinel-type crystal structure as the cathode material Since a high voltage of 4V class can be obtained, it has been put to practical use as a battery having a high energy density.

At present, as a positive electrode material of such a lithium ion secondary battery, a lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, a lithium transition metal composite oxide using nickel which is cheaper than cobalt (LiNiO ₂ ), Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _{1 / 2} Mn _1/2 O ₂ ) and the like have been proposed.

Among these lithium transition metal composite oxides, recently, lithium nickel composite oxides (LiNiO ₂ ), which can reduce the amount of cobalt having a small reserve and a high charge / discharge capacity, and have excellent thermal stability. Lithium nickel manganese composite oxide (LiNi _1/2 Mn _1/2 O ₂ ), and a lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 ) which has better cycle characteristics, low resistance and high output. Mn _1/3 O ₂ ) is receiving attention.

  By the way, some uses of the lithium secondary battery are assumed to be used repeatedly at high rates of charge and discharge (rapid charge and discharge). Lithium-ion secondary battery used as a power source of a vehicle (for example, a lithium-ion secondary battery mounted on a hybrid vehicle using both a lithium-ion secondary battery and a power source having a different operating principle such as a gasoline engine as a power source) A secondary battery is a typical example in which such use is expected. However, the conventional general lithium ion secondary battery shows relatively high durability for a low-rate charge / discharge cycle, but deteriorates in performance for a high-rate charge / discharge cycle ( Internal resistance, etc.). Therefore, the following documents are disclosed for the above problems.

  For example, Patent Literature 1 discloses a technique in which a positive electrode or a negative electrode of a lithium ion secondary battery is formed of an active material having a porous hollow structure. According to the active material having such a porous hollow structure, the contact area with the electrolytic solution is large, lithium ions can easily move, and distortion due to volume expansion of the active material due to insertion of lithium is suppressed, and the like. It is said that a high-capacity, long-life lithium battery that can be rapidly charged is obtained.

  Further, Patent Documents 2 to 4 disclose composite oxide particles (lithium-cobalt composite oxide particles or spinel-type secondary particles) which are hollow spherical secondary particles in which primary particles are aggregated and whose surface has a large number of gaps communicating with the interior. It is described that by using (lithium-manganese composite oxide particles) as a positive electrode active material, the contact area with a nonaqueous electrolyte can be increased to improve the utilization rate of the positive electrode active material.

  Patent Literature 5 describes a lithium phosphate compound having an olivine structure, which improves output by increasing the oil absorption. Patent Literature 6 discloses a performance suitable for high output by a hollow structure having secondary particles in which a plurality of primary particles of a lithium transition metal composite oxide are aggregated and a hollow portion formed inside the secondary particles. It also describes that active material particles with little deterioration due to charge / discharge cycles can be obtained.

  Further, Patent Literature 7 discloses a nucleation step of performing nucleation in an oxidizing atmosphere and an aqueous solution for particle growth containing nuclei formed in the nucleation step, which has a pH of 10.degree. It is controlled so that it is lower than the nucleation stage in the range of 5 to 12.0, and by switching from an oxidizing atmosphere to a mixed atmosphere of oxygen and an inert gas having an oxygen concentration of 1% by volume or less in the middle of the particle growing step, it becomes hollow. A precursor having a structure and an active material obtained by firing the precursor have been proposed.

JP-A-8-321300 JP-A-10-74516 JP-A-10-83816 JP-A-10-74517 JP 2012-104290 A JP 2011-119092 A JP 2012-246199 A

  However, these conventional active materials and their production methods have a problem that the oil absorption is low and sufficient output characteristics cannot be obtained.

  Thus, the present invention provides a transition metal composite hydroxide, a method for producing a transition metal composite hydroxide, a lithium transition metal composite oxide active material, An object is to provide a lithium ion secondary battery.

  The transition metal composite hydroxide according to one embodiment of the present invention is a transition metal composite hydroxide that is a precursor of a positive electrode active material for a lithium ion secondary battery, wherein the transition metal composite hydroxide has a crystal structure. Is a two-layer structure consisting of a different central portion and an outer peripheral portion, wherein the central portion is made of an alpha-type transition metal hydroxide in which water molecules are inserted between crystal layers of the transition metal hydroxide, and the outer peripheral portion is transitional. It is characterized by comprising a beta-type transition metal hydroxide containing no water molecules between crystal layers of the metal composite hydroxide.

  In this way, it is possible to provide a transition metal composite hydroxide that has a higher oil absorption amount and can exhibit excellent output characteristics when used as a precursor of a positive electrode active material for a lithium ion secondary battery. Can be.

In this case, in one aspect of the present invention, the transition metal complex hydroxide represented by the general _{formula: Ni x Co y Mn z A} t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.7 , 0.1 ≦ y ≦ 0.4, 0.1 ≦ z ≦ 0.4, 0 <t ≦ 0.1, 0 ≦ a ≦ 0.5, where A is Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and one or more additional elements selected from W).

  In this way, when used as a precursor of the positive electrode active material for a lithium ion secondary battery, the value of the positive electrode resistance can be reduced and the battery performance can be improved.

At this time, in one embodiment of the present invention, the transition metal composite hydroxide has an average particle size D50 of 3 μm or more and 8 μm or less, (D90−D10) / D50 of 1.0 or less, and a BET specific surface area of 10 m ² / g or more and 30 m ² / g or less.

  By doing so, it is possible to prevent a decrease in the charge / discharge capacity per volume and to improve the dispersibility of the positive electrode active material.

  In one embodiment of the present invention, there is provided a method for producing a transition metal composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery, comprising an aqueous transition metal raw material solution containing one or more transition metal compounds and an ammonium ion supply. The aqueous solution for nucleation including the body is controlled so that the pH based on a liquid temperature of 25 ° C. is 12.5 or more, the ammonium ion concentration is 25 g / L or less, and the oxygen concentration in the atmosphere is 10% by volume or more. A nucleation step of generating a nucleus by supplying the nucleus to the crystallization reaction tank, and a first particle growth step and a second particle growth step of particle growth of the generated nucleus, the first particle growth In the step, the aqueous solution for particle growth containing the nuclei generated in the nucleation step is mixed with an aqueous solution having a pH of 10.5 to 11.5 based on a liquid temperature of 25 ° C. and an ammonium ion concentration of 25 g / L or less in an atmosphere. Oxygen The transition metal raw material aqueous solution and the ammonium ion supplier are continuously supplied while controlling the temperature to be 10% by volume or more, and in the second particle growth step, the pH at a liquid temperature of 25 ° C. is adjusted. The transition metal raw material aqueous solution and the ammonium ion supplier are continuously connected while controlling so that the concentration of oxygen is 11.5 to 12.0, the ammonium ion concentration is 25 g / L or less, and the oxygen concentration in the atmosphere is 1% by volume or less. It is characterized in that it is supplied on a regular basis.

  In this manner, when used as a precursor of a positive electrode active material for a lithium ion secondary battery, a method for producing a transition metal composite hydroxide that has a higher oil absorption compared to the conventional art and can exhibit excellent output characteristics. Can be provided.

In one embodiment of the present invention, there is provided a lithium transition metal composite oxide active material used for a lithium ion secondary battery, wherein a center of a particle of the lithium transition metal composite oxide active material is a space; The lithium transition metal composite oxide has an α-NaFeO ₂ type crystal structure including at least nickel as one of the transition metals.

  In this manner, when used in a lithium ion secondary battery, a lithium transition metal composite oxide active material that has a higher oil absorption than conventional ones and can exhibit excellent output characteristics can be provided.

In this case, in one aspect of the present invention, the lithium transition metal composite oxide is represented by the general _{formula: Li 1 + s Ni x Co} y Mn z A t O 2 (-0.05 ≦ s ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.4, 0.1 ≦ z ≦ 0.4, 0 <t ≦ 0.1), where A is Al, Ti, It may include one or more elements selected from V, Cr, Zr, Nb, Mo, Hf, Ta, and W.

  By doing so, the value of the positive electrode resistance can be reduced, and the battery performance can be improved.

  One embodiment of the present invention is a lithium ion secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein at least one of the positive electrode and the negative electrode includes the lithium transition metal composite oxide active material. And

  By doing so, it is possible to provide a lithium ion secondary battery capable of exhibiting excellent output characteristics.

  According to the present invention, a transition metal composite hydroxide, a method for producing a transition metal composite hydroxide, a lithium transition metal composite oxide active material, which has a higher oil absorption compared to conventional ones and can exhibit excellent output characteristics And a lithium ion secondary battery.

FIG. 1 is a process diagram schematically illustrating a method for producing a transition metal composite hydroxide according to an embodiment of the present invention. FIG. 2 is a process diagram schematically showing a method for producing a lithium transition metal composite oxide active material according to one embodiment of the present invention.

  In view of the fact that the battery performance of a lithium ion secondary battery is greatly affected by the performance of the positive electrode active material used for the positive electrode, the present inventor has conducted intensive studies to solve the above-described problems. , An alpha-type transition metal hydroxide in which water molecules are inserted between crystal layers of a transition metal hydroxide, and an outer peripheral portion from a beta-type transition metal hydroxide containing no water molecules between crystal layers of a transition metal composite hydroxide. As a result, a positive electrode active material having a large oil absorption has many paths through which lithium ions enter and leave when the positive electrode is manufactured, and can reduce the reaction resistance of the secondary battery, thereby obtaining excellent output characteristics. With the knowledge that there is, the present invention has been completed. Hereinafter, preferred embodiments of the present invention will be described.

