JP2018095505A - Composite hydroxide containing transition metal and process for manufacturing the same and cathode active material for non-aqueous electrolyte secondary battery and process for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material which has improved output capacity as well as improved capacity characteristic and cycle characteristic, and a composite hydroxide containing transition metal as its precursor, by production on an industrial scale.SOLUTION: The process comprises a nucleation step where a nucleus is generated under non-oxidation atmosphere, and a particle growth step where the nucleus obtained in the nucleation step grows, and in the particle growth step, a first step under non-oxidation atmosphere, a second step under oxidation atmosphere, a third step under non-oxidation atmosphere, a fourth step under oxidation atmosphere, and an outer-shell formation step under non-oxidation atmosphere are switched in this order to produce a composite hydroxide containing transition metal, the composite hydroxide containing transition metal comprising a lamination structure outside of a center part made of primary tabular particles, the lamination structure being composed of a first low-density layer made of primary fine particles, a first high-density layer made of primary tabular particles, a second low-density layer made of primary fine particles, and an outer shell part made of primary tabular particles. A cathode active material obtained from the precursor comprises a plural of cavities inside and holes which communicate between the cavities and an outer part so that an electrolyte and an auxiliary conductive agent can infiltrate into the inner part.SELECTED DRAWING: Figure 1

Description

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

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

  As a secondary battery satisfying such requirements, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. This lithium ion secondary battery includes 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 a material for the negative electrode and the positive electrode.

  Among these lithium ion secondary batteries, a 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, and therefore has a high energy density. Currently, research and development are actively conducted, and some are being put into practical use.

As a positive electrode active material for a non-aqueous electrolyte secondary battery, which is a positive electrode material of the lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) particles that are relatively easy to synthesize, nickel that is cheaper than cobalt was 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 (LiMn ₂ O ₄ ) using manganese ) Particles, lithium 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 excellent in cycle characteristics and output characteristics, it is necessary that the positive electrode active material for a nonaqueous 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 have a large specific surface area and can sufficiently ensure a reaction area with the electrolyte solution, and the positive electrode is made thin, and between the positive and negative electrodes of lithium ions. This is because the internal resistance of the secondary battery can be reduced by reducing the moving distance. In addition, particles having a narrow particle size distribution have a substantially constant voltage applied to each particle in the electrode, and therefore, it is possible to suppress a decrease in battery capacity due to selective deterioration of the fine particles.

  Here, in order to reduce the positive electrode resistance, which is an internal resistance component of the secondary battery, and further improve the output characteristics, a space in which the electrolyte can enter the positive electrode active material for the non-aqueous electrolyte secondary battery It is effective to form a part. The positive electrode active material for a non-aqueous electrolyte secondary battery having such a hollow structure is less in comparison with the electrolyte solution than the positive electrode active material for a non-aqueous electrolyte secondary battery having a solid particle size. Since the reaction area can be increased, the positive electrode resistance can be greatly reduced. In addition, it is known that the positive electrode active material for nonaqueous electrolyte secondary batteries will inherit the property of the transition metal containing composite hydroxide used as the precursor. Therefore, in order to obtain the positive electrode active material for a non-aqueous electrolyte secondary battery described above, it is necessary to appropriately control the particle size, particle size distribution, particle structure, and the like of the transition metal-containing composite hydroxide serving as the precursor. Necessary.

  For example, in JP2012-246199A, JP2013-147416A, and WO2012 / 1318181, a nucleation process in which nucleation is mainly performed, and a particle growth process in which particle growth is mainly performed, A method for producing a transition metal-containing composite hydroxide serving as a precursor of a positive electrode active material by separating the crystallization reaction into two stages is disclosed. In this method, by appropriately adjusting the pH value and reaction atmosphere in the nucleation step and the particle growth step, a low-density central part consisting of only fine primary particles with a small particle size and a narrow particle size distribution, and a plate A transition metal-containing composite hydroxide 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 having a transition metal-containing composite hydroxide having such a configuration 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. The hollow structure which consists of these can be provided. Therefore, in the secondary battery using the positive electrode active material for these nonaqueous electrolyte secondary batteries, it is considered that the battery capacity, output characteristics, and cycle characteristics are improved at the same time.

JP 2012-246199 A JP 2013-147416 A JP 2011-119092 A WO2012 / 131881

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

  In view of the above-mentioned problems, the present invention has a structure capable of further improving the output characteristics without damaging the battery capacity and cycle characteristics when a non-aqueous electrolyte secondary battery is configured. It aims at providing the positive electrode active material for nonaqueous electrolyte secondary batteries, and the transition metal containing composite hydroxide which is the precursor. Moreover, an object of this invention is to provide the manufacturing method for obtaining the positive electrode active material and transition metal containing composite hydroxide which have such a structure efficiently on an industrial scale.

  A first aspect of the present invention is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery, in which a plurality of plate-like primary particles and fine primary particles having a particle size smaller than the plate-like primary particles are aggregated It is related with the transition metal containing composite hydroxide which consists of the secondary particle formed in this way.

  The secondary particles are formed on the outer side of the central portion made of the plate-like primary particles, on the outer side of the central portion, and on the outer side of the first low-density layer made of the fine primary particles. A first high-density layer composed of the plate-like primary particles, a second low-density layer formed outside the first high-density layer and composed of the fine primary particles, and a second low-density layer. And an outer shell formed of the plate-like primary particles.

  Furthermore, between the second low-density layer and the outer shell portion, the outer high-density layer formed on the outside of the second low-density layer and made of the plate-like primary particles, and on the outer side of the outer high-density layer It is also possible to further include at least one laminated structure formed and formed of an external low density layer made of the fine primary particles.

  The average ratio of the outer diameter of the central portion to the particle size of the secondary particles is in the range of 20% to 60%, and the average ratio of the thickness of the first low density layer to the particle size of the secondary particles is The average ratio of the thickness of the first high-density layer to the particle size of the secondary particles is in the range of 8% to 33%, and the second low-density layer is in the range of 8% to 33%. The average ratio of the thickness to the particle size of the secondary particles is in the range of 8% to 23%, and the average ratio of the thickness of the outer shell layer to the particle size of the secondary particles is 4% to It is preferable to be in the range of 18%.

  In addition, when a laminated structure is provided between the second low density layer and the outer shell portion, the average ratio of the thickness of the external high density layer to the particle size of the secondary particles is 4% to 18%. The ratio of the thickness of the outer low density layer to the particle size of the secondary particles is preferably in the range of 8% to 23%.

  The average particle size of the plate-like primary particles is in the range of 0.3 μm to 3 μm, the average particle size of the fine primary particles is smaller than the average particle size of the plate-like primary particles, and It is preferable that it exists in the range of 01 micrometer-0.3 micrometer.

  The average particle size of the secondary particles is in the range of 1 μm to 15 μm, and the value of [(d90−d10) / average particle size] which is an index indicating the spread of the particle size distribution of the secondary particles is 0. .65 or less is preferable.

The composition of the transition metal composite hydroxide of the present invention is not particularly limited, but 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, It is preferably represented by one or more additive elements selected from V, Cr, Zr, Nb, Mo, Hf, Ta, and W).

  Moreover, when it has the said composition, the said addition element M can take a various presence form, if it exists in the range of the above-mentioned composition ratio in the whole secondary particle. For example, the additive element M is uniformly distributed inside the transition metal composite hydroxide and / or the surface of the transition metal composite hydroxide is coated with a compound containing the additive element M. Is preferred.

  In the second aspect of the present invention, a raw material aqueous solution containing at least a transition metal element and an aqueous solution containing an ammonium ion supplier are mixed to form a reaction aqueous solution, which is used for a non-aqueous electrolyte secondary battery by a crystallization reaction. The present invention relates to a method for producing a transition metal composite hydroxide that is a precursor of a positive electrode active material.

The method for producing the transition metal composite hydroxide of the present invention comprises:
A nucleation step of adjusting the pH value of the reaction aqueous solution at a reference temperature of 25 ° C. to a range of 12.0 to 14.0 and performing nucleation in a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less; The pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step is adjusted to be lower than the pH value in the nucleation step and from 10.5 to 12.0, based on a liquid temperature of 25 ° C. And a particle growth step for growing the nucleus, and
In the grain growth step, a first stage for maintaining the non-oxidizing atmosphere from the start of the grain growth process, and after the first stage, the oxygen concentration is switched to an oxidizing atmosphere exceeding 5% by volume, and the oxidation is performed. A second stage for maintaining the oxidizing atmosphere, a third stage for switching from the oxidizing atmosphere to the non-oxidizing atmosphere after the second stage, and maintaining the non-oxidizing atmosphere, and after the third stage, A fourth stage for switching from the non-oxidizing atmosphere to the oxidizing atmosphere to maintain the oxidizing atmosphere, and after the fourth stage, the non-oxidizing atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere. And an outer shell forming step for maintaining the temperature.

  In the above, the first stage is a time in the range of 0.5% to 15% with respect to the whole grain growth process, and the second stage is 4% to 22% with respect to the whole grain growth process. And the third stage is a time in the range of 10% to 40% with respect to the whole grain growth process, and the fourth stage is 15% to the whole grain growth process time. It is preferable that the time is in the range of 40%, and the outer shell portion formation stage is in the range of 10% to 45% with respect to the entire grain growth process time.

  Furthermore, between the fourth stage and the outer shell forming stage, switching from the oxidizing atmosphere to the non-oxidizing atmosphere to maintain the non-oxidizing atmosphere, and forming the outer high-density layer, After the progress of the layer forming step, the combination with the external low density layer forming step of switching from the non-oxidizing atmosphere to the oxidizing atmosphere and maintaining the oxidizing atmosphere may be provided at least once.

  In this case, the external high-density layer formation step is set to a time in the range of 10% to 40% with respect to the entire particle growth process, and the external low-density layer formation step is set to the entire particle growth process time. On the other hand, the time is preferably in the range of 15% to 40%.

According to the method for producing a transition metal composite hydroxide of the present invention, 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, A transition metal composite hydroxide having a composition represented by one or more additive elements selected from Mo, Hf, Ta, and W can be obtained.

  Further, 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 can be further provided.

  A 3rd aspect of this invention is related with the positive electrode active material used as a positive electrode material of a nonaqueous electrolyte secondary battery. The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention comprises secondary particles formed by agglomerating a plurality of primary particles, and a plurality of void portions dispersed in the secondary particles; and It is characterized by comprising at least one communicating hole for communicating the void portion and the outside of the secondary particle.

  The said structure WHEREIN: It is preferable that the average hole diameter of the said space | gap part exists in the range of 0.1 micrometer-2 micrometers. Moreover, it is preferable that the average internal diameter of the said communicating hole exists in the range of 0.2 micrometer-0.7 micrometer.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention preferably has a specific surface area per unit volume of the secondary particles of 3.5 m ² / cm ³ or more, and the ratio of the secondary particles surface ^area, a 2.7m ² /g~4.0m 2 / g, and a tap density of the secondary particles was measured based on JIS Z2512 is preferably not 1.0 g / cm ³ or more.

  The average particle size of the secondary particles is in the range of 1 μm to 15 μm, and the value of [(d90−d10) / average particle size] which is an index indicating the spread of the particle size distribution of the secondary particles is 0. .70 or less is preferable.

The composition of the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is not particularly limited, but is represented by 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 It is preferably represented by one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W).

  In the above case, the additive element M is uniformly distributed inside the positive electrode active material for a non-aqueous electrolyte secondary battery and / or the positive electrode active material for the non-aqueous electrolyte secondary battery by a compound containing the additive element M. The surface of the substance is preferably coated.

A 4th aspect of this invention is related with the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is a mixing step in which a transition metal-containing composite hydroxide according to the first aspect of the present invention and a lithium compound are mixed to form a lithium mixture. When,
A firing step of firing the lithium mixture in an oxidizing atmosphere at a temperature in the range of 650 ° C. to 1000 ° C. to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal-containing composite oxide; It is characterized by having.

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

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

According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the lithium transition metal-containing composite oxide is converted into 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), a positive electrode for a non-aqueous electrolyte secondary battery having a composition represented by An active material can be obtained.

  A fifth aspect of the present invention relates to a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The positive electrode material for the non-aqueous electrolyte secondary battery according to the second aspect of the present invention is used as the positive electrode material of the positive electrode. It is characterized by the fact that an active material is used.

  By using the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention as a precursor of the transition metal-containing composite hydroxide according to the present invention as a positive electrode material for the non-aqueous electrolyte secondary battery, its battery capacity and cycle characteristics It is possible to provide a non-aqueous electrolyte secondary battery with further improved output characteristics without impairing the characteristics. Further, according to the present invention, the positive electrode active material for a non-aqueous electrolyte secondary battery that contributes to the improvement of such battery characteristics and the transition metal-containing composite hydroxide as a precursor thereof are produced on an industrial scale. It can be possible to manufacture efficiently. For this reason, the industrial significance of the present invention is extremely large.

FIG. 1 is a cross-sectional view schematically showing the structure of the transition metal-containing composite hydroxide of the present invention. FIG. 2 is an FE-SEM image (observation magnification: 5,000 times) showing a cross section of the positive electrode active material for a nonaqueous electrolyte secondary battery obtained in Example 1. FIG. 3 is a schematic cross-sectional view of a 2032 type coin battery used for battery evaluation. FIG. 4 is a schematic explanatory diagram of an impedance evaluation measurement example and an equivalent circuit used for analysis.

  The present inventors have a hollow structure obtained based on the prior art such as WO2012 / 131881 and having a small particle size, a narrow particle size distribution, and comprising an outer shell portion and a space portion inside the outer shell portion. In addition, for the positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter referred to as “positive electrode active material”), intensive studies were conducted to further improve the output characteristics.

  As a result, first, in the particle growth step, the reaction atmosphere can be switched in a short time by supplying the atmosphere gas to the reaction system using an air diffuser while continuing the supply of the raw material aqueous solution. In addition, by switching the reaction atmosphere, it has been found that it is possible to alternately stack a high-density layer composed only of plate-like primary particles and a low-density layer composed of fine primary particles. It was.

  Secondly, by switching the reaction atmosphere as described above, a central portion composed of plate-like primary particles and a low density layer (hereinafter referred to as “first low density”) formed on the outside of the central portion and composed of the fine primary particles. Layer ”), a high-density layer formed on the outside of the first low-density layer and made of the plate-like primary particles (hereinafter referred to as“ first high-density layer ”), and a first high-density layer A low-density layer (hereinafter referred to as “second low-density layer”) formed on the outside and made of the fine primary particles, and an outer shell portion formed on the outside of the second low-density layer and made of plate-like primary particles It was found that a transition metal-containing composite hydroxide comprising:

  Third, the positive electrode active material obtained using the transition metal-containing composite hydroxide as a precursor is composed of secondary particles formed by agglomerating a plurality of primary particles, and is dispersed inside the secondary particles. The present inventors have found that a plurality of existing voids and a structure including at least one communication hole communicating the voids and the outside of the secondary particles are provided.

