JP7172301B2 - Transition metal composite hydroxide, method for producing transition metal composite hydroxide, lithium transition metal composite oxide active material, and lithium ion secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a transition metal composite hydroxide that is a precursor of a positive electrode active material for lithium ion secondary batteries, 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 smart phones and tablet PCs, there is a strong demand for the development of small, lightweight secondary batteries with high energy density. In addition, there is a strong demand for the development of high-power secondary batteries as power sources for motor drives, particularly power sources for transportation equipment.

As a secondary battery that satisfies such requirements, 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 desorbing and intercalating lithium is used as an active material for the negative electrode and the positive electrode. Lithium ion secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using lithium metal composite oxides having a layered or spinel crystal structure as positive electrode materials. can obtain a voltage as high as 4 V, and is being put to practical use as a battery with a high energy density.

Currently, lithium-cobalt composite oxides (LiCoO ₂ ), which are relatively easy to synthesize, and lithium-transition metal composite oxides (LiNiO ₂ ) using nickel, which is cheaper than cobalt, are currently used as positive electrode materials for such lithium-ion secondary batteries. 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 ) have been proposed.

Among these lithium-transition metal composite oxides, lithium-nickel composite oxide (LiNiO ₂ ), which is capable of reducing the amount of cobalt used and has a high charge-discharge capacity and has excellent thermal stability, has recently been developed. Lithium-nickel-manganese composite oxide (LiNi _1/2 Mn _1/2 O ₂ ), and lithium-nickel-cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) has attracted attention.

By the way, among the uses of lithium secondary batteries, there are those that are assumed to be repeatedly charged and discharged at a high rate (rapid charge and discharge). Lithium-ion secondary batteries used as a power source for automobiles (for example, lithium-ion secondary batteries installed in hybrid vehicles that use both a lithium-ion secondary battery and a power source with a different operating principle, such as a gasoline engine, as a power source) secondary battery) is a representative example that is assumed to be used in this way. However, conventional general lithium-ion secondary batteries exhibit relatively high durability against low-rate charge/discharge cycles, but their performance deteriorates against high-rate charge/discharge cycles ( It was known that it is easy to cause an increase in internal resistance, etc.). Therefore, the following documents are disclosed with respect to the above problems.

For example, Patent Literature 1 describes a technique of forming a positive electrode or a negative electrode of a lithium ion secondary battery from an active material having a porous hollow structure. According to such an active material with a porous hollow structure, the contact area with the electrolyte increases, which facilitates the movement of lithium ions, and also suppresses the distortion caused by the volume expansion of the active material due to the insertion of lithium. It is said that a high-capacity, long-life lithium battery that can be rapidly charged can be obtained.

Further, in Patent Documents 2 to 4, composite oxide particles (lithium-cobalt composite oxide particles or spinel-type particles) which are hollow spherical secondary particles in which primary particles are aggregated and have a large number of gaps leading to the inside on the surface Lithium-Manganese Composite Oxide Particles) is used as a positive electrode active material to increase the contact area with the non-aqueous electrolyte and improve the utilization rate of the positive electrode active material.

Further, Patent Document 5 describes a lithium phosphate compound having an olivine structure, which improves output by increasing oil absorption. Further, in Patent Document 6, a hollow structure having a secondary particle in which a plurality of primary particles of a lithium transition metal composite oxide are aggregated and a hollow portion formed inside the secondary particle shows performance suitable for high output. In addition, it is described that active material particles that are less deteriorated by charge-discharge cycles can be obtained.

Furthermore, in Patent Document 7, a nucleation step of generating nuclei in an oxidizing atmosphere, and an aqueous solution for particle growth containing the nuclei formed in the nucleation step are prepared at a pH of 10.0 at a liquid temperature of 25° C. standard. It is controlled to be lower than the nucleation stage in the range of 5 to 12.0, and in the middle of the particle growth process, the oxidizing atmosphere is switched to a mixed atmosphere of oxygen and inert gas with an oxygen concentration of 1% by volume or less. A structured precursor 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 manufacturing methods have a problem that they have a low oil absorption, and sufficient output characteristics cannot be obtained.

Therefore, 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, and a An object of the present invention is to provide a lithium ion secondary battery.

A transition metal composite hydroxide according to one aspect 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, and the transition metal composite hydroxide has a crystal structure is a two-layer structure consisting of a central portion and an outer peripheral portion, wherein the central portion is composed of an alpha-type transition metal hydroxide in which water molecules are inserted between the crystal layers of the transition metal hydroxide, and the outer peripheral portion is a transition It is characterized by being composed of a beta-type transition metal hydroxide that does not contain water molecules between crystal layers of the metal composite hydroxide.

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

At this time, in one aspect of the present invention, the transition metal composite hydroxide has the general formula: Ni _x Co _y Mnz At (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 Al, Ti, V, Cr, Zr, one or more additive elements selected from Nb, Mo, Hf, Ta and W).

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

At this time, in one aspect of the present invention, 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.

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

In one aspect 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 supplying an aqueous transition metal raw material solution containing one or more transition metal compounds and ammonium ions The aqueous solution for nucleation containing nucleation is controlled so that the pH is 12.5 or more at a liquid temperature of 25 ° C., the ammonium ion concentration is 25 g / L or less, and the oxygen concentration in the atmosphere is 10% by volume or more. a nucleus generation step of supplying the nuclei to a crystallization reaction tank to generate nuclei; a first grain growth step and a second grain growth step of growing the generated nuclei into grains; In the step, the aqueous solution for particle growth containing the nuclei generated in the nucleation step is heated in an atmosphere with a pH of 10.5 to 11.5 and an ammonium ion concentration of 25 g/L or less at a liquid temperature of 25 ° C. While controlling the oxygen concentration of 10% by volume or more, the transition metal raw material aqueous solution and the ammonium ion donor are continuously supplied, and in the second particle growth step, at a liquid temperature of 25 ° C. While controlling the pH to be 11.5 to 12.0, the ammonium ion concentration to be 25 g/L or less, and the oxygen concentration in the atmosphere to be 1% by volume or less, the transition metal raw material aqueous solution and the ammonium ion donor are mixed. is continuously supplied.

In this way, when used as a precursor of a positive electrode active material for lithium ion secondary batteries, a method for producing a transition metal composite hydroxide that can exhibit high oil absorption and excellent output characteristics compared to conventional methods is provided. can provide.

According to one aspect of the present invention, there is provided a lithium-transition metal composite oxide active material used in a lithium-ion secondary battery, wherein a hollow portion in which the 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 containing at least nickel as one of the transition metals, and the lithium-transition metal composite oxide active material The DBP oil supply amount is 40.3 ml/100 g or more .

In this way, it is possible to provide a lithium-transition metal composite oxide active material that, when used in a lithium ion secondary battery, has a higher oil absorption than conventional ones and can exhibit excellent output characteristics.

At this time, in one aspect of the present invention, the lithium-transition metal composite oxide has the general formula: Li _1+s Ni _x Co _y Mn _z At 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, One or more elements selected from V, Cr, Zr, Nb, Mo, Hf, Ta, W may be included.

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

In one aspect of the present invention, there is provided a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode contains the lithium transition metal composite oxide active material. and

By doing so, it is possible to provide a lithium ion secondary battery that can exhibit excellent output characteristics.

ADVANTAGE OF THE INVENTION According to the present invention, a transition metal composite hydroxide, a method for producing a transition metal composite hydroxide, and a lithium-transition metal composite oxide active material have a higher oil absorption than conventional ones and can exhibit excellent output characteristics. and a lithium ion secondary battery.

