JP2021051880A - Positive electrode active material for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material for lithium ion secondary batteries, capable of achieving more excellent output characteristics when used in lithium ion secondary batteries.SOLUTION: A positive electrode active material comprises a lithium nickel manganese cobalt (NMC)-containing composite oxide. The positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles, and has [BET specific surface area/DBP absorption amount] that is a ratio of a BET specific surface area with respect to a DBP absorption amount measured according to JIS K 6217-4:2008 of 0.048 or more.SELECTED DRAWING: None

Description

The present invention relates to a positive electrode active material for a lithium ion secondary battery made of a composite oxide containing lithium nickel manganese manganese cobalt, and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery as a positive electrode material.

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

As a secondary battery satisfying such a requirement, there is a lithium ion secondary battery. This lithium ion secondary battery is composed of a negative electrode, a positive electrode, a non-aqueous electrolyte, a solid electrolyte, and the like, and the active material used as the material for the negative electrode and the positive electrode includes a material capable of desorbing and inserting lithium. used. As the non-aqueous electrolyte, a non-aqueous electrolyte solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent, a nonflammable solid electrolyte having ionic conductivity, and the like are used.

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

As positive electrode materials for such lithium ion secondary batteries, lithium cobalt composite oxide (LiCoO _{2 ), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO 2} ) using nickel, which is cheaper than cobalt, and lithium nickel. Cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _0.5 Mn) Lithium transition metal-containing composite oxides such as _0.5 O _{2) have been proposed.}

In order to obtain a lithium ion secondary battery having excellent cycle characteristics and output characteristics, it is necessary that the positive electrode active material, which is the positive electrode material thereof, is composed of particles having a small particle size and a narrow particle size distribution. Particles having a small particle size have a large specific surface area, a sufficient reaction area with the electrolytic solution can be secured, the positive electrode can be made thin, and the moving distance between the positive electrode and the negative electrode of lithium ions can be shortened. It enables reduction of positive electrode resistance. Further, since the particles having a narrow particle size distribution can make the voltage applied to the particles uniform in the electrode, it is possible to suppress a decrease in battery capacity due to selective deterioration of the fine particles.

In order to further improve the output characteristics, it is effective to form a space in which the electrolytic solution can enter inside the positive electrode active material. Since such a positive electrode active material can have a larger reaction area with an electrolytic solution than a positive electrode active material having a solid structure having the same particle size, it is possible to significantly reduce the positive electrode resistance. It becomes.

For example, Japanese Patent Application Laid-Open No. 2012-246199, Japanese Patent Application Laid-Open No. 2013-147416, and WO2012 / 131881 have two stages, a nucleation step mainly for nucleation and a particle growth step mainly for particle growth. A method for producing a transition metal-containing composite hydroxide as a precursor of a positive electrode active material by a clearly separated crystallization reaction is disclosed. In these methods, the pH value and the reaction atmosphere in the nucleation step and the particle growth step are appropriately adjusted, so that the particle size distribution is narrow with a small particle size, and the central part having a low density composed of fine primary particles and the plate shape. Alternatively, transition metal-containing composite hydroxide particles composed of a high-density outer shell composed of needle-shaped primary particles are obtained, and the positive electrode active material obtained from such composite hydroxide particles has a hollow structure. It has a large contact area with the electrolytic solution, which makes it possible to improve the output characteristics.

Japanese Unexamined Patent Publication No. 2016-094307 includes a nuclear generation step and a particle growth step, and supplies an oxidizing agent in the particle growth step after a certain period of time has elapsed from the start of the particle growth step under predetermined conditions. By performing the operation of starting and stopping the supply of the oxidizing agent at least once after a lapse of a predetermined time, a low-density portion in which fine primary particles are aggregated and a plate-shaped primary portion are performed on the outside of the central portion. It is disclosed that a structure of composite hydroxide particles in which high-density portions in which particles are aggregated is laminated is formed.

In WO2014 / 181891 and JP-A-2018-104276, the pH value of the nucleation aqueous solution containing at least a metal compound containing a transition metal and an ammonium ion feeder is set to 12.0 to 14.0. The pH value of the nucleation step of performing nucleation and the aqueous solution for particle growth containing the generated nuclei is lower than the pH value of the nucleation step and is 10.5-12.0. It is equipped with a particle growth step in which the pH is controlled to grow, and the initial stage of the nucleation step and the particle growth step is set to a non-oxidizing atmosphere. A method for producing a transition metal-containing composite hydroxide particle is disclosed, which comprises performing an atmosphere control for switching to an oxidizing atmosphere at least once. By this method, a small particle size, a narrow particle size distribution, a central portion formed by agglomeration of plate-shaped or needle-shaped primary particles, and fine primary particles agglomerated on the outside of the central portion were formed. A transition metal-containing composite hydroxide particle having two laminated structures in which a low-density layer and a high-density layer formed by aggregating plate-shaped primary particles are alternately laminated can be obtained.

The positive electrode active material having these structures and using a transition metal-containing composite hydroxide as a precursor has a small particle size and a narrow particle size distribution, and has a hollow structure, a structure having a space portion, or a multilayer structure having a space portion. It becomes a thing. Therefore, in a secondary battery using these positive electrode active materials, it is considered that the battery capacity, output characteristics and cycle characteristics can be improved at the same time.

Further, from the viewpoint of increasing the output density of the lithium ion secondary battery, it has been proposed to adjust the particle properties of the positive electrode active material. For example, JP-A-2012-109166 discloses, a BET specific surface area 0.5m ² /g~1.9m ² / g of the positive electrode active material, and / or a DBP (dibutyl phthalate) absorption amount 20 ml / 100 g By doing so, it is disclosed that a secondary battery having low internal resistance and excellent output characteristics can be realized. Further, in Japanese Patent Application Laid-Open No. 2015-191854, when the BET specific surface area (m ² / g) of the positive electrode active material is S and the DBP absorption amount (ml / 100 g) is Q, the BET specific surface area and DBP absorption In a two-dimensional coordinate system with a quantity as a variable, (S, Q) are (0.1,30), (0.95,30), (1.7,37.5), (1.7, 71) Of the five coordinate points (0.1 and 54), by setting them within the range of a pentagon that connects adjacent coordinate points in a straight line, it has both high overcharge resistance and excellent battery characteristics. It is disclosed that a secondary battery will be realized.

Japanese Unexamined Patent Publication No. 2012-246199 Japanese Unexamined Patent Publication No. 2013-147416 WO2012 / 131881 Japanese Unexamined Patent Publication No. 2016-094307 WO2014 / 181891 JP-A-2018-104276 Japanese Unexamined Patent Publication No. 2012-109166 JP 2015-191854

However, there is still room for improvement in the output characteristics of the positive electrode active material described in these documents, and further improvement in the output characteristics is required.

In view of the above problems, an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery capable of realizing better output characteristics when used in a lithium ion secondary battery. To do.

The present invention has further studied the relationship between the particle structure and particle properties of the secondary particles constituting the positive electrode active material and the output characteristics, and as a result, the ratio of the BET specific surface area to the amount of DBP (dibutyl phthalate) absorbed. It was found that the output characteristics can be further improved by setting the "BET specific surface area / DBP absorption amount" to a specific range. The present invention has been completed based on such findings.

That is, the present invention is a positive electrode active material for a lithium ion secondary battery made of a composite oxide containing lithium nickel manganese cobalt.
The positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles, and has a BET specific surface area with respect to the amount of DBP (dibutyl phthalate) absorbed measured according to JIS K 6217-4: 2008. It is characterized in that "BET specific surface area / DBP absorption amount", which is a ratio of (specific surface area measured by the BET method), is 0.048 or more.

In the positive electrode active material of the present invention, the "BET specific surface area / DBP absorption amount" is preferably 0.050 or more and 0.100 or less.

In the positive electrode active material of the present invention, the product of the BET specific surface area and d50 obtained from the volume integrated value measured by the laser light diffraction / scattering type particle size analyzer for the secondary particles is 9.0 or more. Is preferable.

The d50 of the positive electrode active material of the present invention is preferably 3 μm or more and 15 μm or less.

In the positive electrode active material of the present invention, [(d90-d10) / d50], which is an index showing the spread of the particle size distribution of the secondary particles obtained from the volume integrated value, is preferably 1.0 or less. ..

The BET specific surface area of the positive electrode active material of the present invention ^{is preferably 1.5 m 2} / g or more and 5.0 m ² / g or less.

The amount of DBP absorbed by the positive electrode active material of the present invention is preferably 30 ml / 100 g or more and 65 ml / 100 g or less.

In the positive electrode active material of the present invention, it is preferable that the secondary particles include an agglomerated portion in which the primary particles are electrically conductive with each other and a space portion in which the primary particles are dispersed and exist in the agglomerated portion. Further, it is preferable that the secondary particles are further provided with an outer shell portion that is electrically conductive with the agglomerated portion on the outside of the agglomerated portion.

In the positive electrode active material of the present invention, when the crystallite diameter of the primary particles is determined from the half-value width of the peak of the (003) plane by X-ray diffraction using the Scheller formula, the crystallite diameter is 30 nm or more and 150 nm. The following is preferable.

The tap density of the positive electrode active material of the present invention ^{is preferably 0.8 g / cm 3} or more and 2.0 g / cm ³ or less.

The lithium nickel manganese cobalt-containing composite oxide has a general formula: Li _{1 + u} Ni _x Mn _y Co _z M _t O ₂ (−0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0. 9, 0 <y ≦ 0.5, 0 <z ≦ 0.5, 0 ≦ t ≦ 0.1, M is Mg, Al, Si, Ca, Ti, V, Cr, Zr, Nb, Mo, Hf , Ta, W), and preferably has a hexagonal crystal structure having a layered structure.