The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and can be modified without departing from the gist of the present invention. Also, not all of the configurations described in the present embodiment are necessarily indispensable as means for solving the present invention. A transition metal composite hydroxide, a method for producing a transition metal composite hydroxide, a lithium transition metal composite oxide active material, and a lithium ion secondary battery according to an embodiment of the present invention will be described in the following order.
1. 1. Transition metal composite hydroxide 2. Method for producing transition metal composite hydroxide 2-1. Nucleation step 2-2. First particle growth step 2-3. Second particle growth step 2-4. 2. Control of pH, control of reaction atmosphere, substances and solutions used in each step, reaction conditions, etc. in each step. 3. Lithium transition metal composite oxide active material Method for producing lithium transition metal composite oxide active material 4-1. Heat treatment step 4-2. Mixing step 4-3. Firing step 5. Lithium ion secondary battery

<1. Transition metal composite hydroxide>
The transition metal composite hydroxide according to one embodiment of the present invention is a precursor of a positive electrode active material for a lithium ion secondary battery. The transition metal composite hydroxide has a two-layer structure including a central portion and an outer peripheral portion having different crystal structures, and the central portion is an alpha-type transition metal in which water molecules are inserted between crystal layers of the transition metal hydroxide. The outer peripheral portion is made of a beta-type transition metal hydroxide containing no water molecules between crystal layers of the transition metal composite hydroxide. Hereinafter, the composition, average particle size, particle size distribution, particle structure, and crystal structure of the transition metal composite hydroxide according to one embodiment of the present invention will be described.

(composition)
Transition metal composite hydroxide according to an embodiment of the present invention, the composition has the general _{formula: Ni x Co y Mn z A} t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0. 7, 0.1 ≦ y ≦ 0.4, 0.1 ≦ z ≦ 0.4, 0 <t ≦ 0.1, 0 ≦ a ≦ 0.5, where A is Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta, W, or at least one additional element).

  When a transition metal composite hydroxide having such a composition is used as a precursor to produce a lithium transition metal composite oxide, an electrode using the lithium transition metal composite oxide as a positive electrode active material is used in a secondary battery. In addition, the value of the measured positive electrode resistance can be reduced, and the battery performance can be improved.

  When a positive electrode active material is obtained using the above transition metal composite hydroxide as a raw material, the material ratio (Ni: Mn: Co: M) of each constituent element of the transition metal composite hydroxide is determined by the obtained positive electrode active material. It is also maintained in substances. Therefore, the material ratio of the composite hydroxide of the present invention is adjusted to be the same as the material ratio required for the intended positive electrode active material.

(Average particle size)
The transition metal composite hydroxide according to one embodiment of the present invention has an average particle diameter D50 of more than 1 μm and 15 μm or less, preferably an average particle diameter of 3 μm or more and 8 μm or less. By setting the average particle diameter of the transition metal composite hydroxide in such a range, the average particle diameter of the positive electrode active material obtained from the transition metal composite hydroxide as a raw material exceeds 1 μm, and is 15 μm or less. Can be adjusted. Since the particle size distribution of the positive electrode active material becomes close to the particle size distribution of the transition metal composite hydroxide used as a raw material, it affects the characteristics of a battery using the positive electrode active material having the above particle size as a positive electrode material.

  When the average particle size of the transition metal composite hydroxide is 1 μm or less, the average particle size of the obtained positive electrode active material is also small, and the specific surface area of the positive electrode active material is increased. Although an output is obtained, the filling density of the positive electrode is reduced, the charge / discharge capacity per volume is reduced, and the dispersibility of the conductive additive and the positive electrode active material may be deteriorated when preparing the electrode paste. In addition, since the voltage applied to the individual positive electrode active material particles in the electrode becomes non-uniform, the particles to which a high voltage is applied deteriorate as charge and discharge are repeated, and the charge and discharge capacity of the secondary battery is reduced. May decrease.

  Conversely, when the average particle size of the composite hydroxide exceeds 15 μm, the specific surface area of the obtained positive electrode active material decreases, and the interface with the electrolyte decreases, so that the number of paths for lithium ions to enter and exit decreases. Therefore, the resistance of the positive electrode may increase and the output characteristics of the battery may decrease.

(Particle size distribution)
The transition metal composite hydroxide according to one embodiment of the present invention has an index [(D90-D10) / average particle size] of 1.0 or less, preferably 0.70 or less, which is an index indicating the spread of the particle size distribution. It is preferably prepared so that

  As described above, the particle size distribution of the positive electrode active material is strongly affected by the composite hydroxide as a raw material.For example, if fine particles or coarse particles are mixed in the transition metal composite hydroxide, Similarly, fine particles or coarse particles are present. That is, when [(D90−D10) / average particle size] exceeds 1.0 and the particle size distribution is wide, fine particles or coarse particles may be present in the positive electrode active material in some cases.

  When a positive electrode is manufactured using a positive electrode active material containing a large amount of fine particles, the fine particles may cause a local reaction and generate heat, thereby lowering the safety of the secondary battery and selectively deteriorating the fine particles. Therefore, the cycle characteristics deteriorate. On the other hand, when a positive electrode is formed using a positive electrode active material having a large number of large-diameter particles, a reaction area between the electrolyte and the positive electrode active material cannot be sufficiently obtained, and the output characteristics of the secondary battery deteriorate due to an increase in reaction resistance. I do.

  The method for determining the average particle diameter and D90 and D10 is not particularly limited, but for example, can be determined from the integrated volume value measured by a laser diffraction / scattering particle size analyzer. The average particle diameter can be D50, which is a particle diameter whose cumulative volume is 50% of the total particle volume, based on the same concept as D10 and D90.

(Particle structure)
The transition metal composite hydroxide according to one embodiment of the present invention is composed of substantially spherical secondary particles formed by aggregating a plurality of primary particles. The shape of the primary particles constituting the secondary particles can take various forms such as a plate shape, a needle shape, a rectangular parallelepiped shape, an elliptical shape, and a ridge shape. Further, in addition to the aggregation state in which the particles are aggregated in a random direction, the transition metal composite hydroxide according to an embodiment of the present invention also has a form in which the major axis directions of the particles are radially aligned from the center to the outer peripheral direction. It can be applied to objects.

  In the transition metal composite hydroxide according to one embodiment of the present invention, it is particularly preferable that the plate-like and / or needle-like primary particles aggregate in random directions to form secondary particles. In the case of such a structure, voids are generated almost uniformly between the primary particles, and in the process of mixing with the lithium compound and firing, the molten lithium compound sufficiently diffuses into the secondary particles, and the lithium and the transition metal complex are mixed. This is because the reaction of the hydroxide easily proceeds.

  The average particle diameter of the primary particles constituting the secondary particles is preferably in the range of 0.3 to 3.0 μm. When the size of the primary particles is in the above range, appropriate voids are obtained between the primary particles, and sufficient diffusion of lithium into the secondary particles during firing is easily performed. The average particle size of the primary particles is more preferably from 0.4 to 1.5 μm.

  If the average particle size of the primary particles is less than 0.3 μm, the sintering temperature is lowered during the firing process, the sintering of the secondary particles increases, and the coarse particles in which the secondary particles are aggregated form the positive electrode active material. May be included. On the other hand, when the average particle size of the primary particles exceeds 3 μm, the diffusion of the lithium compound into the secondary particles becomes difficult, and the firing temperature must be increased in order to obtain sufficient crystallinity of the obtained positive electrode active material. It is necessary to perform firing at such a high temperature, so that sintering and agglomeration between the secondary particles occur, coarse particles are generated, and the positive electrode active material may deviate from an appropriate particle size distribution. .

  In the transition metal composite hydroxide according to one embodiment of the present invention, the structure of the secondary particles of the positive electrode active material is preferably a hollow structure having a dense outer shell portion and a hollow portion where no active material exists. The precursor used in the synthesis of the above-mentioned cathode active material having a hollow structure includes an aggregate of fine and coarse primary particles forming a hollow portion and an aggregate of dense primary particles forming an outer shell portion outside the hollow portion. Is preferably a transition metal composite hydroxide provided on the outer peripheral portion.

  The particle structure of such a transition metal composite hydroxide is composed of an aggregate of two or more types of primary particles having different densities and sizes.

  The transition metal composite hydroxide, which is a precursor of the positive electrode active material having the hollow structure, has a structure in which a central portion has many gaps in which fine primary particles are connected, and an outer shell portion has a large and thick plate-like primary particle. It is preferable that the structure be more dense than the central portion composed of When such a transition metal composite hydroxide reacts with a lithium compound, sintering proceeds at a lower temperature in the center than in the outer shell, and the primary particles at the center move from the center of the secondary particles to the outer periphery. Shrink. In addition, since the density of the transition metal composite hydroxide is low in the central part, the shrinkage rate when reacting with the lithium compound becomes large, and as a result, the central part of the obtained lithium transition metal composite oxide particles has a sufficient size. A hollow portion, which is a space having a height, is formed.

  In order to form such a hollow structure, the properties of the primary particles of the transition metal composite hydroxide greatly affect. That is, it is preferable that fine primary particles are agglomerated in random directions at the center and larger primary particles are agglomerated in random directions at the outer periphery. Aggregation in a random direction causes the central portion to shrink uniformly in all directions, so that a hollow portion having a sufficient size can be formed when the lithium transition metal composite oxide is formed.

  Further, the average particle size of the fine primary particles at the center is preferably from 0.01 to 0.3 μm, more preferably from 0.1 to 0.3 μm. If the average particle size of the fine primary particles is less than 0.01 μm, a sufficiently large central portion may not be formed in the transition metal composite hydroxide. Shrinkage is not sufficient, and a sufficient space may not be obtained after firing. The properties of the primary particles of the outer shell may be as described above.

  Secondary particles constituting the positive electrode active material composed of the lithium transition metal composite oxide obtained using such a transition metal composite hydroxide as a raw material have a hollow structure, and the ratio of the thickness of the outer shell to the particle diameter. The ratio of the outer peripheral portion to the particle diameter of the transition metal composite hydroxide secondary particles is substantially maintained. Therefore, by setting the ratio of the thickness of the outer peripheral portion to the secondary particle diameter in the above range, a sufficient hollow portion can be formed in the lithium transition metal composite oxide.

  The particle diameter of the fine primary particles in the center of the transition metal composite hydroxide and the larger primary particles in the outer peripheral portion, and the thickness of the outer peripheral portion are, for example, a plurality of transition metal composite hydroxide secondary particles in an epoxy resin. After performing embedding in a cross section and performing cross-section polisher processing, the cross section of the exposed particles can be measured by observing with a scanning electron microscope.

