JP2019212396A - Method for manufacturing positive electrode active material for lithium ion secondary battery, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To enhance output characteristics of a secondary battery.SOLUTION: A method for manufacturing a positive electrode active material for a lithium ion secondary battery, which comprises lithium transition metal composite oxide particles, comprises: a mixing step S2 of mixing a lithium compound with transition metal composite hydroxide particles which are 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 and 0≤a≤0.5, provided that M represents one or more additive elements selected from Nb, Mo, Ta, Zr and W), and of which the index [(d90-d10)/MV] showing an extent of spread of a particle size distribution is 0.65 or less, thereby forming a lithium mixture; a temporarily baking step S3 of temporarily baking the lithium mixture formed in the mixing step at a temperature of 750-900°C in an oxidizing atmosphere; and a baking step S5 of baking the lithium mixture, which has been temporarily baked in the temporarily baking step, at a higher temperature of 760-1050°C than the temporarily baking temperature in an oxidizing atmosphere.SELECTED DRAWING: Figure 1

Description

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

  In recent years, with the widespread use of portable information terminals such as smartphones and tablet PCs, development of small and lightweight secondary batteries having high energy density is strongly desired. In addition, development of a high output secondary battery is strongly desired as a power source for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles. As a secondary battery satisfying such requirements, there is a lithium ion secondary battery. This lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material used as a material for the negative electrode and the positive electrode.

Among these lithium ion secondary batteries, a lithium ion secondary battery using a layered or spinel-type lithium transition metal composite oxide as a positive electrode active material can obtain a voltage of 4V, and therefore has a high energy density. Currently, research and development are actively conducted, and some are being put into practical use. As a positive electrode active material of such a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) particles that are relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) particles using nickel that 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 ( Lithium 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 excellent in 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 size have a large specific surface area, and when used as a positive electrode active material, a sufficient reaction area with the electrolytic solution can be secured, and the positive electrode is made thin, and a lithium ion positive electrode This is because the positive electrode resistance can be reduced because the moving distance between the negative electrodes can be shortened. In addition, since particles having a narrow particle size distribution can make the voltage applied to the particles uniform within the electrode, it is possible to suppress a decrease in battery capacity due to selective deterioration of the fine particles.

  For example, Patent Documents 1 to 5 disclose a transition that becomes a precursor of a positive electrode active material by a crystallization reaction that is clearly separated into two stages of a nucleation step that mainly performs nucleation and a particle growth step that mainly performs particle growth. A method for producing 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 reaction atmosphere in the nucleation step and the particle growth step. Using such a precursor, A positive electrode active material having a narrow particle size distribution is obtained. In addition, by controlling the atmosphere of the nucleation step that mainly performs nucleation and the particle growth step that mainly performs particle growth, a low-density central portion composed of fine primary particles and a high density composed of plate-like or needle-like primary particles. Transition metal composite hydroxide particles composed of a density outer shell portion are obtained, and a positive electrode active material having a hollow structure is obtained using such a precursor.

JP 2011-116580 A JP 2012-246199 A JP 2013-147416 A International Publication No. 2012/131881 Japanese Patent Laid-Open No. 2016-210684

  However, although the production methods described in these documents can improve the output characteristics by improving the particle structure, it is required to further improve the battery capacity and the cycle characteristics. In particular, by suppressing aggregation of particles of the positive electrode active material after the firing step, the output characteristics such as battery capacity and positive electrode resistance of a secondary battery using the positive electrode active material as the positive electrode active material are further improved and improved. It is hoped that.

  The present invention has been made in view of the above problems, and has been made new and improved, which can further improve and improve the output characteristics of the secondary battery by using it as the positive electrode active material of the secondary battery. It aims at providing the manufacturing method of the positive electrode active material for lithium ion secondary batteries, the positive electrode active material for lithium ion secondary batteries, and a lithium ion secondary battery.

One aspect of the present invention is a method for producing a lithium transition metal composite oxide cathode active material for a lithium ion secondary battery consisting of particles, 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 additive elements selected from Nb, Mo, Ta, Zr, and W), and is an index indicating the spread of the particle size distribution [(d90-d10) / MV] is 0.65 The following is a mixing step of mixing the transition metal composite hydroxide particles and the lithium compound to form a lithium mixture, and calcining the lithium mixture formed in the mixing step at 750 ° C. to 900 ° C. in an oxidizing atmosphere. Calcination step and oxidizing atmosphere of the lithium mixture calcined in the calcining step , Having a firing step of firing at a calcination temperature higher than, and 760 ° C. to 1050 ° C..

