JP2019220361A - Positive electrode active material for lithium ion secondary battery, method for manufacturing the same and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, which enables the control of the specific surface area of a positive electrode active material to enhance the battery capacity and cycle characteristic, a method for manufacturing the positive electrode active material, and a lithium ion secondary battery.SOLUTION: A method for manufacturing a positive electrode active material for a lithium ion secondary battery comprises: a mixing step of mixing a lithium compound and particles of a transition metal composite hydroxide represented by the general formula (A), NiMnCoM(OH)(x+y+z+t=1, 0.3≤x≤0.8, 0.05≤y≤0.55, 0≤z≤0.4, 0≤t≤0.1, 0≤a≤0.5, and M is one or more additive elements selected from Nb, Mo, Ta, Zr and W), of which [(d90-d10)/MV] indicative of the spread of a particle size distribution is 0.65 or less; a preliminary baking step of preliminarily baking a lithium mixture formed by the mixing step at 550-745°C in an oxidizing atmosphere; and a baking step of baking the lithium mixture preliminarily baked in the preliminary baking step at 760-1050°C in an oxidizing atmosphere.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery as a positive electrode active material.

  In recent years, with the spread of portable information terminals such as smartphones and tablet PCs, development of a small and lightweight non-aqueous electrolyte secondary battery having a high energy density has been strongly desired. Also, 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 demands, there is a lithium ion secondary battery. The lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of removing and inserting lithium is used as an active material used as a material of the negative electrode and the positive electrode.

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

As the positive electrode active material of such a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) particles, which are relatively easy to synthesize, and lithium nickel composite oxide (LiNiO ₂ ) particles using nickel which is cheaper than cobalt , Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) particles, lithium manganese composite oxide (LiMn ₂ O ₄ ) particles using manganese, lithium nickel manganese composite oxide ( LiNi transition metal composite oxide particles such as LiNi _0.5 Mn _0.5 O ₂ ) particles have been proposed.

  By the way, in order to obtain a lithium ion secondary battery having excellent cycle characteristics and output characteristics, it is necessary that the positive electrode active material is composed of particles having a small particle size and a narrow particle size distribution. This is because particles having a small particle diameter have a large specific surface area, and when used as a positive electrode active material, not only can a sufficient reaction area with an electrolytic solution be secured, but also the positive electrode can be made thin and lithium ions can be formed. This is because the moving distance between the positive electrode and the negative electrode can be shortened, so that the positive electrode resistance can be reduced. In addition, particles with a narrow particle size distribution can make the voltage applied to the particles uniform within the electrode, so that a decrease in battery capacity due to selective deterioration of the particles can be suppressed.

  For example, Patent Documents 1 to 4 disclose a precursor of a positive electrode active material by a crystallization reaction that is clearly separated into two stages of a nucleation step of mainly performing nucleation and a particle growth step of mainly performing particle growth. Thus, a method for producing transition metal composite hydroxide particles is disclosed. In these methods, a precursor having a small particle size and a narrow particle size distribution is obtained by appropriately adjusting the pH value and the reaction atmosphere in the nucleation step and the particle growth step. A positive electrode active material having a narrow particle size distribution is obtained. Further, by controlling the atmosphere of the nucleation step of mainly performing nucleation and the atmosphere of the particle growth step of mainly performing particle growth, a low-density center portion composed of fine primary particles and a high-density portion composed of plate-like or needle-like primary particles are formed. A transition metal composite hydroxide particle composed of an outer shell having a high density is obtained, and a cathode active material having a hollow structure is obtained using such a precursor.

JP 2011-116580 A JP 2012-246199 A JP 2013-147416 A WO2012 / 131881

  However, although the production methods described in these patent documents can improve the output characteristics by improving the particle structure, it is necessary to control the specific surface area of the positive electrode active material to further improve the battery capacity and cycle characteristics. ing.

  In view of the above problems, the present invention provides a positive electrode for a lithium ion secondary battery, which can control a specific surface area of a positive electrode active material and further improve battery capacity and cycle characteristics when a secondary battery is configured. An object is to provide an active material and a method for producing the active material. Another object of the present invention is to provide a lithium ion secondary battery using the positive electrode active material.

  The present inventors have conducted intensive studies based on the conventional techniques such as Patent Document 3 in order to further improve the battery capacity and cycle characteristics of a positive electrode active material for a lithium ion secondary battery (hereinafter, also referred to as “positive electrode active material”). Was piled up. As a result, in the step of firing the mixture of the precursor and the lithium compound, after calcination at a specific temperature and then firing, it is possible to suppress the sintering and aggregation of the secondary particles constituting the positive electrode active material, It has been found that it is possible to improve characteristics when used in a battery. The present invention has been completed based on these findings.

That is, one aspect of the present invention is a method for producing a cathode active material for a lithium ion secondary battery, the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1, 0.3 ≦ x ≦ 0.8, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is Nb, Mo , Ta, Zr, W), and a transition metal composite water having [(d90−d10) / MV] of 0.65 or less, which is an index indicating the spread of the particle size distribution. A mixing step of mixing the oxide particles and the lithium compound to form a lithium mixture; a calcining step of calcining the lithium mixture formed in the mixing step at 550 ° C. to 745 ° C. in an oxidizing atmosphere; Firing the lithium mixture calcined in the firing step in an oxidizing atmosphere at 760 ° C. to 1050 ° C. And a degree.

  According to one embodiment of the present invention, after calcination at a specific temperature, calcination can suppress sintering and aggregation of the secondary particles constituting the positive electrode active material, and provide characteristics when used in a battery. Can be improved.

  At this time, in one embodiment of the present invention, in the calcining step, the carbon content in the calcined lithium mixture may be controlled to be 1.2% by mass or less.

  By controlling the carbon content within the above range, the specific surface area of the positive electrode active material can be set within an appropriate range.

  Further, in one embodiment of the present invention, before the firing step, a pre-firing crushing step of crushing the lithium mixture calcined in the calcination step may be further provided.

  In this way, by crushing the lithium mixture calcined in the calcining step, it becomes possible to suppress the sintering and aggregation of the secondary particles constituting the positive electrode active material after the sintering step.

  In one embodiment of the present invention, in the mixing step, the ratio of the lithium mixture to the sum of the number of atoms of a metal other than lithium contained in the lithium mixture and the number of lithium atoms is 1: 0.95 to 1 .5 may be adjusted.

  In this case, a positive electrode active material having a desirable composition range can be obtained.

  In one embodiment of the present invention, the method may further include a heat treatment step in which the transition metal composite hydroxide particles are heat-treated at 105 ° C to 750 ° C before the mixing step.

  By doing so, the remaining moisture until after the firing step can be reduced to a certain amount, so that variations in the composition of the obtained positive electrode active material can be suppressed.

Another aspect of the present invention, there is provided a cathode active material for a lithium ion secondary battery comprising a lithium transition metal composite oxide particles, the general formula _{(B): Li 1 + u} Ni x Mn y Co z M t O 2 (−0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0.8, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0. 1, M is one or more additional elements selected from Nb, Mo, Ta, Zr, and W), has a hexagonal crystal structure having a layered structure, and a plurality of primary particles are aggregated. When the positive electrode active material is observed using a scanning electron microscope, the number of the aggregated particles in which five or more secondary particles are aggregated with respect to the number of the secondary particles in the observation visual field is formed. ratio of the number is not more than 0.7%, a specific surface area of 0.3m ² /g~4.0m ² / g.

  According to another embodiment of the present invention, the specific surface area is controlled and the aggregation of the secondary particles constituting the positive electrode active material is suppressed, so that the output characteristics when used in a secondary battery are improved.

  At this time, in another embodiment of the present invention, [(d90−d10) / MV], which is an index indicating the spread of the particle size distribution, may be 0.55 or less.

  With this configuration, when used as the positive electrode active material of the secondary battery, the voltage applied to the particles in the electrode can be made uniform, so that a decrease in battery capacity due to selective deterioration of the particles can be suppressed. .

  In another aspect of the present invention, the secondary particles may have an average particle size of 3 μm to 15 μm.

  In this way, when used as a positive electrode active material of a secondary battery, safety and output characteristics can be improved in increasing the battery capacity per unit volume of the secondary battery.

  Another embodiment of the present invention is a lithium ion secondary battery including at least a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the positive electrode for a lithium ion secondary battery described above is used as a positive electrode active material of the positive electrode. This is a lithium ion secondary battery in which an active material is used.

  According to another aspect of the present invention, there is provided a lithium ion secondary battery having further improved output characteristics such as battery capacity and positive electrode resistance.

  According to the present invention, when a secondary battery is configured, a specific surface area is controlled, and a positive electrode active material that can further improve battery capacity and cycle characteristics can be provided. A battery can be provided. Therefore, the industrial significance of the present invention is extremely large.

FIG. 1 is a process diagram schematically showing a method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention. It is a schematic sectional drawing of the coin type battery used for the battery evaluation of the Example of the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention. (A) is a Nyquist plot showing measurement results of impedance evaluation of an example of the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention, and (B) is used for analysis of the impedance evaluation. It is a schematic explanatory view of the equivalent circuit shown.

Hereinafter, a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery according to the present invention will be described in the following order. The present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.
1. 1. transition metal composite hydroxide particles 2. Method for producing transition metal composite hydroxide particles Production method of positive electrode active material for lithium ion secondary battery 3-1. Heat treatment step 3-2. Mixing step 3-3. Calcination process 3-4. Disintegration step before firing 3-5. Firing step 3-6. Crushing process 4. 4. Positive electrode active material for lithium ion secondary battery Lithium ion secondary battery

<1. Transition metal composite hydroxide particles>
First, transition metal composite hydroxide particles (hereinafter, referred to as “composite hydroxide particles”) used as a precursor of a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention will be described. The composite hydroxide particles are preferably composed of secondary particles formed by aggregating a plurality of plate-like primary particles. Further, the secondary particles have a central portion formed by agglomeration of fine primary particles, and preferably have an outer peripheral portion formed by aggregating plate-like primary particles outside the central portion, More preferably, the central portion contains a higher concentration of the additional element than the peripheral portion. By using the composite hydroxide particles having such a central portion, it becomes possible to obtain a positive electrode active material having a hollow structure having higher output characteristics. The average particle size of the secondary particles is preferably 3 μm to 15 μm.