FIG. 1 is a process drawing showing an outline of a method for producing a transition metal composite hydroxide according to one embodiment of the present invention. FIG. 2 is a process drawing showing an outline of 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 in the positive electrode, the present inventors have made intensive studies to solve the above problems. , the alpha-type transition metal hydroxide in which water molecules are inserted between the crystal layers of the transition metal hydroxide, and the peripheral part is from the beta-type transition metal hydroxide that does not contain water molecules between the crystal layers of the transition metal composite hydroxide. As a result, the positive electrode active material with a large oil absorption has many paths for lithium ions to enter and exit when the positive electrode is manufactured, and the reaction resistance of the secondary battery can be reduced, making it possible to obtain excellent output characteristics. The present invention has been completed by obtaining the knowledge that there is. Preferred embodiments of the present invention will be described below.

The embodiments described below do not unduly limit the scope of the invention described in the claims, and can be modified without departing from the gist of the invention. Moreover, not all the configurations described in the present embodiment are essential as the solution means of 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 one embodiment of the present invention will be described in the following order.
1. Transition metal composite hydroxide 2 . Production method of transition metal composite hydroxide 2-1. Nucleation step 2-2. First particle growth step 2-3. Second particle growth step 2-4. 2. pH control, reaction atmosphere control, substances and solutions used in each step, reaction conditions, etc. in each step; Lithium transition metal composite oxide active material 4 . Method for producing lithium-transition metal composite oxide active material 4-1. Heat treatment process 4-2. Mixing step 4-3. Firing process 5 . lithium ion secondary battery

<1. Transition metal composite hydroxide>
A transition metal composite hydroxide according to one embodiment of the present invention is a precursor of a positive electrode active material for lithium ion secondary batteries. The transition metal composite hydroxide has a two-layer structure consisting of a central portion and a peripheral portion having different crystal structures, and the central portion is an alpha-type transition metal in which water molecules are inserted between the crystal layers of the transition metal hydroxide. It is characterized in that it is made of a hydroxide, and the outer peripheral portion is made of a beta-type transition metal hydroxide that does not contain water molecules between the crystal layers of the transition metal composite hydroxide. 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 are described below.

(composition)
The composition of the transition metal composite hydroxide according to one embodiment of the present invention is represented by the general formula: NixCoyMnzAt(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 Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta, and W).

If a lithium-transition metal composite oxide is produced using a transition metal composite hydroxide having such a composition as a precursor, an electrode using this lithium-transition metal composite oxide as a positive electrode active material is used in a secondary battery. Furthermore, the value of the positive electrode resistance to be measured can be lowered, and the battery performance can be improved.

When the positive electrode active material is obtained using the transition metal composite hydroxide as a raw material, the material amount ratio (Ni: Mn: Co: M) of each constituent element of this transition metal composite hydroxide is It is also maintained in matter. Therefore, the material amount ratio of the composite hydroxide of the present invention is prepared so as to be the same as the material amount ratio required for the desired positive electrode active material.

(Average particle size)
The transition metal composite hydroxide according to one embodiment of the present invention is prepared to have an average particle size D50 of more than 1 μm and 15 μm or less, preferably an average particle size 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 for a positive electrode active material obtained using the transition metal composite hydroxide as a raw material exceeds 1 μm and is 15 μm or less. can be adjusted to Since the particle size distribution of the positive electrode active material is close to the particle size distribution of the raw transition metal composite hydroxide, it affects the characteristics of the battery using the positive electrode active material having the above particle size as the 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 positive electrode active material obtained is also small, and the specific surface area of the positive electrode active material is increased. Output can be obtained, but the packing density of the positive electrode is lowered, the charge/discharge capacity per volume is lowered, and the dispersibility of the conductive aid and the positive electrode active material may be deteriorated when preparing the electrode paste. In addition, the voltage applied to the individual positive electrode active material particles in the electrode becomes uneven, and the particles to which the high voltage is applied deteriorate with repeated charging and discharging, and the charging and discharging capacity of the secondary battery decreases. 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 is reduced, and the interface with the electrolyte solution is reduced, resulting in fewer paths for lithium ions to enter and exit. Therefore, the resistance of the positive electrode increases and the output characteristics of the battery may deteriorate.

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

As described above, the particle size distribution of the positive electrode active material is strongly affected by the raw material composite hydroxide. For example, if fine particles or coarse particles are mixed in the transition metal composite hydroxide, , as well as fine or coarse particles will be 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.

When a positive electrode is manufactured using a positive electrode active material containing many fine particles, the fine particles may react locally and generate heat, which reduces the safety of the secondary battery and selectively deteriorates the fine particles. Therefore, cycle characteristics deteriorate. On the other hand, when a positive electrode is formed using a positive electrode active material in which many large-sized particles are present, the reaction area between the electrolyte and the positive electrode active material is not sufficiently secured, and the reaction resistance increases, resulting in deterioration of the output characteristics of the secondary battery. do.

Although the method for determining the average particle size, D90, and D10 is not particularly limited, they can be determined, for example, from volume integrated values measured with a laser beam diffraction/scattering particle size analyzer. As for the average particle size, D50, which is the particle size at which the cumulative volume is 50% of the total particle volume, can be used in the same way as D10 and D90.

(particle structure)
A transition metal composite hydroxide according to one embodiment of the present invention is composed of substantially spherical secondary particles formed by aggregation of a plurality of primary particles. The shape of the primary particles that make up the secondary particles can take various forms such as plate-like, needle-like, rectangular parallelepiped, elliptical, and rhombohedral shapes. In addition, as for the aggregation state, in addition to the case of aggregation in random directions, the transition metal composite hydroxide according to one embodiment of the present invention can also have a form in which the major axis directions of the particles are aligned radially from the center toward the outer peripheral direction. It can be applied to objects.

In particular, in the transition metal composite hydroxide according to one embodiment of the present invention, it is preferable that 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 diffuses sufficiently into the secondary particles, resulting in a composite of lithium and transition metal. This is because the reaction of hydroxide proceeds easily.

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

When the average particle diameter of the primary particles is less than 0.3 μm, the sintering temperature is lowered in the firing process, the secondary particles are sintered more frequently, and coarse particles obtained by agglomeration of the secondary particles become the positive electrode active material. may become included. On the other hand, when the average particle size of the primary particles exceeds 3 μm, diffusion of the lithium compound into the interior of the secondary particles becomes difficult. Firing at such a high temperature may cause sintering and agglomeration between secondary particles to generate coarse particles, and the positive electrode active material may deviate from the 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 for synthesizing the positive electrode active material having the hollow structure includes an aggregate of fine and coarse primary particles forming the hollow portion and an aggregate of dense primary particles forming the outer shell portion outside the hollow portion. A transition metal composite hydroxide having at the outer peripheral portion is preferred.

The particle structure of such a transition metal composite hydroxide is composed of aggregates 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 a hollow structure, has a structure in which fine primary particles are connected in the center with many gaps, and the outer shell is a plate-like primary particle with a large thickness. It is preferable that the structure is denser than the central part. In such a transition metal composite hydroxide, sintering progresses from a lower temperature in the central part than in the outer shell part during the reaction with the lithium compound, and the primary particles in the central part move from the center to the outer peripheral part of the secondary particles. contracting. In addition, since the density of the transition metal composite hydroxide is low in the central portion, the shrinkage rate when reacting with the lithium compound is also large, and as a result, the lithium transition metal composite oxide particles obtained have a sufficient size in the central portion. A hollow portion, which is a space having a thickness, is formed.