  Fourth, the communication hole formed in the positive electrode active material allows the electrolytic solution and the conductive auxiliary agent to enter the secondary particles. As a result, not only in the outer surface of the positive electrode active material but also in the inside thereof. It is possible to provide a reaction field with the electrification solution, and when a positive electrode active material having such a structure is used as a positive electrode material for a nonaqueous electrolyte secondary battery, the knowledge that an effect of lower positive electrode resistance can be obtained is obtained. It was.

  The present invention has been completed based on these findings.

1. Transition metal-containing composite hydroxide (1-1) Structure of transition metal-containing composite hydroxide The transition metal-containing composite hydroxide of the present invention (hereinafter referred to as “composite hydroxide”) is a non-aqueous electrolyte secondary battery. It is a precursor of a positive electrode active material for use, and is composed of a plurality of plate-like primary particles and secondary particles formed by agglomerating fine primary particles having a smaller particle size than the plate-like primary particles.

  In particular, the secondary particles constituting the composite hydroxide of the present invention, as shown in FIG. 1, are formed in a central portion 21 made of plate-like primary particles, and on the outer side of the central portion and made of fine primary particles. 1 low-density layer 22, formed on the outside of the first low-density layer, and formed on the outside of the first high-density layer, the first high-density layer 23 made of plate-like primary particles, and the fine primary particles The second low-density layer 24 is made of, and the outer shell portion 25 made of plate-like primary particles is formed outside the second low-density layer.

  In the composite hydroxide of the present invention, a mode in which a laminated structure including a high density layer and a low density layer is further provided outside the second low density layer can be employed. That is, between the second low-density layer and the outer shell portion, it is formed outside the second low-density layer, and is formed outside the high-density layer made of plate-like primary particles and outside the external high-density layer. In addition, at least one laminated structure including an external low-density layer made of fine primary particles can be further provided.

  Hereinafter, the structure of the composite hydroxide of the present invention will be described in detail. When the term “low density layer” is used, it means both the first low density layer and the second low density layer. The structure having a density layer includes this external low density layer. Similarly, the term “high-density layer” simply means the first high-density layer, but the structure having the external high-density layer includes this external high-density layer.

  First, since the central part, the high-density layer and the outer shell part have a structure composed of plate-like primary particles, compared with a low-density layer composed of fine primary particles that are smaller and less thick, sintering can be performed from a higher temperature range. proceed. As a result, the low-density layer, which starts sintering from a relatively low temperature region and has a fast progress of sintering, has a composite hydroxide as a positive electrode active material than the central portion, the high-density layer, and the outer shell portion. At the time of firing, the amount of thermal deformation increases.

  In particular, in the secondary particles constituting the composite hydroxide of the present invention, the outer shell portion composed of one high-density layer is not provided around the center portion constituted by the fine primary particles as in the conventional structure. Rather, it is composed of plate-like primary particles, and has a laminated structure in which a plurality of low-density layers having a predetermined thickness are sandwiched between a central portion having a predetermined thickness, a high-density layer, and an outer shell portion.

  With such a configuration, when firing, a structure portion with many gaps in which fine primary particles are connected like a low density layer has a larger amount of thermal deformation than the center portion, the high density layer and the outer shell portion. It contracts non-uniformly toward the center, high-density layer or outer shell to form a discontinuous space, that is, a void. At the same time, the central portion, the high-density layer, and the outer shell portion are close to each other or substantially integrated by shrinkage to form a main portion in the positive electrode active material. At this time, along with the formation of the main part, a part of the void part passes through the high-density part and the outer shell part as a communication hole, and communicates the outside of the secondary particle and the void part.

  In the secondary particles constituting the composite hydroxide, the low density layer does not have to be uniformly formed between the central portion, the high density layer, and the outer shell portion. As long as at least one communication hole is formed in the part, such a structure in which such a low density layer is partially formed is also included in the scope of the present invention.

(1-2) Average particle diameter of transition metal-containing composite hydroxide The average particle diameter of secondary particles constituting the composite hydroxide of the present invention is 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably 3 μm to It is adjusted to 10 μm. The average particle diameter of the positive electrode active material correlates with the average particle diameter of the composite hydroxide. For this reason, it becomes possible to set the average particle diameter of a positive electrode active material to a predetermined | prescribed range by setting the average particle diameter of a composite hydroxide in such a 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 particle size analyzer. .

(1-3) Particle Size Distribution of Transition Metal-Containing Composite Hydroxide [(d90-d10) / Average Particle Size] which is an index showing the spread of the particle size distribution of secondary particles constituting the composite hydroxide of the present invention The value is adjusted to 0.65 or less, preferably 0.55 or less, more preferably 0.50 or less, and still more preferably 0.45 or less.

  The particle size distribution of the positive electrode active material is strongly influenced by the composite hydroxide that is a precursor thereof. For this reason, for example, when a positive electrode active material is produced using a composite hydroxide containing a large amount of fine particles and coarse particles as a precursor, the positive electrode active material also contains many fine particles and coarse particles. Thus, the safety, cycle characteristics, and output characteristics of a secondary battery using the same 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 as the precursor so that the value of [(d90-d10) / average particle size] is 0.65 or less. This makes it possible to avoid the above-described problems related to the battery characteristics, particularly the safety and cycle characteristics due to the selective deterioration of fine particles. However, when considering production on an industrial scale, producing a composite hydroxide in a powder state in which the value of [(d90-d10) / average particle size] is excessively small is the yield, productivity, Or it is not realistic from the viewpoint of production cost. Therefore, the lower limit value of [(d90−d10) / average particle diameter] 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 accumulated volume is 10% of the total volume of all particles, d90 is When the number of particles is accumulated by the same method, it means a particle size in which the accumulated volume is 90% of the total volume of all particles. d10 and d90 can be determined from the volume integrated value measured with a laser light diffraction / scattering particle size analyzer, similarly to the average particle size of the composite hydroxide.

(1-4) Thickness of center part, high density layer, low density layer and outer shell part In the composite hydroxide of the present invention, the outer diameter of the center part relative to the particle diameter of the secondary particles, the first low density By controlling the ratio of the thickness of each of the layer, the first high-density layer, the second low-density layer and the outer shell, or the external high-density layer and the external low-density layer in the above range, A positive electrode active material having a plurality of voids dispersed inside and at least one communication hole that communicates the voids with the outside of the secondary particles is formed. Therefore, in the secondary particles constituting the composite hydroxide, the outer diameter of the central portion with respect to the particle size, and the first low density layer, the first high density layer, the second low density layer, and the outer shell portion Alternatively, the particle structure of the positive electrode active material can be set in an appropriate range by appropriately controlling the ratio of the thicknesses of the external high-density layer and the external low-density layer.

  In the composite hydroxide having the structure of the present invention, in the secondary particles constituting the composite hydroxide, the average ratio of the outer diameter of the central portion to the particle size (hereinafter referred to as “central particle size ratio”) is 20 % To 60% is preferable, 25% to 55% is more preferable, and 30% to 50% is more preferable. With such a configuration, in the composite hydroxide, in the positive electrode active material obtained by using such a composite hydroxide as a precursor with the high-density layer, each low-density layer, and the outer shell portion having an appropriate thickness. It is possible to provide a predetermined gap and a communication hole. If the size of the central part exceeds this range, the composite hydroxide has a low density layer, a high density layer and an outer shell part that exceed the scope of the present invention. There is a possibility that a structure with a communication hole inside cannot be obtained.

  The average ratio of the thickness of the first low density layer to the particle size of the secondary particles (hereinafter referred to as “first low density layer particle size ratio”) is preferably in the range of 8% to 33%. % To 30% is preferable, and 15% to 25% is more preferable.

  The ratio of the thickness of the first high-density layer to the average particle size of the secondary particles (hereinafter referred to as “first high-density layer particle size ratio”) is preferably in the range of 8% to 33%, It is more preferably in the range of 10% to 30%, and further preferably in the range of 15% to 25%.

  The average ratio of the thickness of the second low density layer to the particle size of the secondary particles (hereinafter referred to as “second low density layer particle size ratio”) is preferably in the range of 8% to 23%. % To 30% is preferable, and 15% to 25% is more preferable.

  The average ratio of the thickness of the outer shell portion to the particle size of the secondary particles (hereinafter referred to as “outer shell particle size ratio”) is preferably in the range of 4% to 18%, and is preferably 5% to 15%. More preferably, it is in the range of 8% to 12%.

  By setting the first low density layer particle size ratio, the first high density layer particle size ratio, the second low density layer particle size ratio, and the outer shell portion particle size ratio within this range, the composite water having such a structure can be obtained. In the positive electrode active material obtained using the oxide, it is possible to form secondary particles (main part) in which voids and communication holes of appropriate sizes are formed. When the respective low density layer particle size ratios are too small, voids large enough to form communication holes communicating with the outside in the obtained positive electrode active material are not generated during firing of the composite hydroxide. Conversely, if the particle size ratio of each of the low density layers is too large, the center, the high density layer, and the outer shell are not sufficiently connected or integrated when firing the composite hydroxide, which is desirable in the positive electrode active material. The structure of can not be obtained. In this case, since the central portion, the high-density layer, and the outer shell portion are not electrically connected to each other, the effect of reducing the positive electrode resistance cannot be obtained.

  If the high-density layer particle size ratio and the outer shell particle size ratio are too small, the predetermined structure of the secondary particles is not maintained in the production stage or filling stage of the positive electrode active material, and the secondary particles may be destroyed. There is a possibility that a void having a sufficiently large communication hole may not be formed inside. On the other hand, if the high-density layer particle size ratio and the outer shell particle size ratio are too large, communication holes penetrating these layers will not be formed during firing of the composite hydroxide, and sufficient electrolysis will occur in the internal voids. There is a possibility that penetration of the liquid and the conductive auxiliary agent becomes insufficient.

  In the composite hydroxide of the present invention, an external high-density layer formed of plate-like primary particles formed between the second low-density layer and the outer shell portion and outside the second low-density layer, and the outside thereof At least one laminated structure formed on the outside of the high-density layer and composed of an external low-density layer made of fine primary particles can be further provided.

  In this case, when a laminated structure is provided between the second low density layer and the outer shell portion, the average ratio of the thickness of the external high density layer to the particle size of the secondary particles is 4% to 18%. %, And the ratio of the thickness of the external low density layer to the particle size of the secondary particles is preferably in the range of 8% to 23%.

  In the present invention, as long as the basic center portion, the first low density layer, the first high density layer, the second low density layer, and the outer shell portion have a predetermined thickness, the high density layer and the low density layer are low. Even when one or more laminated structures composed of density layers are further provided, basically, when the composite hydroxide having such a structure is fired, the central portion, the first high-density layer, and the external high-density layer And the outer shell part is substantially integrated by sintering shrinkage, and a structure in which the void part formed inside communicates with the outside through the communication hole is obtained. Therefore, in such a structure, while maintaining the structure of the entire positive electrode active material that is difficult to be collapsed, the number of places where the voids are formed is increased, and further, communication holes that communicate the voids and the outside are formed. As a result of the increase in the number of parts, it is possible to further reduce the positive electrode resistance.

  Here, the central part particle size ratio, the first low density layer particle size ratio, the first high density particle size ratio, the second low density layer particle size ratio, the outer shell particle size ratio, and the external low altitude layer particle size The ratio and the external low density layer particle size ratio can be determined by observing the cross section of the composite hydroxide with a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM).

  Specifically, first, the cross section of the secondary particle is observed in a field of view that allows the central part, each layer, and the outer shell part of the secondary particle to be distinguished. 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 these values are respectively determined as the particle size and center of the secondary particle. The outer diameter of the part. Further, the thicknesses of the respective layers and outer shells at arbitrary positions at three or more locations are measured for one secondary particle, and the average value is obtained. Here, the thickness of each layer is an arbitrary point from the innermost edge of the layer in the cross section of the secondary particle, and is the length between two points where the length to the outermost edge of the layer is the shortest. .

  By dividing the outer diameter of these central parts, the thickness of each layer, and the thickness of the outer shell part by the particle diameter of the secondary particles constituting the composite hydroxide, 1 low density layer particle size ratio, first high density particle size ratio, second low density particle size ratio, outer shell particle size ratio, and external high density layer particle size ratio and external low density layer particle size ratio Ask for each. The same measurement is performed on 10 or more composite hydroxides, and the average value thereof is calculated, whereby the central part particle size ratio, the first low density layer particle size ratio, the first high value in the entire sample are calculated. The density particle size ratio, the second low density particle size ratio, the outer shell particle size ratio, and the external high density layer particle size ratio and the external low density layer particle size ratio are finally determined.

(1-5) Primary particles In the composite hydroxide of the present invention, the fine primary particles that are constituent elements of the central portion and the low-density layer preferably have an average particle diameter of 0.01 μm to 0.3 μm. More preferably, it is 0.1 μm to 0.3 μm. Here, when 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 obtained satisfactorily. 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 step in the low temperature region in the firing step for producing the positive electrode active material, and the central portion In addition, since the difference in volume shrinkage between the low density layer, the high density layer and the outer shell portion is small, a sufficiently large void portion is not formed inside the secondary particles of the positive electrode active material, or the positive electrode active material In the secondary particles of the substance, there is a case where a sufficiently large communication hole that communicates the void portion and the outside of the secondary particle is not formed.

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

  On the other hand, the plate-like primary particles forming the central part, the high density layer, and the outer shell part of the secondary particles constituting the composite hydroxide preferably have an average particle diameter of 0.3 μm to 3 μm, and 0.4 μm More preferably, it is -1.5 micrometers, and it is further more preferable that it is 0.4 micrometer-1.0 micrometer. When the average particle size of the plate-like single particles is less than 0.3 μm, the volume shrinkage of the plate-like primary particles also occurs in the low temperature region in the firing step for producing the positive electrode active material. Since the difference in volume shrinkage with the density layer becomes small, a sufficient number of voids cannot be obtained inside the positive electrode active material, or formation of communication holes that communicate the voids with the outside of the secondary particles In some cases, a sufficiently large gap portion that leads to is not formed. On the other hand, when the average particle size of the plate-like primary particles is larger than 3 μm, it is necessary to perform firing at a higher temperature in order to increase the crystallinity of the positive electrode active material in the firing step when producing the positive electrode active material. Sintering between the secondary particles constituting the hydroxide proceeds, and it becomes difficult to set the average particle size and particle size distribution of the positive electrode active material within a predetermined range.