The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, or a positive electrode, a negative electrode, and a solid electrolyte, and is a positive electrode active material used for the positive electrode. It is characterized in that a positive electrode active material for a battery is used.

In the positive electrode active material for a lithium ion secondary battery of the present invention, the contact area with the electrolytic solution can be increased, and the output characteristics can be improved. Therefore, the lithium ion secondary battery to which the positive electrode active material for the lithium ion secondary battery of the present invention is applied can provide high output characteristics, and thus its industrial significance is very large.

FIG. 1 outlines the structure of secondary particles of a nickel-manganese cobalt-containing composite oxide, which is a precursor used for obtaining a positive electrode active material for a lithium ion secondary battery according to an example of an embodiment of the present invention. It is a sectional view. FIG. 2 is a schematic cross-sectional view of a 2032 type coin battery used for battery evaluation. FIG. 3 is a schematic explanatory view of a measurement example of impedance evaluation and an equivalent circuit used for analysis.

1. 1. Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for lithium ion secondary battery of the present invention (hereinafter referred to as "positive electrode active material") is a positive electrode active material composed of a composite oxide containing lithium nickel manganese cobalt. The positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles, and has a BET specific surface area (BET specific surface area) with respect to the amount of DBP (dibutyl phthalate) absorbed measured according to JIS K 6217-4: 2008. The "BET specific surface area / DBP absorption amount", which is the ratio of the specific surface area measured by the BET method), is 0.048 or more, preferably 0.050 or more.

The positive electrode active material of the present invention is a lithium nickel manganese cobalt-containing composite oxide, that is, a ternary positive electrode active material containing at least nickel, manganese, and cobalt (NMC) as transition metals.

Among the lithium transition metal-containing composite oxides, the lithium nickel-manganese-cobalt-containing composite oxide is the most weather-resistant and easy-to-handle material in the development of the lithium transition metal-containing composite oxide. It is an important material.

The present invention relates to a ternary positive electrode active material for a lithium ion secondary battery made of a lithium nickel manganese cobalt-containing composite oxide (NMC) containing at least nickel, manganese, and cobalt as a transition metal, and its particle surface. And by making the particle properties inside the particles more appropriate, the contact area with the electrolytic solution can be made larger, and when a lithium ion secondary battery is constructed, the output characteristics can be further improved. It is characterized by points.

(1) BET Specific Surface Area / DBP Absorption Amount In the present invention, the BET specific surface area is the surface area obtained by analyzing the amount of nitrogen adsorbed on the surface of the powder sample of the positive electrode active material measured by the nitrogen gas adsorption method by the BET method. means.

For the amount of DBP absorbed, DBP (dibutyl phthalate or di-normal-butyl phthalate) was used as the reagent liquid, and "JIS K 6217-4: 2008 (Carbon Black for Rubber-Basic Characteristics-Part 4: Oil Absorption" It means the measured value obtained according to the procedure described in "How to determine the amount (including compressed sample))". However, since the operation process is complicated, the oil absorption amount is generally measured by using an absorption amount measuring device marketed in accordance with JIS. Since the measurement result is calculated by the amount of absorption per 100 g of the sample, the unit is represented by "ml / 100 g".

The "BET specific surface area / DBP absorption amount" in the present invention is an index of particle properties on the particle surface and inside the particles of the secondary particles constituting the positive electrode active material.

As the BET specific surface area increases, the contact area between the positive electrode active material and the electrolyte increases, and the output characteristics of the lithium ion secondary battery (hereinafter referred to as “secondary battery”) can be significantly improved.

The DBP absorption amount is an index showing the abundance ratio of the space part existing in the secondary particles (hereinafter referred to as "space part ratio"), and as the DBP absorption amount increases, the space part ratio also increases, and the BET specific surface area is increased. It tends to increase.

In the positive electrode active material of the present invention, by making the "BET specific surface area / DBP absorption amount", which is the ratio of the BET specific surface area to the DBP absorption amount, larger than before, the spatial part ratio or more that takes in the electrolyte inside the secondary particles or more. In addition, the contact area with the electrolytic solution can be increased, and its output characteristics can be further improved. If the DBP absorption amount is made too large in order to increase the BET specific surface area, the bulk density of the positive electrode active material is lowered, the filling property is lowered, and the capacity per volume of the battery is lowered. In addition, since the strength of the secondary particles of the positive electrode active material is lowered, the cycle characteristics may be deteriorated. In the present invention, since the "BET specific surface area / DBP absorption amount" is large, it is possible to increase the BET specific surface area and improve the output characteristics while suppressing the decrease in filling property and strength.

However, if the BET specific surface area / DBP absorption amount becomes too large, the thermal stability may decrease when used as a positive electrode material for a secondary battery. Therefore, it is preferably 0.100 or less. It is more preferably 095 or less.

(2) BET Specific Surface Area In the positive electrode active material of the present invention, as long as the "BET specific surface area / DBP absorption amount", which is an index of the particle properties of the secondary particles constituting the positive electrode active material, is within the above range, the positive electrode is used. The BET specific surface area of the active material is not particularly limited. However, the BET specific surface area of the positive electrode active material of the present invention ^{is preferably 1.5 m 2} / g or more and 5.0 m ² / g or less, and 2.0 m ² / g or more and 4.5 m ² / g or less. Is more preferable.

In the present invention, if the specific surface area of the positive electrode active material ^{is less than 1.5 m 2} / g, a sufficient reaction area between the positive electrode active material and the electrolyte cannot be sufficiently secured when the secondary battery is configured, and the secondary battery cannot be secured sufficiently. It may not be possible to sufficiently improve the output characteristics of the battery. On the other hand, if the specific surface area ^{exceeds 5.0 m 2} / g, the reaction area between the positive electrode active material and the electrolyte becomes too large, and the durability of the secondary battery may decrease.

(3) DBP absorption amount The DBP absorption amount is not particularly limited as long as the above-mentioned "BET specific surface area / DBP absorption amount" is within the above range. However, the amount of DBP absorbed by the positive electrode active material of the present invention is preferably 30 ml / 100 g or more and 65 ml / 100 g or less, and more preferably 40 ml / 100 g or more and 55 ml / 100 g or less.

In the present invention, if the amount of DBP absorbed by the positive electrode active material is less than 30 ml / 100 g, a sufficient BET specific surface area may not be obtained due to the fact that a sufficient space is not formed. On the other hand, when the amount of DBP absorbed exceeds 65 ml / 100 g, there are structurally too many spaces inside the secondary particles, the bulk density of the positive electrode active material becomes low, and the filling property is lowered. When the next battery is configured, the battery capacity per unit volume may not be sufficiently obtained.

(4) Particle Structure The positive electrode active material of the present invention is composed of secondary particles formed by aggregating a plurality of primary particles. In the present invention, as long as the particle properties of the secondary particles constituting the positive electrode active material are within the above-mentioned range with respect to the index of "BET specific surface area / DBP absorption amount", the above-mentioned BET specific surface area and / Alternatively, the structure of the secondary particles is not particularly limited as long as it is within the range of the amount of DBP absorbed.

However, in the positive electrode active material of the present invention, the secondary particles are formed by aggregating the primary particles and electrically conducting with each other, and a space portion existing dispersed in the agglomerated portion. It is preferable to provide.

Here, "electrically conductive" means that the agglomerated portions of the primary particles are structurally connected to each other and are in a state of being electrically conductive. The "space portion" is a pore portion formed in the agglomerated portion. The space part exists apart from each other due to the presence of the primary particles forming the agglomerate part, but communicates with each other outside the particle and the space part through the grain boundaries and voids between the primary particles, and enters the space part. Electrolytes and conductive auxiliaries can enter.

In the positive electrode active material having the particle structure of the preferred embodiment of the present invention, since the electrolyte enters the inside of the secondary particles through the grain boundaries, voids or spaces between the primary particles, not only the surface of the secondary particles but also the surface of the secondary particles , Lithium can be desorbed and inserted even inside the secondary particles. Moreover, in this positive electrode active material, since the agglomerated portions are electrically conductive with each other and the cross-sectional area of the conduction path is sufficiently large, the resistance (internal resistance) inside the secondary particles can be significantly reduced. .. Further, by controlling the space portion to an appropriate size, for example, by dispersing the space portion smaller and larger than before, the BET specific surface area can be increased with respect to the DBP absorption amount. That is, since such a structure makes it possible for the secondary particles to have a particle property having a sufficient BET specific surface area while having an appropriate space ratio, a positive electrode active material having such a particle structure is used as a positive electrode. When a secondary battery is constructed by using it as a material, its output characteristics can be further improved.

In the positive electrode active material of the present invention, it is more preferable that the secondary particles are further provided with an outer shell portion that is electrically conductive with the agglomerated portion on the outside of the agglomerated portion. Here, the "outer shell portion" means a layered structural portion formed on the outermost side of the secondary particles. By providing the secondary particles with an outer shell portion, the particle structure thereof can be made more rigid, and it becomes possible to more appropriately prevent the destruction of the secondary particles during filling and use. Even in this case, the electrolyte and the conductive auxiliary agent can enter the inside of the secondary particles, particularly the space, from the grain boundaries and voids of the primary particles constituting the outer shell portion. Further, since the outer shell portion is also electrically conductive with the agglomerated portion and the cross-sectional area of the conduction path is sufficiently large, the resistance (internal resistance) inside the secondary particles can be further reduced.

(5) Product of BET specific surface area and d50 In the positive electrode active material of the present invention, the volume of the BET specific surface area and the secondary particles constituting the positive electrode active material measured by a laser light diffraction / scattering type particle size analyzer. The product with d50 (median diameter) obtained from the integrated value is preferably 9.0 or more.