Formation of such a hollow structure is greatly affected by the properties of the primary particles of the transition metal composite hydroxide. That is, it is preferable that fine primary particles are aggregated in random directions in the central portion, and larger primary particles are aggregated in random directions in the peripheral portion. Agglomeration in random directions causes uniform shrinkage in the central portion in all directions, and hollow portions having a sufficient size can be formed when the lithium-transition metal composite oxide is formed.

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

The secondary particles constituting the positive electrode active material made of the lithium-transition metal composite oxide obtained by 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 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 diameter of the secondary particles within the above range, sufficient hollow portions can be formed in the lithium-transition metal composite oxide.

In addition, the particle size of the fine primary particles in the central part of the transition metal composite hydroxide and the larger primary particles in the outer peripheral part, and the thickness of the outer peripheral part are determined, for example, by combining the plurality of transition metal composite hydroxide secondary particles with an epoxy resin. It can be measured by observing the exposed grain cross-section after embedding in such as and cross-section polishing, using a scanning electron microscope.

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

(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. A transition metal composite hydroxide according to one embodiment of the present invention is characterized in that the crystal structures of the central portion and the outer peripheral portion are different.

Nickel hydroxide has an alpha-type structure and a beta-type structure. The alpha-type structure has a structure in which the layers of the beta-type structure Ni--OH . It is characterized by having a molecule inserted therein. Due to such a structure, the nickel hydroxide with the alpha structure has a larger volume per unit mass than the nickel hydroxide with the beta structure, and easily forms coarser crystals. Therefore, nickel hydroxide preferably has an alpha-type structure when forming the central portion composed of the fine primary particles, and nickel hydroxide has a beta-type structure when forming the outer peripheral portion composed of larger primary particles. A structure is preferred.

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. The higher the crystallization pH, the easier it is to take the beta structure. Conversely, in a non-oxidizing atmosphere with a low oxygen concentration during the crystallization reaction, the higher the crystallization pH, the easier it is to take the alpha-type structure, and the lower the crystallization pH, the easier it is to take the beta-type structure.

However, when forming the central portion of the transition metal hydroxide, it is necessary to proceed with the crystallization reaction in an oxidizing atmosphere, and when forming the peripheral portion, it is necessary to proceed with the crystallization reaction in a non-oxidizing atmosphere. It is important to control the pH to a lower value and to a higher value when forming the peripheral portion. More specifically, after performing the nucleation step in an oxidizing atmosphere and 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 raised to increase the outer circumference. By forming the part, a transition metal composite hydroxide having an alpha structure in the central part and a beta structure in the outer peripheral part can be produced. A detailed manufacturing method will be described later.

Since there is a clear difference in the X-ray diffraction pattern between the alpha-type structure and the beta-type structure of nickel hydroxide, the formed crystal structure can be confirmed by X-ray diffraction. Since the oxide has an alpha-type structure in the center and a beta-type structure in the outer periphery, it is difficult to identify 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 was performed. Alternatively, it is possible to estimate the internal crystal structure of the transition metal composite hydroxide by obtaining the relationship of the peak area ratios. Alternatively, the transition metal hydroxide may be collected in each of the first particle growth step S21 and the second particle growth step S22, which will be described later, and subjected to X-ray diffraction measurement.

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 than conventional ones 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. A method for producing a transition metal composite hydroxide according to one embodiment of the present invention, as shown in FIG. was controlled so that the pH at a liquid temperature of 25° C. was 12.5 or more, the ammonium ion concentration was 25 g/L or less, and the oxygen concentration in the atmosphere was 10% by volume or more, and supplied to the crystallization reaction tank. It has a nucleus generation step S10 for generating nuclei, and a first grain growth step S21 and a second grain growth step S22 for grain-growing the generated nuclei.

In the conventional crystallization method disclosed in Patent Document 5, the boundary between a coarse aggregate of fine primary particles forming the hollow portion and an aggregate of dense primary particles in the outer peripheral portion surrounding it is relatively uneven. Since the amount was small, the inside of the outer shell portion of the lithium-transition metal composite oxide obtained after firing had a shape with little unevenness. On the other hand, 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 the central portion and a dense primary It is characterized by having an aggregate of particles. Each step will be described below.

<2-1. Nucleation step>
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 substance amount ratio to prepare an aqueous transition metal raw material solution. do. In the method for producing a transition metal composite hydroxide according to one embodiment of the present invention, the material amount ratio of each transition metal in the resulting transition metal composite hydroxide is the same as the material amount ratio of each transition metal in the mixed aqueous solution. becomes.

Therefore, water is added so that the substance amount ratio of each transition metal in the transition metal raw material aqueous solution is the same as the substance amount ratio of each transition metal in the transition metal composite hydroxide according to one embodiment of the present invention. A transition metal raw material aqueous solution is prepared by adjusting the ratio of each transition metal compound to be dissolved.

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 supplier. The pH of the ammonium ion donor is adjusted to 12.5 or more, preferably 12.5 to 14.0 at a liquid temperature of 25° C. by adjusting the supply amount of the alkaline aqueous solution. Further, by adjusting the supply amount of the ammonia aqueous solution, the ammonium ion concentration in the pre-reaction aqueous solution is 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 pre-reaction aqueous solution is also adjusted to preferably 20 to 60°C, more preferably 35 to 60°C. The pH of the pre-reaction aqueous solution in the reaction tank and the concentration of ammonium ions can be measured with a general pH meter and ion meter, respectively.

After adjusting the pH, ammonium ion concentration and temperature of the pre-reaction aqueous solution, an ammonium ion donor is supplied into the reaction vessel while stirring. As a result, an aqueous solution for nucleation in which the ammonium ion donor and the aqueous transition metal raw material solution are mixed is obtained in the reaction tank. Fine nuclei of the transition metal composite hydroxide are generated in the aqueous solution for nucleation. At this time, since the pH of the aqueous solution for nucleation is within the above range, the transition metal element in the supplied raw material aqueous solution causes only nucleation, and the generated nuclei hardly grow, and only nucleation proceeds. .

Since the pH and ammonium ion concentration of the aqueous solution for nucleation decrease with the nucleation caused by the supply of the raw material aqueous solution, an ammonium supplier containing an aqueous alkaline solution and an aqueous ammonia solution is supplied to the aqueous solution for nucleation. By adjusting the amount, the pH of the aqueous solution for nucleation is maintained in the range of 12.5 to 14.0 and the ammonium ion concentration in the range of 3 to 25 g/L at a liquid temperature of 25°C. do.

By supplying the raw material aqueous solution, the alkaline aqueous solution, and the ammonia aqueous solution to the nucleation aqueous solution, new nuclei are continuously generated in the nucleation aqueous solution. Then, when a predetermined amount of nuclei is generated in the nucleation aqueous solution, the nucleation step S10 is terminated. Whether or not a predetermined amount of nuclei has been generated is determined by the amount of metal salt added to the aqueous solution for nucleation. In addition, the ammonium donor and the transition metal raw material aqueous solution 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 with a good particle size distribution, the total amount, that is, to obtain a transition metal composite hydroxide It 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.

