Transition metal-containing composite hydroxide and method for producing the same, positive electrode active material for non-aqueous electrolyte secondary battery and method for producing the same, and non-aqueous electrolyte secondary battery

Abstract

To provide a transition metal-containing composite hydroxide that is a precursor of a positive electrode active material for a secondary battery capable of further improving output characteristics while maintaining capacity characteristics and cycle characteristics equivalent to those of a positive electrode active material with a solid structure.SOLUTION: A transition metal-containing composite hydroxide comprises at least one low-density layer consisting of secondary particles formed by agglomeration of plate-like primary particles and formed by agglomeration of fine primary particles having a particle size smaller than that of the plate-like primary particles within a range of up to 30% relative to the particle size of the secondary particles from a surface of the secondary particles among the secondary particles, an average ratio of a thickness of the at least one low-density layer relative to the particle size of the secondary particles is in a range of 3% to 15%, and no gentle density gradient is formed between a portion formed by agglomeration of the plate-like primary particles and the low-density layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transition metal-containing composite hydroxide, a method for producing the same, and the transition metal-containing composite hydroxide. a positive electrode active material for a non-aqueous electrolyte secondary battery, the positive electrode active material having the precursor The present invention relates to a non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery as a positive electrode material. [Background technology]

[0002] In recent years, with the spread of portable electronic devices such as mobile phones and laptop computers, high energy density There is a strong demand for the development of small, lightweight non-aqueous electrolyte secondary batteries with high reliability. electric vehicles, such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery electric vehicles There is also a strong demand for the development of high-output secondary batteries as power sources for automobiles.

[0003] A secondary battery that meets these requirements is a lithium-ion battery, which is a type of non-aqueous electrolyte secondary battery. This lithium-ion secondary battery is composed of a negative electrode, a positive electrode, and a non-aqueous electrolyte. The negative and positive electrode materials are made of active materials capable of desorbing and inserting lithium. Substances are used.

[0004] Among these lithium-ion secondary batteries, those with a layered rock salt or spinel crystal structure Lithium-ion secondary batteries using lithium transition metal-containing composite oxides as the positive electrode material are 4V class. Since a voltage of 1000kJ / cm2 can be obtained, research and development is currently being actively conducted on this type of battery as it has a high energy density. It is being studied and some practical applications are underway.

[0005] As a positive electrode active material for non-aqueous electrolyte secondary batteries, which is a positive electrode material for lithium ion secondary batteries, Lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, is cheaper than cobalt. Lithium nickel composite oxide (LiNiO2) using precious nickel, lithium nickel Cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), manganese The lithium manganese composite oxide (LiMn2O4) and lithium nickel manganese composite Oxide (LiNi 0.5 Mn 0.5 Lithium-transition metal-containing composite oxides such as O2 have been proposed. It has been done.

[0006] By the way, in order to obtain a lithium-ion secondary battery with excellent cycle characteristics and output characteristics, The positive electrode active material for a non-aqueous electrolyte secondary battery is composed of particles with small particle diameters and a narrow particle size distribution. This is because particles with small particle size have a large specific surface area and are difficult to react with the electrolyte. Not only can the area be secured sufficiently, but the positive electrode can be made thin and the lithium ion can be By shortening the distance traveled between the positive and negative electrodes, the positive electrode resistance can be reduced. In addition, particles with a narrow particle size distribution are subjected to the voltage applied to each particle within the electrode. Since the voltage remains almost constant, the decrease in battery capacity due to selective degradation of fine particles can be suppressed. This is because it becomes possible to:

[0007] For example, Japanese Patent Application Laid-Open No. 2012-246199, Japanese Patent Application Laid-Open No. 2013-147416, and WO2012 / 131881, which describes a nucleation step in which nucleation is mainly performed. The crystallization reaction is clearly separated into two stages: the first stage in which particle growth occurs and the second stage in which particle growth occurs. This results in the formation of transition metal-containing composite hydroxides, which are composed of secondary particles with small particle diameters and narrow particle size distributions. The methods for producing the product are also disclosed. By appropriately adjusting the pH value and reaction atmosphere in the long-term process, it is possible to produce a product that consists only of fine primary particles. and a high-density outer shell consisting of only plate-like or needle-like primary particles. We have obtained transition metal-containing composite hydroxides.

[0008] The positive electrode active material for non-aqueous electrolyte secondary batteries using this transition metal-containing composite hydroxide as a precursor is It has a narrow particle size distribution and a hollow structure consisting of an outer shell and a space inside it. Therefore, in secondary batteries using these positive electrode active materials for non-aqueous electrolyte secondary batteries, It is believed that the battery capacity, output characteristics, and cycle characteristics can be improved simultaneously. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-246199 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-147416 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-119092 [Patent Document 4] WO2012 / 131881 publication Summary of the Invention [Problem to be solved by the invention]

[0010] Assuming application to power sources such as electric vehicles, the positive electrode active material for non-aqueous electrolyte secondary batteries Therefore, further improvement of output characteristics is required without compromising the battery capacity or cycle characteristics. To this end, it is necessary to further reduce the positive electrode resistance in the positive electrode active material for non-aqueous electrolyte secondary batteries. It is necessary to reduce it to

[0011] However, a non-aqueous electrolyte having a hollow structure consisting of an outer shell and a space inside it The positive electrode active material for secondary batteries is designed to reduce the positive electrode resistance compared to positive electrode active materials with a solid structure. However, the total amount of electrochemical reaction per volume is small, so the volumetric energy density ( This is disadvantageous from the viewpoint of improving the battery capacity per unit volume.

[0012] In view of the above-mentioned problems, the present invention provides a method for producing a secondary battery using a cathode active material, which can effectively reduce the amount of carbon dioxide particles in the battery. A structure that enables further improvement of output characteristics without compromising capacity or cycle characteristics A positive electrode active material for a non-aqueous electrolyte secondary battery having a structure, and a transition metal-containing precursor thereof Another object of the present invention is to provide such a composite hydroxide. and a method for efficiently obtaining a transition metal-containing composite hydroxide on an industrial scale. The purpose is to: [Means for solving the problem]

[0013] A first aspect of the present invention is a transition metal oxide used as a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery. In particular, the transition metal-containing composite hydroxide of the present invention is a plate-like The secondary particles are formed by agglomeration of the primary particles, and the secondary particles are The secondary particles are separated from the surface by up to 30% of the particle size of the plate-like primary particles. At least one low-density layer formed by agglomeration of fine primary particles having a particle size; The average ratio of the thickness of the at least one low-density layer to the particle diameter of the secondary particles is 3% to In addition, when there are two or more low-density layers, The average ratio of the total thickness of the low-density layer to the particle diameter of the secondary particles is set to a range of 3% to 15%. do.

[0014] More specifically, the transition metal-containing composite hydroxide of the present invention is a composite hydroxide having a main component consisting of the plate-like primary particles. a low-density layer formed on the outside of the main portion and made of the fine primary particles; The transition metal of the present invention has an outer shell formed on the surface of the substrate and made of the plate-like primary particles. The metal-containing composite hydroxide has a main part made of the plate-like primary particles and a front part formed on the outside of the main part. a first low-density layer made of the fine primary particles; and a plate-like a high density layer made of primary particles; and a fine particle layer formed on the outside of the high density layer and made of the fine primary particles. a second low-density layer; and an outer shell portion formed on the outside of the second low-density layer and consisting of the plate-like primary particles. It is equipped with:

[0015] The average ratio of the outer diameter of the main part to the particle diameter of the secondary particles is in the range of 65% to 95%. The thickness of the outer shell portion or the total thickness of the outer shell portion and the high density layer is The average ratio to the particle size is preferably in the range of 2% to 15%.

[0016] The average particle size of the plate-like primary particles is in the range of 0.3 μm to 3 μm, and The average particle size of the fine primary particles is preferably in the range of 0.01 μm to 0.3 μm.

[0017] Furthermore, 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 showing the spread of particle size distribution, is 0. Preferably .65 or less.

[0018] The transition metal-containing composite hydroxide of the present invention is not necessarily limited by its composition, but The transition metal-containing composite hydroxide of the present invention is represented by the general formula (A): Ni x Mn y Co z M t (OH) 2+a (x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z ≦0.4, 0≦t≦0.1, 0≦a≦0.5, M is Mg, Ca, Al, Ti, V, Cr , Zr, Nb, Mo, Hf, Ta, and one or more additional elements selected from W It is preferable that the composition of the present invention is

[0019] In this case, the additional element M is in a form in which it is uniformly distributed inside the secondary particles, and / or Alternatively, the surface of the secondary particles is coated with a compound containing the additional element M. It can exist.

[0020] The second aspect of the present invention is a method for producing a nitriding agent by dissolving an aqueous solution of ammonium hydroxide in a raw material solution containing at least a transition metal element. The reaction solution is mixed with an aqueous solution containing an ion donor, and a non-aqueous solution is formed by a crystallization reaction. A method for producing a transition metal-containing composite hydroxide, which is a precursor of a positive electrode active material for an electrolyte secondary battery. Regarding.

[0021] The method for producing a transition metal-containing composite hydroxide of the present invention comprises the steps of: The pH value of the reaction aqueous solution at a liquid temperature of 25°C is adjusted to a range of 12.0 to 14.0. a nucleation step in which nucleation is carried out in a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less; The pH value of the reaction aqueous solution containing the nuclei obtained in the nucleation step at a liquid temperature of 25°C is The pH value is adjusted to be lower than that of the nucleation step and to be 10.5 to 12.0. a particle growing step of growing the nuclei; Equipped with.

[0022] In particular, in the method for producing a transition metal-containing composite hydroxide of the present invention, The particle growth process is performed for 70% to 90% of the time from the start of the particle growth process. In the initial and middle stages of the process, the non-oxidizing atmosphere is maintained, and in the later stages of the particle growth process, In this case, the non-oxidizing atmosphere is switched to an oxidizing atmosphere having an oxygen concentration of more than 5% by volume. After that, the atmosphere is controlled to switch the oxidizing atmosphere to the non-oxidizing atmosphere again. It is characterized by:

[0023] In addition, in the later stage of the particle growth process, the non-oxidizing atmosphere is switched to the oxidizing atmosphere. After a time period ranging from 0.5 to 20% of the entire particle growth process has elapsed from the time of replacement. After the second switching from the oxidizing atmosphere to the non-oxidizing atmosphere, From the end of the particle growth step, the range of 3% to 20% of the entire particle growth step It is preferable to maintain the non-oxidizing atmosphere for a certain period of time.

[0024] In the method for producing a transition metal-containing composite hydroxide of the present invention, the obtained transition metal-containing composite hydroxide Although not necessarily limited by the composition of the hydroxide, the transition metal-containing composite hydroxide is generally 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 selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W. It is preferable to have a composition represented by the formula (one or more additive elements selected from the group consisting of Cr, Ni, Ni, and Al).

[0025] After the particle growth step, the surface of the secondary particles constituting the transition metal-containing composite hydroxide A coating step of coating the surface of the substrate with a compound containing the additional element M may be further provided. Cut.

[0026] A third aspect of the present invention is a cathode material for a non-aqueous electrolyte secondary battery, comprising a plurality of primary particles. The lithium-transition metal-containing composite oxide is composed of secondary particles formed by the aggregation of The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0027] In particular, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a tap density of 1.6 g / cm 3 The above is the case where the actually measured specific surface area of the secondary particles is assumed to be a perfect sphere. The surface roughness index value, which is the value obtained by dividing the surface area by the geometric surface area of the secondary particles, is in the range of 3.6 to 10. It is characterized in that

[0028] The average particle size of the secondary particles is in the range of 1 μm to 15 μm, and the particle size of the secondary particles is The value of [(d90-d10) / average particle size], which is an index showing the spread of the distribution, is 0.70 or less. It is preferable that:

[0029] The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is not necessarily limited by its composition. However, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is represented by the general formula (B): Li 1+u Ni x M n y Co z M t O2(-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 It is made of a hexagonal lithium nickel manganese composite oxide represented by the additive element preferable.

[0030] A fourth aspect of the present invention is a method for forming a lithium mixture by mixing a precursor with a lithium compound. a mixing step of mixing the lithium mixture in an oxidizing atmosphere at a temperature in the range of 650°C to 1000°C; and firing the resulting mixture at a temperature of 100° C. to 120° C. to form a positive electrode for a non-aqueous electrolyte secondary battery, the positive electrode comprising a lithium-transition metal-containing composite oxide. and a firing step for obtaining the active material. In particular, in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the precursor is The above-mentioned transition metal-containing composite hydroxide of the present invention or the transition metal-containing composite hydroxide of the present invention The present invention is characterized in that heat-treated particles are used.

[0031] In the mixing step, the number of lithium atoms contained in the lithium mixture is The ratio of the number of atoms of metal elements other than the total number of atoms is in the range of 0.95 to 1.5. It is preferable to adjust the amount of the lithium compound mixed.

[0032] In addition, before the mixing step, the transition metal-containing composite hydroxide is heated to 105°C to 750°C. The method may further include a heat treatment step of performing heat treatment at a temperature within the range.

[0033] In the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte Although it is not necessarily limited by the composition of the positive electrode active material for secondary batteries, The lithium transition metal-containing composite oxide constituting the positive electrode active material is represented by the general formula (B): Li 1+U N ix Mn y Co z M t O2(-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 It is preferable to have a composition represented by the above additive elements.

