JP6862786B2 - Method for Producing Transition Metal-Containing Composite Hydroxide and Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery - Google Patents

Description

The present invention relates to a method for producing a transition metal-containing composite hydroxide which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the transition metal-containing composite hydroxide as a precursor. The present invention relates to a method for producing a positive electrode active material for use.

In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density. There is also a strong demand for the development of high-output secondary batteries as power sources for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

As a secondary battery satisfying such a requirement, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. This 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 inserting lithium is used as the material of the negative electrode and the positive electrode.

Among these lithium ion secondary batteries, the lithium ion secondary battery using a layered or spinel type lithium transition metal-containing composite oxide as a positive electrode material can obtain a voltage of 4V class, and thus has a high energy density. Currently, research and development are being actively carried out, and some are being put into practical use.

As the positive electrode active material for the non-aqueous electrolyte secondary battery, which is the positive electrode material of this lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) particles, which are relatively easy to synthesize, and nickel, which is cheaper than cobalt, were used. Lithium nickel composite oxide (LiNiO ₂ ) particles, lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) particles, lithium manganese composite oxide using manganese (LiMn ₂ O ₄₎ ) Particles, lithium nickel transition metal-containing composite oxides such as lithium nickel-manganese composite oxide (LiNi _0.5 Mn _0.5 O _{2) particles have been proposed.}

By the way, in order to obtain a lithium ion secondary battery having excellent cycle characteristics and output characteristics, it is necessary that the positive electrode active material for a non-aqueous electrolyte secondary battery is composed of particles having a small particle size and a narrow particle size distribution. It becomes. This is because particles having a small particle size not only have a large specific surface area and can sufficiently secure a reaction area with the electrolytic solution, but also have a thin positive electrode and between the positive electrode and the negative electrode of lithium ions. This is because the positive electrode resistance can be reduced by shortening the moving distance. Further, since the voltage applied to each particle in the electrode is substantially constant for the particles having a narrow particle size distribution, it is possible to suppress a decrease in battery capacity due to selective deterioration of the fine particles.

Here, in order to further improve the output characteristics, it is effective to form a space in which the electrolytic solution can penetrate inside the positive electrode active material for the non-aqueous electrolyte secondary battery. The positive electrode active material for a non-aqueous electrolyte secondary battery having a hollow structure composed of such an outer shell portion and a space portion inside the outer shell portion has a solid structure non-aqueous electrolyte secondary material having the same particle size. Since the reaction area with the electrolytic solution can be increased as compared with the positive electrode active material for a battery, the positive electrode resistance can be significantly reduced. It is known that the positive electrode active material for a non-aqueous electrolyte secondary battery inherits the particle properties of the transition metal-containing composite hydroxide as a precursor thereof. Therefore, in order to obtain the above-mentioned positive electrode active material for a non-aqueous electrolyte secondary battery, it is necessary to appropriately control the particle size, particle size distribution, particle structure, etc. of the transition metal-containing composite hydroxide as a precursor thereof. You will need it.

For example, Japanese Patent Application Laid-Open No. 2012-246199, Japanese Patent Application Laid-Open No. 2013-147416, and WO2012 / 131881 include a nucleation step in which nucleation is mainly performed and a particle growth step in which particle growth is mainly performed. A method for producing a transition metal-containing composite hydroxide as a precursor of a positive electrode active material by separating the crystallization reaction into two steps is disclosed. In this method, by appropriately adjusting the pH value and the reaction atmosphere in the nucleation step and the particle growth step, a low-density central part having a small particle size, a narrow particle size distribution, and only fine primary particles, and a plate A transition metal-containing composite hydroxide composed of secondary particles composed of a high-density outer shell composed of only primary particles is obtained.

The positive electrode active material for a non-aqueous electrolyte secondary battery using a transition metal-containing composite hydroxide having such a structure as a precursor has a small particle size, a narrow particle size distribution, and an outer shell portion and a space portion inside the outer shell portion. It can be provided with a hollow structure composed of. Therefore, it is considered that the battery capacity, output characteristics, and cycle characteristics of the secondary battery using the positive electrode active material for the non-aqueous electrolyte secondary battery are improved at the same time.

Further, Japanese Patent Application Laid-Open No. 2011-119022 aims to provide a positive electrode active material which exhibits performance suitable for increasing the output of a non-aqueous electrolyte secondary battery and is less deteriorated by a charge / discharge cycle. Lithium having a perforated hollow structure composed of secondary particles in which a plurality of particles are aggregated, and having a space portion formed inside the outer shell portion of the secondary particles and a through hole penetrating from the outside to the space portion. Transition metal-containing composite oxides are disclosed. It is considered that the positive electrode active material having such a perforated hollow structure further reduces the positive electrode resistance and further improves the output characteristics.

Japanese Unexamined Patent Publication No. 2012-246199 Japanese Unexamined Patent Publication No. 2013-147416 WO2012 / 131881 Japanese Unexamined Patent Publication No. 2011-119092

Assuming application to power sources such as electric vehicles, the positive electrode active material for non-aqueous electrolyte secondary batteries is required to further improve the output characteristics without impairing the battery capacity and cycle characteristics. For that purpose, it is necessary to further reduce the positive electrode resistance in the positive electrode active material for the non-aqueous electrolyte secondary battery.

In view of the above problems, the present invention is a non-aqueous electrolyte having a structure capable of further improving the output characteristics of a secondary battery without impairing its battery capacity and cycle characteristics. An object of the present invention is to provide a production method for efficiently obtaining a positive electrode active material for a secondary battery and a transition metal-containing composite hydroxide which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery on an industrial scale. And.

The method for producing a transition metal-containing composite hydroxide of the present invention is a method for producing a transition metal-containing composite hydroxide which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery by a crystallization reaction. A nuclear production step in which the reaction aqueous solution is controlled so that the pH value at a liquid temperature of 25 ° C. is 12.0 to 14.0 by supplying an aqueous solution of a raw material containing at least a transition metal element, and nuclear formation is performed. The pH value of the aqueous solution for particle growth containing the nuclei obtained in the nucleation step is lower than the pH value in the nucleation step at a liquid temperature of 25 ° C., and 10.5-12.0. It is provided with a particle growth step of growing the nucleus by controlling the pH.

In particular, in the method for producing a transition metal-containing composite hydroxide of the present invention, the particle growth step is the first step of maintaining the supersaturation of the transition metal element in the reaction aqueous solution from the start of the particle growth step. After the lapse of the first stage, the supersaturation degree is switched to a state lower than the first stage to maintain the supersaturation degree, and after the lapse of the second stage, the supersaturation degree is changed from the second stage. A third step of switching to a high state and maintaining the supersaturation degree, and a fourth step of switching the supersaturation degree to a state lower than the third step and maintaining the supersaturation degree after the lapse of the third step. It is characterized by having.

It is preferable to switch the degree of supersaturation by controlling the pH value of the reaction aqueous solution based on the liquid temperature of 25 ° C. In this case, in the particle growth step, the pH value of the reaction aqueous solution in a state of high supersaturation based on a liquid temperature of 25 ° C. is adjusted to be in the range of 11.0 to 12.0. The pH value of the reaction aqueous solution under a low supersaturation degree based on a liquid temperature of 25 ° C. is adjusted to be in the range of 10.5 to 11.5 and lower than the pH value under a high supersaturation degree. Is preferable.

The first step is the time in the range of 0.5% to 20% with respect to the whole of the particle growth process, and the second step is the time in the range of 10% to 80% with respect to the whole of the particle growth step. The third step is the time in the range of 2% to 30% of the total particle growth process time, and the fourth step is 10% to 80% of the total particle growth process time. It is preferably in the range of time.

Another aspect of the method for producing a transition metal-containing composite hydroxide of the present invention is a fifth step of switching the supersaturation degree to a state higher than the fourth step and maintaining the supersaturation degree after the lapse of the fourth step. And, after the lapse of the fifth stage, the supersaturation degree is switched to a state lower than the fifth stage, and the sixth stage for maintaining the supersaturation degree is further provided.

In this case, the first step is the time in the range of 0.5% to 20% with respect to the whole of the particle growth step, and the second step is 10% to 75% with respect to the whole of the particle growth step. The time in the range of%, the third step is the time in the range of 2% to 30% with respect to the total of the particle growth process, and the fourth step is the time of 10% to the total of the particle growth process. The time ranged from 75%, the fifth step was the time in the range of 2% to 30% of the total particle growth process time, and the sixth step was the total particle growth process time. The time is preferably in the range of 10% to 75%.

Wherein the transition metal-containing composite hydroxide of the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, The composition is preferably represented by one or more additive elements selected from Hf, Ta, and W). In this case, after the particle growth step, a coating step may be further provided in which the surface of the transition metal-containing composite hydroxide is coated with the compound containing the additive element M.

The method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention includes a crystallization step for obtaining the transition metal-containing composite hydroxide using the above-mentioned production method of the present invention.
A mixing step of mixing the transition metal-containing composite hydroxide and a lithium compound to form a lithium mixture, and
A firing step of calcining the lithium mixture at a temperature in the range of 650 ° C. to 1000 ° C. in an oxidizing atmosphere to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery composed of a lithium transition metal-containing composite oxide.
To be equipped.

In the mixing step, the lithium compounds are mixed so that the ratio of the number of lithium atoms contained in the lithium mixture to the total number of atoms of metal elements other than lithium is in the range of 0.95 to 1.5. It is preferable to adjust the amount.

Prior to the mixing step, it is preferable to further include a heat treatment step of heat-treating the transition metal composite hydroxide at a temperature in the range of 105 ° C. to 750 ° C.

The lithium transition metal-containing composite oxide is _{subjected to the general formula (B): Li 1 + U} Ni _x Mn _y Co _z M _t O ₂ (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦). 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo , Hf, Ta, W (one or more additive elements selected from)).

By using the positive electrode active material for a non-aqueous electrolyte secondary battery produced by using the transition metal composite hydroxide obtained by the method for producing a transition metal-containing composite hydroxide of the present invention as a precursor, a conventional hollow structure is used. Or, compared to a non-aqueous electrolyte secondary battery that uses a positive electrode active material with a perforated hollow structure as the positive electrode material, a non-aqueous electrolyte secondary battery with further improved output characteristics without impairing its battery capacity and cycle characteristics. It is possible to provide it, and its industrial significance is extremely great.

FIG. 1 is a cross-sectional view schematically showing the structure of secondary particles constituting the transition metal composite hydroxide obtained by the method for producing a transition metal-containing composite hydroxide of the present invention. FIG. 2 is an FE-SEM image showing the surface of the positive electrode active material for a non-aqueous electrolyte secondary battery using the transition metal-containing composite hydroxide obtained in Example 1 as a precursor. FIG. 3 is an FE-SEM image showing a cross section of a positive electrode active material for a non-aqueous electrolyte secondary battery using the transition metal-containing composite hydroxide obtained in Example 1 as a precursor. FIG. 4 is an FE-SEM image showing the surface of the positive electrode active material for a non-aqueous electrolyte secondary battery using the transition metal-containing composite hydroxide obtained in Comparative Example 1 as a precursor. FIG. 5 is an FE-SEM image showing a cross section of a positive electrode active material for a non-aqueous electrolyte secondary battery using the transition metal-containing composite hydroxide obtained in Comparative Example 1 as a precursor. FIG. 6 is a schematic cross-sectional view of a 2032 type coin battery used for battery evaluation. FIG. 7 is a schematic explanatory view of a measurement example of impedance evaluation and an equivalent circuit used for analysis.

The present inventors have a small particle size, a narrow particle size distribution, and a space inside the outer shell, which is obtained based on the prior art such as WO2004 / 181891 and JP2011-110992. Regarding the positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter referred to as "positive electrode active material") having a hollow structure consisting of parts or a hollow structure with holes, further improvement of the output characteristics was intensively studied.

As a result, in the positive electrode active material, by providing a through hole in the outer shell portion that penetrates to the space portion, not only is it possible to sufficiently invade the space portion existing inside the positive electrode active material, but also the electrolytic solution can sufficiently penetrate. By allowing the conductive additive to enter the space through the through hole, it is possible to positively use the inner and outer surfaces of the secondary particles constituting the positive electrode active material as a reaction field with the electrolytic solution. , It was found that the positive electrode resistance of the positive electrode active material can be sufficiently reduced.

In order to obtain a positive electrode active material having such a structure, secondary particles constituting a transition metal-containing composite hydroxide (hereinafter referred to as “composite hydroxide”) are formed by forming a central portion composed of fine primary particles and the said secondary particles. A high-density layer formed on the outside of the central portion and composed of plate-shaped primary particles, a low-density layer formed on the outside of the high-density layer and composed of the fine primary particles, and formed on the outside of the low-density layer. By having a structure including an outer shell portion having an outer shell layer made of the plate-shaped primary particles, that is, a portion forming the outer shell portion of the positive electrode active material by firing is made of one layer of plate-shaped primary particles. Rather than being composed of only high-density layers, a low-density layer composed of fine primary particles having a predetermined radial thickness is sandwiched between a high-density layer composed of plate-shaped primary particles and an outer shell layer in the radial direction. By forming a three-layer structure, it is possible to form through holes in the outer shell of the positive electrode active material due to the low density layer, which allows not only the electrolytic solution but also the conductive auxiliary agent to enter. I got the finding that there is.

Further, in order to obtain a composite hydroxide composed of secondary particles having such a structure, the degree of supersaturation of the transition metal in the reaction aqueous solution is controlled while continuing to supply the raw material aqueous solution in the particle growth step. As a result, it was found that a high-density layer composed of plate-shaped primary particles and a low-density layer composed of fine primary particles can be alternately laminated.

In addition, by using a composite hydroxide having such a structure as a precursor, the positive electrode active material is composed of secondary particles having a small particle size, a narrow particle size distribution, a high sphericity, and excellent filling properties. I got the finding that it can be done.

The present invention has been completed based on these findings.

1. 1. Transition Metal-Containing Composite Hydroxide (1-1) Structure of Transition Metal-Containing Composite Hydroxide The composite hydroxide obtained by the method for producing a transition metal-containing composite hydroxide of the present invention is for a non-aqueous electrolyte secondary battery. It is a precursor of a positive electrode active material, and is composed of a plurality of plate-shaped primary particles and secondary particles formed by aggregating fine primary particles having a particle size smaller than the plate-shaped primary particles.

In particular, as shown in FIG. 1, the secondary particles constituting the composite hydroxide obtained by the present invention are formed in a central portion (21) composed of fine primary particles and outside the central portion, and are plate-shaped primary particles. At least one laminated structure consisting of a high-density layer (22) formed by agglomeration of particles and a low-density layer (23) composed of fine primary particles formed outside the high-density layer, and the low. It has a structure formed on the outside of the density layer and composed of an outer shell portion (25) composed of an outer shell layer (24) composed of the plate-shaped primary particles. That is, the secondary particles have a structure composed of a central portion and an outer shell portion, and the outer shell portion is composed of at least one laminated structure composed of a high-density layer and a low-density layer, and an outer shell layer. It has a multi-layer structure of three or more layers.

In the composite hydroxide obtained by the present invention, the outer shell portion has a structure in which a high-density layer and a low-density layer are laminated one by one inside the outer shell layer, and the inside of the outer shell layer. A structure in which two high-density layers and two low-density layers are laminated can also be adopted. That is, a second high-density layer made of the plate-shaped primary particles formed inside the outer shell layer and outside the laminated structure of the high-density layer and the low-density layer, and a second high-density layer. It can be configured by a five-layer multi-layer structure further including a laminated structure formed on the outside of the layer and composed of a second low-density layer composed of the fine primary particles.