The transition metal composite hydroxide preferably has a BET specific surface area of 10 m ² / g or more and 30 m ² / g or less. If the BET specific surface area of the transition metal composite hydroxide is less than 10 m ² / g, when a lithium ion secondary battery is formed, a sufficient reaction area with the electrolyte cannot be secured, and the output characteristics are not sufficiently improved. It may be difficult to improve. On the other hand, when it exceeds 30 m ² / g, it may be difficult to obtain sufficient safety when a lithium ion secondary battery is configured.

(Crystal structure)
The transition metal composite hydroxide is composed of a central portion composed of fine primary particles and an outer peripheral portion composed of larger primary particles. The transition metal composite hydroxide according to one embodiment of the present invention is characterized in that the central part and the outer peripheral part have different crystal structures.

  Nickel hydroxide has an alpha-type structure and a beta-type structure. The alpha-type structure has a structure in which the layers of Ni-OH ... OH-Ni of the beta-type structure are spread and the lamination is shifted, and water is interposed between these layers. It is characterized in that a molecule is inserted. Due to such a structure, the nickel hydroxide having an alpha structure has a larger volume per unit mass than the nickel hydroxide having a beta structure, and thus it is easy to form a sparser crystal. Therefore, when creating the central portion composed of the fine primary particles, the nickel hydroxide preferably has an alpha-type structure, and when creating the outer peripheral portion composed of the larger primary particles, the nickel hydroxide is beta-type. It is preferably a structure.

  The relationship between the crystallization conditions and the crystal structure of nickel hydroxide is affected by the oxygen concentration in the atmosphere during the crystallization reaction.In an oxidizing atmosphere with a high oxygen concentration, the lower the crystallization pH, the easier it is to take the alpha-type structure, The higher the crystallization pH, the easier it is to adopt a beta-type structure. Conversely, in a non-oxidizing atmosphere having a low oxygen concentration during the crystallization reaction, a higher crystallization pH tends to take an alpha-type structure, and a lower crystallization pH tends to take a beta-type structure.

  However, when creating the center of the transition metal hydroxide, it is necessary to proceed with the crystallization reaction in an oxidizing atmosphere, and when creating the outer periphery, the crystallization reaction needs to proceed in a non-oxidizing atmosphere. It is important to control the pH to be lower and the pH to be higher when forming the outer periphery. More specifically, after the nucleation step is performed in an oxidizing atmosphere and at a high pH, the central portion is formed at a low pH in the oxidizing atmosphere, the atmosphere is switched to a non-oxidizing atmosphere, and the pH is increased to increase the outer periphery. By forming the portion, a transition metal composite hydroxide having an alpha structure at the center and a beta structure at the outer periphery can be produced. The detailed manufacturing method will be described later.

  Since the alpha-type structure and the beta-type structure of nickel hydroxide have a clear difference in the X-ray diffraction pattern, the crystal structure formed can be confirmed by X-ray diffraction. Since the oxide has an alpha-type structure at the center and a beta-type structure at the outer periphery, it is difficult to identify even the internal structure by ordinary powder X-ray diffraction. Therefore, after dissolving and removing the surface of the transition metal composite oxide with an acid or the like, X-ray diffraction measurement is performed, and the amount of dissolution removal using the particle size distribution of the transition metal hydroxide as an index and the diffraction peak height of each of the alpha type and beta type are determined. Alternatively, the internal crystal structure of the transition metal composite hydroxide can be estimated by determining the relationship between the peak area ratios. Further, a transition metal hydroxide may be collected for each of the first particle growth step S21 and the second particle growth step S22 described below, and X-ray diffraction measurement may be performed.

  As described above, according to the transition metal composite hydroxide according to one embodiment of the present invention, it is possible to provide a transition metal composite hydroxide that has a higher oil absorption compared to the related art and can exhibit excellent output characteristics. be able to.

<2. Method for producing transition metal composite hydroxide>
Next, a method for producing a transition metal composite hydroxide according to one embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, a method for producing a transition metal composite hydroxide according to an embodiment of the present invention includes a transition metal raw material aqueous solution containing one or more transition metal compounds and an ammonium nucleation aqueous solution containing an ammonium ion donor. Is supplied to the crystallization reactor while controlling the pH at a liquid temperature of 25 ° C. to 12.5 or more, the ammonium ion concentration to 25 g / L or less, and the oxygen concentration in the atmosphere to 10% by volume or more. The method includes a nucleus generation step S10 for generating nuclei, and a first particle growth step S21 and a second particle growth step S22 for growing particles of the generated nuclei.

  In the conventional crystallization method disclosed in Patent Document 5, the boundary between a coarse aggregate of fine primary particles forming a hollow portion and a dense primary particle aggregate on an outer peripheral portion surrounding the aggregate is relatively uneven. Because of the small amount, the inside of the outer shell portion of the lithium transition metal composite oxide obtained after the firing had a shape with little unevenness. In contrast, the transition metal composite hydroxide obtained by the production method according to one embodiment of the present invention has a coarse aggregate of fine primary particles forming a central portion, and a dense primary particle of an outer peripheral portion surrounding the aggregate. It is characterized by having an aggregate of particles. Hereinafter, each step will be described.

<2-1. Nucleation process>
In the method for producing a transition metal composite hydroxide according to one embodiment of the present invention, first, a plurality of transition metal compounds containing at least nickel are dissolved in water at a predetermined mass ratio to prepare a transition metal raw material aqueous solution. I do. In the method for producing a transition metal composite hydroxide according to one embodiment of the present invention, the substance ratio of each transition metal in the obtained transition metal composite hydroxide is the same as the substance ratio of each transition metal in the mixed aqueous solution. Becomes

  Therefore, the water content ratio of each transition metal in the transition metal raw material aqueous solution is the same as the material ratio of each transition metal in the transition metal composite hydroxide according to one embodiment of the present invention. The ratio of each transition metal compound to be dissolved is adjusted to prepare a transition metal raw material aqueous solution.

  On the other hand, an alkaline aqueous solution such as an aqueous sodium hydroxide solution, an aqueous solution containing ammonium ions, and water are supplied to the reaction tank and mixed to prepare an ammonium ion supply body. By adjusting the supply amount of the alkaline aqueous solution, the pH of the ammonium ion supplier is adjusted to be 12.5 or more, preferably 12.5 to 14.0, based on a liquid temperature of 25 ° C. Further, by adjusting the supply amount of the aqueous ammonia solution, the ammonium ion concentration in the aqueous solution before the reaction is adjusted to preferably 3 to 25 g / L, more preferably 5 to 20 g / L, and still more preferably 5 to 15 g / L. Adjust to. The temperature of the aqueous solution before the reaction is also adjusted to preferably 20 to 60 ° C, more preferably 35 to 60 ° C. The pH of the aqueous solution before the reaction in the reaction tank and the concentration of ammonium ion can be measured by a general pH meter and an ion meter, respectively.

  After adjusting the pH, ammonium ion concentration, and temperature of the aqueous solution before the reaction, an ammonium ion supplier is supplied into the reaction vessel with stirring. Thereby, an aqueous solution for nucleation in which the ammonium ion supplier and the aqueous solution of the transition metal raw material are mixed is obtained in the reaction tank. Fine nuclei of the transition metal composite hydroxide are generated in the nucleation aqueous solution. At this time, since the pH of the aqueous solution for nucleation is in the above range, the transition metal element in the supplied raw material aqueous solution causes only nucleation, and the generated nucleus hardly grows, and only nucleation proceeds. .

  Since the pH of the aqueous solution for nucleation and the concentration of ammonium ions decrease with the nucleation due to the supply of the raw material aqueous solution, the aqueous solution for nucleation is supplied and supplied with an ammonium supplier including an aqueous alkali solution and an aqueous ammonia solution. By adjusting the amount, the pH of the aqueous solution for nucleation is controlled so as to be maintained in the range of 12.5 to 14.0 and the ammonium ion concentration in the range of 3 to 25 g / L based on the liquid temperature of 25 ° C. I do.

  By the supply of the raw material aqueous solution, the aqueous alkali solution and the aqueous ammonia solution to the aqueous solution for nucleation, generation of new nuclei is continuously continued in the aqueous solution for nucleation. Then, when a predetermined amount of nuclei is generated in the nucleus generation aqueous solution, the nucleation step S10 ends. Whether a predetermined amount of nuclei has been generated is determined by the amount of metal salt added to the aqueous solution for nucleation. Also, the above-mentioned ammonium supplier and aqueous solution of the transition metal raw material are appropriately supplied until a predetermined amount of nuclei is generated.

  The amount of nuclei generated in the nucleation step S10 is not particularly limited, but in order to obtain a composite hydroxide having a good particle size distribution, in order to obtain a total amount, that is, to obtain a transition metal composite hydroxide. Is preferably 0.1 to 2% by mass, more preferably 1.5% by mass or less of the total transition metal compound supplied to the metal.

<2-2. First Particle Growth Process>
After the nucleation step S10, in the first particle growth step S21, the aqueous solution for particle growth containing nuclei is adjusted to a pH of 10.5 to 11.5, preferably 10.8 to 11 at a liquid temperature of 25 ° C. 0.3 to obtain a first aqueous solution for particle growth in which particles have grown. Specifically, this pH control is performed by adjusting the supply amount of the alkaline aqueous solution.

  When the pH of the first aqueous solution for particle growth is in the above range, the nucleus growth reaction occurs preferentially to the nucleus formation reaction. Therefore, in the first particle growth step S21, the nucleus grows (particle growth) with almost no new nuclei generated in the first aqueous solution for particle growth, and the transition metal composite having a predetermined particle diameter is formed. A hydroxide is formed. Further, by performing the crystallization reaction at the above pH under an oxidizing atmosphere, a transition metal composite hydroxide having an alpha-type structure is preferentially generated, and a central portion composed of fine primary particles is formed.

  As in the nucleation reaction, the pH and ammonium ion concentration of the first aqueous solution for particle growth decrease with the growth of particles. And supplying the ammonium feed containing the solution so as to maintain the pH of the aqueous solution for particle growth in the range of 10.5 to 11.5 and the concentration of ammonium ion in the range of 3 to 25 g / L based on the liquid temperature of 25 ° C. Control. In addition, since the concentration of the transition metal ion also decreases, an aqueous solution of the transition metal raw material is supplied as appropriate.