[0034] A fifth aspect of the present invention is a non-aqueous electrolytic cell comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. In particular, in the non-aqueous electrolyte secondary battery of the present invention, the positive electrode material of the positive electrode is The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is used. do. [Effects of the Invention]

[0035] According to the present invention, when a non-aqueous electrolyte secondary battery is constructed, a positive electrode active material having a solid structure is provided. It is possible to improve the output characteristics without impairing the battery capacity or cycle characteristics. Furthermore, according to the present invention, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery. and a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, which can contribute to improving such battery characteristics. To efficiently produce transition metal-containing composite hydroxides as precursors in industrial-scale production. Therefore, the present invention is of great industrial significance. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 is a cross-sectional view that schematically shows the structure of a secondary particle that constitutes the transition metal-containing composite hydroxide of the present invention. [Figure 2]FIG. 2 is an FE-SEM image (observation magnification: 5,000 times) showing the surface of the positive electrode active material for a non-aqueous electrolyte secondary battery obtained in Example 1. [Figure 3] FIG. 3 is an FE-SEM image (observation magnification: 5,000 times) showing the surface of the positive electrode active material for a non-aqueous electrolyte secondary battery obtained in Comparative Example 1. [Figure 4] FIG. 4 is a schematic cross-sectional view of a 2032-type coin battery used for battery evaluation. [Figure 5] FIG. 5 is a schematic explanatory diagram of an example of impedance evaluation measurement and the equivalent circuit used for analysis. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present inventors have investigated the use of a method for producing a fine particle having a small particle size and a particle size distribution, which is described in WO2004 / 181891 and the like. A non-aqueous electrolytic cell having a narrow cloth and a hollow structure consisting of an outer shell and a space inside it. Further improving the battery characteristics of the positive electrode active material for secondary batteries (hereinafter referred to as "positive electrode active material"). To this end, intensive research was carried out.

[0038] Compared with positive electrode active materials with a solid structure, the hollow structure of the positive electrode active material allows the electrolyte to The contact area with the electrode becomes larger, which reduces the positive electrode resistance. Due to the hollow structure, the total amount of electrochemical reaction per volume is small, so the volume energy In terms of battery density (battery capacity per unit volume), it is inferior to solid-structure positive electrode active materials. There is a problem.

[0039] The present inventors have focused on the influence of the powder characteristics of the positive electrode active material on the positive electrode resistance, and have investigated the influence of the powder characteristics As a result of extensive research into the properties of the positive electrode, we have developed a method for forming a solid structure of the positive electrode active material while creating an uneven surface. By increasing the surface roughness of each secondary particle, i.e., Increasing the surface area improves the contact area with the electrolyte, reducing the battery's positive electrode resistance By increasing the temperature and facilitating electrochemical reactions, it is possible to improve the output characteristics. I learned that this is possible.

[0040] In order to obtain such a structure of the positive electrode active material, the precursor, transition metal-containing complex water, In the oxide manufacturing process, an atmospheric gas is supplied using an aeration tube, and a raw material aqueous solution is supplied. The reaction atmosphere can be switched between non-oxidizing and oxidizing atmospheres in a short time without interrupting the supply of gas. By switching the primary particles, fine particles are formed near the surface of the secondary particles formed by the aggregation of the plate-like primary particles. It has been found that it is possible to have a low density layer formed by aggregation of secondary particles.

[0041] Furthermore, by using a transition metal-containing composite hydroxide having such a structure as a precursor, As a result, an uneven shape is formed on the surface, and a positive electrode active material consisting of secondary particles with large surface roughness is obtained. By using a positive electrode active material with such a structure, the battery capacity of a positive electrode active material with a solid structure can be increased. It is known that it is possible to further improve output characteristics without impairing power or cycle characteristics. I got the idea.

[0042] The present invention was completed based on these findings.

[0043] 1.Transition metal-containing composite hydroxide (1-1) Structure of transition metal-containing composite hydroxides a) Secondary particle structure The transition metal-containing composite hydroxide of the present invention (hereinafter referred to as "composite hydroxide") has a plate-like structure. It consists of secondary particles formed by aggregation of primary particles, and has platelets near the surface of the secondary particles. At least one layer formed by aggregation of fine primary particles having a particle size smaller than that of the crystalline primary particles It is characterized by having a low density layer.

[0044] In the composite hydroxide of the present invention, the low-density layer is formed from the surface of the secondary particle relative to the particle size. It is in the range of up to 30%, preferably up to 25%, more preferably up to 20%. The low density layer exists in this range, and the composite hydroxide obtained by firing the composite hydroxide has a low density. The surface of the positive electrode active material is roughened by forming an uneven shape on the surface. This has the effect of increasing the product.

[0045] The low density layer may be partially exposed on the surface of the secondary particles, but this is not prohibited. In general, the low-density layer is entirely covered by an outer shell made up of plate-like primary particles. It is preferable.

[0046] The thickness of the low-density layer is set to a level that can modify the surface properties of the positive electrode active material. Specifically, the ratio of the low density to the particle size of the secondary particles of the composite hydroxide, which is an index of the thickness of the low density layer, The average ratio of the layer thickness (hereinafter referred to as "low-density layer particle size ratio") is set to the range of 3% to 15%. The particle size ratio of the low-density layer is preferably in the range of 5% to 10%. By setting the content in such a range, the particle size can be increased in the positive electrode active material using the composite hydroxide as a precursor. The effect of increasing the surface area of the substrate can be sufficiently secured. If more than 10 ... The ratio is set in the range of 3% to 15%, preferably in the range of 5% to 10%.

[0047] A preferred embodiment of the structure of the transition metal-containing composite hydroxide of the present invention is as shown in FIG. a main portion 21 made of the plate-like primary particles and a fine primary particle formed on the outside of the main portion. a low-density layer 22 made of the plate-like primary particles; and an outer shell portion formed on the outside of the low-density layer and made of the plate-like primary particles. 23. Alternatively, the structure of the transition metal-containing composite hydroxide of the present invention may be a main part consisting of the plate-like primary particles and a fine primary particle formed on the outside of the main part, a first low-density layer formed on the outside of the first low-density layer and consisting of the plate-like primary particles; a second low-density layer formed on the outside of the high-density layer and consisting of the fine primary particles; and an outer shell portion formed on the outside of the second low-density layer and consisting of the plate-like primary particles. can also be taken.

[0048] However, the present invention is not limited to such a structure. It is not necessary for the low density layer to uniformly cover the entire main part of the secondary particle, but the low density layer may partially cover the main part. Also, even if there are multiple low-density layers, these may not be in a high-density state. It is not necessary to form a distinct laminate structure with each layer.

[0049] The average ratio of the outer diameter of the main part to the particle diameter of the secondary particles (hereinafter referred to as "main part particle diameter ratio") is 6 It is preferably in the range of 5% to 95%, and more preferably in the range of 70% to 93%. It is more preferable that the ratio of the main particle diameter is in the range of 80% to 90%. As a result, secondary particles having a substantially solid structure can be realized in the obtained positive electrode active material. By increasing the total amount of electrochemical reaction per volume, the volumetric energy density (per unit volume) It is possible to secure sufficient battery capacity. The particle size ratio of the main part is smaller than 65%. In this case, the resulting positive electrode active material contains secondary particles that have a porous structure, which is different from the solid structure. This increases the likelihood of

[0050] The average thickness of the outer shell or the total thickness of the outer shell and the high density layer relative to the diameter of the secondary particles The average particle size ratio (hereinafter referred to as "outer shell particle size ratio") is preferably in the range of 2% to 15%, It is more preferable that the content of the outer shell is in the range of 5% to 10%. If the particle size ratio of the outer shell is less than 2%, the transition Secondary particles are maintained during the manufacturing process of the metal-containing composite hydroxide or the manufacturing process of the positive electrode active material. On the other hand, if the thickness of the outer shell exceeds 15%, The outer shell structure is maintained by the positive electrode active material, and secondary particles with a porous structure, which differs from the solid structure, exist. more likely to exist.

[0051] In addition, in the structure in which a low-density layer and a high-density layer are laminated near the surface of the secondary particle, The average ratio of the thickness of the outer shell to the diameter of the secondary particles is 2% or more, and the diameter of the outer shell is As long as the ratio is within the above range, the densified layer can have any thickness.

[0052] Here, the particle size ratio of the main part, the particle size ratio of the low-density layer, and the particle size ratio of the outer shell are determined by the cross section of the composite hydroxide. Observe using a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM) Specifically, in a field of view where the low density layer can be distinguished, In the cross section of a secondary particle of the composite hydroxide, the maximum length between any two points on the outer edge of the secondary particle is The diameter of the secondary particles is measured and the value is taken as the particle diameter of the composite hydroxide. The thickness of the main part, low density layer and outer shell at three or more arbitrary positions for one particle is calculated. Measure and calculate the average value.

[0053] The thickness of the low-density layer is determined by the distance from the outer edge of the low-density layer to any point on the cross section of the secondary particle of the composite hydroxide. The distance between the two points that is the shortest from the boundary between the low-density layer and the main part is taken as the length. By dividing the thickness of the low-density layer by the particle size of the composite hydroxide, the particle size of the composite hydroxide can be calculated. The ratio of the thickness of the low-density layer to the particle size of the low-density layer, i.e., the particle size ratio of the low-density layer, is obtained. By performing this on 10 or more complex hydroxides and calculating the average value, the entire sample The low density layer particle size ratio can be calculated.

[0054] If necessary, low-density and high-density layers may be laminated on the main body and outer shell, or near the surface. If structures exist, each structure can be measured in the same way as the low density layer. Cut.

[0055] c) Fine primary particles In the composite hydroxide of the present invention, the fine primary particles that are components of the low-density layer have an average particle size of However, it is preferable that the thickness is 0.01 μm to 0.3 μm, and more preferably 0.1 μm to 0.3 μm. Here, when the average particle size of the fine primary particles is less than 0.01 μm, On the other hand, the average particle size of the fine primary particles may not be sufficient to obtain a sufficient thickness of the dense layer. When the particle size is larger than 0.3 μm, the density difference between the plate-like primary particle portion and the low-density layer is small. During the calcination process for producing the positive electrode active material, the particle surface of the composite hydroxide is calcined. As a result of sintering and densification, the surface of the positive electrode active material may not be sufficiently rough. .

[0056] The shape of such fine primary particles is preferably needle-like. Because the particles have a shape with a certain degree of orientation, when they aggregate, they form a structure with many gaps. This results in a low density layer and a layer consisting of plate-like primary particles. Therefore, the difference in density between the part and the other part can be made sufficiently large.

[0057] The average particle size of the fine primary particles is determined by embedding composite hydroxides in resin etc. After smoothing the part where the particles were embedded using a polisher or other method, can be obtained by observing using a scanning electron microscope (SEM) as follows: First, the maximum outer diameter of 10 or more fine primary particles present in the cross section of one composite oxide is calculated. The diameters of the fine primary particles in the composite hydroxide are measured, and the average value is calculated. Next, the same measurements and calculations were carried out for 10 or more complex hydroxides. Finally, the particle size of the fine primary particles in these composite hydroxides is calculated. By averaging the particle sizes of the particles, the average particle size of the fine primary particles in the entire sample can be calculated. can be done.

[0058] d) Plate-like primary particles The portion other than the low-density layer of the secondary particles of the composite hydroxide of the present invention, i.e., the basic structure The plate-like primary particles that form the main part and outer shell part, or the high density layer and outer shell part, are flat. The average particle size is preferably 0.3 μm to 3 μm, and more preferably 0.4 μm to 1.5 μm. More preferably, the thickness is 0.4 μm to 1.0 μm. When the average particle size of the secondary particles is less than 0.3 μm, the secondary particles are easily sintered during the firing process when preparing the positive electrode active material. The volume shrinkage occurs even at low temperatures, and the difference in the volume shrinkage amount between the low-density layer and the composite is small. As a result of sintering and densification of the hydroxide particle surface, the particle surface of the positive electrode active material becomes sufficiently uneven. On the other hand, when the average particle size of the plate-like primary particles is larger than 3 μm, In the firing step when preparing the positive electrode active material, in order to increase the crystallinity of the positive electrode active material, This requires firing at a higher temperature, which promotes sintering between the composite hydroxide particles and increases the average particle size of the positive electrode active material. It becomes difficult to set the particle size and particle size distribution within a predetermined range. The diameter can be determined in the same manner as for the fine primary particles.

[0059] (1-2) Average particle size of transition metal-containing composite hydroxide The average particle size of the secondary particles constituting the composite hydroxide of the present invention is 1 μm to 15 μm, preferably The average particle size of the positive electrode active material is adjusted to 3 μm to 12 μm, and more preferably 3 μm to 10 μm. The particle size correlates with the average particle size of this composite hydroxide. By setting the average particle size of the positive electrode active material having this composite hydroxide as a precursor, The diameter can be set within a predetermined range.

[0060] In the present invention, the average particle size of the composite hydroxide means the volume-based average particle size (MV). For example, it can be calculated from the volume integrated value measured by a laser light diffraction scattering particle size analyzer. can.

[0061] (1-3) Particle size distribution of transition metal-containing composite hydroxides The composite hydroxide of the present invention has a particle size distribution [(d90-d10) / The value of [average particle size] is 0.65 or less, preferably 0.55 or less, more preferably 0.50 or less. It is adjusted to be lower.

[0062] The particle size distribution of the positive electrode active material is strongly influenced by the composite hydroxide that is its precursor. For example, a composite hydroxide containing many fine particles and coarse particles is used as a precursor to produce a positive electrode active material. When a cathode active material is produced, many fine particles and coarse particles are included in the cathode active material. This allows the secondary battery to maintain its high safety and cycle characteristics while also achieving sufficient output characteristics. Therefore, the particle size distribution of the composite hydroxide, which is the precursor, cannot be improved. If the value of [(d90-d10) / average particle size] is adjusted to 0.65 or less, This narrows the particle size distribution of the positive electrode active material that uses this as a precursor, preventing selective degradation of fine particles. However, it is possible to avoid problems related to safety and cycle characteristics that arise from this. When considering large-scale production, the value of [(d90-d10) / average particle size] of the composite hydroxide It is not possible to produce a powder state with an excessively small particle size from the viewpoint of yield, productivity, or production costs. Therefore, the lower limit of [(d90-d10) / average particle size] is 0 It is preferable to set it to around .25.

[0063] Here, d10 is the number of particles at each particle size of the powder sample, starting from the smallest particle size. The particle size is the particle size at which the cumulative volume is 10% of the total volume of all particles. When the number of particles is accumulated using the same method, the particle whose accumulated volume is 90% of the total volume of all particles is The d10 and d90 mean the average particle diameter of the composite hydroxide, as well as the laser light diffraction It can be determined from the volume integrated value measured with a scattering particle size analyzer.

[0064] (1-4) Composition of transition metal-containing composite hydroxides The composite hydroxide of the present invention is characterized by the particle structure of its secondary particles. The composition of the composite hydroxide of the present invention is not particularly limited, provided that it is represented by 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 M 1 selected from g, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W It is preferable that the composite hydroxide is represented by the formula (one or more added elements). By using a compound of the general formula (B): Li 1+u Ni x Mn y Co z M t O2(- 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, and one or more additive elements selected from W. Therefore, a positive electrode active material that satisfies the above requirements can be easily obtained, and higher battery performance can be achieved.