First, since the central portion has a structure with many gaps in which fine primary particles are connected, the composite hydroxide is compared with a high-density layer composed of larger and thicker plate-shaped primary particles and an outer shell portion. During firing to obtain a positive electrode active material, sintering proceeds from a low temperature region and shrinks from the center of the particles to the high-density layer side where sintering progresses slowly, and a space is created in the center. As described above, since the central portion has a low density and a large shrinkage rate, the central portion is a space having a sufficient size. Therefore, the positive electrode active material obtained after firing has a hollow structure composed of an outer shell portion and a space portion inside the outer shell portion.

In particular, the secondary particles constituting the composite hydroxide of the present invention do not have an outer shell portion consisting of only one high-density layer around the central portion as in the conventional structure, but have a high-density layer. It has a laminated structure in which a low-density layer having a predetermined radial thickness is sandwiched between the outer shell layer and the outer shell layer.

With such a configuration, at the time of firing, the structural portion having many gaps in which the fine primary particles constituting the low-density layer are connected contracts toward the high-density layer and the outer shell layer, thereby forming a space portion. The space portion does not have a radial thickness sufficient to retain its shape. Therefore, as the high-density layer and the outer shell layer are sintered, they are substantially integrated while absorbing the low-density portion to form a single outer shell portion. Due to insufficient volume integral, the high-density layer and the outer shell layer contract during firing to form a through hole having a sufficient size and penetrating the integrated outer shell portion inside and outside. it is conceivable that.

Here, the low-density layer may include plate-shaped primary particles, and the inclusion of the plate-shaped primary particles facilitates the integration of the high-density layer and the outer shell layer. On the other hand, if the number of plate-shaped primary particles becomes too large, the shrinkage of the low-density layer decreases. Therefore, even when the low-density layer contains plate-shaped primary particles, the abundance ratio of the plate-shaped primary particles is preferably 50% or less with respect to the cross-sectional area of the low-density layer.

Further, in the secondary particles constituting the composite hydroxide, the low-density layer does not need to be formed in the entire circumferential direction of the secondary particles between the high-density layer and the outer shell layer, and is a positive electrode active material. A structure in which such a low-density layer is partially formed is also included in the scope of the present invention as long as at least one through hole having a sufficient size is formed in the outer shell portion of the above.

In the secondary particles constituting the positive electrode active material obtained by using the composite hydroxide of the present invention as a precursor, the electrical conduction of the entire outer shell portion is ensured, and the penetration formed in the outer shell portion is ensured. When the holes have a predetermined length and inner diameter, not only the electrolytic solution but also the conductive auxiliary agent can sufficiently penetrate into the space existing inside the outer shell portion through the through holes. Therefore, the inner and outer surfaces of the secondary particles (outer shell portion) can be positively used as a reaction field with the electrolytic solution, and the internal resistance of the positive electrode active material can be significantly reduced.

(1-2) Average Particle Size of Transition Metal-Containing Composite Hydroxide The average particle size of the secondary particles constituting the composite hydroxide obtained by the present invention is 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably. It is adjusted to 3 μm to 10 μm. The average particle size of the positive electrode active material correlates with the average particle size of the composite hydroxide that is its precursor. Therefore, by setting the average particle size of the composite hydroxide in such a range, it is possible to set the average particle size of the positive electrode active material in a predetermined range.

In the present invention, the average particle size of the composite hydroxide means a volume-based average particle size (MV), and can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering type particle size analyzer. ..

(1-3) Particle Size Distribution of Transition Metal-Containing Composite Hydroxide This is an index showing the spread of the particle size distribution of the secondary particles constituting the composite hydroxide obtained by the present invention [(d90-d10) / average particle size. ] Is adjusted to 0.65 or less, preferably 0.55 or less, and more preferably 0.50 or less.

The particle size distribution of the positive electrode active material is strongly influenced by the composite hydroxide that is its precursor. Therefore, for example, when a positive electrode active material is prepared using a composite hydroxide containing many fine particles or coarse particles as a precursor, the positive electrode active material also contains many fine particles or coarse particles. Therefore, the safety, cycle characteristics, and output characteristics of the secondary battery using this cannot be sufficiently improved. Therefore, the particle size distribution of the positive electrode active material is adjusted by adjusting the particle size distribution of the composite hydroxide, which is the precursor thereof, so that the value of [(d90-d10) / average particle size] is 0.65 or less. It is possible to avoid the above-mentioned problems related to battery characteristics, particularly safety and cycle characteristics caused by selective deterioration of fine particles. However, when considering industrial-scale production, it is possible to produce a composite hydroxide in a powder state in which the value of [(d90-d10) / average particle size] is excessively small in terms of yield, productivity, and so on. Or it is not realistic from the viewpoint of production cost. Therefore, the lower limit of the value of [(d90-d10) / average particle size] is preferably about 0.25.

Here, d10 means a particle size in which the number of particles in each particle size of the powder sample is accumulated from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles, and d90 is , Means a particle size in which the cumulative volume is 90% of the total volume of all particles when the number of particles is accumulated by the same method. Similar to the average particle size of the composite hydroxide, d10 and d90 can be obtained from the volume integrated values measured by the laser light diffraction scattering type particle size analyzer.

(1-4) Thickness of Central Area, High Density Layer, Low Density Layer and Outer Shell Layer In the composite hydroxide obtained by the present invention, the ratio of the outer diameter of the central part to the particle size of the secondary particles, and The ratio of the total thickness of the high-density layer and the outer shell layer to the particle size of the secondary particles, which constitutes the outer shell portion of the positive electrode active material, is determined by the positive electrode active material using the secondary particles as a precursor. However, it hardly changes. Therefore, in the secondary particles constituting the composite hydroxide, the ratio of the outer diameter of the central portion to the particle size and the thickness of each of the high density layer, the low density layer and the outer shell layer should be appropriately controlled. This makes it possible to set the particle structure of the positive electrode active material in an appropriate range.

[When the outer shell has a three-layer structure]
When the outer shell portion of the composite hydroxide has only one laminated structure composed of a high-density layer and a low-density layer inside the outer shell layer, that is, when it has a three-layer structure, it constitutes a composite hydroxide. In the secondary particles, the average ratio of the outer diameter of the central portion to the particle diameter (hereinafter referred to as “central particle size ratio”) is preferably in the range of 35% to 85%, preferably 40% to 80%. It is more preferably in the range, even more preferably in the range of 55% to 75%. With such a configuration, in the positive electrode active material, a space portion having a sufficient size can be formed inside the secondary particles, and the surface area inside the outer shell portion of the secondary particles can be secured. Further, in the composite hydroxide, in the positive electrode active material obtained by setting the high-density layer, the low-density layer, and the outer shell layer constituting the outer shell portion as appropriate thicknesses and using such a composite hydroxide as a precursor. It is possible to form an outer shell portion having an appropriate thickness and having a predetermined through hole penetrating in the radial direction.

Further, in the secondary particles constituting the composite hydroxide, the average ratio of the total thickness of the high-density layer and the outer shell layer constituting the outer shell portion of the composite hydroxide to the particle size of the secondary particles (hereinafter referred to as “)”. The "high density layer total particle size ratio") is preferably in the range of 5% to 30%, more preferably in the range of 8% to 25%, and in the range of 10% to 20%. Is even more preferable. By setting the total particle size ratio of the high-density layer in this range, it is possible to form a low-density layer having a predetermined size, and in addition, the high density at the time of firing for producing the positive electrode active material. Excessive volume shrinkage of the layer and the outer shell layer can be suppressed, and an outer shell portion having an appropriate thickness can be formed in the positive electrode active material.

The ratio of the thickness of only the high-density layer to the particle size of the secondary particles (hereinafter referred to as “high-density layer particle size ratio”) is preferably in the range of 2.5% to 15%, and is preferably 3% to 15%. It is more preferably in the range of%, and even more preferably in the range of 3% to 10%. If the particle size ratio of the high-density layer is smaller than 2.5%, through holes cannot be formed due to shrinkage when the composite hydroxide is integrated with the outer shell layer at the time of firing, or conversely, its morphology collapses. There is a possibility that it will end up. On the other hand, if the high-density layer particle size ratio exceeds 15%, a sufficiently low-density layer cannot be formed between the high-density layer and the outer shell layer, or an outer shell layer having a sufficient thickness cannot be formed. When the oxide is fired, the shrinkage of the high-density layer is insufficient to form through holes, and there is a possibility that a space remains between the high-density layer and the outer shell layer. , A desired structure may not be obtained, which includes an outer shell portion provided with a through hole penetrating in the radial direction and a space portion inside the outer shell portion.

The ratio of the thickness of the outer shell layer to the particle size of the secondary particles (hereinafter referred to as “outer shell layer particle size ratio”) is also preferably in the range of 2.5% to 15%, preferably 2.5%. It is more preferably in the range of ~ 12%, and even more preferably in the range of 2.5% to 10%. By setting the outer shell layer particle size ratio in this range, the shape and average particle size of secondary particles can be appropriately controlled in the positive electrode active material, and an outer shell portion having an appropriate thickness can be formed. It becomes. If the outer shell layer particle size ratio is smaller than 2.5%, the form of the composite hydroxide may collapse during firing. On the other hand, if the outer shell layer particle size ratio exceeds 15%, a sufficiently low density layer cannot be formed between the high density layer and the outer shell portion, or a high density layer having a sufficient thickness cannot be formed, and further. In the case of firing the composite hydroxide, through holes cannot be formed, and there is a possibility that a space portion remains between the high-density layer and the outer shell portion, and a desired structure can be obtained in the obtained positive electrode active material. You may not be able to do it.

On the other hand, the ratio of the thickness of the low-density layer to the particle size of the secondary particles (hereinafter referred to as "low-density layer particle size ratio") is preferably in the range of 2% to 20%, and is preferably 2% to 10%. It is more preferably in the range of 2% to 8%. By setting the low-density layer particle size ratio in this range, it becomes possible to form an outer shell portion in which a through hole having an appropriate thickness and an appropriate size is formed in the positive electrode active material. .. When the low-density layer particle size ratio is smaller than 2%, voids large enough to form a predetermined through hole in the outer shell portion of the positive electrode active material are not generated during firing of the composite hydroxide. On the contrary, if the particle size ratio of the low-density layer exceeds 20%, a space is formed between the high-density layer and the outer shell layer when the composite hydroxide is fired, and the high-density layer and the outside are formed. The shell portion is not substantially integrated, and the desired structure cannot be obtained in the obtained positive electrode active material.

Here, the central particle size ratio, the high density layer total particle size ratio, the high density layer particle size ratio, the outer shell layer particle size ratio, and the low density layer particle size ratio refer to the cross section of the composite hydroxide. , Can be obtained by observing with a scanning electron microscope (SEM) such as an electric field emission scanning electron microscope (FE-SEM). Specifically, first, the cross section of the secondary particles is observed in a field of view to which the central portion, the high-density layer, the low-density layer, and the outer shell layer of the secondary particles can be discriminated.

The maximum length between any two points on the outer edge of the secondary particle and the maximum length between any two points on the outer edge of the central part are measured, and their values are measured as the particle size and center of the secondary particle, respectively. The outer diameter of the part. Further, the thicknesses of the high-density layer, the low-density layer, and the outer shell layer at three or more arbitrary positions are measured with respect to one secondary particle, and the average value thereof is obtained. Here, as for the thickness of the high-density layer, an arbitrary point is selected from the innermost edge of the high-density layer in the cross section of the secondary particles, and the length to the boundary between the high-density layer and the low-density layer is the shortest. Let it be the length between points. Similarly, for the thickness of the low-density layer, an arbitrary point is selected from the innermost edge of the low-density layer in the cross section of the secondary particles, and the length to the boundary between the low-density layer and the outer shell layer is the shortest. The length is between two points. Further, as for the thickness of the outer shell layer, similarly, an arbitrary point is selected from the innermost edge of the outer shell layer in the cross section of the secondary particle, and the length between the two points where the length to the outer edge of the secondary particle is the shortest is selected. Let's say.

By dividing the outer diameter of these central parts, the thickness of the high-density layer, the thickness of the low-density layer, and the thickness of the outer shell layer by the particle size of the secondary particles constituting the composite hydroxide, The central particle size ratio, the high-density layer particle size ratio, the low-density layer particle size ratio, and the outer shell layer particle size ratio are determined, respectively. By performing the same measurement on 10 or more composite hydroxides and calculating the average number of them, the central particle size ratio, high-density layer particle size ratio, and low-density layer particle size in the entire sample are calculated. The ratio and the outer shell layer particle size ratio are finally determined. The total particle size ratio of the high-density layer is obtained from the finally obtained high-density layer particle size ratio and the outer shell layer particle size ratio.

[When the outer shell has a five-layer structure]
When the outer shell portion of the composite hydroxide includes two laminated structures composed of a high-density layer and a low-density layer inside the outer shell layer, that is, a first high-density layer, a first low-density layer, and a first When having a five-layer structure including two high-density layers, a second low-density layer, and an outer shell layer, the central particle size ratio is preferably in the range of 35% to 80%, and is preferably 40% to 80%. It is more preferably in the range of 75% and even more preferably in the range of 55% to 75%.

Further, the total particle size ratio of the high-density layer, which is the average ratio of the total thickness of the first high-density layer, the second high-density layer, and the outer shell layer to the particle size of the secondary particles, is 8% to 30%. It is preferably in the range of%, more preferably in the range of 8% to 25%, and even more preferably in the range of 10% to 25%.

The high-density layer particle size ratio, which is the average ratio of the thickness of each high-density layer to the particle size of the secondary particles, is preferably in the range of 2.5% to 15%, and preferably 3% to 3%. It is more preferably in the range of 12%, even more preferably in the range of 3% to 10%.

Similarly, the outer shell layer particle size ratio is preferably in the range of 2.5% to 15%, more preferably in the range of 3% to 12%, and in the range of 3% to 10%. Is even more preferable.

On the other hand, the total particle size ratio of the low density layer, which is the average ratio of the total thickness of the first low density layer and the second low density layer to the particle size of the secondary particles, is in the range of 2% to 20%. It is preferably in the range of 3% to 15%, more preferably in the range of 3% to 10%. The low density layer particle size ratio, which is the average ratio of the thickness of each low density layer to the particle size of the secondary particles, is preferably in the range of 1% to 10%, and is in the range of 2% to 7%. Is more preferable.

In the present invention, even when the outer shell portion has two or more laminated structures composed of a high-density layer and a low-density layer inside the outer shell layer, basically, composite hydroxylation having such a structure is provided. When the product is fired, the first high-density layer, the second high-density layer, and the outer shell layer are substantially integrated by sintering shrinkage. In this case as well, a structure of an outer shell portion provided with a predetermined through hole that allows the electrolytic solution and the conductive auxiliary agent to enter the space portion can be obtained while maintaining the durability of the entire positive electrode active material. It is possible to further reduce the positive electrode resistance.