Here, d50 is a particle size in which the volume of each secondary particle is accumulated from the smaller particle size side, and the cumulative volume is 50% of the total volume of all the secondary particles (the particle size is set to 100% of the total volume). When the cumulative curve of the distribution is obtained, it means the particle size of the point where this cumulative curve is 50%).

In general, when the particle size of the secondary particles constituting the positive electrode active material is large, the BET specific surface area tends to decrease, and when the particle size of the secondary particles is small, the BET specific surface area tends to increase. In the positive electrode active material of the present invention, by setting the product of the BET specific surface area and d50 to 9.0 or more, the BET specific surface area can be sufficiently secured even when the particle size of the secondary particles is large. The contact area between the positive electrode active material and the electrolyte is sufficient, and when a secondary battery is constructed, its output characteristics can be improved.

From this viewpoint, in the present invention, the product of the BET specific surface area of the positive electrode active material and d50 is more preferably 9.5 or more, and further preferably 10.0 or more. However, from the viewpoint of thermal stability and durability of the secondary battery, the product of the BET specific surface area of the positive electrode active material and d50 is preferably 25.0 or less, and more preferably 20.0 or less. preferable.

(6) d50 (median diameter)
In the positive electrode active material of the present invention, the d50 of the secondary particles constituting the positive electrode active material is preferably 3 μm or more and 15 μm or less obtained from the volume integrated value measured by the laser light diffraction / scattering type particle size analyzer. It is more preferably 4 μm or more and 10 μm or less, and further preferably 4 μm or more and 8 μm or less.

If the d50 of the positive electrode active material is within such a range, not only can the battery capacity per unit volume of the secondary battery using this positive electrode active material be increased, but also its safety and output characteristics are improved. It becomes possible. If d50 is less than 3 μm, the filling property of the positive electrode active material is lowered, and the battery capacity per unit volume may not be increased. On the other hand, when d50 exceeds 15 μm, the reaction area of the positive electrode active material decreases and the interface with the electrolyte decreases, so that it becomes difficult to improve the output characteristics of the secondary battery using this positive electrode active material. There is.

(7) Particle Size Distribution In the positive electrode active material of the present invention, [(d90-d10) / d50], which is an index indicating the spread of the particle size distribution of the secondary particles constituting the positive electrode active material, is 1.0 or less. It is preferably 0.7 or less, more preferably 0.6 or less.

As described above, the positive electrode active material composed of secondary particles having a narrow particle size distribution has a small proportion of fine particles and coarse particles, and a secondary battery using these is excellent in safety, cycle characteristics, and output characteristics. It becomes a thing.

On the other hand, when [(d90-d10) / d50] exceeds 1.0, the proportion of fine particles and coarse particles in the positive electrode active material increases. For example, if the proportion of fine particles is high, the secondary battery tends to generate heat due to the local reaction of the fine particles, which not only reduces the safety but also causes the cycle due to the selective deterioration of the fine particles. The characteristics may be inferior. Further, if the proportion of coarse particles is large, the reaction area between the electrolyte and the positive electrode active material cannot be sufficiently secured, and the output characteristics may be inferior.

Assuming industrial-scale production, it is not realistic to use a positive electrode active material having an excessively small [(d90-d10) / d50]. Therefore, in consideration of cost and productivity, the lower limit of [(d90-d10) / d50] is preferably about 0.25.

The meanings of d10 and d90 in the index [(d90-d10) / d50] indicating the spread of the particle size distribution, and how to obtain them are the same as in the case of d50 described above. That is, d90 means a particle size in which the volume of each particle is accumulated from the smaller particle size side and the accumulated volume is 90% of the total volume of all particles. d10 means a particle size in which the volume of each particle is accumulated from the smaller particle size side and the accumulated volume is 10% of the total volume of all particles.

(8) Primary Particles In the positive electrode active material of the present invention, the primary particles constituting the secondary particles are preferably formed in a size having an average particle size in the range of 0.05 μm or more and 0.5 μm or less.

The size of the primary particles is determined by embedding the secondary particles in a resin or the like and making the cross section observable by cross-section polisher processing or the like, and then observing the cross section using an SEM such as FE-SEM. The maximum outer diameter (major axis diameter) of 10 or more primary particles existing in the cross section of the secondary particles is measured, the average value is obtained, and this value is taken as the particle size of the primary particles in the secondary particles. Next, for 10 or more secondary particles, the particle size of the primary particles is similarly determined. Finally, the average particle size of the primary particles in all of these secondary particles is determined by obtaining the average particle size obtained for these secondary particles.

If the average particle size of the primary particles is less than 0.05 μm, there is a possibility that the primary particles become fragile and a problem that sufficient battery performance cannot be obtained may occur. On the other hand, if the average particle size of the primary particles exceeds 0.5 μm, the diffusion distance in the solid in the particles becomes long, which may cause a problem that sufficient battery performance cannot be obtained.

(9) Crystallet diameter obtained from the X-ray diffraction pattern of the (003) plane In the positive electrode active material of the present invention, the crystal of the primary particles is crystallized from the half-value width of the peak of the (003) plane by X-ray diffraction using the Scheller formula. When the child diameter is determined, the crystallite diameter is preferably 30 nm or more and 150 nm or less, more preferably 40 nm or more and 130 nm or less, and further preferably 70 nm or more and 125 nm or less. A positive electrode active material having a crystallite diameter in such a range is preferable because it has extremely high crystallinity, can reduce the positive electrode resistance of the secondary battery, and can improve its output characteristics.

When the crystallite diameter of the (003) plane is less than 30 nm, the primary particles are fine, the pores existing between the primary particles in the positive electrode active material are too fine, and the electrolyte does not enter the positive electrode active material. Therefore, the reaction area between the positive electrode active material and the electrolyte may decrease, and the output characteristics of the secondary battery may decrease. On the other hand, when the crystallite diameter of the (003) plane exceeds 150 nm, the primary particles become too coarse, the proportion of pores in the secondary particles is extremely reduced, and the entry path of the electrolyte is reduced. The reaction area with the electrolyte may decrease, and the output characteristics of the secondary battery may deteriorate.

(10) Tap Density In order to increase the usage time of portable electronic devices and the mileage of electric vehicles, increasing the capacity of secondary batteries has become an important issue. On the other hand, the thickness of the electrodes of the secondary battery is required to be about several μm due to problems of packing of the entire battery and electron conductivity. Therefore, it is necessary not only to use a high-capacity positive electrode active material, but also to improve the filling property of the positive electrode active material and to increase the capacity of the secondary battery as a whole.

From this point of view, in the positive electrode active material of the present invention, the tap density, which is an index of filling property (sphericality of secondary particles constituting the positive electrode active material), is 0.8 g / cm ³ or more and 2.0 g / cm. It is preferably ^{3 or less.}

When the tap density is ^{less than 0.8 g / cm 3} , even if the BET specific surface area is increased, the filling property is low and the battery capacity of the entire secondary battery may not be sufficiently improved. The upper limit of the tap density is not particularly limited, but in the case of the particle structure of the present invention, the upper limit under normal manufacturing conditions is about ^{2.0 g / cm 3.} The tap density is ^{more preferably 1.0 g / cm 3} or more, and further preferably 1.1 g / cm ³ or more.

The tap density represents the bulk density after tapping the sample powder collected in a container 100 times based on JIS Z-2504, and can be measured using a shaking specific gravity measuring device.

(11) Composition The present invention relates to a positive electrode active material composed of a lithium nickel manganese cobalt-containing composite oxide, that is, a ternary positive electrode active material containing at least nickel, manganese, and cobalt (NMC) as transition metals. It is widely applicable, and its composition is not particularly limited.

However, the present invention has the general _{formula: Li 1 + u Ni x Mn} y Co z M t O 2 (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1,0.3 ≦ x ≦ 0.9,0 <y ≦ 0.5, 0.0 <z ≦ 0.5, 0 ≦ t ≦ 0.1, M is Mg, Al, Si, Ca, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, It can be suitably applied to a positive electrode active material composed of a lithium nickel manganese cobalt-containing composite oxide having a hexagonal crystal structure having a layered structure and represented by one or more additive elements selected from W). it can.

In this positive electrode active material, the value of u indicating the excess amount of lithium (Li) is preferably −0.05 or more and 0.50 or less, more preferably 0 or more and 0.50 or less, and further preferably 0 or more and 0.35. It is as follows. By restricting the value of u to the above range, the output characteristics and battery capacity of the secondary battery using this positive electrode active material as the positive electrode material can be improved. On the other hand, if the value of u is less than −0.05, the positive electrode resistance of the secondary battery becomes large, so that the output characteristics may not be improved. On the other hand, if it exceeds 0.50, not only the initial discharge capacity decreases, but also the positive electrode resistance may increase.

Nickel (Ni) is an element that contributes to increasing the potential and capacity of secondary batteries. The value of x indicating the content is preferably 0.3 or more and 0.9 or less, more preferably 0.4 or more and 0.7 or less, and further preferably 0.4 or more and 0.6 or less. If the value of x is less than 0.3, it may not be possible to sufficiently improve the energy density of the secondary battery using this positive electrode active material. On the other hand, when the value of x exceeds 0.9, the content of other elements that improve the output characteristics and durability decreases, and the characteristics as a positive electrode active material may not be sufficiently obtained.

Manganese (Mn) is an element that contributes to the improvement of thermal stability. The value of y indicating the content is preferably more than 0 and 0.5 or less, more preferably 0.1 or more and 0.4 or less. If the value of y exceeds 0.5, Mn may elute from the positive electrode active material during high temperature operation, and the charge / discharge cycle characteristics may deteriorate.