  According to one aspect of the present invention, in the step of firing the mixture of the precursor and the lithium compound, the secondary particles constituting the positive electrode active material are sintered by calcining after firing at a higher temperature than before. Since aggregation is suppressed, output characteristics when used in a secondary battery can be improved.

  At this time, in one mode of the present invention, it may be further provided with a crushing step of crushing the lithium mixture calcined in the calcining step before the calcining step.

  By doing so, by crushing the lithium mixture calcined in the calcining process, some of the particles that have been sintered in the calcining process are crushed, so the positive electrode after the sintering process Sintering and aggregation of the secondary particles constituting the active material can be suppressed.

  In the aspect of the present invention, in the mixing step, the lithium mixture may be formed by a ratio of the sum of the substance amounts of metals other than lithium contained in the lithium mixture and the substance amount of lithium being 1: 0.95. It is good also as adjusting so that it may become -1.5.

  In this way, a positive electrode active material applicable to a secondary battery having desired output characteristics can be produced.

  Moreover, in 1 aspect of this invention, it is good also as having further the heat processing process which heat-processes the said transition metal composite hydroxide particle at 105 to 750 degreeC before the said mixing process.

  In this way, the moisture remaining 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 is a positive electrode active material for a lithium ion secondary battery comprising lithium transition metal composite oxide particles, wherein the lithium transition metal composite oxide particles 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, where M is one or more additive elements selected from Nb, Mo, Ta, Zr, and W) and has a layered structure Agglomerated particles having a structure and consisting of secondary particles formed by agglomerating a plurality of primary particles, and having 5 or more secondary particles agglomerated when observed using a scanning electron microscope The ratio of the ratio to the number of secondary particles in the visual field is 0.7% or less.

  According to another aspect of the present invention, the aggregation of 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 aspect of the present invention, [(d90−d10) / MV], which is an index indicating the spread of the particle size distribution, may be 0.52 or less.

  In this way, when used as a positive electrode active material for a 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 fine particles can be suppressed. .

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

  If it does in this way, when it uses for the positive electrode active material of a secondary battery, it will become possible to improve safety | security and an output characteristic, when increasing the battery capacity per unit volume of a secondary battery.

  Still another embodiment of the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and the positive electrode active material for a lithium ion secondary battery according to any one of the above-described positive electrode active materials. It is a lithium ion secondary battery in which a substance is used.

  According to still another aspect of the present invention, output characteristics such as battery capacity and positive electrode resistance can be further improved and improved.

  As described above, according to the present invention, by using the secondary battery as a positive electrode active material, output characteristics such as battery capacity and positive electrode resistance of the secondary battery can be further improved and improved.

It is a flowchart which shows the outline of the manufacturing method of the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention. It is a schematic sectional drawing of the coin-type battery used for 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 which shows the measurement result of the impedance evaluation of the Example of the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention, (B) is used for the analysis of the said impedance evaluation It is a schematic explanatory drawing of the equivalent circuit.

  Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.

  The present inventors further aim to improve the battery capacity and cycle characteristics of a positive electrode active material for lithium ion secondary batteries (hereinafter also referred to as “positive electrode active material”) based on the prior art such as Patent Document 3 described above. In order to achieve this, we have conducted extensive research. As a result, in the step of firing the mixture of the precursor and the lithium compound, after calcining at a specific temperature, firing can suppress sintering aggregation of the secondary particles constituting the positive electrode active material, It was found that the characteristics when used in a battery can be improved. The present invention has been completed based on these findings.

1. 1. Transition metal composite hydroxide particles 1-1. Transition metal composite hydroxide particles In the process of producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, transition metal composite hydroxide particles (hereinafter referred to as “composite hydroxide particles”). ) As a precursor of a positive electrode active material for a lithium ion secondary battery. The composite hydroxide particles are preferably composed of secondary particles formed by aggregation of a plurality of plate-like primary particles. The secondary particles preferably have a central portion formed by agglomerating fine primary particles, and preferably include an outer peripheral portion formed by agglomerating the plate-like primary particles outside the central portion. More preferably, the central portion contains a higher concentration of additive elements than the outer peripheral portion. By using the composite hydroxide particles having such a central portion, it is possible to obtain a positive electrode active material having a hollow structure having higher output characteristics. In addition, it is preferable that the average particle diameter of the secondary particle of the composite hydroxide particle in this embodiment is 3 μm to 15 μm.