(1-5) Primary Particles In the composite hydroxide obtained by the present invention, the fine primary particles which are the components of the central portion and the low density layer have an average particle size in the range of 0.01 μm to 0.3 μm. It is preferable, and it is more preferable that it is in the range of 0.1 μm to 0.3 μm. Here, if the average particle size of the fine primary particles is less than 0.01 μm, the thickness of the low-density layer may not be satisfactorily obtained. On the other hand, when the average particle size of the fine primary particles is larger than 0.3 μm, the volume shrinkage due to heating does not sufficiently proceed during the firing in the low temperature range in the firing step for producing the positive electrode active material, and the central portion. And because the difference in volume shrinkage between the low density layer and the high density layer and the outer shell layer is small, a central portion having a sufficiently large void is not formed in the center of the secondary particles of the positive electrode active material. Alternatively, in the outer shell portion of the secondary particles of the positive electrode active material, a through hole having a sufficient size that communicates the central portion and the outer side of the secondary particles may not be formed.

The shape of such fine primary particles is preferably needle-shaped. Since the needle-shaped primary particles have a shape having a one-dimensional directionality, when the particles are aggregated, a structure having many gaps, that is, a structure having a low density is formed. As a result, the density difference between the central portion and the low density layer and the high density layer and the outer shell layer can be made sufficiently large.

On the other hand, the plate-shaped primary particles forming the high-density layer of the secondary particles constituting the composite hydroxide and the outer shell layer preferably have an average particle size in the range of 0.3 μm to 3 μm, preferably 0.4 μm to 0.4 μm. It is more preferably in the range of 1.5 μm, and even more preferably in the range of 0.4 μm to 1.0 μm. When the average particle size of the plate-shaped primary particles is less than 0.3 μm, the volume shrinkage of the plate-shaped primary particles also occurs in the firing step for producing the positive electrode active material even in the low temperature region. Since the difference in volume shrinkage between the outer shell layer and the central portion and the low-density layer becomes small, a sufficient hollow structure cannot be obtained in the positive electrode active material, or through holes are formed in the outer shell portion of the positive electrode active material. In some cases, it may not be possible to obtain a sufficient amount of absorption of the low-density layer that leads to. On the other hand, when the average particle size of the plate-shaped primary particles is larger than 3 μm, firing at a higher temperature is required in order to increase the crystallinity of the positive electrode active material in the firing step when producing the positive electrode active material, which is a composite. Sintering between the secondary particles constituting the hydroxide progresses, and it becomes difficult to set the average particle size and particle size distribution of the positive electrode active material within a predetermined range.

When the fine primary particles are composed of needle-shaped primary particles, the difference in average particle size between the fine primary particles and the plate-shaped primary particles is preferably 0.1 μm or more, and more preferably 0.2 μm or more. When the fine primary particles have another structure, for example, a structure close to a plate-shaped primary particle, the difference in average particle size between the fine primary particle and the plate-shaped primary particle is preferably 0.2 μm or more, preferably 0.3 μm or more. It is more preferable to have.

The average particle size of the fine primary particles and the plate-shaped primary particles is determined by embedding a composite hydroxide in a resin or the like and performing cross-section polisher processing to make the cross section observable, and then scanning the cross section with an electric field. It can be determined by observing with a scanning electron microscope (FE-SEM) as follows. First, the maximum outer diameter (major axis diameter) of 10 or more fine primary particles or plate-shaped primary particles existing in the cross section of the secondary particles constituting the composite hydroxide is measured, and the average value of the number is obtained. The value is taken as the particle size of the fine primary particles or the plate-shaped primary particles in the secondary particles. Next, for 10 or more secondary particles, the particle sizes of the fine primary particles and the plate-shaped primary particles are similarly determined. Finally, the average particle size of the fine primary particles or plate-shaped primary particles of the entire composite hydroxide containing these secondary particles is determined by obtaining the average number of particle sizes obtained for these secondary particles. ..

(1-6) Composition of Transition Metal-Containing Composite Hydroxide Since the composite hydroxide obtained by the present invention is characterized by the particle structure of its secondary particles, the composite hydroxide to which the present invention is applied. The composition of an object is not limited. However, the present invention relates to compounds of the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55,0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W. It is preferably applied to a composite hydroxide having a composition represented by one or more selected additive elements). By using a composite hydroxide having such a composition as a precursor, a positive electrode active material represented by the composition of the general formula (B), which can realize higher battery performance, can be easily obtained.

In a composite hydroxide having such a composition, the additive element M can be crystallized together with transition metals (nickel, cobalt, and manganese) by a crystallization reaction and uniformly dispersed in the composite hydroxide. However, after the crystallization reaction, the outermost surface of the secondary particles constituting the composite hydroxide may be coated with a compound mainly containing the additive element M. Further, in the mixing step at the time of producing the positive electrode active material, it is also possible to mix the compound containing the additive element M together with the lithium compound with the composite hydroxide. Moreover, you may use these methods together. Regardless of which method is used, it is necessary to adjust the content of the additive element M in the composite hydroxide so that the positive electrode active material finally has a composition represented by the above general formula (B). It becomes.

2. Method for Producing Transition Metal-Containing Composite Hydroxide (2-1) Supply Aqueous Solution In the method for producing a composite hydroxide of the present invention, at least a transition metal, preferably nickel, nickel and manganese, or nickel is contained in a reaction vessel. A reaction aqueous solution is formed by supplying a raw material aqueous solution containing manganese and cobalt, and a composite hydroxide is obtained by a crystallization reaction while adjusting the pH value of the reaction aqueous solution within a predetermined range with a pH adjusting agent.

a) Aqueous solution of raw material In the present invention, the ratio of metal elements contained in the aqueous solution of raw material is substantially the composition of the obtained composite hydroxide. Therefore, it is necessary to appropriately adjust the content of each metal component in the raw material aqueous solution according to the composition of the target composite hydroxide. For example, when trying to obtain a composite hydroxide having a composition represented by the general formula (A), the ratio of metal elements in the raw material aqueous solution is set to Ni: Mn: Co: M = x: y: z. Adjusted so that t (however, x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1) It is necessary to do. However, when the additive element M is introduced in a separate step as described above, the additive element M is not contained in the raw material aqueous solution. It is also possible to change the presence or absence of the additive element M added or the content ratio of the transition metal or the additive element M in the nucleation step and the particle growth step.

The transition metal compound for preparing the raw material aqueous solution is not particularly limited, but from the viewpoint of ease of handling, it is preferable to use a water-soluble nitrate, sulfate, hydrochloride or the like, and the raw material cost and halogen are used. From the viewpoint of preventing contamination of the components, it is particularly preferable to use a sulfate.

Further, an additive element M (M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) is added to the composite hydroxide. When it is contained, a water-soluble compound is also preferable as the compound for supplying the additive element M, for example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, and the like. Panadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate, ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate, ammonium tungstate and the like can be preferably used.

The concentration of the raw material aqueous solution is determined based on the total amount of substances of the metal compounds, but is preferably 1 mol / L to 2.6 mol / L, and more preferably 1.5 mol / L to 2.2 mol / L. If the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized substances per reaction tank volume is small, so that the productivity is lowered. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol / L, the saturation concentration at room temperature is exceeded, so that crystals of each metal compound may reprecipitate and clog the piping or the like.

The metal compound does not necessarily have to be supplied to the reaction tank as a raw material aqueous solution. For example, when a crystallization reaction is carried out using a metal compound that reacts when mixed to produce a compound other than the target compound, the concentrations of all the metal compound aqueous solutions are individually adjusted to the above range. An aqueous metal compound may be prepared and supplied into the reaction vessel at a predetermined ratio as an aqueous solution of each metal compound.

The amount of the raw material aqueous solution supplied is such that the concentration of the product in the reaction aqueous solution is preferably 30 g / L to 200 g / L, more preferably 80 g / L to 150 g / L at the end of the particle growth step. To. If the concentration of the product is less than 30 g / L, the agglutination of the primary particles may be insufficient. On the other hand, if it exceeds 200 g / L, the reaction aqueous solution is not sufficiently agitated in the reaction vessel, and the aggregation conditions become non-uniform, so that the particle growth may be biased.

b) Alkaline aqueous solution The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. .. The alkali metal hydroxide can be added directly to the reaction aqueous solution in a solid state, but it is preferable to add it as an aqueous solution from the viewpoint of ease of pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% by mass to 50% by mass, more preferably 20% by mass to 30% by mass. By setting the concentration of the aqueous alkali metal solution in such a range, the amount of solvent supplied to the reaction system, that is, the amount of water can be suppressed, and the local pH value can be increased depending on the addition position in the reaction vessel. Since it can be prevented, it becomes possible to efficiently obtain a composite hydroxide having a narrow particle size distribution.

The method of supplying the alkaline aqueous solution is not particularly limited as long as the pH value of the reaction aqueous solution is not locally increased and is maintained within a predetermined range. For example, the reaction aqueous solution can be sufficiently agitated and supplied by a pump such as a metering pump that can control the flow rate.

(2-2) Crystallization reaction In the method for producing a composite hydroxide of the present invention, the crystallization reaction is carried out in two steps, a nucleation step in which nucleation is mainly carried out and a particle growth step in which particle growth is mainly carried out. By changing the supersaturation degree of the metal element contained in the reaction aqueous solution while continuing to supply the raw material aqueous solution in the particle growth step, while adjusting the conditions of the crystallization reaction in each step. It is characterized by controlling the particle size.

[Nucleation process]
In the nucleation step, first, a transition metal compound which is a raw material of a composite hydroxide is dissolved in water to prepare an aqueous raw material solution. Further, an alkaline aqueous solution is supplied into the reaction vessel, and a pre-reaction aqueous solution having a pH value of 12.0 to 14.0 measured based on a liquid temperature of 25 ° C. is prepared. Here, the pH value of the pre-reaction aqueous solution can be measured with a pH meter.

Next, the raw material aqueous solution is supplied while stirring the pre-reaction aqueous solution. As a result, a reaction aqueous solution in the nucleation step, that is, an aqueous solution for nucleation is formed in the reaction vessel. Since the pH value of this reaction aqueous solution is in the above range, nucleation occurs preferentially in the nucleation step with almost no growth of nuclei. In the nucleation step, the pH value of the reaction aqueous solution changes with the formation of nuclei. Therefore, an alkaline aqueous solution is supplied in a timely manner, and the pH value of the reaction aqueous solution at a liquid temperature of 25 ° C. is 12.0 to 14.0. Control to be maintained in range.

Further, during the nucleation step, fine primary particles are formed by maintaining a high degree of supersaturation in the reaction aqueous solution in the reaction vessel. That is, both nucleation and particle growth (crystal growth) in crystallization are driven by a supersaturated state, but in the nucleation step, by generating and maintaining a high supersaturated state, it is used as a driving force for nucleation. , Dominates nucleation and particle growth.

The degree of supersaturation changes the conditions of the reaction field of the crystallization reaction, such as cooling the reaction field of the crystallization reaction, adding a solvent that reduces the solubility of the solute, causing a chemical reaction, and changing the pH. In the present invention, which can be changed by means, it is preferable to control the degree of supersaturation by changing the pH because of the simplicity of the operation.

Transition metal-containing composite hydroxide, in particular, the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0 .55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, In the range of composition represented by one or more additive elements selected from Ta and W), the pH value measured based on the liquid temperature of 25 ° C. in the nucleation step is controlled in the range of 12.0 to 14.0. By doing so, it is possible to increase the degree of supersaturation and control the range in which nucleation becomes dominant.

Therefore, when controlling the degree of supersaturation by changing the pH, it is possible to control the degree of supersaturation according to the composition of the raw material which is the solute, for example, by the pH value of the reaction aqueous solution, and the degree of supersaturation is set to pH. It can also be obtained indirectly as a value.

In the nucleation step, the raw material aqueous solution and the alkaline aqueous solution are supplied to the reaction aqueous solution to continuously continue the nucleation reaction, and when a predetermined amount of nuclei are generated in the reaction aqueous solution, the nucleation step is performed. finish.

At this time, the amount of nuclei produced can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the reaction aqueous solution. The amount of nuclei produced in the nucleation step is not particularly limited, but in order to obtain a composite hydroxide having a narrow particle size distribution, the metal in the metal compound contained in the raw material aqueous solution supplied through the nucleation step and the particle growth step. It is preferably 0.1 atomic% to 2 atomic%, more preferably 0.1 atomic% to 1.5 atomic%, based on the total amount of the element. The reaction time in the nucleation step is usually about 0.2 minutes to 5 minutes.

[Particle growth process]
After the nucleation step is completed, the pH value of the nucleation aqueous solution in the reaction vessel at a liquid temperature of 25 ° C. is adjusted to 10.5 to 12.0, and the reaction aqueous solution in the particle growth step, that is, the particle growth aqueous solution is prepared. Form. The pH value can also be adjusted by stopping the supply of the alkaline aqueous solution, but in order to obtain a composite hydroxide having a narrow particle size distribution, the pH value is adjusted after stopping the supply of all the aqueous solutions. Is preferable. Specifically, after stopping the supply of all the aqueous solutions, it is preferable to adjust the pH value by supplying the reaction aqueous solution with an inorganic acid having the same group as the metal compound used for preparing the raw material aqueous solution.

Thus, the transition metal-containing composite hydroxide, in particular, the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo , Hf, Ta, W (one or more additive elements selected from)), the degree of supersaturation in the particle growth step can be controlled to a range in which particle growth is dominant. That is, by lowering the pH value, the degree of supersaturation can be lowered and the particle growth can be maintained in a dominant range.

Next, the supply of the raw material aqueous solution is restarted while stirring the reaction aqueous solution. At this time, since the pH value of the reaction aqueous solution is in the above range, new nuclei are hardly generated, particle growth proceeds, and until the secondary particles of the transition metal-containing composite hydroxide reach a predetermined particle size. Continue the crystallization reaction. In the particle growth step as well, the pH value of the reaction aqueous solution and the complexing agent concentration change with the particle growth. Therefore, an alkaline aqueous solution and a complexing agent aqueous solution are supplied in a timely manner to maintain the pH value in the above range. It is necessary to maintain the concentration of the complexing agent within a certain range. The total reaction time in the particle growth step is usually about 1 hour to 6 hours.

In particular, in the method for producing a composite hydroxide of the present invention, the degree of supersaturation was controlled to a relatively high state within a range suitable for particle growth, and the state was maintained high enough to form fine primary particles. As it is, the particles are grown to form the central part of the secondary particles constituting the composite hydroxide in the initial stage of the particle growth process (first stage).

Next, after the completion of the initial stage of the particle growth step, the supersaturation degree of the reaction aqueous solution is switched to a state low enough to form plate-shaped primary particles while continuing to supply the raw material aqueous solution, and this supersaturation degree is maintained. (Second stage). As a result, a first high-density layer is formed around the central portion of the secondary particles constituting the composite hydroxide. In the particle growth step, a complexing agent such as an aqueous ammonia solution may be added to facilitate the control of the degree of supersaturation.

Then, while continuing to supply the raw material aqueous solution, the supersaturation degree in the reaction aqueous solution is switched to a state high enough to form fine primary particles, and the supersaturation degree is maintained (third step). As a result, the first low-density layer is formed so as to cover the high-density layer. At this time, in order to prevent excessive mixing of the plate-shaped primary particles when the conditions are changed, the supply of the raw material aqueous solution may be temporarily stopped when the switching takes time.

Further, while continuing to supply the raw material aqueous solution, the supersaturation degree in the reaction aqueous solution is switched again to a state low enough to form plate-like primary particles, and the supersaturation degree is maintained (fourth step). By switching, a second high-density layer (outer shell layer) is formed so as to cover the first low-density layer. By controlling the switching of the degree of supersaturation, a structure having a low-density layer between high-density layers outside the central portion of the secondary particles constituting the composite hydroxide, that is, a high-density layer, a low-density layer, and an outside A multi-layer structure consisting of shells is formed.