Cobalt (Co) is an element that contributes to the improvement of charge / discharge cycle characteristics. The value of z indicating the content is preferably more than 0 and 0.5 or less, more preferably 0.1 or more and 0.4 or less. If the value of z exceeds 0.3, the initial discharge capacity of the secondary battery using this positive electrode active material may decrease.

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

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

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

2. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material of the present invention has the above-mentioned "BET specific surface area / DBP absorption amount", which is at least an index of the particle properties of the secondary particles constituting the positive electrode active material. As long as it is within the range, the manufacturing method is not particularly limited.

For example, the secondary particles constituting the precursor have a central portion formed by aggregating the primary particles and agglomerating the plate-shaped primary particles, and the plate-shaped primary particles are formed outside the central portion. Nickel, which is a precursor having two or more laminated structures in which a low-density layer formed by aggregating smaller fine primary particles and a high-density layer formed by aggregating the plate-shaped primary particles are laminated. By preparing a manganese-cobalt composite hydroxylated substance, then mixing it with a lithium compound, and firing the obtained lithium mixture, it is possible to obtain a positive electrode active material having the particle properties of the present invention.

(1) Heat Treatment Step In the method for producing a positive electrode active material of the present invention, a heat treatment step is optionally provided before the mixing step to nickel manganese cobalt composite hydroxide (hereinafter referred to as “composite hydroxide”). May be mixed with the lithium compound after being made into heat-treated particles by heat treatment. Here, the heat-treated particles include nickel-manganese-cobalt composite oxide (hereinafter referred to as "composite oxide") converted into an oxide in the heat-treatment step, or composite hydroxide from which excess water has been removed in the heat-treatment step. A mixture of composite oxides is also included.

The heat treatment step is a step of converting the composite hydroxide into a composite oxide by heating it to 350 ° C. or higher and 650 ° C. or lower and heat-treating it. As a result, it is possible to suppress a decrease in the BET specific surface area of the positive electrode active material, and it is possible to easily control the "BET specific surface area / DBP absorption amount" of the obtained positive electrode active material.

If the heating temperature in the heat treatment step is less than 350 ° C., too much composite hydroxide remains, and it may not be possible to sufficiently suppress variations in the “BET specific surface area / DBP absorption amount” of the positive electrode active material. On the other hand, if the heating temperature exceeds 650 ° C., the BET specific surface area of the positive electrode active material becomes too low, no further effect can be expected, and the production cost increases.

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

The heat treatment time is not particularly limited, but is preferably at least 1 hour, and more preferably 5 hours or more and 15 hours or less, from the viewpoint of conversion to a composite oxide.

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

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

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

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

(3) Temporary firing step When lithium hydroxide or lithium carbonate is used as the lithium compound, the lithium mixture is placed at a temperature lower than the firing temperature described later and at 350 ° C. or higher after the mixing step and before the firing step. A calcining step of calcining at 800 ° C. or lower, preferably 450 ° C. or higher and 750 ° C. or lower may be performed. Thereby, lithium can be sufficiently diffused in the composite hydroxide or the heat-treated particles, and a more uniform lithium composite oxide can be obtained.

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

(4) Firing step The calcining step is a step of calcining the lithium mixture obtained in the mixing step under predetermined conditions, and diffusing lithium into the composite hydroxide or heat-treated particles to cause a reaction to obtain a lithium composite oxide. Is.

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

a) Firing temperature The calcination temperature of the lithium mixture needs to be 700 ° C. or higher and 920 ° C. or lower. If the firing temperature is less than 700 ° C., the composite hydroxide or heat-treated particles do not sufficiently react with lithium, and excess lithium or unreacted composite hydroxide or heat-treated particles remain, or the obtained positive electrode active material crystals. The sex may be insufficient. On the other hand, if the firing temperature exceeds 920 ° C., the BET specific surface area of the positive electrode active material may decrease, the “BET specific surface area / DBP absorption amount” may become too small, and the secondary flow particles of the positive electrode active material may become too small. It sinters violently between them, causing abnormal grain growth and increasing the proportion of irregularly shaped coarse particles.

By appropriately adjusting the firing temperature, it is possible to control the "BET specific surface area / DBP absorption amount" and further, the product of the BET specific surface area and d50. As the firing temperature increases, both the "BET specific surface area / DBP absorption amount" and the product of the BET specific surface area and d50 tend to decrease. From the viewpoint of controlling the "BET specific surface area / DBP absorption amount" of the positive electrode active material, the firing temperature of the lithium mixture is preferably 720 ° C. or higher and 920 ° C. or lower, and more preferably 750 ° C. or higher and 900 ° C. or lower. ..

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

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

c) Baking atmosphere The atmosphere at the time of firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume or more and 100% by volume or less, and an oxygen concentration of 50% by volume or more and 100% by volume or less. It is more preferable to have the atmosphere of. It is particularly preferable to create a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. That is, firing is preferably performed in the atmosphere or an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the positive electrode active material may be insufficient.

(5) Crushing Step The secondary particles constituting the positive electrode active material obtained by the firing step may be aggregated or slightly sintered. In such a case, it is preferable to crush the agglomerate or the sintered body. Thereby, the average particle size and the particle size distribution of the obtained positive electrode active material can be adjusted in a suitable range. In addition, crushing means that mechanical energy is applied to an agglomerate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and the secondary particles themselves are hardly destroyed. It means the operation of separating and loosening agglomerates.

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

As described above, the "BET specific surface area / DBP absorption amount" of the finally obtained positive electrode active material can be controlled by adjusting the heat treatment conditions and firing conditions of the composite hydroxide and / or the heat-treated particles. It is possible.

(6) Method for Producing Composite Hydroxide The positive electrode active material of the present invention is not particularly limited to the particle structure of the composite hydroxide as a precursor thereof and the method for producing the same, but the finally obtained positive electrode active material. From the viewpoint of more easily controlling the "BET specific surface area / DBP absorption amount", it is preferable to use the composite hydroxide obtained by the following method for producing a composite hydroxide as a precursor.

That is, the positive electrode active material of the present invention is, for example, a space in which secondary particles are formed by aggregating primary particles and are electrically conductive with each other, and a space in which the secondary particles are dispersed in the agglomerated portion. By having a structure including a portion, or a structure including an agglomerated portion, a space portion, and an outer shell portion, the particle properties within the scope of the present invention, that is, "BET specific surface area / DBP absorption amount", and further , The product of the BET specific surface area and d50 can be easily provided.

The particle structure of such a positive electrode active material can be obtained by controlling the particle structure of the composite hydroxide as a precursor. The composite hydroxide as a precursor for obtaining the positive electrode active material having the above-mentioned particle structure is preferably produced by the following crystallization reaction.

(A) Crystallization reaction The composite hydroxide forms a reaction aqueous solution by supplying an aqueous solution containing at least a transition metal and an aqueous solution containing an ammonium ion feeder into the reaction vessel, and the complex hydroxide is subjected to a crystallization reaction. can get.

The crystallization reaction is carried out by controlling the pH value of the reaction aqueous solution based on a liquid temperature of 25 ° C. to be 12.0 or more and 14.0 or less, thereby performing nucleation and the nucleation. The pH value of the reaction aqueous solution containing nuclei obtained in the step at a liquid temperature of 25 ° C. is controlled to be lower than the pH value of the nucleation step and in the range of 10.5 or more and 12.0 or less. This includes a particle growth step of growing the nucleus.

Then, (1) the reaction atmosphere in the first stage (initial stage) of the nucleation generation step and the particle growth step is adjusted to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less, and (2) the particle growth step. After the first step, the reaction atmosphere is changed from the non-oxidizing atmosphere to an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume, and an oxidizing agent is supplied to obtain the second step of the particle growth step. 3) The reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere to be the third stage of the particle growth step, and (4) the reaction atmosphere is changed from the non-oxidizing atmosphere to the oxidizing atmosphere. The oxidant is supplied at the same time as switching to the fourth stage of the particle growth step, and (5) the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere to obtain the fifth stage of the particle growth step. It is preferable to do so.

Further, (6) the sixth step of the particle growth step, in which the reaction atmosphere is switched from the non-oxidizing atmosphere to the oxidizing atmosphere and an oxidizing agent is supplied to perform crystallization, and (7) the above. It is more preferable to provide the seventh step of the particle growth step in which the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere to perform crystallization.

[Nucleation process]
In the nucleation step, first, a transition metal compound as a raw material in this step is dissolved in water to prepare an aqueous raw material solution. At the same time, an alkaline aqueous solution and an aqueous solution containing an ammonium ion feeder are supplied and mixed in the reaction vessel, and the pH value measured at a liquid temperature of 25 ° C. is 12.0 or more and 14.0 or less, and the ammonium ion concentration is 3 g. A pre-reaction aqueous solution having a temperature of / L or more and 25 g / L or less is prepared. The pH value of the pre-reaction aqueous solution can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

Next, the raw material aqueous solution is supplied while stirring the pre-reaction aqueous solution. As a result, a nucleation aqueous solution, which is a reaction aqueous solution in the nucleation step, is formed in the reaction vessel. Since the pH value of this aqueous solution for nucleation is in the above range, nucleation occurs preferentially in the nucleation step with almost no growth of nuclei. In the nucleation step, the pH value of the nucleation aqueous solution and the concentration of ammonium ions change with nucleation, so an alkaline aqueous solution and an ammonia aqueous solution are supplied in a timely manner, and the pH value of the solution in the reaction vessel is 25. It is necessary to control the pH to be maintained in the range of 12.0 or more and 14.0 or less based on the ° C., and the concentration of ammonium ions is maintained in the range of 3 g / L or more and 25 g / L or less.