  Thereafter, when the transition metal composite hydroxide has grown to the target central part particle size, the first particle growth step S21 is completed.

<2-3. Second Particle Growth Step>
After the first particle growth step S21 is completed, in the second particle growth step S22, the supply of the transition metal raw material aqueous solution is temporarily stopped, and the pH of the first particle growth aqueous solution based on a liquid temperature of 25 ° C. is set to 11.1. The second aqueous solution for particle growth is further obtained by controlling the particle size to 5 to 12.0. Specifically, the pH control is performed by adjusting the supply amount of the aqueous alkali solution. Further, the atmosphere gas is switched to a non-oxidizing atmosphere having an oxygen concentration of 0.1% or less.

  When the pH of the second aqueous solution for particle growth is in the above range, the particles generated in the first particle growth step S21 further grow (particle growth), and a transition metal composite hydroxide having a predetermined particle diameter is formed. It is formed. At this time, a transition metal composite hydroxide having a beta structure is preferentially generated by performing a crystallization reaction at the above pH under a non-oxidizing atmosphere, and the fine primary particles generated in the first particle growth step S21 are formed. An outer peripheral portion composed of primary particles larger than the particles is formed.

  Also in the second particle growth step S22, the pH and the ammonium ion concentration of the aqueous solution for particle growth decrease with the particle growth by the supply of the aqueous solution of the transition metal raw material. And an ammonium supplier containing an aqueous alkali solution and an aqueous ammonia solution, the pH of the aqueous solution for particle growth is in the range of 11.5 to 12.0 based on the liquid temperature of 25 ° C., and the concentration of ammonium ion is 3 to 25 g. / L.

  Thereafter, when the transition metal composite hydroxide in the second particle growth step S22 has grown to the target particle diameter of the transition metal composite hydroxide, the second particle growth step S22 ends.

  Incidentally, the particle size of the transition metal composite hydroxide in each step, if the relationship between the amount of the transition metal compound added to each reaction aqueous solution in each step and the particle size distribution of the obtained particles is determined by a preliminary test, It can be easily determined from the amount of the transition metal compound added in each step.

  Further, as shown in FIG. 1, the pH of the aqueous solution for particle growth containing nuclei after the nucleation step S10 is adjusted, and the first and second particle growth steps S21 and S22 are continued from the nucleation step S10. Therefore, there is an advantage that the transition to the particle growth step can be performed quickly. Further, the transition from the nucleation step S10 to the particle growth step can be made only by adjusting the pH of the reaction aqueous solution, and the adjustment of the pH can be easily performed by temporarily stopping the supply of the alkaline aqueous solution. There are advantages. This advantage is the same when shifting from the first grain growth step S21 to the second grain growth step S22.

  The pH of the reaction aqueous solution can also be adjusted by adding sulfuric acid to the reaction aqueous solution when an inorganic acid of the same kind as the acid constituting the transition metal compound, for example, a sulfate is used as the transition metal compound.

Further, in the case of obtaining an alpha-type transition metal composite hydroxide having a coarse structure in the first particle growth step S21, while maintaining the oxidizing atmosphere, the stirring rotation speed in the reaction vessel is increased. It is preferable to perform the crystallization reaction by optimizing the power for the stirring place per unit volume so as to be in the range of 0.5 to 4 kW / m ³ . By setting the oxidizing atmosphere in the first particle growth step S21 as described above, the aggregation of the fine primary particles is promoted rather than the growth of the primary particles, and an aggregate of low-density fine primary particles having many voids is formed. Cheap.

On the other hand, in order to obtain a beta-structured transition metal composite hydroxide having a dense structure in the second particle growth step S22, while maintaining the non-oxidizing atmosphere, the stirring rotation speed in the reaction vessel is increased by the unit of the reaction solution. It is preferable to carry out the crystallization reaction in such a manner that the power for the stirring station per volume is in the range of 0.5 to 4 kW / m ³ . In this way, by suppressing the oxidation and optimizing the agitation in the second particle growth step S22, the growth of the primary particles is further promoted, and the growth of the large and dense primary particles can be promoted.

  Next, control of pH, control of a reaction atmosphere, substances and solutions used in each step, and reaction conditions in each step will be described in detail.

<2-4. PH control, reaction atmosphere control, substances and solutions used in each step, reaction conditions, etc. in each step>
(PH control)
In the nucleation step S10, it is necessary to control the pH of the aqueous solution for nucleation at a liquid temperature of 25 ° C. in the range of 12.5 to 14.0, preferably 12.5 to 13.5. When the pH exceeds 14.0, there is a problem that the generated nucleus becomes too fine, and the reaction aqueous solution gels. When the pH is less than 12.5, a nucleus growth reaction occurs at the same time as the nucleus formation, so that the range of the particle size distribution of the nuclei formed is widened and the nuclei become heterogeneous. That is, in the nucleation step S10, by controlling the pH of the reaction aqueous solution within the above range, nucleus growth can be suppressed and almost only nucleation can occur, and the nuclei to be formed are also homogeneous and in a range of particle size distribution. Can be narrow.

  On the other hand, in the first particle growth step S21, the pH of the aqueous solution for particle growth containing nuclei at a liquid temperature of 25 ° C. is in the range of 10.5 to 11.5, preferably 10.7-11.2. Need to be controlled. When the pH exceeds 11.5, newly formed nuclei increase, and fine secondary particles are secondarily generated, so that a hydroxide having a good particle size distribution cannot be obtained. If the pH is less than 10.5, the solubility due to ammonium ions is high, and the amount of metal ions remaining in the liquid without being precipitated increases, so that the production efficiency deteriorates. That is, in the first particle growth step S21, by controlling the pH of the aqueous solution for particle growth containing nuclei in the above range, only the nuclei generated in the nucleation step S10 are preferentially caused to grow, and Nucleation can be suppressed, and when a particle is grown in the above pH range under an oxidizing atmosphere, a transition metal composite hydroxide having an alpha structure is preferentially generated. The composite hydroxide is a coarse particle composed of fine primary particles and can have a uniform particle diameter.

  In the second particle growth step S22, the pH of the first aqueous solution for particle growth is controlled so that the pH based on a liquid temperature of 25 ° C. is in the range of 11.5 to 12.0, preferably 11.5 to 11.8. There is a need to. When particles are grown in the above pH range in a non-oxidizing atmosphere, a transition metal composite hydroxide having a beta structure is preferentially generated, and thus the obtained transition metal composite hydroxide is subjected to a first-stage particle growth process. These are dense particles composed of primary particles larger than the primary particles obtained in the above, and can be uniform in particle size.

  In both the nucleation step S10 and the first and second particle growth steps S21 and S22, it is preferable that the fluctuation range of the pH is within 0.2 of the set value. When the fluctuation range of the pH is large, nucleation and particle growth are not constant, and a uniform transition metal composite hydroxide having a narrow particle size distribution range may not be obtained.

(Control of reaction atmosphere)
The particle structure of the transition metal composite hydroxide according to one embodiment of the present invention is controlled by the reaction atmosphere in the nucleation step S10, the first particle growth step S21, and the second particle growth step S22.

  By controlling the reaction atmosphere in the initial stage of the nucleation step S10 and the first particle growth step S21 to an oxidizing atmosphere, the central portion composed of fine primary particles can have a low density. Specifically, in the oxidizing atmosphere in the nucleation step S10 and the first particle growth step S21, the oxygen concentration in the space inside the reaction tank is 10% by volume or more, preferably 20% by volume or more. In particular, it is preferable that the atmosphere be easy to control (oxygen concentration: 21% by volume). By setting the atmosphere in which the oxygen concentration exceeds 10% by volume, the average particle size of the primary particles can be as fine as 0.01 to 0.3 μm. On the other hand, when the oxygen concentration is 10% by volume or less, the average particle size of the primary particles in the central portion may exceed 0.3 μm. The upper limit of the oxygen concentration is not particularly limited, but if it exceeds 30% by volume, the average particle size of the primary particles may be less than 0.01 μm, which is not preferable.

  On the other hand, when the atmosphere in the reaction tank during the second particle growth step S22 is controlled to a non-oxidizing atmosphere, the growth of the primary particles forming the transition metal composite hydroxide is promoted, and the primary particles are large and dense. Secondary particles having an appropriately large particle size are formed. In particular, by setting the oxygen concentration to 1% by volume or less, preferably 0.5% by volume or less, more preferably 0.3% by volume or less in a non-oxidizing atmosphere, relatively large primary particles are generated and aggregated. Particle growth is promoted, and a transition metal composite hydroxide having a dense and moderately large outer peripheral portion can be obtained.

  Means for keeping the reaction vessel space in such an atmosphere include flowing an inert gas such as nitrogen to the reaction vessel space, and bubbling the inert gas into the reaction solution. Can be

  The switching of the atmosphere in the second particle growth step S22 is performed such that a transition metal composite hydroxide is formed in the finally obtained positive electrode active material so as to obtain a hollow portion where fine particles are not generated and cycle characteristics are not deteriorated. The timing is determined in consideration of the size of the central portion of. For example, the first particle growth step S21 may be performed in a range of 0 to 40% from the start of the first particle growth step S21 with respect to the entire time of the first and second particle growth steps S21 and S22. Preferably, the reaction is performed in the range of 0 to 30%, more preferably, in the range of 0 to 25%. If the switching is performed at a time point exceeding 40% of the total time of the first and second particle growth steps S21 and S22, the formed central part becomes large, and the outer shell part with respect to the particle diameter of the secondary particles is increased. Is too thin. On the other hand, if the switching to the second particle growth step S22 is performed before the start of the second particle growth step S22, that is, during the nucleation step S10, the central portion becomes too small or the above-described central portion and outer peripheral portion are reduced. No secondary particles having a two-layer structure consisting of

(Transition metal compound)
As the transition metal compound, a compound containing a target transition metal is used. As the compound to be used, a water-soluble compound is preferably used, and examples thereof include a nitrate, a sulfate and a hydrochloride. For example, as a metal compound of nickel, cobalt, and manganese, nickel sulfate, manganese sulfate, and cobalt sulfate are preferably used.