[0065] In such composite hydroxides, the added element (M) is converted into the transition metal ( It is crystallized with nickel, cobalt and manganese and uniformly dispersed in the composite hydroxide. However, after the crystallization reaction, the outermost surface of the secondary particles that make up the composite hydroxide can be The positive electrode active material may be coated with a compound mainly containing the element (M). In the mixing process, the lithium compound and the additive element (M) are added to the composite hydroxide. It is also possible to mix a compound containing the compound, or these methods may be used in combination. Even when the above method is used, the composite hydroxide finally contains the composition represented by the general formula (A). It is necessary to adjust the content so as to obtain a desired composition including the above.

[0066] In the composite hydroxide represented by the general formula (A), the nickel and manganese constituting it are The composition range of iron, cobalt, and additive element M and its critical significance are as follows: Therefore, the explanation of these matters will be omitted here. Abbreviated.

[0067] 2. Method for producing transition metal-containing composite hydroxide (2-1) Supply aqueous solution In the method for producing a composite hydroxide of the present invention, at least a transition metal, preferably , nickel, nickel and manganese, or nickel, manganese and cobalt-containing raw materials A reaction aqueous solution is formed by supplying an aqueous solution containing an ammonium ion donor. The pH value of the reaction aqueous solution is adjusted to a predetermined range using a pH adjuster, and the crystallization reaction is carried out. , to obtain a composite hydroxide.

[0068] a) Raw material aqueous solution In the present invention, the ratio of the metal elements contained in the raw material aqueous solution is Therefore, the raw material aqueous solution has a composition ratio that is almost equal to the composition of the target composite hydroxide. In response to this, it is necessary to appropriately adjust the content of each metal component. When a composite hydroxide represented by the general formula (A) is to be obtained, the metal element in the raw material aqueous solution The ratio of elements is Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1, 0 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1) However, as mentioned above, the additive element M is introduced in a separate process. In this case, the raw material solution should not contain the additive element M. In the crystal growth process, whether or not an additive element M is added, or whether or not a transition metal or additive element M is included, The ownership ratio can also be changed.

[0069] The transition metal compound for preparing the raw material aqueous solution is not particularly limited, but From the viewpoint of ease of handling, it is preferable to use water-soluble nitrates, sulfates, hydrochlorides, etc. From the viewpoint of raw material costs and preventing contamination with halogen components, it is particularly preferable to use sulfates. stomach.

[0070] In addition, the additive element M (M is Mg, Ca, Al, Ti, V, Cr, Zr) in the composite hydroxide , Nb, Mo, Hf, Ta, W) In the case of the compound for supplying the additional element M, a water-soluble compound is also preferred. For example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, peroxo Ammonium titanate, potassium titanium oxalate, vanadium sulfate, ammonium vanadate um, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate, molybdenum Ammonium sulfate, hafnium sulfate, sodium tantalate, sodium tungstate, Ammonium tungstate and the like can be suitably used.

[0071] The concentration of the raw material aqueous solution is determined based on the total amount of the metal compounds, but is preferably 1 mol / L to 2.6 mol / L, more preferably 1.5 mol / L to 2.2 mol / L. If the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized material per volume of the reactor will be small. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol / L, Because the concentration exceeds the saturation concentration at room temperature, crystals of metal compounds are reprecipitated, clogging pipes, etc. There is a risk.

[0072] The metal compound does not necessarily have to be supplied to the reaction vessel as a raw material aqueous solution. When mixed, metal compounds react to produce compounds other than the target compound. When carrying out a crystallization reaction using the above-mentioned method, the total concentration of the aqueous solution of all metal compounds should be adjusted to fall within the above range. Aqueous solutions of metal compounds were prepared individually, and the respective metal compounds were dissolved in a predetermined amount. In this case, the catalyst may be supplied to the reaction vessel.

[0073] The amount of the raw material aqueous solution to be supplied is determined based on the amount of the product in the reaction aqueous solution at the end of the particle growth step. The concentration of the substance is preferably 30 g / L to 200 g / L, more preferably 80 g / L to 150 If the product concentration is less than 30 g / L, the primary particles will not aggregate sufficiently. On the other hand, if the concentration exceeds 200 g / L, the stirring of the reaction solution in the reaction tank may become Insufficient stirring can lead to uneven aggregation conditions, which can cause uneven particle growth. .

[0074] b) Alkaline aqueous solution The alkaline aqueous solution used to adjust the pH value of the reaction aqueous solution is not particularly limited, and may be water. Common alkali metal hydroxide solutions such as sodium hydroxide and potassium hydroxide can be used. It is also possible to add the alkali metal hydroxide in a solid state directly to the reaction aqueous solution. However, it is preferable to add it as an aqueous solution from the viewpoint of ease of pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% by mass to 50% by mass. The concentration of the aqueous alkali metal solution is more preferably 20% by mass to 30% by mass. By setting the temperature in this range, the amount of solvent supplied to the reaction system, i.e., the amount of water, can be reduced, It is possible to prevent a local increase in pH value depending on the addition position in the reaction vessel, so that the particle size It becomes possible to efficiently obtain composite hydroxides with a narrow distribution.

[0075] The method of supplying the alkaline aqueous solution is to prevent the pH value of the reaction solution from becoming locally high. There are no particular limitations as long as the temperature is maintained within a predetermined range. The mixture may be supplied by a pump capable of controlling the flow rate, such as a metering pump, while stirring thoroughly.

[0076] c) an aqueous solution containing an ammonium ion donor The aqueous solution containing the ammonium ion donor also contains ammonium ions in the reaction aqueous solution. There are no particular limitations as long as the ammonia can be supplied. For example, ammonia water or Ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride Any aqueous solution can be used.

[0077] When aqueous ammonia is used as the ammonium ion donor, its concentration is preferably The content is preferably 20% by mass to 30% by mass, and more preferably 22% by mass to 28% by mass. By setting the concentration of the ammonium hydroxide in this range, the amount of ammonium hydroxide released from the reaction tank due to evaporation, etc. Ammonia loss can be minimized, improving production efficiency. This becomes:

[0078] The method for supplying the aqueous solution containing the ammonium ion donor is the same as that for the alkaline aqueous solution. The liquid can be supplied by a pump capable of controlling the flow rate.

[0079] (2-2) Crystallization reaction In particular, in the method for producing a composite hydroxide of the present invention, the crystallization reaction is carried out mainly in the manner of nucleation. The crystallization reaction is clearly divided into two stages: the nucleation process and the particle growth process, where particle growth mainly occurs. The crystallization reaction conditions in each process are adjusted, and in the particle growth process, While continuing to supply the raw material aqueous solution, the reaction atmosphere, i.e., the atmosphere inside the reaction aqueous solution, is The atmosphere is switched between a non-oxidizing atmosphere and an oxidizing atmosphere as needed. When switching the gas, the atmospheric gas, i.e., the oxidizing gas or the inert gas, is introduced into the reaction solution. The reactive gas is fed into the reaction system, and the gas is brought into direct contact with the aqueous reaction solution, allowing the reaction atmosphere to be switched quickly. As a result, the above particle structure, i.e., the low density layer and the outer shell portion are formed on the surface of the secondary particle. The grain structure is a stack of layers, or a stack of a first low-density layer, a high-density layer, a second low-density layer and an outer shell. It is possible to efficiently obtain a composite hydroxide having a layered particle structure, average particle size, and particle size distribution. It is possible.

[0080] [Nucleation process] In the nucleation process, first, a transition metal compound, which is the raw material for the composite hydroxide, is dissolved in water. At the same time, an alkaline aqueous solution and an ammonium ion solution are added to the reaction vessel. The aqueous solution containing the ion supplying agent is mixed with the raw aqueous solution, and the temperature is measured at 25°C. The pH value to be determined is 12.0 to 14.0, and the ammonium ion concentration is 3 g / L to 25 g / L. Prepare a reaction solution with a pH value of 1000. The ammonium ion concentration can be measured using an ion meter.

[0081] Next, the raw material aqueous solution is supplied to the reaction solution while stirring it. In the nucleation step, an aqueous reaction solution is formed. The pH value of this aqueous reaction solution is within the above range. Therefore, in the nucleation process, nuclei do not grow much and nucleation occurs preferentially. In the nucleation process, the pH value and ammonium ion concentration of the reaction solution change with the generation of nuclei. The concentration of ammonium hydroxide changes, so an alkaline solution and an ammonia solution are supplied at the appropriate time to control the reaction. The pH value of the aqueous solution is in the range of pH 12.0 to 14.0 at a liquid temperature of 25°C. The concentration of ON is controlled to be maintained in the range of 3 g / L to 25 g / L.

[0082] During the nucleation step, an inert gas is passed through the reaction solution in the reaction vessel to maintain the reaction atmosphere. The atmosphere in the reaction vessel is adjusted to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. The method of supplying the reaction solution to the reaction solution is to supply it to the space in the reaction vessel that is in contact with the reaction solution, or to spray it. or by directly supplying the solution into the reaction solution using a trachea or the like. However, the reaction atmosphere in the nucleation process is adjusted by supplying an inert gas into the reaction vessel. That's enough.

[0083] In the nucleation step, the reaction solution contains a raw material aqueous solution, an alkaline aqueous solution, and ammonium By supplying an aqueous solution containing an ion donor, the nucleation reaction continues continuously, and the reaction The nucleation step is terminated when a predetermined amount of nuclei are generated in the reaction solution.

[0084] In this case, the amount of nuclei produced is determined based on the amount of metal compounds contained in the raw material aqueous solution supplied to the reaction aqueous solution. The amount of nuclei produced in the nucleation step is not particularly limited, but it can be judged from the particle size. To obtain a composite hydroxide with a narrow distribution, it is necessary to supply the hydroxide through the nucleation process and the particle growth process. The concentration of the metal element in the metal compound contained in the raw aqueous solution is 0.1 atomic % to 2 atomic %. It is preferable that the content of the nuclei is 0.1 atomic % to 1.5 atomic %. The reaction time in the synthesis step is usually about 1 to 5 minutes.

[0085] [Particle growth process] After the nucleation process is completed, the pH value of the aqueous solution for nucleation in the reaction tank is set to 10.5 at a liquid temperature of 25°C. The pH value is adjusted to 12.0 to form the reaction solution for the particle growth process. Although this can be adjusted by stopping the supply of the aqueous solution, it is difficult to obtain a composite hydroxide with a narrow particle size distribution. In order to achieve this, it is preferable to stop the supply of all aqueous solutions and then adjust the pH value. Specifically, after stopping the supply of all aqueous solutions, the reaction aqueous solution is added with the raw material aqueous solution. The pH value is adjusted by supplying an inorganic acid having the same group as the metal compound used in the preparation. It is preferable.

[0086] Next, while stirring this reaction aqueous solution, the supply of the raw material aqueous solution is resumed. Since the pH value of the aqueous solution is within the above range, new nuclei are hardly generated and the growth of nuclei proceeds. The crystallization reaction is continued until the secondary particles of the composite hydroxide reach a predetermined particle size. During the growth process, the pH value and ammonium ion concentration of the reaction solution change with particle growth. The pH and pH values change, so alkaline and ammonia solutions are supplied at appropriate times. It is necessary to maintain the concentration of ammonium ions within the above range. The total reaction time is usually about 1 hour to 6 hours.

[0087] In particular, in the method for producing a composite hydroxide of the present invention, in the initial and middle stages of the particle growth process, The non-oxidizing atmosphere is continued from the nucleation step through the process, and the non-oxidizing atmosphere is maintained. Then, in the later stage of the particle growth process, the raw material aqueous solution is continuously supplied, and the raw material aqueous solution is added to the reaction aqueous solution. By directly supplying oxidizing gas, the oxygen concentration can be increased from a non-oxidizing atmosphere to an atmosphere with an oxygen concentration of more than 5% by volume. After switching to an oxidizing atmosphere, the raw material aqueous solution was again continuously supplied, and the reaction solution was By supplying inert gas directly to the It is characterized by performing atmosphere control.

[0088] Here, the initial and middle stages of the particle growth process, i.e., in a non-oxidizing atmosphere The time for forming the main part of the composite hydroxide is 70% to 100% of the entire period of the particle growth process. 90% of the time, preferably 75% to 90% of the time, more preferably 80% to In the present invention, the basic structure of the obtained positive electrode active material is a solid structure. Therefore, the larger the main part, the greater the total amount of electrochemical reaction per volume. This is preferable from the viewpoint of ensuring sufficient product energy density (battery capacity per unit volume). Therefore, sufficient time must be secured in the initial and middle stages of the particle growth process to allow the secondary particles to grow. On the other hand, if the time for the latter part of the particle growth step is too short, the secondary particles obtained may be Therefore, it becomes impossible to obtain a complex hydroxide structure that can sufficiently improve the surface of the silicon.

[0089] Therefore, in the method for producing a composite hydroxide of the present invention, the latter part of the particle growth step is preferably Preferably, the time is in the range of 10% to 30%, more preferably, the time is in the range of 10% to 25%, and even more preferably, More preferably, the time is set to a range of 10% to 20%, and the reaction occurs in the latter stage of this particle growth process. By temporarily and quickly switching the reaction atmosphere from a non-oxidizing atmosphere to an oxidizing atmosphere, This forms a low-density layer in part of the vicinity of the surface of the secondary particles made of plate-like primary particles. When the thickness layer is formed in the initial and middle stages, the secondary particles in the obtained positive electrode active material However, it may have a structure other than a solid structure.

[0090] In addition, the reaction atmosphere in the later stage of the particle growth process is changed to a non-oxidizing atmosphere. From the point of switching from the atmosphere to the oxidizing atmosphere, the temperature is preferably 0. The time is in the range of 5 to 20%, more preferably in the range of 3 to 15%, and even more preferably The oxidizing atmosphere is maintained for a period of time ranging from 4% to 10% to form a low-density layer consisting of fine primary particles. Then, the atmosphere is quickly switched from an oxidizing atmosphere to a non-oxidizing atmosphere. The surface of the secondary particle is formed by aggregation of plate-like primary particles (outer shell). The chemical atmosphere is preferably maintained until the end of the particle growth process, i.e., for the entire particle growth process. or in the range of 3% to 20% of the time, more preferably in the range of 3% to 18% of the time, and even more preferably Preferably, it is maintained for a period of time in the range of 4% to 10%.