(1) Particle Structure a) Structure of Secondary Particles The preferred composite hydroxide particles used in the present invention are substantially spherical secondary particles formed by aggregating a plurality of plate-like primary particles. Further, it is preferable that the inside of the particle has a structure having a central portion composed of fine primary particles and an outer peripheral portion composed of plate-like primary particles larger than the fine primary particle outside the central portion. Due to such a structure in which the plurality of plate-like primary particles are aggregated, in the sintering step of forming the lithium nickel manganese composite oxide as the positive electrode active material according to one embodiment of the present invention, diffusion of lithium into the particles is prevented. Since it is sufficiently performed, a favorable positive electrode active material having a uniform distribution of lithium can be obtained. Such composite hydroxide particles and a method for producing the same are disclosed in detail in, for example, Patent Documents 1 and 2.

  Here, since the central portion has a structure with many gaps in which fine primary particles are connected, shrinkage due to sintering in the firing step is lower than that in the outer peripheral portion made of plate-like primary particles having a larger thickness. appear. For this reason, sintering progresses from a low temperature during sintering, and shrinks from the center of the particle to the outer peripheral side where sintering progresses slowly, so that a space is created at the center. Further, since the central portion is considered to have a low density and has a large shrinkage, the central portion is a space having a sufficient size. Thereby, the positive electrode active material obtained after firing has a hollow structure.

  Further, it is more preferable that the plate-like primary particles aggregate in random directions to form secondary particles. By the plate-like primary particles agglomerating in random directions, voids are generated almost uniformly between the primary particles, and when mixed with the lithium compound and fired, the molten lithium compound spreads into the secondary particles, Is sufficiently diffused. Further, by being agglomerated in random directions, the composite hydroxide particles having the above-mentioned central portion, the shrinkage of the central portion in the above-mentioned firing step also occurs uniformly, so that a sufficient size inside the positive electrode active material. This is preferable because it can form a space having.

  In order to form a space during the firing, the fine primary particles preferably have an average particle size of 0.01 to 0.3 μm, and more preferably 0.1 to 0.3 μm. Further, the plate-like primary particles preferably have an average particle size of 0.3 to 3 μm, more preferably 0.4 to 1.5 μm, and particularly preferably 0.4 to 1.0 μm. preferable.

(2) Average Particle Size The composite hydroxide particles used for the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention have an average secondary particle size of 3 μm to 15 μm, preferably 3 μm to 12 μm. It is more preferably adjusted to 3 μm to 10 μm. The average particle size of the secondary particles correlates with the average particle size of the positive electrode active material having the composite hydroxide particles as a precursor. For this reason, by controlling the average particle diameter of the secondary particles in such a range, it is possible to control the average particle diameter of the positive electrode active material having the composite hydroxide particles as a precursor within a predetermined range. Become.

  In the present invention, the average particle size of the secondary particles means a volume-based average particle size (MV), which can be determined from, for example, a volume integrated value measured by a laser light diffraction / scattering particle size analyzer.

(3) Particle Size Distribution The composite hydroxide particles used for the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention is an index indicating the spread of the particle size distribution [(d90−d10) / average particle size] Is adjusted to 0.65 or less, preferably 0.55 or less, more preferably 0.50 or less.

  The particle size distribution of the positive electrode active material is strongly affected by the composite hydroxide particles that are its precursor. Therefore, when a composite hydroxide particle containing a large number of fine particles and coarse particles is used as a precursor, the positive electrode active material also contains a large amount of fine particles and coarse particles, and a secondary battery using the same may be used. Safety, cycle characteristics and output characteristics cannot be sufficiently improved. On the other hand, if ((d90−d10) / average particle diameter) is adjusted to be 0.65 or less at the stage of the composite hydroxide particles, the positive electrode active material using this as a precursor can be obtained. The particle size distribution can be narrowed, and the above-described problem can be avoided. However, on the premise of production on an industrial scale, it is not realistic to use composite hydroxide particles having an excessively small [(d90−d10) / average particle size]. Therefore, in consideration of cost and productivity, the lower limit of [(d90−d10) / average particle diameter] is preferably set to about 0.25.

  In addition, d10 accumulates the number of particles in each particle size from the smaller particle size side, and a particle size whose accumulated volume becomes 10% of the total volume of all particles, d90 similarly accumulates the number of particles, It means the particle size whose cumulative volume is 90% of the total volume of all particles. d10 and d90 can be determined from the volume integrated value measured by the laser light diffraction / scattering particle size analyzer in the same manner as the average particle diameter.

(4) Composition composite hydroxide particles used for the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention have the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (X + y + z + t = 1, 0.3 ≦ x ≦ 0.8, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M Is one or more additional elements selected from Nb, Mo, Ta, Zr, and W). By using such composite hydroxide particles as a precursor, a positive electrode active material represented by the following general formula (B) can be easily obtained, and higher battery performance can be realized.

  In the composite hydroxide particles represented by the general formula (A), the composition ranges of nickel, manganese, cobalt, and the additional element M constituting the composite hydroxide particles and the critical significance thereof are represented by a general formula (B) described later. This is the same as the positive electrode active material to be used. Therefore, a description of these matters is omitted here.

<2. Method for producing transition metal composite hydroxide particles>
Next, a method for producing the transition metal composite hydroxide particles described above will be described. The composite hydroxide particles used for the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention include, for example, a raw material aqueous solution containing at least a transition metal and an aqueous solution containing an ammonium ion supplier in a reaction vessel. Is supplied to form a reaction aqueous solution, which is obtained by a method of producing transition metal composite hydroxide particles to be a precursor of a positive electrode active material for a lithium ion secondary battery by a crystallization reaction.

  In particular, the crystallization reaction is carried out by adjusting the pH value of the aqueous reaction solution at a liquid temperature of 25 ° C. to a range of 12.0 to 14.0 to perform nucleation and a nucleus obtained in the nucleation step. The pH value at the liquid temperature of 25 ° C. of the reaction aqueous solution containing is controlled to be lower than the pH value in the nucleation step and to be 10.5-12.0 to grow the nuclei. It is preferred that the distinction be made clearly in two stages. In addition, the reaction atmosphere in the initial stage of the nucleation step and the particle growth step is adjusted to an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume, and the reaction atmosphere is changed from the oxidizing atmosphere to 5% by volume or less in the particle growing step. Switching to a non-oxidizing atmosphere is preferred.

  The method for producing the composite hydroxide particles is not limited by the composition, as long as the above-mentioned structure, average particle size and particle size distribution can be realized, but the composite hydroxide represented by the general formula (A) It can be suitably applied to material particles.

(1) Crystallization Reaction In the method for producing composite hydroxide particles, the crystallization reaction is clearly separated into two stages, a nucleation step mainly for nucleation and a particle growth step mainly for particle growth. By adjusting the crystallization conditions in the step, particularly in the particle growth step, by switching the reaction atmosphere, it is possible to efficiently obtain composite hydroxide particles having the above-mentioned particle structure, average particle diameter and particle size distribution. And

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

  Next, a raw material aqueous solution is supplied while stirring the pre-reaction aqueous solution. Thereby, a nucleus forming aqueous solution which is a reaction aqueous solution in the nucleation step is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is in the above-described range, nuclei hardly grow in the nucleation step, and nucleation occurs preferentially. In the nucleation step, the pH value of the aqueous solution for nucleation and the concentration of ammonium ion change with the nucleation, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied at appropriate times, and the pH value of the solution in the reaction tank is adjusted to 25 ° C. It is necessary to control so that the pH is maintained in the range of 12.0 to 14.0 on the basis of ° C. and the concentration of ammonium ion is maintained in the range of 3 g / L to 25 g / L.

  In the nucleation step, the reaction atmosphere is adjusted to an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume. As a result, a central portion formed by agglomeration of fine primary particles can be formed inside the composite hydroxide particles, and a cathode active material having a hollow structure can be formed by using the composite hydroxide particles as a precursor. Can be obtained, so that the reaction area with the electrolytic solution can be further increased.

  In the nucleation step, a new nucleus is continuously generated by supplying the aqueous solution for nucleation with a raw material aqueous solution, an aqueous alkali solution and an aqueous solution containing an ammonium ion donor. Then, when a predetermined amount of nuclei has been generated in the aqueous solution for nucleation, the nucleation step is ended.

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

[Grain growth step]
After the nucleation step, the pH value of the nucleation aqueous solution in the reaction tank is adjusted to 10.5 to 12.0 based on a liquid temperature of 25 ° C. to form a particle growth aqueous solution which is a reaction aqueous solution in the particle growth step. I do. The pH value can be adjusted also by stopping the supply of the alkaline aqueous solution. However, in order to obtain composite hydroxide particles having a narrow particle size distribution, the supply of all the aqueous solutions is temporarily stopped to adjust the pH value. Is preferred. Specifically, it is preferable to adjust the pH value by stopping the supply of all the aqueous solutions and then supplying the nucleation aqueous solution with the same kind of inorganic acid as the acid constituting the metal compound as the raw material.

  Next, the supply of the raw material aqueous solution is restarted while stirring the aqueous solution for particle growth. At this time, since the pH value of the aqueous solution for particle growth is in the above-mentioned range, almost no new nuclei are generated, nucleus (particle) growth proceeds, and composite hydroxide particles having a predetermined particle size are formed. You. In the particle growth step, the pH value and the ammonium ion concentration of the aqueous solution for particle growth change with the particle growth, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied at appropriate times to maintain the pH value and the ammonium ion concentration in the above ranges. It is necessary to do.

  In particular, in the method for producing composite hydroxide particles, the reaction atmosphere is switched from an oxidizing atmosphere to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less during the particle growing step. This makes it possible to obtain composite hydroxide particles having the above-described particle structure.