(Additive element)
As the additional element (at least one element selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), it is preferable to use a water-soluble compound, for example, titanium sulfate, peroxo. Ammonium titanate, titanium potassium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, zirconium nitrate, niobium oxalate, ammonium molybdate, sodium tungstate, ammonium tungstate can be used. .

  When such an additive element is uniformly dispersed inside the composite hydroxide, in the nucleation step S10 and the first and second particle growth steps S21 and S22, an aqueous solution for nucleation and particle growth containing nuclei are used. An aqueous solution in which a salt containing the one or more additional elements is dissolved, or an aqueous solution for dissolving the salt containing the one or more additional elements, or the one or more additional elements The aqueous solution in which the salt is dissolved and the above aqueous solution are simultaneously supplied into the crystallization tank, and the added element can be co-precipitated in a state where the added element is uniformly dispersed inside the composite hydroxide.

  When the surface of the composite hydroxide is coated with the additional element, for example, the composite hydroxide is slurried with an aqueous solution containing the additional element, and the slurry is controlled so as to have a predetermined pH. If an aqueous solution containing at least one or more additional elements is added and the additional elements are precipitated on the surface of the composite hydroxide by a crystallization reaction, the surface can be uniformly coated with the additional elements. In this case, an alkoxide solution of the additive element may be used instead of the aqueous solution containing the additive element. Furthermore, the surface of the composite hydroxide can also be coated with the additional element by spraying an aqueous solution or slurry containing the additional element on the composite hydroxide and drying. Further, a slurry in which the composite hydroxide and the salt containing the one or more additional elements are suspended is spray-dried, or the composite hydroxide and the salt containing the one or more additional elements are mixed by a solid phase method. And the like.

  When the surface is coated with the additional element, the atomic ratio of the additional element ions present in the mixed aqueous solution is reduced by the amount to be coated, so that the atomic ratio of the metal ions of the obtained composite hydroxide is reduced. Can be matched. The step of coating the surface of the particles with the additional element may be performed on the particles after the heat treatment of the transition metal composite hydroxide.

(Concentration of raw material aqueous solution)
The concentration of the transition metal raw material aqueous solution is preferably 1 to 2.6 mol / L, more preferably 1.5 to 2.4 mol / L, and still more preferably 1.8 to 2.2 mol / L in terms of the total amount of the transition metal compound. L. When the concentration of the aqueous solution of the transition metal raw material is less than 1 mol / L, the productivity of the transition metal composite hydroxide per volume of the reaction vessel decreases, which is not preferable because the productivity decreases. On the other hand, if the salt concentration of the transition metal raw material aqueous solution exceeds 2.6 mol / L, there is a risk that the transition metal raw material aqueous solution may freeze in the pipe and clog the pipe when the liquid temperature is low. Alternatively, it is necessary to heat, which is costly.

  In addition, the transition metal compound does not necessarily need to be supplied to the reaction tank as a transition metal raw material aqueous solution.For example, when a transition metal compound that reacts to produce a compound when mixed is used, the total of the total transition metal compound aqueous solution is used. An aqueous solution of a metal compound may be individually prepared so that the concentration falls within the above range, and the aqueous solution of each metal compound may be simultaneously supplied to the reaction vessel at a predetermined ratio as an aqueous solution.

  Further, the amount of the aqueous solution of the transition metal raw material or the aqueous solution of each metal compound to be supplied to the reaction tank is preferably such that the slurry concentration of the transition metal composite hydroxide at the time of completion of the crystallization reaction is approximately 30 to 250 g / L. Is preferably 80 to 150 g / L. When the slurry concentration is less than 30 g / L, the aggregation of the primary particles may be insufficient. When the slurry concentration is more than 250 g / L, the diffusion of the added mixed aqueous solution in the reaction tank is not sufficient, This is because there is a case where the grain growth is biased.

(Complexing agent)
In the method for producing a transition composite hydroxide, it is preferable to use a non-reducing complexing agent. If a reducing complexing agent is used, the solubility of manganese in the reaction aqueous solution becomes too large, and a transition metal composite hydroxide having a high tap density cannot be obtained. The non-reducing complexing agent is not particularly limited, and may be any as long as it can form a complex by binding to nickel, cobalt, and manganese ions in an aqueous solution. For example, an ammonium ion donor, ethylenediaminetetraacetic acid, nitrite triacetic acid, uracil diacetate, glycine and the like can be mentioned.

  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.

(Ammonia concentration)
The ammonia concentration in the reaction aqueous solution is maintained at a constant value within a range of preferably 3 to 25 g / L, more preferably 5 to 20 g / L, and still more preferably 5 to 15 g / L.

  Ammonia becomes an ammonium ion and acts as a complexing agent for the transition metal element. If the ammonia concentration is less than 3 g / L, the solubility of the transition metal ion cannot be kept constant, and the shape and the particle size are reduced. Well-shaped plate-like hydroxide primary particles are not formed, and a gel-like nucleus is easily formed.

  On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of the transition metal ion is large, and the hydroxide is densely formed. Therefore, the finally obtained positive electrode active material for a lithium ion secondary battery is also dense. It may have a structure, a small particle size, and a low specific surface area. Further, when the solubility of the transition metal ion becomes too large, the amount of the transition metal ion remaining in the reaction aqueous solution increases, and a shift in the substance ratio of each transition metal element occurs.

  Further, when the ammonia concentration fluctuates, the solubility of the transition metal ion fluctuates and a uniform hydroxide is not formed. Therefore, the ammonia concentration in the reaction aqueous solution is preferably maintained 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.

(Reaction liquid temperature)
In the reaction tank, the temperature of the reaction solution is preferably set at 20 to 60 ° C, more preferably 35 to 60 ° C. When the temperature of the reaction solution is lower than 20 ° C., nucleation is likely to occur due to low solubility of the transition metal ion, and control becomes difficult. On the other hand, when the temperature exceeds 60 ° C., the volatilization of ammonia is promoted, so that an excessive amount of ammonium ion donor must be added to maintain a predetermined ammonia concentration, which increases the cost.

(Alkaline aqueous solution)
The alkaline aqueous solution for adjusting the pH in the reaction aqueous solution is not particularly limited, and for example, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide can be used. In the case of such an alkali metal hydroxide, it may be supplied directly to the reaction aqueous solution, but it is preferable to add the alkali metal hydroxide as an aqueous solution to the aqueous solution in the reaction tank because of easy pH control of the reaction aqueous solution in the reaction tank.

  The method of adding the alkaline aqueous solution to the reaction vessel is not particularly limited, and the pH of the reaction aqueous solution is controlled to a predetermined value by a pump capable of controlling the flow rate, such as a metering pump, while sufficiently stirring the reaction aqueous solution. What is necessary is just to add so that it may be maintained in the range.

(production equipment)
In the method for producing a transition metal composite hydroxide according to one embodiment of the present invention, a batch-type apparatus that does not collect products until the reaction is completed is used. For example, a batch crystallization reaction tank equipped with a stirrer is used. When such an apparatus is employed, there is no problem that the growing particles are collected at the same time as the overflow liquid, unlike a continuous crystallization apparatus that collects a product by a general overflow. Uniform particles can be obtained.

  Further, since it is necessary to control the reaction atmosphere, a device capable of controlling the atmosphere such as a closed type device is used. By using such an apparatus, the obtained composite hydroxide can have the above structure, and the nucleation reaction and the particle growth reaction can proceed almost uniformly, so that the particle size distribution is excellent. Particles, that is, particles with a narrow range of particle size distribution, can be obtained.

  The transition metal composite hydroxide obtained through the above-described steps has a two-layer structure including a central portion and an outer peripheral portion having different crystal structures, and the central portion has water molecules between crystal layers of the transition metal hydroxide. It is characterized by comprising an inserted alpha-type transition metal hydroxide, wherein the outer peripheral portion comprises a beta-type transition metal hydroxide containing no water molecules between crystal layers of the transition metal composite hydroxide.

  As described above, according to the method for producing a transition metal composite hydroxide according to one embodiment of the present invention, there is provided a transition metal composite hydroxide that has a higher oil absorption compared to the conventional art and can exhibit excellent output characteristics. Can be done.

<3. Lithium transition metal composite oxide active material>
The lithium transition metal composite oxide active material according to one embodiment of the present invention is used for a lithium ion secondary battery. Further, the lithium transition metal composite oxide active material includes a hollow portion in which the center of the particles of the active material is a space, and an outer shell portion covering the hollow portion. The lithium transition metal composite oxide includes at least nickel as one of transition metals. It is characterized by having an α-NaFeO ₂ type crystal structure.

(composition)
Lithium transition metal composite oxide active material according to an embodiment of the present invention is a positive electrode active material, the composition has the general _{formula: Li 1 + s Ni x Co} y Mn z A t O 2 (-0.05 ≦ s ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.4, 0.1 ≦ z ≦ 0.4, 0 <t ≦ 0.1, A is preferably adjusted so as to be represented by Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, or W).

  In the lithium transition metal composite oxide active material according to one embodiment of the present invention, the value of s indicating the excess amount of lithium is in a range from −0.05 to 0.50. When the excess amount s of lithium is less than -0.05, the reaction resistance of the positive electrode in the lithium ion secondary battery using the obtained lithium transition metal composite oxide active material increases, and the output of the battery decreases. In some cases. On the other hand, when the excess amount s of lithium exceeds 0.50, the initial discharge capacity when the lithium transition metal composite oxide active material is used for the positive electrode of a battery decreases, and the reaction resistance of the positive electrode also increases. There are cases.

  In order to further reduce the reaction resistance, the excess amount s of lithium is preferably 0 or more, more preferably 0 or more and 0.35 or less, and 0 or more and 0.20 or less. Is more preferred. When x representing the nickel content in the above general formula is 0.7 or less and y is 0.1 or more, the lithium excess amount s is 0.10 or more from the viewpoint of increasing the capacity. Is more preferable.

  The value of y indicating the content of cobalt is 0.1 or more and 0.4 or less. When the value of y is in such a range, the charge / discharge capacity, cycle characteristics, and safety of the secondary battery when used as a positive electrode active material can be compatible at a high level.