The present invention is characterized in that the degree of supersaturation is switched at least three times in the particle growth step. However, after that, in the same manner, the switching of the supersaturation degree can be repeated twice, that is, the fifth step having a low supersaturation degree and the sixth step having a high supersaturation degree can be further carried out. By controlling the switching of the degree of supersaturation, a structure having two laminated structures consisting of a high-density layer and a low-density layer outside the central portion of the secondary particles constituting the composite hydroxide, that is, the first An outer shell portion having a multilayer structure including a high-density layer, a first low-density layer, a second high-density layer, a second low-density layer, and an outer shell layer is formed.

In such a method for producing a composite hydroxide, the metal ions in the reaction aqueous solution are precipitated as solid nuclei or primary particles in the nucleus formation step and the particle growth step. Therefore, the ratio of the liquid component to the amount of metal ions in the reaction aqueous solution increases. Since the metal ion concentration in the reaction aqueous solution decreases as the reaction progresses, the growth of the composite hydroxide may be stagnant, especially in the particle growth step. Therefore, in order to suppress an increase in the proportion of the liquid component, that is, a decrease in the apparent metal ion concentration, a part of the liquid component of the reaction aqueous solution is discharged to the outside of the reaction vessel from the end of the nucleation step to the middle of the particle growth step. It is preferable to do so. Specifically, the supply of the raw material aqueous solution, the alkaline aqueous solution, and the aqueous solution containing the complexing agent to the reaction vessel and the stirring of the reaction aqueous solution are temporarily stopped, and the solid component in the reaction aqueous solution, that is, the composite hydroxide is precipitated. , It is preferable to discharge only the supernatant of the reaction aqueous solution to the outside of the reaction vessel. By such an operation, the metal ion concentration in the reaction aqueous solution can be maintained, so that the particle growth can be prevented from stagnation and the particle size distribution of the obtained composite hydroxide can be controlled within a suitable range. However, the density as a powder can also be improved.

[Controlling particle size of composite hydroxide]
The particle size of the secondary particles constituting the composite hydroxide can be controlled by the time required for the nucleation formation step and the particle growth step, the pH value of the reaction aqueous solution, the supply amount of the raw material aqueous solution, and the like in each step. For example, when the nucleation step is performed at a high pH value, the time for performing the nucleation step is lengthened, or the metal concentration of the raw material aqueous solution is increased, the amount of nucleation produced in the nucleation step increases, and the particles After the growth step, a composite hydroxide having a relatively small particle size is obtained. On the contrary, when the amount of nucleation produced in the nucleation step is suppressed or the time required for the particle growth step is sufficiently lengthened, a composite hydroxide having a large particle size can be obtained.

[Another Embodiment of the crystallization reaction]
In the method for producing a composite hydroxide of the present invention, a component adjusting aqueous solution adjusted to a pH value suitable for the particle growth step is prepared separately from the reaction aqueous solution, and the component adjusting aqueous solution is used in this component adjusting aqueous solution after the nucleation step. A particle growth step may be carried out by adding and mixing a reaction aqueous solution, preferably one obtained by removing a part of liquid components from the reaction aqueous solution after the nucleation formation step, and using this as the reaction aqueous solution.

In this case, since the nucleation step and the particle growth step can be separated more reliably, the reaction aqueous solution in each step can be controlled to an optimum state. In particular, since the pH value of the reaction aqueous solution can be controlled in an optimum range from the start of the particle growth step, the particle size distribution of the obtained composite hydroxide can be made narrower.

(2-3) pH value In the method for producing a composite hydroxide of the present invention, the pH value at a liquid temperature of 25 ° C. is set to the range of 12.0 to 14.0 when the nucleation step is performed. When performing the step, it is necessary to control the step to be lower than the nucleation step and in the range of 10.5 to 12.0. Further, by changing the pH value within the above range in each step, the degree of supersaturation of the reaction aqueous solution is in the range of 12.0 to 14.0 where nucleation is dominant, or particle growth is dominant. It can be adjusted in the range of 10.5 to 12.0. That is, increasing the pH value increases the degree of supersaturation, and decreasing the pH value decreases the degree of supersaturation.

Further, in the present invention, the degree of supersaturation is changed by further changing the pH value in the particle growth step. That is, in the first, third, and fifth stages of the particle growth process in which the degree of supersaturation is high, the degree of supersaturation is finely primary by controlling the pH value in the range of 11.0 to 12.0. The pH value in the range of 10.5 to 11.5 and in the state where the degree of supersaturation is high in the second stage, the fourth stage and the sixth stage where the degree of supersaturation is low and the state is high enough to form particles. By controlling it to be lower, the degree of supersaturation is set to a state low enough to form plate-like primary particles larger than the fine primary particles.

In each step of the nucleation step and the particle growth step, it is preferable to control the fluctuation amount of the pH value during the crystallization reaction within ± 0.2 with respect to the set value. When the fluctuation amount of the pH value is large, the nucleation amount in the nucleation step and the degree of particle growth in the particle growth step are not constant, so that it becomes difficult to obtain a composite hydroxide having a narrow particle size distribution. There is. Therefore, a complexing agent such as an aqueous ammonia solution may be added particularly to the particle growth step.

a) pH value in the nucleation step In the nucleation step, the pH value of the reaction aqueous solution based on the liquid temperature of 25 ° C. is 12.0 to 14.0, preferably 12.3 to 13.5, more preferably 12. It is necessary to control the range larger than 5 and 13.3 or less. This makes it possible to suppress the growth of nuclei in the reaction aqueous solution and give priority only to nucleation, so that the nuclei produced in this step have a homogeneous size and a narrow particle size distribution. Further, by making the pH value higher than 12.5, it is possible to surely form a structure having many gaps in which fine primary particles are connected at the center of the secondary particles of the composite hydroxide. When the pH value is less than 12.0, the growth of nuclei progresses with nucleation, so that the particle size of the obtained composite hydroxide becomes non-uniform and the particle size distribution becomes wide. On the other hand, if the pH value is higher than 14.0, the nuclei formed become too fine, which causes a problem that the reaction aqueous solution gels.

b) pH value in the particle growth step Of the particle growth steps, the pH value of the reaction aqueous solution based on the liquid temperature of 25 ° C. is 11 in the first, third, and fifth stages where the supersaturation of the reaction aqueous solution is high. In the second, fourth, and sixth stages, which are controlled in the range of 0 to 12.0, preferably 11.5 to 12.0 and have a low degree of supersaturation, 10.5-11.5. It is necessary to control the range of 10.8 to 11.3. As a result, the formation of new nuclei is suppressed, the particle growth can be prioritized, and the obtained composite hydroxide can be made homogeneous and have a narrow particle size distribution.

When the pH value is higher than 12.0, the amount of nucleation generated during the particle growth step increases, the particle size of the obtained composite hydroxide becomes non-uniform, and the particle size distribution becomes wide. Further, when the pH value is lower than 11.0 in the first stage, the third stage, and the fifth stage where the degree of supersaturation is high, the ratio of the plate-shaped primary particles among the primary particles formed in each stage is large. Therefore, it may not be possible to obtain the desired structure of the outer shell portion. On the other hand, when the pH value is less than 10.5, the ammonium ion concentration increases and the solubility of metal ions increases, so that not only the rate of the crystallization reaction slows down but also the amount of metal ions remaining in the reaction aqueous solution increases. However, productivity is reduced. On the other hand, when the pH value is higher than 11.5 in the second, fourth, and sixth stages where the degree of supersaturation is low, the proportion of fine primary particles among the primary particles formed in each stage increases. Therefore, it may not be possible to obtain the desired structure of the outer shell portion.

When the pH value of the reaction aqueous solution is 12.0 based on the liquid temperature of 25 ° C., the boundary condition between nucleation and particle growth, that is, the first stage of the nucleation step and the particle growth step where the degree of supersaturation is high. Since it is the boundary condition of the third stage and the fifth stage, it can be a condition of either the nucleation step or the particle growth step depending on the presence or absence of nuclei present in the reaction aqueous solution. For example, if the pH value of the nucleation step is higher than 12.0 and a large amount of nucleation is performed, and then the pH value of the first step of the particle growth step is 12.0, the reactants are contained in the reaction aqueous solution. Since a large amount of nuclei are present, particle growth occurs preferentially, and a composite hydroxide having a narrow particle size distribution can be obtained. On the other hand, when the pH value of the nucleation step is 12.0, in the nucleation step, since there are no nuclei to grow in the reaction aqueous solution, nucleation occurs preferentially, and the first step of the subsequent particle growth step. By making the pH value in 12.0 lower than 12.0, the growth of the nucleated nuclei (particle growth) can be promoted.

In either case, the pH value in the particle growth step may be controlled to be lower than the pH value in the nucleation step, and in order to more clearly separate nucleation and particle growth, the pH value in the particle growth step Is preferably 0.5 or more lower than the pH value of the nucleation step, and more preferably 1.0 or more.

In the present invention, in the first, third, and fifth stages of the particle growth step, the degree of supersaturation is lower than that in the nucleation step, that is, the pH value is lower, but the particle growth. In comparison with the second, fourth, and sixth stages of the process, the relatively high degree of supersaturation, that is, the high pH value is maintained, so that fine primary particles are formed by particle growth. To.

Also, in order to clearly separate the second, fourth, and sixth stages of the particle growth process, which have a low degree of supersaturation, from the first, third, and fifth stages, which have a high degree of supersaturation. Is preferably 0.3 or more lower than the pH value in the high supersaturation state, and more preferably 0.5 or more lower than the pH value in the high supersaturation state.

c) Timing of pH value control It is necessary to control the pH value (supersaturation degree control) in the particle growth step at an appropriate timing so that a composite hydroxide having the desired particle structure is formed. ..

Even during the particle growth step, the pH value can be adjusted by stopping the supply of the alkaline aqueous solution, but after stopping the supply of all the aqueous solutions once in order to obtain a composite hydroxide having a narrow particle size distribution. , It is preferable to adjust the pH value.

The pH value switching time is about 0.4% to 2% with respect to the entire particle growth step, and more preferably about 0.4% to 1%. This time is also common when switching the pH value from a high state to a low state or from a low state to a high state. Therefore, although it is possible to strictly control the pH value switching time independently, it is usually sufficient to include it in the time after the pH value switching.

[When the outer shell has a three-layer structure]
In the particle growth step, the atmosphere is controlled three times between the formation of the central portion and the formation of the outer shell portion, and one low-density layer sandwiched between two high-density layers is formed on the outside of the central portion. When trying to obtain an outer shell having a three-layer structure, the crystallization reaction time in a state where the supersaturation degree (pH value) of the initial stage (first stage) of the particle growth process is high is the entire particle growth process time. On the other hand, it is in the range of 0.5% to 20%, preferably in the range of 1% to 15%, and more preferably in the range of 3% to 10%. That is, the pH value is 0.5% to 20%, which is the crystallization reaction time of the initial stage (first stage), with respect to the total particle growth process time from the start of the particle growth process. By lowering, the state of high supersaturation is switched to the state of low supersaturation. When the pH value drops to the set value, the supply amount of the alkaline aqueous solution or the inorganic acid to the reaction aqueous solution is adjusted to keep the pH value constant, thereby shifting to the second stage. The reaction time in such a range in the initial stage (first stage) forms a central portion of appropriate size in combination with the nucleation step.

Next, the crystallization reaction time (supersaturation degree) in the state where the supersaturation degree (pH value) is low (second stage) after the start of switching from the state where the first supersaturation degree (pH value) is high (first stage) Including the time to switch from the high state to the low state) is in the range of 10% to 80%, preferably in the range of 30% to 75%, and more preferably in the range of 40% to 70, based on the total particle growth process time. It is in the range of%. That is, from the time when the supply of the alkaline aqueous solution is stopped or the time when the supply of the inorganic acid is started in order to switch the pH value to the low state in order to keep the degree of supersaturation low, with respect to the entire particle growth process time. After the crystallization reaction time of the second stage of 10% to 80% has elapsed, the pH value is raised by continuously supplying an alkaline aqueous solution to increase the degree of supersaturation from low to high. Switch to the state. When the pH value rises to the set value, the supply amount of the alkaline aqueous solution or the inorganic acid to the reaction aqueous solution is adjusted to keep the pH value constant, thereby shifting to the third stage. The reaction time in such a range in the second step forms a high density layer (having a predetermined high density layer particle size ratio) of appropriate thickness.

Further, the crystallization reaction time in the second high supersaturation degree (pH value) state (third stage) after the start of switching from the first low supersaturation degree (pH value) state (second stage). (Including the time to switch from the low supersaturation state to the high supersaturation state) is in the range of 2% to 30%, preferably in the range of 3% to 20%, more preferably 5 with respect to the total particle growth process time. It is in the range of% to 15%. That is, from the time when the supply of the alkaline aqueous solution into the reaction aqueous solution was started in order to switch the pH value to the high state in order to make the supersaturation degree high, the crystals of the third stage were used for the entire particle growth process time. After the analysis reaction time of 2% to 30% has elapsed, the degree of supersaturation is lowered by lowering the pH value by stopping the supply of the alkaline aqueous solution to the reaction aqueous solution or supplying an inorganic acid. Switches from a high state to a low state and shifts to the fourth stage. The reaction time in such a range in the third step forms a low density layer (having a predetermined low density layer particle size ratio) of appropriate thickness.

The second time to form the outer shell layer from the second time when the supersaturation degree (pH value) is high (third stage) to the end of the particle growth process (the end of the crystallization reaction) after the start of switching. The crystallization reaction time of the particle growth step in a state where the degree of supersaturation (pH value) is high (fourth step) is in the range of 10% to 80%, preferably 10% to the total of the total particle growth step time. It is in the range of 60%, more preferably in the range of 15% to 50%. After the crystallization reaction time of the fourth stage, which is 10% to 80%, has elapsed, the supply of the raw material aqueous solution is terminated to terminate the crystallization reaction. The reaction time in such a range in the fourth step forms an outer shell layer of appropriate thickness (having a predetermined outer shell layer particle size ratio).

That is, by sequentially switching the degree of supersaturation (pH value) at the timing as described above, the degree of supersaturation is switched, and the size of the central portion and the thickness of the high-density layer, the low-density layer, and the outer shell layer are suitable. It becomes possible to control the range.

[When the outer shell has a five-layer structure]
In the particle growth step, the atmosphere is controlled five times between the formation of the central portion and the formation of the outer shell layer, and two laminated structures consisting of a high-density layer and a low-density layer are provided inside the outer shell layer. When trying to obtain a composite hydroxide having a layered outer shell, the crystallization reaction time in a high pH value in the initial stage (first stage) of the particle growth step is the entire particle growth step time. On the other hand, it is in the range of 0.5% to 20%, preferably in the range of 1% to 15%, and more preferably in the range of 3% to 10%. After the lapse of the initial stage (first stage), the pH value is lowered to switch from a high supersaturation state to a low supersaturation state.

Crystallization reaction time (high degree of supersaturation) in the state where the degree of supersaturation (pH value) is low (second stage) after the start of switching from the state where the first degree of supersaturation (pH value) is high (first stage) The range from 10% to 75%, preferably from 30% to 75%, more preferably from 40% to 70%, is in the range of 10% to 75%, more preferably from 40% to 70%, based on the total particle growth process time). Is. After the lapse of the second stage, the pH value is increased to switch from a low supersaturation state to a high supersaturation state.