(1) Particle structure Suitable composite hydroxide particles used in the process of manufacturing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention are formed by aggregation of a plurality of plate-like primary particles. It is a substantially spherical secondary particle. Moreover, it is preferable that the inside of a particle | grain has a structure which has a center part which consists of a fine primary particle, and has the outer peripheral part which consists of a plate-shaped primary particle larger than a fine primary particle outside the said center part. In the sintering step of forming a lithium nickel manganese composite oxide, which is a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, with a structure in which a plurality of plate-like primary particles are aggregated, Since lithium is sufficiently diffused into the cathode, a good positive electrode active material with a uniform lithium distribution can be obtained. Such composite hydroxide particles and the production method thereof are disclosed in detail, for example, in Patent Document 1 and Patent Document 2 described above.

  Here, since the central portion has a structure with many gaps in which fine primary particles are connected, the shrinkage due to sintering is lower in the firing step than in the outer peripheral portion made of thicker plate-like primary particles. Arising from. For this reason, sintering proceeds from a low temperature during firing, shrinks from the center of the particles to the outer peripheral side where the progress of the sintering is slow, and a space is created in the center. Further, since the central portion is considered to have a low density and the shrinkage rate is large, the central portion becomes a sufficiently large space. Thereby, the positive electrode active material obtained after baking becomes a hollow structure.

  Furthermore, it is more preferable if the plate-like primary particles are aggregated in random directions to form secondary particles. When the plate-like primary particles aggregate in a random direction, voids are formed almost uniformly between the primary particles, and when mixed with the lithium compound and baked, the molten lithium compound reaches the secondary particles, Is sufficiently diffused. In addition, since the composite hydroxide particles having the central part are uniformly agglomerated in the random direction, shrinkage of the central part in the firing step is equally generated. It is preferable because it can form a space. At this time, in order to form a space during the firing, the fine primary particles preferably have an average particle diameter of 0.01 to 0.3 μm, and more preferably 0.1 to 0.3 μm. preferable. 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 in the process of manufacturing the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention preferably have an average particle size of secondary particles of 3 μm to 12 μm. More preferably, it is 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. Therefore, by controlling the average particle size of the secondary particles in such a range, the average particle size of the positive electrode active material having the composite hydroxide particles as a precursor can be controlled within a predetermined range. Become. In the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the average particle diameter of the secondary particles means a volume-based average particle diameter (MV), for example, a laser light diffraction scattering type It can obtain | require from the volume integrated value measured with the particle size analyzer.

(3) Particle size distribution The composite hydroxide particles used in the process of producing 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 diameter] 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 influenced by the composite hydroxide particles that are precursors thereof. For this reason, when a composite hydroxide particle containing a large amount of fine particles and coarse particles is used as a precursor, the positive electrode active material also contains a lot of fine particles and coarse particles. Safety, cycle characteristics, and output characteristics cannot be sufficiently improved.

  On the other hand, if it is adjusted so that [(d90-d10) / average particle size] is 0.65 or less at the stage of the composite hydroxide particles, The particle size distribution can be narrowed, and the above-described problems can be avoided. However, on the premise of production on an industrial scale, it is not practical to use a composite hydroxide particle 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 about 0.25.

  Here, d10 referred to here means the particle diameter in which the number of particles in each particle diameter is accumulated from the smaller particle diameter side, and the accumulated volume is 10% of the total volume of all particles, and d90 is similarly It means a particle size in which the number of particles is accumulated and the accumulated volume is 90% of the total volume of all particles. Moreover, d10 and d90 can be calculated | required from the volume integrated value measured with the laser beam diffraction scattering type particle size analyzer similarly to an average particle diameter.

(4) Composition composite hydroxide particles used in the process of producing a positive 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 represented by one or more additive 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 general formula (B) described later can be easily obtained, and higher battery performance can be realized.

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

1-2. Method for Producing Transition Metal Composite Hydroxide Particles Composite hydroxide particles used in the process of producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention include, for example, at least a transition metal in a reaction vessel. A transition metal composite hydroxide that forms a reaction aqueous solution by supplying an aqueous solution containing an ammonium ion and an aqueous solution containing an ammonium ion supplier and becomes a precursor of a positive electrode active material for a lithium ion secondary battery by a crystallization reaction Obtained by the method of producing particles.