  The value of z indicating the manganese content is 0.1 or more and 0.4 or less. When the value of z is in such a range, the transition metal composite hydroxide as a precursor has a central part composed of fine primary particles and an outer part composed of primary particles larger than the fine primary particles outside the central part. In some cases, the structure may have a shell. When the manganese content exceeds 0.4, there is a problem that the capacity of the battery used as the positive electrode active material decreases and the resistance increases.

  Further, as represented by the above general formula, it is more preferable that the lithium transition metal composite oxide active material according to one embodiment of the present invention is adjusted to contain an additional element. By including the above-mentioned additional element, it is possible to improve the durability characteristics and output characteristics of a battery using the same as the positive electrode active material.

  In particular, when the additive element is uniformly distributed on the surface or inside of the particle, the above effect can be obtained in the whole particle, and the above effect can be obtained with a small amount of addition, and a decrease in capacity can be suppressed.

  Further, in order to obtain an effect with a smaller addition amount, it is preferable to increase the concentration of the added element on the particle surface rather than on the inside of the particle.

  If the atomic ratio t of the additional element A to all atoms exceeds 0.1, the amount of metal elements contributing to the Redox reaction decreases, which is not preferable because the battery capacity decreases. Therefore, the additive element M is adjusted so that the above atomic ratio t falls within the above range.

(Average particle size)
The lithium transition metal composite oxide active material according to one embodiment of the present invention has an average particle size of more than 1 μm and 15 μm or less, preferably more than 3 μm and preferably 10 μm or less. When the average particle size is 5 μm or less, the tap density may decrease, and when the positive electrode is formed, the packing density of the particles may decrease, and the battery capacity per positive electrode volume may decrease. On the other hand, if the average particle size exceeds 15 μm, the specific surface area of the lithium transition metal composite oxide active material decreases, and the interface with the electrolyte of the battery decreases. The characteristics may deteriorate.

  Therefore, if the lithium transition metal composite oxide active material according to one embodiment of the present invention is adjusted to the above range, in a battery using the positive electrode active material of the lithium transition metal composite oxide active material for the positive electrode, Battery capacity can be increased, and excellent battery characteristics such as high safety and high output can be obtained.

(Particle size distribution)
The lithium transition metal composite oxide active material according to one embodiment of the present invention has an index [(D90-D10) / average particle diameter] of 1.0 or less, preferably 0.1, which is an index indicating the spread of the particle size distribution. It is preferable to be composed of secondary particles of lithium transition metal composite oxide having a very high homogeneity of 70 or less. When the particle size distribution is wide, the positive electrode active material contains many fine particles with a very small particle size with respect to the average particle size and many large particles with a very large particle size with respect to the average particle size. May be. When a positive electrode is formed using a positive electrode active material having a large amount of fine particles, heat may be generated due to local reaction of the fine particles, which reduces safety and selectively deteriorates the fine particles. Therefore, the cycle characteristics deteriorate. On the other hand, when a positive electrode is formed using a lithium transition metal composite oxide active material having many coarse particles, the reaction area between the electrolyte and the positive electrode active material cannot be sufficiently obtained, and the battery output due to an increase in the reaction resistance is increased. Decrease.

  Therefore, by setting the particle size distribution of the lithium transition metal composite oxide active material to 0.70 or less in the above index [(D90-D10) / average particle size], the ratio of fine particles and coarse particles can be reduced, A battery using the lithium transition metal composite oxide active material for the positive electrode has excellent safety, and has good cycle characteristics and battery output. The average particle diameter, D90 and D10 are the same as those used for the above-described composite hydroxide, and the measurement can be performed in the same manner.

  Note that, similarly to the composite hydroxide as the precursor, it is difficult to classify a positive electrode active material having a wide normal distribution to obtain a positive electrode active material having a narrow particle size distribution also for the lithium transition metal composite oxide active material. Has been confirmed.

(Tap density)
In the lithium transition metal composite oxide active material according to one embodiment of the present invention, the tap density, which is an index of the packing density when tapping is performed, is preferably 1.0 g / cm ³ or more, and is preferably 1.3 g / cm ^3. cm ³ or more is more preferable.

For consumers and electric vehicles, increasing the capacity of the battery is a very important issue in order to extend the operating time and the mileage of the battery.In addition to increasing the capacity of the active material itself, the amount of active material used as an electrode is also important. It is required to fill a large amount. On the other hand, the electrode thickness of the secondary battery is about several tens of microns due to the problem of packing of the whole battery and the problem of electron conductivity. In particular, when the tap density is less than 1.0 g / cm ³ , the amount of active material that can be put in a limited electrode volume decreases, and the capacity of the entire secondary battery cannot be increased.

The upper limit of the tap density is not particularly limited, but the upper limit under normal manufacturing conditions is about 3.0 g / cm ³ .

(Characteristic)
For example, when the lithium transition metal composite oxide active material is used for a positive electrode of a 2032 type coin battery, a high initial discharge capacity of 150 mAh / g or more, a low positive electrode resistance, and a high cycle capacity retention rate are obtained, It shows excellent characteristics as a positive electrode active material for a lithium ion secondary battery.

  As described above, according to the lithium transition metal composite oxide active material of one embodiment of the present invention, when used in a lithium ion secondary battery, the oil absorption is higher than in the past, and excellent output characteristics can be exhibited. A lithium transition metal composite oxide active material can be provided.

<4. Method for producing lithium transition metal composite oxide active material>
The method for producing a lithium transition metal composite oxide active material according to one embodiment of the present invention is not particularly limited as long as the positive electrode active material can be produced so as to have the above-described average particle diameter, particle size distribution, particle structure, and composition. However, it is preferable to employ the following method since the lithium transition metal composite oxide active material can be more reliably produced.

  The method for producing a lithium transition metal composite oxide active material includes a mixing step S40 of mixing a transition metal composite hydroxide as a raw material with a lithium compound to form a lithium mixture, and firing the mixture formed in the mixing step S40. Although the firing step S50 is included, a heat treatment step S30 of heat-treating the transition metal composite hydroxide may be added before the mixing step S40.

  That is, as shown in FIG. 2, the method for producing a lithium transition metal composite oxide active material according to one embodiment of the present invention includes a heat treatment step S30 of heat-treating a transition metal composite hydroxide, And a firing step S50 of firing the mixture formed in the mixing step S40 to obtain a lithium transition metal composite oxide active material. Hereinafter, each step will be described.

<4-1. Heat treatment process>
The heat treatment step S30 is a step of subjecting the transition metal composite hydroxide obtained by the above-described method for producing a transition metal composite hydroxide to a heat treatment at a temperature of 105 to 750 ° C, preferably 105 to 400 ° C. By performing the heat treatment step S30, moisture contained in the composite hydroxide is removed. By performing the heat treatment step S30, the moisture remaining in the particles up to the firing step S50 can be reduced to a certain amount. For this reason, it is possible to prevent the ratio of the number of metal atoms and the ratio of lithium atoms in the obtained transition metal oxide active material from varying.

  Note that it is only necessary to remove water to such an extent that there is no variation in the number of metal atoms or the ratio of lithium atoms in the transition metal oxide active material. It is not necessary to perform heat treatment at a temperature of 400 ° C. or less, but it is sufficient to reduce the variation by setting the heating temperature to 400 ° C. or more and converting all the composite hydroxides to composite oxides. Good. In the post-firing step S50 also, the oxide is converted into the composite oxide during heating, but the above-mentioned variation can be suppressed to a lesser extent by heat treatment.

  In the heat treatment step S30, when the heating temperature is lower than 105 ° C., the excess water in the composite hydroxide cannot be removed, and the above-described variation may not be able to be suppressed. On the other hand, when the heating temperature exceeds 750 ° C., the particles are sintered by the heat treatment, and a composite oxide having a uniform particle size cannot be obtained. The above-mentioned variation can be suppressed by previously determining the metal component contained in the composite hydroxide under the heat treatment conditions by analysis and determining the ratio to the lithium compound.

  The atmosphere in which the heat treatment is performed is not particularly limited, and may be a non-reducing atmosphere, but is preferably performed in an air stream that can be easily performed.

  The heat treatment time is not particularly limited, but if it is less than 1 hour, excess water of the composite hydroxide may not be sufficiently removed in some cases. Therefore, it is preferably at least 1 hour or more, more preferably 5 to 15 hours.

  The equipment used for the heat treatment is not particularly limited, and may be any equipment capable of heating the composite hydroxide in a non-reducing atmosphere, preferably in an air stream, such as an electric furnace without gas generation. Is preferably used.

<4-2. Mixing process>
The mixing step S40 includes a transition metal composite hydroxide or a composite hydroxide heat-treated in the heat treatment step S30 (hereinafter, sometimes referred to as “heat-treated particles”) and a substance containing lithium, for example, a lithium compound. And mixing to obtain a lithium mixture.

  Here, the heat-treated particles include not only the composite hydroxide from which residual moisture has been removed in the heat treatment step S30, but also the composite oxide converted into an oxide in the heat treatment step S30, or a mixed particle thereof.

  The transition metal composite hydroxide or the heat-treated particles and the lithium compound are the same as the number of atoms of metals other than lithium in the lithium mixture, that is, the sum of the numbers of atoms of nickel, manganese, cobalt, and additional elements (Me); They are mixed so that the ratio (Li / Me) to the number of atoms (Li) is 0.95 to 1.5, preferably 1 to 1.35, and more preferably 1 to 1.20. That is, since Li / Me does not usually change before and after the sintering step S50, Li / Me mixed in the mixing step S40 becomes Li / Me in the positive electrode active material, so that Li / Me in the lithium mixture may be obtained. And Li / Me in the positive electrode active material to be mixed.

  The lithium compound used to form the lithium mixture is not particularly limited, but, for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferable in that it is easily available. . Particularly, considering ease of handling and stability of quality, it is more preferable to use lithium hydroxide or lithium carbonate or a mixture thereof.

  It is preferable that the lithium mixture is sufficiently mixed before firing. When mixing is not sufficient, there is a possibility that Li / Me varies between individual particles, and problems such as insufficient battery characteristics can be obtained.

  In addition, a general mixer can be used for mixing, for example, a shaker mixer, a Reedige mixer, a Julia mixer, a V blender, or the like can be used. It is sufficient that the composite oxide or the heat-treated particles and the substance containing lithium are sufficiently mixed.