<2-2. First particle growth step>
After completion of 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. .3 to obtain a first aqueous solution for particle growth in which particles are 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 within the above range, the growth reaction of nuclei takes precedence over the generation reaction of nuclei. Therefore, in the first particle growth step S21, almost no new nuclei are generated in the first aqueous solution for particle growth, nuclei grow (particle growth), and the transition metal composite having a predetermined particle diameter A hydroxide is formed. In addition, by carrying out the crystallization reaction at the above pH in an oxidizing atmosphere, the transition metal composite hydroxide having an alpha structure is preferentially produced, and a central portion composed of fine primary particles is formed.

As with the nucleation reaction, the pH and the ammonium ion concentration of the first aqueous solution for particle growth decrease with particle growth. by supplying an ammonium supplier containing the Control. In addition, since the concentration of transition metal ions also decreases, the transition metal raw material aqueous solution is also supplied as appropriate.

After that, when the transition metal composite hydroxide has grown to the target particle size of the central portion, the first particle growth step S21 is terminated.

<2-3. Second particle growth step>
After completion of the first particle growth step S21, in the second particle growth step S22, the supply of the transition metal raw material aqueous solution is temporarily stopped, and the first aqueous solution for particle growth is adjusted to a pH of 11.0 at a liquid temperature of 25°C. A second aqueous solution for grain growth is obtained by controlling the grains to be 5 to 12.0. Specifically, this pH control is performed by adjusting the supply amount of the alkaline aqueous solution. Also, the atmosphere gas is switched to a non-oxidizing atmosphere with an oxygen concentration of 0.1% or less.

When the pH of the second aqueous solution for particle growth is within the above range, the particles generated in the first particle growth step S21 grow further (particle growth) to form a transition metal composite hydroxide having a predetermined particle diameter. It is formed. At this time, by performing the crystallization reaction at the above pH in a non-oxidizing atmosphere, the transition metal composite hydroxide with a beta structure is preferentially generated, and the fine primary crystals generated in the first particle growth step S21 A perimeter is formed that consists of primary particles that are larger than the particles.

In the second particle growth step S22 as well, the pH and the ammonium ion concentration of the aqueous solution for particle growth decrease as the particles grow by supplying the aqueous transition metal raw material solution. and an ammonium supplier containing an aqueous alkaline solution and an aqueous ammonia solution, so that the pH of the aqueous solution for particle growth is in the range of 11.5 to 12.0 at a liquid temperature of 25° C., and the concentration of ammonium ions is in the range of 3 to 25 g. /L.

After that, when the transition metal composite hydroxide in the second particle growth step S22 has grown to the target particle size of the transition metal composite hydroxide, the second particle growth step S22 is finished.

The particle size of the transition metal composite hydroxide in each step can be determined by determining 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 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 has been completed is adjusted to perform the first and second particle growth steps S21 and S22 following the nucleation step S10. is performed, there is an advantage that the transition to the grain growth process can be quickly performed. Furthermore, the transition from the nucleation step S10 to the particle growth step can be made simply by adjusting the pH of the reaction aqueous solution, and the pH can be easily adjusted 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 an inorganic acid of the same kind as the acid constituting the transition metal compound, for example, sulfuric acid when a sulfate is used as the transition metal compound.

Further, in the first particle growth step S21, when obtaining a coarsely structured alpha-type transition metal composite hydroxide, while maintaining an oxidizing atmosphere, the stirring rotation speed in the reaction vessel is set to It is preferable to optimize the power required for stirring per unit volume in the range of 0.5 to 4 kW/m ³ to carry out the crystallization reaction. By creating an oxidizing atmosphere in the first particle growth step S21 in this way, 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 with many voids is formed. Cheap.

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

Next, pH control, reaction atmosphere control, 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 to be in the range of 12.5 to 14.0, preferably 12.5 to 13.5 at a liquid temperature of 25°C. If the pH exceeds 14.0, the resulting nuclei become too fine, and there is a problem of gelation of the aqueous reaction solution. On the other hand, if the pH is less than 12.5, a nucleus growth reaction occurs along with nucleation, so that the nuclei formed have a wide range of particle size distribution and become heterogeneous. That is, in the nucleation step S10, by controlling the pH of the reaction aqueous solution within the above range, the growth of nuclei can be suppressed and only nucleation can occur, and the nuclei formed are homogeneous and have a particle size distribution range. can be narrow.

On the other hand, in the first particle growth step S21, the aqueous solution for particle growth containing nuclei has a pH in the range of 10.5 to 11.5, preferably 10.7 to 11.2 at a liquid temperature of 25°C. should be controlled as If the pH exceeds 11.5, the number of newly generated nuclei increases and secondary fine secondary particles are generated, so that a hydroxide with a good particle size distribution cannot be obtained. Further, if the pH is less than 10.5, the solubility of ammonium ions is high, and the amount of metal ions that remain in the liquid without precipitating out increases, resulting in poor production efficiency. 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 growth of the nuclei generated in the nucleation step S10 is preferentially caused, and new nucleation can be suppressed, and when particle growth is caused in the above pH range in an oxidizing atmosphere, a transition metal composite hydroxide with an alpha structure is preferentially generated, so the resulting transition metal The composite hydroxide is coarse particles composed of fine primary particles, and can be of uniform particle size.

In the second particle growth step S22, the pH of the first aqueous solution for particle growth is controlled to be in the range of 11.5 to 12.0, preferably 11.5 to 11.8 at a liquid temperature of 25°C. There is a need to. When particles are grown in the above pH range in a non-oxidizing atmosphere, transition metal composite hydroxides having a beta-type structure are preferentially produced, so the transition metal composite hydroxides obtained are the first stage of the particle growth process. It is a dense particle composed of primary particles larger than the primary particles obtained in (1) and can be made uniform in particle size.

In both the nucleation step S10 and the first and second grain growth steps S21 and S22, the fluctuation range of pH is preferably within 0.2 above and below the set value. If the range of pH fluctuation is large, nucleation and particle growth may not be constant, and a uniform transition metal composite hydroxide with a narrow particle size distribution may not be obtained.

(Control of reaction atmosphere)
The grain 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 grain growth step S21 and the second grain growth step S22.

By controlling the reaction atmosphere in the initial stages 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 be made to have a low density. Specifically, the oxidizing atmosphere in the nucleus generation step S10 and the first grain growth step S21 has an oxygen concentration of 10% by volume or more, preferably 20% by volume or more in the inner space of the reaction vessel. In particular, it is preferable to use an air atmosphere (oxygen concentration: 21% by volume) that is easy to control. By creating an atmosphere in which the oxygen concentration exceeds 10% by volume, it is possible to make the average particle size of the primary particles 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 diameter 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 become less than 0.01 μm, which is not preferable.

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

Means for maintaining such an atmosphere in the inner space of the reaction vessel include circulating an inert gas such as nitrogen into the inner space of the reaction vessel and bubbling the inert gas into the reaction solution. be done.

The change of the atmosphere in the second particle growth step S22 is carried out so that in the finally obtained positive electrode active material, the transition metal composite hydroxide The timing is determined by considering the size of the central part of the . For example, the first grain growth step S21 can be performed in the range of 0 to 40% from the start of the first grain growth step S21 with respect to the total time of the first and second grain growth steps S21 and S22. It is preferably carried out in the range of 0 to 30%, more preferably in the range of 0 to 25%. If the switching is performed at a point exceeding 40% of the total time of the first and second particle growth steps S21 and S22, the central portion formed becomes larger, and the outer shell portion with respect to the particle size of the secondary particles. becomes too thin. On the other hand, before the start of the second grain growth step S22, that is, when switching to the second grain growth step S22 during the nucleation step S10, the central portion becomes too small, or the above-described central portion and the outer peripheral portion Secondary particles having a two-layer structure consisting of are not formed.