  In such a method for producing composite hydroxide particles, in the nucleation step and the particle growth step, metal ions are precipitated as primary particles forming nuclei or composite hydroxide particles. For this reason, the ratio of the liquid component to the metal component in the aqueous solution for nucleation and the aqueous solution for particle growth increases. As a result, apparently, the concentration of the raw material aqueous solution is reduced, and in particular, in the particle growing step, the growth of the composite hydroxide particles may be stagnated. Therefore, in order to suppress the increase in the liquid component, it is preferable to discharge a part of the liquid component of the aqueous solution for particle growth to the outside of the reaction tank after the nucleation step and during 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 donor are temporarily stopped, and the nuclei and the composite hydroxide particles in the aqueous solution for particle growth are settled, and the aqueous solution for particle growth is settled. Preferably, the supernatant is drained. 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 the particle growth is prevented, and the particle size distribution of the obtained composite hydroxide particles is controlled in a suitable range. In addition to this, the density of the secondary particles as a whole can be improved.

[Addition of additional elements]
The concentration of the additional element with respect to the elements other than the additional element in the raw material aqueous solution is set to be higher in the oxidizing atmosphere than in the non-oxidizing atmosphere. The concentration in an oxidizing atmosphere is preferably at least twice, more preferably at least five times the concentration in a non-oxidizing atmosphere. Particularly preferably, an aqueous solution containing the additive element is added in an oxidizing atmosphere, and the addition of the aqueous solution containing the additive element is stopped in a non-oxidizing atmosphere. The central part where the fine primary particles formed in the oxidizing atmosphere aggregated shrinks to the inside of the outer peripheral part formed by the aggregation of the plate-like primary particles formed in the non-oxidizing atmosphere when manufacturing the positive electrode active material. To form a hollow portion. Therefore, the additive element added in the oxidizing atmosphere diffuses to the outer peripheral portion, and is more present on the surface of the primary particles forming the outer shell of the positive electrode active material, whereas the additive element added in the non-oxidizing atmosphere is As a result, a large amount of the additional element is present inside the primary particles, and a concentrated layer of the additional element is formed on the surface of the primary particles. By forming the concentrated layer on the surface of the primary particles in contact with the electrolytic solution, it becomes possible to effectively function the additional element for improving the output characteristics. By making the concentration of the additional element added in the oxidizing atmosphere higher than the concentration of the additional element in the non-oxidizing atmosphere, the amount of the additional element in the concentrated layer can be increased, and it can function more effectively. be able to.

  Further, in the particle growing step, the concentration of the additional element is set to 35% to 75% with respect to the time from switching from the oxidizing atmosphere to the non-oxidizing atmosphere to the end of the particle growing step. By making the concentration higher than the range of 75%, the concentration of the additional element on the surface side can be made higher than 50% to 80% of the thickness of the outer peripheral portion than on the inner side of the outer peripheral portion. By forming such a layer containing a higher concentration of the additive element than the inner side on the surface side of the outer peripheral portion, it is possible to further uniformly form a concentrated layer in the positive electrode active material and improve battery characteristics. .

[Control of particle size of composite hydroxide particles]
The particle size of the composite hydroxide particles obtained as described above is controlled by the time of the particle growth step and the nucleation step, the pH value of the aqueous solution for nucleation and the aqueous solution for particle growth, and the supply amount of the raw material aqueous solution. Can be. For example, by performing the nucleation step at a high pH value or by increasing the time of the particle generation step, the amount of the metal compound contained in the raw material aqueous solution to be supplied is increased, and the nucleation amount is increased. The particle size of the resulting composite hydroxide particles can be reduced. Conversely, by suppressing the amount of nuclei generated in the nucleation step, the particle size of the resulting composite hydroxide particles can be increased.

[Another embodiment of crystallization reaction]
In the method for producing composite hydroxide particles, separately from the nucleation aqueous solution, a component adjustment aqueous solution adjusted to a pH value and an ammonium ion concentration suitable for the particle growth step is prepared. The aqueous solution for nucleation after the step, preferably the aqueous solution for nucleation after the nucleation step, in which a part of the liquid component is removed is added and mixed, and this is used as an aqueous solution for particle growth, and the particle growing step is performed. Is also good.

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

(2) Supply Aqueous Solution a) Raw Material Aqueous Solution In one embodiment of the present invention, the ratio of the metal element in the raw material aqueous solution is approximately the composition ratio of the obtained composite hydroxide particles. For this reason, in the raw material aqueous solution, it is necessary to appropriately adjust the content of each metal element according to the composition of the target composite hydroxide particles. For example, when obtaining the composite hydroxide particles represented by the general formula (A) described above, the ratio of the metal element in the raw material aqueous solution is set to Ni: Mn: Co: M = x: y: z : T (where x + y + z + t = 1, 0.3 ≦ x ≦ 0.80, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1) It is necessary to do.

  The compound of the transition metal for preparing the raw material aqueous solution is not particularly limited, but it is preferable to use water-soluble nitrates, sulfates, and hydrochlorides from the viewpoint of easiness of handling, and it is preferable to use cost and halogen compounds. From the viewpoint of preventing contamination, it is particularly preferable to use a sulfate.

  When the composite hydroxide particles contain the additional element M (M is one or more types of additional elements selected from Nb, Mo, Ta, Zr, and W), the additional element M is supplied. As the compound of the above, similarly, a water-soluble compound is preferable, and for example, niobium oxalate, ammonium molybdate, sodium tantalate, sodium tungstate, ammonium tungstate and the like can be suitably used.

  The concentration of the raw material aqueous solution is preferably 1 mol / L to 2.6 mol / L, more preferably 1.5 mol / L to 2.2 mol / L, in total of the metal compounds. If the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized substances per reaction tank decreases, and the productivity decreases. On the other hand, when the concentration of the raw material aqueous solution exceeds 2.6 mol / L, the concentration of the raw material aqueous solution exceeds the saturation concentration at room temperature.

  The above-mentioned metal compound does not necessarily need to be supplied to the reaction tank as a raw material aqueous solution. For example, when a crystallization reaction is performed using a metal compound that reacts when mixed to produce a compound other than the target compound, individual crystallization reactions are performed so that the total concentration of all aqueous metal compound solutions is within the above range. An aqueous solution of a metal compound may be prepared and supplied as an aqueous solution of an individual metal compound into the reaction vessel at a predetermined ratio.

  In addition, as for the supply amount of the raw material aqueous solution, the concentration of the product in the aqueous solution for particle growth is preferably 30 g / L to 200 g / L, more preferably 80 g / L to 150 g / L at the end of the particle growth step. To do. If the concentration of the product is less than 30 g / L, the aggregation of the primary particles may be insufficient. On the other hand, if it exceeds 200 g / L, the aqueous solution of the metal salt for nucleation or the aqueous solution of the metal salt for particle growth may not sufficiently diffuse into the reaction tank, and the particle growth may be biased.

b) Alkaline aqueous solution The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the reaction aqueous solution, but is preferably added as an aqueous solution because of easy pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% by mass to 50% by mass, more preferably 20% by mass to 30% by mass. By regulating the concentration of the aqueous alkali metal solution in such a range, it is possible to prevent the pH value from locally increasing at the addition position while suppressing the amount of the solvent (the amount of water) supplied to the reaction system. Thus, composite hydroxide particles having a narrow particle size distribution can be efficiently obtained.

  The method of supplying the aqueous alkali solution is not particularly limited as long as the pH value of the aqueous reaction solution does not locally increase and is maintained within a predetermined range. For example, the reaction aqueous solution may be supplied by a pump capable of controlling the flow rate, such as a metering pump, while sufficiently stirring.

c) Aqueous solution containing ammonium donor An aqueous solution containing an ammonium ion donor is not particularly limited. For example, aqueous ammonia or an aqueous solution such as ammonium sulfate, ammonium chloride, ammonium carbonate or ammonium fluoride is used. Can be.

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

  In addition, the supply method of the aqueous solution containing the ammonium ion supplier can also be supplied by a pump whose flow rate can be controlled, similarly to the alkaline aqueous solution.

(3) pH value In the method for producing composite hydroxide particles, the pH value at a liquid temperature of 25 ° C is set in the range of 12.0 to 14.0 in the nucleation step, and 10.5 in the particle growth step. It is necessary to control the range to ２．０12.0. In any step, the fluctuation range of the pH value during the crystallization reaction is preferably controlled within ± 0.2. When the fluctuation range of the pH value is large, the nucleation amount and the ratio of particle growth are not constant, and it is difficult to obtain composite hydroxide particles having a narrow particle size distribution.

a) Nucleation Step In the nucleation step, the pH value of the reaction aqueous solution (aqueous solution for nucleation) is 12.0 to 14.0, preferably 12.3 to 13.5, based on a liquid temperature of 25 ° C. It is necessary to control it preferably in the range of 12.5 to 13.3. This makes it possible to suppress the growth of nuclei and give priority to nucleation, and the nuclei generated in this step can be uniform and have a narrow particle size distribution. On the other hand, when the pH value is less than 12.0, the growth of nuclei (particles) proceeds along with the nucleation, so that the obtained composite hydroxide particles have a non-uniform particle size and the particle size distribution is deteriorated. On the other hand, if the pH value exceeds 14.0, the generated nuclei become too fine, and a problem arises in that the aqueous solution for nucleation gels.

b) Particle growth step In the particle growth step, the pH value of the reaction aqueous solution (particle growth aqueous solution) is 10.5 to 12.0, preferably 11.0 to 12.0, more preferably 11.0 to 12.0, based on a liquid temperature of 25 ° C. Needs to be controlled in the range of 11.5-12.0. As a result, generation of new nuclei is suppressed, and it is possible to give priority to particle growth, and the obtained composite hydroxide particles can be uniform and have a narrow particle size distribution. On the other hand, when the pH value is less than 10.5, the ammonium ion concentration increases and the solubility of metal ions increases, so that not only does the crystallization reaction speed slow down, but also the amount of metal ions remaining in the reaction aqueous solution increases. And the productivity deteriorates. On the other hand, if the pH value exceeds 12.0, the amount of nuclei generated during the particle growth step increases, the particle size of the obtained composite hydroxide particles becomes non-uniform, and the particle size distribution deteriorates.