Crystallization reaction time (high supersaturation) in the low supersaturation (pH value) state (third stage) after the start of switching from the first high supersaturation (pH value) state (second stage) The range from 2% to 30%, preferably 3% to 20%, more preferably 5% to 15%, is in the range of 2% to 30%, more preferably 5% to 15%, based on the total particle growth process time). Is. After the lapse of the third stage, the pH value is lowered to switch from a high supersaturation state to a low supersaturation state.

Crystallization reaction time (from the state of low supersaturation) in the state of high supersaturation (pH value) (fourth stage) after the start of switching from the second low degree of supersaturation (pH value) (third stage) (Including time to switch to high state) is in the range of 10% to 75%, preferably 30% to 75%, more preferably 40% to 70% of the total particle growth process time. is there. After the lapse of the fourth stage, the pH value is lowered to switch from a high supersaturation state to a low supersaturation state.

Crystallization reaction time (low supersaturation) in a high supersaturation (pH value) state (fifth stage) after the start of switching from the second low supersaturation (pH value) state (fourth stage) The range from 2% to 30%, preferably 3% to 20%, more preferably 5% to 15%, is in the range of 2% to 30%, more preferably 5% to 15%, based on the total particle growth process time). Is. After the lapse of the fifth stage, the pH value is lowered to switch from a high supersaturation state to a low supersaturation state.

The third time to form the outer shell layer from the state where the supersaturation degree (pH value) is high (the fifth stage) to the end of the particle growth process (the end of the crystallization reaction) after the start of switching. The crystallization reaction time of the particle growth step in a state where the degree of supersaturation (pH value) is low (sixth step) is 10% to 75%, preferably 10% to 60% of the total particle growth step time. , More preferably in the range of 15% to 50%. After the lapse of the sixth step, the supply of the raw material aqueous solution is terminated, and the crystallization reaction is terminated.

By sequentially switching the degree of supersaturation (pH value) at such a timing, the size of the central portion and the high-density layer, the low-density layer, the second high-density layer, and the second low-density constituting the outer shell portion are formed. It is possible to control the thickness of the layer and the outer shell layer within a suitable range.

In the particle growth step of the present invention, a multi-layered layered structure is formed in the outer shell portion by changing the degree of supersaturation in the reaction aqueous solution. The degree of supersaturation can also be controlled by changing it. In this case, the reaction temperature is changed while controlling the pH value in the particle growth step within the above range and the fluctuation amount of the pH value during the crystallization reaction within 0.2 with respect to the set value. The degree of supersaturation in the reaction aqueous solution is changed by taking measures such as making the reaction aqueous solution.

(2-4) Reaction temperature The temperature of the reaction aqueous solution, that is, the reaction temperature of the crystallization reaction is preferably in the range of 20 ° C. or higher, more preferably 20 ° C. to 60 ° C. throughout the nucleation step and the particle growth step. It needs to be controlled. If the reaction temperature is less than 20 ° C., nucleation is likely to occur due to the low solubility of the reaction aqueous solution, and it becomes difficult to control the average particle size and particle size distribution of the obtained composite hydroxide. The upper limit of the reaction temperature is not particularly limited, but when the reaction temperature exceeds 60 ° C., volatilization of water in the reaction aqueous solution is promoted, and control of the supersaturation degree in the reaction aqueous solution to a certain range is complicated. May become.

In the particle growth step of the present invention, it is also possible to control the degree of supersaturation by changing the reaction temperature as described above. In this case, in the above temperature range, the second, fourth, and sixth stages of the particle growth process having a low degree of supersaturation and the first, third, and fifth stages having a high degree of supersaturation are included. For clear separation, the reaction temperature in a low supersaturation state is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, than the reaction temperature in a high supersaturation state.

(2-5) Coating Step In the method for producing a composite hydroxide of the present invention, the inside of particles is added by adding a compound containing the additive element M to the raw material aqueous solution, particularly to the raw material aqueous solution used in the particle growth step. A composite hydroxide in which the additive element M is uniformly dispersed can be obtained. However, when the effect of adding the additive element M is to be obtained with a smaller amount of addition, the additive element M is added to the surface of the secondary particles constituting the transition metal-containing composite hydroxide after the particle growth step. It is preferable to carry out a coating step of coating with the containing compound.

The coating method is not particularly limited as long as the composite hydroxide can be uniformly coated with the compound containing the additive element M. For example, a composite hydroxide is slurried, its pH value is controlled within a predetermined range, and then an aqueous solution for coating in which a compound containing the additive element M is dissolved is added to form secondary particles constituting the composite hydroxide. By precipitating a compound containing the additive element M on the surface, a composite hydroxide uniformly coated with the compound containing the additive element M can be obtained. In this case, instead of the coating aqueous solution, an alkoxide aqueous solution of the additive element M may be added to the slurried composite hydroxide. Alternatively, the composite hydroxide may be coated by spraying an aqueous solution or slurry in which a compound containing the additive element M is dissolved and drying the composite hydroxide without making it into a slurry. Further, a method of spray-drying a slurry in which the composite hydroxide and the compound containing the additive element M are suspended, or a method of mixing the composite hydroxide and the compound containing the additive element M by a solid phase method and the like. It can also be covered with.

When the surface of the composite hydroxide is coated with the additive element M, the raw material aqueous solution and the coating are used so that the composition of the composite hydroxide after coating matches the composition of the target composite hydroxide. It is necessary to appropriately adjust the composition of the aqueous solution. Further, the coating step may be performed on the heat-treated particles after the composite hydroxide is heat-treated in the heat treatment step at the time of manufacturing the positive electrode active material.

(2-6) Production apparatus The crystallization apparatus for producing the composite hydroxide of the present invention, that is, the reaction vessel is not particularly limited as long as the reaction atmosphere can be switched. , Those having a means for directly supplying atmospheric gas into the reaction vessel, such as an air diffuser, are preferable. Further, in carrying out the present invention, it is particularly preferable to use a batch type crystallization apparatus that does not collect the precipitated product until the crystallization reaction is completed. In the case of such a crystallization device, unlike the continuous crystallization device that recovers the product by the overflow method, the growing particles are not recovered at the same time as the overflow liquid, so that the low-density layer and the high-density layer The particle structure is controlled, and a composite hydroxide having a narrow particle size distribution can be obtained with high accuracy. Further, in the method for producing a composite hydroxide of the present invention, it is necessary to appropriately control the reaction atmosphere during the crystallization reaction, so that it is particularly preferable to use a closed crystallization device.

3. 3. Positive electrode active material for non-aqueous electrolyte secondary battery (3-1) Particle structure of positive electrode active material a) Structure of secondary particles Transition metal-containing composite hydroxylation obtained by the method for producing a transition metal-containing composite hydroxide of the present invention. As shown in FIG. 2, the positive electrode active material obtained by using a substance as a precursor is composed of secondary particles formed by aggregating a plurality of primary particles. That is, the secondary particles are composed of aggregates of primary particles. In particular, in the positive electrode active material obtained by using the transition metal-containing composite hydroxide of the present invention as a precursor, the entire secondary particles are not a solid structure composed of sintered aggregates of primary particles, as shown in FIG. As shown, the secondary particles are formed in the outer shell portion formed by aggregating the primary particles, the central portion formed by the internal space existing inside the outer shell portion, and the outer shell portion. It is characterized by having a through hole for communicating the central portion and the outside. That is, the secondary particles constituting the positive electrode active material have a hollow structure including an outer shell portion and a space portion inside the outer shell portion and communicating with the outside through a through hole.

In a positive electrode active material having such a particle structure, not only the electrolytic solution but also the conductive auxiliary agent easily penetrates into the central portion of the secondary particles, that is, the internal space, through the through holes formed in the outer shell portion. , Not only the outer surface of the outer shell of the secondary particles, but also the inner surface of the outer shell of the secondary particles and the portion of the outer shell exposed to the through hole, the desorption and insertion of lithium are sufficient. It will be possible. Therefore, the positive electrode resistance can be further reduced, and the output characteristics can be improved accordingly.

Further, such a structure is formed by aggregating a plurality of primary particles and has a high degree of sphere, that is, the whole is composed of substantially spherical (including spherical and elliptical) secondary particles, and This is realized in a positive electrode active material composed of a lithium transition metal-containing composite oxide having a small particle size and a narrow particle size distribution.

A secondary battery using a positive electrode active material having such a structure comprises a positive electrode active material having the same composition as compared with a conventional secondary battery using a positive electrode active material having a small particle size and a narrow particle size distribution. Since not only the outer surface of the secondary particles (outer shell part) but also the inner surface thereof can be used more efficiently as a reaction field with the electrolytic solution, the battery capacity and cycle characteristics can be improved. It is possible to further improve the output characteristics while maintaining the same level.

b) Outer shell part The ratio of the thickness of the outer shell part to the particle size of the secondary particles constituting the positive electrode active material obtained by using the transition metal-containing composite hydroxide obtained by the present invention as a precursor (hereinafter, “positive electrode activity”). The outer shell particle size ratio of the substance) is preferably 5% to 40%, more preferably 10% to 35%, and even more preferably 15% to 30%. This makes it possible to improve the output characteristics of the secondary battery using the positive electrode active material without impairing the battery capacity and the cycle characteristics. On the other hand, when the outer shell particle size ratio of the positive electrode active material is less than 5%, it becomes difficult to secure the physical durability of the positive electrode active material, and the cycle characteristics of the secondary battery may deteriorate. is there. On the other hand, when the outer shell particle size ratio of the positive electrode active material becomes larger than 40%, the ratio of the central portion (the ratio of the inner diameter of the outer shell to the particle size of the secondary particles) decreases, and the reaction with the electrolytic solution Since problems such as not being able to secure a sufficient area and insufficient formation of through holes occur, it may be difficult to improve the output characteristics of the secondary battery.

Here, the outer shell particle size ratio of the positive electrode active material can be obtained as follows using an SEM image of a cross section of the positive electrode active material. First, the thickness of the outer shell is measured at three or more arbitrary positions per particle on the SEM image of the cross section of the positive electrode active material, and the average value is obtained. Here, the thickness of the outer shell portion is a distance between two points where the distance from the outer edge of the outer shell portion of the positive electrode active material to the surface where the outer shell portion faces inward into the inner void is the shortest. The same measurement is performed on 10 or more positive electrode active materials, and the average value thereof is calculated to obtain the average thickness of the outer shell portion. Then, by dividing the average thickness of the outer shell portion by the average particle size of the positive electrode active material, the ratio of the thickness of the outer shell portion to the particle size of the positive electrode active material can be obtained. In the positive electrode active material of the present invention, a part of the outer shell portion may be broken due to volume shrinkage during firing, and the internal voids may be exposed to the outside. In such a case, the outer shell portion may be determined by presuming that the broken portions are connected, and the thickness of the outer shell portion may be measured at the measurable portion.

Specifically, the thickness of the outer shell portion depends on the average particle size of the secondary particles, but is preferably in the range of 0.1 μm to 6 μm, more preferably in the range of 0.2 μm to 5 μm, and further preferably in the range of 0. It is in the range of 2 μm to 3 μm.

c) Through hole The positive electrode active material obtained by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is formed in an outer shell portion and includes a through hole that communicates the central portion with the outside. It is characterized by.

This through hole exists between the layers of the outer shell portion when the outer shell portion constituting the composite hydroxide forms an integrated outer shell portion by sintering shrinkage during firing of the composite hydroxide. It is formed due to the shrinkage of the low-density layer, and at least one is formed in the outer shell portion in a state where the outer shell portion communicates with the central portion and the outside of the hollow structure. From the viewpoint of allowing the electrolytic solution and the conductive auxiliary agent to penetrate to the central portion, it is sufficient that one secondary particle has one through hole having a predetermined size. However, it is possible that a plurality of such through holes are present in the outer shell portion, and the number of through holes is preferably in the range of 1 to 5 per secondary particle, and more preferably 1 to 5. There are three ranges.

Since the through holes are sufficiently large with respect to the secondary particle size, the number of through holes can be measured by observing the cross section or surface of the secondary particles with a scanning microscope. By changing the focus in the surface observation, it can be confirmed that the hole is a through hole. In surface observation, the orientation of the secondary particles is considered to be random, and the through holes are not always present in the orientation of the observable secondary particles. That is, when the secondary particles are rotated by two orthogonal axes in the plane perpendicular to the observation direction, the position where the through hole can be observed is near the upper surface, and at most 25 near the upper surface in each rotation axis. The angle is about%. Therefore, even if there are through holes on the back surface or the side surface, it is difficult to distinguish them. Therefore, if the through holes are observed at 5% or more, preferably 6% or more of the number of secondary particles in which the entire particles can be observed, It is probable that almost all secondary particles have through holes. Since it is appropriate to exclude secondary particles whose through holes are difficult to observe with respect to the number of particles per secondary particle, the number of through holes is averaged by the number of particles in the particles in which through holes are observed. It is required by doing.

The size (inner diameter) of each through hole must be large enough to allow the electrolytic solution to penetrate into the positive electrode active material, and the ratio of the inner diameter to the thickness of the outer shell (hereinafter, "through hole inner diameter"). The ratio) is 0.3 or more, preferably 0.3 to 5, and more preferably 0.4 to 3. When the through-hole inner diameter ratio is less than 0.3, the inner diameter of the through-hole becomes too small with respect to the thickness of the outer shell, resulting in a through-hole having a relatively small inner diameter and a long length. When used in a battery, the electrolytic solution cannot sufficiently penetrate into the internal space (central part) formed in the battery, and the conductive auxiliary agent cannot penetrate to the central part or the conductive auxiliary agent that can penetrate decreases. Output characteristics and battery capacity are reduced. When the through-hole inner diameter ratio exceeds 5, the inner diameter of the through-hole becomes relatively large and the strength of the secondary particles decreases, and the physical durability of the positive electrode active material may be insufficient.

The inner diameter is preferably in the range of 0.2 μm to 1.0 μm, more preferably in the range of 0.2 μm to 0.7 μm, and further preferably in the range of 0.3 μm to 0.6 μm. If the inner diameter of the through hole is smaller than 0.2 μm, the electrolytic solution may not sufficiently penetrate into the secondary particles, and the conductive auxiliary agent may not be able to penetrate into the secondary particles. On the other hand, the upper limit of the inner diameter of the through hole depends on the average particle size of the secondary particles constituting the positive electrode active material, but from the viewpoint of ensuring its physical durability, it is 5% of the average particle size of the secondary particles. It is preferably about 20%.

The inner diameter (average inner diameter) of the through hole is the through hole (the space connecting the outside and the center of the secondary particle) in the secondary particles where the through hole selected arbitrarily can be confirmed using the SEM image of the cross section of the positive electrode active material. ) And the shortest distance between the two points on the boundary between the outer part and the outer part are taken as the measured values of the through holes of the secondary particles, and the same measurement is performed on 10 or more secondary particles. It is obtained by calculating the average value by the number of pieces. When there are multiple through-holes in the secondary particle, the average value by the number is calculated from the measured value of each through-hole in the secondary particle and used as the measured value of the secondary particle, and the other secondary particles. Calculate the average value together with the measured value of. Since the cross-section observation is an arbitrary cross-section, the center of the through-hole is not necessarily the cross-section, and a value smaller than the true diameter may be measured by deviating from the center. The inner diameter of is averaged including values smaller than the true diameter. Even if the inner diameter of such a through hole is specified, a sufficient effect can be obtained by specifying the inside diameter in the above range.