(Transition metal compound)
As the transition metal compound, a compound containing the desired transition metal is used. The compound to be used is preferably a water-soluble compound such as nitrates, sulfates and hydrochlorides. For example, nickel sulfate, manganese sulfate, and cobalt sulfate are preferably used as metal compounds of nickel, cobalt, and manganese.

(additive element)
The additive element (one or more elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) is preferably a water-soluble compound, such as 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, etc. can be used. .

In the case of uniformly dispersing the additional element inside the composite hydroxide, in the nucleation step S10 and the first and second particle growth steps S21 and S22, the nucleation aqueous solution and the nucleus-containing particle growth An aqueous solution obtained by dissolving a salt containing the one or more additive elements is added to the aqueous solution for grain growth, the first aqueous solution for grain growth, or the second aqueous solution for grain growth, or the one or more additive elements are added. The aqueous solution in which the containing salt is dissolved and the above aqueous solution are simultaneously fed into the crystallization tank, and the additive element can be coprecipitated in a state of being uniformly dispersed inside the composite hydroxide.

Further, when the surface of the composite hydroxide is coated with the additive element, for example, the composite hydroxide is slurried with an aqueous solution containing the additive element, and the pH is controlled to a predetermined value. By adding an aqueous solution containing more than one seed of the additive element and depositing the additive element on the surface of the composite hydroxide by a crystallization reaction, the surface can be uniformly coated with the additive element. 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 additive element by spraying an aqueous solution or slurry containing the additive element onto the composite hydroxide and drying it. Alternatively, 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. It can be coated by a method such as

When the surface is coated with the additive element, the atomic ratio of the additive 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 in the resulting composite hydroxide and the can be matched. In addition, the step of coating the surface of the particles with the additive element may be performed on the particles after heat-treating 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 substance amount of the transition metal compounds. Let L. If the concentration of the transition metal raw material aqueous solution is less than 1 mol/L, the production amount of the transition metal composite hydroxide per volume of the reaction tank is low, which is not preferable because the productivity is lowered. On the other hand, when the salt concentration of the transition metal raw material aqueous solution exceeds 2.6 mol/L, there is a danger of freezing inside the pipes and clogging the pipes when the liquid temperature of the transition metal raw material aqueous solution is low. Alternatively, it needs to be heated, which is costly.

Also, the transition metal compound does not necessarily have to be supplied to the reaction tank as an aqueous transition metal raw material solution. Aqueous metal compound solutions may be separately prepared so that the concentration falls within the above range, and these aqueous solutions of individual metal compounds may be simultaneously supplied into the reaction vessel at a predetermined ratio.

Furthermore, the amount of the transition metal raw material aqueous solution and the aqueous solution of each metal compound supplied to the reaction tank is preferably such that the slurry concentration of the transition metal composite hydroxide at the time of finishing the crystallization reaction is approximately 30 to 250 g / L. is preferably 80 to 150 g/L. If the slurry concentration is less than 30 g / L, the aggregation of primary particles may be insufficient, and if it exceeds 250 g / L, the mixed aqueous solution to be added will not diffuse sufficiently in the reaction tank This is because the grain growth may be biased.

(complexing agent)
It is preferable to use a non-reducing complexing agent in the method for producing the transition compound hydroxide. If a reducing complexing agent is used, the solubility of manganese in the reaction aqueous solution becomes too high, and a transition metal composite hydroxide with a high tap density cannot be obtained. The non-reducing complexing agent is not particularly limited as long as it can combine with nickel ions, cobalt ions and manganese ions in an aqueous solution to form a complex. Examples include ammonium ion donors, ethylenediaminetetraacetic acid, nitritotriacetic acid, uracildiacetic acid and glycine.

Ammonium ion donors are not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used.

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

Since ammonia turns into ammonium ions and acts as a complexing agent for transition metal elements, if the ammonia concentration is less than 3 g/L, the solubility of transition metal ions cannot be kept constant, and the shape and particle size change. Since uniform plate-like primary hydroxide particles are not formed and gel-like nuclei are likely to be formed, the particle size distribution tends to be widened.

On the other hand, when the concentration of ammonia exceeds 25 g/L, the solubility of transition metal ions is high, and hydroxides are densely formed. It may become structured, have a small particle size, and have a low specific surface area. Further, when the solubility of the transition metal ions becomes too large, the amount of transition metal ions remaining in the reaction aqueous solution increases, causing a deviation in the substance amount ratio of each transition metal element.

Further, when the ammonia concentration fluctuates, the solubility of the transition metal ions fluctuates, preventing uniform hydroxide formation. Therefore, it is preferable to keep the ammonia concentration in the reaction aqueous solution at a constant value. For example, the ammonia concentration is preferably maintained at a desired concentration with a width of about 5 g/L between the upper limit and the lower limit.

(Reaction liquid temperature)
In the reaction tank, the temperature of the reaction solution is preferably set to 20-60°C, more preferably 35-60°C. If the temperature of the reaction solution is lower than 20° C., the solubility of transition metal ions is low, and nuclei are likely to occur, making control difficult. On the other hand, when the temperature exceeds 60°C, volatilization of ammonia is accelerated, so an excess ammonium ion donor must be added in order to maintain a predetermined ammonia concentration, resulting in high 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 alkaline metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. In the case of such an alkali metal hydroxide, it may be supplied directly into the reaction aqueous solution, but it is preferable to add it as an aqueous solution to the aqueous reaction solution in the reaction vessel from the viewpoint of ease of pH control of the reaction aqueous solution in the reaction vessel.

The method of adding the alkaline aqueous solution to the reaction vessel is not particularly limited, either. Additions may be made so that the range is maintained.

(production equipment)
In the method for producing a transition metal composite hydroxide according to one embodiment of the present invention, a batch-type apparatus is used in which the product is not recovered until the reaction is completed. For example, it is a batch crystallization reactor equipped with a stirrer. When such an apparatus is adopted, unlike a continuous crystallizer in which the product is recovered by general overflow, the growing particles are not recovered at the same time as the overflow liquid. Uniform particles can be obtained.

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

The transition metal composite hydroxide obtained through the above steps has a two-layer structure consisting of a central portion and a peripheral portion having different crystal structures, and the central portion contains water molecules between the crystal layers of the transition metal hydroxide. The transition metal hydroxide is composed of an alpha-type transition metal hydroxide inserted therein, and the outer peripheral portion is composed of a beta-type transition metal hydroxide containing no water molecules between the 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, a transition metal composite hydroxide having a higher oil absorption than conventional ones and capable of exhibiting excellent output characteristics is provided. can do

<3. Lithium Transition Metal Composite Oxide Active Material>
A lithium transition metal composite oxide active material according to one embodiment of the present invention is used in a lithium ion secondary battery. Further, the lithium-transition metal composite oxide active material particles are composed of a hollow portion in which the center of the particle is a space and an outer shell portion that covers the hollow portion. It is characterized by having an α-NaFeO ₂ type crystal structure, including one.

(composition)
A lithium-transition metal composite oxide active material according to one embodiment of the present invention is a positive electrode active material, and has a composition represented by the general formula: Li _1+s Ni _x Co _{y Mnz} At 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 to be represented by one or more additive elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W).

In the lithium-transition metal composite oxide active material according to one embodiment of the present invention, the value of s, which indicates the excess amount of lithium, ranges 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. may be lost. 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. Sometimes.