  When the pH value is 12.0, it is a boundary condition between nucleation and nucleus growth. Therefore, depending on the presence or absence of nuclei present in the reaction aqueous solution, either the nucleation step or the particle growth step should be performed. Can be. That is, if the pH value in the nucleation step is higher than 12.0 and a large amount of nuclei are generated, and the pH value in the particle growth step is 12.0, a large amount of nuclei are present in the reaction aqueous solution. Growth occurs preferentially, and composite hydroxide particles having a narrow particle size distribution can be obtained. On the other hand, when the pH value in the nucleation step is 12.0, since there is no nucleus to grow in the reaction aqueous solution, nucleation occurs preferentially, and the pH value in the particle growth step is made lower than 12.0. Then, the generated nuclei grow and good composite hydroxide particles can be obtained. In any case, the pH value in the particle growth step may be controlled to a value lower than the pH value in the nucleation step. In order to clearly separate nucleation and particle growth, the pH value in the particle growth step must be controlled. It is preferably lower than the pH value in the production step by 0.5 or more, more preferably lower by 1.0 or more.

(4) Reaction Atmosphere The preferable structure in which the composite hydroxide particles have a central portion as described above controls the pH value of the reaction aqueous solution in the nucleation step and the particle growth step as described above, and also performs the reaction in these steps. It is formed by controlling the atmosphere. Therefore, in such a method for producing composite hydroxide particles, the reaction atmosphere is controlled while controlling the pH value in each step. That is, after controlling the pH value in each step as described above, by adjusting the initial reaction atmosphere of the nucleation step and the particle growth step to an oxidizing atmosphere, the central portion where the fine primary particles are aggregated is formed. You. Further, by switching from the oxidizing atmosphere to the non-oxidizing atmosphere during the particle growth step, an outer peripheral portion where the plate-like primary particles are aggregated is formed outside the central portion.

  In such control of the reaction atmosphere, the fine primary particles constituting the central portion are usually plate-like and / or needle-like, but depending on the composition of the composite hydroxide particles, a rectangular parallelepiped shape, an elliptical shape, and a ridged shape. Shapes such as shapes can also be taken. In this regard, the same applies to the plate-like primary particles constituting the outer peripheral portion. Therefore, the reaction atmosphere in each stage is appropriately controlled according to the desired composition of the composite hydroxide particles.

a) Oxidizing Atmosphere At the stage of forming the central portion of the composite hydroxide particles, the reaction atmosphere is controlled to an oxidizing atmosphere. Specifically, control is performed so that the oxygen concentration in the reaction atmosphere exceeds 5% by volume, preferably 10% by volume or more, and more preferably the air atmosphere (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere in such a range, the average particle size of the primary particles is in the range of 0.01 μm to 0.3 μm, so that the central portion formed of fine primary particles is formed. Can be.

  The upper limit of the oxygen concentration in the reaction atmosphere at this stage is not particularly limited, but when the oxygen concentration is excessively high, the average particle size of the primary particles becomes less than 0.01 μm, and the low-density layer has a sufficient density. May not be large. For this reason, the oxygen concentration is preferably set to 30% by volume or less.

b) Non-oxidizing atmosphere On the other hand, the reaction atmosphere in the step of forming the outer peripheral portion of the composite hydroxide particles is controlled to a weakly oxidizing atmosphere or a non-oxidizing atmosphere. Specifically, the mixed atmosphere of oxygen and an inert gas is controlled so that the oxygen concentration in the reaction atmosphere is 5% by volume or less, preferably 2% by volume or less, more preferably 1% by volume or less. Thereby, the nuclei generated in the nucleation step can be grown to a certain range while suppressing unnecessary oxidation, so that the outer periphery of the composite hydroxide particles has an average particle diameter of 0.3 μm to 3 μm. Within the range, the plate-like primary particles can have a structure in which the primary particles are aggregated, and an outer peripheral portion having a sufficient difference in primary particle diameter from the above-described central portion can be formed.

c) Timing of Atmosphere Control In the particle growth step, the above-described atmosphere control needs to be performed at an appropriate timing so that composite hydroxide particles having a target particle structure are formed.

  The switching of the atmosphere in the particle growth step is performed by changing the size of the central portion of the composite hydroxide particles so that a hollow portion is obtained in which the fine particles are not generated and the cycle characteristics are not deteriorated in the finally obtained positive electrode active material. Is determined in consideration of the timing. For example, the time is 0 to 40%, preferably 0 to 30%, more preferably 0 to 25% from the start of the particle growth step to the entire time of the particle growth step. If the above switching is performed at a time point exceeding 40% of the entire particle growth process time, the formed central portion becomes large, and the thickness of the outer peripheral portion with respect to the particle size of the secondary particles becomes too thin. On the other hand, if the above switching is performed before the start of the particle growth step, that is, during the nucleation step, the central portion becomes too small or secondary particles having the above structure are not formed.

d) Switching method Conventionally, the reaction atmosphere is switched during the crystallization step by flowing an atmosphere gas into the reaction tank or inserting a conduit having an inner diameter of about 1 mm to 50 mm into the reaction aqueous solution and bubbling with the atmosphere gas. I was going. However, in such a conventional technique, it takes a long time to switch the reaction atmosphere, so it is necessary to stop the supply of the raw material aqueous solution during the switching. Therefore, when switching the reaction atmosphere while supplying the raw material aqueous solution, it is preferable to use an air diffuser. The air diffuser is constituted by a conduit having a large number of fine holes on its surface, and can discharge a large number of fine gases (bubbles) into a liquid, so that the reaction atmosphere can be switched in a short time. Therefore, it is not necessary to stop the supply of the raw material aqueous solution when the reaction atmosphere is switched, and it is possible to improve the production efficiency.

  As such an air diffuser, it is preferable to use a ceramic one having excellent resistance under a high pH environment. In addition, the smaller the pore size of the air diffuser, the more fine bubbles can be released, so that the reaction atmosphere can be switched with high efficiency. In the present invention, it is preferable to use an air diffuser having a pore diameter of 100 μm or less, and more preferably to use an air diffuser having a pore diameter of 50 μm or less.

(5) Ammonium ion concentration The ammonium ion concentration in the reaction aqueous solution is maintained at a constant value within a range of preferably 3 g / L to 25 g / L, more preferably 5 g / L to 20 g / L. Since ammonium ions function as a complexing agent in the reaction aqueous solution, if the ammonium ion concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, and the reaction aqueous solution tends to gel, and It is difficult to obtain composite hydroxide particles having a uniform particle size. On the other hand, when the ammonium ion concentration exceeds 25 g / L, the solubility of metal ions becomes too large, so that the amount of metal ions remaining in the reaction aqueous solution increases, which causes a composition deviation and the like.

  If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ion fluctuates, and uniform composite hydroxide particles cannot be formed. For this reason, it is preferable that the fluctuation range of the ammonium ion concentration be controlled within a certain range through the nucleation step and the particle growth step, and specifically, it is preferable to control the fluctuation range to ± 5 g / L.

(6) Reaction Temperature The temperature (reaction temperature) of the reaction aqueous solution needs to be controlled to preferably 20 ° C. or higher, more preferably 20 ° C. to 60 ° C., throughout the nucleation step and the particle growth step. If the reaction temperature is lower than 20 ° C., nucleation is likely to occur due to the low solubility of the reaction aqueous solution, and it is difficult to control the average particle size and particle size distribution of the obtained composite hydroxide particles. The upper limit of the reaction temperature is not particularly limited. However, if the temperature exceeds 60 ° C., the volatilization of ammonia is promoted, and an ammonium ion supplier supplied to control the ammonium ion in the reaction aqueous solution within a certain range. , The amount of the aqueous solution containing is increased, and the production cost is increased.

(7) Coating Step A coating step may be provided to add an additional element to the positive electrode active material. The coating method is not particularly limited as long as the composite hydroxide particles can be uniformly coated with the compound containing the additional element M. For example, after the composite hydroxide particles are slurried and the pH value is controlled in a predetermined range, an aqueous solution (aqueous solution for coating) in which a compound containing the additional element M is added is added to the surface of the composite hydroxide particles. By depositing the compound containing the additional element M, composite hydroxide particles uniformly coated with the compound containing the additional element can be obtained. In this case, in place of the coating aqueous solution, an alkoxide solution of the additional element may be added to the slurried composite hydroxide particles. Further, the coating may be performed by spraying and drying an aqueous solution or slurry in which the compound containing the additional element is dissolved, without forming the composite hydroxide particles into a slurry. Furthermore, coating is performed by a method of spray-drying a slurry in which the composite hydroxide particles and the compound containing the additive element are suspended, or a method of mixing the compound hydroxide particles and the compound containing the additive element by a solid phase method. You can also.

  When the surface of the composite hydroxide particles is coated with the additional element, the raw material aqueous solution and the raw material aqueous solution are mixed so that the composition of the composite hydroxide particles after coating matches the composition of the target composite hydroxide particles. It is necessary to appropriately adjust the composition of the coating aqueous solution. Further, the coating step may be performed on the heat-treated particles after heat-treating the composite hydroxide particles.

(8) Production apparatus A crystallization apparatus (reaction tank) for producing composite hydroxide particles is not particularly limited as long as the reaction atmosphere can be switched by the above-described diffuser. Absent. However, it is preferable to use a batch crystallization apparatus that does not collect the precipitated product until the crystallization reaction is completed. With such a crystallizer, unlike a continuous crystallizer that recovers the product by the overflow method, the growing particles are not collected at the same time as the overflow liquid. Object particles can be easily obtained. Further, in the method for producing composite hydroxide particles of the present invention, it is necessary to appropriately control the reaction atmosphere during the crystallization reaction, and thus it is preferable to use a closed crystallization apparatus.

<3. Method for producing positive electrode active material for lithium ion secondary battery>
Next, a method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention will be described. FIG. 1 is a process diagram schematically showing a method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention. The method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention have the general formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.8, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, M is Nb, Mo, Ta, Transition metal composite hydroxide particles having [(d90-d10) / MV] of 0.65 or less, which is represented by one or more additional elements selected from Zr and W) and is an index indicating the spread of the particle size distribution. Mixing a lithium compound with a lithium compound to form a lithium mixture; a calcining step S3 of calcining the lithium mixture formed in the mixing step S2 at 550 ° C. to 745 ° C. in an oxidizing atmosphere; The lithium mixture formed with the lithium mixture calcined in the baking step S3 is placed in an oxidizing atmosphere at 7 Calcined at 0 ° C. to 1050 ° C. and a firing step S5. Before the mixing step S2, a heat treatment step S1 for heat-treating the transition metal composite hydroxide particles may be provided. Before the firing step S5, the lithium mixture calcined in the calcination step S3 is crushed. It is preferable to have a pre-firing crushing step S4. According to such a manufacturing method, a positive electrode active material described later can be easily obtained. Hereinafter, each step will be described in detail.