In the nucleation step, it is necessary to circulate the inert gas in the reaction vessel and adjust the reaction atmosphere to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less, preferably 2% by volume or less. It is usually preferable to adjust the reaction atmosphere before starting the supply of the raw material aqueous solution. As a result, agglomerated portions are sufficiently formed inside the positive electrode active material using this composite hydroxide as a precursor, and it is possible to suppress a decrease in particle density due to the formation of space portions.

In the nucleation step, by supplying an aqueous solution containing a raw material aqueous solution, an alkaline aqueous solution and an ammonium ion feeder to the nucleation aqueous solution, the generation of new nuclei is continuously continued. Then, when a predetermined amount of nuclei are generated in the nucleation aqueous solution, the nucleation step is terminated.

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

[Particle growth process]
After the nucleation step is completed, the pH value of the nucleation aqueous solution in the reaction vessel is adjusted to 10.5 or more and 12.0 or less based on the liquid temperature of 25 ° C., and the particle growth aqueous solution which is the reaction aqueous solution in the particle growth step is prepared. Form. The pH value can also be adjusted by stopping the supply of the alkaline aqueous solution, but in order to obtain secondary particles of the composite hydroxide having a narrow particle size distribution, the pH value is temporarily stopped by stopping the supply of all the aqueous solutions. It is preferable to adjust. Specifically, after stopping the supply of all the aqueous solutions, it is preferable to adjust the pH value by supplying the nucleation aqueous solution with an inorganic acid of the same type as the acid constituting the metal compound as a raw material.

Next, the supply of the raw material aqueous solution is restarted while stirring the particle growth aqueous solution. At this time, since the pH value of the aqueous solution for particle growth is in the above range, new nuclei are hardly generated, nuclei (particles) growth progresses, and secondary particles of a composite hydroxide having a predetermined particle size. Is formed. Also in the particle growth step, the pH value and ammonium ion concentration of the aqueous solution for particle growth change with the growth of particles, so an alkaline aqueous solution and an aqueous ammonia solution are supplied in a timely manner to maintain the pH value and ammonium ion concentration within the above ranges. It is necessary to do.

In particular, in the method for producing a composite hydroxide in this example, the reaction atmosphere is changed from a non-oxidizing atmosphere to oxygen by introducing an atmospheric gas while continuing to supply the raw material aqueous solution in the middle of the particle growth step. An operation is performed such as switching to an oxidizing atmosphere having a concentration of more than 5% by volume, or switching from this non-oxidizing atmosphere to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less.

In the particle growth step, an inert gas and / or an oxidizing gas is circulated in the reaction aqueous solution in the reaction vessel using an air diffuser to switch from an oxidizing atmosphere to a non-oxidizing atmosphere, or to make the particles non-oxidizing. It is preferable to quickly switch from the atmosphere to the oxidizing atmosphere. As a method of supplying the inert gas and / or the oxidizing gas to the reaction aqueous solution in the reaction vessel, it is possible to supply the inert gas and / or the oxidizing gas to the space in the reaction vessel in contact with the reaction aqueous solution. / Or it is preferable to adopt a method of directly supplying the oxidizing gas into the reaction aqueous solution. As a result, the time for switching the atmosphere can be shortened, and a composite hydroxide having an appropriate particle structure can be obtained.

In such a method for producing a composite hydroxide, metal ions are precipitated as nuclei or primary particles in the nucleation step and the particle growth step. Therefore, the ratio of the liquid component to the metal component in the nucleation aqueous solution and the particle growth aqueous solution increases. As a result, the concentration of the raw material aqueous solution apparently decreases, and the growth of secondary particles of the composite hydroxide may be stagnant, especially in the particle growth step. Therefore, in order to suppress the increase of the liquid component, it is preferable to discharge a part of the liquid component of the aqueous particle growth solution to the outside of the reaction vessel from the end of the nucleation step to the middle of the particle growth step. Specifically, the supply and stirring of the aqueous solution containing the raw material aqueous solution, the alkaline aqueous solution and the ammonium ion feeder are temporarily stopped, the nuclei and the composite hydroxide in the particle growth aqueous solution are precipitated, and the supernatant of the particle growth aqueous solution is settled. It is preferable to drain the liquid. By such an operation, the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth can be increased, so that the stagnation of particle growth can be prevented and the particle size distribution of the secondary particles of the obtained composite hydroxide is in a preferable range. Not only can it be controlled, but the density of the secondary particles as a whole can also be improved.

[Control of particle size of secondary particles of composite hydroxide]
The particle size of the secondary particles of the composite hydroxide can be controlled by the time of the particle growth step and the nucleation step, the pH value of the nucleation aqueous solution and the particle growth aqueous solution, and the supply amount of the raw material aqueous solution. For example, by carrying out the nucleation step at a high pH value or by lengthening the time of the particle formation step, the amount of the metal compound contained in the supplied raw material aqueous solution can be increased, and the amount of nucleation produced can be increased. The particle size of the secondary particles of the composite hydroxide to be obtained can be reduced. On the contrary, by suppressing the amount of nucleation produced in the nucleation step, the particle size of the secondary particles of the obtained composite hydroxide can be increased.

[Another Embodiment of the crystallization reaction]
In the method for producing a composite hydroxide of the present invention, a component adjusting aqueous solution adjusted to a pH value and ammonium ion concentration suitable for the particle growth step is prepared separately from the nucleation aqueous solution, and the component adjusting aqueous solution is used. , Aqueous solution for nucleation after the nucleation step, preferably an aqueous solution for nucleation after the nucleation step from which a part of the liquid component is removed is added and mixed, and this is used as an aqueous solution for particle growth in the particle growth step. May be done.

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

[Supply aqueous solution]
a) Aqueous solution of raw material In this example, the ratio of metal elements contained in the aqueous solution of raw material is approximately the composition ratio of the obtained composite hydroxide.

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, chlorides, etc., and cost and halogens are used. From the viewpoint of preventing the mixing of sulfates, it is particularly preferable to use sulfates preferably.

Further, the additive element M (M is one or more additive elements selected from Mg, Al, Si, Ca, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) in the composite hydroxide. ) Is contained, the compound for supplying the additive element M is also preferably a water-soluble compound, for example, magnesium sulfate, aluminum sulfate, sodium silicate, calcium sulfate, titanium sulfate, peroxotitanic acid. Preferable compounds include ammonium, potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate, ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate, ammonium tungstate, etc. Can be used.

The concentration of the raw material aqueous solution is preferably 1 mol / L or more and 2.6 mol / L or less, and more preferably 1.5 mol / L or more and 2.2 mol / L or less in total of the metal compounds.

As for the supply amount of the raw material aqueous solution, the concentration of the product in the particle growth aqueous solution is preferably 30 g / L or more and 200 g / L or less, more preferably 80 g / L or more and 150 g / L or less at the end of the particle growth step. To be.

b) Alkaline aqueous solution The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. Although the alkali metal hydroxide can be added directly to the reaction aqueous solution, it is preferable to add it as an aqueous solution because of the ease of pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 30% by mass or less.

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

c) Aqueous solution containing an ammonium feeder The aqueous solution containing an ammonium ion feeder is also not particularly limited, and for example, aqueous ammonia or an aqueous solution such as ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride is used. can do.

When aqueous ammonia is used as the ammonium ion feeder, the concentration thereof is preferably 20% by mass or more and 30% by mass or less, and more preferably 22% by mass or more and 28% by mass or less. By regulating the concentration of ammonia water in such a range, it is possible to minimize the loss of ammonia due to volatilization and the like, so that it is possible to improve the production efficiency.

The method of supplying the aqueous solution containing the ammonium ion feeder can also be supplied by a pump capable of controlling the flow rate, as in the case of the alkaline aqueous solution.

[pH value]
In the method for producing a composite hydroxide of the present invention, the pH value of the reaction aqueous solution based on the liquid temperature of 25 ° C. is set in the range of 12.0 or more and 14.0 or less in the nucleation step, and 10. It is necessary to control within the range of 5 or more and 12.0 or less. In any of the steps, it is preferable to control the fluctuation range of the pH value during the crystallization reaction within ± 0.2. When the fluctuation range of the pH value is large, the nucleation amount and the particle growth ratio are not constant, and it becomes difficult to obtain secondary particles of a composite hydroxide having a narrow particle size distribution. The pH value of the reaction aqueous solution can be measured with a pH meter.

[Reaction atmosphere]
a) Non-oxidizing atmosphere In the production method of the present invention, by setting the reaction atmosphere to a non-oxidizing atmosphere, it is possible to form a central portion of secondary particles and a high-density layer composed of plate-shaped primary particles. it can. By introducing a non-oxidizing gas such as an inert gas, the oxygen concentration in the reaction atmosphere becomes a non-oxidizing atmosphere of 5% by volume or less, preferably 2% by volume or less, and more preferably 1% by volume or less. As described above, it is necessary to control the mixed atmosphere of oxygen and the inert gas.

b) Oxidizing atmosphere Specifically, the oxygen concentration in the reaction atmosphere is preferably 10% by volume or more, more preferably the air atmosphere (oxygen concentration: 21% by volume) so as to exceed 5% by volume. It needs to be controlled. It is preferably 1.0% by volume or more, and more preferably 2.0% by volume or more. By controlling the oxygen concentration in the reaction atmosphere within such a range, particle growth is suppressed, and the low-density layer is composed of fine primary particles having a size sufficiently different from that of the plate-shaped primary particles, as described above. A low density layer having a sufficient density difference from the central portion and the high density layer can be formed.

c) Oxidizing agent In the stage of crystallization in an oxidizing atmosphere in the particle growth step, by supplying an oxidizing agent to the aqueous solution for particle growth under predetermined conditions, a low-density part in which finer primary particles are aggregated and a low-density part. A structure is formed in which high-density portions in which plate-shaped primary particles are aggregated are laminated. Although the details are unknown, by using the atmosphere control in the particle growth process and the supply of the oxidant together in this way, the primary particles in the low-density part become finer, and the laminated structure of the low-density part and the high-density part becomes finer. By clarifying, it becomes possible to control the "BET specific surface area / DBP absorption amount", which is the particle property of the secondary particles constituting the positive electrode active material, within the range of the present invention.