  The difference in average particle size between the fine primary particles and the plate-like primary particles is preferably 0.1 μm or more, and more preferably 0.2 μm or more. In addition, even when the fine primary particles have another structure, for example, a structure closer to a plate shape than a needle shape, the difference in average particle size between the fine primary particles and the plate-like primary particles is preferably 0.2 μm or more, More preferably, it is 0.3 μm or more.

  In addition, the average particle diameter of the fine primary particles and the plate-like primary particles is determined by embedding the composite hydroxide in a resin or the like and making it possible to observe the cross section by cross section polisher processing. Observation can be performed using an SEM such as SEM, and can be obtained as follows. Specifically, first, the maximum outer diameter (major axis diameter) of 10 or more fine primary particles or plate-like primary particles existing in the cross section of the secondary particles constituting the composite oxide is measured, and the average value is calculated. This value is determined as the particle size of the fine primary particles or plate-like primary particles in the secondary particles. Next, the particle diameters of fine primary particles and plate-like primary particles are similarly determined for 10 or more secondary particles. Finally, by determining the average particle diameter obtained for these secondary particles, the average particle diameter of the fine primary particles or plate-like primary particles of the entire composite hydroxide containing these secondary particles is determined.

(1-6) Composition of transition metal-containing composite hydroxide Since the composite hydroxide of the present invention is characterized by the particle structure of its secondary particles, it relates to the composite hydroxide to which the present invention is applied. Although the composition thereof is not limited, the present invention is not limited to 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, It is suitably applied to a composite hydroxide represented by one or more additive elements selected from Nb, Mo, Hf, Ta, and W. By using the composite hydroxide having such a composition as a precursor, a positive electrode active material represented by the composition of the general formula (B) that can realize higher battery performance can be easily obtained.

  In the composite hydroxide having such a composition, the additive element (M) is crystallized together with transition metals (nickel, cobalt, and manganese) by a crystallization reaction, and is 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). In addition, in the mixing step in producing the positive electrode active material, it is possible to mix a compound containing the additive element (M) together with the lithium compound in the composite hydroxide. Moreover, you may use these methods together. Regardless of which method is used, it is necessary to adjust the content so that the composite hydroxide finally has a desired composition including the composition represented by the general formula (A).

  In the composite hydroxide represented by the general formula (A), the composition range of nickel, manganese, cobalt, and the additive element M constituting the composite hydroxide and the critical significance thereof are represented by the general formula (B). The same as the positive electrode active material. For this reason, description of these matters is omitted here.

2. Method for producing transition metal composite hydroxide (2-1) Supply aqueous solution In the method for producing composite hydroxide of the present invention, at least a transition metal, preferably nickel, nickel and manganese, or nickel and manganese in the reaction vessel. And a raw material aqueous solution containing cobalt and an aqueous solution containing an ammonium ion supplier to form a reaction aqueous solution, and by adjusting the pH value of the reaction aqueous solution to a predetermined range with a pH adjuster, A composite hydroxide is obtained.

a) Raw Material Aqueous Solution In the present invention, the ratio of metal elements contained in the raw material aqueous solution is substantially the composition of the composite hydroxide obtained. For this reason, it is necessary for the raw material aqueous solution to appropriately adjust the content of each metal component according to the composition of the target composite hydroxide. For example, when a composite hydroxide having a composition represented by the general formula (A) is to be obtained, the ratio of metal elements in the raw material aqueous solution is set to Ni: Mn: Co: M = x: y: z. ; T (where 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, as described above, when the additive element M is introduced in a separate process, the additive element M is not included in the raw material aqueous solution. Further, in the nucleation step and the particle growth step, it is possible to change whether or not the additive element M is added or the content ratio of the transition metal and the additive element M.

  The transition metal compound for preparing the raw material aqueous solution is not particularly limited, but from the viewpoint of easy handling, it is preferable to use water-soluble nitrates, sulfates, hydrochlorides, etc. From the viewpoint of preventing mixing of components, it is particularly preferable to use 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) in the composite hydroxide. When contained, the compound for supplying the additive element M is preferably a water-soluble compound, for example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, Vanadium 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 suitably used.

  The concentration of the raw material aqueous solution is determined based on the total amount of the metal compound, but is preferably 1 mol / L to 2.6 mol / L, more preferably 1.5 mol / L to 2.2 mol / L. When the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized material per reaction tank volume decreases, and thus productivity decreases. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol / L, it exceeds the saturation concentration at room temperature, and thus the crystals of the respective metal compounds may reprecipitate and clog piping and the like.

  The metal compound is not necessarily supplied to the reaction vessel as a raw material aqueous solution. For example, when a crystallization reaction is performed using a metal compound that reacts when mixed to produce a compound other than the target compound, the total concentration of all the metal compound aqueous solutions is within the above range. You may prepare metal compound aqueous solution separately, and you may supply in a reaction tank in predetermined ratio as aqueous solution of each metal compound.

  The supply amount of the raw material aqueous solution 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. When the concentration of the product is less than 30 g / L, the primary particles may be insufficiently aggregated. On the other hand, if it exceeds 200 g / L, the reaction aqueous solution is not sufficiently stirred in the reaction tank, and the aggregation conditions become non-uniform, which may cause uneven grain growth.

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. . Although the alkali metal hydroxide can be directly added to the reaction aqueous solution in a solid state, it is preferably added as an aqueous solution from the viewpoint of ease of pH control. In this case, the concentration of the alkali metal hydroxide aqueous 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 alkali metal aqueous solution in such a range, the amount of solvent supplied to the reaction system, that is, the amount of water is suppressed, and the local pH value is increased by the addition position in the reaction tank. Therefore, it is possible to efficiently obtain composite transition metal composite hydroxide particles having a narrow particle size distribution.

  The method for 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 may be supplied by a pump capable of controlling the flow rate such as a metering pump while sufficiently stirring.

c) Aqueous solution containing ammonium ion donor The aqueous solution containing an ammonium ion donor is not particularly limited as long as ammonium ions can be supplied in the reaction aqueous solution. For example, aqueous ammonia, ammonium sulfate, ammonium chloride, An aqueous solution of ammonium carbonate, ammonium fluoride or the like can be used.

  When ammonia water is used as the ammonium ion supplier, the concentration is preferably 20% by mass to 30% by mass, more preferably 22% by mass to 28% by mass. By setting the concentration of the ammonia water in such a range, loss of ammonia from the reaction tank due to volatilization or the like can be suppressed to the minimum, so that production efficiency can be improved.

  In addition, the supply method of the aqueous solution containing an ammonium ion supply body can also be supplied by a pump capable of controlling the flow rate, similarly to the alkaline aqueous solution.

(2-2) Crystallization Reaction In the method for producing a composite hydroxide of the present invention, the crystallization reaction is performed in two steps: a nucleation step in which nucleation is mainly performed and a particle growth step in which particle growth is mainly performed. In the particle growth process, the supply of the raw material aqueous solution is continued while the reaction atmosphere, that is, the atmosphere in the reaction aqueous solution is changed to a non-oxidizing atmosphere. It is characterized by switching appropriately to an oxidizing atmosphere. In particular, at the time of switching the atmosphere, an atmosphere gas, that is, an oxidizing gas, an inert gas, or a mixed gas thereof is sent into the reaction aqueous solution, and these gases and the reaction aqueous solution are brought into direct contact so that the reaction atmosphere can be quickly changed. By switching, it is possible to efficiently obtain a composite hydroxide having a particle structure in which the above-described low-density layer and high-density layer are laminated, an average particle size, and a particle size distribution.

[Nucleation process]
In the nucleation step, first, a transition metal compound as a raw material for the composite hydroxide is dissolved in water to prepare a raw material aqueous solution. At the same time, an aqueous solution containing an alkaline aqueous solution and an ammonium ion supplier is supplied into the reaction vessel. This is mixed with a raw material aqueous solution to prepare a reaction aqueous solution having a pH value of 12.0 to 14.0 and an ammonium ion concentration of 3 g / L to 25 g / L measured on the basis of a liquid temperature of 25 ° C. Here, the pH value of the reaction aqueous solution can be measured by a pH meter, and the ammonium ion concentration can be measured by an ion meter.

  Next, the aqueous raw material solution is supplied while stirring the aqueous reaction solution. Thereby, the reaction aqueous solution in a nucleation process is formed in a reaction tank. Since the pH value of the reaction aqueous solution is in the above range, in the nucleation step, nucleation occurs preferentially with almost no nuclei growing. In the nucleation step, the pH value of the reaction aqueous solution and the ammonium ion concentration change with the generation of the nuclei, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied in a timely manner. The pH is controlled so that the concentration of ammonium ions is maintained in the range of 3 g / L to 25 g / L in the range of pH 12.0 to 14.0.

  Further, during the nucleation step, an inert gas is circulated through the reaction aqueous solution in the reaction tank to adjust the reaction atmosphere to a non-oxidizing atmosphere having an oxygen concentration lower than 5% by volume. Here, the supply method of the inert gas to the reaction aqueous solution in the reaction tank may be either the supply to the space in the reaction tank in contact with the reaction aqueous solution or the method of supplying directly into the reaction aqueous solution using an air diffuser or the like. This method is also possible. However, it is sufficient to adjust the reaction atmosphere in the nucleation step by supplying an inert gas into the reaction vessel.

  In the nucleation step, by supplying an aqueous solution containing an aqueous raw material solution, an alkaline aqueous solution, and an ammonium ion supplier to the reaction aqueous solution, the nucleation reaction is continuously continued, and a predetermined amount of nuclei are contained in the reaction aqueous solution. At the time of generation, the nucleation process is terminated.

  At this time, the amount of nuclei generated 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 nucleation in the nucleation step is not particularly limited, but in order to obtain a composite hydroxide with 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 preferable to set it as 0.1 atomic%-2 atomic% with respect to the whole quantity of an element, and it is more preferable to set it as 0.1 atomic%-1.5 atomic%. The reaction time in the nucleation step is usually about 0.2 to 5 minutes.

[Particle growth process]
After completion of the nucleation step, the pH value of the aqueous solution for nucleation in the reaction vessel is adjusted to 10.5 to 12.0 on the basis of the liquid temperature of 25 ° C. to form a reaction aqueous solution in the particle growth step. The pH value can be adjusted by stopping the supply of the alkaline aqueous solution. However, in order to obtain composite hydroxide particles with a narrow particle size distribution, the pH value is adjusted after stopping the supply of all the aqueous solutions. It is preferable to do. Specifically, after stopping the supply of all 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.

  Next, the supply of the raw material aqueous solution is resumed while stirring the reaction aqueous solution. At this time, since the pH value of the reaction aqueous solution is in the above range, almost no new nuclei are generated, the growth of the nuclei proceeds, and the secondary particles of the transition metal composite hydroxide reach a predetermined particle size. Continue the crystallization reaction. In the particle growth process, the pH value and ammonium ion concentration of the reaction aqueous solution change as the particle grows. Therefore, an alkaline aqueous solution and an aqueous ammonia solution are supplied in a timely manner, and the pH value and ammonium ion concentration are maintained within the above ranges. is necessary. In addition, the whole reaction time in a particle growth process is about 1 hour-about 6 hours normally.

  In particular, in the method for producing a composite hydroxide of the present invention, while maintaining the inert atmosphere in the nucleation step, in the first stage of the particle growth step, the central part of the secondary particles constituting the composite hydroxide is determined. Form. Next, after the completion of the first stage of the particle growth process, by continuously supplying the oxidizing gas into the reaction aqueous solution while continuing the supply of the raw material aqueous solution, the reaction atmosphere is changed from the non-oxidizing atmosphere to the oxygen concentration. Switch to an oxidizing atmosphere higher than 5% by volume. In the second stage of the particle growth process, a first low-density layer (first low-density layer) is formed around the center of the secondary particles constituting the composite hydroxide. Subsequently, after the completion of the second stage of the particle growth process, by supplying the inert gas directly into the reaction aqueous solution while continuing the supply of the raw material aqueous solution, non-oxidation with an oxygen concentration of 5% by volume or less from the oxidizing atmosphere is performed. Switch back to sexual atmosphere. In the third stage of the grain growth process, the first high-density layer (first high-density layer) is formed so as to cover the first low-density layer. Next, after completion of the third stage of the particle growth process, by supplying the oxidizing gas directly into the reaction aqueous solution while continuing the supply of the raw material aqueous solution, the oxygen concentration is higher than 5% by volume from the non-oxidizing atmosphere. Switch back to sexual atmosphere. In the fourth stage of the grain growth process, a second low-density layer (second low-density layer) is formed so as to cover the first high-density layer. Further, after the completion of the fourth stage of the particle growth process, non-oxidation with an oxygen concentration of 5% by volume or less from an oxidizing atmosphere is performed by supplying an inert gas directly into the reaction aqueous solution while continuing to supply the raw material aqueous solution. Switch back to sexual atmosphere. In the fifth stage (outer shell forming stage) of the grain growth process, the outer shell is formed so as to cover the second low-density layer.

  By controlling the atmosphere switching as described above, a laminated structure in which one high-density layer is sandwiched between two low-density layers between the center part of the secondary particles constituting the composite hydroxide and the outer shell part, That is, the central portion, the first low density layer, the first high density layer, the second low density layer, and the outer shell portion are arranged in order from the inside of the secondary particles constituting the composite hydroxide. A laminated structure is formed.

  In the particle growth step, an inert gas and / or an oxidizing gas is circulated in the reaction aqueous solution in the reaction vessel, and the reaction atmosphere is changed from an oxidizing atmosphere having an oxygen concentration higher than 5% by volume to an oxygen concentration of 5% by volume or less. It is preferable to quickly switch to a non-oxidizing atmosphere or from a non-oxidizing atmosphere to an oxidizing atmosphere. The method of supplying the inert gas and / or oxidizing gas to the reaction aqueous solution in the reaction tank can also be supplied to the space in the reaction tank in contact with the reaction aqueous solution. It is preferable to adopt a method of supplying directly. Thereby, the switching time of the atmosphere can be shortened, and even when the thickness of the high density layer, the low density layer, or the outer shell portion is designed to be small, the reaction time for that can be easily controlled.