(3-1. Heat treatment step)
In the method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention, optionally, a heat treatment step S1 is provided before the mixing step S2 to convert the composite hydroxide particles into heat treatment particles. It may be mixed with a lithium compound. Here, the heat-treated particles include not only composite hydroxide particles from which excess water has been removed in the heat treatment step, but also transition metal composite oxide particles converted to oxides by the heat treatment step (hereinafter, “composite oxide particles”). ") Or mixtures thereof.

  The heat treatment step S1 is a step of removing excess moisture contained in the composite hydroxide particles by heating the composite hydroxide particles to 105 ° C to 750 ° C and performing a heat treatment. This makes it possible to reduce the amount of water remaining until after the firing step S5 to a certain amount, thereby suppressing a variation in the composition of the obtained positive electrode active material.

  The heating temperature in the heat treatment step S1 is 105 ° C. to 750 ° C. If the heating temperature is lower than 105 ° C., excess water in the composite hydroxide particles cannot be removed, and the variation may not be sufficiently suppressed. On the other hand, if the heating temperature exceeds 750 ° C., not only no further effect can be expected, but also the production cost increases.

  In addition, in the heat treatment step S1, since it is sufficient that water can be removed to such an extent that the number of atoms of each metal component in the positive electrode active material and the ratio of the number of atoms of Li do not vary, all composite hydroxide particles are not necessarily composite. There is no need to convert to oxide particles. However, in order to reduce the variation in the number of atoms of each metal component and the ratio of the number of atoms of Li, all of the composite hydroxide particles are converted into composite oxide particles by heating to 400 ° C. or more. Is preferred. The above-described variation can be further suppressed by previously determining the metal component contained in the composite hydroxide particles under the heat treatment conditions by analysis and determining the mixing ratio with the lithium compound.

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

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

(3-2. Mixing step)
The mixing step S2 is a step of mixing a lithium compound with the composite hydroxide particles or the heat-treated particles to obtain a lithium mixture.

  In the mixing step S2, the ratio of the number of atoms (Li) of metal atoms other than lithium in the lithium mixture, specifically, nickel, cobalt, manganese, and the additional element M to the number of atoms of lithium (Li) (Li / Me) so as to be 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, and still more preferably 1.0 to 1.2. It is necessary to mix the composite hydroxide particles or the heat-treated particles with the lithium compound. That is, since Li / Me does not change before and after the sintering step S5, the composite hydroxide particles or the heat-treated particles and lithium are mixed so that Li / Me in the mixing step S2 becomes Li / Me of the intended cathode active material. It is necessary to mix the compounds.

  Although the lithium compound used in the mixing step S2 is not particularly limited, it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate or a mixture thereof from the viewpoint of availability. In particular, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate, and it is more preferable to use lithium carbonate.

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

(3-3. Calcination process)
In the calcining step S3, the lithium mixture formed in the mixing step S2 is calcined in an oxidizing atmosphere at 550 ° C to 745 ° C, preferably 580 ° C to 720 ° C. This allows lithium to sufficiently diffuse and react in the composite hydroxide particles or the heat-treated particles, thereby suppressing sintering and aggregation of the secondary particles in the subsequent firing step S5. That is, by calcining, the lithium compound is consumed by the reaction with the composite hydroxide particles or the heat-treated particles, and the lithium compound remaining after the calcining is greatly reduced. In the next firing step S5, it is necessary to maintain the temperature at a high temperature in order to enhance the crystallinity of the lithium transition metal composite oxide particles, and during this holding, the lithium compound melts and the secondary particles of the lithium transition metal composite oxide form Sintering agglomeration proceeds rapidly. By greatly reducing the lithium compound by calcination, sintering and aggregation of the secondary particles can be suppressed.

  The holding time at the above temperature is preferably 1 hour to 10 hours, and more preferably 3 hours to 6 hours. The atmosphere in the calcining step S3 is preferably an oxidizing atmosphere, as in the later-described firing step S5, and more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume.

  Further, the carbon content of the calcined particles is controlled so as to be preferably 1.2% by mass or less, more preferably 0.3% by mass to 1.0% by mass. The carbon content is derived from, for example, lithium carbonate or the like as a raw material. Thereby, the remaining lithium compound is further reduced, the specific surface area of the positive electrode active material is controlled to a preferable range, and the sintering and aggregation of the secondary particles of the lithium transition metal composite oxide in the firing step S5 is further suppressed. In addition, the crystallinity can be sufficiently increased. Since the carbon content can be measured by a high frequency-infrared combustion method, the control of the carbon content can be easily controlled by the calcining temperature and time so as to be within the above range.

(3-4. Crushing step before firing)
The lithium composite oxide particles obtained in the calcination step S3 may have agglomeration or slight sintering. In such a case, it is preferable to crush the aggregates or sintered bodies of the lithium composite oxide particles by the crushing step before calcination S4 before the calcination step S5. Thereby, the average particle size and the particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range.

  As a crushing method, a known means can be used as in the crushing step S6 described later, 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.

(3-5. Firing step)
In the firing step S5, the lithium mixture is fired under predetermined conditions to diffuse lithium into the composite hydroxide particles or the heat-treated particles to increase the crystallinity of the reacted particles, thereby obtaining lithium transition metal composite oxide particles. It is a process.

  The composite hydroxide particles are secondary particles having a central portion formed by agglomeration of fine primary particles, and an outer peripheral portion formed by aggregating plate-like primary particles outside the central portion. In this case, in the calcining step S5 and the calcining step S3 in the preceding step, the central portion and the high-density layer of the composite hydroxide particles and the heat-treated particles shrink and sinter to form aggregates of primary particles in the positive electrode active material. . On the other hand, since the low-density layer is composed of fine primary particles, sintering starts at a lower temperature than in the center or the high-density layer composed of plate-like primary particles larger than the fine primary particles. In addition, the low-density layer has a larger amount of shrinkage than the central part and the high-density layer. For this reason, the fine primary particles constituting the low-density layer shrink toward the center where the sintering progresses slowly or toward the high-density layer, and a space having an appropriate size is formed. At this time, the high-density part in the low-density layer shrinks while maintaining the connection with the central part and the high-density layer. Therefore, in the obtained positive electrode active material, the outer shell and the aggregated part are electrically separated. Electrical conduction and a sufficient cross-sectional area of the path can be ensured. As a result, the internal resistance of the positive electrode active material is significantly reduced, and when a secondary battery is configured, the output characteristics can be improved without impairing the battery capacity and cycle characteristics.

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

  The furnace used in the firing step S5 is not particularly limited as long as the furnace can heat the lithium mixture in the air or in an oxygen stream. However, from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace without gas generation is preferable, and any of a batch type or a continuous type electric furnace can be suitably used. This applies to the furnace used in the heat treatment step S1 and the calcining step S3.

a) Firing temperature The firing temperature of the lithium mixture needs to be higher than the calcining temperature and 760 ° C to 1050 ° C, preferably 790 ° C to 1000 ° C. If the calcination temperature is lower than 760 ° C., lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, so that excess lithium, unreacted composite hydroxide particles or the heat-treated particles remain, or the obtained lithium composite The crystallinity of the oxide particles becomes insufficient. On the other hand, when the sintering temperature exceeds 1050 ° C., the lithium composite oxide particles sinter violently, causing abnormal grain growth and increasing the proportion of irregularly shaped coarse particles.

  Further, the rate of temperature rise in the firing step S5 is preferably 2 ° C./min to 10 ° C./min, more preferably 5 ° C./min to 10 ° C./min. Further, during the firing step S5, it is preferable to maintain the temperature near the melting point of the lithium compound for preferably 1 hour to 5 hours, more preferably 2 hours to 5 hours. Thereby, the composite hydroxide particles or the heat-treated particles can more uniformly react with the lithium compound.

b) Firing time Of the firing times, the holding time at the above firing temperature is preferably at least 2 hours, more preferably 4 hours to 24 hours. If the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, and excess lithium or unreacted composite hydroxide particles or the heat-treated particles remain or The resulting lithium composite oxide particles may have insufficient crystallinity.

  After completion of the holding time, the cooling rate from the firing temperature to at least 200 ° C. is preferably 2 ° C./min to 10 ° C./min, more preferably 3 ° C./min to 7 ° C./min. By controlling the cooling rate in such a range, it is possible to prevent the equipment such as the sagger from being damaged by rapid cooling while securing the productivity.

c) Firing atmosphere The firing atmosphere is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume, and a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. It is particularly preferred that That is, firing is preferably performed in the air or an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium composite oxide particles may be insufficient.

(3-6. Crushing step)
In the lithium composite oxide particles obtained in the firing step S5, aggregation or slight sintering may occur. In such a case, it is preferable to crush the aggregates or sintered bodies of the lithium composite oxide particles in the crushing step S6. Thereby, the average particle size and the particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range. In addition, crushing means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles generated by sintering necking between the secondary particles during firing, and the secondary particles themselves are almost not destroyed. It means an operation of separating and loosening aggregates.

  Known methods can be used as the crushing method. 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.

<4. Positive active material for lithium ion secondary battery>
Next, a positive electrode active material for a lithium ion secondary battery manufactured by the method for manufacturing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention will be described. One embodiment of the present invention provides:
A positive active material for a lithium ion secondary battery comprising a lithium transition metal composite oxide particles, the general formula _{(B): Li 1 + u} Ni x Mn y Co z M t O 2 (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0.8, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Nb, Mo , Ta, Zr, W), a secondary particle formed by agglomeration of a plurality of primary particles having a hexagonal crystal structure having a layered structure. When the positive electrode active material was observed using a scanning electron microscope, the ratio of the number of aggregated particles in which five or more secondary particles aggregated to the number of secondary particles in the observation field of view was 0.7%. or less, a specific surface area of 0.3m ² /g~4.0m ² / g. Hereinafter, characteristics of the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention will be described in detail.