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. In addition, when x indicating the content of nickel in the above general formula is 0.7 or less and y is 0.1 or more, the lithium excess amount s is set to 0.10 or more from the viewpoint of increasing the capacity. is more preferable.

The value of y, which indicates the content of cobalt, is set to 0.1 or more and 0.4 or less. When the value of y is within such a range, it is possible to achieve a high level of compatibility between the charge/discharge capacity, cycle characteristics, and safety of the secondary battery when used as the positive electrode active material.

The value of z, which indicates the content of manganese, is 0.1 or more and 0.4 or less. When the value of z is within such a range, the transition metal composite hydroxide as a precursor has a central portion composed of fine primary particles and an outer portion composed of primary particles larger than the fine primary particles outside the central portion. It may have a structure with a shell. When the content of manganese 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, the lithium-transition metal composite oxide active material according to one embodiment of the present invention is more preferably adjusted to contain an additive element. By containing the above additive element, it is possible to improve the durability characteristics and output characteristics of a battery using this as a positive electrode active material.

In particular, by uniformly distributing the additive element on the surface or inside the particle, the above effect can be obtained for the entire particle, and the addition of a small amount of the element can achieve the above effect while suppressing a decrease in capacity.

Furthermore, in order to obtain the effect with a smaller addition amount, it is preferable to increase the concentration of the additive element in the particle surface rather than in the particle interior.

If the atomic number ratio t of the additive element A to all atoms exceeds 0.1, the amount of metal elements that contribute to the Redox reaction is reduced, which is not preferable because the battery capacity is lowered. Therefore, the additional element M is adjusted so that the atomicity 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 10 μm or less. When the average particle diameter is 5 μm or less, the tap density is lowered, and when the positive electrode is formed, the packing density of the particles is lowered, and the battery capacity per volume of the positive electrode may be lowered. On the other hand, when the average particle diameter 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, thereby increasing the resistance of the positive electrode and increasing the output of the battery. 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, a battery using the positive electrode active material of this lithium-transition metal composite oxide active material for the positive electrode can achieve The battery capacity can be increased, and excellent battery characteristics such as high safety and high output can be obtained.

(particle size distribution)
In the lithium-transition metal composite oxide active material according to one embodiment of the present invention, [(D90-D10)/average particle diameter], which is an index showing the spread of the particle size distribution, is 1.0 or less, preferably 0.0. It is preferably composed of secondary particles of a lithium-transition metal composite oxide having extremely high homogeneity with a particle size of 70 or less. When the particle size distribution is wide, the positive electrode active material contains many fine particles whose particle size is very small compared to the average particle size and coarse particles whose particle size is extremely large compared to the average particle size. may become. When a positive electrode is formed using a positive electrode active material in which many fine particles are present, heat may be generated due to local reactions of the fine particles, which reduces safety and selectively deteriorates the fine particles. Therefore, the cycle characteristics deteriorate. On the other hand, when the positive electrode is formed using a lithium-transition metal composite oxide active material in which many coarse particles are present, the reaction area between the electrolytic solution and the positive electrode active material is not sufficiently secured, and the reaction resistance increases, resulting in increased battery output. decreases.

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 this lithium-transition metal composite oxide active material for the positive electrode is excellent in safety and has good cycle characteristics and battery output. The average particle size, D90, and D10 are the same as those used for the composite hydroxide described above, and can be measured in the same manner.

As for the lithium-transition metal composite oxide active material, it is difficult to classify a positive electrode active material having a broad normal distribution to obtain a positive electrode active material having a narrow particle size distribution, similarly to the precursor composite hydroxide. It has been confirmed that

(tap density)
The lithium-transition metal composite oxide active material according to one embodiment of the present invention preferably has a tap density, which is an index of packing density when tapped, of 1.0 g/cm ³ or more, and preferably 1.3 g/cm 3 or more. cm ³ or more is more preferable.

For consumer products and electric vehicles, increasing the capacity of batteries has become a very important issue in order to extend the usage time and driving distance of batteries. A lot of filling is required. 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 electronic conductivity. In particular, when the tap density is less than 1.0 g/cm ³ , the amount of active material that can be accommodated in the limited electrode volume is reduced, and the overall capacity of the secondary battery cannot be increased.

Although the upper limit of the tap density is not particularly limited, 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 the 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 can be obtained. It exhibits excellent characteristics as a positive electrode active material for lithium ion secondary batteries.

As described above, according to the lithium-transition metal composite oxide active material according to one embodiment of the present invention, when used in a lithium-ion secondary battery, the oil absorption is higher than before, 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 the 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 average particle size, particle size distribution, particle structure and composition. However, if the following method is adopted, the lithium-transition metal composite oxide active material can be produced more reliably, which is preferable.

A method for producing a lithium-transition metal composite oxide active material comprises a mixing step S40 of mixing a transition metal composite hydroxide and a lithium compound as raw materials to form a lithium mixture, and firing the mixture formed in the mixing step S40. However, a heat treatment step S30 for 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 for heat-treating the transition metal composite hydroxide, and A mixing step S40 of mixing the lithium compound to form a lithium mixture, 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. Each step will be described below.

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

It should be noted that all the composite hydroxides need not be converted to transition metal composite oxides, as long as the moisture can be removed to the extent that there is no variation in the ratio of the number of metal atoms and the number of lithium atoms in the transition metal oxide active material. Heat treatment at a temperature of 400° C. or less is sufficient, but in order to further reduce the variation, the heating temperature is set to 400° C. or more to convert all the composite hydroxides to composite oxides. good. In the firing step S50, which is a post-process, the composite oxide is also converted to a composite oxide during heating, but the heat treatment can further suppress the above variation.

In the heat treatment step S30, if the heating temperature is less than 105° C., excess moisture in the composite hydroxide cannot be removed, and the above variations may not 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. By determining the metal components contained in the composite hydroxide according to the heat treatment conditions in advance by analysis and determining the ratio to the lithium compound, the above variation can be suppressed.

The atmosphere in which the heat treatment is performed is not particularly limited as long as it is a non-reducing atmosphere.

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

The equipment used for the heat treatment is not particularly limited as long as it can heat the composite hydroxide in a non-reducing atmosphere, preferably in an air stream, such as an electric furnace that does not generate gas. is preferably used.

<4-2. Mixing process>
In the mixing step S40, 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”), etc., and a substance containing lithium, such as a lithium compound to obtain a lithium mixture.

Here, the heat-treated particles include not only composite hydroxides from which residual moisture has been removed in the heat treatment step S30, but also composite oxides converted to oxides in the heat treatment step S30, or mixed particles thereof.

The transition metal composite hydroxide or heat-treated particles and the lithium compound are the number of metal atoms other than lithium in the lithium mixture, that is, the sum of the number of atoms of nickel, manganese, cobalt and additive elements (Me), and the number of lithium 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, more preferably 1 to 1.20. That is, since Li/Me usually does not change before and after the firing step S50, the Li/Me mixed in this mixing step S40 becomes Li/Me in the positive electrode active material, so the Li/Me in the lithium mixture is It is mixed so as to be the same as Li/Me in the positive electrode active material to be used.

The lithium compound used to form the lithium mixture is not particularly limited, but for example, lithium hydroxide, lithium nitrate, lithium carbonate, or mixtures thereof are preferred in terms of easy availability. . In particular, it is more preferable to use lithium hydroxide, lithium carbonate, or a mixture thereof, considering ease of handling and stability of quality.

In addition, it is preferable that the lithium mixture is thoroughly mixed before firing. Insufficient mixing may cause Li/Me to vary among individual particles, resulting in problems such as insufficient battery performance.