  The present invention is characterized in that the atmosphere is switched at least four times as described above during the crystallization reaction. In the same manner, before the formation of the outer shell portion in the outer shell portion forming stage, the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere and from the non-oxidizing atmosphere to the oxidizing atmosphere. The control can be repeated. When such control of atmosphere switching is repeated twice, two high-density layers become three low-density layers between the central part and outer shell part of the secondary particles constituting the composite hydroxide. The sandwiched structure, that is, the central part, the first low density layer, the first high density layer, the second low density layer, and the external high density in order from the inside of the secondary particles constituting the composite hydroxide. A laminated structure is formed in which a layer, an external low-density layer, and an outer shell are arranged.

  In such a method for producing a composite hydroxide, metal ions in the reaction aqueous solution are precipitated as solid nuclei or primary particles in the nucleation step and the particle growth step. For this reason, the ratio of the liquid component to the amount of metal ions in the reaction aqueous solution increases. As the reaction proceeds, the concentration of metal ions in the aqueous reaction solution decreases, so that the growth of the composite hydroxide may stagnate particularly 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 out of the reaction tank during the particle growth step after the nucleation step. It is preferable to do. Specifically, the supply of the raw material aqueous solution, the alkaline aqueous solution, and the aqueous solution containing the ammonium ion supplier to the reaction vessel and the stirring of the aqueous reaction solution are temporarily stopped, and the solid component in the reaction aqueous solution, that is, the composite hydroxide is allowed to settle. Thus, it is preferable to discharge only the supernatant of the reaction aqueous solution to the outside of the reaction tank. By such an operation, the metal ion concentration in the reaction aqueous solution can be maintained, so that the particle growth is prevented from stagnation and the particle size distribution of the resulting composite hydroxide can be controlled within a suitable range. In addition, the density as a powder can be improved.

[Particle size control of composite hydroxide]
The particle size of the secondary particles constituting the composite hydroxide can be controlled by the time for performing the nucleation step and the particle growth step, the pH value of the reaction aqueous solution in each step, the supply amount of the raw material aqueous solution, and the like. For example, when the nucleation step is performed at a high pH value, when the time for performing the nucleation step is increased, or when the metal concentration of the raw material aqueous solution is increased, the amount of nucleation generated in the nucleation step increases. Thus, a composite hydroxide having a relatively small particle size can be obtained after the particle growth step. On the other hand, a composite hydroxide having a large particle size can be obtained by suppressing the amount of nuclei generated in the nucleation step, or by sufficiently increasing the time for performing the particle growth step.

[Another Embodiment of Crystallization Reaction]
In the method for producing a composite hydroxide of the present invention, a component adjusting aqueous solution adjusted to a pH value and an ammonium ion concentration suitable for the particle growth step is prepared separately from the reaction aqueous solution. The particle growth step may be carried out by adding and mixing a reaction aqueous solution after the production step, preferably a solution obtained by removing a part of the liquid component from the reaction aqueous solution after the nucleation step, and using this as the reaction aqueous solution.

  In this case, since the nucleation step and the particle growth step can be more reliably separated, 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 within the optimum range from the start of the particle growth step, the particle size distribution of the resulting composite hydroxide can be made narrower.

(2-3) pH value In the method for producing a composite hydroxide of the present invention, when the nucleation step is performed, the pH value based on a liquid temperature of 25 ° C. is in the range of 12.0 to 14.0. When performing a process, it is necessary to control in the range of 10.5 to 12.0. In any 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 amount of variation in pH value is large, the amount of nucleation in the nucleation step and the degree of particle growth in the particle growth step are not constant, making it difficult to obtain composite hydroxide particles having a narrow particle size distribution. .

a) pH value of the nucleation step In the nucleation step, the pH value of the reaction aqueous solution is 12.0 to 14.0, preferably 12.3 to 13.5, more preferably 12 based on the liquid temperature of 25 ° C. It is necessary to control within a range greater than .5 and less than 13.3. Thereby, it is possible to suppress the growth of nuclei in the reaction aqueous solution and give priority to only the nucleation, and the nuclei generated in this step can have a uniform size and a narrow particle size distribution. Further, by making the pH value higher than 12.5, it is possible to further narrow the particle size distribution in the next particle growth step as a result of further giving priority to nucleation. When the pH value is less than 12.0, the growth of nuclei proceeds with the nucleation, so that the resulting composite hydroxide has a non-uniform particle size and a wide particle size distribution. On the other hand, if the pH value is higher than 14.0, the generated nuclei become too fine, which causes a problem that the aqueous reaction solution gels.

b) pH value of the particle growth step In the particle growth step, the pH value of the reaction aqueous solution is 10.5 to 12.0, preferably 11.0 to 12.0, more preferably 11 based on the liquid temperature of 25 ° C. It is necessary to control within the range of .5 to 12.0. Thereby, generation of new nuclei is suppressed, it is possible to give priority to particle growth, and the resulting composite hydroxide can be made homogeneous and have a narrow particle size distribution. 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 crystallization reaction is slowed but also the amount of metal ions remaining in the reaction aqueous solution increases. And productivity is reduced. On the other hand, when the pH value is higher than 12.0, the amount of nucleation during the particle growth step increases, the particle size of the resulting composite hydroxide becomes non-uniform, and the particle size distribution becomes wide.

  When the pH value of the reaction aqueous solution at 25 ° C. is 12.0, it is a boundary condition between nucleation and nucleation, so the nucleation process or particle growth depends on the presence or absence of nuclei present in the reaction aqueous solution. Any condition of the process can be used. 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 particle growth step is 12.0, a large amount of nuclei that become reactants in the reaction aqueous solution. Therefore, particle growth occurs preferentially, and composite hydroxide particles having a narrow particle size distribution can be obtained. On the other hand, when the pH value of the nucleation step is 12.0, there is no nucleus that grows in the reaction aqueous solution, so that nucleation occurs preferentially, and the pH value of the particle growth step is made smaller than 12.0. The growth of the generated nuclei proceeds.

  In any case, the pH value of the particle growth process may be controlled at a value lower than the pH value of the nucleation process. In order to more clearly separate nucleation and particle growth, the pH value of the particle growth process is used. Is preferably lower by 0.5 or more than the pH value of the nucleation step, more preferably by 1.0 or more.

(2-4) Reaction Atmosphere In the method for producing a composite hydroxide of the present invention, control of the reaction atmosphere is important as well as control of the pH value in each step. That is, by controlling the pH value in each step and further adjusting the reaction atmosphere up to the first stage of the nucleation step and the particle growth step to a non-oxidizing atmosphere, nuclei are generated, and thereafter As a result of grain growth, a central portion in which the plate-like primary particles are aggregated is formed.

  In the present invention, fine primary particles can be obtained by quickly switching the reaction atmosphere to the oxidizing atmosphere by supplying the oxidizing gas directly into the reaction aqueous solution while continuing the supply of the raw material aqueous solution in the middle of the particle growth process. By switching to the formation of a layer formed by agglomeration, and by quickly switching from an oxidizing atmosphere to a non-oxidizing atmosphere, the formation of a layer formed by agglomeration of plate-like primary particles can be switched to a low density. A structure in which a layer and a high-density layer are stacked can be obtained.

  In such control of the reaction atmosphere, the fine primary particles contained in the low-density layer are in the shape of needles, but can take shapes such as a rectangular parallelepiped shape, an elliptical shape, and a ridged surface shape depending on the composition of the composite hydroxide. The same applies to the plate-like primary particles constituting the high-density layer. Therefore, in the method for producing a composite hydroxide of the present invention, it is necessary to appropriately control the reaction atmosphere at each stage according to the composition of the target composite hydroxide.

a) Non-oxidizing atmosphere In the production method of the present invention, the reaction atmosphere in the step of forming the central portion, the high-density layer and the outer shell portion composed of plate-like primary particles is controlled to a non-oxidizing atmosphere. Specifically, an inert gas such as argon or nitrogen, oxygen, or the like so that the oxygen concentration in the reaction atmosphere is 5% by volume or less, preferably 2% by volume or less, more preferably 1% by volume or less. A mixed gas of an oxidizing gas and an inert gas can be used. As a result, it is possible to grow the nuclei generated in the nucleation step to a certain range while sufficiently reducing the oxygen concentration in the reaction atmosphere to suppress unnecessary oxidation, so that a high density layer of composite hydroxide can be formed. The plate-like primary particles having an average particle size in the range of 0.3 μm to 3 μm and a narrow particle size distribution can be aggregated.

b) Oxidizing atmosphere On the other hand, in the step of forming the low density layer, the reaction atmosphere is controlled to an oxidizing atmosphere. Specifically, the oxygen concentration in the reaction atmosphere is controlled so as to exceed 5% by volume, preferably 10% by volume or more, more preferably the atmospheric air (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere in such a range, the oxygen concentration in the reaction atmosphere is sufficiently increased to suppress the growth of primary particles, and the average particle size of the fine primary particles is 0.01 μm to 0 μm. Therefore, a low-density layer having a sufficient density difference from the high-density layer is formed.

  The upper limit of the oxygen concentration in the oxidizing atmosphere is not particularly limited, but if the oxygen concentration is excessively high, the average particle size of the primary particles becomes less than 0.01 μm, and the low-density layer has a sufficient thickness. It may not be possible. For this reason, the oxygen concentration in the oxidizing atmosphere is preferably 30% by volume or less. In addition, in order to clarify the difference in heat shrinkage due to the difference in size between the fine primary particles constituting the low-density layer and the plate-like primary particles constituting the high-density layer and the outer shell, the atmosphere is switched. The difference in oxygen concentration before and after is preferably 3% by volume or more, preferably 10% by volume or more.

c) Timing of Atmosphere Control Atmosphere control in the particle growth process needs to be performed at an appropriate timing so that a composite hydroxide having a target particle structure is formed.

  In the method for producing the composite hydroxide of the present invention, when the atmospheric gas is directly supplied to the reaction aqueous solution, the oxygen dissolved amount in the reaction aqueous solution, that is, the reaction aqueous solution as the reaction field, is the oxygen concentration in the reaction tank. Change without delay to change. Therefore, the atmosphere switching time can be confirmed by measuring the oxygen concentration in the reaction vessel. On the other hand, when the atmospheric gas is supplied to the space in contact with the reaction aqueous solution in the reaction tank, a time lag occurs between the change in the dissolved oxygen amount in the reaction aqueous solution and the change in the oxygen concentration in the reaction tank. Until the change in oxygen concentration in the reactor becomes stable, the dissolved oxygen amount in the reaction solution cannot be immediately confirmed as the correct value. Similarly, it is confirmed by the measured value after the oxygen concentration in the reaction vessel has stabilized. Is possible. As described above, in any case, the switching time of the atmosphere obtained based on the oxygen concentration in the reaction vessel can be set as the switching time of the dissolved oxygen amount in the reaction aqueous solution as the reaction field. The temporal control of the reaction atmosphere can be appropriately performed based on the oxygen concentration in the tank.

  In the present invention, the time required for switching the atmosphere is about 1% to 2% with respect to the whole particle growth process. This time is also common when switching from the non-oxidizing atmosphere to the oxidizing atmosphere, or from the oxidizing atmosphere to the non-oxidizing atmosphere. Therefore, it is possible to strictly manage the atmosphere switching time alone, but it is usually sufficient to manage it by including it in the time of the non-oxidizing atmosphere or oxidizing atmosphere after the atmosphere switching.

  In the present invention, the crystallization reaction time of the first stage in the non-oxidizing atmosphere of the particle growth process is preferably in the range of 0.5% to 15%, more preferably 3% with respect to the entire particle growth process time. % To 13%, and more preferably 5% to 10%. A reaction with this range of reaction times in a non-oxidizing atmosphere results in the formation of an appropriately sized center. After the elapse of a predetermined time, the introduction of the oxidizing gas into the reaction aqueous solution is started, the non-oxidizing atmosphere is switched to the oxidizing atmosphere, and the first stage is shifted to the second stage.

  The crystallization reaction time in the second stage in the oxidizing atmosphere after the start of switching from the non-oxidizing atmosphere in the first stage (including the switching time from the non-oxidizing atmosphere to the oxidizing atmosphere) is the particle growth process time. The total content is preferably 4% to 22%, more preferably 4% to 20%, and still more preferably 5% to 18%. By the reaction in this range of reaction time in an oxidizing atmosphere, a first low-density layer that can form an appropriately sized void in the positive electrode active material is formed. After a predetermined time has elapsed, the introduction of an inert gas or a mixed gas of an oxidizing gas and an inert gas into the reaction aqueous solution is started to switch from an oxidizing atmosphere to a non-oxidizing atmosphere. From the second stage to the third stage Migrate to

  The crystallization reaction time (including the switching time from the oxidizing atmosphere to the non-oxidizing atmosphere) in the third stage in the non-oxidizing atmosphere after the start of switching from the oxidizing atmosphere in the second stage is the particle growth process time. The total content is preferably in the range of 10% to 40%, more preferably in the range of 12% to 35%, and still more preferably in the range of 14% to 30%. The reaction in this range of reaction time in a non-oxidizing atmosphere enables the positive electrode active material to form a void portion having a communication hole capable of communicating with the outside on the inside thereof. A high density layer is formed. After the elapse of a predetermined time, the introduction of the oxidizing gas into the reaction aqueous solution is started, the non-oxidizing atmosphere is switched to the oxidizing atmosphere, and the third stage is shifted to the fourth stage.

  The crystallization reaction time in the fourth stage in the second oxidizing atmosphere after the start of switching from the non-oxidizing atmosphere in the third stage is preferably 15% to 40% with respect to the entire particle growth process time. More preferably in the range of 20% to 38%, still more preferably in the range of 25% to 35%. By the reaction in this range of reaction time in an oxidizing atmosphere, a second low-density layer that can form a void having an appropriate size in the positive electrode active material is formed. After the elapse of a predetermined time, introduction of an inert gas or a mixed gas of an oxidizing gas and an inert gas into the reaction aqueous solution is started to switch from an oxidizing atmosphere to a non-oxidizing atmosphere. Move to (outer shell formation stage).

  Finally, the crystallization reaction time until the end of the crystallization reaction in the fifth stage (outer shell formation stage) in the second non-oxidizing atmosphere after the start of the switching from the fourth stage oxidizing atmosphere is the particle size. The total growth process time is preferably in the range of 10% to 45%, more preferably in the range of 12% to 40%, and still more preferably in the range of 15% to 35%. The outer shell portion that enables the positive electrode active material to form a void portion with a communication hole that can communicate with the outside, by reaction within this range of reaction time in a non-oxidizing atmosphere. Is formed.

  That is, by sequentially switching the reaction atmosphere at the timing as described above, it is possible to control the size of the central portion and the thicknesses of the high-density layer, the low-density layer, and the outer shell portion within a suitable range.