[0091] The reaction atmosphere for this crystallization reaction is switched by supplying an inert gas or an oxidizing gas to the reaction vessel. It is preferable to carry out the reaction quickly by directly supplying the reactant to the aqueous solution. In the present invention, the reaction atmosphere is switched in the later stage of the particle growth process using an air diffuser or the like. By supplying the atmospheric gas directly into the reaction solution, the reaction atmosphere can be switched in a short time. This makes it possible to do so.

[0092] In the method for producing such a composite hydroxide, the nucleation step and the particle growth step are Therefore, the metal ions in the reaction solution are precipitated as solid nuclei or primary particles. Therefore, the ratio of the liquid component to the amount of metal ions in the reaction solution increases. In both cases, the metal ion concentration in the reaction aqueous solution decreases, particularly in the particle growth step. The growth of the complex hydroxides may stagnate. In other words, in order to suppress the decrease in the apparent metal ion concentration, the particle growth process is started after the nucleation process is completed. During this process, it is preferable to discharge a part of the liquid component of the reaction aqueous solution to the outside of the reaction vessel. Specifically, a raw material aqueous solution, an alkaline aqueous solution, and water containing an ammonium ion donor The supply of the solution to the reaction vessel and the stirring of the reaction solution were temporarily stopped, and the solid components in the reaction solution, That is, the composite hydroxide is allowed to settle and only the supernatant of the reaction aqueous solution is discharged from the reaction vessel. By such an operation, the metal ion concentration in the reaction aqueous solution can be maintained. This prevents particle growth from stagnating and favorably regulates the particle size distribution of the resulting composite hydroxide. Not only can the density be controlled within an appropriate range, but the density of the powder can also be improved. Cut.

[0093] [Particle size control of composite hydroxides] The particle size of the composite hydroxide obtained as described above is determined by the nucleation step and particle growth step. During this time, the pH value of the reaction solution in each process and the amount of raw material solution supplied are controlled. For example, the nucleation step can be carried out at a high pH value or When the time for which the reaction is carried out is extended or the metal concentration of the raw solution is increased, the nucleation The amount of nuclei generated in the synthesis process increases, and the composite hydroxide with a relatively small particle size is obtained after the particle growth process. On the other hand, it is possible to suppress the amount of nuclei generated in the nucleation process or to obtain a particle size. By extending the time for the seed growth process sufficiently, it is possible to obtain a composite hydroxide with a large particle size. can.

[0094] [Another embodiment of the crystallization reaction] In the method for producing a composite hydroxide of the present invention, a p suitable for the particle growth step is added separately from the reaction aqueous solution. A component-adjusting aqueous solution adjusted to the H value and ammonium ion concentration was prepared. The aqueous solution to be used is a reaction aqueous solution after the nucleation step, preferably a solution obtained from the reaction aqueous solution after the nucleation step. The part of the body components removed is added and mixed, and this is used as a reaction solution to grow particles. The process may be carried out.

[0095] In this case, the nucleation process and the particle growth process can be separated more reliably. The reaction solution in each step can be controlled to an optimum state. The pH value of the reaction solution can be controlled within the optimum range from the start of the process, In this case, the particle size distribution of the composite hydroxide can be made narrower.

[0096] (2-3) pH value In the method for producing a composite hydroxide of the present invention, the pH value at a liquid temperature of 25°C is set to 1.0. When performing the process, the range is 12.0 to 14.0, and when performing the particle growth process, the range is 10.5 It is necessary to control the temperature within the range of 1.0 to 12.0. The amount of fluctuation in the pH value during the reaction is preferably controlled within a range of ±0.2 relative to the set value. When the pH value fluctuates significantly, the amount of nuclei generated in the nucleation process and the amount of nuclei generated in the particle growth process are different. Since the degree of particle growth is not constant, it is difficult to obtain a composite hydroxide with a narrow particle size distribution. It becomes difficult.

[0097] a) pH value of the nucleation process In the nucleation process, the pH value of the reaction solution is set to 12.0 to 14.0 at a liquid temperature of 25°C. 0, preferably 12.3 to 13.5, more preferably greater than 12.5 and equal to or less than 13.3 This will suppress the growth of nuclei in the reaction solution and prevent nucleation. It is possible to prioritize only the formation of nuclei, and the nuclei formed in this process are of uniform size, and When the pH value is less than 12.0, nucleation occurs and the particle size distribution becomes narrow. The growth of nuclei also progresses, so the particle size of the resulting composite hydroxide becomes non-uniform and the particle size distribution becomes broad. On the other hand, if the pH value is higher than 14.0, the nuclei that are generated become too fine, The problem of gelling of the reaction solution occurs.

[0098] b) pH value during particle growth In the particle growth process, the pH value of the reaction solution is set to 10.5 to 12 at a liquid temperature of 25°C. 0.0, preferably 11.0 to 12.0, more preferably 11.5 to 12.0. This suppresses the generation of new nuclei and prioritizes grain growth. This makes it possible to obtain a composite hydroxide that is homogeneous and has 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 metal ions The solubility of the compound increases, which not only slows down the crystallization reaction but also increases the amount of the compound remaining in the reaction solution. The amount of metal ions increases, and productivity decreases. The amount of nucleation during the particle growth process increases, and the particle size of the resulting composite hydroxide becomes non-uniform. The intensity distribution becomes wider.

[0099] In addition, in both processes, the fluctuation of the pH value during the crystallization reaction was within 0. It is preferable to control the pH value within a range of 2. If the pH value fluctuates greatly, The amount of nucleation in the step and the degree of particle growth in the step of particle growth are not constant, so the particle size It becomes difficult to obtain a composite hydroxide with a narrow distribution.

[0100] When the pH value of the reaction aqueous solution is 12.0 at a liquid temperature of 25°C, nucleation and nucleation The presence or absence of nuclei in the reaction solution determines the nucleation process or particle size distribution. For example, the pH value of the nucleation step can be set to 12 After the pH value is increased to above 0.0 to allow for a large amount of nucleation, the particle growth process is carried out at a pH of 12.0. Since there are many nuclei in the reaction solution, particle growth occurs first, and the particles On the other hand, if the pH value of the nucleation process is 12.0, a composite hydroxide with a narrow diameter distribution can be obtained. Then, since there are no nuclei to grow in the reaction solution, nucleation occurs first, and particle formation does not occur. By reducing the pH value of the long-term process to less than 12.0, the generated nuclei grow and produce good complex hydroxy acids. You can obtain a compound.

[0101] In either case, the pH value in the particle growth step is controlled to be lower than the pH value in the nucleation step. To separate nucleation and particle growth more clearly, the pH of the particle growth process should be controlled. The pH value is preferably at least 0.5 lower than the pH value in the nucleation step, and more preferably at least 1.0 lower. It is more preferable to do so.

[0102] (2-4) Reaction atmosphere In the method for producing a composite hydroxide of the present invention, the pH value is controlled in each step. In the present invention, the nucleation process and particle growth process are carried out in a controlled manner. By maintaining a non-oxidizing reaction atmosphere for most of the process, the generated nuclei Therefore, the composite hydroxide of the present invention basically grows to become a plate-like primary particle. The entire particle is formed by agglomeration of plate-like primary particles. In the later stage of the long-term process, the reaction atmosphere is temporarily switched to an oxidizing atmosphere, The particles grow into fine primary particles, and the aggregation of these fine primary particles results in the formation of secondary particles. , forming a low density layer or a low density layer near the surface.

[0103] a) Non-oxidizing atmosphere In the manufacturing method of the present invention, basically, from the nucleation step, two compounds constituting a composite hydroxide are produced. The reaction atmosphere in most stages of forming the structure of the primary particles is controlled to a non-oxidizing atmosphere. Specifically, the oxygen concentration in the reaction atmosphere is 5% by volume or less, preferably 2% by volume or less. Inert gases such as argon and nitrogen, or Alternatively, it may be necessary to use a mixture of an oxidizing gas such as oxygen and an inert gas. This allows the oxygen concentration in the reaction atmosphere to be sufficiently reduced to suppress unnecessary oxidation while promoting nucleation. The nuclei generated in the synthesis process can be grown to a certain extent, so the secondary formation of composite hydroxides can be achieved. The basic structure of the particles is plate-like with an average particle size in the range of 0.3 μm to 3 μm and a narrow particle size distribution. It can be configured by a structure in which secondary particles are aggregated.

[0104] b) Oxidizing atmosphere On the other hand, in the stage of forming the low-density layer of composite hydroxide, the reaction atmosphere is controlled to be an oxidizing atmosphere. Specifically, the oxygen concentration in the reaction atmosphere is preferably set to more than 5% by volume. The oxygen concentration is preferably 10% by volume or more, and more preferably air (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere within this range, the reaction atmosphere By increasing the oxygen concentration in the The average particle size is in the range of 0.01 μm to 0.3 μm, so the basic skeleton of the composite hydroxide is formed. The plate-like primary particles are aggregated to form a particle (main part and outer shell part), which has a sufficient density difference from the particle (main part and outer shell part). A low density layer is formed.

[0105] Although there is no particular upper limit for the oxygen concentration in the reaction atmosphere at this stage, If the oxygen concentration is too high, the average particle size of the fine primary particles will be less than 0.01 μm, resulting in low density. The layer may not be thick enough. Therefore, the oxygen concentration should be 30% by volume or less. In addition, the part formed by aggregation of plate-like primary particles (main part and outer shell) is preferably In order to clarify the difference between the high-density layer and the low-density layer, the difference in oxygen concentration before and after the atmosphere change was measured. It is preferable that the amount of the hydroxybenzoate is 3% by volume or more, and more preferably 10% by volume or more.

[0106] c) Timing of atmospheric control In the particle growth process, the above-mentioned atmosphere control is performed to grow composite hydroxide having the desired particle structure. It needs to be done at the right time so that things can be formed.

[0107] In the method for producing a composite hydroxide of the present invention, an atmospheric gas is directly supplied into the reaction aqueous solution. In this case, the amount of dissolved oxygen in the reaction atmosphere, i.e., the reaction field, is The change occurs without delay in response to changes in oxygen concentration. Therefore, the atmosphere switching time is This can be confirmed by measuring the oxygen concentration in the reaction vessel. When supplying atmospheric gas to the space in contact with the reaction solution, the amount of dissolved oxygen in the reaction solution must be There is a time lag between the change in temperature and the change in oxygen concentration in the reactor. Until the amount of dissolved oxygen in the reaction solution is determined, it is not possible to confirm the correct value. Similarly, it is possible to confirm the stability of the oxygen concentration in the reactor by measuring it. In either case, the time required to switch the atmosphere was determined based on the oxygen concentration in the reaction vessel. The time required for switching the amount of dissolved oxygen in the reaction aqueous solution, which is the reaction field, can be used as the reaction time. The reaction atmosphere can be appropriately controlled over time based on the oxygen concentration in the reaction vessel.

[0108] The time required for switching the atmosphere is approximately 0.4% to 2% of the entire particle growth process. This time is the time required to change from a non-oxidizing atmosphere to an oxidizing atmosphere, or from an oxidizing atmosphere to a non-oxidizing atmosphere. Therefore, the time for switching the atmosphere is strictly determined independently. However, it is usually necessary to control the temperature in a non-oxidizing or oxidizing atmosphere after the atmosphere change. It is sufficient to include it in the time spent in a chemical atmosphere.

[0109] d) How to switch Conventional methods for switching the reaction atmosphere during the crystallization process include the use of a reactor, more specifically, To do this, an atmospheric gas is passed through the space in contact with the reaction solution in the reaction vessel, or an atmospheric gas is passed through the reaction solution. A conduit with a diameter of approximately 1 mm to 50 mm is inserted, and the reaction solution is bubbled with atmospheric gas. In these methods, the dissolved oxygen in the reaction solution is It is difficult to change the atmosphere in a short time, as in the method for producing a composite hydroxide of the present invention. In addition, during the changeover from the non-oxidizing atmosphere to the oxidizing atmosphere in the particle growth process, At this time, it is necessary to stop the supply of the raw aqueous solution. If there is no granularity, a gentle density gradient will be formed inside the composite hydroxide, and the low-density layer will not be sufficiently It is thought that the thickness cannot be increased.

[0110] In contrast, in the method for producing a composite hydroxide of the present invention, the non-oxidizing During the changeover from the atmosphere to the oxidizing atmosphere, the raw material aqueous solution is continuously supplied and the reaction aqueous solution is It is preferable to switch the atmosphere by directly supplying the atmospheric gas into the liquid. This eliminates the need to stop the supply of raw material aqueous solutions when switching the reaction atmosphere, improving production efficiency. This will enable us to improve the efficiency.

[0111] In addition, the time required for switching the reaction atmosphere by directly supplying the atmospheric gas into the reaction aqueous solution is The time, i.e., the time for switching the atmosphere, is set to a value that allows a composite hydroxide having the above structure to be obtained. However, from the viewpoint of facilitating the control of particle structure, 0.4% to 2% of the reaction time in the atmosphere and the entire particle growth process time It is preferable that the content is in the range of 0.4% to 1%.

[0112] Here, the means for supplying the atmospheric gas into the reaction aqueous solution is to supply the atmospheric gas to the entire reaction aqueous solution. Such a means would be, for example, a means that can directly supply It is preferable to use an air pipe. The air pipe is made up of a conduit with many fine holes on its surface. This allows the release of many fine bubbles into the liquid, which improves the contact between the reaction solution and the bubbles. The large area makes it easy to control the switching time according to the amount of atmospheric gas supplied. Cut.