(3-2) Average particle size The average particle size of the secondary particles constituting the positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor is 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably. Is 3 μm to 10 μm. If the average particle size of the positive electrode active material is within such a range, not only can the battery capacity per unit volume of the secondary battery using this positive electrode active material be increased, but also safety and output characteristics are improved. can do. On the other hand, when the average particle size is less than 1 μm, the filling property of the positive electrode active material is lowered, and the battery capacity per unit volume cannot be increased. On the other hand, when the average particle size is larger than 15 μm, the contact interface with the electrolytic solution is reduced and the reaction area of the positive electrode active material is reduced, so that it is difficult to improve the output characteristics.

The average particle size of the positive electrode active material means a volume-based average particle size (MV), and can be obtained by measurement with a laser light diffraction / scattering type particle size analyzer.

(3-3) Particle Size Distribution The value of [(d90-d10) / average particle size], which is an index showing the spread of the particle size distribution of the positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor, is 0.70 or less, preferably 0.60 or less, more preferably 0.55 or less, and the positive electrode active material of the present invention is composed of powder having an extremely narrow particle size distribution. Such a positive electrode active material has a small proportion of fine particles and coarse particles, and a secondary battery using the positive electrode active material has excellent safety, cycle characteristics, and output characteristics.

On the other hand, when the value of [(d90-d10) / average particle size] exceeds 0.70, the proportion of fine particles and coarse particles in the positive electrode active material increases. For example, in a secondary battery using a positive electrode active material having a large proportion of fine particles, the secondary battery tends to generate heat due to the local reaction of the fine particles, which not only reduces safety but also fine particles. Due to the selective deterioration of the particles, the cycle characteristics become inferior. Further, in the secondary battery using the positive electrode active material having a large proportion of coarse particles, the reaction area between the electrolytic solution and the positive electrode active material cannot be sufficiently secured, and the output characteristics are inferior.

On the other hand, when considering industrial-scale production, it is a good idea to prepare a powdered composite hydroxide having an excessively small value of [(d90-d10) / average particle size] as a precursor. Not realistic in terms of productivity, or production cost. Therefore, the lower limit of [(d90-d10) / average particle size] of the positive electrode active material is preferably about 0.25.

Here, d10 means a particle size in which the number of particles in each particle size of the powder sample is accumulated from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles, and d90 is a particle size. It means a particle size in which the cumulative volume is 90% of the total volume of all particles when the number of particles is accumulated by the same method. Similar to the average particle size of the positive electrode active material, d10 and d90 can be obtained from the volume integrated values measured by the laser light diffraction / scattering type particle size analyzer.

(3-4) In the positive electrode active material obtained composite hydroxide obtained by a specific surface area of the present invention as a precursor, the specific surface area ^is preferably 1.3m ² /g~4.0m 2 / g , and more preferably 1.5m ² /g~3.0m ² / g. A positive electrode active material having a specific surface area in such a range has a large contact area with an electrolytic solution, and the output characteristics of a secondary battery using the positive electrode active material can be significantly improved. On the other hand, when the specific surface area of the positive electrode active material ^{is less than 1.3 m 2} / g, the reaction area with the electrolytic solution cannot be secured when the secondary battery is configured, and the output characteristics are sufficient. It becomes difficult to improve. On the other hand, when the specific surface area of the positive electrode active material ^{is larger than 4.0 m 2} / g, the reactivity with the electrolytic solution becomes too high, so that the thermal stability may decrease.

Here, the specific surface area of the positive electrode active material can be measured, for example, by the BET method by adsorbing nitrogen gas.

(3-5) Tap Density In the positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor, the tap density, which is an index of filling property, ^{is preferably 1.1 g / cm 3} or more. It is more preferably 1.2 g / cm ³ or more, and further preferably 1.3 g / cm ³ or more. When the tap density is ^{less than 1.1 g / cm 3} , the filling property is low and the battery capacity of the entire secondary battery may not be sufficiently improved. On the other hand, the upper limit of the tap density is not particularly limited, but the upper limit under normal manufacturing conditions is about ^{3.0 g / cm 3.}

The tap density represents the bulk density after tapping the sample powder collected in the container 100 times based on JIS Z2512: 2012, and can be measured using a shaking specific gravity measuring device.

(3-6) Area per unit volume The positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor is a unit which is a large index for the filling property of the positive electrode active material as well as the tap density. The surface area per volume is preferably 2.0 m ² / cm ³ or more, more preferably 2.1 m ² / cm ³ or more, and further preferably 2.3 m ² / cm ³ or more. As a result, the contact area with the electrolytic solution can be increased while ensuring the filling property of the positive electrode active material as a powder, so that the output characteristics and the battery capacity can be improved at the same time. The surface area per unit volume can be determined by the product of the specific surface area of the positive electrode active material and the tap density.

(3-7) Composition Since the positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor is characterized by the particle structure of its secondary particles, as long as it has the above-mentioned particle structure, Its composition is not limited. However, the general formula _{(B): Li 1 + u} Ni x Mn y Co z M t O 2 (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W. It can be suitably applied to a positive electrode active material having a composition represented by one or more additive elements).

In this positive electrode active material, the value of u indicating the excess amount of lithium (Li) is preferably −0.05 or more and 0.50 or less, more preferably 0 or more and 0.50 or less, and further preferably 0 or more and 0.35 or less. And. By setting the value of u within the above range, the output characteristics and battery capacity of the secondary battery using this positive electrode active material as the positive electrode material can be improved. On the other hand, when the value of u is less than −0.05, the positive electrode resistance of the secondary battery becomes large, so that the output characteristics cannot be improved. On the other hand, when it is larger than 0.50, not only the initial discharge capacity is lowered, but also the positive electrode resistance is increased.

Nickel (Ni) is an element that contributes to increasing the potential and capacity of the secondary battery, and the value of x indicating the content thereof is preferably 0.3 or more and 0.95 or less, more preferably 0. 3 or more and 0.9 or less. If the value of x is less than 0.3, the battery capacity of the secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of x exceeds 0.95, the content of other metal elements decreases, and the effect cannot be obtained.

Manganese (Mn) is an element that contributes to the improvement of thermal stability, and the value of y indicating its content is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.45 or less. And. If the value of y is less than 0.05, the thermal stability of the secondary battery using this positive electrode active material cannot be improved. On the other hand, if the value of y exceeds 0.55, Mn is eluted from the positive electrode active material during high temperature operation, and the charge / discharge cycle characteristics are deteriorated.

Cobalt (Co) is an element that contributes to the improvement of charge / discharge cycle characteristics, and the value of z indicating its content is 0 or more and 0.55 or less, preferably 0.10 or more and 0.55 or less. If the value of z exceeds 0.4, the initial discharge capacity of the secondary battery using this positive electrode active material will be significantly reduced.

The positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor contains an additive element M in addition to the above transition metal element in order to further improve the durability and output characteristics of the secondary battery. You may. Examples of such additive element M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum. One or more selected from (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W) can be used.

The value of t indicating the content of the additive element M is preferably 0 or more and 0.1 or less, more preferably 0.001 or more and 0.05 or less. When the value of t is larger than 0.1, the metal elements that contribute to the Redox reaction decrease, so that the battery capacity decreases.

Such an additive element M may be uniformly dispersed inside the particles of the positive electrode active material, or may cover the particle surface of the positive electrode active material. Further, the surface of the particles may be coated after being uniformly dispersed inside the particles. In any case, it is necessary to control the content of the additive element M so as to be within the above range.

Incidentally, in the above-mentioned positive electrode active material, if further improved battery capacity of the secondary battery using the same is the composition of the general formula _{(B1): Li 1 + u} Ni x Mn y Co z M t O 2 ( −0.05 ≦ u ≦ 0.20, x + y + z + t = 1, 0.7 <x ≦ 0.95, 0.05 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0 ≦ t ≦ 0.1 , M is preferably adjusted so as to be represented by one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W). In particular, in order to achieve both thermal stability, the value of x in the general formula (B1) is more preferably 0.7 <x ≦ 0.9, and 0.7 <x ≦ 0.85. Is more preferable.

On the other hand, if further improved thermal stability, its composition formula _{(B2): Li 1 + u} Ni x Mn y Co z M t O 2 (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta, W (one or more additive elements selected from)).

4. Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery By using the composite hydroxide obtained by the present invention as a precursor, a positive electrode active material having a predetermined structure, average particle size, and particle size distribution can be synthesized. Can be done. When such a positive electrode active material is produced on an industrial scale, the above-mentioned composite hydroxide is mixed with a lithium compound to obtain a lithium mixture, and the obtained lithium mixture is mixed in an oxidizing atmosphere at 650. It is preferable to synthesize the positive electrode active material by a production method including a firing step of firing at a temperature in the range of ° C. to 1000 ° C. If necessary, steps such as a heat treatment step and a calcining step may be added to the above steps. By such a production method, the above-mentioned positive electrode active material, particularly the positive electrode active material represented by the above general formula (B) can be easily obtained.

(4-1) Heat Treatment Step In the method for producing a positive electrode active material using a composite hydroxide as a precursor of the present invention, a heat treatment step is optionally provided before the mixing step to heat-treat the composite hydroxide. It may be mixed with a lithium compound after being made into particles. Here, the heat-treated particles include not only the composite hydroxide from which excess water has been removed in the heat treatment step, but also a transition metal-containing composite oxide converted into an oxide by the heat treatment step, or a mixture thereof. ..

The heat treatment step is a step of removing excess water contained in the composite hydroxide by heating the composite hydroxide to a temperature in the range of 105 ° C to 750 ° C and heat-treating it. As a result, the amount of water remaining until after the firing step can be reduced to a certain amount, and variations in the composition of the obtained positive electrode active material can be suppressed. When the heating temperature is less than 105 ° C., the excess water in the composite hydroxide cannot be removed, and the variation may not be sufficiently suppressed. On the other hand, when the heating temperature is higher than 700 ° C., not only the further effect cannot be expected, but also the production cost increases.

Further, in the heat treatment step, it is sufficient that water can be removed to the extent that the number of atoms of each metal component in the positive electrode active material and the ratio of the number of atoms of Li do not vary. There is no need to convert things. However, in order to reduce the variation in the number of atoms of each metal component and the ratio of the number of atoms of Li, it is heated to 400 ° C. or higher to convert all the composite hydroxides into composite oxides. Is preferable. The above-mentioned variation can be further suppressed by determining the metal component ratio contained in the composite hydroxide under the heat treatment conditions in advance by chemical analysis and determining the mixing ratio with the lithium compound.

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

The heat treatment time is not particularly limited, but is preferably at least 1 hour, more preferably 5 hours to 15 hours, from the viewpoint of sufficiently removing excess water in the composite hydroxide.

(4-2) Mixing Step The mixing step is a step of mixing a lithium compound with a composite hydroxide or heat-treated particles to obtain a lithium mixture.

In the mixing step, the ratio of the sum (Me) of the atomic numbers of metal atoms other than lithium in the lithium mixture, specifically nickel, cobalt, manganese, and the additive element M, to the atomic number of lithium (Li) ( Li / Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, and even more preferably 1.0 to 1.2. It is necessary to mix the composite hydroxide or heat-treated particles with the lithium compound. That is, since the Li / Me value does not change before and after the firing step, the composite hydroxide or heat treatment is performed so that the Li / Me value in the mixing step becomes the Li / Me value of the target positive electrode active material. It is necessary to mix the particles with the lithium compound.

The lithium compound used in the mixing step is not particularly limited, but it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof from the viewpoint of easy availability. In particular, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate.

It is preferable that the composite hydroxide or heat-treated particles and the lithium compound are sufficiently mixed so as not to generate fine powder. Insufficient mixing may cause variations in Li / Me values among the individual particles, making it impossible to obtain sufficient battery characteristics. A general mixer can be used for mixing. For example, a shaker mixer, a lady gemixer, a julia mixer, a V blender and the like can be used.

(4-3) Temporary firing step When lithium hydroxide or lithium carbonate is used as the lithium compound, the lithium mixture is mixed at a temperature lower than the firing temperature and 350 before the mixing step and the firing step. A calcining step of calcining may be performed at ° C. to 800 ° C., preferably 450 ° C. to 780 ° C. Thereby, lithium can be sufficiently diffused in the composite hydroxide or the heat-treated particles, and a more uniform positive electrode active material can be obtained.

The holding time at the above temperature is preferably 1 hour to 10 hours, and preferably 3 hours to 6 hours. Further, the atmosphere in the calcining step is preferably an oxidizing atmosphere as in the firing step described later, and more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume.

(4-4) Firing step The firing step is a step of calcining the lithium mixture obtained in the mixing step under predetermined conditions and diffusing lithium into the composite hydroxide or heat-treated particles to obtain a positive electrode active material. is there.

In this firing step, since the central portion of the composite hydroxide or heat-treated particles has a structure with many gaps in which fine primary particles are connected, sintering proceeds from a low temperature region, and sintering proceeds from the center of the particles. It contracts toward the slow high-density layer to form an internal space of a predetermined size at the center of the secondary particles.

The high-density layer and the outer shell layer (or the first high-density layer, the second high-density layer, and the outer shell layer) of the composite hydroxide and the heat-treated particles are sintered and shrunk and substantially integrated. In the positive electrode active material, primary particle aggregates are formed in one outer shell.

On the other hand, since the low-density layer is composed of fine primary particles, sintering starts in a lower temperature region than the high-density layer and the outer shell layer, as in the central portion. At this time, since the low-density layer has a larger volume shrinkage than the high-density layer and the outer shell layer, the fine primary particles constituting the low-density layer are the high-density layer and the outer shell layer in which the sintering progresses slowly. Due to volume shrinkage in the direction, between the high-density layer and the outer shell layer, or between the first high-density layer and the second high-density layer, and between the second high-density layer and the outer shell layer, A gap of appropriate size is formed. Since these voids do not have a radial thickness sufficient to retain their shape, they are absorbed by the high-density layer or the outer shell layer as the high-density layer or the outer shell layer is sintered, and the absorbed volume. Due to the shortage of water, the high-density layer and the outer shell layer shrink while being integrated during firing, and in the outer shell of the positive electrode active material formed, through holes that communicate the internal space of the secondary particles with the outside. To form. The area between the high-density layer and the outer shell (or between the first high-density layer and the second high-density layer and between the second high-density layer and the outer shell) is baked. Due to the integration by shrinkage, the entire outer shell is electrically conductive.

As described above, in the positive electrode active material using the composite hydroxide obtained by the production method of the present invention as a precursor, the entire outer shell portion is electrically conductive, and the cross-sectional area of the conduction path is sufficient. It can be said that it is secured. As a result, it becomes possible to use the inner and outer surfaces of the positive electrode active material as a reaction field with the electrolytic solution as an integral outer shell, and the internal resistance of the positive electrode active material is significantly reduced to form a secondary battery. In addition, it is possible to improve the output characteristics without impairing the battery capacity and cycle characteristics.

The particle structure of such a positive electrode active material is basically determined according to the particle structure of the composite hydroxide as a precursor, but it may be affected by its composition, firing conditions, and the like. After conducting a preliminary test, it is preferable to appropriately adjust each condition so as to obtain a desired structure.