  Similarly, when the external high-density layer and the external low-density layer are formed before the outer shell forming step, the fifth in the non-oxidizing atmosphere after the start of switching from the oxidizing atmosphere in the fourth stage is similarly performed. The crystallization reaction time (including the switching time from the oxidizing atmosphere to the non-oxidizing atmosphere) at the stage (outer high-density layer forming stage) is preferably 10% to 40% with respect to the entire particle growth process time. More preferably, the range is 12% to 35%, and further preferably the range is 14% to 30%. In addition, the crystallization reaction time in the sixth stage (external low-density layer forming stage) in the third oxidizing atmosphere after the start of switching from the non-oxidizing atmosphere in the fifth stage is the entire time of the particle growth process. On the other hand, it is preferably in the range of 15% to 40%, more preferably in the range of 20% to 38%, and still more preferably in the range of 25% to 35%. After the sixth stage, the introduction of an inert gas or a mixed gas of an oxidizing gas and an inert gas into the reaction aqueous solution is started to switch from the oxidizing atmosphere to the non-oxidizing atmosphere, and the seventh stage (outer shell) Part formation stage).

  If the reaction time in each stage is out of these ranges, the secondary particles constituting the positive electrode active material may not form a plurality of sufficiently large voids inside the main part, or may be There is no communication hole between them, the center part and the outer agglomerated layer are not connected or integrated, so that they are not electrically connected to each other, or the outer shell part is peeled off and becomes fine powder. In some cases, a positive electrode active material composed of secondary particles having a desired structure may not be formed.

d) Switching method The switching of the reaction atmosphere during the conventional crystallization process is performed by circulating an atmospheric gas in the reaction tank, more specifically, in a space in contact with the reaction aqueous solution in the reaction tank, or by an inner diameter of 1 mm in the reaction aqueous solution. In general, it is carried out by inserting a conduit of about 50 mm and bubbling the reaction aqueous solution with an atmospheric gas. In this case, it is difficult to switch the atmosphere in a short time with respect to the amount of oxygen dissolved in the reaction aqueous solution as in the method for producing a composite hydroxide of the present invention. In this case, during the switching from the non-oxidizing atmosphere to the oxidizing atmosphere in the particle growth process, it is necessary to stop the supply of the raw material aqueous solution. At this time, if the supply of the raw material aqueous solution is not stopped, a gentle density gradient is formed inside the composite hydroxide, and it is considered that the low density layer cannot be made sufficiently thick.

  In contrast, in the method for producing a composite hydroxide of the present invention, the atmosphere gas is contained in the reaction aqueous solution while continuing the supply of the raw material aqueous solution during the switching from the non-oxidizing atmosphere to the oxidizing atmosphere in the particle growth step. It is characterized in that the atmosphere is switched by supplying directly. Therefore, it is not necessary to stop the supply of the raw material aqueous solution when switching the reaction atmosphere, so that the production efficiency can be improved.

  Note that the time required for switching the reaction atmosphere by directly supplying the atmospheric gas into the reaction aqueous solution, that is, the time for switching the atmosphere is limited as long as the transition metal composite hydroxide particles having the above structure can be obtained. However, from the viewpoint of facilitating the control of the particle structure, within the reaction time of the atmosphere to be switched and within the range of 0.4% to 2% with respect to the entire particle growth process time Is preferable, and the range of 0.4% to 1% is more preferable.

  Here, the means for supplying the atmospheric gas into the aqueous reaction solution needs to be means capable of directly supplying the atmospheric gas into the aqueous reaction solution. As such means, for example, an air diffuser can be used. The diffuser tube is composed of a conduit having a large number of fine holes on the surface, and can release a large number of fine bubbles in the liquid. Therefore, the contact area between the reaction aqueous solution and the bubbles is large, and it depends on the supply amount of atmospheric gas. Thus, the switching time can be easily controlled.

  As such an air diffuser, it is preferable to use a ceramic tube excellent in chemical resistance under a high pH environment. In addition, the smaller the hole diameter of the air diffusing tube, the more fine bubbles can be discharged, so that the reaction atmosphere can be switched in a short time. In the present invention, it is preferable to use an air diffuser having a pore diameter of 100 μm or less, and more preferably an air diffuser having a diameter of 50 μm or less.

  The method for supplying the atmospheric gas is not particularly limited as long as it generates fine bubbles and increases the contact area between the reaction aqueous solution and the bubbles. Similarly, those that can generate bubbles from the holes and finely pulverize and disperse the bubbles with a stirring blade or the like can be suitably used.

(2-5) Ammonium ion concentration The ammonium ion concentration in the aqueous reaction solution is preferably maintained at a constant value within a range of 3 g / L to 25 g / L, more preferably 5 g / L to 20 g / L. Since ammonium ions function as a complexing agent in the reaction aqueous solution, if the ammonium ion concentration is less than 3 g / L, the solubility of the metal ions cannot be kept constant, and the reaction aqueous solution is easily gelled. Further, it becomes difficult to obtain transition metal composite hydroxide particles having a uniform particle size. On the other hand, when the ammonium ion concentration exceeds 25 g / L, the solubility of metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, causing a composition shift of the composite hydroxide.

  If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of metal ions fluctuates and a uniform composite hydroxide cannot be formed. For this reason, it is preferable to control the fluctuation amount of the ammonium ion concentration within a certain range between the nucleation step and the particle growth step, and specifically, to control the fluctuation amount within 5 g / L from the set value. Is preferred.

(2-6) Reaction temperature The temperature of the reaction aqueous solution, that is, the reaction temperature of the crystallization reaction, is preferably 20 ° C. or higher, more preferably 20 ° C. to 60 ° C. throughout the nucleation step and the particle growth step. It is necessary to control. When the reaction temperature is less than 20 ° C., the solubility of the reaction aqueous solution becomes low, so that nucleation is likely to occur, and it becomes difficult to control the average particle size and particle size distribution of the resulting composite hydroxide. The upper limit of the reaction temperature is not particularly limited, but when it exceeds 60 ° C., the volatilization of ammonia is promoted, and an ammonium ion supplier that is supplied to control ammonium ions in the aqueous reaction solution within a certain range. The production cost increases because the amount of the aqueous solution containing is increased.

(2-7) Coating step In the method for producing a transition metal composite hydroxide of the present invention, a compound in which the additive element M is uniformly dispersed inside the particles by adding a compound containing the additive element M in the raw material aqueous solution. A hydroxide can be obtained. However, when the effect of adding the additive element M is to be obtained with a smaller addition amount, the surface of the secondary particles constituting the composite hydroxide is made of a compound containing the additive element M after the particle growth step. It is preferable to perform a coating step for coating.

  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, the composite hydroxide is slurried and the pH value is controlled within a predetermined range, and then an aqueous solution for coating in which the compound containing the additive element M is dissolved is added, and the secondary particles constituting the composite hydroxide are added. By precipitating the 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 slurry of the composite hydroxide. Moreover, you may coat | cover by spraying and drying the aqueous solution or slurry which melt | dissolved the compound containing the addition element M, without making a composite hydroxide into a slurry. Further, a method in which a slurry in which the compound hydroxide and the compound containing the additive element M are suspended is spray-dried, or a method in which the compound hydroxide and the compound containing the additive element M are mixed by a solid phase method. Can also be coated.

  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. Moreover, you may perform a coating | covering process with respect to the heat-processed particle after heat-processing a composite hydroxide in the heat processing process at the time of manufacture of a positive electrode active material.

(2-8) Production apparatus The crystallizer for producing the composite hydroxide of the present invention, that is, the reaction vessel, is particularly limited as long as the reaction atmosphere can be switched by the above-mentioned diffuser tube. Never happen. In the practice of the present invention, it is particularly preferable to use a batch crystallizer that does not collect the precipitated product until the crystallization reaction is completed. In the case of such a crystallizer, unlike the continuous crystallizer that recovers the product by the overflow method, the growing particles are not recovered at the same time as the overflow liquid. Can be obtained with high accuracy. Moreover, since it is necessary for the manufacturing method of the composite hydroxide of this invention to control reaction atmosphere during crystallization reaction appropriately, it is especially preferable to use a closed-type crystallization apparatus.

3. Positive electrode active material for non-aqueous electrolyte secondary battery (3-1) Particle structure of positive electrode active material a) Structure of secondary particle The positive electrode active material of the present invention is a secondary particle formed by aggregating a plurality of primary particles. Consists of In particular, in the positive electrode active material of the present invention, as shown in FIG. 2, the secondary particles (main part) are dispersed in the interior of the plurality of voids, the voids and the secondary particles. It is characterized by including at least one communication hole that communicates with the outside.

  In the positive electrode active material having such a particle structure, only the electrolytic solution is present in the void supported by the main part inside the secondary particle through the communication hole formed on the surface of the secondary particle. In addition, since the conductive auxiliary agent also enters, not only the surface of the main part of the secondary particles but also the surface of the part exposed inside the main part of the secondary particles with respect to the voids and the communication holes are lithium and It becomes a reaction field with the electrolytic solution, and lithium can be desorbed and inserted. Therefore, in the secondary battery using the positive electrode active material having such a structure, the output characteristics can be improved by further reducing the electrode resistance while maintaining the battery capacity and the cycle characteristics.

(Main part)
The main part constituting the basic skeleton of the secondary particles of the positive electrode active material of the present invention is constituted by secondary particles obtained by aggregating a plurality of primary particles, and has a substantially spherical appearance. By firing the composite hydroxide of the present invention, the central portion, the high-density layer, and the outer shell (or even the external high-density layer) constituting the composite hydroxide are substantially integrated by sintering. It is constituted by doing. The main portion includes a plurality of voids on the inner side, in particular, on the outer diameter side thereof, and has at least strength for stably supporting the voids.

(Void)
On the other hand, the void portion is a closed space portion that is stably supported by the main portion inside the main portion. There are a plurality of gaps, and communicate with the outside through the communication holes. The size of the void is arbitrary as long as the shape can be maintained in the secondary particles, but the average pore diameter is preferably in the range of 0.1 μm to 2 μm, more preferably 0.2 μm. It is in the range of ˜1.5 μm, more preferably in the range of 0.2 μm to 1 μm. In addition, although the hole diameter of a space | gap part receives the influence of formation of a communicating hole, it respond | corresponds fundamentally to the thickness of the low density layer in a composite hydroxide. Further, the number of voids is arbitrary depending on the size of the voids, but it is preferable that a plurality of voids exist.

  Note that the average pore size of the voids was determined by embedding the positive electrode active material in a resin, etc., and making the cross-section observable by cross-section polisher processing, etc., and then observing the cross-section using an SEM such as FE-SEM. And can be obtained as follows. Specifically, first, the maximum outer diameter of 10 or more voids present in the cross section of the secondary particles constituting the positive electrode active material is measured, the average value thereof is obtained, and this value is determined in the secondary particles. It is set as the hole diameter of a space | gap part. Next, the pore diameter of the void portion is similarly determined for 10 or more secondary particles. Finally, the average pore diameter of the entire positive electrode active material containing these secondary particles is determined by determining the average of the pore diameters obtained for these secondary particles.

(Communication hole)
The positive electrode active material of the present invention is characterized in that it is provided with a communication hole formed in the main part and communicating between the void part existing inside the main part of the secondary particle and the outside of the secondary particle.

  The communication hole is a substantially cylindrical space portion that communicates the outside of the secondary particles and the inside of the void portion inside the main portion. Regarding the arrangement of the communication holes, one communication hole is connected to the inside of the plurality of voids and communicates with the outside of the secondary particles, and one void is connected to the plurality of communication holes to form the secondary particles. Arrangements communicating with the outside of the apparatus are also included in the present invention.

  The size (average inner diameter) of each communication hole is sufficient if the electrolyte solution and the conductive additive can penetrate into the voids existing inside the main part, but the average diameter is preferably 0.00. It is in the range of 2 μm to 0.7 μm, more preferably in the range of 0.3 μm to 0.6 μm. If the average diameter of the communication holes is smaller than 0.2 μm, there is a possibility that the electrolyte solution and the conductive additive are not sufficiently infiltrated. On the other hand, the upper limit value of the size (average inner diameter) of the communication holes is the average particle size of the secondary particles constituting the positive electrode active material and the physical durability of the main part including the outer shell portion constituting the secondary particles. From the viewpoint, and further, from the viewpoint of coexistence of formation of an appropriately sized void and communication hole by the production method of the present invention, the thickness is about 0.7 μm.

  The average inner diameter of the communication hole is measured by using the SEM image of the cross section of the positive electrode active material, and measuring the width of the communication hole where the cross section can be seen, that is, the inner diameter as the maximum length between any two points. The inner diameter of the communication hole in the next particle. The same measurement is performed on three or more communication holes in the secondary particle, and the average value thereof is set as the average inner diameter of the communication hole in the secondary particle. These measurements are performed on 10 or more positive electrode active materials, and the average value thereof is calculated, whereby the average inner diameter of the communication holes formed in the positive electrode active material in the entire sample is finally determined.

(3-2) Average Particle Size The average particle size of the secondary particles constituting the positive electrode active material of the present invention is 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably 3 μm to 10 μm. If the average particle diameter of the positive electrode active material is in 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 the 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 decreased, and the reaction area of the positive electrode active material is decreased, so that it is difficult to improve output characteristics.

  The average particle diameter of the positive electrode active material means a volume-based average particle diameter (MV) as in the case of the composite hydroxide described above. For example, the volume measured with a laser light diffraction / scattering particle size analyzer It can be obtained from the integrated value.

(3-3) Particle size distribution The value of [(d90-d10) / average particle size] which is an index indicating the spread of the particle size distribution of the positive electrode active material of the present invention is 0.70 or less, preferably 0.60 or less, More preferably, it is 0.55 or less, More preferably, it is 0.45 or less, and the positive electrode active material of this invention is comprised by the powder with a very 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 material has excellent safety, cycle characteristics, and output characteristics.

  On the other hand, when the value of [(d90−d10) / average particle diameter] exceeds 0.70, the ratio 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 with a high proportion of fine particles, the secondary battery is likely to generate heat due to local reaction of fine particles, which not only reduces safety but also reduces fineness. Cycle characteristics are inferior due to selective degradation of the particles. In addition, in a secondary battery using a positive electrode active material with a large proportion of coarse particles, a sufficient reaction area between the electrolytic solution and the positive electrode active material cannot be ensured, resulting in poor output characteristics.

  On the other hand, when considering production on an industrial scale, as a precursor, producing a composite hydroxide in a powder state with an excessively small value of [(d90-d10) / average particle size] From the viewpoint of productivity, or production cost, it is not realistic. Therefore, the lower limit of [(d90−d10) / average particle diameter] of the positive electrode active material is preferably about 0.25.