[0113] Such diffusers are made of ceramic, which has excellent chemical resistance in high pH environments. It is preferable to use a diffuser with a smaller hole diameter. Therefore, it is possible to switch the reaction atmosphere in a short time. In this case, it is preferable to use an aeration tube with a pore size of 100 μm or less, and It is more preferable to use

[0114] The method of supplying the atmospheric gas that can be suitably applied to the present invention is a method of supplying the atmospheric gas by generating fine bubbles as described above. Any means can be used as long as it can generate bubbles and increase the contact area between the reaction aqueous solution and the bubbles. Therefore, even if it is a device other than an aeration tube, bubbles can be generated from the holes in the conduit and applied to the agitator blades, etc. Therefore, by using a device that can finely crush and disperse the bubbles, The atmosphere can be switched with high efficiency.

[0115] (2-5) Ammonium ion concentration The ammonium ion concentration in the reaction aqueous solution is preferably 3 g / L to 25 g / L, more preferably Preferably, the concentration is kept constant within the range of 5 g / L to 20 g / L. Ammonium ions act as complexing agents, so ammonium ions at concentrations below 3 g / L In this case, the solubility of metal ions cannot be kept constant, and the reaction solution tends to gel. This makes it difficult to obtain a composite hydroxide with a uniform shape and particle size. If the metal ion concentration exceeds 25 g / L, the solubility of the metal ions becomes too high, resulting in a reaction. The amount of metal ions remaining in the reaction solution increases, causing deviations in the composition of the composite hydroxide. .

[0116] If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ions will also fluctuate. Therefore, the nucleation process and the particle growth process are not performed. During this time, it is preferable to control the fluctuation of the ammonium ion concentration within a certain range. It is preferable to control the fluctuation of the concentration to within 5 g / L from the set value.

[0117] (2-6) Reaction temperature The temperature of the reaction solution, i.e., the reaction temperature of the crystallization reaction, is maintained between the nucleation step and the particle growth step. It is necessary to control the temperature to preferably 20°C or higher, more preferably in the range of 20°C to 60°C. If the reaction temperature is lower than 20°C, the solubility of the reaction solution will be low, which will result in a decrease in nucleation. This makes it difficult to control the average particle size and particle size distribution of the resulting composite hydroxide. There is no particular upper limit to the reaction temperature, but if it exceeds 60°C, ammonia This promotes the evaporation of ammonium ions and serves to control the concentration of ammonium ions in the reaction solution within a certain range. The amount of aqueous solution containing the ammonium ion donor to be supplied increases, which increases production costs. It ends up happening.

[0118] (2-7) Coating process In the method for producing a composite hydroxide of the present invention, the raw material aqueous solution is used, particularly in the particle growth step. By adding a compound containing the additive element M to the raw material aqueous solution, the additive element M is A composite hydroxide in which element M is uniformly dispersed can be obtained. In order to obtain the effect of adding the additive element M, the compound is added after the particle growth process. It is preferable to carry out a coating step in which the surface of the hydroxide particles is coated with a compound containing the additional element M. stomach.

[0119] The coating method involves uniformly coating the composite hydroxide with a compound containing the additive element M. As far as possible, there is no particular limitation. For example, a composite hydroxide is made into a slurry and the After controlling the pH value within a predetermined range, the coating solution containing the compound containing the additive element M is By adding the element M and precipitating a compound containing the element M on the surface of the composite hydroxide particles, A composite hydroxide uniformly coated with a compound containing element M can be obtained. Instead of the coating solution, a composite hydroxide was prepared by slurrying an alkoxide solution of the added element M. Alternatively, the compound containing the additive element M may be added to the mixture without forming the composite hydroxide into a slurry. Alternatively, the coating may be performed by spraying an aqueous solution or slurry containing the compound dissolved therein onto the substrate and then drying the same. Furthermore, a method of spray-drying a slurry in which the composite hydroxide and the compound containing the added element M are suspended is also available. or by mixing the composite hydroxide with a compound containing the added element M by a solid phase method. It can also be coated by a method.

[0120] In addition, when the particle surface of the composite hydroxide is coated with the added element M, the composite hydroxide after coating The raw material aqueous solution and the coating solution are adjusted so that the composition of the product matches the composition of the target composite hydroxide. It is necessary to appropriately adjust the composition of the aqueous solution. In the heat treatment step of (2), the heat treatment may be performed on the heat-treated particles after the composite hydroxide is heat-treated. .

[0121] (2-8) Manufacturing equipment The crystallizer for producing the composite hydroxide of the present invention, i.e., the reaction tank, is provided with an atmosphere such as an aeration tube. The reaction atmosphere can be switched by supplying the ambient gas directly into the reaction vessel. In the practice of the present invention, the crystallization reaction is completed. It is particularly preferred to use a batch crystallizer in which the precipitated product is not recovered until the crystallization is complete. In the case of such a crystallizer, a continuous crystallizer that recovers the product by the overflow method is used. Unlike other systems, growing particles are not collected at the same time as the overflow liquid, so the particles It is possible to precisely obtain a composite hydroxide having a narrow molecular weight distribution. The manufacturing method requires proper control of the reaction atmosphere during the crystallization reaction, so a closed It is particularly preferred to use a crystallizer.

[0122] 3.Cathode active material for non-aqueous electrolyte secondary batteries (3-1) Particle structure of positive electrode active material As shown in FIG. 2, the positive electrode active material of the present invention is a secondary active material formed by agglomeration of a plurality of primary particles. It consists of particles with a tap density of 1.5 g / cm 3 The above is the actual measurement ratio table of the secondary particles The area is the geometric surface area of the secondary particle when it is assumed to be a perfect sphere. The surface roughness index value, which is the value obtained by dividing the surface roughness index by the surface roughness index, is in the range of 3.6 to 10. There are.

[0123] Specifically, when the composite hydroxide is baked, the plate-like primary particles that make up the composite hydroxide aggregate. The part formed by the above (main part and outer shell part, or main part, high density layer and During this process, the area near the surface (between the main part and the outer shell, or between the main part and the high temperature part) shrinks due to sintering. The low-density layer (between the high-density layer or the high-density layer and the outer shell) is made up of gaps formed by fine primary particles. Because of the structure with many gaps, sintering starts from the low temperature region, and the sintering progresses slowly in the surrounding area. The secondary particles shrink toward the high density area composed of thin plate-like primary particles, creating a hollow structure. As the body shrinks during sintering, the outer surface (shell) of the hollow structure pushes the hollow structure. The secondary particles shrink and collapse, forming irregularities on their surfaces due to this collapse.

[0124] In the positive electrode active material having such a particle structure, there are no voids inside the particles, and the Since the secondary particles are essentially solid, the total amount of electrochemical reaction per volume is increased, It is possible to ensure sufficient volumetric energy density (battery capacity per unit volume). On the other hand, it is possible to increase the reaction area between the secondary particles and the electrolyte on the surface of the secondary particles compared to conventional methods. The unevenness allows for lithium intercalation without reducing the tap density. Therefore, in a secondary battery using this positive electrode active material, The battery capacity and cycle life are similar to those of conventional solid-structure positive electrode active materials with small particle size and narrow particle size distribution. While maintaining the characteristics, the output characteristics can be further improved by reducing the positive electrode resistance. .

[0125] Furthermore, from the viewpoint of ease of insertion and desorption of lithium, the crystalline structure is preferably a hexagonal system. It is preferable that the crystal structure has a layered structure.

[0126] (3-2) Average particle size The average particle size of the secondary particles constituting the positive electrode active material obtained by the method for producing a positive electrode active material of the present invention The diameter is 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably 3 μm to 10 μm. If the average particle size of the positive electrode active material is in this range, If it is possible to increase the battery capacity per unit volume of a secondary battery using this positive electrode active material, In addition, safety and output characteristics can be improved. If the average particle size is less than 1 μm, the filling efficiency of the positive electrode active material decreases, and the battery capacity per unit volume decreases. On the other hand, when the average particle size of the positive electrode active material is larger than 15 μm, The contact surface with the electrolyte is reduced, and the reaction area of the positive electrode active material is reduced, improving output characteristics. It becomes difficult to do so.

[0127] The average particle size of the positive electrode active material is the volume-based average particle size, as in the case of the composite hydroxide. This refers to particle size (MV), for example, the volume integrated value measured by a laser light diffraction / scattering particle size analyzer. It can be found from

[0128] (3-3) Particle size distribution The particle size distribution of the secondary particles constituting the positive electrode active material obtained by the method for producing the positive electrode active material of the present invention The value of [(d90-d10) / average particle size], which is an index showing the spread of the fabric, is 0.70 or less. Preferably it is 0.60 or less, more preferably 0.55 or less, and the particle size distribution is extremely narrow. This positive electrode active material has a low ratio of fine particles and coarse particles. The secondary battery used has excellent safety, cycle characteristics and output characteristics.

[0129] On the other hand, when the value of [(d90-d10) / average particle size] exceeds 0.70, the positive electrode activity The proportion of fine particles and coarse particles in the material increases. For example, in the case of a positive electrode active material with a high proportion of fine particles, In secondary batteries using materials, the secondary battery is prone to heat generation due to local reactions of fine particles. Not only does this decrease safety, but selective deterioration of fine particles can also lead to cycle-specific Furthermore, in secondary batteries using positive electrode active materials with a high proportion of coarse particles, , the reaction area between the electrolyte and the positive electrode active material cannot be secured sufficiently, resulting in poor output characteristics. This becomes:

[0130] On the other hand, when considering industrial-scale production, the particle size distribution of the positive electrode active material, [(d Creating a powder state with an excessively small value of [(90-d10) / average particle size] will result in poor yield and productivity. , or it is not realistic from the viewpoint of production cost. Therefore, [(d90-d10) The lower limit of [average particle diameter / average particle diameter] is preferably about 0.25.

[0131] The index showing the particle size distribution of the positive electrode active material [(d90-d10) / average particle size] is The meaning of d10 and d90 in the above and how to calculate them are Since they are similar, the explanation will be omitted here.

[0132] (3-4) Specific surface area The positive electrode active material obtained by the method for producing a positive electrode active material of the present invention has a specific surface area of 0.7 m 2 / g~3.0m 2 / g, and 1.0m 2 / g~2.0m 2 / g The positive electrode active material having a specific surface area in this range has a contact area with the electrolyte. This makes it possible to significantly improve the output characteristics of secondary batteries that use this material. The specific surface area of the positive electrode active material is 0.7m 2 When the value is less than / g, when a secondary battery is configured, However, it is difficult to secure a reaction area with the electrolyte, making it difficult to sufficiently improve the output characteristics. On the other hand, if the specific surface area of the positive electrode active material is 3.0 m 2 When it is larger than / g, the The reactivity may become too high, resulting in reduced thermal stability.

[0133] Here, the specific surface area of the positive electrode active material is measured, for example, by the BET method using nitrogen gas adsorption. It is possible.

[0134] (3-5) Tap density Increasing the capacity of secondary batteries to extend the usage time of portable electronic devices and the driving range of electric vehicles On the other hand, the thickness of the electrodes in secondary batteries is important in terms of packing and power supply. Due to the problem of low electrical conductivity, it is required to have a thickness of about several micrometers. Not only do we use high-capacity cathode active materials, but we also increase the sphericity of the secondary particles. It is necessary to improve the filling property of the secondary battery and increase the capacity of the secondary battery as a whole.

[0135] From this viewpoint, the positive electrode active material of the present invention has a packing property (a secondary particle constituting the positive electrode active material). The tap density, which is an index of the sphericity of the particles, is 1.5 g / cm 3 or more, 1.6 g / cm 3 It is preferable that the density is 1.8 g / cm or more. 3 More preferably, it is 2.0 or more. g / cm 3 It is more preferable that the tap density is 1.5 g / cm or more. 3 When less than However, the filling property is low, and the battery capacity of the entire secondary battery may not be improved sufficiently. On the other hand, the upper limit of the tap density is not particularly limited, but under normal manufacturing conditions The upper limit is 3.0 g / cm 3 It will be about that amount.

[0136] Here, the tap density is the density of a sample taken in a container based on JIS Z 2512:2012. The bulk density of the sample powder after tapping it 100 times is measured using a shaking specific gravity measuring instrument. It can be determined.

[0137] (3-6) Surface roughness index The positive electrode active material of the present invention has a structure in which the particle surfaces of the secondary particles constituting the positive electrode active material are larger than those of the conventional structure. In the present invention, the irregularities on the particle surface of the positive electrode active material are The degree of shape, i.e., the roughness of the particle surface caused by the uneven shape, can be quantitatively evaluated. The surface roughness index of the surface of the secondary particles is used to evaluate and judge the surface of this surface. The roughness index is defined as shown in formula (1). That is, the surface roughness index is the surface roughness of the positive electrode active material. It is defined as the specific surface area of the positive electrode active material normalized by the particle size of the material, and is measured by the BET method. It is the value obtained by dividing the specific surface area by the geometric surface area when the particle is assumed to be a perfect sphere.

[0138] In formula (1), SSA BET means the specific surface area of the particles measured by the BET method, and the unit is m2 / g. Also, SSA SPHE As shown in equation (2), assuming the particle is a perfect sphere, The unit is m2 / g. Particle radius of secondary particles of the substance, D R is the true density of the positive electrode active material. The true density can be measured by a true density measuring device using a vapor adsorption method or a true density measuring device using a vapor adsorption method.

[0139]

number

[0140]

number

[0141] In the positive electrode active material of the present invention, the above surface roughness index is in the range of 3.6 to 10, preferably 3. The surface roughness index is preferably in the range of 6 to 8, and more preferably in the range of 3.6 to 6. As a result, the positive electrode active material has more irregularities on the particle surface than particles with a normal structure. The specific surface area is large, which increases the reaction area with the electrolyte and significantly reduces the positive electrode resistance. Furthermore, since the tap density is high, the packing density in the battery container is also high. When used as a battery positive electrode, it has a high volumetric energy density and excellent output characteristics. On the other hand, if the surface roughness index is less than 3.6, the surface of the secondary particles and the electrolyte and The contact area with the conductive additive is not large enough, and the positive electrode resistance is not reduced sufficiently. stomach.

[0142] In the present invention, the upper limit of the surface roughness index is limited by the structure of the secondary particles. In other words, if the surface roughness index becomes too large, the unevenness of the particle surface becomes excessively large. , the gaps between particles become larger, and the tap density is 1.5 g / cm 3 Less than and This reduces the filling efficiency of the positive electrode active material, making it difficult to sufficiently improve the battery capacity of the entire secondary battery. Therefore, the structure of secondary particles, average particle size, particle size distribution, specific surface area, It is necessary to set the upper limit of the surface roughness index taking the product into consideration. In this case, the surface roughness index is used to ensure a sufficient contact area between the surface of the secondary particles and the electrolyte and conductive additive. While maintaining the above, the tap density is sufficiently secured, i.e., 1.5 g / cm 3That is all. Taking this into consideration, the above range is obtained.