The furnace used in the firing step is not particularly limited as long as it can fire the lithium mixture in the atmosphere or an oxygen stream. However, from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace can be preferably used. The same applies to the furnaces used in the heat treatment step and the calcining step.

a) Firing temperature The calcination temperature of the lithium mixture needs to be 650 ° C to 1000 ° C. When the calcination temperature is less than 650 ° C., lithium is not sufficiently diffused into the composite hydroxide or heat-treated particles, and excess lithium or unreacted composite hydroxide or heat-treated particles remain, or the obtained positive electrode. The crystallinity of the active material may be insufficient. On the other hand, when the firing temperature is higher than 1000 ° C., the particles of the positive electrode active material are violently sintered, causing abnormal grain growth, and the proportion of amorphous coarse particles increases.

When the positive electrode active material represented by the general formula (B1) is to be obtained, the firing temperature is preferably 650 ° C to 900 ° C. On the other hand, when the positive electrode active material represented by the general formula (B2) is to be obtained, the firing temperature is preferably 800 ° C. to 980 ° C.

The rate of temperature rise in the firing step is preferably 2 ° C./min to 10 ° C./min, and more preferably 5 ° C./min to 10 ° C./min. Further, during the firing step, it is preferable to hold the lithium compound at a temperature near the melting point for preferably 1 hour to 5 hours, more preferably 2 hours to 5 hours. Thereby, the composite hydroxide or the heat-treated particles and the lithium compound can be reacted more uniformly.

b) Baking time Of the firing times, the holding time at the above-mentioned firing temperature is preferably at least 2 hours, more preferably 4 hours to 24 hours. If the holding time at the calcination temperature is less than 2 hours, lithium does not sufficiently diffuse into the composite hydroxide or heat-treated particles, and excess lithium or unreacted composite hydroxide or heat-treated particles remain, or the obtained positive electrode. There is a risk that the crystallinity of the active material will be insufficient.

After the holding time is completed, the cooling rate from the firing temperature to at least 200 ° C. is preferably 2 ° C./min to 10 ° C./min, and more preferably 33 ° C./min to 77 ° C./min. By controlling the cooling rate within such a range, it is possible to prevent the equipment such as the bowl from being damaged by quenching while ensuring the productivity.

c) Baking atmosphere The atmosphere at the time of firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume, and a mixed atmosphere of oxygen having an oxygen concentration and an inert gas. Is particularly preferable. That is, firing is preferably performed in the atmosphere or an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the positive electrode active material may be insufficient.

(4-5) Crushing Step The positive electrode active material obtained by the firing step may be aggregated or slightly sintered. In such a case, it is preferable to physically crush the aggregate or sintered body of the positive electrode active material. Thereby, the average particle size and the particle size distribution of the obtained positive electrode active material can be adjusted in a suitable range. In addition, crushing is to apply mechanical energy to an agglomerate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and separate the secondary particles themselves with almost no destruction. It means an operation of loosening agglomerates.

As a crushing method, a known means can be used, and for example, a pin mill, a hammer mill, or the like can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

5. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery using the above-mentioned positive electrode active material includes the same components as a general non-aqueous electrolyte secondary battery, such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution. .. It should be noted that the embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery may be applied to embodiments to which various modifications and improvements have been made based on the embodiments described in the present specification. It is possible.

(5-1) Components a) Positive electrode Using the positive electrode active material obtained by using the composite hydroxide of the present invention as a precursor, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.

First, a conductive material and a binder are mixed with the positive electrode active material, and if necessary, activated carbon and a solvent for adjusting the viscosity are added, and these are kneaded to prepare a positive electrode mixture paste. At that time, the mixing ratio of each of the positive electrode mixture pastes is also an important factor in determining the performance of the non-aqueous electrolyte secondary battery. For example, 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 parts by mass to 95 parts by mass, as in the case of the positive electrode of a general non-aqueous electrolyte secondary battery. The content of the conductive material can be 1 part by mass to 20 parts by mass, and the content of the binder can be 1 part by mass to 20 parts by mass.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like in order to increase the electrode density. In this way, a sheet-shaped positive electrode can be produced. The sheet-shaped positive electrode can be cut into an appropriate size according to the target battery and used for manufacturing the battery. The method for producing the positive electrode is not limited to the above-exemplified method, and other methods may be used.

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

The binder serves to hold the active material particles together, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin or polyacrylic. Acids can be used.

In addition, if necessary, a solvent that disperses the positive electrode active material, the conductive material, and the activated carbon and dissolves the binder can be added to the positive electrode mixture. Specifically, as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

b) Negative electrode A metallic lithium, a lithium alloy, or the like can be used for the negative electrode. Further, a negative electrode mixture prepared by mixing a binder with a negative electrode active material capable of occluding and desorbing lithium ions and adding an appropriate solvent to form a paste is applied to the surface of a metal leaf current collector such as copper. , Dried, and if necessary, compressed to increase the electrode density can be used.

Examples of the negative electrode active material include lithium-containing substances such as metallic lithium and lithium alloys, natural graphite capable of occluding and desorbing lithium ions, organic compound fired bodies such as artificial graphite and phenol resin, and carbon substances such as coke. A powdery substance can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and as a solvent for dispersing these active substances and the binder, an organic substance such as N-methyl-2-pyrrolidone can be used. A solvent can be used.

c) Separator The separator is arranged so as to be sandwiched between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding an electrolyte. As such a separator, for example, a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used, but is not particularly limited as long as it has the above-mentioned function.

d) Non-aqueous electrolytic solution The non-aqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

As an organic solvent
Cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate,
Chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate,
Ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane,
Sulfur compounds such as ethyl methyl sulfone and butane sulton,
One selected from phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used alone or in combination of two or more.

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

The non-aqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(5-2) Structure The non-aqueous electrolyte secondary battery composed of the above-mentioned positive electrode, negative electrode, separator, and non-aqueous electrolyte solution can have various shapes such as a cylindrical shape and a laminated shape.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte solution to communicate with the positive electrode current collector and the outside. A non-aqueous electrolyte secondary battery is completed by connecting the positive electrode terminal and the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead or the like and sealing the battery case. ..

(5-3) Characteristics The non-aqueous electrolyte secondary battery using the positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor is excellent in battery capacity and cycle characteristics, and has higher output characteristics than the conventional structure. Has also been dramatically improved. Moreover, even in comparison with a conventional secondary battery using a positive electrode active material made of a lithium nickel-based composite oxide, the thermal stability and safety are not inferior.

For example, when a 2032 type coin battery as shown in FIG. 6 is constructed using a positive electrode active material obtained by using the composite hydroxide of the present invention as a precursor, it is 150 mAh / g or more, preferably 158 mAh / g or more. The initial discharge capacity, the positive electrode resistance of 1.10 Ω or less, preferably 1.00 Ω or less, and the 500 cycle capacity retention rate of 75% or more, preferably 80% or more can be simultaneously achieved.

(5-4) Applications The non-aqueous electrolyte secondary battery using the positive electrode active material obtained by using the composite hydroxide obtained by the present invention as a precursor has the battery capacity, output characteristics, and cycle characteristics as described above. It is excellent and can be suitably used as a power source for small portable electronic devices (notebook personal computers, mobile phones, etc.) that require these characteristics at a high level. Further, among these characteristics, the non-aqueous electrolyte secondary battery has significantly improved output characteristics and is also excellent in safety, so that it is possible to reduce the size and increase the output. However, since an expensive protection circuit can be simplified, it can be suitably used as a power source for transportation equipment whose mounting space is limited.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. Further, these are examples of embodiments of the present invention, and the present invention is not limited to these contents. In the following examples and comparative examples, unless otherwise specified, special grade reagents manufactured by Wako Pure Chemical Industries, Ltd. were used for producing the transition metal-containing composite hydroxide and the positive electrode active material. Further, during the nuclear formation step and the particle growth step, the pH value of the reaction aqueous solution was measured by a pH controller (NPH-690D, manufactured by Nisshin Rika Co., Ltd.), and the sodium hydroxide aqueous solution was supplied based on the measured values. By adjusting the amount, the pH value of the reaction aqueous solution in each step was controlled within a range of ± 0.2 with respect to the set value of the step.

(Example 1)
a) Production of transition metal-containing composite hydroxide [nucleation step]
First, 1.4 L of water was put into a 6 L reaction tank and the temperature in the tank was set to 70 ° C. while stirring. At this time, nitrogen gas was circulated in the reaction vessel for 30 minutes, and the oxygen concentration in the space inside the reaction vessel was set to 1% by volume or less. Subsequently, an appropriate amount of a 25 mass% sodium hydroxide aqueous solution was supplied into the reaction vessel, and the pH value was adjusted to 13.1 based on the liquid temperature of 25 ° C. to form a pre-reaction aqueous solution.

At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate are mixed with water so that the molar ratio of each metal element is Ni: Mn: Co: Zr = 33.1: 33.1: 33.1: 0.2. To prepare a 2 mol / L raw material aqueous solution.

Next, this raw material aqueous solution was supplied to the pre-reaction aqueous solution at a flow rate of 10 ml / min to form a reaction aqueous solution, and nucleation was carried out for 3 minutes by a crystallization reaction. During this treatment, a 25 mass% sodium hydroxide aqueous solution was supplied in a timely manner, and the pH value of the reaction aqueous solution was maintained in the range of 13.1 ± 0.2 based on the liquid temperature of 25 ° C.

[Particle growth process]
After the nucleation step was completed, the supply of all the aqueous solutions into the reaction vessel was temporarily stopped, and 37% by mass sulfuric acid was added into the reaction vessel, and the pH value of the reaction aqueous solution was 11.8 based on the liquid temperature of 25 ° C. It was adjusted to be. After confirming that the pH value had reached a predetermined value, the raw material aqueous solution and the sodium tungstate aqueous solution were supplied, and the nuclei produced in the nucleation step were grown.

After 7 minutes (2.9% of the total particle growth process time) from the start of the particle growth step, 37% by mass sulfuric acid was added to the reaction vessel while continuing to supply the raw material aqueous solution to prepare the reaction aqueous solution. The pH value was adjusted to 11.0 based on the liquid temperature of 25 ° C. (switching operation 1).

After 150 minutes (62.5% of the total particle growth process time) have elapsed from the start of the switching operation 1, a 25 mass% sodium hydroxide aqueous solution is added into the reaction vessel while the raw material aqueous solution is being supplied. The pH value of the reaction aqueous solution was adjusted to 11.8 based on the liquid temperature of 25 ° C. (switching operation 2).

After 20 minutes (8.3% of the total particle growth process time) had elapsed from the start of the switching operation 2, the switching operation 1 was performed again.

After 63 minutes (26.3% of the total particle growth process time) had elapsed from the start of the switching operation 1, the supply of all the aqueous solutions to the reaction vessel was stopped, and the particle growth process was completed. In the particle growth step, a 25% by mass sodium hydroxide aqueous solution was supplied in a timely manner, and the pH value of the reaction aqueous solution was maintained within the above range.

At the end of the particle growth step, the concentration of the product in the aqueous reaction was 86 g / L. Then, the obtained product was washed with water, filtered, and dried to obtain a powdery composite hydroxide.

b) Evaluation of composite hydroxide [Composition]
Using this composite hydroxide as a sample, the elemental fraction was measured using an ICP emission spectroscopic analyzer (ICPE-9000, Shimadzu Corporation, Shimadzu Corporation). The composite hydroxide was found in the general formula: Ni _0. It was confirmed that it was represented by _.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 (OH) _2.

[Particle structure]
When the composite hydroxide was observed with a field emission scanning electron microscope (FE-SEM: manufactured by JEOL Ltd., JSM-6360LA), the composite hydroxide was substantially spherical and had a substantially uniform particle size. It was confirmed that it was composed of secondary particles. Further, a part of the composite hydroxide was embedded in the resin, and the cross section of the secondary particles was observed by FE-SEM in a state where the cross section of the secondary particles could be observed by cross-section polishing. As a result, the secondary particles constituting this composite hydroxide have a central portion formed by aggregating fine primary particles, and plate-shaped primary particles are aggregated and formed on the outside of the central portion. It has one laminated structure in which a high-density layer and a low-density layer formed by agglomerating fine primary particles are laminated, and has an outer shell layer in which plate-shaped primary particles are further agglomerated on the outside thereof. confirmed.

At this time, when the average particle size of the primary particles was measured and calculated, the average particle size of the fine primary particles was 0.2 μm, and the average particle size of the plate-shaped primary particles was 0.5 μm. Furthermore, when the central particle size ratio, the high-density layer total particle size ratio, the high-density layer particle size ratio, the low-density layer particle size ratio, and the outer shell layer particle size ratio were also measured and calculated, they were 67, respectively. %, 12.5%, 8.5%, 4%, and 4%.

[Average particle size and particle size distribution]
Using a laser light diffraction / scattering type particle size analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.), the average particle size of the secondary particles constituting the composite hydroxide was measured, and d10 and d90 were measured to measure the particle size distribution. The value of [(d90-d10) / average particle size], which is an index showing the spread of, was calculated. As a result, the average particle size of the composite hydroxide was 5.1 μm, and the value of [(d90-d10) / average particle size] was 0.42.

c) Preparation of positive electrode active material The obtained composite hydroxide was subjected to a heat treatment step and heat-treated at 120 ° C. for 12 hours in an air (oxygen concentration: 21% by volume) air flow to obtain heat-treated particles. .. Then, as a mixing step, the heat-treated particles and lithium carbonate are mixed so that the Li / Me value becomes 1.14, and a shaker mixer device (TURBULA Type T2C manufactured by Willie et Bacoffen (WAB)) is used. The mixture was thoroughly mixed using to obtain a lithium mixture.

Next, a firing step was performed on this lithium mixture, and the temperature was raised from room temperature to 950 ° C. at a heating rate of 2.5 ° C./min in an air stream (oxygen concentration: 21% by volume). The mixture was fired for a long time and cooled to room temperature at a cooling rate of about 4 ° C./min. Since the positive electrode active material thus obtained had aggregated or lightly sintered, a crushing step was carried out, and the positive electrode active material was crushed to adjust the average particle size and the particle size distribution.

d) Evaluation of positive electrode active material [Composition]
Using this positive electrode active material as a sample, the elemental fraction was measured using an ICP emission spectroscopic analyzer. The positive electrode active material was found to have the general formula: Li _1.14 Ni _0.331 Mn _0.331 Co _0.331 Zr. It was confirmed that it was represented by _0.002 W _0.005 O _2.

[Average particle size and particle size distribution]
Using a laser light diffraction / scattering type particle size analyzer, the average particle size of this positive electrode active material is measured, and d10 and d90 are measured, which is an index showing the spread of the particle size distribution [(d90-d10) / average particle size. Diameter] was calculated. As a result, the average particle size of this positive electrode active material was 5.3 μm, and [(d90-d10) / average particle size] was 0.43.