(1) Particle Structure a) Structure of Secondary Particle The positive electrode active material according to one embodiment of the present invention is composed of secondary particles formed by aggregating a plurality of primary particles. In order to have higher output characteristics, it is preferable that the secondary particles include an outer shell portion and a hollow portion in which the primary particles do not exist inside the outer shell portion.

  In a positive electrode active material having a hollow structure, the electrolyte infiltrates from the grain boundaries or voids between the primary particles, and lithium is inserted and removed at the reaction interface on the surface of the primary particles on the hollow side inside the particles. In addition, the transfer of electrons is not hindered, and the output characteristics can be improved.

b) Outer Shell In the positive electrode active material having a hollow structure, the outer shell preferably has a thickness of 5 to 45%, more preferably 8 to 38% in terms of the particle diameter of the secondary particles. preferable. Further, the absolute value is more preferably in the range of 0.4 to 2.5 μm, particularly preferably in the range of 0.5 to 2.0 μm. When the ratio of the thickness of the outer shell portion is less than 5%, the strength of the secondary particles is reduced, so that the particles are destroyed when handling the powder and when the battery is used as a positive electrode, and fine particles are generated. make worse. On the other hand, when the ratio of the thickness of the outer shell portion exceeds 45%, the electrolyte solution decreases from the grain boundaries or voids where the electrolyte solution can enter the hollow portion inside the particle, and the surface area contributing to the battery reaction decreases. As a result, the positive electrode resistance increases and the output characteristics deteriorate. The ratio of the thickness of the outer shell to the secondary particle diameter can be determined in the same manner as in the case of the composite hydroxide particles.

(2) Average Particle Size The positive electrode active material according to one embodiment of the present invention is adjusted so that the average particle size is preferably 3 μm to 15 μm, more preferably 3 μm to 10 μm. If the average particle size of the positive electrode active material is in such a range, not only can the battery capacity per unit volume of a secondary battery using this positive electrode active material be increased, but also the safety and output characteristics are improved. can do. On the other hand, when the average particle diameter is less than 3 μm, the filling property of the positive electrode active material is reduced, and the battery capacity per unit volume may not be sufficiently increased. On the other hand, when the average particle size exceeds 15 μm, the reaction area of the positive electrode active material decreases, and the interface with the electrolyte decreases, so that the output characteristics may not be sufficiently improved.

  Incidentally, the average particle diameter of the positive electrode active material means a volume-based average particle diameter (MV) as in the case of the composite hydroxide particles described above, and is, for example, a volume integration measured by a laser light diffraction / scattering particle size analyzer. It can be determined from the value.

(3) Particle Size Distribution When the positive electrode active material according to one embodiment of the present invention is observed using a scanning electron microscope, five or more secondary particles aggregate with respect to the number of secondary particles in the observation visual field. The ratio of the number of the aggregated particles is 0.7% or less. When measuring the ratio of the number of aggregated particles in which five or more secondary particles are aggregated, the total number of secondary particles to be measured must be a sufficient number of particles to be considered as the average of all the secondary particles of the positive electrode active material. If the number of particles is too large, counting becomes difficult. For example, when observed at a magnification of 1000 times, about 800 to 1100 secondary particles are included in the entire visual field, which is considered to be an appropriate number of particles to be measured as the number of aggregated particles of the entire positive electrode active material. In this case, the total number of the aggregated particles in which the secondary particles are aggregated is preferably 6 / field or less, more preferably 3 / field or less, and is preferably 0.7 when expressed by the ratio of the aggregated secondary particles. % Or less, more preferably 0.4% or less. By reducing the aggregated particles, the distribution of the positive electrode active material particles in the positive electrode becomes uniform, the insertion and extraction of Li and the flow of current can be made uniform, and the battery capacity and cycle characteristics can be improved. When the aggregated particles increase, the distribution of the positive electrode active material particles in the positive electrode becomes uneven, and it is difficult to improve the battery characteristics.

  Further, [(d90-d10) / average particle diameter (MV)], which is an index indicating the spread of the particle size distribution, is preferably 0.55 or less, more preferably 0.50 or less. Be composed. Such a positive electrode active material has a small ratio of fine particles and coarse particles, and a secondary battery using the same has more excellent safety, cycle characteristics, and output characteristics.

  On the other hand, when [(d90-d10) / average particle size] exceeds 0.55, the ratio of fine particles and coarse particles in the positive electrode active material increases. For example, in a secondary battery using a positive electrode active material having a high proportion of fine particles, the secondary battery is likely to generate heat due to a local reaction of the fine particles, which not only lowers safety but also reduces fineness. The cycle characteristics may be inferior due to the selective deterioration of the particles. Further, in a secondary battery using a positive electrode active material having a large proportion of coarse particles, a sufficient reaction area between the electrolytic solution and the positive electrode active material cannot be secured, and output characteristics may be poor.

  On the other hand, on the premise of production on an industrial scale, it is not realistic to use a cathode active material having an excessively small [(d90−d10) / average particle diameter]. Therefore, in consideration of cost and productivity, the lower limit of [(d90−d10) / average particle diameter] is preferably set to about 0.25.

  The meanings of d10 and d90 in the index [(d90−d10) / average particle diameter] indicating the spread of the particle size distribution, and how to obtain them are the same as those of the composite hydroxide particles described above. Is omitted.

(4) Crystallite diameter The cathode active material of the present invention preferably has a crystallite diameter of 100 nm to 160 nm, and more preferably 110 nm to 150 nm. By controlling the crystallite diameter in the above range, the cycle characteristics and output can be further improved.

(5) Composition positive electrode active material of the present invention have the general formula _{(B): Li 1 + u} Ni x Mn y Co z M t O 2 (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1,0. 3 ≦ x ≦ 0.80, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is selected from Nb, Mo, Ta, Zr, W (At least one additional element).

  In this positive electrode active material, the value of u indicating the excess amount of lithium (Li) is preferably -0.05 to 0.50, more preferably 0 to 0.50, and further preferably 0 to 0.35. The following is assumed. By regulating the value of u within the above range, the output characteristics and battery capacity of a secondary battery using this positive electrode active material as a positive electrode material can be improved. On the other hand, when the value of u is less than -0.05, the positive electrode resistance of the secondary battery increases, so that the output characteristics cannot be improved. On the other hand, if it exceeds 0.50, not only the initial discharge capacity decreases, but also the positive electrode resistance increases.

  Nickel (Ni) is an element that contributes to increasing the potential and the capacity of the secondary battery, and the value of x indicating the content is 0.3 or more and 0.80 or less, more preferably 0.3 or more. 0.60 or less. If the value of x is less than 0.3, the secondary battery capacity using this positive electrode active material cannot be improved. On the other hand, when the value of x exceeds 0.80, the content of other elements decreases, and the effect cannot be obtained.

  Manganese (Mn) is an element that contributes to improvement in thermal stability, and the value of y indicating its content is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. And If the value of y is less than 0.05, the thermal stability of a secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of y exceeds 0.55, Mn elutes from the positive electrode active material during high-temperature operation, and the charge / discharge cycle characteristics deteriorate.

  Cobalt (Co) is an element that contributes to the improvement of charge-discharge cycle characteristics, and the value of z indicating the content is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.35 or less. I do. If the value of z exceeds 0.4, the initial discharge capacity of a secondary battery using this positive electrode active material will be significantly reduced.

  In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material according to one embodiment of the present invention may contain an additional element M in addition to the above-described metal elements. Examples of the additional element M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum. One or more selected from (Mo), hafnium (Hf), tantalum (Ta), lanthanum (La), and tungsten (W) can be used. Among these, it is particularly preferable to use at least one selected from niobium (Nb), molybdenum (Mo), tantalum (Ta), zirconium (Zr), and tungsten (W).

  The value of t indicating the content of the additional element M is preferably from 0 to 0.1, more preferably from 0.001 to 0.05. When the value of t exceeds 0.1, the metal element contributing to the Redox reaction decreases, and the battery capacity decreases.

Positive electrode active material according to an embodiment of (6) The specific surface area present invention has a specific surface area ^is preferably ^{0.3m 2 /g~4.0m 2 / g, 0.5m} 2 / g~3. More preferably, it is 0 m ² / g. A positive electrode active material having a specific surface area in such a range has a large contact area with an electrolytic solution, and can greatly improve the output characteristics of a secondary battery using the same. On the other hand, if the specific surface area of the positive electrode active material is less than 0.3 m ² / g, it is not possible to secure a reaction area with the electrolyte when a secondary battery is formed, and the output characteristics are sufficiently improved. It will be difficult to do so. On the other hand, when the specific surface area of the positive electrode active material exceeds 4.0 m ² / g, the reactivity with the electrolytic solution becomes too high, so that the thermal stability may decrease.

  The specific surface area of the positive electrode active material can be measured, for example, by a BET method using nitrogen gas adsorption.

(7) Tap Density In order to extend the use time of portable electronic devices and the mileage of electric vehicles, increasing the capacity of secondary batteries is an important issue. On the other hand, the thickness of the electrode of the secondary battery is required to be about several microns due to packing of the whole battery and problems of electron conductivity. For this reason, it is necessary not only to use a high-capacity positive electrode active material, but also to enhance the filling property of the positive electrode active material and increase the capacity of the entire secondary battery. From such a viewpoint, in the positive electrode active material of the present invention, the tap density, which is an index of the filling property, is preferably 1.0 g / cm ³ or more, and more preferably 1.2 g / cm ³ or more. . If the tap density is less than 1.0 g / cm ³ , the filling property is low, and the battery capacity of the entire secondary battery may not be sufficiently improved. On the other hand, the upper limit of the tap density is not particularly limited, but the upper limit under normal manufacturing conditions is about 3.0 g / cm ³ .

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

5. Lithium-ion secondary battery Lastly, a lithium-ion secondary battery according to one embodiment of the present invention will be described. The lithium ion secondary battery according to one embodiment of the present invention includes at least a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and as the positive electrode active material of the positive electrode, the above-described positive electrode for a lithium ion secondary battery. Active materials are used. The positive electrode active material can be suitably used for a lithium ion secondary battery, but is not necessarily limited to the secondary battery used. A lithium ion secondary battery according to one embodiment of the present invention includes components similar to a general lithium ion secondary battery, such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Hereinafter, each constituent member and the like will be described. However, the embodiment described below is merely an example, and the lithium ion secondary battery according to the embodiment of the present invention is based on the embodiment described in this specification. Thus, it is also possible to apply the present invention to various modified and improved embodiments.