  In addition, the meaning of d10 and d90 in the index [(d90−d10) / average particle diameter] indicating the spread of the particle size distribution in the positive electrode active material, and how to obtain them are the same as in the above composite hydroxide. .

(3-4) a positive electrode active material having a specific surface area of the present invention has a specific surface area ^is preferably ^{0.7m 2 /g~4.0m 2 / g, 1.0m} 2 /g~3.0m 2 / More preferably, it is g. The positive electrode active material having a specific surface area in such a range has a large contact area with the electrolytic solution, and can greatly improve the output characteristics of a secondary battery using the positive electrode active material. On the other hand, when the specific surface area of the positive electrode active material is less than 0.7 m ² / g, when the secondary battery is configured, the reaction area with the electrolytic solution cannot be secured, and the output characteristics are sufficient. It will be difficult to improve. On the other hand, when the specific surface area of the positive electrode active material is larger than 3.0 m ² / g, the reactivity with the electrolytic solution becomes too high, and the thermal stability may be lowered.

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

(3-5) Tap density Increasing the capacity of secondary batteries is an important issue in order to extend the usage time of portable electronic devices and the travel distance of electric vehicles. On the other hand, the thickness of the electrode of the secondary battery is required to be about several μm because of problems of packing of the whole battery and electronic conductivity. For this reason, not only a high-capacity positive electrode active material is used, but also the filling property of the positive electrode active material is improved by increasing the sphericity of the secondary particles, thereby increasing the capacity of the secondary battery as a whole. Necessary.

From such a viewpoint, in the positive electrode active material of the present invention, it is preferable that the tap density, which is an index of filling property (sphericity of the secondary particles constituting the positive electrode active material), is 1.0 g / cm ³ or more. 1.2 g / cm ³ or more is more preferable, and 1.3 g / cm ³ or more is more preferable. When the tap density is less than 1.0 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 .

  In addition, the tap density in this invention represents the bulk density after tapping the sample powder extract | collected in the container 100 times based on JISZ-2512: 2012, and can measure it using a shake specific gravity measuring device. it can.

(3-6) Specific surface area per unit volume In the positive electrode active material of the present invention, the specific surface area per unit volume, which is a large index for the filling property of the positive electrode active material, is 3.5 m ² / cm ³ or more, preferably 3.6 m ² / cm ³ or more, more preferably 3.8 m ² / cm ³ or more, and still more preferably 4.0 m ² / cm ³ or more. Thereby, the contact area with the electrolytic solution can be increased while ensuring the filling property as the powder of the positive electrode active material, so that the output characteristics and the battery capacity can be improved at the same time. Further, the upper limit of the specific surface area per unit volume is preferably 6.0 m ² / cm ³ or less, more preferably 5.5 m ² / cm ³ or less, from the viewpoint of obtaining higher filling properties. More preferably, it is 5.0 m ² / cm ³ or less. In the present invention, the specific 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 of positive electrode active material Since the positive electrode active material of the present invention is characterized by the particle structure of its secondary particles, its composition is limited as long as it has the particle structure described above. However, the present invention is not limited 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, It can be suitably applied to a positive electrode active material represented by one or more additive elements selected from Ta and W.

  In this positive electrode active material, the value of u indicating an 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 a 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 increases, and thus 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 x indicating the content thereof is preferably 0.3 or more and 0.95 or less, more preferably 0.8. 3 to 0.9. 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, if 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 contributing to the improvement of thermal stability, and the value of y indicating the content thereof is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. And If the value of y is less than 0.05, the thermal stability of a secondary battery using this positive electrode active material cannot be improved. On the other hand, if the value of y exceeds 0.55, Mn elutes from the positive electrode active material during high temperature operation, and the charge / discharge cycle characteristics deteriorate.

  Cobalt (Co) is an element contributing to the improvement of charge / discharge cycle characteristics, and the value of z indicating the content thereof is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.35 or less. To do. When the value of z exceeds 0.4, the initial discharge capacity of the secondary battery using this positive electrode active material is significantly reduced.

  In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material of the present invention may contain an additive element M in addition to the above transition metal element. Examples of the 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 element that contributes to the Redox reaction decreases, so that the battery capacity decreases.

  Such additive element M may be uniformly dispersed inside the positive electrode active material particles, or the particle surface of the positive electrode active material may be coated. Furthermore, the surface 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 to be in 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 ≦ 0.1, 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. More preferably.

On the other hand, when further improving the thermal stability, the composition is expressed by the general 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, and W are preferably adjusted so as to be expressed by an additive element selected from Nb, Mo, Hf, Ta, and W.

4). Method for producing positive electrode active material for non-aqueous electrolyte secondary battery The method for producing a positive electrode active material of the present invention uses the composite hydroxide described above as a precursor, and has a predetermined structure, an average particle size, and a particle size distribution. There is no particular limitation as long as the active material can be synthesized. However, when industrial scale production is carried out, the above-mentioned composite hydroxide is mixed with a lithium compound to obtain a lithium mixture, and the obtained lithium mixture is 650 ° C to 1000 ° C in an oxidizing atmosphere. It is preferable to synthesize the positive electrode active material by a manufacturing method including a baking step of baking at a temperature in the range of ° C. In addition, you may add processes, such as a heat treatment process and a calcination process, to the process mentioned above as needed. By such a production method, the above-described positive electrode active material, in particular, the positive electrode active material represented by the general formula (B) can be easily obtained.

(4-1) Heat treatment step In the method for producing a positive electrode active material of the present invention, a heat treatment step is optionally provided before the mixing step, and the composite hydroxide is heat treated particles and then mixed with the lithium compound. Also good. 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 (hereinafter referred to as “composite oxide”) that has been converted into an oxide by the heat treatment step. ) Or a mixture thereof.

  The heat treatment step is a step of removing excess moisture contained in the composite hydroxide by heating the composite hydroxide to a temperature in the range of 105 ° C. to 750 ° C. for heat treatment. Thereby, the water | moisture content which remains after a baking process can be reduced to a fixed amount, and the dispersion | variation in the composition of the positive electrode active material obtained can be suppressed. When the heating temperature is lower than 105 ° C., excess moisture in the composite hydroxide cannot be removed, and variation may not be sufficiently suppressed. On the other hand, when the heating temperature is higher than 750 ° C., not only a further effect cannot be expected, but the production cost increases.

  In addition, in the heat treatment step, it is sufficient if water can be removed to such an extent that the number of atoms of each metal component in the positive electrode active material and the ratio of the number of Li atoms do not vary. There is no need to convert everything. However, in order to reduce the variation in the number of atoms of each metal component and the ratio of the number of Li atoms, heating to 400 ° C. or higher converts all composite hydroxides to composite oxides. It is preferable. In addition, the above-mentioned dispersion | variation can be suppressed more by previously calculating | requiring the metal component ratio contained in the composite hydroxide by heat processing conditions by chemical analysis, and determining the mixing ratio with a lithium compound.

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

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

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

  In the mixing step, the ratio of the number of metal elements other than lithium in the lithium mixture, specifically, the sum of the number of atoms of nickel, cobalt, manganese, and additive element M (Me) to the number of atoms 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 the 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 and 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 because of availability. In particular, lithium hydroxide or lithium carbonate is preferably used in consideration of ease of handling and quality stability.

  It is preferable that the composite hydroxide or the heat-treated particles and the lithium compound are sufficiently mixed so that no fine powder is generated. If the mixing is insufficient, the value of Li / Me varies among individual particles, and sufficient battery characteristics may not be obtained. In addition, a general mixer can be used for mixing. For example, a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like can be used.

(4-3) Calcination Step When lithium hydroxide or lithium carbonate is used as the lithium compound, the lithium mixture is treated at a temperature lower than the firing temperature and 350 after the mixing step and before the firing step. A calcining step of calcining may be performed at a temperature of from 800 ° C to 800 ° C, preferably from 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. The atmosphere in the calcination step is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume, as in the baking step described later.

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

  In this firing step, the center part, the high density layer and the outer shell part (or the external high density layer) of the composite hydroxide and the heat-treated particles are sintered and contracted while being converted from the hydroxide to the oxide. In the positive electrode active material, primary particle aggregates are formed as one main part.

  On the other hand, since the low density layer is configured to include fine primary particles, sintering starts in a lower temperature region than the center portion, the high density layer, and the outer shell portion. At this time, since the low-density layer has a larger volume shrinkage than the center, the high-density layer, and the outer shell, the fine primary particles constituting the low-density layer are the center, the high-density Volume shrinks in the direction in contact with the layer and the outer shell. At this time, between the central portion and the high-density layer and between the high-density layer and the outer shell portion, specifically, between the central portion and the first high-density layer and between the first high-density layer and the outer portion. A gap having an appropriate size is formed between the shell and the shell. These voids are divided by the deformation accompanying sintering shrinkage of the central part, the high-density layer and the outer shell part, and are irregularly dispersed, and a plurality of voids are formed inside the main part of the formed positive electrode active material. Part is formed.

  Furthermore, as the firing proceeds, the center, high-density layer, and outer shell are further deformed to form a plurality of clear voids, and the high-density layer and outer shell press the voids. Due to the pressure to be formed, a communication hole is formed in the outer shell portion on the outermost surface side of the secondary particle, which communicates the inside of the void and the outside of the secondary particle. Further, in the course of firing the composite hydroxide, communication holes are also formed in the high-density layer, and a plurality of voids existing in the radial direction are connected to each other inside the secondary particles. As described above, gaps generated when the central portion, the high-density layer, and the outer shell portion are substantially connected or integrated during sintering shrinkage are also included in the void portion of the present invention.

  In the positive electrode active material of the present invention, a composite hydroxide comprising a low-density layer made of fine primary particles and a central portion made of plate-like primary particles, a high-density layer and an outer shell portion is fired to oxidize from the hydroxide. In addition to the conversion into a product, by utilizing the difference in the degree of volume shrinkage during sintering between the low-density layer and the central portion, the high-density layer, and the outer shell portion, a plurality of voids and a part thereof are particles. It can be configured to communicate with the outside through a communication hole. As a result, the contact surface area between the electrolytic solution and the positive electrode active material is increased, and the conductive auxiliary agent can also enter the inside, so that the internal resistance of the positive electrode active material is greatly reduced and the secondary battery is configured. In this case, the output characteristics can be improved 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 that is the precursor, but may be affected by its composition, firing conditions, etc. It is preferable to appropriately adjust each condition so as to obtain a desired structure after conducting a preliminary test.

  In addition, the furnace used for a baking process is not specifically limited, What is necessary is just to be able to bake a lithium mixture in air | atmosphere or 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 suitably used. The same applies to the furnace used in the heat treatment step and the calcining step.

a) Firing temperature The firing temperature of the lithium mixture is required to be 650 ° C to 1000 ° C. When the firing temperature is less than 650 ° C., lithium is not sufficiently diffused in the composite hydroxide or heat-treated particles, and surplus lithium, unreacted composite hydroxide or heat-treated particles remain, or the obtained positive electrode The crystallinity of the active material may become insufficient. On the other hand, when the firing temperature is higher than 1000 ° C., the particles of the positive electrode active material are vigorously sintered, abnormal grain growth occurs, and the ratio of coarse particles increases, causing the particle size distribution to widen.

  In addition, when it is going to obtain the positive electrode active material represented by the said general formula (B1), it is preferable that a calcination temperature shall be 650 degreeC-900 degreeC. On the other hand, when it is intended to obtain the positive electrode active material represented by the general formula (B2), the firing temperature is preferably set to 800 ° C to 980 ° C.

  Moreover, it is preferable that the temperature increase rate in a baking process shall be 2 degree-C / min-10 degree-C / min, and it is more preferable to set it as 5 to 10 degree-C / min. Further, during the firing step, it is preferably maintained at a temperature near the melting point of the lithium compound for 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) Firing time Of the firing time, the holding time at the firing temperature described above is preferably at least 2 hours, and more preferably 4 to 24 hours. When the holding time at the firing temperature is less than 2 hours, lithium is not sufficiently diffused into the composite hydroxide or heat-treated particles, and excess lithium, unreacted composite hydroxide or heat-treated particles remain, or a positive electrode obtained There is a possibility that the crystallinity of the active material may be insufficient.

  The cooling rate from the firing temperature to at least 200 ° C. after the holding time is preferably 2 ° C./min to 10 ° C./min, more preferably 33 ° C./min to 77 ° C./min. By controlling the cooling rate within such a range, it is possible to prevent the facilities such as the mortar from being damaged by the rapid cooling while securing the productivity.

c) Firing atmosphere The atmosphere during 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 the above oxygen concentration and an inert gas. It is particularly preferable that That is, firing is preferably performed in the air or in an oxygen stream. When 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 agglomerated 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 diameter and particle size distribution of the positive electrode active material obtained can be adjusted to a suitable range. Crushing means adding mechanical energy to agglomerates composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing and separating them with almost no destruction of the secondary particles themselves. This means an operation of loosening the aggregates.

  As a crushing method, a known means can be used, for example, a pin mill or a hammer mill 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. Nonaqueous electrolyte secondary battery The nonaqueous electrolyte secondary battery of the present invention includes the same constituent members as those of a general nonaqueous electrolyte secondary battery, such as a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution. Note that the embodiments described below are merely examples, and the nonaqueous electrolyte secondary battery of the present invention is applied to various modified and improved embodiments based on the embodiments described in the present specification. It is also possible to do.

(5-1) Constituent member a) Positive electrode Using the positive electrode active material of the present invention, for example, a positive electrode of a nonaqueous electrolyte secondary battery is produced as follows.

  First, a conductive material and a binder are mixed into the positive electrode active material of the present invention, and activated carbon and a solvent such as viscosity adjustment are added as necessary, and these are kneaded to prepare a positive electrode mixture paste. At that time, the mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the nonaqueous 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 in the same manner as the positive electrode of a general nonaqueous 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, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size according to the target battery and used for battery production. Note that the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

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

  The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin or polyacrylic. An acid can be used.

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

b) Negative electrode For the negative electrode, metallic lithium, lithium alloy, or the like can be used. In addition, a negative electrode active material capable of occluding and desorbing lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste of the negative electrode mixture on the surface of a metal foil current collector such as copper. It is possible to use one that is dried and compressed to increase the electrode density as necessary.