[Particle structure]
When the positive electrode active material was observed by FE-SEM (see FIG. 2), it was confirmed that the positive electrode active material was composed of secondary particles having a substantially spherical shape and having substantially uniform particle sizes. Further, a part of this positive electrode active material was embedded in a resin, and the cross section of the particles was made observable by cross-section polishing, and observed by FE-SEM (see FIG. 3). As a result, this positive electrode active material is composed of substantially spherical secondary particles in which a plurality of primary particles are aggregated, has an internal space (central portion of a hollow structure) in the center of the secondary particles, and is on the outside thereof. Confirmed that the outer shell was hollow particles arranged in a substantially spherical shell shape. The outer shell particle size ratio of the outer shell was 18%. In addition, the number of secondary particles in which the entire particle can be observed from the surface observation of the particle, which communicates the internal space existing in the center of the secondary particle in the outer shell and the outside, is 6.5. Through holes were observed in%. Further, from the cross-sectional observation of the particles, the inner diameter (average inner diameter) of the through hole was 0.5 μm, and the through hole inner diameter ratio was 0.52.

[Specific surface area, tap density, and specific surface area per unit volume]
Using this positive electrode active material as a sample, the specific surface area is measured by a flow-type gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb), and the tap density is measured by a tapping machine (Kuramochi Kagaku Kikai Seisakusho, KRS-406). , Each was measured. As a result, the specific surface area of this positive electrode active material was 1.51 m ² / g, and the tap density was 1.53 g / cm ³ . The specific surface area per unit volume obtained from these measured values was 2.31 m ² / cm ³ .

e) Preparation of secondary battery The positive electrode active material obtained above: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. Then, the positive electrode (1) was prepared by drying in a vacuum dryer at 120 ° C. for 12 hours.

Next, using this positive electrode (1), a 2032 type coin battery (B) having the structure shown in FIG. 6 was produced in a glove box having an argon (Ar) atmosphere with a dew point controlled at −80 ° C. A lithium metal having a diameter of 17 mm and a thickness of 1 mm is used for the negative electrode (2) of this 2032 type coin battery, and ethylene carbonate (EC) and diethyl carbonate (DEC) _{using 1 M LiClO 4 as a supporting electrolyte are used as the electrolytic solution.} (Manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used. Further, as the separator (3), a polyethylene porous membrane having a film thickness of 25 μm was used. The 2032 type coin battery (B) has a gasket (4) and is assembled into a coin-shaped battery by a positive electrode can (5) and a negative electrode can (6).

f) Battery evaluation [Initial discharge capacity]
After the 2032 type coin battery is manufactured and left to stand for about 24 hours, the open circuit voltage OCV (Open Circuit Voltage) stabilizes, and then the current density with respect to the positive electrode is 0.1 mA / cm ² and the cutoff voltage is 4.3 V. A charge / discharge test was carried out to measure the discharge capacity when the battery was charged until it became full, and after a one-hour rest, and then discharged until the cutoff voltage became 3.0 V, and the initial discharge capacity was determined. As a result, the initial discharge capacity was 159.4 mAh / g. A multi-channel voltage / current generator (manufactured by Advantest Co., Ltd., R6741A) was used for the measurement of the initial discharge capacity.

[Positive electrode resistance]
The resistance value was measured by the AC impedance method using a 2032 type coin battery charged with a charging potential of 4.1 V. A frequency response analyzer and a potentiogalvanostat (manufactured by Solartron) were used for the measurement, and the Nyquist plot shown in FIG. 7 was obtained. Since the plot appears as the sum of the solution resistance, the negative electrode resistance and the capacitance, and the characteristic curve showing the positive electrode resistance and the capacitance, the fitting was calculated using an equivalent circuit, and the value of the positive electrode resistance was calculated. As a result, the positive electrode resistance was 1.035Ω.

[Cycle characteristics]
The 500-cycle capacity retention rate was calculated by repeating the above charge / discharge test and measuring the 500th discharge capacity with respect to the initial discharge capacity. As a result, it was confirmed that the capacity retention rate of 500 cycles was 82.1%.

Tables 1 to 4 show the production conditions of the above-mentioned transition metal-containing composite hydroxide and positive electrode active material, their characteristics, and the results of various performances of a battery using them. The results of Examples 2 to 18 and Comparative Examples 1 to 9 below are also shown in Tables 1 to 4.

(Example 2)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth process (2.9% of the total particle growth process time), and the switching operation 2 is performed from the switching operation 1 to 96 minutes (2.9% of the total particle growth process time). It is performed after 39.5% of the total particle growth process time has elapsed, and then the switching operation 1 is performed 20 minutes after the switching operation 2 (8.2% of the total particle growth process time). After that, the same procedure as in Example 1 was carried out except that the crystallization reaction was continued for 120 minutes (49.4% with respect to the total particle growth step time), and a composite hydroxide, a positive electrode active material, and a secondary battery were prepared. And evaluated them.

(Example 3)
In the particle growth step, the switching operation 1 is performed 24 minutes after the start of the particle growth step (10% of the total particle growth step time), and the switching operation 2 is performed from the switching operation 1 to 150 minutes (particle growth). It was performed after 62.5% of the total process time had elapsed, and then the switching operation 1 was performed after 20 minutes (8.3% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 46 minutes (19.2% with respect to the total particle growth step time), and the composite hydroxide, the positive electrode active material, and the secondary battery were used. They were prepared and evaluated.

(Example 4)
In the particle growth step, the switching operation 1 is performed 24 minutes after the start of the particle growth step (10% of the total particle growth step time), and the switching operation 2 is performed from the switching operation 1 to 96 minutes (particle growth). It was performed after 40% of the total process time had elapsed, and then the switching operation 1 was performed after 20 minutes (8.3% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 100 minutes (41.7% with respect to the total particle growth step time), and the composite hydroxide, the positive electrode active material, and the secondary battery were added. They were prepared and evaluated.

(Example 5)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth process (2.9% of the total particle growth process time), and the switching operation 2 is performed from the switching operation 1 to 168 minutes (2.9% of the total particle growth process time). It was performed after 70% of the total particle growth process time had elapsed, and then the switching operation 1 was performed after 20 minutes (8.3% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 45 minutes (18.8% of the total particle growth step time), and the composite hydroxide, the positive electrode active material, and the secondary battery were added. They were prepared and evaluated.

(Example 6)
In the particle growth step, the switching operation 1 is performed 24 minutes after the start of the particle growth step (10% of the total particle growth step time), and the switching operation 2 is performed from the switching operation 1 to 60 minutes (particle growth). It was performed after 25% of the total process time had elapsed, and then the switching operation 1 was performed after 36 minutes (15% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 120 minutes (50% of the total particle growth step time), and the transition metal-containing composite hydroxide, the positive electrode active material, and the secondary battery were added. They were prepared and evaluated.

(Example 7)
In the particle growth step, the switching operation 1 is performed 12 minutes after the start of the particle growth step (5% of the total particle growth step time), and the switching operation 2 is performed from the switching operation 1 to 144 minutes (particle growth). It was performed after 60% of the total process time had elapsed, and then the switching operation 1 was performed after 12 minutes (5% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 72 minutes (30% of the total particle growth step time), and the transition metal-containing composite hydroxide, the positive electrode active material, and the secondary battery were added. They were prepared and evaluated.

(Example 8)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth process (2.9% of the total particle growth process time), and the switching operation 2 is performed from the switching operation 1 to 120 minutes (2.9% of the total particle growth process time). It was performed after 50% of the total particle growth process time had elapsed, and then the switching operation 1 was performed after 36 minutes (15% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 77 minutes (32.1% of the total particle growth step time), the transition metal-containing composite hydroxide, the positive electrode active material, and the secondary. Batteries were made and evaluated.

(Example 9)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth step (3% of the total particle growth step time), and the switching operation 2 is performed from the switching operation 1 to 120 minutes (particle growth). It was performed after 52.4% of the total process time had elapsed, and then the switching operation 1 was performed after 18 minutes (7.9% of the total particle growth process time) had elapsed from the switching operation 2. Then, the crystallization reaction was continued for 33 minutes (14.4% of the total particle growth process time), and then switching operation 1 to 18 minutes (7.9% of the total particle growth process time). ) After that, the switching operation 2 was performed, and then the crystallization reaction was continued until 33 minutes (14.4% of the total particle growth process time) had elapsed from the switching operation 2. Except for this operation, the same procedure as in Example 1 was carried out, and a transition metal-containing composite hydroxide, a positive electrode active material and a secondary battery were prepared and evaluated.

(Comparative Example 1)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth step (2.9% of the total particle growth step time), and then 233 minutes (relative to the total particle growth step time). 97.1%) A composite hydroxide was prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued until it was completed. 4 and 5 show FE-SEM images of the surface and cross section of the composite hydroxide obtained in Comparative Example 1 and the surface and cross section of the positive electrode active material, respectively.

(Comparative Example 2)
In the particle growth step, the switching operation 1 is performed 72 minutes after the start of the particle growth step (30% of the total particle growth step time), and the switching operation 2 is performed from the switching operation 1 to 120 minutes (particle growth). It was performed after 50% of the total process time had elapsed, and then the switching operation 1 was performed after 3 minutes (1.25% of the total particle growth process time) had elapsed from the switching operation 2. Then, the same as in Example 1 except that the crystallization reaction was continued for 45 minutes (18.75% of the total particle growth step time), the transition metal-containing composite hydroxide, the positive electrode active material, and the secondary. Batteries were made and evaluated. In the obtained positive electrode active material, the particle structure of the secondary particles was a hollow structure without through holes.

(Comparative Example 3)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth process (2.9% of the total particle growth process time), and the switching operation 2 is performed from the switching operation 1 to 96 minutes (2.9% of the total particle growth process time). It was performed after 40% of the total particle growth process time had elapsed, and then the switching operation 1 was performed after 96 minutes (40% of the total particle growth process time) had elapsed from the switching operation 2. After that, the same as in Example 1 except that the crystallization reaction was continued for 41 minutes (17.1% with respect to the total particle growth step time), the transition metal-containing composite hydroxide, the positive electrode active material, and the secondary. Batteries were made and evaluated. In the obtained positive electrode active material, the particle structure of the secondary particles was a hollow structure without through holes.
(Comparative Example 4)
In the particle growth step, the switching operation 1 is performed 7 minutes after the start of the particle growth process (2.9% of the total particle growth process time), and the switching operation 2 is performed from the switching operation 1 to 15 minutes (2.9% of the total particle growth process time). It was performed after 6.3% of the total particle growth process time had elapsed, and then the switching operation 1 was performed after 20 minutes (8.3% of the total particle growth process time) had elapsed from the switching operation 2. .. After that, the same as in Example 1 except that the crystallization reaction was continued for 198 minutes (82.5% of the total particle growth step time), and the transition metal-containing composite hydroxide, positive electrode active material, and secondary were used. Batteries were made and evaluated. In the obtained positive electrode active material, the particle structure of the secondary particles was a hollow structure without through holes.

1 Positive electrode (evaluation electrode)
2 Negative electrode 3 Separator 4 Gasket 5 Positive electrode can 6 Negative electrode can B 2032 type coin battery 21 Central part 22 High density layer 23 Low density layer 24 Outer shell layer 25 Outer shell part

Claims (12)

A reaction aqueous solution is formed by supplying an aqueous solution of a raw material containing at least a transition metal element, and a transition metal-containing composite hydroxide which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery is produced by a crystallization reaction. It ’s a method,
A nucleation step in which the pH value of the reaction aqueous solution is controlled to be 12.0 to 14.0 based on a liquid temperature of 25 ° C. and nucleation is performed.
The pH value of the reaction aqueous solution containing the nucleation obtained in the nucleation step based on a liquid temperature of 25 ° C. is adjusted to be lower than the pH value in the nucleation step and to be 10.5-12.0. It is provided with a particle growth step for growing the nuclei, and
The particle growth step is a first step of maintaining the supersaturation of the transition metal element in the reaction aqueous solution in a high state from the start of the particle growth step, and after the lapse of the first step, the supersaturation is set to the first step. A second step of switching to a lower state and maintaining the supersaturation degree, and a third step and a third step of switching the supersaturation degree to the higher state and maintaining the supersaturation degree after the lapse of the second step. After the lapse of time, the supersaturation degree is switched to the low state, and has a fourth step of maintaining the supersaturation degree.
A method for producing a transition metal-containing composite hydroxide. The method for producing a transition metal-containing composite hydroxide according to claim 1, wherein the degree of supersaturation is switched by controlling the pH value of the reaction aqueous solution based on a liquid temperature of 25 ° C. In the particle growth step, the pH value of the reaction aqueous solution in a state of high supersaturation based on a liquid temperature of 25 ° C. is adjusted to be in the range of 11.0 to 12.0, and the state of low supersaturation. 2. The pH value of the reaction aqueous solution in the above, based on a liquid temperature of 25 ° C., is adjusted to be in the range of 10.5 to 11.5 and lower than the pH value in a state where the degree of supersaturation is high. The method for producing a transition metal-containing composite hydroxide according to the above method. The first step is the time in the range of 0.5% to 20% with respect to the whole of the particle growth process, and the second step is the time in the range of 10% to 80% with respect to the whole of the particle growth step. The third step is the time in the range of 2% to 30% with respect to the whole of the particle growth process, and the fourth step is the time in the range of 10% to 80% with respect to the whole of the particle growth step. The method for producing a transition metal-containing composite hydroxide according to any one of claims 1 to 3, wherein the time is set to. After the lapse of the fourth stage, the supersaturation degree is switched to a state higher than the fourth stage to maintain the supersaturation degree, and after the lapse of the fifth stage, the supersaturation degree is lower than the fifth stage. The method for producing a transition metal-containing composite hydroxide according to any one of claims 1 to 3, further comprising a sixth step of switching to a state and maintaining the degree of supersaturation. The first step is the time in the range of 0.5% to 20% with respect to the whole of the particle growth process, and the second step is the time in the range of 10% to 75% with respect to the whole of the particle growth step. The third step is the time in the range of 2% to 30% with respect to the total particle growth process time, and the fourth step is the time in the range of 10% to 75% with respect to the total particle growth process time. The time is defined as the fifth step, which is in the range of 2% to 30% of the total particle growth process time, and the sixth step is 10% to 75% of the total particle growth process time. The method for producing a transition metal-containing composite hydroxide according to claim 5, wherein the time is in the range of%. Wherein the transition metal-containing composite hydroxide of the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, The method for producing a transition metal-containing composite hydroxide according to any one of claims 1 to 6, wherein the composition is represented by one or more additive elements selected from Hf, Ta, and W). The production of the transition metal-containing composite hydroxide according to claim 7, further comprising a coating step of coating the surface of the transition metal-containing composite hydroxide with the compound containing the additive element M after the particle growth step. Method. A crystallization step for obtaining the transition metal-containing composite hydroxide using the production method according to any one of claims 1 to 8.
A mixing step of mixing the transition metal-containing composite hydroxide and a lithium compound to form a lithium mixture, and
A firing step of calcining the lithium mixture at a temperature in the range of 650 ° C. to 1000 ° C. in an oxidizing atmosphere to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery composed of a lithium transition metal-containing composite oxide.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. In the mixing step, the lithium compounds are mixed so that the ratio of the number of lithium atoms contained in the lithium mixture to the total number of atoms of metal elements other than lithium is in the range of 0.95 to 1.5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 9, wherein the amount is adjusted. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 9 or 10, further comprising a heat treatment step of heat-treating the transition metal composite hydroxide at a temperature in the range of 105 ° C. to 750 ° C. prior to the mixing step. Method of manufacturing active material. The lithium transition metal-containing composite oxide is _{subjected to the general formula (B): Li 1 + U} Ni _x Mn _y Co _z M _t O ₂ (−0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦. 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 9 to 11, wherein the composition is represented by (one or more additive elements selected from Hf, Ta, and W).

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