The oxidizing agent is not particularly limited as long as it can generate finer primary particles by its oxidizing action and form a low-density portion of the composite hydroxide particles. For example, hydrogen peroxide. Various oxidizing agents such as (H ₂ O ₂ ), chromic acid (H ₂ CrO ₄ ), dichromic acid (H ₂ Cr ₂ O ₇ ) and hypochlorous acid (HClO) can be used.

Of these oxidizing agents, it is preferable to use hydrogen peroxide. The reason for this is that since hydrogen peroxide is composed only of oxygen and water, there is no possibility that impurities are incorporated into the obtained composite hydroxide particles. In addition, since hydrogen peroxide is instantly decomposed into oxygen and water in the aqueous solution for particle growth, the oxidizing action can be exerted only while the hydrogen peroxide is being supplied, and the oxidized state of the aqueous solution for particle growth is exhibited. This is because accurate control is possible. Further, since hydrogen peroxide directly releases oxygen in the aqueous solution for particle growth, metal ions, particularly manganese ions, can be efficiently oxidized.

The oxidizing agent is preferably supplied in a liquid state that is easy to handle and can make the oxidized state of the particle growth aqueous solution uniform. For example, when hydrogen peroxide is used as the oxidizing agent, it is preferably supplied as a hydrogen peroxide solution, and the concentration thereof is more preferably 2% by mass to 30% by mass and 2% by mass to 6% by mass. Is even more preferable.

The amount of the oxidizing agent supplied complements the oxidizing action of the metal ions contained in the raw material aqueous solution due to the oxidizing atmosphere, and the oxidizing agent is added even in a smaller amount than that of the prior art, for example, Japanese Patent Application Laid-Open No. 2016-94307. The effect of adding the above can be obtained. Since this supply amount differs depending on the oxidizing action of the oxidizing agent, it is preferable to carry out a preliminary test or the like and appropriately adjust the supply amount according to the type of the oxidizing agent used and the supply conditions (temperature of the particle growth aqueous solution, etc.).

For example, when hydrogen peroxide is used as an oxidizing agent, the amount of hydrogen peroxide supplied (H) is the molar amount of the total amount of metal ions (Me) contained in the raw material aqueous solution supplied at the same time while the hydrogen peroxide is supplied. The ratio (H / Me) may be 0.015 or less, preferably 0.01 or less. At this time, it is preferable to supply hydrogen peroxide at a constant ratio according to the amount of the raw material aqueous solution supplied. As a result, finer primary particles are formed while the hydrogen peroxide is being supplied. If the supply amount is excessively large, the primary particles may become excessively fine, or fine primary particles may be formed even after switching to the non-oxidizing atmosphere, and a clear laminated structure cannot be obtained. The lower limit of the supply amount of hydrogen peroxide may be such that the oxidation of metal ions can be promoted, and the H / Me ratio is preferably 0.001 or more, more preferably 0.02 or more.

d) Switching of reaction atmosphere The crystallization reaction (including the switching time between atmospheres) in each atmosphere from the first stage to the fifth stage of the particle growth stage or from the first stage to the seventh stage is more detailed. Is as follows.

When the particle growth step is performed from the first step to the fifth step, the switching of the reaction atmosphere is defined by the ratio of the amount of metal added in each step to the total amount of metal added in the particle growth step. Regarding the ratio of crystallization reaction in each stage to the entire particle growth process, the first stage is 10% or more and 20% or less, the second stage is 5% or more and 35% or less, and the third stage is 15% or more and 35%. The fourth step may be 10% or more and 40% or less, the fifth step may be 20% or more and 50% or less, and the ratio of the entire crystallization reaction in an oxidizing atmosphere may be in the range of 10% to 60%. preferable. The ratio of the crystallization reaction in the fourth stage to the second stage is preferably in the range of 1.2 times or more and 2.0 times or less.

When the particle growth step is carried out from the first step to the seventh step, the reaction atmosphere is switched so that the ratio of the crystallization reaction in each step to the entire particle growth step is 5% or more and 15% or less in the first step. , 2nd stage is 5% or more and 25% or less, 3rd stage is 10% or more and 30% or less, 4th stage is 10% or more and 35% or less, 5th stage is 15% or more and 30% or less, It is preferable that the 6th step is 10% or more and 40% or less, the 7th step is 30% or more and 50% or less, and the ratio of the entire crystallization reaction in an oxidizing atmosphere is in the range of 10% to 50%. The ratio of the crystallization reaction in the sixth stage to the second and fourth stages is preferably in the range of 1.2 times or more and 2.0 times or less.

By such a crystallization reaction, it is composed of a plurality of plate-shaped primary particles and secondary particles formed by aggregating fine primary particles smaller than the plate-shaped primary particles, and the secondary particles are mainly the plate-shaped primary particles. A central portion formed by agglomeration of particles, a first low-density layer formed mainly by aggregating the fine primary particles, and outside the first low-density layer, mainly outside the central portion. A first high-density layer formed by aggregating the plate-shaped primary particles, and a second low-density layer mainly formed by aggregating the fine primary particles on the outside of the first high-density layer. A composite hydroxide having a second high-density layer formed by aggregating the plate-shaped primary particles on the outside of the second low-density layer can be obtained.

Alternatively, the secondary particles, which are schematically shown in FIG. 1, are mainly formed by aggregating the plate-shaped primary particles in a central portion and outside the central portion by aggregating the fine primary particles. On the outside of the first low-density layer and the first low-density layer, mainly on the outside of the first high-density layer formed by agglomeration of the plate-shaped primary particles and the first high-density layer. A second low-density layer formed mainly by agglomerating the fine primary particles, and a second high-density layer mainly formed by agglomerating the plate-shaped primary particles outside the second low-density layer. The third low-density layer formed by aggregating the fine primary particles mainly on the outside of the second high-density layer, and the plate-shaped primary particles mainly agglomerated on the outside of the third low-density layer. A composite hydroxide having a third high-density layer formed therein is obtained.

The above-mentioned method for producing a composite hydroxide and the particle structure obtained thereby are only examples for obtaining the particle properties of the positive electrode active material of the present invention, but a composite hydroxide having such a particle structure is used as a precursor. By doing so, the positive electrode active material of the present invention can be easily obtained.

3. 3. Lithium-ion secondary battery The lithium-ion secondary battery of the present invention can have the same configuration as a general non-aqueous electrolyte secondary battery, which includes components such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. .. Alternatively, the lithium ion secondary battery of the present invention can have the same configuration as a general solid electrolyte secondary battery including components such as a positive electrode, a negative electrode, and a solid electrolyte. That is, the present invention can be widely applied from a non-aqueous electrolyte secondary battery to an all-solid-state lithium ion secondary battery as long as it is a secondary battery that charges and discharges by removing and inserting lithium ions. The embodiments described below are merely examples, and the present invention is applied to a lithium ion secondary battery in which various modifications and improvements have been made based on the embodiments described in the present specification. It is possible.

(1) Components a) Positive electrode Using the above-mentioned positive electrode active material, for example, a positive electrode of a lithium ion secondary battery is manufactured as follows.

First, a conductive material and a binder are mixed with the positive electrode active material of the present invention, and if necessary, activated carbon and a solvent for adjusting the viscosity are added, and these are kneaded to prepare a positive electrode mixture paste. At that time, the mixing ratio of each of the positive electrode mixture pastes is also an important factor in determining the performance of the lithium ion secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass to 95 parts by mass, as in the case of the positive electrode of a general lithium ion secondary battery. The content of the conductive material can be 1 part by mass to 20 parts by mass, and the content of the binder can be 1 part by mass to 20 parts by mass.

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

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

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

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

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

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

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

d) Electrolyte Non-aqueous electrolyte As the non-aqueous electrolyte used in the secondary battery, a non-aqueous electrolyte solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent is used.

Examples of the organic solvent used in the non-aqueous electrolyte solution include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and further. One or more selected from ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. Can be mixed and used.

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

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

On the other hand, the solid electrolyte used in the solid electrolyte secondary battery such as all-solid lithium secondary _battery, use of such _{Li 1.3 Al 0.3 Ti 1.7 (PO} 4) 3 and _{Li 2} S-SiS 2 be able to. The solid electrolyte has a property of being able to withstand a high voltage. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

Inorganic solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes.

As the oxide solid electrolyte, an oxide containing oxygen (O) and having lithium ion conductivity and electron insulating property can be used. For example, Lithium Phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ NX, LiBO ₂ NX, LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO _{4- Li 3} PO ₄ , Li ₄ SiO _{4- Li 3} VO ₄ , Li ₂ O-B ₂ O _3- P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O _3- ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0) ≦ X ≦ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TIO ₃ (0 ≦ X ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ etc. Can be done.

As the sulfide solid electrolyte, a sulfide containing sulfur (S) and having lithium ion conductivity and electron insulating property can be used. For example, Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li _{2 SP 2} S ₅ , LiI-Li _{2 SB 2} S ₃ , Li _{3 PO 4 -Li 2 S-Si} 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O 5, LiI-Li 3 PO 4 -P ₂ S _{5 and the} like can be used.