(1) Components a) Positive electrode A positive electrode of a lithium ion secondary battery is produced using the above-described positive electrode active material, for example, as follows.

  First, a positive electrode active material according to one embodiment of the present invention, a conductive material and a binder are mixed, and further, if necessary, activated carbon and a solvent such as viscosity adjustment are added, and these are kneaded to form a positive electrode mixture. Make a paste. At that time, the respective mixing ratios in the positive electrode mixture paste are also important factors that determine 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 a general positive electrode of a lithium ion secondary battery. The content of the conductive material can be 1 to 20 parts by mass, and the content of the binder can be 1 to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil, dried, and the solvent is scattered. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. Thus, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut to an appropriate size according to the intended battery and used for battery production. Note that the method for manufacturing the positive electrode is not limited to the above-described example, and another method may be used.

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

  The binder plays a role of retaining the active material particles, and is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin or polyacryl. Acids can be used.

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

b) Negative electrode For the negative electrode, metallic lithium, lithium alloy, or the like can be used. In addition, a binder is mixed with a negative electrode active material capable of absorbing and desorbing lithium ions, and a suitable solvent is added to form a paste-like negative electrode mixture, which is applied to the surface of a metal foil current collector such as copper. , Dried, and, if necessary, compressed to increase the electrode density.

  Examples of the negative electrode active material include a lithium-containing material such as metallic lithium and a lithium alloy, a natural graphite capable of absorbing and desorbing lithium ions, an organic compound such as artificial graphite and a phenol resin, and a carbon material such as coke. A powder can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder similarly to the positive electrode, and an organic material such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material and the binder. Solvents can be used.

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

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

  As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, furthermore, tetrahydrofuran, 2-methyltetrahydrofuran And one compound selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, or a mixture of two or more. it can.

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.

  In addition, the non-aqueous electrolyte may include a radical scavenger, a surfactant, a flame retardant, and the like.

  It is also possible to configure a lithium ion secondary battery using a solid electrolyte instead of a non-aqueous electrolyte, and when a solid electrolyte is used, the lithium ion secondary battery can be used for safety and high charge in a charged state. The charge / discharge characteristics at a rate are improved. Therefore, the positive electrode active material of the present invention can exhibit the intended effect not only for a non-aqueous electrolyte but also for a lithium ion secondary battery using a solid electrolyte.

(2) Lithium ion secondary battery The lithium ion secondary battery according to one embodiment of the present invention, which includes the above-described positive electrode, negative electrode, separator, and non-aqueous electrolyte, has various shapes such as a cylindrical shape and a stacked shape. can do. In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolytic solution to communicate with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and are sealed in a battery case to complete a lithium ion secondary battery.

(3) Characteristics of Lithium Ion Secondary Battery As described above, the lithium ion secondary battery according to one embodiment of the present invention uses the positive electrode active material of the present invention as a positive electrode material, and thus has a battery capacity and an output characteristic. And excellent cycle characteristics. Moreover, it can be said that even in comparison with a conventional secondary battery using a positive electrode active material composed of lithium nickel-based composite oxide particles, thermal stability and safety are excellent.

(4) Applications As described above, the lithium ion secondary battery of the present invention is excellent in battery capacity, output characteristics, and cycle characteristics, and small portable electronic devices (notebook personal computers) in which these characteristics are required at a high level. It can be suitably used as a power source for a computer or a mobile phone. In addition, the lithium ion secondary battery of the present invention is excellent in safety, not only can be downsized and has high output, but also can simplify an expensive protection circuit, so that the mounting space is limited. It can also be suitably used as a power source for transportation equipment that receives it.

  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, the composite hydroxide particles and the positive electrode active material were manufactured using special grade reagents manufactured by Wako Pure Chemical Industries, Ltd. During the nucleation step and the particle growth step, the pH value of the reaction aqueous solution is measured by a pH controller (Nippon Rika, NPH-690D), and the supply amount of the aqueous sodium hydroxide solution is adjusted based on the measured values. Thus, the fluctuation range of the pH value of the reaction aqueous solution in each step was controlled within a range of ± 0.2.

(Example 1)
[Production of composite hydroxide particles]
(Nucleation process)
In Example 1, first, the temperature in the tank was set at 40 ° C. while stirring and stirring half of the water in the reaction tank (34 L). At this time, the inside of the reaction tank was set to an air atmosphere (oxygen concentration: 21% by volume). An appropriate amount of a 25% by mass aqueous solution of sodium hydroxide and 25% by mass aqueous ammonia are added to the water in the reaction tank, and the pH of the reaction liquid in the tank is adjusted to 13.0 based on a liquid temperature of 25 ° C. did. Further, the ammonia concentration in the reaction solution was adjusted to 10 g / L to obtain an aqueous solution before the reaction.

  At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were mixed with water so that the molar ratio of each metal element was Ni: Mn: Co: Zr = 33.1: 33.1: 33.1: 0.2. To prepare a 1.8 mol / L raw material aqueous solution.

  This mixed aqueous solution was added to the pre-reaction aqueous solution in the reaction tank at a rate of 88 ml / min to obtain a reaction aqueous solution. At the same time, a 25% by mass aqueous ammonia solution and a 25% by mass aqueous sodium hydroxide solution are added to the reaction aqueous solution at a constant rate, and while maintaining the ammonia concentration in the reaction aqueous solution (nucleation aqueous solution) at the above value, Crystallization was performed for 2 minutes and 30 seconds to control nucleation while controlling the value at 13.0 (nucleation pH value).

(Grain growth process)
After the nucleation was completed, the supply of all aqueous solutions was temporarily stopped, and sulfuric acid was added to adjust the pH value to 11.6 based on a liquid temperature of 25 ° C., thereby forming an aqueous solution for particle growth. . To the reaction aqueous solution (particle growth aqueous solution), the supply of the raw material aqueous solution and the 25% by mass aqueous sodium hydroxide solution was restarted, and the aqueous solution of sodium tungstate was additionally supplied as the raw material aqueous solution. The pH value was maintained at the above value, and the crystallization was continued to grow the particles. The concentration and flow rate of the aqueous solution of sodium tungstate were adjusted to suit the composition. After the particle growth for 30 minutes, the liquid supply was once stopped, and nitrogen gas was flowed at 5 L / min until the inside of the reaction tank became a non-oxidizing atmosphere having an oxygen concentration of 0.2% by volume or less. Thereafter, the supply of the aqueous solution of the raw material and the aqueous solution of sodium tungstate was restarted, and crystallization was performed for 2 hours from the start of growth while maintaining the ammonia concentration and the pH value.

  When the inside of the reaction tank became full, crystallization was stopped, stirring was stopped, and the mixture was allowed to stand, thereby promoting precipitation of the product. Then, after half of the supernatant was taken out of the reaction tank, crystallization was restarted, crystallization was performed for 2 hours (total 4 hours), and crystallization was terminated.

  The product was washed with water, filtered and dried to obtain composite hydroxide particles. Note that the switching from the air atmosphere to the nitrogen atmosphere was performed at the time of 12.5% of the entire grain growth process time from the start of the grain growth process.

  In the crystallization, the pH was controlled by adjusting the supply flow rate of the aqueous sodium hydroxide solution using a pH controller, and the fluctuation range was within a range of 0.2 above and below the set value.

[Analysis of composite hydroxide]
The obtained composite hydroxide was subjected to chemical analysis by ICP emission spectroscopy after dissolving the sample with an inorganic acid. The composition was found to be Ni _0.331 Mn _0.331 Co _0.331 Zr _{0. 002} W _0.005 (OH) _{2 + a} (0 ≦ a ≦ 0.5).

  Further, for this composite hydroxide, the value [(d90−d10) / average particle size] indicating the average particle size and the particle size distribution was measured using a laser diffraction scattering type particle size distribution analyzer (Microtrack HRA, manufactured by Nikkiso Co., Ltd.). It was determined by calculating from the volume integrated value measured using the above method. As a result, the average particle size was 5.2 μm, and the value of [(d90−d10) / average particle size] was 0.48.

  Next, the obtained composite hydroxide particles were observed by an SEM (manufactured by Hitachi High-Technologies Corporation, scanning electron microscope S-4700) (magnification: 1000 times). It was confirmed that the particles were spherical and the particle diameters were substantially uniform.

  In addition, a sample of the obtained composite hydroxide particles was embedded in a resin and subjected to cross-section polisher processing, and the result of SEM observation with a magnification of 10,000 times was performed. Are composed of secondary particles, and the secondary particles are larger than the fine primary particles outside the central portion, the central portion being composed of needle-like and flaky fine primary particles (having a particle size of about 0.3 μm). It was confirmed that it was composed of plate-shaped primary particles (particle diameter: about 0.6 μm) and an outer peripheral portion. The thickness of the outer shell with respect to the secondary particle diameter, determined from SEM observation of this cross section, was 12%.

[Manufacture of positive electrode active material]
The composite hydroxide particles were weighed and mixed with lithium hydroxide such that Li / Me = 1.12 to prepare a lithium mixture. The mixing was performed using a shaker mixer (TURBULA Type T2C, manufactured by Willy & Bacoffen (WAB)).

  The obtained lithium mixture was calcined at 600 ° C. for 4 hours in the air (oxygen: 21% by volume). After crushing the calcined lithium mixture, the mixture was heated at a rate of 5 ° C./min, baked at 970 ° C. for 3 hours, cooled, and crushed to obtain a positive electrode active material.

[Measurement of carbon content after calcination]
The carbon content (TC amount) contained in the calcined lithium mixture was measured by a high-frequency combustion-infrared absorption method using a carbon analyzer (LECO, model number: CS-600). % By mass.

[Analysis of positive electrode active material]
When the particle size distribution of the obtained positive electrode active material was measured by the same method as for the composite hydroxide particles, the average particle size was 4.7 μm, and the value of [(d90−d10) / average particle size] was 0. Was .48.

  In addition, when the SEM observation and the cross-sectional SEM observation of the positive electrode active material were performed in the same manner as the composite hydroxide particles, the obtained positive electrode active material was substantially spherical, and the particle diameter was substantially uniform. It was confirmed that. When observed at a magnification of 1000 using a scanning electron microscope, the ratio of the number of aggregated particles in which five or more secondary particles aggregated to the number of secondary particles in the observation visual field was 0.40%. Met.