In addition, a general mixer can be used for mixing, for example, a shaker mixer, Loedige mixer, Julia mixer, V blender, etc. can be used, and the transition metal composite hydroxide etc. is not destroyed. , the composite oxide or the heat-treated particles and the lithium-containing substance should be sufficiently mixed.

<4-3. Baking 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 sintered in the sintering step S50, lithium in the lithium-containing substance diffuses into the transition metal composite hydroxide or heat-treated particles, forming a lithium-transition metal composite oxide.

(firing temperature)
Firing of the lithium mixture is carried out at 650-1000°C. If the firing temperature is lower than 650° C., the diffusion of lithium into the transition metal composite oxide is insufficient, leaving excess lithium and unreacted transition metal composite oxide, or the crystal structure is not sufficiently arranged. As a result, sufficient battery characteristics cannot be obtained when used in batteries. On the other hand, if the temperature exceeds 1000° C., intense sintering occurs between the lithium-transition metal composite oxides, and abnormal grain growth occurs, resulting in coarse particles and a failure to maintain the shape of spherical secondary particles. In either case, not only does the battery capacity decrease, but the positive electrode resistance also increases.

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

(Baking time)
Of the firing time, the holding time at the predetermined temperature is preferably at least 1 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 produced sufficiently.

(calcination)
In particular, when lithium hydroxide or lithium carbonate is used as the lithium compound, before the firing step S50, 1 to 10°C lower than the firing temperature and at a temperature of 350 to 800 ° C., preferably 450 to 780 ° C. It is preferable to calcine after holding for about an hour, preferably 3 to 6 hours. Alternatively, by slowing down the rate of temperature rise until the firing temperature is reached, substantially the same effect as in the case of calcining can be obtained. That is, it is preferable to calcine at the reaction temperature of lithium hydroxide or lithium carbonate and the transition metal composite oxide. In this case, if the reaction temperature of lithium hydroxide or lithium carbonate is maintained near the above-mentioned temperature, diffusion of 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 firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 10 to 100% by volume, and particularly preferably an atmosphere containing a mixture of oxygen and an inert gas having the above oxygen concentration. That is, it is preferable to conduct the reaction in the air or in an oxygen stream. If the oxygen concentration is less than 10% by volume, the oxidation may be insufficient and the crystallinity of the lithium-transition metal composite oxide may be insufficient.

The furnace used for sintering is not particularly limited as long as it can be heated in an air or oxygen stream, but from the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is recommended. Batch or continuous furnaces are preferably used.

(crushing)
The lithium-transition metal composite oxide obtained by sintering may be agglomerated or slightly sintered. In this case, it may be pulverized to obtain the lithium-transition metal composite oxide, that is, the positive electrode active material of the present invention. In addition, crushing refers to applying mechanical energy to aggregates composed of multiple secondary particles generated by sintering necking between secondary particles during firing, and almost without destroying the secondary particles themselves. It is an operation to separate secondary particles and loosen aggregates.

A method for producing a lithium-transition metal composite oxide active material according to an 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 above-described The lithium-transition metal composite oxide active material particles are composed of a hollow portion in which the center of the particle is a space and an outer shell 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. At least one of the positive electrode and the negative electrode contains the lithium-transition metal composite oxide active material described above.

The embodiments described below are merely examples, and the lithium ion secondary battery according to one embodiment of the present invention has various modifications and improvements based on the embodiments described herein. It can also be applied to morphology.

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

First, a powdery lithium-transition metal composite oxide active material obtained according to an embodiment of the present invention is mixed with a conductive material and a binder, and if necessary, activated carbon and a solvent such as viscosity adjustment are added. Then, these are kneaded to prepare a positive electrode mixture paste. At that time, the mixing ratio of each component in the positive electrode mixture paste is also an important factor that determines the performance of the lithium ion secondary battery. When the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass, and the content of the conductive material is 60 to 95 parts by mass, similar to the positive electrode of a general lithium ion secondary battery. It is desirable that the content of the binder is 1 to 20 parts by mass and the content of the binder is 1 to 20 parts by mass.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size depending on the intended battery, and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the above examples, and other methods may be used.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin and polyacrylic. 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. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. 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 such as metal lithium or a lithium alloy, or a negative electrode active material capable of intercalating and deintercalating lithium ions, and adding an appropriate solvent to form a paste. The mixture is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as required.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon materials such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. 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 from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

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

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, and the like, or a mixture of two or more thereof is used. be able to.

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

Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

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

The oxide-based solid electrolyte is not particularly limited, and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO4, _{Li4SiO4 - Li3VO4} , Li2O _{- B2O3 - P2O5 ,} Li2O _{- SiO2} , Li2O _{- B2O3 -} ZnO, _{Li1 + X AlXTi 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 and the like.

The sulfide-based solid electrolyte is not particularly limited, and any solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP 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.

Inorganic solid electrolytes other than those described above may be used, such as Li ₃ N, LiI, Li ₃ N--LiI--LiOH, and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may also 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 electrolytic solution, an ionic liquid in which a lithium salt is dissolved may be used. Note that an ionic liquid is a salt that is composed of cations and anions other than lithium ions and that exhibits a liquid state even at room temperature.

(3-5) Shape and configuration of battery The lithium ion secondary battery according to one embodiment of the present invention, which is composed of the positive electrode, negative electrode, separator, and non-aqueous electrolyte described above, has a cylindrical shape or a laminated shape. etc. can be made into various shapes.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicated with the positive electrode current collector and the outside. A current collecting lead or the like is used to connect between the positive electrode terminal and between the negative electrode current collector and the negative electrode terminal leading to the outside, and the battery case is sealed to complete the 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 and a low positive electrode resistance of 10Ω or less, and has high capacity and high output. In addition, it can be said that the thermal stability is high and the safety is also excellent in comparison with conventional positive electrode active materials of lithium cobalt oxides or lithium transition metal oxides.

(3-7) Applications The lithium ion secondary battery according to one embodiment of the present invention is suitable as a power source for small portable electronic devices (laptop personal computers, mobile phone terminals, etc.) that always require high capacity.

In addition, the lithium ion secondary battery according to one embodiment of the present invention is also suitable as a battery for driving a motor that requires high output. As the size of the battery increases, it becomes difficult to ensure safety, and an expensive protection circuit is essential. 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. Furthermore, since it is possible to reduce the size and increase the output, it is suitable as a power supply for transportation equipment that 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 detail with reference to examples. . However, the present invention is not limited to these examples.

(Example)
(Nucleation step S10)
First, 10 L of water was put into a reaction vessel with an effective volume of 60 L, and the temperature inside the vessel was adjusted to 40° C. while stirring. At this time, air was fed into the reaction vessel at a rate of 5 L/min to create an oxidizing atmosphere (oxygen concentration: 21% by volume). Appropriate amounts of 20% by mass aqueous sodium hydroxide solution and 25% by mass aqueous ammonia were added to the reaction vessel to adjust the pH of the reaction liquid in the vessel to 13.0 at a liquid temperature of 25°C. Also, the concentration of ammonia in the pre-reaction aqueous solution was adjusted to 10 g/L to prepare an ammonium supplier.

Separately, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in water to adjust the total transition metal element concentration to prepare a transition metal raw material aqueous solution of 2 mol/L. In this transition metal raw material aqueous solution, the material amount ratio (molar ratio) of each metal was adjusted to 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 ammonia water and 20% by mass aqueous sodium hydroxide solution was also added at a constant rate to raise the pH of the nucleation aqueous solution to 13.0 based on the liquid temperature of 25° C., and the ammonia concentration was maintained at 10 g/L, nucleation was performed.