  In particular, the crystallization reaction is carried out by adjusting the pH value of the aqueous reaction solution at 25 ° C. in the range of 12.0 to 14.0 to nucleate, and the nucleation step obtained in the nucleation step. In the particle growth step, the pH of the aqueous solution containing the reaction is controlled so as to be lower than the pH value of the nucleation step and 10.5 to 12.0, and the nuclei are grown. It is preferable to make a distinction between the 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 in the particle growth step, the reaction atmosphere is 5% by volume or less from the oxidizing atmosphere. It is preferable to switch to a non-oxidizing atmosphere. The production method of the composite hydroxide particles is not limited by the composition as long as the structure, the average particle size and the particle size distribution described above can be realized, but the composite hydroxide represented by the general formula (A) It can apply suitably with respect to a thing particle.

(1) Crystallization reaction In the manufacturing method of the composite hydroxide particles, the crystallization reaction is clearly separated into two stages, a nucleation process mainly performing nucleation and a particle growth process mainly performing particle growth, By adjusting the crystallization conditions in each step, particularly by switching the reaction atmosphere in the particle growth step, it is possible to efficiently obtain composite hydroxide particles having the above-described particle structure, average particle size and particle size distribution. It is possible.

[Nucleation process]
In the nucleation step, first, a transition metal compound as a raw material in this step is dissolved in water to prepare a raw material aqueous solution. At the same time, an aqueous alkali solution and an aqueous solution containing an ammonium ion supplier are supplied and mixed in the reaction tank, and the pH value measured on the basis of the 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 that is L-25 g / L. The pH value of the aqueous solution before reaction can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

  Next, the raw material aqueous solution is supplied while stirring the pre-reaction aqueous solution. As a result, a nucleation aqueous solution that is a reaction aqueous solution in the nucleation step is formed in the reaction vessel. Since the pH value of this aqueous solution for nucleation is in the above-mentioned range, in the nucleation step, nucleation occurs preferentially with almost no growth of nuclei. In the nucleation step, the pH value of the aqueous solution for nucleation and the concentration of ammonium ions change with the nucleation. Therefore, an alkaline aqueous solution and an aqueous ammonia solution are supplied as needed, and the pH value of the liquid in the reaction vessel is adjusted to a liquid temperature of 25 It is necessary to control so that the concentration of ammonium ions is maintained in the range of 3 g / L to 25 g / L in the range of pH 12.0 to 14.0 on the basis of ° C.

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

  In the nucleation step, new nuclei are continuously generated by supplying an aqueous solution containing a raw material aqueous solution, an alkaline aqueous solution and an ammonium ion supplier to the nucleation aqueous solution. Then, when a predetermined amount of nuclei is generated in the aqueous solution for nucleation, the nucleation step is finished. At this time, the amount of nucleation 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 It is preferable to set it as 0.1 atomic%-2 atomic% with respect to the metal element in a compound, and it is more preferable to set it as 0.1 atomic%-1.5 atomic%.

[Particle growth process]
After completion of the nucleation step, the pH value of the aqueous solution for nucleation in the reaction vessel is adjusted to 10.5 to 12.0 on the basis of the liquid temperature of 25 ° C. to form an aqueous solution for particle growth that is a reaction aqueous solution in the particle growth step. To do. The pH value can be adjusted by stopping the supply of the alkaline aqueous solution, but in order to obtain composite hydroxide particles having a narrow particle size distribution, the supply of all the aqueous solutions is once stopped and the pH value is adjusted. It is preferable. Specifically, after the supply of all aqueous solutions is stopped, it is preferable to adjust the pH value by supplying the nucleation aqueous solution with the same kind of inorganic acid as the acid constituting the raw metal compound.

  Next, supply of the raw material aqueous solution is resumed 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-described range, almost no new nuclei are generated, and the growth of the nuclei (particles) proceeds to form composite hydroxide particles having a predetermined particle size. The In the particle growth process, the pH value and ammonium ion concentration of the aqueous solution for particle growth change as the particle grows. Therefore, an alkaline aqueous solution and an aqueous ammonia solution are supplied in a timely manner, and the pH value and the ammonium ion concentration are maintained within the above ranges. It is necessary to do.

  In particular, in the method for producing composite hydroxide particles used in the process of producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the reaction atmosphere is changed from an oxidizing atmosphere during the particle growth process. Switch to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. This makes it possible to obtain composite hydroxide particles having the above-described particle structure.