  Examples of the negative electrode active material include lithium-containing materials such as metallic lithium and lithium alloys, natural graphite capable of occluding and desorbing lithium ions, sintered organic compounds such as artificial graphite and phenolic resins, and carbon materials such as coke. A powdery body can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, as in the case of the positive electrode, and an organic material such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing these active materials and the binder. A solvent can be used.

c) Separator The separator is disposed between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding the electrolyte. As such a separator, for example, a thin film such as polyethylene or polypropylene and a film having many fine pores can be used. However, the separator is not particularly limited as long as it has the above function.

d) Non-aqueous electrolyte The non-aqueous electrolyte 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 sultone,
Phosphorus compounds such as triethyl phosphate and trioctyl phosphate,
1 type selected from these etc. can be used individually or in mixture of 2 or more types.

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

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

(5-2) Structure The nonaqueous electrolyte secondary battery of the present invention composed of the above positive electrode, negative electrode, separator, and nonaqueous electrolyte can be formed in various shapes such as a cylindrical shape and a laminated shape.

  In any case, the positive electrode and the negative electrode are laminated through a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and sealed in a battery case to complete a nonaqueous electrolyte secondary battery. .

(5-3) Characteristics Since the non-aqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention as a positive electrode material as described above, the battery capacity and cycle characteristics are excellent, and the output characteristics are conventional. This is a dramatic improvement over the structure. In addition, thermal stability and safety are sufficiently maintained in comparison with a secondary battery using a positive electrode active material made of a conventional lithium nickel composite oxide.

  For example, when the positive electrode active material of the present invention is used to form a 2032 type coin battery as shown in FIG. 5, an initial discharge capacity of 150 mAh / g or more, preferably 158 mAh / g or more, and 1.20Ω or less, A positive electrode resistance of preferably 1.0Ω or less, more preferably 0.97Ω or less, and a 500 cycle capacity maintenance ratio of 75% or more, preferably 80% or more can be achieved at the same time.

(5-4) Applications The nonaqueous electrolyte secondary battery of the present invention is excellent in battery capacity and output characteristics as described above, and is a small portable electronic device (notebook personal computer) that requires these characteristics at a high level. It can be suitably used for a power source of a computer or a mobile phone. In addition, the nonaqueous electrolyte secondary battery of the present invention is excellent in safety, and not only can be reduced in size and output, but also an expensive protection circuit can be simplified. It can also be suitably used as a power source for transportation equipment such as electric vehicles and hybrid cars that are subject to restrictions.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. Moreover, these are examples of the embodiments of the present invention, and the present invention is not limited to these contents. In the following examples and comparative examples, Wako Pure Chemical Industries, Ltd. reagent-grade samples were used for producing transition metal-containing composite hydroxides and positive electrode active materials, respectively, unless otherwise specified. During the nucleation step and the particle growth step, the pH value of the reaction aqueous solution is measured by a pH controller (manufactured by Nisshin Rika Co., Ltd., NPH-690D). By adjusting the amount, the pH value of the reaction aqueous solution in each step was controlled within a range of variation of ± 0.2 with respect to the set value of the step.

Example 1
a) Production of transition metal composite hydroxide particles [nucleation process]
First, the temperature in the tank was set to 40 ° C. while stirring by putting 1.4 L of water in the 6 L reaction tank. At this time, nitrogen was circulated in the reaction tank for 30 minutes, and the reaction atmosphere was a non-oxidizing atmosphere (oxygen concentration: about 2% by volume). Subsequently, an appropriate amount of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water is supplied into the reaction vessel so that the pH value is 12.8 based on the liquid temperature of 25 ° C. and the ammonium ion concentration is 10 g / L. Was adjusted to form an aqueous solution before reaction.

  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. 2 mol / L of raw material aqueous solution was prepared.

  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 performed for 1 minute by crystallization reaction. During this treatment, 25% by mass of sodium hydroxide aqueous solution and 25% by mass of ammonia water were supplied in a timely manner to maintain the pH value and ammonium ion concentration of the reaction aqueous solution in the above ranges.

[Particle growth process]
After the nucleation step is completed, supply of all aqueous solutions into the reaction vessel is temporarily stopped, and sulfuric acid is added to the reaction vessel so that the pH value of the aqueous reaction solution becomes 11.6 based on the liquid temperature of 25 ° C. Adjusted. After confirming that the pH value reached a predetermined value, the raw material aqueous solution and the sodium tungstate aqueous solution were supplied to grow the nuclei generated in the nucleation step. After a lapse of 16 minutes from the start of the particle growth process (6.7% with respect to the total particle growth process time), a ceramic air diffuser (Kinoshita) having a pore diameter of 20 μm to 30 μm while continuing to supply the raw material aqueous solution Using Rika Kogyo Co., Ltd.), air was circulated in the reaction aqueous solution, and the reaction atmosphere was adjusted to an oxidizing atmosphere having an oxygen concentration of 21% by volume (switching operation 1).

  After 36 minutes (15.0% of the total particle growth process time) from the start of the switching operation 1, nitrogen was passed through the reaction vessel while continuing to supply the raw material aqueous solution, and the reaction atmosphere was non-oxidized. The sex atmosphere was adjusted (switching operation 2).

  Then, after 49 minutes (20.4% with respect to the entire particle growth process time) from the start of the switching operation 2, the switching operation 1 was performed again.

  After a lapse of 74 minutes from the start of the switching operation 1 (30.8% with respect to the entire particle growth process time), the switching operation 2 was performed again.

  Thereafter, after 65 minutes (27.1% with respect to the total particle growth process time) from the start of the switching operation 2, the supply of all aqueous solutions to the reaction vessel was stopped, and the particle growth process was completed. In the particle growth step, 25% by mass of sodium hydroxide aqueous solution and 25% by mass of ammonia water were supplied in a timely manner, and the pH value and ammonium ion concentration of the reaction aqueous solution were maintained within the above ranges.

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

b) Evaluation of composite hydroxide [Composition]
The composite hydroxide as a sample, ICP emission spectrophotometer (Shimadzu Corporation Shimadzu, ICPE-9000) was measured elemental fraction using a composite hydroxide of the general formula: Ni _{0 .331} Mn _0.331 Co _0.331 Zr _0.002 W _0.005 (OH) ₂ was confirmed.

[Particle structure]
When the composite hydroxide was observed with a field emission scanning electron microscope (FE-SEM: JSM-6360LA, manufactured by JEOL Ltd.), the composite hydroxide was substantially spherical and had a uniform particle size. It was confirmed to be 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 made observable by cross section polishing, and observed with FE-SEM (manufactured by JEOL Ltd., JSM-6360LA). 1). As a result, the secondary particles constituting this composite hydroxide have a central portion formed by aggregation of plate-like primary particles, and fine primary particles are formed by aggregation outside the central portion. The first low-density layer, the first high-density layer formed by aggregation of plate-like primary particles on the outside of the first low-density layer, and the fine primary particles on the outside of the first high-density layer It was confirmed that the second low-density layer formed by agglomeration of the particles had a laminated structure in which the second low-density layer was laminated, and an outer shell portion where the plate-like primary particles were further agglomerated on the outer side.

  When the average particle diameter of the primary particles was measured and calculated, the average particle diameter of the fine primary particles was 0.2 μm, and the average particle diameter of the plate-like primary particles was 0.5 μm.

  Further, measurement and calculation were performed for the center part particle size ratio, the first low density layer particle size ratio, the first high density layer particle size ratio, the second low density layer particle size ratio, and the outer shell part particle size ratio. However, they were 40%, 20%, 15%, 15%, and 10%, respectively.

[Average particle size and particle size distribution]
Using a laser light diffraction / scattering particle size analyzer (manufactured by Nikkiso Co., Ltd., Microtrac HRA), the average particle size of secondary particles constituting the composite hydroxide is measured, and d10 and d90 are measured, and the particle size distribution is measured. The value of [(d90−d10) / average particle diameter], which is an index indicating the spread of the particle size, was calculated. As a result, the average particle size of the secondary particles constituting 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 stream (oxygen concentration: 21 vol%) to obtain heat treated particles. . Thereafter, as a mixing step, the heat-treated particles and lithium carbonate are mixed so that the value of Li / Me is 1.14, and a shaker mixer apparatus (manufactured by Willy et Bacofen (WAB), TURBULA Type T2C) is used. And mixed well to obtain a lithium mixture.

  Next, a firing step is performed on the lithium mixture, and the temperature is raised to 950 ° C. at a rate of 2.5 ° C./min in the air (oxygen concentration: 21% by volume), and this temperature is maintained for 4 hours. And then cooled to room temperature at a cooling rate of about 4 ° C./min. Since the positive electrode active material thus obtained was agglomerated or slightly sintered, a crushing step was performed, the positive electrode active material was crushed, and the average particle size and particle size distribution were adjusted.

d) Evaluation of positive electrode active material [Composition]
When this positive electrode active material was used as a sample and the element fraction was measured using an ICP emission spectroscopic analyzer, this positive electrode active material had a 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]
The average particle size of this positive electrode active material is measured using a laser light diffraction / scattering particle size analyzer, and d10 and d90 are measured, which is an index indicating the spread of the particle size distribution [(d90-d10) / average particle Diameter] was calculated. As a result, the average particle diameter of the positive electrode active material was 5.1 μm, and [(d90−d10) / average particle diameter] was 0.41.

[Particle structure]
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. 2). As a result, this positive electrode active material was confirmed to have a porous structure in which a plurality of primary particles were aggregated and a plurality of voids were dispersed inside the particles. In addition, the voids dispersed in the particles in the portion where the voids do not exist (main part) communicated with the outside of the particles through a plurality of communication holes. The average pore diameter of the plurality of voids was 1.8 μm. The average inner diameter of the plurality of communication holes was 0.4 μm.

[Specific surface area and tap density]
Using this positive electrode active material as a sample, the specific surface area was measured by a flow-type gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb), and the tap density was measured by a tapping machine (Kuramo Scientific Instruments Co., Ltd., KRS-406). , Respectively. As a result, the specific surface area of this positive electrode active material was 2.93 m ² / g, and the tap density was 1.43 g / cm ³ .

e) Production 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 produced by drying at 120 degreeC for 12 hours in a vacuum dryer.

Next, using this positive electrode (1), a 2032 type coin battery (B) was produced in a glove box in an argon (Ar) atmosphere in which the dew point was controlled at −80 ° C. The negative electrode (2) of the 2032 type coin battery uses lithium metal having a diameter of 17 mm and a thickness of 1 mm, and the electrolytic solution is ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte. The equivalent liquid mixture (made by Toyama Pharmaceutical Co., Ltd.) was used. The separator (3) was a polyethylene porous film having a thickness of 25 μm. 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, it is left for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is 0.1 mA / cm ² and the cut-off voltage is 4.3 V. A charge / discharge test was performed to measure the discharge capacity when the battery was discharged until the cut-off voltage reached 3.0 V after a 1 hour rest, and the initial discharge capacity was determined. As a result, the initial discharge capacity was 159.6 mAh / g. A multi-channel voltage / current generator (manufactured by Advantest Corporation, R6741A) was used for the measurement of the initial discharge capacity.

[Positive electrode resistance]
Using a 2032 type coin battery charged at a charging potential of 4.1 V, the resistance value was measured by the AC impedance method. For the measurement, a Nyquist plot shown in FIG. 6 was obtained using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron). Since the plot is expressed as the sum of the characteristic curves indicating the solution resistance, the negative electrode resistance and the capacity, and the positive electrode resistance and the capacity, fitting calculation was performed using an equivalent circuit to calculate the value of the positive electrode resistance. As a result, the positive electrode resistance was 0.924Ω.

  Tables 1 to 3 show the preparation conditions of the transition metal-containing composite hydroxide particles and the positive electrode active material, the characteristics thereof, and the results of various performances of the battery using them. The results of the following Examples 2 to 18 and Comparative Examples 1 to 8 are also shown in Tables 1 to 3.

(Example 2)
In the particle growth process, the switching operation 1 is performed after 16 minutes (6.7% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 36 minutes from the switching operation 1 ( The switching operation 1 is performed after 30 minutes (12.5% with respect to the entire particle growth process time) has elapsed from the switching operation 2 and then 30 minutes (12.5% with respect to the entire particle growth process time). Thereafter, the switching operation 2 is performed 65 minutes after the switching operation 1 (27.1% with respect to the entire particle growth process time), and then 93 minutes (38.8% with respect to the entire particle growth process time). ) A composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

(Example 3)
In the particle growth process, the switching operation 1 is performed after 16 minutes (6.7% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 36 minutes from the switching operation 1 ( After 15.0%) of the entire grain growth process time, the switching operation 1 was performed after 71 minutes (29.6% of the entire grain growth process time) from the switching operation 2. . Thereafter, the switching operation 2 is performed after 83 minutes (34.6% of the entire particle growth process time) have elapsed from the switching operation 1, and then 34 minutes (14.2% of the entire particle growth process time). ) A composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

Example 4
In the particle growth process, the switching operation 1 is performed after 16 minutes (6.7% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 36 minutes from the switching operation 1 ( After 15.0%) of the entire grain growth process time, the switching operation 1 was performed after 30 minutes (12.5% of the entire grain growth process time) after the switching operation 2. . Thereafter, the switching operation 2 is performed after 93 minutes (38.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

(Example 5)
In the particle growth process, the switching operation 1 is performed after 16 minutes (6.7% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 36 minutes from the switching operation 1 ( After 15.0%) of the entire grain growth process time, the switching operation 1 was performed after 71 minutes (29.6% of the entire grain growth process time) from the switching operation 2. . Thereafter, the switching operation 2 is performed after the lapse of 52 minutes (21.7% with respect to the total particle growth process time) from the switching operation 1, and then 65 minutes (27.1% with respect to the total particle growth process time). ) A composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

(Example 6)
In the particle growth process, the switching operation 1 is performed 10 minutes after the start of the particle growth process (4.2% of the total particle growth process time), and the switching operation 2 is performed for 12 minutes from the switching operation 1 ( The switching operation 1 was performed after 79 minutes (32.9% with respect to the entire particle growth process time) after switching operation 2 and 79 minutes later. . Thereafter, the switching operation 2 is performed after 74 minutes (30.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

(Example 7)
In the particle growth process, the switching operation 1 is performed after 22 minutes (9.2% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed 44 minutes from the switching operation 1 ( After the passage of 18.3%) of the whole grain growth process time, and after that, after switching operation 2 to 35 minutes (14.6% of the whole grain growth process time), switching operation 1 was performed. . Thereafter, the switching operation 2 is performed after 74 minutes (30.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

(Example 8)
In the particle growth process, the switching operation 1 is performed 7 minutes after the start of the particle growth process (2.9% of the entire particle growth process time), and the switching operation 2 is performed 45 minutes from the switching operation 1 ( 18.8% of the entire grain growth process time), and after that, switching operation 2 was performed after 49 minutes (20.4% of the entire grain growth process time) from switching operation 2. . Thereafter, the switching operation 2 is performed after 74 minutes (30.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

Example 9
In the particle growth process, the switching operation 1 is performed 30 minutes after the start of the particle growth process (12.5% with respect to the entire particle growth process time), and the switching operation 2 is performed for 22 minutes from the switching operation 1 ( 9.2% of the entire grain growth process time), and after that, switching operation 1 was performed after 49 minutes (20.4% of the entire grain growth process time) from switching operation 2. . Thereafter, the switching operation 2 is performed after 74 minutes (30.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued.