[0143] (3-7) Composition The positive electrode active material obtained by the method for producing a positive electrode active material of the present invention has a particle structure of its secondary particles. Therefore, as long as the grain structure described above is maintained, the composition is not particularly limited. Although it is not possible to obtain a compound having the general formula (B): Li 1+u Ni x Mn y Co z M t O2(-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, and W (one or more additive elements selected from the group consisting of It is preferable that the lithium-nickel-manganese composite oxide is made of the above.

[0144] In this positive electrode active material, the value of u, which indicates the excess amount of lithium (Li), is preferably −0 0.05 or more and 0.50 or less, more preferably 0 or more and 0.50 or less, and even more preferably 0 or more and 0 By setting the value of u within the above range, this positive electrode active material can be used as a positive electrode material. The output characteristics and battery capacity of the secondary battery used as the material can be improved. When the value of u is less than -0.05, the positive electrode resistance of the secondary battery increases, resulting in a decrease in output characteristics. On the other hand, when it is larger than 0.50, the initial discharge capacity decreases. Not only that, the positive electrode resistance also increases.

[0145] Nickel (Ni) is an element that contributes to the high potential and high capacity of secondary batteries. The value of x, which indicates the content, is preferably 0.3 or more and 0.95 or less, more preferably 0.3 or more. If the value of x is less than 0.3, the battery capacity of the secondary battery using this positive electrode active material will be On the other hand, if the value of x exceeds 0.95, the content of other elements is reduced and the effect cannot be obtained.

[0146] Manganese (Mn) is an element that contributes to improving thermal stability, and the value of y indicates its content. is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. If the value of y is less than 0.05, the thermal stability of the secondary battery using this positive electrode active material is not improved. On the other hand, if the value of y exceeds 0.55, the positive electrode active material is depleted during high-temperature operation. Mn dissolves, and the charge-discharge cycle characteristics deteriorate.

[0147] Cobalt (Co) is an element that contributes to improving charge-discharge cycle characteristics. The value of z is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.35 or less. When the value of z exceeds 0.4, the initial discharge capacity of the secondary battery using this positive electrode active material becomes It will decrease significantly.

[0148] The cathode active material obtained by the method for producing the cathode active material of the present invention has excellent durability and output of the secondary battery. In order to further improve the mechanical properties, an additional element M may be contained in addition to the above metal elements. Such additive elements M include magnesium (Mg), calcium (Ca), aluminum (Al), and Al (Al), Titanium (Ti), Vanadium (V), Chromium (Cr), Zirconium (Z r), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), One or more selected from tungsten (W) can be used.

[0149] The value of t indicating the content of the added 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 greater than 0.1, the metal elements contributing to the Redox reaction decrease, resulting in a decrease in the battery capacity.

[0150] Such an added element M may be uniformly dispersed inside the particles of the positive electrode active material, or may coat the surface of the particles of the positive electrode active material. Further, it may coat the surface after being uniformly dispersed inside the particles. In any case, it is necessary to control the content of the added element M so as to be within the above range.

[0151] In addition, in the above positive electrode active material, when further improving the battery capacity of the secondary battery using this, its composition is represented by the general formula (B1): Li Ni 1+u Ni x Mn y Co z M t O2(- 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 one or more added elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W), and it is preferably adjusted as follows. In particular, when aiming for compatibility with thermal stability, the value of x in the general formula (B1) is more preferably 0.7 < x ≦ 0.9, and even more preferably 0.7 < x ≦ 0.85.

[0152] On the other hand, when aiming for further improvement of thermal stability, its composition is represented by the general formula (B2): Li1 +u Ni x Mn y Co zM t O2(-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 A Addition of one or more selected from l, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W It is preferable to adjust the amount of the element so that it is expressed as:

[0153] 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 above-mentioned composite hydroxide as a precursor, As long as it is possible to synthesize a positive electrode active material having the structure, average particle size and particle size distribution, However, when carrying out industrial-scale production, the above-mentioned complex water a mixing step of mixing the oxide with a lithium compound to obtain a lithium mixture; and a firing step of firing the mixture at 650°C to 1000°C in an oxidizing atmosphere. It is preferable to synthesize the positive electrode active material by the method described above. In this case, a heat treatment step, a calcination step, or the like may be added. The positive electrode active material, particularly the positive electrode active material represented by general formula (B), can be easily obtained.

[0154] (4-1) Heat treatment process In the method for producing a positive electrode active material of the present invention, a heat treatment step may be optionally provided before the mixing step. Alternatively, the composite hydroxide may be heat-treated to form heat-treated particles, which may then be mixed with the lithium compound. Here, the heat-treated particles contain only composite hydroxides from which excess water has been removed in the heat treatment step. The transition metals obtained by converting the complex hydroxides into oxides through a heat treatment process are not Metal-containing complex oxides and mixtures thereof are also included.

[0155] The heat treatment process involves heating the composite hydroxide to 105°C to 750°C. This is a process to remove excess water contained in the composite hydroxide. The residual moisture can be reduced to a certain level, and the composition of the resulting positive electrode active material can be uniform. When the heating temperature is less than 105°C, excess water in the composite hydroxide On the other hand, if the heating temperature is If the temperature is higher than 700℃, not only can no further effect be expected, but production costs will also increase. It ends up like this.

[0156] In addition, in the heat treatment process, the number of atoms of each metal component in the positive electrode active material and the number of Li atoms It is sufficient to remove moisture to the extent that there is no variation in the ratio of It is not necessary to convert the hydroxide into a composite oxide. However, the atoms of each metal component In order to reduce the variation in the number of Li atoms and the ratio of Li atoms, the temperature should be increased to 400°C or higher. It is preferable to heat the mixture to convert all of the complex hydroxides into complex oxides. The metal component ratio contained in the composite hydroxide under the treatment conditions is determined in advance by chemical analysis. By determining the mixing ratio with the lithium compound, the above-mentioned variations can be further suppressed. can be done.

[0157] The atmosphere in which the heat treatment is performed is not particularly limited, and may be a non-reducing atmosphere. It is preferable to carry out the treatment in an air stream, which is easy to carry out.

[0158] The heat treatment time is not particularly limited, but it is preferable to use a time period long enough to sufficiently remove excess water from the composite hydroxide. From this viewpoint, it is preferable to set the time to at least 1 hour, and more preferably 5 to 15 hours. More preferable.

[0159] (4-2) Mixing process The mixing step includes mixing a lithium compound with the composite hydroxide or the heat-treated particles described above, This is the step of obtaining a lithium mixture.

[0160] In the mixing step, metal atoms other than lithium in the lithium mixture, specifically, nickel, The sum of the number of atoms of cobalt, manganese, and the additive element M (Me) and the number of lithium atoms (L i) the ratio (Li / Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably or 1.0 to 1.35, more preferably 1.0 to 1.2. Alternatively, it is necessary to mix the heat-treated particles with a lithium compound. Since the Li / Me value does not change before and after the mixing process, the Li / Me value in the mixing process is the same as the target value. The composite hydroxide or heat-treated particles and Li were mixed so that the Li / Me value of the positive electrode active material was It is necessary to mix a lithium compound.

[0161] The lithium compound used in the mixing step is not particularly limited, but it is preferable to use a lithium compound that is easily available. Therefore, lithium hydroxide, lithium nitrate, lithium carbonate or a mixture thereof can be used. In particular, considering ease of handling and stability of quality, lithium hydroxide or It is preferred to use lithium carbonate.

[0162] The composite hydroxide or heat-treated particles and the lithium compound are mixed sufficiently to prevent the generation of fine powder. If the mixture is insufficient, the Li / Me value will vary between individual particles. This may cause a problem in the battery, making it impossible to obtain sufficient battery characteristics. Mixers can be used, for example, shaker mixers, Lödige mixers, Ju A rear mixer, V blender, etc. can be used.

[0163] (4-3) Calcination process When lithium hydroxide or lithium carbonate is used as the lithium compound, Then, before the firing step, the lithium mixture is heated at a temperature lower than the firing temperature and at a temperature of 350°C to A calcination step may be carried out at 800°C, preferably 450°C to 780°C. This allows lithium to be sufficiently diffused in the composite hydroxide or heat-treated particles, A more uniform positive electrode active material can be obtained.

[0164] The retention time at the above temperature is preferably 1 hour to 10 hours, more preferably 3 hours to 6 hours. The atmosphere in the calcination step is preferably the same as that in the firing step described later. In particular, it is preferable to use an oxidizing atmosphere, and the oxygen concentration is preferably 18% by volume to 100% by volume. It is more preferable to set the following.

[0165] (4-4) Firing process In the firing step, the lithium mixture obtained in the mixing step is fired under predetermined conditions to form a composite. Lithium is diffused into the mixed hydroxide or heat-treated particles to form a lithium transition metal-containing composite acid. This is a process for obtaining a positive electrode active material made of a cation.

[0166] In this firing step, the composite hydroxide and the outer shell or outermost part of the heat-treated particles are fired. While the sintering shrinks, the low-density layer consisting of fine primary particles near the surface As sintering progresses, the particles become smaller compared to the surrounding plate-like primary particles (main and outer shell). Therefore, the fine primary particles contained in the low density layer are concentrated in the main part where sintering progresses slowly. The outer shell or the outermost part shrinks during sintering, forming a hollow structure. As the particles shrink, the hollow structure collapses, causing unevenness on the surface of the secondary particles. As a result, when the positive electrode active material obtained above is used as a positive electrode material for a secondary battery, In this case, the internal resistance is significantly reduced, improving the output characteristics without impairing the battery capacity. It becomes possible.

[0167] The particle structure of such a positive electrode active material is basically the same as that of the composite hydroxide precursor. However, it may be affected by the composition and firing conditions, After conducting preliminary tests, it is necessary to adjust the conditions appropriately to achieve the desired structure. preferable.

[0168] The furnace used in the firing step is not particularly limited, and may be fired in air or oxygen. However, it is necessary to maintain a uniform atmosphere in the furnace. From this viewpoint, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace is suitable. In this regard, the furnace used in the heat treatment step and the calcination step is The same applies to

[0169] a) Firing temperature The firing temperature of the lithium mixture must be 650°C to 1000°C. When the temperature is less than 650°C, lithium does not diffuse sufficiently into the composite hydroxide or heat-treated particles. In addition, excess lithium, unreacted composite hydroxides, or heat-treated particles may remain, and the resulting positive On the other hand, if the firing temperature is 1000 If the temperature is higher than 100°C, the particles of the positive electrode active material will be sintered severely, causing abnormal grain growth and resulting in defects. This results in an increase in the proportion of regular coarse particles.

[0170] In addition, when it is desired to obtain a positive electrode active material represented by the above general formula (B1), the baking temperature is The temperature is preferably 650 to 900° C. On the other hand, the positive electrode active material represented by the general formula (B2) When it is desired to obtain the above, the firing temperature is preferably set to 800°C to 980°C.

[0171] The temperature rise rate in the firing step is preferably 2°C / min to 10°C / min. It is more preferable that the firing rate is 10°C / min to 10°C / min. The temperature is maintained at a temperature near the melting point for preferably 1 to 5 hours, more preferably 2 to 5 hours. This allows the composite hydroxide or the heat-treated particles to be more easily mixed with the lithium compound. This allows the reaction to occur more uniformly.

[0172] b) Baking time During the firing time, the holding time at the firing temperature is preferably at least 2 hours. Preferably, the holding time at the firing temperature is 4 to 24 hours, and more preferably, 2 to 3 hours. If the time is shorter than this, lithium does not diffuse sufficiently into the composite hydroxide or heat-treated particles, and excess lithium is released. The resulting positive electrode active material may contain unreacted hydroxides or heat-treated particles. There is a risk that the quality may be insufficient.

[0173] After the holding time is over, the cooling rate from the firing temperature to at least 200°C is 2°C / min. Preferably, the temperature is 10°C / min or lower, and more preferably 33°C / min to 77°C / min. By controlling the cooling rate within this range, productivity can be ensured while also reducing the cost of designing saggers and other items. This can prevent the equipment from being damaged by rapid cooling.

[0174] c) Firing atmosphere The atmosphere during firing is preferably an oxidizing atmosphere, and the oxygen concentration is 18% by volume to 10% by volume. It is more preferable to use an atmosphere of 0% by volume, and a mixed atmosphere of oxygen and inert gas with the above oxygen concentration is used. It is particularly preferable to carry out the firing in an atmosphere, i.e., in air or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the positive electrode active material will be insufficient. There is a risk.

[0175] (4-5) Crushing process The positive electrode active material obtained by the firing process may have agglomerated or slightly sintered. In such cases, it is preferable to physically crush the aggregates or sintered bodies of the positive electrode active material. This allows the average particle size and particle size distribution of the resulting positive electrode active material to be adjusted to a suitable range. The term "crushing" refers to the process of breaking up the particles into smaller pieces, which occurs during firing due to sintering necking between secondary particles. Mechanical energy is applied to the agglomerate consisting of multiple secondary particles, and the secondary particles themselves are almost completely broken down. It refers to the process of separating and breaking down agglomerates without destroying them.

[0176] As a crushing method, known means can be used, for example, a pin mill or a hammer. A mill or the like can be used. In this case, the crushing force should be adjusted so as not to destroy the secondary particles. It is preferable to adjust it to an appropriate range.

[0177] 5.Nonaqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte solution, and the like. The battery is provided with the same components as a general non-aqueous electrolyte secondary battery. For illustrative purposes only, the non-aqueous electrolyte secondary battery of the present invention may be implemented based on the embodiments described herein. It is also possible to apply the present invention in various modified and improved forms.

[0178] (5-1) Components a) Positive electrode The above-described positive electrode active material can be used to form a positive electrode of a non-aqueous electrolyte secondary battery, for example, as follows. Prepare the following.