  In such a method for producing composite hydroxide particles, metal ions are precipitated as primary particles forming nuclei or composite hydroxide particles in the nucleation step and the particle growth step. 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, the concentration of the raw material aqueous solution is apparently decreased, and in particular, in the particle growth step, the growth of the composite hydroxide particles may be stagnant. Therefore, in order to suppress an 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 in the middle of the particle growth step after the nucleation step.

  Specifically, the supply and stirring of the aqueous solution containing the raw material aqueous solution, the alkaline aqueous solution and the ammonium ion supplier are temporarily stopped, and the nuclei and composite hydroxide particles in the aqueous solution for particle growth are allowed to settle, It is preferable to discharge the supernatant. By such an operation, the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth can be increased, so that stagnation of particle growth is prevented and the particle size distribution of the resulting composite hydroxide particles is controlled within a suitable range. In addition, the density of the secondary particles as a whole can be improved.

[Adding additive elements]
The concentration of the additive element with respect to elements other than the additive element in the raw material aqueous solution is set higher in the oxidizing atmosphere than in the non-oxidizing atmosphere. The concentration in the oxidizing atmosphere is preferably at least twice, more preferably at least five times the concentration in the non-oxidizing atmosphere. Particularly preferably, an aqueous solution containing an 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 fine primary particles formed in an oxidizing atmosphere aggregate is shrunk to the inside of the outer peripheral part formed by aggregation of plate-like primary particles formed in a non-oxidizing atmosphere when the positive electrode active material is manufactured. To form a hollow portion.

  Therefore, the additive element added in the oxidizing atmosphere diffuses to the outer peripheral part and is present on the surface of the primary particles forming the outer shell part of the positive electrode active material, whereas the additive element added in the non-oxidizing atmosphere is , A large amount is present inside the primary particle, and a concentrated layer of the additive element is formed on the surface of the primary particle. By forming a concentrated layer on the surface of the primary particles that come into contact with the electrolytic solution, it becomes possible to effectively function an additive element that improves output characteristics. By making the concentration of the additive element added in the oxidizing atmosphere higher than the concentration added in the non-oxidizing atmosphere, the amount of the additive element in the concentrated layer can be increased and function more effectively. be able to.

  Further, in the particle growth step, the concentration of the additive element is set to 35% to 75% in a range of 35% to 75% with respect to the time from the switching from the oxidizing atmosphere to the non-oxidizing atmosphere until the end of the particle growth step. % Higher than the concentration in the range of 50% to 80% of the thickness of the outer peripheral portion, the concentration of the additive element on the surface side can be higher than the inner side of the outer peripheral portion. By forming such a layer containing an additive element having a higher concentration than the inner side on the surface side of the outer peripheral portion, it becomes possible to further improve the battery characteristics by further uniforming the formation of the concentrated layer in the positive electrode active material. .

[Control of particle size of composite hydroxide particles]
The particle size of the composite hydroxide particles obtained as described above should be controlled by the time of the particle growth step and nucleation step, the pH value of the aqueous solution for nucleation and aqueous solution for particle growth, and the supply amount of the raw material aqueous solution. Can do. For example, by performing the nucleation step at a high pH value or by lengthening 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 amount of nucleation is increased. The particle size of the composite hydroxide particles can be reduced. On the other hand, the particle size of the resulting composite hydroxide particles can be increased by suppressing the amount of nuclei produced in the nucleation step.

[Another Embodiment of Crystallization Reaction]
In the method for producing composite hydroxide particles used in the process of producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, a pH value suitable for the particle growth step, in addition to the aqueous solution for nucleation, and Prepare a component adjustment aqueous solution adjusted to the ammonium ion concentration, and remove a part of the liquid component from the nucleation aqueous solution after the nucleation step, preferably from the nucleation aqueous solution after the nucleation step. The particles may be added and mixed to form an aqueous solution for particle growth, and the particle growth step may be performed.

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

(2) Supply aqueous solution In the manufacturing method of the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention, it becomes a composition ratio of the composite hydroxide particle from which the ratio of the metal element in raw material aqueous solution is obtained substantially. . For this reason, it is necessary for the raw material aqueous solution to appropriately adjust the content of each metal element according to the composition of the target composite hydroxide particles. For example, when trying to obtain the composite hydroxide particles represented by the general formula (A) described above, the ratio of the metal element in the aqueous raw material solution is set to Ni: Mn: Co: M = x: y: z; t (however, x + y + z + t = 1, 0.3 ≦ x ≦ 0.80, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1) It will be necessary.