<4-3. Firing process>
The firing step S50 is a step of firing the lithium mixture obtained in the mixing step S40 to form a lithium transition metal composite oxide. When the lithium mixture is fired in the firing step S50, lithium in the lithium-containing substance diffuses into the transition metal composite hydroxide or the heat-treated particles, so that a lithium transition metal composite oxide is formed.

(Firing temperature)
The calcination of the lithium mixture is performed at 650-1000 ° C. If the calcination temperature is lower than 650 ° C., diffusion of lithium into the transition metal composite oxide is not sufficient, and excess lithium and unreacted transition metal composite oxide remain or the crystal structure is not sufficiently prepared. As a result, when used for a battery, sufficient battery characteristics cannot be obtained. On the other hand, when the temperature exceeds 1000 ° C., severe sintering occurs between the lithium transition metal composite oxides and abnormal grain growth occurs, so that the grains become coarse and the form of spherical secondary particles cannot be maintained. In any case, not only does the battery capacity decrease, but also the value of the positive electrode resistance increases.

  The firing temperature is preferably from 800 to 980 ° C, more preferably from 850 to 950 ° C.

(Firing time)
Of the firing time, the holding time at the predetermined temperature is preferably at least one hour or more, more preferably 2 to 10 hours. If the time is less than 1 hour, the lithium transition metal composite oxide may not be sufficiently generated.

(Calcination)
In particular, when lithium hydroxide or lithium carbonate is used as the lithium compound, before the firing step S50, the firing temperature is lower than the firing temperature and 350 to 800 ° C, preferably 450 to 780 ° C. It is preferable to perform calcination by holding for about an hour, preferably for 3 to 6 hours. Alternatively, the same effect as in the case of calcining can be obtained by slowing the rate of temperature rise until the temperature reaches the firing temperature. That is, it is preferable to perform calcination at the reaction temperature of lithium hydroxide or lithium carbonate and the transition metal composite oxide. In this case, if the temperature of the lithium hydroxide or lithium carbonate is maintained near the above reaction temperature, diffusion of the lithium into the heat-treated particles is sufficiently performed, and a uniform lithium transition metal composite oxide can be obtained.

(Firing atmosphere)
The atmosphere during the firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 10 to 100% by volume, and particularly preferably a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. That is, it is preferable to carry out the reaction in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 10% by volume, the oxidation may not be sufficient, and the crystallinity of the lithium transition metal composite oxide may not be sufficient.

  The furnace used for firing is not particularly limited, as long as it can be heated in the air to oxygen stream, but from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas is used. Preferably, a batch or continuous furnace is used.

(Crushing)
The lithium transition metal composite oxide obtained by calcination may have agglomeration or slight sintering. In this case, crushing may be performed, whereby the lithium transition metal composite oxide, that is, the positive electrode active material of the present invention can be obtained. In addition, 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 at the time of firing, without substantially destroying the secondary particles themselves. This is the operation of separating the secondary particles and loosening the aggregates.

The method for producing a lithium transition metal composite oxide active material according to one embodiment of the present invention can include the above steps, and the lithium transition metal composite oxide active material obtained through the above-described steps is The center of the particles of the lithium transition metal composite oxide active material is a hollow portion in which the center is a space and an outer shell portion covering the hollow portion, and the lithium transition metal composite oxide contains at least nickel as one of the transition metals. , Α-NaFeO ₂ type crystal structure.

<5. Lithium ion secondary battery>
A lithium ion secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. Further, at least one of the positive electrode and the negative electrode contains the above-described lithium transition metal composite oxide active material.

  The embodiment described below is merely an example, and a lithium ion secondary battery according to an embodiment of the present invention has been subjected to various changes and improvements based on the embodiment described in this specification. It is also possible to apply to the form.

(3-1) Positive electrode For example, a positive electrode of a lithium ion secondary battery is manufactured as follows using a lithium transition metal composite oxide active material that is a positive electrode active material obtained according to an embodiment of the present invention. .

  First, a conductive material and a binder are mixed with a powdery lithium transition metal composite oxide active material obtained according to an embodiment of the present invention, and activated carbon or a solvent such as viscosity adjustment is further added as necessary. Then, these are kneaded to produce a positive electrode mixture paste. At that time, the respective mixing ratios in the positive electrode mixture paste are also important factors that determine the performance of the lithium ion secondary battery. When the solid content of the positive electrode mixture excluding the solvent is set to 100 parts by mass, the content of the positive electrode active material is set to 60 to 95 parts by mass, and the content of the conductive material is set to 60 to 95 parts by mass similarly to the positive electrode of a general lithium ion secondary battery. It is desirable that the content be 1 to 20 parts by mass and the content of the binder be 1 to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil, dried, and the solvent is scattered. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. Thus, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut to an appropriate size according to the intended battery, and used for battery production. However, the method of manufacturing the positive electrode is not limited to the above-described example, and another method may be used.

  As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, or the like) or a carbon black-based material such as acetylene black or Ketjen black can be used.

  The binder plays a role of binding the active material particles, and is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacryl. Acids can be used.

  Further, if necessary, a solvent for dispersing the positive electrode active material, the conductive material and the activated carbon and dissolving the binder can be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can also be added to the positive electrode mixture in order to increase the electric double layer capacity.

(3-2) Negative Electrode The negative electrode is prepared by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, such as metallic lithium or a lithium alloy, and adding an appropriate solvent to form a negative electrode. The mixture is applied to the surface of a metal foil current collector such as copper, dried, and, if necessary, compressed to increase the electrode density.

  As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite and a phenol resin, and a powdered carbon material such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder similarly to the positive electrode, and an organic material such as N-methyl-2-pyrrolidone is used as a solvent for dispersing the active material and the binder. Solvents can be used.

(3-3) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and may be a thin film such as polyethylene or polypropylene having a large number of fine pores.

(3-4) Electrolyte A non-aqueous electrolyte or a solid electrolyte can be used as the electrolyte. The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

  As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, and chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, further, tetrahydrofuran, 2-hydrogen carbonate One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used.

  Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  On the other hand, as the solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, or the like is used.

The oxide solid electrolyte is not particularly limited, and any oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, for example, 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), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≦ X ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ etc. I can do it.

The sulfide-based solid electrolyte is not particularly limited, and any electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. The sulfide-based solid electrolyte, for _{example, 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.

In addition, as the inorganic solid electrolyte, one other than the above may be used. For example, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, or the like may be used.

  The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and examples thereof include polyethylene oxide, polypropylene oxide, and copolymers thereof. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

  Further, as the non-aqueous electrolyte, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and that is liquid even at normal temperature.

(3-5) Shape and Configuration of Battery The lithium ion secondary battery according to one embodiment of the present invention, which includes the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte described above, has a cylindrical shape or a stacked shape. And various other shapes.

  In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicates with the positive electrode current collector and the outside. A positive electrode terminal and a negative electrode current collector and a negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and sealed in a battery case to complete a lithium ion secondary battery.

(3-6) Characteristics The lithium ion secondary battery according to one embodiment of the present invention has a high initial discharge capacity of 150 mAh / g or more, a low positive electrode resistance of 10 Ω or less, a high capacity, and a high output. Also, in comparison with a conventional lithium-cobalt-based oxide or lithium-transition metal-based oxide positive electrode active material, it can be said that thermal stability is high and safety is excellent.

(3-7) Use The lithium ion secondary battery according to one embodiment of the present invention is suitable for a power supply of a small portable electronic device (a notebook personal computer, a mobile phone terminal, or the like) which always requires a high capacity.

  Further, the lithium ion secondary battery according to one embodiment of the present invention is also suitable for a battery as a motor drive power supply requiring high output. As the size of the battery increases, it becomes difficult to ensure safety, and an expensive protection circuit is indispensable. On the other hand, the lithium ion secondary battery according to one embodiment of the present invention has excellent safety without increasing the size of the battery. The expensive protection circuit can be simplified and the cost can be reduced. Further, since it is possible to reduce the size and increase the output, it is suitable as a power supply for transportation equipment which is limited in mounting space.

  Next, the transition metal composite hydroxide, the method for producing the transition metal composite hydroxide, the lithium transition metal composite oxide active material, and the lithium ion secondary battery according to one embodiment of the present invention will be described in more detail with reference to examples. . Note that the present invention is not limited to these examples.

(Example)
(Nucleation step S10)
First, 10 L of water was put into a reaction tank having an effective volume of 60 L, and the temperature in the tank was adjusted to 40 ° C. while stirring. At this time, air was fed into the reaction tank at a rate of 5 L / min to form an oxidizing atmosphere (oxygen concentration: 21% by volume). An appropriate amount of a 20% by mass aqueous solution of sodium hydroxide and 25% by mass of aqueous ammonia were added to the reaction tank, and the pH of the reaction solution in the tank was adjusted to 13.0 based on a liquid temperature of 25 ° C. Further, the concentration of ammonia in the aqueous solution before the reaction was adjusted to 10 g / L to obtain an ammonium supplier.

  Separately, nickel sulfate, manganese sulfate and cobalt sulfate were dissolved in water to prepare a 2 mol / L aqueous solution of a transition metal raw material having a total transition metal element concentration. In this transition metal raw material aqueous solution, the amount ratio (molar ratio) of each metal was adjusted so that Ni: Mn: Co = 1: 1: 1.

  This transition metal raw material aqueous solution was added at 100 ml / min for 3 minutes to cause a nucleation reaction. At the same time, an ammonium supplier containing 25% by mass aqueous ammonia and a 20% by mass aqueous sodium hydroxide solution was also added at a constant rate to adjust the pH of the aqueous solution for nucleation to 13.0 based on a liquid temperature of 25 ° C. Was maintained at 10 g / L to perform nucleation.

(First particle growth step)
After the nucleation step S10, the pH was adjusted by adding 64% by mass sulfuric acid until the pH of the aqueous solution for particle growth containing nuclei reached 11.0 based on a liquid temperature of 25 ° C.