(Comparative Example 1)
In the particle growth process, the switching operation 1 is performed 10 minutes after the start of the particle growth process (4.2% with respect to the total particle growth process time), and the switching operation 2 is performed for 30 minutes from the switching operation 1 ( After 12.5%) of the entire grain growth process time, the switching operation 1 was performed after 26 minutes (10.8% of the entire grain growth process time) after the switching operation 2. . Thereafter, the switching operation 2 is performed 57 minutes after the switching operation 1 (23.8% with respect to the total particle growth process time), and then 117 minutes (48.8% with respect to the total particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 1 is composed of a plurality of primary particles aggregated, and has a porous structure in which a plurality of voids are dispersed inside the particles. Although it communicated with the outside of the particles, the average inner diameter of the communication holes was 0.1 μm.

(Comparative Example 2)
In the particle growth process, the switching operation 1 is performed after 18 minutes (7.5% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 40 minutes from the switching operation 1 ( 16.7% of the entire grain growth process time), and after that, switching operation 2 was performed after 75 minutes (31.2% of the entire grain growth process time). . Thereafter, the switching operation 2 is performed 87 minutes after the switching operation 1 (36.3% with respect to the total particle growth process time), and then 20 minutes (8.3% with respect to the total particle growth process time). ) A transition metal composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 2 was composed of a plurality of primary particles aggregated, and had a porous structure in which a plurality of voids were dispersed inside the particles. Observation by SEM did not confirm the communication holes between these voids and the outside of the particles.

(Comparative Example 3)
In the particle growth process, the switching operation 1 is performed 10 minutes after the start of the particle growth process (4.2% of the total particle growth process time), and the switching operation 2 is performed for 20 minutes from the switching operation 1 ( After the lapse of 8.3% with respect to the whole grain growth process time, after that, after switching operation 2 to 36 minutes (15.0% with respect to the whole grain growth process time), switching operation 1 was performed. . Thereafter, the switching operation 2 is performed 109 minutes after the switching operation 1 (45.4% with respect to the entire particle growth process time), and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 3 is composed of a plurality of primary particles aggregated, and has a porous structure in which a plurality of voids are dispersed inside the particles. Although it communicated with the outside of the particles, the average inner diameter of the communication holes was 0.1 μm.

(Comparative Example 4)
In the particle growth process, the switching operation 1 is performed after 16 minutes (6.7% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 36 minutes from the switching operation 1 ( 15.0% of the entire grain growth process time), and after that, switching operation 2 was performed after 71 minutes (29.6% of the entire grain growth process time). . Thereafter, the switching operation 2 is performed 24 minutes after the switching operation 1 (10.0% with respect to the entire particle growth process time), and then 93 minutes (38.8% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 4 is composed of a plurality of primary particles aggregated, and has a porous structure in which a plurality of voids are dispersed inside the particles. Although it communicated with the outside of the particles, the average inner diameter of the communication holes was 0.1 μm.

(Comparative Example 5)
In the particle growth process, the switching operation 1 is performed 6 minutes after the start of the particle growth process (2.5% with respect to the total particle growth process time), and the switching operation 2 is performed for 16 minutes from the switching operation 1 ( After the passage of 6.7% of the entire grain growth process time, the switching operation 1 was performed after 101 minutes (42.1% of the whole grain growth process time) from switching operation 2. . Thereafter, the switching operation 2 is performed after the lapse of 52 minutes (21.7% with respect to the total particle growth process time) from the switching operation 1, and then 65 minutes (27.1% with respect to the total particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 5 was composed of a plurality of primary particles aggregated, and had a porous structure in which a plurality of voids were dispersed inside the particles. Observation by SEM did not confirm the communication holes between these voids and the outside of the particles.

(Comparative Example 6)
In the particle growth process, the switching operation 1 is performed after 22 minutes (9.2% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 60 minutes from the switching operation 1 ( After 25.0%) of the entire grain growth process time, the switching operation 1 was performed after 19 minutes (7.9% of the entire grain growth process time) after switching operation 2. . Thereafter, the switching operation 2 is performed after 74 minutes (30.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 5 was composed of a plurality of primary particles aggregated, and had a porous structure in which a plurality of voids were dispersed inside the particles. Observation by SEM did not confirm the communication holes between these voids and the outside of the particles.

(Comparative Example 7)
In the particle growth process, the switching operation 1 is performed 6 minutes after the start of the particle growth process (2.5% with respect to the entire particle growth process time), and the switching operation 2 is performed for 60 minutes from the switching operation 1 ( After 25.0%) of the entire grain growth process time, the switching operation 1 was carried out after 57 minutes (23.8% of the total grain growth process time) after the switching operation 2. . Thereafter, the switching operation 2 is performed after the lapse of 52 minutes (21.7% with respect to the total particle growth process time) from the switching operation 1, and then 65 minutes (27.1% with respect to the total particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 7 was composed of a plurality of primary particles aggregated and had a porous structure in which a plurality of voids were dispersed inside the particles. Observation by SEM did not confirm the communication holes between these voids and the outside of the particles.

(Comparative Example 8)
In the particle growth process, the switching operation 1 is performed after 22 minutes (9.2% of the total particle growth process time) from the start of the particle growth process, and the switching operation 2 is performed for 8 minutes from the switching operation 1 ( After the elapse of 3.3%), the switching operation 1 was performed after 71 minutes from the switching operation 2 (29.6% with respect to the entire particle growth process time). . Thereafter, the switching operation 2 is performed after 74 minutes (30.8% with respect to the entire particle growth process time) have elapsed from the switching operation 1, and then 65 minutes (27.1% with respect to the entire particle growth process time). ) A composite hydroxide particle, a positive electrode active material, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that the crystallization reaction was continued. The positive electrode active material obtained in Comparative Example 8 is composed of a plurality of primary particles aggregated and has a porous structure in which a plurality of voids are dispersed inside the particles. Observation by SEM did not confirm the communication holes between these voids and the outside of the particles.

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 Center Part 22 First Low Density Layer 23 First High Density Layer 24 Second Low Density Layer 25 Outer Shell Part

Claims (24)

A transition metal-containing composite hydroxide comprising a plurality of plate-like primary particles and secondary particles formed by agglomerating fine primary particles having a particle size smaller than the plate-like primary particles,
The secondary particles are formed on the outer side of the central portion made of the plate-like primary particles, on the outer side of the central portion, and on the outer side of the first low-density layer made of the fine primary particles. A first high-density layer composed of the plate-like primary particles, a second low-density layer formed outside the first high-density layer and composed of the fine primary particles, and a second low-density layer. And an outer shell portion made of the plate-like primary particles,
The average ratio of the outer diameter of the central portion to the particle size of the secondary particles is in the range of 20% to 60%, and the average ratio of the thickness of the first low density layer to the particle size of the secondary particles is The average ratio of the thickness of the first high-density layer to the particle size of the secondary particles is in the range of 8% to 33%, and the second low-density layer is in the range of 8% to 33%. The average ratio of the thickness to the particle size of the secondary particles is in the range of 8% to 23%, and the average ratio of the thickness of the outer shell layer to the particle size of the secondary particles is 4% to In the range of 18%,
Transition metal-containing composite hydroxide.   Between the second low-density layer and the outer shell portion, it is formed outside the second low-density layer, and is formed outside the external high-density layer made of the plate-like primary particles and the external high-density layer. The transition metal-containing composite hydroxide according to claim 1, further comprising at least one laminated structure composed of an external low-density layer made of the fine primary particles.   The average ratio of the thickness of the outer high-density layer to the particle size of the secondary particles is in the range of 4% to 18%, and the thickness of the outer low-density layer to the particle size of the secondary particles The transition metal-containing composite hydroxide according to claim 2, wherein the ratio is in the range of 8% to 23%.   The average particle size of the plate-like primary particles is in the range of 0.3 μm to 3 μm, the average particle size of the fine primary particles is smaller than the average particle size of the plate-like primary particles, and The transition metal containing composite hydroxide in any one of Claims 1-3 which exists in the range of 01 micrometer-0.3 micrometer.   The average particle size of the secondary particles is in the range of 1 μm to 15 μm, and the value of [(d90−d10) / average particle size] which is an index indicating the spread of the particle size distribution of the secondary particles is 0. The transition metal-containing composite hydroxide according to any one of claims 1 to 4, which is .65 or less. 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 one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W The transition metal-containing composite hydroxide according to any one of claims 1 to 5, represented by:   The additive element M is uniformly distributed inside the transition metal-containing composite hydroxide, and / or the surface of the transition metal-containing composite hydroxide is coated with a compound containing the additive element M. The transition metal-containing composite hydroxide according to claim 6. A raw material aqueous solution containing at least a transition metal element and an aqueous solution containing an ammonium ion supplier are mixed to form a reaction aqueous solution, which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery by a crystallization reaction. A method for producing transition metal composite hydroxide particles, comprising:
A nucleation step of adjusting the pH value of the reaction aqueous solution at a reference temperature of 25 ° C. to a range of 12.0 to 14.0 and performing nucleation in a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less;
The pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step is adjusted so that the pH value based on a liquid temperature of 25 ° C. is lower than the pH value of the nucleation step and is 10.5 to 12.0. And a particle growth step for growing the nucleus,
In the grain growth step,
Maintaining the non-oxidizing atmosphere from the start of the grain growth process for a time in the range of 0.5% to 15% with respect to the whole grain growth process;
After the first stage, the oxygen concentration is switched to an oxidizing atmosphere exceeding 5% by volume, and the oxidizing atmosphere is maintained for a time in the range of 4% to 22% with respect to the whole of the grain growth process. Stages,
After the second stage, the third stage is switched from the oxidizing atmosphere to the non-oxidizing atmosphere, and the non-oxidizing atmosphere is maintained for a time in the range of 10% to 40% with respect to the whole of the grain growth process. When,
After the third stage, a fourth stage in which the non-oxidizing atmosphere is switched to the oxidizing atmosphere and the oxidizing atmosphere is maintained for a time in a range of 15% to 40% with respect to the whole of the particle growth process; ,
After the fourth stage, the outer shell portion is switched from the oxidizing atmosphere to the non-oxidizing atmosphere, and the non-oxidizing atmosphere is maintained for a time in the range of 10% to 45% with respect to the whole of the particle growth process. The formation stage;
Provide
A method for producing a transition metal-containing composite hydroxide.   An external high-density layer forming step of switching from the oxidizing atmosphere to the non-oxidizing atmosphere to maintain the non-oxidizing atmosphere between the fourth step and the outer shell forming step, and the external high-density layer formation The transition according to claim 8, wherein after the progress of the step, the combination with the external low density layer forming step of switching from the non-oxidizing atmosphere to the oxidizing atmosphere and maintaining the oxidizing atmosphere is provided at least once. A method for producing a metal-containing composite hydroxide.   The external high-density layer forming step is performed for a time in the range of 10% to 40% with respect to the entire particle growth process, and the external low-density layer forming step is set to 15% with respect to the entire particle growth process time. The method for producing a transition metal-containing composite hydroxide according to claim 9, wherein the time is in a range of% to 40%. 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, Hf The manufacturing method of the transition metal containing composite hydroxide in any one of Claims 8-10 made into the composition represented by the 1 or more types of additional element selected from Ta, W).   The production of a transition metal-containing composite hydroxide according to claim 11, further comprising a coating step of coating the surface of the transition metal-containing composite hydroxide with a compound containing the additive element M after the particle growth step. Method. A positive electrode active material used for a positive electrode of a nonaqueous electrolyte secondary battery,
Consisting of secondary particles formed by agglomerating a plurality of primary particles, communicating a plurality of voids dispersed in the secondary particles, and the voids and the outside of the secondary particles, at least A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising one communication hole and having a specific surface area per unit volume of the secondary particles of 3.5 m ² / cm ³ or more.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 13, wherein an average pore diameter of the void portion is in a range of 0.1 μm to 2 μm.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 13 or 14, wherein an average inner diameter of the communication hole is in a range of 0.2 µm to 0.7 µm. A specific surface area of the secondary particles ^is 2.7m ² /g~4.0m 2 / g, and a tap density of the secondary particles was measured based on JIS Z2512 is 1.0 g / cm ³ or more The positive electrode active material for nonaqueous electrolyte secondary batteries according to any one of claims 13 to 15.   The average particle size of the secondary particles is in the range of 1 μm to 15 μm, and the value of [(d90−d10) / average particle size] which is an index indicating the spread of the particle size distribution of the secondary particles is 0. The positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 13 to 16, which is 70 or less. 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 The positive electrode active material for nonaqueous electrolyte secondary batteries according to any one of claims 13 to 17, which is represented by one or more additional elements).   The additive element M is uniformly distributed inside the positive electrode active material for a non-aqueous electrolyte secondary battery and / or the surface of the positive electrode active material for the non-aqueous electrolyte secondary battery is covered with a compound containing the additive element M The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 18. A mixing step of mixing the transition metal-containing composite hydroxide according to any one of claims 1 to 7 and a lithium compound to form a lithium mixture,
A firing step of firing the lithium mixture in an oxidizing atmosphere at a temperature in the range of 650 ° C. to 1000 ° C. to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery comprising 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 compound is mixed such that the ratio of the number of lithium atoms contained in the lithium mixture to the total number of metal element atoms other than lithium is in the range of 0.95 to 1.5. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 20 which adjusts quantity.   The non-aqueous electrolyte secondary battery according to claim 20 or 21, further comprising a heat treatment step of heat-treating the transition metal composite hydroxide particles at a temperature in a range of 105 ° C to 750 ° C before the mixing step. A method for producing a positive electrode active material. The lithium transition metal-containing composite oxide is represented by 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 manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries in any one of Claims 20-22 made into the composition represented by 1 or more types of additional elements selected from Hf, Ta, and W). A positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 13 to 19 is used as a positive electrode material of the positive electrode. Non-aqueous electrolyte secondary battery.