As the inorganic solid electrolytes other than an oxide solid electrolyte and a sulfide solid electrolyte, for _example, Li ₃ N, LiI, etc. may be used Li 3 N-LiI-LiOH.

As the organic solid electrolyte, a polymer compound exhibiting ionic conductivity can be used. For example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. In addition, the organic solid electrolyte may contain a supporting salt (lithium salt).

When a solid electrolyte is used, the solid electrolyte can be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(2) Configuration of Lithium Ion Secondary Battery The configuration of the lithium ion secondary battery is not particularly limited, and the configuration of the non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and the like, and a solid electrolyte secondary. The next battery may have a configuration including a positive electrode, a negative electrode, a solid electrolyte, and the like. Further, the shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be adopted.

In the case of a non-aqueous electrolyte secondary battery, for example, a positive electrode and a negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte to form a positive electrode body that communicates with a positive electrode current collector and the outside. A lithium ion secondary battery is completed by connecting the terminals and the negative electrode current collector and the negative electrode terminals communicating with the outside using a current collecting lead or the like and sealing the battery case.

(3) Characteristics of Lithium Ion Secondary Battery As described above, the lithium ion secondary battery of the present invention uses the positive electrode active material of the present invention as the positive electrode material, and therefore is particularly excellent in capacity characteristics and output characteristics.

(4) Applications of Lithium Ion Secondary Battery As described above, the lithium ion secondary battery of the present invention is excellent in capacity characteristics and output characteristics, and a small portable electronic device in which these characteristics are required at a high level (4). It can be suitably used as a power source for notebook personal computers, smartphones, tablet terminals, digital cameras, etc.). Further, the lithium ion secondary battery of the present invention is not only capable of miniaturization and high output, but also has excellent safety and durability, and can simplify an expensive protection circuit. It can also be suitably used as a power source for transportation equipment such as electric vehicles, which are limited in space.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, unless otherwise specified, a reagent special grade sample manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. was used for producing the composite hydroxide and the positive electrode active material. In addition, the pH value of the reaction aqueous solution was measured by a pH controller (NPH-690D, manufactured by Nisshin Rika Co., Ltd.) through the nucleation formation step and the particle growth step, and the amount of sodium hydroxide aqueous solution supplied was determined based on this measured value. By adjusting, the fluctuation range of the pH value of the reaction aqueous solution in each step was controlled within the range of ± 0.2.

(Example 1)
a) Production of composite hydroxide [Nucleation step]
First, 14 L of water was put into the reaction vessel and the temperature in the vessel was set to 40 ° C. while stirring. At this time, nitrogen gas was circulated in the reaction vessel for 30 minutes, and the reaction atmosphere was a non-oxidizing atmosphere having an oxygen concentration of 2% by volume or less. Subsequently, an appropriate amount of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water are supplied into the reaction vessel so that the pH value is 12.6 based on the liquid temperature of 25 ° C. and the ammonium ion concentration is 10 g / L. A pre-reaction aqueous solution was formed by adjusting to.

At the same time, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in water so that the molar ratio of each metal element was Ni: Co: Mn = 38: 32: 30, and a 2 mol / L raw material aqueous solution was prepared. ..

Next, the raw material aqueous solution was supplied to the pre-reaction aqueous solution at 115 ml / min to form an aqueous solution for the nucleation step, and nucleation was performed for 1 minute. At this time, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution were supplied in a timely manner to maintain the pH value and ammonium ion concentration of the nucleation aqueous solution within the above ranges.

[Particle growth process]
After the completion of nucleation, the supply of all the aqueous solutions was temporarily stopped, and sulfuric acid was added to adjust the pH value to 11.2 based on the liquid temperature of 25 ° C. to form an aqueous solution for particle growth. .. After confirming that the pH value has reached a predetermined value, the first raw material aqueous solution is supplied at a constant rate of 115 ml / min, which is the same as in the nucleation step, and the nuclei (particles) generated in the nucleation step are produced. Grow up.

As the first step, crystallization in a non-oxidizing atmosphere was continued for 30 minutes (12.5% with respect to the entire particle growth step) from the start of the particle growth step, and then the supply of the raw material aqueous solution was continued. Air is circulated in the reaction vessel using a ceramic diffuser tube (manufactured by Kinoshita Rika Kogyo Co., Ltd.) having a pore size of 20 μm to 30 μm, and the reaction atmosphere is adjusted to an oxidizing atmosphere having an oxygen concentration of 21% by volume. (Switching operation 1).

As the second step, crystallization in the oxidizing atmosphere is continued for 30 minutes (12.5% with respect to the entire particle growth process) from the switching operation 1, and 10% by mass hydrogen peroxide solution is supplied in the oxidizing atmosphere. After supplying 0.01 as the molar ratio (H / Me) to the total amount of metal ions (Me) contained in the raw material aqueous solution, nitrogen is circulated in the reaction vessel using an air diffuser while the raw material aqueous solution is being supplied. The reaction atmosphere was adjusted to a non-oxidizing atmosphere having an oxygen concentration of 2% by volume or less (switching operation 2).

As the third step, after the crystallization in the non-oxidizing atmosphere was continued for 40 minutes (16.7% with respect to the entire particle growth step) from the switching operation 2, the air diffuser was opened while the supply of the raw material aqueous solution was continued. Air was circulated in the reaction vessel using the mixture, and the oxygen concentration was adjusted to an oxidizing atmosphere of 21% by volume (switching operation 3).

As the fourth step, the crystallization reaction in the oxidizing atmosphere is continued for 30 minutes (12.5% with respect to the entire particle growth process) from the switching operation 3, and 10% by mass hydrogen peroxide solution is supplied in the oxidizing atmosphere. After supplying 0.01 as the molar ratio (H / Me) to the total amount (Me) of metal ions contained in the raw material aqueous solution, nitrogen is added to the reaction vessel using an air diffuser while the raw material aqueous solution is being supplied. After distribution, the reaction atmosphere was adjusted to a non-oxidizing atmosphere having an oxygen concentration of 2% by volume or less (switching operation 4).

As the fifth step, after continuing the crystallization reaction in a non-oxidizing atmosphere for 110 minutes (45.8% with respect to the entire particle growth process) from the switching operation 4, the supply of all aqueous solutions including the raw material aqueous solution is stopped. By doing so, the particle growth process was completed. Then, the obtained product was washed with water, filtered and dried to obtain a powdery composite hydroxide.

In the particle growth step, 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water were supplied in a timely manner through this step, and the pH value and ammonium ion concentration of the particle growth aqueous solution were maintained within the above ranges. ..

[Particle structure]
A part of the composite hydroxide particles is embedded in the resin and cross-section polish processing is performed to make the cross section observable, and then 10 or more composite hydroxide particles are placed in a field emission scanning electron microscope (FE-SEM: Japan). Observed by JSM-6360LA) manufactured by Electronics Co., Ltd. As a result, the composite hydroxide particles have a central portion formed by aggregating the plate-shaped primary particles, and the plate-shaped primary particles and the fine primary particles are aggregated and formed on the outside of the central portion. It was confirmed that the product had two laminated structures in which a density layer and a high-density layer formed by aggregating plate-shaped primary particles were laminated.

The average ratio from the center to the outer diameter of each part with respect to the particle size of the secondary particles is taken as the particle size ratio, and the center particle size ratio of the composite hydroxide particles, the first low density layer particle size ratio, and the first high When the density layer particle size ratio and the second low density layer particle size ratio were also measured and calculated, they were 50.3%, 66.9%, 76.1%, and 83.8%, respectively.

b) Preparation of positive electrode active material The composite hydroxide obtained as described above is heat-treated at 400 ° C. for 12 hours in an air (oxygen concentration: 21% by volume) air stream (heat treatment step), and then Li / Me is released. A lithium mixture was sufficiently mixed with lithium hydroxide using a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)) so as to be 1.10 (mixing step).

This lithium mixture is heated to 880 ° C. in an oxygen (oxygen concentration: 100% by volume) airflow at a heating rate of 1.5 ° C./min and held at this temperature for 3 hours to bake and reduce the cooling rate. It was cooled to room temperature at about 4 ° C./min (firing step). The positive electrode active material thus obtained was aggregated or slightly sintered. Therefore, this positive electrode active material was crushed to adjust the average particle size and particle size distribution (crushing step).

c) Evaluation of positive electrode active material [Composition]
Analysis using an ICP emission spectroscopic analyzer (ICPE-9000, manufactured by Shimadzu Corporation) revealed that the composition of this positive electrode active material was as follows: General formula: Li _1.1 Ni _0.38 Co _0.32 Mn _0.30 O It was confirmed that it was represented by _2.

[Particle structure]
A part of the positive electrode active material is embedded in the resin and cross-section polisher (manufactured by JEOL Ltd., IB-19530CP) is processed to make the cross section observable, and then SEM (FE-SEM: manufactured by JEOL Ltd., JSM). It was observed by -6360LA). As a result, the positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles, and the secondary particles are dispersed in the outer shell portion and the inside of the outer shell portion. It was confirmed that it has an agglomerate portion that is electrically conductive with the outer shell portion and a space portion having a pore structure in which no primary particles are present, which exists between the agglomerate portions inside the outer shell portion. ..

[Particle size distribution]
Using a laser light diffraction / scattering type particle size analyzer (Microtrac MT3300EXII manufactured by Microtrac Bell Co., Ltd.), d50 of the positive electrode active material is measured, and d10 and d90 are measured, which is an index showing the spread of the particle size distribution. A certain [(d90-d10) / d50 was calculated. As a result, it was confirmed that the average particle size d50 was 5.2 μm and [(d90-d10) / d50] was 0.41.