  The transition metal compound for preparing the raw material aqueous solution is not particularly limited, but from the viewpoint of ease of handling, it is preferable to use water-soluble nitrate, sulfate, hydrochloride, etc. It is particularly preferable to use a sulfate from the viewpoint of preventing the above. In addition, when the additive element M (M is one or more additive elements selected from Nb, Mo, Ta, Zr, and W) is included in the composite hydroxide particles, the additive element M is supplied. Similarly, a water-soluble compound is preferable as this compound, and for example, zirconium sulfate, 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 the total of the metal compounds, preferably 1 mol / L to 2.6 mol / L, more preferably 1.5 mol / L to 2.2 mol / L. When the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized material per reaction tank is reduced, and thus the productivity is lowered. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol / L, it exceeds the saturation concentration at normal temperature, and thus crystals of each metal compound may reprecipitate and clog piping and the like.

  The metal compound mentioned above does not necessarily have to be supplied to the reaction vessel as a raw material aqueous solution. For example, when a crystallization reaction is performed using a metal compound that reacts when mixed to produce a compound other than the target compound, the total concentration of all the metal compound aqueous solutions is in the above range. Alternatively, an aqueous metal compound solution may be prepared and supplied into the reaction vessel at a predetermined rate as an aqueous solution of individual metal compounds.

  The supply amount of the raw material aqueous solution is such that 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. When the concentration of the product is less than 30 g / L, the primary particles may be insufficiently aggregated. On the other hand, when it exceeds 200 g / L, the metal salt aqueous solution for nucleation or the metal salt aqueous solution for particle growth does not sufficiently diffuse in the reaction tank, and the particle growth may be biased.

  On the other hand, the aqueous alkali solution for adjusting the pH value in the aqueous reaction solution is not particularly limited, and a general aqueous alkali metal hydroxide 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 it is preferably added as an aqueous solution in view of easy pH control. In this case, the concentration of the alkali metal hydroxide aqueous solution is preferably 20% by mass to 50% by mass, more preferably 20% by mass to 30% by mass. By regulating the concentration of the alkali metal aqueous solution to such a range, it is possible to prevent the pH value from being locally increased at the addition position while suppressing the amount of solvent (water amount) supplied to the reaction system. Thus, it becomes possible to efficiently obtain composite hydroxide particles having a narrow particle size distribution. The method for supplying the alkaline aqueous solution is not particularly limited as long as the pH value of the aqueous reaction solution is not locally increased and is maintained within a predetermined range. For example, the reaction aqueous solution may be supplied by a pump capable of controlling the flow rate such as a metering pump while sufficiently stirring.

  The aqueous solution containing the ammonium ion supplier is not particularly limited, and for example, aqueous ammonia or an aqueous solution such as ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride can be used. When ammonia water is used as the ammonium ion supplier, the concentration is preferably 20% by mass to 30% by mass, more preferably 22% by mass to 28% by mass. By restricting the concentration of the ammonia water within such a range, loss of ammonia due to volatilization or the like can be suppressed to a minimum, so that production efficiency can be improved. In addition, the supply method of the aqueous solution containing an ammonium ion supply body can also be supplied by a pump capable of controlling the flow rate, similarly to the alkaline aqueous solution.

(3) pH value In the method for producing composite hydroxide particles used in the process of producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the pH value based on a liquid temperature of 25 ° C. It is necessary to control in the range of 12.0 to 14.0 in the production step and in the range of 10.5 to 12.0 in the particle growth step. 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 amount of nucleation and the rate of particle growth are not constant, and it becomes difficult to obtain composite hydroxide particles having a narrow particle size distribution.

  In the nucleation step, the pH value of the aqueous reaction solution (nucleation aqueous solution) is 12.0 to 14.0, preferably 12.3 to 13.5, more preferably 12.5 to 13 on the basis of the liquid temperature of 25 ° C. It is necessary to control within the range of .3. Thereby, it is possible to suppress the growth of nuclei and prioritize the nucleation, and the nuclei generated in this step can be homogeneous 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 with nucleation, so that the obtained composite hydroxide particles have non-uniform particle sizes, and the particle size distribution deteriorates. On the other hand, when the pH value exceeds 14.0, the nuclei to be produced become too fine, which causes a problem that the aqueous solution for nucleation gels.