[0179] First, the positive electrode active material of the present invention is mixed with a conductive material and a binder, and then an active material is added as needed. Charcoal and a solvent for viscosity adjustment are added, and these are kneaded to prepare a positive electrode composite paste. In this case, the mixing ratio of each component in the positive electrode composite paste also determines the performance of the non-aqueous electrolyte secondary battery. For example, if the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, In the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, the content of the positive electrode active material is set to 60 parts by mass to 9 5 parts by mass, the content of the conductive material is 1 part by mass to 20 parts by mass, and the content of the binder is 1 part by mass to 2 It can be set to 0 parts by mass.

[0180] The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, aluminum foil, Dry the electrode to remove the solvent. If necessary, use a roll press or other method to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-shaped positive electrode is cut to the appropriate size depending on the desired battery, and then used to make the battery. The method for producing the positive electrode is not limited to the above-mentioned example. , or other methods may be used.

[0181] Conductive materials include, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and acetylene. Carbon black materials such as carbon black and ketjen black can be used.

[0182] The binder serves to bind the active material particles together. For example, polyvinyl fluoride Polytetrafluoroethylene (PVDF), Polytetrafluoroethylene (PTFE), Fluoro rubber, Ethylene Propylene diene rubber, styrene butadiene, cellulose resin or polyacrylic acid It can be used.

[0183] In addition, if necessary, the positive electrode active material, conductive material, and activated carbon are dispersed, and the binder is dissolved. A solvent that can be used to dissolve the cathode mixture can be added to the cathode mixture. In addition, an organic solvent such as thiazolinone or thiazolinone can be used for the positive electrode mixture. Activated carbon can also be added to increase the volume.

[0184] b) Negative electrode For the negative electrode, metallic lithium or a lithium alloy can be used. A binder is mixed with a negative electrode active material that can absorb and release ions, and a suitable solvent is added to form a binder. The stripped negative electrode mixture is applied to the surface of a metal foil current collector such as copper, dried, and then, if necessary, To increase the electrode density, a compressed electrode can be used.

[0185] The negative electrode active material may be, for example, a material containing lithium such as metallic lithium or a lithium alloy. materials that can absorb and desorb lithium ions, natural graphite, artificial graphite, and phenol resin Powders of organic compounds such as fats and carbonaceous materials such as coke can be used. In this case, the negative electrode binder may be a fluorine-containing resin such as PVDF, just like the positive electrode. The solvent for dispersing these active materials and binders is N-methyl-2-pyridinium. Organic solvents such as lolidone can be used.

[0186] c) Separator The separator is disposed between the positive electrode and the negative electrode. The separator has the function of separating the electrolyte and retaining the non-aqueous electrolyte. A thin membrane made of polyethylene or polypropylene with many fine holes is used. However, there are no particular limitations as long as the above function is achieved.

[0187] d) Non-aqueous electrolyte The non-aqueous electrolyte includes a non-aqueous electrolyte solution in which a lithium salt, which is a supporting salt, is dissolved in an organic solvent. A non-flammable, ion-conductive solid electrolyte is used.

[0188] The organic solvents used in the non-aqueous electrolyte include: Ethylene carbonate, propylene carbonate, butylene carbonate, and tricarbonate cyclic carbonates such as fluoropropylene carbonate; Diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and di Chain carbonates such as propyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane ether compounds, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, One selected from the above can be used alone, or two or more can be used in combination.

[0189] Supporting salts include LiPF6, LiBF4, LiClO4, LiAsF6, and LiN(CF3 SO2)2, and complex salts thereof can be used.

[0190] The non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, etc. stomach.

[0191] (5-2) Structure The non-aqueous electrolyte secondary battery of the present invention is composed of the above positive electrode, negative electrode, separator, and non-aqueous electrolyte. The batteries can be in a variety of shapes, including cylindrical and stacked.

[0192] In either case, the positive electrode and the negative electrode are stacked with a separator interposed therebetween. The electrode body is impregnated with a non-aqueous electrolyte solution, and a positive electrode current collector and a positive electrode connected to the outside are connected to the positive electrode current collector and the outside. Between the negative electrode current collector and the negative electrode terminal, and between the negative electrode current collector and the negative electrode terminal that leads to the outside, The battery is then sealed in a battery case to complete the non-aqueous electrolyte secondary battery.

[0193] (5-3) Characteristics As described above, the nonaqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention as a positive electrode material. Therefore, the same current density as that of conventional non-aqueous electrolyte secondary batteries using a solid-structure positive electrode active material is obtained. While maintaining the battery capacity and cycle characteristics, the output characteristics have been dramatically improved. In comparison with secondary batteries using a cathode active material made of conventional lithium-nickel-containing composite oxide, In comparison, the thermal stability and safety are at a level that poses no problems.

[0194] For example, a 2032-type coin battery as shown in FIG. 4 can be constructed using the positive electrode active material of the present invention. When formed, the initial discharge capacity is 150 mAh / g or more, preferably 158 mAh / g or more. and a positive electrode resistance of 1.5 Ω or less, preferably 1.4 Ω or less, more preferably 1.3 Ω or less; At the same time, a 500-cycle capacity retention rate of 75% or more, preferably 80% or more, can be achieved. can.

[0195] (5-4)Applications As described above, the non-aqueous electrolyte secondary battery of the present invention has excellent battery capacity, output characteristics, and cycle characteristics. These properties are highly demanding for small portable electronic devices (notebook PCs) This can be suitably used as a power source for personal computers, mobile phones, etc. Among these characteristics, the output characteristics of the nonaqueous electrolyte secondary battery of the present invention are significantly improved, In addition, because it is also highly safe, it is possible to make it smaller and achieve higher output. This simplifies expensive protection circuits, making it ideal for electric vehicles that are limited by space. It can also be suitably used as a power source for transportation equipment such as cars and hybrid cars. [Example]

[0196] The present invention will be described in detail below using examples and comparative examples. The following examples and embodiments are merely examples of the present invention, and the present invention is not limited to these examples. In the comparative examples, unless otherwise specified, composite hydroxides and positive electrode active materials were prepared using materials manufactured by Wako Pure Chemical Industries, Ltd. The samples used were special grade reagents manufactured by Kogyo Co., Ltd. In addition, the nucleation process and particle growth process were carried out The pH value of the reaction solution was controlled using a pH controller (Nisshin Rika Co., Ltd., NPH-690D ) and adjust the amount of sodium hydroxide solution supplied based on this measurement value. The pH value of the reaction solution in each process was measured with a deviation of ±0.05 from the set value of the process. It was controlled within a range of .2.

[0197] Example 1 a) Production of transition metal-containing composite hydroxide [Nucleation process] First, put 1.4 L of water into a 6 L reactor and set the temperature inside the reactor to 40°C while stirring. At this time, nitrogen gas was passed through the reaction vessel for 30 minutes, and the reaction atmosphere was adjusted to an oxygen concentration of 2. Next, a non-oxidizing atmosphere of 25% by volume or less was created in the reaction vessel. The aqueous solution and 25% ammonia water were supplied in appropriate amounts, and the pH value was 12.8 at a liquid temperature of 25°C. The ammonium ion concentration was adjusted to 10 g / L to form a pre-reaction aqueous solution. Ta At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were added, respectively. The molar ratio of the metal elements is Ni:Mn:Co:Zr=33.1:33.1:33.1:0.2 The compound was dissolved in water so that the concentration became 2 mol / L to prepare a 2 mol / L aqueous solution of the raw material.

[0198] Next, this raw water reaction solution was fed to the pre-reaction aqueous solution at a flow rate of 10 ml / min to form the reaction aqueous solution. The nucleation was carried out for 3 minutes by crystallization. During this treatment, 25% by weight of water was added. The sodium hydroxide solution and 25% by mass of ammonia water were supplied at appropriate times to control the pH value and and ammonium ion concentrations were maintained within the above ranges.

[0199] [Particle growth process] After the nucleation step is completed, the supply of all aqueous solutions to the reaction vessel is stopped, and sulfuric acid is added. was added to adjust the pH of the reaction solution to 11.6 at a liquid temperature of 25°C. After confirming that the H value has reached the specified value, the raw material aqueous solution and the sodium tungstate aqueous solution The liquid was supplied to grow the nuclei formed in the nucleation step.

[0200] After 200 minutes (83.4% of the total particle growth time) from the start of the particle growth process After filtering, the raw material solution is continuously supplied to the filter, and the filter is then placed in a ceramic filter with a pore size of 20 μm to 30 μm. The reaction atmosphere was controlled by circulating air through the reaction solution using an air diffuser (manufactured by Kinoshita Rika Kogyo Co., Ltd.). The atmosphere was adjusted to an oxidizing atmosphere with an oxygen concentration of 21% by volume (switching operation 1).

[0201] After 20 minutes (8.3% of the total particle growth process time) have elapsed since the switching operation, While continuing to supply the liquid, nitrogen gas was circulated in the reaction vessel, and the reaction atmosphere was adjusted to an oxygen concentration of 2 The atmosphere was adjusted to a non-oxidizing atmosphere of 0.05% by volume or less (switching operation 2).

[0202] After that, 20 minutes (8.3% of the total particle growth process time) have passed since switching operation 2. The supply of all aqueous solutions was stopped to terminate the particle growth process. In the process, 25% by mass of sodium hydroxide aqueous solution and 25% by mass of ammonia water are added at appropriate times. The pH value and ammonium ion concentration of the reaction solution were maintained within the above ranges.

[0203] At this time, the concentration of the product in the reaction solution was 86 g / L. The product was washed with water, filtered and dried to obtain a powdery composite hydroxide.

[0204] b) Evaluation of transition metal-containing composite hydroxides [composition] This composite hydroxide was used as a sample and analyzed using an ICP emission spectrometer (Shimadzu Corporation, Shimadzu) When the elemental fraction was measured using an ICPE-9000 manufactured by Iwakusho, this composite hydroxide , General formula: Ni 0.331 Mn 0.331 Co 0.331 Zr 0.002 W 0.005 ( It was confirmed that the compound had a composition represented by the formula:

[0205] [Particle structure] The composite hydroxide was observed under a field emission scanning electron microscope (FE-SEM: manufactured by JEOL Ltd., JS When observed using a microscope (M-6360LA), this composite hydroxide was found to be approximately spherical with a particle size of approximately It was confirmed that the composite hydroxide was composed of uniformly aligned secondary particles. The particle is embedded in resin and processed with a cross-section polisher to allow observation of the particle cross section. The sample was then observed using an SEM (JSM-6360LA, manufactured by JEOL Ltd.). As a result, the secondary particles that make up this composite hydroxide are formed by the aggregation of plate-like primary particles. The secondary particles are formed by agglomeration of fine primary particles near the surface. The presence of a low-density layer was confirmed, and a structure similar to the schematic structure shown in Figure 1 was obtained. It was confirmed that this low density layer is formed on the surface of the secondary particles, and is The average particle size of the fine primary particles was 0.2 μm. The average particle size of the plate-like primary particles was 0.5 μm. Furthermore, the particle size ratio of the low-density layer was 5%. The particle size ratio of the main part, the low density layer, and the outer shell part were also measured and calculated. The results were 82%, 5%, and 4%, respectively.

[0206] [Average particle size and particle size distribution] A laser light diffraction / scattering particle size analyzer (Microtrack HRA, manufactured by Nikkiso Co., Ltd.) was used. The average particle size of the composite hydroxide was measured, and d10 and d90 were also measured. The value of [(d90-d10) / average particle size], which is an index showing the spread of the fabric, was calculated. As a result, the average particle size was 5.2 μm, and the value of [(d90-d10) / average particle size] was 0.42. It was.

[0207] c) Preparation of positive electrode active material This composite hydroxide was subjected to a heat treatment process in an air stream (oxygen concentration: 21% by volume). Then, the mixture was heated at 120°C for 12 hours. The mixed hydroxide and lithium carbonate were mixed so that the Li / Me ratio was 1.14, and the mixture was A car mixer (Willie & Bachofen (WAB) TURBULA T) The lithium mixture was obtained by thoroughly mixing using type T2C.

[0208] Next, this lithium mixture was subjected to a baking process in air (oxygen concentration: 21% by volume). The temperature was raised to 950°C at a rate of 2.5°C / min in a stream of air, and the sample was then kept at this temperature for 4 hours. The cathode was then cooled to room temperature at a rate of about 4°C / min. Since the active material had agglomerated or slightly sintered, a crushing process was carried out. The powder was crushed to adjust the average particle size and particle size distribution.

[0209] d) Evaluation of positive electrode active material [composition] The elemental fraction of this positive electrode active material was measured using an ICP optical emission spectrometer. The positive electrode active material is represented by the general formula: Li 1.14 Ni 0.331 Mn 0.331 Co 0. 331 Zr 0.002 W 0.005 It was confirmed that the compound had a composition represented by O2.

[0210] [Particle structure] The surface shape of this positive electrode active material was observed by SEM (see Figure 2). The positive electrode active material is formed as a whole by agglomeration of a plurality of primary particles, and The surface had a noticeable uneven shape.

[0211] The crystalline phase of this positive electrode active material was analyzed using an X-ray diffraction device (X'Pert manufactured by PANalytical Co., Ltd.). PRO) by powder X-ray diffraction and identified by ICDD card database. The crystalline phase of this positive electrode active material was found to be mainly composed of Li 1.14 Ni 0.331 Mn 0.3 31 Co 0.331 Zr 0.002 W 0.005 This is due to the hexagonal layer structure of O2. It was.

[0212] [Average particle size and particle size distribution] The average particle size of this positive electrode active material was measured using a laser light diffraction scattering particle size analyzer. Then, d10 and d90 were measured, and the ratio (d90-d1 0) / average particle size] was calculated. As a result, the average particle size of this positive electrode active material was 5.1 μm. The ratio [(d90-d10) / average particle size] was 0.41.

[0213] [Specific surface area and tap density] This positive electrode active material was used as a sample and measured using a flow type gas adsorption specific surface area measuring device (Yuasa Ioni The specific surface area was measured using a tapping machine (Kuramochika Co., Ltd.) The tap density was measured using a measuring instrument (KRS-406, manufactured by Gakukiki Seisakusho). The specific surface area of the positive electrode active material is 1.14 m 2 / g and the tap density is 1.94 g / cm 3 in there were.