[BET specific surface area and tap density]
The BET specific surface area was measured with a flow-type gas adsorption method specific surface area measuring device (McSorb 1200 series manufactured by Mountech Co., Ltd.), and the tap density was measured with a tapping machine (KRS-406 manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). As a result, it was confirmed that the BET specific surface area was 2.62 m ² / g and the tap density was 1.53 g / cm ^3.

[DBP absorption amount]
As a result of measuring the absorption amount of di-n-butyl phthalate (DBP) with an absorption amount measuring device (S-500, manufactured by Asahi Soken Co., Ltd.) based on "JIS K 6217-4: 2008", the absorption amount of DBP Was confirmed to be 37.3 ml / 100 g.

From the above, the "BET specific surface area / DBP absorption amount" was 0.070, and the product of the BET specific surface area and d50 was 13.6.

[Crystalline diameter]
Using an X-ray diffraction (XRD) device (X'Pert PRO manufactured by Spectris Co., Ltd.), analysis is performed by powder X-ray diffraction with CuKα rays, and each diffraction peak is removed except for the spread of the diffraction peak of the X-ray diffraction pattern. When the crystallite diameter of the (003) plane was calculated from the above using Scheller's formula, it was 105 nm.

d) Preparation of secondary battery A 2032 type coin-type battery 11 as shown in FIG. 2 was produced. Specifically, the positive electrode active material obtained as described above: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg are mixed and pressed to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. After molding, the positive electrode 12 was produced by drying in a vacuum dryer at 120 ° C. for 12 hours.

Next, using the positive electrode 12, a 2032 type coin-shaped battery was manufactured in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C. A lithium metal having a diameter of 17 mm and a thickness of 1 mm is used for the negative electrode 13 of this 2032 type coin-shaped battery, and ethylene carbonate (EC) and diethyl carbonate (DEC) _{using 1 M LiClO 4 as a supporting electrolyte are used as the non-aqueous electrolyte solution.} ) Equal amount mixed solution (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used. Further, as the separator 14, a polyethylene porous membrane having a film thickness of 25 μm was used. In this way, the 2032 type coin-shaped battery 11 having the gasket 15 and the positive electrode can 16 and the negative electrode can 17 was assembled.

e) Battery evaluation [Positive electrode resistance]
The positive electrode resistance is measured by using an impedance measurement method, charging a 2032 type coin-shaped battery with a charging potential of 4.4 V, and using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B), as shown in FIG. Obtained a Nyquist plot. The Nyquist plot shown in FIG. 3 is represented as the sum of the solution resistance, the negative electrode resistance and its capacitance, and the positive electrode resistance (interfacial resistance) and its capacitance. The value of the positive electrode interface resistance was calculated by fitting calculation using the equivalent circuit shown. Regarding the positive electrode interfacial resistance, the positive electrode active material of Comparative Example 1 described later is used as a reference, and the resistance reduction rate with respect to this is shown. As a result, the positive electrode resistance was reduced to 0.83 times that of Comparative Example 1.

Table 1 shows the overall composition and characteristics of the obtained positive electrode active material and the characteristics of the obtained lithium ion secondary battery. Table 1 also shows Examples 2 to 5 and Comparative Example 1 with respect to these.

(Example 2)
The positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the lithium mixture was heated to 850 ° C. and held at this temperature for 3 hours to be calcined.

The average particle size d50 of this positive electrode active material was 5.3 μm, and [(d90-d10) / d50] was 0.41. The BET specific surface area was 3.35 m ² / g, the tap density was 1.46 g / cm ³ , and the DBP absorption amount was 36.3 ml / 100 g. The "BET specific surface area / DBP absorption amount" was 0.092, and the product of the BET specific surface area and d50 was 17.8.

The crystallite diameter of the (003) plane was 89 nm. The positive electrode resistance was reduced to 0.84 times that of Comparative Example 1.

(Example 3)
The lithium mixture was heated to 905 ° C. and held at this temperature for 3 hours to be calcined to obtain a positive electrode active material, which was evaluated in the same manner as in Example 1.

The average particle size d50 of this positive electrode active material was 5.6 μm, and [(d90-d10) / d50] was 0.43. The BET specific surface area was 1.62 m ² / g, the tap density was 1.58 g / cm ³ , and the DBP absorption amount was 30.8 ml / 100 g. The "BET specific surface area / DBP absorption amount" was 0.053, and the product of the BET specific surface area and d50 was 9.1.

The crystallite diameter of the (003) plane was 132 nm. The positive electrode resistance was reduced to 0.89 times that of Comparative Example 1.

(Example 4)
The lithium mixture was heated to 825 ° C. and held at this temperature for 3 hours to be calcined to obtain a positive electrode active material and evaluated in the same manner as in Example 1.

The average particle size d50 of this positive electrode active material was 5.1 μm, and [(d90-d10) / d50] was 0.41. The BET specific surface area was 4.88 m ² / g, the tap density was 1.41 g / cm ³ , and the DBP absorption amount was 54.5 ml / 100 g. The "BET specific surface area / DBP absorption amount" was 0.090, and the product of the BET specific surface area and d50 was 24.9.

The crystallite diameter of the (003) plane was 71 nm. The positive electrode resistance was reduced to 0.87 times that of Comparative Example 1.

(Example 5)
The lithium mixture was heated to 915 ° C. and held at this temperature for 3 hours to be calcined to obtain a positive electrode active material and evaluated in the same manner as in Example 1.

The average particle size d50 of this positive electrode active material was 5.7 μm, and [(d90-d10) / d50] was 0.44. The BET specific surface area was 1.55 m ² / g, the tap density was 1.59 g / cm ³ , and the DBP absorption amount was 30.1 ml / 100 g. The "BET specific surface area / DBP absorption amount" was 0.51, and the product of the BET specific surface area and d50 was 8.8.

The crystallite diameter of the (003) plane was 141 nm. The positive electrode resistance was reduced to 0.92 times that of Comparative Example 1.

(Comparative Example 1)
The positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the lithium mixture was heated to 930 ° C. and held at this temperature for 3 hours for firing.

The average particle size d50 of this positive electrode active material was 5.8 μm, and [(d90-d10) / d50] was 0.48. The BET specific surface area was 1.19 m ² / g, the tap density was 1.86 g / cm ³ , and the DBP absorption amount was 28.8 ml / 100 g. The "BET specific surface area / DBP absorption amount" was 0.041, and the product of the BET specific surface area and d50 was 6.9.

The crystallite diameter of the (003) plane was 151 nm.

When the positive electrode active materials of Examples 1 to 5 within the scope of the present invention are used in a lithium ion secondary battery, the positive electrode resistance is reduced and the output characteristics are all reduced in comparison with Comparative Example 1. Was confirmed to be improving.

11 Coin-type battery 12 Positive electrode (evaluation electrode)
13 Negative electrode 14 Separator 15 Gasket 16 Positive electrode can 17 Negative electrode can

Claims (12)

Lithium Nickel Manganese Cobalt-containing composite oxide is a positive electrode active material for lithium ion secondary batteries.
The positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles.
"BET specific surface area / DBP absorption amount", which is the ratio of the BET specific surface area to the DBP absorption amount measured according to JIS K 6217-4: 2008, is 0.048 or more.
Positive electrode active material for lithium-ion secondary batteries. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the "BET specific surface area / DBP absorption amount" is 0.050 or more and 0.100 or less. The product according to claim 1 or 2, wherein the product of the BET specific surface area and d50 obtained from the volume integrated value measured by the laser light diffraction / scattering type particle size analyzer for the secondary particles is 9.0 or more. Positive electrode active material for lithium-ion secondary batteries. The d50 is 3 μm or more and 15 μm or less, and [(d90-d10) / d50], which is an index showing the spread of the particle size distribution of the secondary particles obtained from the volume integrated value, is 1.0 or less. The positive electrode active material for a lithium ion secondary battery according to claim 3. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the BET specific surface area is 1.5 m ² / g or more and 5.0 m ^{2 / g or less.} The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the DBP absorption amount is 30 ml / 100 g or more and 65 ml / 100 g or less. The second item according to any one of claims 1 to 6, wherein the secondary particles include an agglomerated portion in which the primary particles are electrically conductive with each other and a space portion in which the primary particles are dispersed and exist in the agglomerated portion. Positive electrode active material for lithium-ion secondary batteries. The positive electrode active material for a lithium ion secondary battery according to claim 7, wherein the secondary particles further include an outer shell portion that electrically conducts with the agglomerated portion on the outside of the agglomerated portion. When the crystallite diameter of the primary particle is determined from the half-value width of the peak of the (003) plane by X-ray diffraction using the Scheller formula, the crystallite diameter is 30 nm or more and 150 nm or less, claims 1 to 1. 8. The positive electrode active material for a lithium ion secondary battery according to any one of 8. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 9, wherein the tap density is 0.8 g / cm ³ or more and 2.0 g / cm ^{3 or less.} The lithium nickel manganese cobalt-containing composite oxide has a general formula: Li _{1 + u} Ni _x Mn _y Co _z M _t O ₂ (−0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0. 9, 0 <y ≦ 0.5, 0 <z ≦ 0.5, 0 ≦ t ≦ 0.1, M is Mg, Al, Si, Ca, Ti, V, Cr, Zr, Nb, Mo, Hf , Ta, W), and has a hexagonal crystal structure having a layered structure, according to any one of claims 1 to 10. Positive active material for lithium-ion secondary batteries. The lithium ion secondary battery according to any one of claims 1 to 11, further comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, or a positive electrode, a negative electrode, and a solid electrolyte, as a positive electrode active material used for the positive electrode. A lithium-ion secondary battery in which a positive electrode active material is used.

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