  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 11.5 to 12.2. It is necessary to control within the range of 0. Thereby, generation of new nuclei is suppressed, it is possible to prioritize particle growth, and the resulting composite hydroxide particles can be made homogeneous and have a narrow particle size distribution. On the other hand, when the pH value is less than 10.5, the ammonium ion concentration increases and the solubility of metal ions increases, so that not only the rate of crystallization reaction is slowed but also the amount of metal ions remaining in the reaction aqueous solution increases. And productivity deteriorates. On the other hand, when the pH value exceeds 12.0, the amount of nucleation during the particle growth step increases, the particle size of the resulting composite hydroxide particles becomes non-uniform, and the particle size distribution deteriorates.

  In addition, when the pH value is 12.0, it is a boundary condition between nucleation and nucleation, so it should be either nucleation process or particle growth process depending on the presence or absence of nuclei present in the reaction aqueous solution. Can do. That is, if the pH value of the nucleation step is higher than 12.0 and a large amount of nuclei are produced, and then the pH value of the particle growth step is 12.0, a large amount of nuclei exist 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 of the nucleation step is 12.0, there is no nucleus that grows in the reaction aqueous solution, so nucleation occurs preferentially, and the pH value of the particle growth step is made smaller than 12.0. The produced nuclei grow and good composite hydroxide particles can be obtained. In any case, the pH value of the particle growth process may be controlled to a value lower than the pH value of the nucleation process. To clearly separate nucleation and particle growth, the pH value of the particle growth process is It is preferably 0.5 or more lower than the pH value of the production step, more preferably 1.0 or more.

(4) Reaction atmosphere A preferable structure in which the composite hydroxide particles as described above have a central portion controls the pH value of the reaction aqueous solution in the nucleation step and the particle growth step as described above, and 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 along with the control of the pH value in each step. That is, by controlling the pH value in each step as described above and adjusting the initial reaction atmosphere in the nucleation step and the particle growth step to an oxidizing atmosphere, a central portion where fine primary particles are aggregated is formed. The Further, by switching from an oxidizing atmosphere to a non-oxidizing atmosphere in the middle of the particle growth process, an outer peripheral portion in which 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-shaped and / or needle-shaped, but depending on the composition of the composite hydroxide particles, a rectangular parallelepiped shape, an elliptical shape, a ridged surface shape A shape such as a shape can also be adopted. 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 composition of the target composite hydroxide particles.

  In the step of forming the center portion of the composite hydroxide particles, the reaction atmosphere is controlled to be an oxidizing atmosphere. Specifically, the oxygen concentration in the reaction atmosphere is controlled so as to exceed 5% by volume, preferably 10% by volume or more, more preferably the atmospheric air (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere in such a range, the average particle size of the primary particles is in the range of 0.01 μm to 0.3 μm, so that the center portion formed of fine primary particles is formed. Can do. The upper limit of the oxygen concentration in the reaction atmosphere at this stage is not particularly limited, but if the oxygen concentration is excessively high, the average particle size of the primary particles becomes less than 0.01 μm, and the low-density layer is sufficient. It may not be the size. For this reason, it is preferable that an oxygen concentration shall be 30 volume% or less.

  On the other hand, the reaction atmosphere in the step of forming the outer peripheral portion of the composite hydroxide particles is controlled to be a weak oxidizing atmosphere or a non-oxidizing atmosphere. Specifically, the mixed atmosphere of oxygen and 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, since the nucleus produced | generated at the nucleation process can be grown to a fixed range, suppressing unnecessary oxidation, the average particle diameter is 0.3 micrometer-3 micrometers in the outer peripheral part of a composite hydroxide particle. In the range, the plate-like primary particles can be aggregated, and an outer peripheral portion having a sufficient primary particle diameter difference from the above-described central portion can be formed.

  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 center portion of the composite hydroxide particles so that a hollow portion is obtained in such a degree that fine particles are generated and cycle characteristics are not deteriorated in the finally obtained positive electrode active material. In consideration of this, the timing is determined. For example, it is performed in the range of 0 to 40%, preferably 0 to 30%, more preferably 0 to 25% from the start of the particle growth process with respect to the entire particle growth process time. When the switching is performed at a time point exceeding 40% with respect to the entire particle growth process time, the formed central part becomes large, and the thickness of the outer peripheral part with respect to the particle diameter of the secondary particles becomes too thin. On the other hand, when the switching is performed before the start of the particle growth process, that is, during the nucleation process, the central part becomes too small or secondary particles having the structure are not formed.