For the obtained positive electrode active material, the specific surface area was measured by a fluid surface gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb), and the tap density was measured by a tapping machine (Kuramo Scientific Instruments, KRS-406). , Respectively. As a result, it was confirmed that the specific surface area was 1.4 m ² / g and the tap density was 1.23 g / cm ³ .

  Further, the obtained cathode active material was analyzed by powder X-ray diffraction using Cu-Kα ray using an X-ray diffractometer (X'Pert PRO, manufactured by PANalytical), and the crystal structure of the cathode active material was determined. Consisted of a single phase of hexagonal layered crystal lithium nickel manganese composite oxide. From the obtained X-ray diffraction pattern, the (003) plane crystallite diameter using the Scherrer equation was 121 nm.

Further, by analysis using an ICP emission spectrometer, this positive electrode active material was represented by a general formula: Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ . It was confirmed that it was done.

[Manufacture of coin-type battery and evaluation of battery characteristics]
52.5 mg of a positive electrode active material for a lithium ion secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed, pressed at 100 MPa and formed into a diameter of 11 mm and a thickness of 100 μm. The positive electrode 1 (evaluation electrode) shown in FIG. The produced positive electrode 1 was dried in a vacuum dryer at 120 ° C. for 12 hours. Then, using this positive electrode 1, a 2032 type coin-type battery 10 was produced in a glove box in an Ar atmosphere where the dew point was controlled at -80 ° C.

For the negative electrode 2, a graphite sheet having an average particle diameter of about 20 μm and a polyvinylidene fluoride coated on a copper foil stamped into a disk having a diameter of 14 mm was used, and 1 M LiPF ₆ was used as an electrolyte. A mixed solution (equivalent to Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) was used. As the separator 3, a polyethylene porous film having a thickness of 25 μm was used. The coin-type battery 10 had a gasket 4 and a wave washer 5 and was assembled into a coin-shaped battery with the positive electrode can 6 and the negative electrode can 7. The initial discharge capacity and the positive electrode resistance indicating the performance of the manufactured coin-type battery 10 were evaluated as follows.

a) Initial Discharge Capacity The initial discharge capacity is set to a value of 0.1 mA / cm ² with respect to the positive electrode after the coin-type battery 10 has been left for about 24 hours after being manufactured and the open circuit voltage OCV (Open Circuit Voltage) has stabilized. The capacity when the battery was charged to a cutoff voltage of 4.3 V, and after a one-hour pause was discharged to a cutoff voltage of 3.0 V was defined as an initial discharge capacity.

b) Positive Electrode Resistance The positive electrode resistance is measured by charging the coin-type battery 10 at 25 ° C. with a charging potential of 4.1 V, and using an AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B). Then, a Nyquist plot shown in FIG. 3A is obtained. Since the Nyquist plot is represented as the sum of characteristic curves indicating the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity, the equivalent circuit shown in FIG. A fitting calculation was performed to calculate the value of the positive electrode resistance.

c) Capacity retention rate after 500 cycles The capacity retention rate after 500 cycles is obtained by performing the charge / discharge capacity measurement described in a) above, suspending for 1 hour, and repeating the charge / discharge capacity measurement again for 500 cycles. The ratio was measured by determining the ratio (%) of the discharge capacity after 500 cycles to the initial discharge capacity. As a result, the capacity retention was 81.2%.

  Table 1 shows the characteristics of the composite hydroxide obtained in this example, and Table 2 shows the characteristics of the positive electrode active material and each evaluation of the coin-type battery manufactured using the positive electrode active material. Tables 1 and 2 show the same contents in Examples 2 to 5 and Comparative Example 1 below.

(Example 2)
In Example 2, in the particle growth step, the flow rate of the aqueous solution of sodium tungstate was adjusted such that the concentration of tungsten in the non-oxidizing atmosphere was 20% of the concentration of the additional element (tungsten) in the aqueous solution of the raw material in the oxidizing atmosphere. Except for the adjustment, a positive electrode active material for a lithium ion secondary battery was obtained and evaluated in the same manner as in Example 1. It was confirmed that the composition of the obtained positive electrode active material was represented by Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ .

(Example 3)
In Example 3, a positive electrode active material for a lithium ion secondary battery was obtained and evaluated in the same manner as in Example 1, except that the calcination temperature was 650 ° C and the calcination temperature was 970 ° C.

(Example 4)
In Example 4, a positive electrode active material for a lithium ion secondary battery was obtained and evaluated in the same manner as in Example 1 except that the calcination temperature was 700 ° C and the calcination temperature was 990 ° C.

(Example 5)
In Example 5, a positive electrode active material for a lithium ion secondary battery was obtained and evaluated in the same manner as in Example 1, except that the calcination temperature was 720 ° C and the calcination temperature was 990 ° C.

(Example 6)
In Example 6, a positive electrode active material for a lithium ion secondary battery was prepared in the same manner as in Example 1 except that the calcining temperature was set at 720 ° C., the firing temperature was set at 990 ° C., and the crushing was not performed before firing. Obtained and evaluated.

(Comparative Example 1)
In Comparative Example 1, a positive electrode active material for a lithium ion secondary battery was obtained and evaluated in the same manner as in Example 1 except that the calcination was performed at 980 ° C. without performing calcination.

(Evaluation)
Since the positive electrode active materials for lithium ion secondary batteries of Examples 1 to 6 were manufactured according to the method for manufacturing a positive electrode active material for lithium ion secondary batteries according to one embodiment of the present invention, the carbon content after calcination was reduced. I was able to keep it low. Further, any of the positive electrode active materials of Examples 1 to 6 had a smaller number of agglomerated particles, a higher initial discharge capacity, and a lower positive electrode resistance than Comparative Example 1 which had not been calcined. The cycle characteristics (capacity retention after 500 cycles) also show better results than Comparative Example 1. As described above, it was found that the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention has excellent characteristics with further improved battery capacity and cycle characteristics.

  In Example 6, the carbon content after calcination was kept low because the method of manufacturing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention was suppressed. Crushing (disintegration step before firing S4) is not performed. For this reason, the number of agglomerated particles is not as large as Comparative Example 1, but is large, and the battery capacity and the cycle characteristics are slightly inferior to those of the other Examples 1 to 5. For this reason, in the method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention, performing the pre-firing crushing step S4 is more effective in improving battery capacity and cycle characteristics. It turns out that it is.

  Although each embodiment and each example of the present invention have been described in detail as described above, it is understood by those skilled in the art that many modifications that do not substantially depart from the novel matter and effects of the present invention are possible. Will be easy to understand. Therefore, such modified examples are all included in the scope of the present invention.

  For example, in the description or drawings, a term described at least once together with a broader or synonymous different term can be replaced with the different term in any part of the description or drawing. Further, the configuration and operation of the positive electrode active material for a lithium ion secondary battery and the lithium ion secondary battery are not limited to those described in each embodiment and each example of the present invention, and various modifications can be made.

1 positive electrode (evaluation electrode), 2 negative electrode, 3 separator, 4 gasket, 5 wave washer, 6 positive electrode can, 7 negative electrode can, 10 coin-type battery

Claims (9)

A method for producing a positive electrode active material for a lithium ion secondary battery,
Formula _{(A): Ni x Mn y} Co z M t (OH) 2 + a (x + y + z + t = 1,0.3 ≦ x ≦ 0.8,0.05 ≦ y ≦ 0.55,0 ≦ z ≦ 0 4, 0 ≦ t ≦ 0.1, 0 ≦ a ≦ 0.5, and M is one or more additional elements selected from Nb, Mo, Ta, Zr, and W), and the particle size distribution is broadened. A mixing step of mixing a transition metal composite hydroxide particle having an index of [(d90-d10) / MV] of 0.65 or less with a lithium compound to form a lithium mixture;
A calcining step of calcining the lithium mixture formed in the mixing step at 550 ° C. to 745 ° C. in an oxidizing atmosphere;
A firing step of firing the lithium mixture calcined in the calcining step at 760 ° C. to 1050 ° C. in an oxidizing atmosphere;
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising:   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein in the calcining step, the carbon content in the calcined lithium mixture is controlled to be 1.2% by mass or less.   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, further comprising, before the calcination step, a crushing step before calcination for crushing the lithium mixture calcined in the calcination step. .   In the mixing step, the lithium mixture is adjusted such that the ratio of the sum of the number of atoms of metals other than lithium contained in the lithium mixture to the number of lithium atoms is 1: 0.95 to 1.5. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3.   5. The lithium ion secondary battery according to claim 1, further comprising a heat treatment step of heat-treating the transition metal composite hydroxide particles at 105 ° C. to 750 ° C. before the mixing step. 6. A method for producing a positive electrode active material. A positive electrode active material for a lithium ion secondary battery comprising lithium transition metal composite oxide particles,
Formula _{(B): Li 1 + u} Ni x Mn y Co z M t O 2 (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1,0.3 ≦ x ≦ 0.8,0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, and M is one or more kinds of additional elements selected from Nb, Mo, Ta, Zr, and W). Having a hexagonal crystal structure having a structure,
Consisting of secondary particles formed by aggregation of a plurality of primary particles,
When the positive electrode active material was observed using a scanning electron microscope, the ratio of the number of agglomerated particles obtained by aggregating five or more secondary particles to the number of the secondary particles in the observation visual field was 0.7% or less. There, positive electrode active material for a lithium ion secondary battery which is a specific surface area of 0.3m ² /g~4.0m ² / g.   The positive electrode active material for a lithium ion secondary battery according to claim 6, wherein [(d90-d10) / MV], which is an index indicating the spread of the particle size distribution, is 0.55 or less.   8. The positive electrode active material for a lithium ion secondary battery according to claim 6, wherein the secondary particles have an average particle size of 3 μm to 15 μm. 9. At least a positive electrode, a negative electrode, a separator, a lithium ion secondary battery including a non-aqueous electrolyte,
A lithium ion secondary battery in which the positive electrode active material for a lithium ion secondary battery according to any one of claims 6 to 8 is used as the positive electrode active material of the positive electrode.