[0214] [Surface roughness index] Using a true density measuring device (Micromeritics, AccuPyc1330), The true density of this positive electrode active material was measured and found to be 4.66 g / cm 3 This true density, and using the particle radius of the secondary particles calculated from the above BET specific surface area and average particle size, The surface roughness index of this positive electrode active material was calculated according to the definitions of formulas (1) and (2). As a result, the surface roughness index was 4.52.

[0215]

number

[0216]

number

[0217] e) Preparation of secondary batteries As a prerequisite for fabricating the 2032-type coin battery (B) shown in Figure 4, the positive electrode active material obtained above was : 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg were mixed, After press molding at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm, it was dried in a vacuum oven. The mixture was dried at 120° C. for 12 hours in a sintered state to prepare a positive electrode (1).

[0218] Next, using this positive electrode (1), a 2032-type coin battery (B) having the configuration shown in FIG. The fabrication was carried out in a glove box with an argon (Ar) atmosphere and the temperature controlled at -80°C. The negative electrode (2) of the 2032-type coin battery (B) is a lithium battery with a diameter of 17 mm and a thickness of 1 mm. The electrolyte is ethylene carbonate with 1M LiClO4 as the supporting electrolyte. A mixture of equal amounts of ethylenediaminetetraacetic acid (EC) and diethyl carbonate (DEC) (manufactured 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 separates the positive electrode can (5) and the negative electrode can ( 6) and assembled into a coin-shaped battery.

[0219] f) Battery evaluation [Initial discharge capacity] After making the 2032 type coin battery, let it sit for about 24 hours and measure the open circuit voltage (OCV). After the circuit voltage stabilizes, the current density to the positive electrode is increased to 0.1 m A / cm 2 Charge the battery until the cut-off voltage reaches 4.3V, then rest for 1 hour and then cut off the A charge-discharge test was conducted to measure the discharge capacity when the battery was discharged until the off-state voltage reached 3.0V. The initial discharge capacity was determined to be 159.6 mAh / g. The initial discharge capacity was measured using a multi-channel voltage / current generator (Advan Co., Ltd.). Test R6741A) was used.

[0220] [Positive electrode resistance] Using a 2032 coin battery charged at a charging potential of 4.1V, the AC impedance method was used. The resistance was measured using a frequency response analyzer and a potentiometer. A Nyquist plot shown in Figure 5 was obtained using a neutron detector (Solartron). It is expressed as the sum of the characteristic curves showing the solution resistance, negative electrode resistance and capacity, and positive electrode resistance and capacity. Therefore, a fitting calculation was performed using an equivalent circuit to calculate the positive electrode resistance. The positive electrode resistance was 1.214 Ω.

[0221] [Cycle capacity retention rate] The current density to the positive electrode was 2.0 mA / cm 2 As a result, it charges up to 4.2V and then drops to 2.5V. The ratio of the discharge capacity after 200 cycles of discharging at 1000 mAh to the initial discharge capacity was calculated. The capacity retention rate at 200 cycles was calculated. 0.1%.

[0222] In the above examples, the conditions for preparing the composite hydroxide and the positive electrode active material, as well as the various The properties and the results of the performance of the batteries using them are shown in Tables 1 to 4. The results of Example 5 and Comparative Examples 1 to 4 are also shown in Tables 1 to 4.

[0223] Example 2 In the particle growth process, the switching operation 1 was performed 228 minutes (particle growth Switching operation 2 is performed after 87.5% of the total process time has elapsed, and switching operation 2 is performed after 87.5% of the total process time has elapsed. After 20 minutes (4.2% of the total particle growth time), The same procedure as in Example 1 was repeated except that the crystallization reaction was continued for 8.3% of the total growth time. A composite hydroxide, a positive electrode active material, and a secondary battery were fabricated and evaluated.

[0224] Example 3 In the particle growth process, the switching operation 1 was performed for 190 minutes (particle growth Switching operation 2 is performed after 79.2% of the total process time has elapsed, and switching operation 2 is performed after 30 minutes from switching operation 1. After 12.5 minutes (12.5% of the total particle growth process time), The crystallization reaction was continued for 20 minutes from the start of the experiment (8.3% of the total particle growth process time). In the same manner as in Example 1, a composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated. was carried out.

[0225] Example 4 In the particle growth process, the switching operation 1 was performed for 180 minutes (particle growth Switching operation 2 is performed after 75.0% of the total process time has elapsed, and switching operation 2 is performed after 20 After 8.3 minutes (8.3% of the total particle growth process time), The crystallization reaction was continued for 40 minutes (16.7% of the total particle growth process time). In the same manner as in Example 1, a composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated. went.

[0226] Example 5 In the particle growth process, the switching operation 1 was performed 210 minutes (particle growth Switching operation 2 is performed after 87.5% of the total process time has elapsed, and switching operation 2 is performed after 20% of the total process time has elapsed. After 8.3 minutes (8.3% of the total particle growth process time), The crystallization reaction was continued for 10 minutes (4.2% of the total particle growth process time). In the same manner as in Example 1, a composite hydroxide, a positive electrode active material, and a secondary battery were prepared and evaluated. It was.

[0227] (Comparative Example 1) The same procedure as in Example 1 was performed except that no atmosphere change was performed during the particle growth process. Similarly, composite hydroxides were prepared and evaluated. The results are shown in Table 2. The same procedure as in Example 1 was carried out except that the composite hydroxide of the above was used as a precursor. The batteries were fabricated and evaluated, and the results are shown in Tables 3 and 4 and in Figure 3.

[0228] (Comparative Example 2) In the particle growth process, the switching operation 1 was performed 228 minutes (particle growth Switching operation 2 is performed after 95% of the total process time has elapsed, and switching operation 2 is performed 1 minute (particles) after switching operation 1. After 0.4% of the total time for the child growth process has elapsed, the switching operation is performed from 2 to 11 minutes. The same procedure as in Example 1 was repeated except that the crystallization reaction was continued (4.6% of the total time of the particle growth process). Similarly, composite hydroxides, positive electrode active materials, and secondary batteries were produced and evaluated.

[0229] (Comparative Example 3) In the particle growth process, the switching operation 1 was performed 156 minutes (particle growth Switching operation 2 was performed after 65% of the total process time had elapsed, and 72 minutes ( The particle growth process is carried out after 30% of the total time, and then the switching operation is carried out from 2 to 12 minutes. The same procedure as in Example 1 was repeated except that the crystallization reaction was continued (5% of the total time of the particle growth process). A composite hydroxide, a positive electrode active material, and a secondary battery were fabricated and evaluated.

[0230] Comparative Example 4 In the particle growth process, the switching operation 1 was performed 144 minutes (particle growth Switching operation 2 was performed after 60% of the total process time had elapsed, and 24 minutes ( After the particle growth process (10%) has elapsed, the switching operation is performed from 2 to 72 minutes. The same procedure as in Example 1 was carried out except that the crystallization reaction was continued (30% of the total time of the particle growth process). In this way, composite hydroxides, positive electrode active materials, and secondary batteries were fabricated and evaluated.

[0231] [Table 1]

[0232] [Table 2]

[0233] [Table 3]

[0234] [Table 4]

[0235] Example 6 In the particle growth process, the switching operation 1 was performed 195 minutes (particle growth Switching operation 2 is performed after 80.1% of the total process time has elapsed, and switching operation 2 is performed after 80.1% of the total process time has elapsed. After 4.2 minutes (4.2% of the total particle growth process time) has elapsed, After 10 minutes (4.2% of the entire particle growth process) had elapsed, the raw material solution was continued to be supplied. Then, using a ceramic diffuser with a pore size of 20 μm to 30 μm, the reaction solution was again Air was circulated through the reactor to adjust the reaction atmosphere to an oxidizing atmosphere with an oxygen concentration of 21% by volume (cut Switching operation 3), 10 minutes after switching operation 3 (4.2% of the total particle growth process time) While continuing to supply the raw material aqueous solution, nitrogen gas was again circulated into the reaction vessel, and the reaction atmosphere was The atmosphere was adjusted to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less (switching operation 4). After 4 to 15 minutes (6.3% of the total particle growth process time) of the switching operation, all the aqueous The procedure was the same as in Example 1, except that the supply of the solution was stopped and the particle growth process was completed. The oxide, the positive electrode active material, and the secondary battery were fabricated and evaluated.

[0236] The secondary particles that make up the obtained composite hydroxide are formed by the aggregation of plate-like primary particles. and a first low-density layer, a high-density layer and a second low-density layer are formed in the vicinity of the surface of the secondary particle. It was confirmed that a laminated structure consisting of a low-density layer and an outer shell was present. The second low-density layer is formed from the surface of the secondary particles to a range of up to 13% of the particle diameter of the secondary particles. The average particle size of the fine primary particles was 0.2 μm, and the average particle size of the plate-like primary particles was 0.2 μm. The particle size was 0.5 μm. Furthermore, the particle size ratio of the low-density layer (the sum of the first and second low-density layers) was , 8%. Main part particle size ratio, first low density layer particle size ratio, high density layer, second low density layer particle size ratio The particle size ratio of the outer shell was also measured and calculated, and was found to be 74% and 4% respectively. %, 2%, 4% and 3%.

[0237] The average particle size is 5.1 μm, and the value of [(d90-d10) / average particle size] is 0. The number was 41.

[0238] The obtained positive electrode active material is formed as a whole by agglomeration of a plurality of primary particles, and The surface of the positive electrode active material was markedly uneven. The average particle size of this positive electrode active material was , 5.2 μm, [(d90-d10) / average particle size] value is 4.3, specific surface area is 1.16 m 2 / g, tap density is 1.93g / cm 3 The surface roughness index was 4.68.

[0239] Furthermore, the initial discharge capacity of a 2032-type coin battery using the resulting positive electrode active material was 159. 5mAh / g, positive electrode resistance is 1.205Ω, and 200 cycle capacity retention is 85.2%. there were. [Explanation of symbols]

[0240] 1 Positive electrode (electrode for evaluation) 2 negative electrode 3 Separator 4 gaskets 5 Positive electrode can 6 Anode can B 2032 type coin battery 21 Main Section 22 Low density layer 23 Outer shell

Claims

1. A composition represented by 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 one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), The secondary particles are formed by agglomeration of plate-like primary particles and fine needle-like primary particles having a particle size smaller than that of the plate-like primary particles, the secondary particles have a main portion made of the plate-like primary particles, a low-density layer formed outside the main portion and made of the fine primary particles, and an outer shell portion formed outside the low-density layer and made of the plate-like primary particles, an average ratio of the outer diameter of the main portion to the particle diameter of the secondary particles is in the range of 80% or more and 90% or less; an average ratio of the thickness of the low-density layer to the particle diameter of the secondary particles is in the range of 3% to 8%; and an average ratio of the thickness of the outer shell to the particle diameter of the secondary particles is in the range of 2% or more and 7% or less; Transition metal-containing composite hydroxide.

2. A composition represented by 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 one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), The secondary particles are formed by agglomeration of plate-like primary particles and fine needle-like primary particles having a particle size smaller than that of the plate-like primary particles, the secondary particles have a main portion made of the plate-like primary particles, a low-density layer formed outside the main portion and made of the fine primary particles, and an outer shell portion formed outside the low-density layer and made of the plate-like primary particles, an average ratio of the outer diameter of the main portion to the particle diameter of the secondary particles is in the range of 65% or more and 76% or less; an average ratio of the thickness of the low-density layer to the particle size of the secondary particles is in the range of 10% to 15%; and an average ratio of the thickness of the outer shell to the particle diameter of the secondary particles is in the range of 2% or more and 7.5% or less; Transition metal-containing composite hydroxide.

3. A composition represented by 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 one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), The secondary particles are formed by agglomeration of plate-like primary particles and fine needle-like primary particles having a particle size smaller than that of the plate-like primary particles, the secondary particles comprise a main portion made of the plate-like primary particles, a first low-density layer formed outside the main portion and made of the fine primary particles, a high-density layer formed outside the first low-density layer and made of the plate-like primary particles, a second low-density layer formed outside the high-density layer and made of the fine primary particles, and an outer shell portion formed outside the second low-density layer and made of the plate-like primary particles, an average ratio of the outer diameter of the main portion to the particle diameter of the secondary particles is in the range of 80% or more and 90% or less; an average ratio of the sum of the thicknesses of the first low-density layer and the second low-density layer to the particle diameter of the secondary particles is in the range of 3% to 8%; and an average ratio of the sum of the thicknesses of the outer shell and the high-density layer to the particle diameter of the secondary particles is in the range of 2% or more and 7% or less; Transition metal-containing composite hydroxide.

4. A composition represented by 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 one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W), The secondary particles are formed by agglomeration of plate-like primary particles and fine needle-like primary particles having a particle size smaller than that of the plate-like primary particles, the secondary particles comprise a main portion made of the plate-like primary particles, a first low-density layer formed outside the main portion and made of the fine primary particles, a high-density layer formed outside the first low-density layer and made of the plate-like primary particles, a second low-density layer formed outside the high-density layer and made of the fine primary particles, and an outer shell portion formed outside the second low-density layer and made of the plate-like primary particles, an average ratio of the outer diameter of the main portion to the particle diameter of the secondary particles is in the range of 65% or more and 76% or less; an average ratio of the sum of the thicknesses of the first low-density layer and the second low-density layer to the particle diameter of the secondary particles is in the range of 10% to 15%; and an average ratio of the sum of the thicknesses of the outer shell and the high-density layer to the particle diameter of the secondary particles is in the range of 2% or more and 7.5% or less; Transition metal-containing composite hydroxide.

5. The average particle size of the plate-like primary particles is in the range of 0.3 μm to 3 μm, and the average particle size of the fine primary particles is in the range of 0.01 μm to 0.3 μm. The transition metal-containing composite hydroxide according to any one of claims 1 to 4.

6. The transition metal-containing composite hydroxide according to any one of claims 1 to 5, wherein 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 showing the spread of the particle size distribution of the secondary particles, is 0.65 or less.

7. The transition metal-containing composite hydroxide according to any one of claims 1 to 6, wherein the additional element M is uniformly distributed inside the secondary particles constituting the transition metal-containing composite hydroxide, and / or the surfaces of the secondary particles constituting the transition metal-containing composite hydroxide are coated with a compound containing the additional element M.

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