(First particle growth step)
After completion of the nucleation step S10, 64% by mass sulfuric acid was added to adjust the pH of the nucleus-containing aqueous solution for particle growth until the pH reached 11.0 at a liquid temperature of 25°C.

After the pH of the aqueous solution for particle growth containing nuclei reached 11.0, the supply of 20% by mass sodium hydroxide aqueous solution and 25% by mass aqueous ammonia was resumed to the reaction aqueous solution (aqueous solution for particle growth). , while controlling the pH at 11.6 based on the liquid temperature of 25 ° C., supply the transition metal raw material aqueous solution at 100 L / min to obtain the first aqueous solution for particle growth, and continue crystallization for 180 minutes to grow particles. did Also, the ammonia concentration was maintained at 10 g/L.

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

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

Then, the transition metal composite hydroxide produced was collected by filtration, washed twice with 100 L of deionized water, filtered and dehydrated to a moisture content of 5% or less, and then dried in a vacuum dryer at 0.1 Pa or less at 110 C. for 12 hours to obtain transition metal composite hydroxide particles.

The resulting transition metal composite hydroxide had D10, D50 and D90 of 4.1 μm, 5.0 μm and 6.2 μm, respectively, and (D90−D10)/D50 was 0.42. Also, the BET specific surface area obtained from the nitrogen adsorption isotherm was 21.2 m ² /g. For the average particle size, a laser beam diffraction/scattering particle size analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.) was used. The BET specific surface area was measured using a flow-type gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb).

After completion of 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 was confirmed to have a peak identified as that of nickel hydroxide having an alpha structure. A peak identified as a beta-type structure was confirmed for the transition metal composite hydroxide of . The X-ray diffraction was measured using XRD (X'Pert, PROMRD, manufactured by PANALYTICAL).

In addition, 10 g of the obtained transition metal composite hydroxide was put into 100 ml of 0.1N dilute sulfuric acid, stirred for 5, 10, 20, 30, and 60 minutes, collected, filtered, and vacuum-dried. As a result of the measurement, the longer the treatment time with dilute sulfuric acid, the higher the ratio of the first peak identified as that of beta-structured nickel hydroxide to the first peak identified as that of alpha-structured nickel hydroxide. It became smaller and the sample treated for 60 minutes showed only peaks identified as those of nickel hydroxide in the alpha structure.

From the above, it was determined that the resulting transition metal composite hydroxide was a nickel hydroxide type crystal with an alpha type structure in the central portion and a beta type structure in the outer peripheral portion.

(Heat treatment process, mixing process, firing process)
After the obtained transition metal composite hydroxide was heat-treated at 150° C. for 12 hours, commercially available lithium carbonate was added so that the molar ratio of metal and lithium (Li/M ratio) was 1.2, and the mixture was placed in a shaker mixer. The mixture was thoroughly mixed using an apparatus (TURBULA Type T2C manufactured by Willie et Bakkofen (WAB)) to obtain a mixture. This mixture was sintered at 950° C. in an air stream (oxygen: 21% by volume) and then pulverized 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 in accordance with JIS K6217-4:2008. As a result, the oil absorption was 40.3 ml/100 g.

In addition, the positive electrode resistance of the coin cell was measured by the AC impedance method using a coin battery charged at a charging potential of 4.1 V and using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) to obtain a Nyquist plot. Obtained.

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

(Comparative example)
The transition metal composite hydroxide and the A lithium transition metal composite oxide active material was obtained.

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

In addition, after the obtained transition metal composite hydroxide was treated in the same manner as in Examples, the result of measurement by X-ray diffraction showed that only peaks identified as those of nickel hydroxide with a beta structure were observed at any treatment time. I didn't. From this, it was determined that all of the transition metal composite hydroxides obtained were nickel hydroxide type crystals with a beta type structure.

Also, 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 in the comparative example. Moreover, the positive electrode resistance of the coin cell in the example is lower than that in 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 oil absorption compared to the conventional 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 provide.

Although the embodiments and examples of the present invention have been described in detail as described above, it should be understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present invention. , will be easily understood. Accordingly, all such modifications are intended to be included within the scope of the present invention.

For example, a term described at least once in the specification or drawings together with a different broader or synonymous term can be replaced with the different term anywhere in the specification or drawings. In addition, the transition metal composite hydroxide, the method for producing the transition metal composite hydroxide, the lithium transition metal composite oxide active material, and the configuration and operation of the lithium ion secondary battery have also been described in each embodiment and each example of the present invention. It is not limited to one, and various modified implementations are possible.

S10 nucleation step, S21 first grain growth step, S22 second grain growth step,
S30 heat treatment step, S40 mixing step, S50 firing 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 consisting of a central portion and an outer peripheral portion with different crystal structures,
The central portion is composed of an alpha-type transition metal hydroxide in which water molecules are inserted between crystal layers of the transition metal hydroxide,
A transition metal composite hydroxide, wherein the outer peripheral portion is made of a beta-type transition metal hydroxide that does not contain water molecules between crystal layers of the transition metal composite hydroxide. The transition metal composite hydroxide has the general formula: NixCoyMnzAt(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 selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W 2. The transition metal composite hydroxide according to claim 1, characterized by being represented by one or more 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, characterized by: A method for producing a transition metal composite hydroxide, which is a precursor of a positive electrode active material for lithium ion secondary batteries,
An aqueous solution for nucleation containing an aqueous transition metal raw material containing one or more transition metal compounds and an ammonium ion donor having a pH of 12.5 or more and an ammonium ion concentration of 25 g/L or less at a liquid temperature of 25° C., a nucleation step of controlling the oxygen concentration in the atmosphere to be 10% by volume or more and supplying it to the crystallization reaction tank to generate nuclei;
a first grain growth step and a second grain growth step for grain-growing the generated nuclei;
In the first particle growth step, the aqueous solution for particle growth containing the nuclei generated in the nucleation step has a pH of 10.5 to 11.5 and an ammonium ion concentration of 25 g at a liquid temperature of 25 ° C. /L or less, continuously supplying the transition metal raw material aqueous solution and the ammonium ion donor while controlling the oxygen concentration in the atmosphere to be 10% by volume or more,
In the second particle growth step, control is performed so that the pH is 11.5 to 12.0 at a liquid temperature of 25° C., the ammonium ion concentration is 25 g/L or less, and the oxygen concentration in the atmosphere is 1% by volume or less. and continuously supplying the aqueous transition metal raw material solution and the ammonium ion donor. A lithium transition metal composite oxide active material used in a lithium ion secondary battery,
The lithium-transition metal composite oxide active material comprises a hollow portion in which the center of the particle is a space, and an outer shell covering the hollow portion,
The lithium transition metal composite oxide has an α-NaFeO ₂ -type crystal structure containing at least nickel as one of the transition metals ,
A lithium-transition metal composite oxide active material, wherein the DBP oil supply amount of the lithium-transition metal composite oxide active material is 40.3 ml/100 g or more . The lithium transition metal composite oxide has the general formula: Li _1+s Ni _x Co _y Mn _z At 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), and A is Al, Ti, V, Cr, Zr, Nb, Mo, Hf, 6. The lithium-transition metal composite oxide active material according to claim 5, comprising at least one element selected from Ta and W. A lithium ion secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
7. 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 or 6.

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