  After the pH of the aqueous solution for particle growth containing the nucleus reached 11.0, the supply of the aqueous solution of 20% by mass sodium hydroxide and the aqueous solution of 25% by mass ammonia to the reaction aqueous solution (aqueous solution for particle growth) was restarted. While maintaining the pH at 11.6 based on a liquid temperature of 25 ° C., a transition metal raw material aqueous solution is supplied at 100 L / min to obtain a first aqueous solution for particle growth, and crystallization is continued for 180 minutes to grow particles. Was done. Further, the ammonia concentration was maintained at 10 g / L.

(Second particle growth step)
After the completion of the first particle growth step S21, the supply of the aqueous solution of the transition metal raw material solution was temporarily stopped, and nitrogen gas was flowed at 10 L / min until the oxygen concentration in the space inside the reaction tank became 0.1% by volume or less. . The pH of the first aqueous solution for particle growth was adjusted by adding a 20% aqueous sodium hydroxide solution until the pH of the aqueous solution for particle growth reached 11.6 based on a liquid temperature of 25 ° C.

  Thereafter, the supply of the transition metal raw material aqueous solution was restarted at 100 L / min to obtain a second aqueous solution for particle growth, and crystallization was performed for 210 minutes.

  The resulting transition metal composite hydroxide is collected by filtration, washed twice with 100 L of deionized water, and dehydrated by filtration to a moisture content of 5% or less. Drying at 12 ° C. for 12 hours gave transition metal composite hydroxide particles.

In the obtained transition metal composite hydroxide, D10, D50, and D90 were 4.1 μm, 5.0 μm, and 6.2 μm, respectively, and (D90−D10) / D50 was 0.42. The BET specific surface area determined by the nitrogen adsorption isotherm was 21.2 m ² / g. In addition, the average particle diameter used the laser beam diffraction-scattering type particle size analyzer (Microtrack HRA by Nikkiso Co., Ltd.). As the BET specific surface area, a fluidized gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb) was used.

  After each of the first particle growth step S21 and the second particle growth step S22, the transition metal composite hydroxide was sampled and measured by X-ray diffraction. As a result, the transition metal composite hydroxide after completion of the first particle growth step S21 has a peak identified as that of nickel hydroxide having an alpha-type structure, whereas, after the completion of the second particle growth step S22. In the transition metal composite hydroxide, a peak identified as a beta type structure was confirmed. The X-ray diffraction was measured using XRD (X @ Pert, PROMRD, manufactured by PANALYTICAL).

  Further, 10 g of the obtained transition metal composite hydroxide was put into 100 ml of 0.1 N thin sulfuric acid, and the mixture was stirred for 5, 10, 20, 30, and 60 minutes, collected, filtered, and dried under vacuum to obtain an X-ray diffraction sample. As a result of the measurement, the ratio of the first peak identified as that of beta-type nickel hydroxide to the first peak identified as that of alpha-type nickel hydroxide increases as the treatment time with thin sulfuric acid becomes longer. In the sample treated for 60 minutes, only a peak identified as that of nickel hydroxide having an alpha structure was observed.

  From the above, it was determined that the obtained transition metal composite hydroxide was a nickel hydroxide type crystal having an alpha structure at the center and a beta structure at the outer periphery.

(Heat treatment process, mixing process, firing process)
After heat-treating the obtained transition metal composite hydroxide at 150 ° C. for 12 hours, commercially available lithium carbonate is added so that the molar ratio of metal and lithium (Li / M ratio) becomes 1.2, and a shaker mixer is added. The mixture was sufficiently mixed by using an apparatus (TURBULA Type T2C manufactured by Willy & Bacoffen (WAB)) to obtain a mixture. This mixture was calcined at 950 ° C. in a stream of air (oxygen: 21% by volume) and further crushed to obtain a lithium transition metal composite oxide active material.

  Then, the oil absorption of the obtained lithium transition metal composite oxide active material and the positive electrode resistance of the coin cell were measured.

  The oil absorption was the DBP absorption measured according to JIS K6217-4: 2008. As a result, the oil absorption was 40.3 ml / 100 g.

  The positive electrode resistance of the coin cell was measured by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (1255B, manufactured by Solartron) by charging a coin-type battery at a charging potential of 4.1 V, and a Nyquist plot was obtained. Obtained.

  Since the obtained Nyquist plot is represented as a solution resistance, a negative electrode resistance and its capacity, and a sum of characteristic curves showing the positive electrode resistance and its capacity, fitting calculation is performed using an equivalent circuit based on this Nyquist plot, The value of the positive electrode resistance was calculated. As a result, the positive electrode resistance was 3.1Ω.

(Comparative example)
Except that the atmosphere in the reaction tank in the nucleation step S10 and the first particle growth step S21 was changed to a non-oxidizing atmosphere (oxygen concentration: 0.1% by volume), the transition metal composite hydroxide and A lithium transition metal composite oxide active material was obtained.

D10, D50, and D90 of the obtained transition metal composite hydroxide were 3.9 μm, 4.8 μm, and 6.1 μm, respectively, and (D90−D10) / D50 was 0.46. The BET specific surface area determined by the nitrogen adsorption isotherm was 19.8 m ² / g.

  Further, after treating the obtained transition metal composite hydroxide in the same manner as in the example, as a result of measurement by X-ray diffraction, only a peak identified as that of nickel hydroxide having a beta structure was observed at any treatment time. Did not. From this, it was determined that all the transition metal composite hydroxides obtained were nickel hydroxide type crystals having a beta type structure.

  The oil absorption was 24.8 ml / 100 g, and the positive electrode resistance was 4.8Ω.

  Table 1 shows the results of the above Examples and Comparative Examples.

(Evaluation results of Examples and Comparative Examples)
The oil absorption of the lithium transition metal composite oxide active material in the example was higher than that of the comparative example. Further, the positive electrode resistance of the coin cell in the example is lower than that of the comparative example, and excellent output characteristics can be exhibited.

  As described above, the transition metal composite hydroxide, the method for producing the transition metal composite hydroxide, the lithium transition metal composite oxide active material, and the lithium ion secondary battery according to one embodiment of the present invention have higher oil absorption than the conventional one. A transition metal composite hydroxide, a method for producing a transition metal composite hydroxide, a lithium transition metal composite oxide active material, and a lithium ion secondary battery, which can exhibit excellent output characteristics with a high amount and a low resistance value. Could be offered.

  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. Also, the transition metal composite hydroxide, the method for producing the transition metal composite hydroxide, the configuration and operation of the lithium transition metal composite oxide active material and the lithium ion secondary battery have been described in each embodiment and each example of the present invention. The present invention is not limited to this, and various modifications can be made.

S10 nucleation step, S21 first particle growth step, S22 second particle growth step,
S30 heat treatment step, S40 mixing step, S50 baking step

Claims (7)

A transition metal composite hydroxide that is a precursor of a positive electrode active material for a lithium ion secondary battery,
The transition metal composite hydroxide has a two-layer structure composed of a central portion and a peripheral portion having different crystal structures,
The central portion is made of an alpha-type transition metal hydroxide in which water molecules are inserted between crystal layers of the transition metal hydroxide,
The transition metal composite hydroxide, wherein the outer peripheral portion is made of a beta-type transition metal hydroxide containing no water molecules between crystal layers of the transition metal composite hydroxide. The transition metal complex hydroxide represented by the general _{formula: Ni x Co y Mn z A} t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.7,0.1 ≦ y ≦ 0.4 , 0.1 ≦ z ≦ 0.4, 0 <t ≦ 0.1, 0 ≦ a ≦ 0.5, A is from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W The transition metal composite hydroxide according to claim 1, wherein the transition metal composite hydroxide is represented by one or more selected additional elements. The transition metal composite hydroxide has an average particle diameter D50 of 3 μm or more and 8 μm or less, (D90−D10) / D50 of 1.0 or less, and a BET specific surface area of 10 m ² / g or more and 30 m ² / g or less. The transition metal composite hydroxide according to claim 1 or 2, wherein: A method for producing a transition metal composite hydroxide that is a precursor of a positive electrode active material for a lithium ion secondary battery,
An aqueous solution for nucleation including an aqueous solution of a transition metal material containing one or more transition metal compounds and an ammonium ion supplier has a pH of 12.5 or more at a liquid temperature of 25 ° C. and an ammonium ion concentration of 25 g / L or less, A nucleation step of controlling the oxygen concentration in the atmosphere to be 10% by volume or more and supplying the oxygen concentration to the crystallization reaction tank to generate nuclei;
It has a first particle growth step and a second particle growth step of growing the generated nuclei,
In the first particle growth step, the pH of the aqueous solution for particle growth containing the nuclei generated in the nucleation step is 10.5 to 11.5 based on a liquid temperature of 25 ° C., and the ammonium ion concentration is 25 g. / L or less, while continuously controlling the oxygen concentration in the atmosphere to be 10% by volume or more, continuously supplying the aqueous solution of the transition metal raw material and the ammonium ion supplier,
In the second particle growth step, control is performed so that the pH at a liquid temperature of 25 ° C. is 11.5-12.0, the ammonium ion concentration is 25 g / L or less, and the oxygen concentration in the atmosphere is 1% by volume or less. A method for producing a transition metal composite hydroxide, wherein the aqueous solution of the transition metal raw material and the ammonium ion supplier are continuously supplied to the mixture. A lithium transition metal composite oxide active material used for a lithium ion secondary battery,
A hollow portion in which the center of the particles of the lithium transition metal composite oxide active material is a space, and an outer shell portion covering the hollow portion,
The lithium transition metal composite oxide active material according to claim 1, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ type crystal structure containing at least nickel as one of transition metals. The lithium transition metal composite oxide is represented by the general _{formula: Li 1 + s Ni x Co} y Mn z A t O 2 (-0.05 ≦ s ≦ 0.50, x + y + z + t = 1,0.3 ≦ x ≦ 0. 7, 0.1 ≦ y ≦ 0.4, 0.1 ≦ z ≦ 0.4, 0 <t ≦ 0.1), where A is Al, Ti, V, Cr, Zr, Nb, Mo, The lithium transition metal composite oxide active material according to claim 5, comprising one or more elements selected from Hf, Ta, and W. A lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte,
A lithium ion secondary battery, wherein at least one of the positive electrode and the negative electrode contains the lithium transition metal composite oxide active material according to claim 5.

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