  Conventionally, switching of the reaction atmosphere during the crystallization step is performed by circulating an atmosphere gas in the reaction tank or by 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. . However, in such a conventional technique, since it takes a long time to switch the reaction atmosphere, it is necessary to stop the supply of the raw material aqueous solution during the switching. Therefore, when the reaction atmosphere is switched while supplying the raw material aqueous solution, it is preferable to use an air diffuser. The diffuser tube is constituted by a conduit having a large number of fine holes on the surface, and can release a large number of fine gases (bubbles) into the liquid, so that the reaction atmosphere can be switched in a short time. For this reason, it is not necessary to stop the supply of the raw material aqueous solution when the reaction atmosphere is switched, and the production efficiency can be improved.

  As such an air diffuser, it is preferable to use a ceramic tube excellent in resistance under a high pH environment. In addition, the smaller the hole diameter of the air diffusing tube, 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 an air diffuser having a diameter of 50 μm or less.

(5) Ammonium ion concentration The ammonium ion concentration in the aqueous reaction solution is preferably kept constant within a range of 3 g / L to 25 g / L, more preferably 5 g / L to 20 g / L. Since ammonium ions function as a complexing agent in the reaction aqueous solution, if the ammonium ion concentration is less than 3 g / L, the solubility of the metal ions cannot be kept constant, and the reaction aqueous solution is easily gelled. It becomes 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 the metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, which causes a composition shift or the like. If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of metal ions fluctuates, and uniform composite hydroxide particles are not formed. For this reason, it is preferable to control the fluctuation range of the ammonium ion concentration within a certain range through the nucleation step and the particle growth step, and specifically, it is preferable to control the fluctuation range of ± 5 g / L.

(6) Reaction temperature The temperature of the aqueous reaction solution (reaction temperature) is preferably controlled to 20 ° C. or more, more preferably 20 ° C. to 60 ° C., through the nucleation step and the particle growth step. When the reaction temperature is less than 20 ° C., the solubility of the reaction aqueous solution becomes low, so that nucleation easily occurs, and it becomes difficult to control the average particle size and particle size distribution of the resulting composite hydroxide particles. The upper limit of the reaction temperature is not particularly limited, but when it exceeds 60 ° C., the volatilization of ammonia is promoted, and an ammonium ion supplier that is supplied to control ammonium ions in the aqueous reaction solution within a certain range. As a result, the amount of the aqueous solution containing water increases and the production cost increases.

(7) Coating process In order to add an additional element to a positive electrode active material, you may provide a coating process. The coating method is not particularly limited as long as the composite hydroxide particles can be uniformly coated with the compound containing the additive element M. For example, after slurrying composite hydroxide particles and controlling the pH value within a predetermined range, an aqueous solution (a coating aqueous solution) in which a compound containing additive element M is dissolved is added to the surface of the composite hydroxide particles. By precipitating the compound containing the additive element M, composite hydroxide particles uniformly coated with the compound containing the additive element can be obtained. In this case, instead of the aqueous solution for coating, an alkoxide solution of an additive element may be added to the composite hydroxide particles made into a slurry. Moreover, you may coat | cover by spraying and drying the aqueous solution or slurry which melt | dissolved the compound containing an addition element, without making a composite hydroxide particle into a slurry. Furthermore, the slurry in which the compound hydroxide compound and the compound containing the additive element are suspended is spray-dried, or the compound hydroxide compound and the compound containing the additive element are mixed by a solid phase method. You can also

  When the surface of the composite hydroxide particles is coated with an additive element, the raw material aqueous solution and the coating are made 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 aqueous solution. Moreover, you may perform a coating process with respect to the heat-processed particle after heat-processing the composite hydroxide particle.

(8) Manufacturing apparatus As a crystallization apparatus (reaction tank) for manufacturing composite hydroxide particles used in the process of manufacturing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the above-described is used. There is no particular limitation as long as the reaction atmosphere can be switched by the air diffuser. However, it is preferable to use a batch crystallizer that does not collect the precipitated product until the crystallization reaction is completed. Unlike a continuous crystallizer that recovers a product by the overflow method, such a crystallizer does not collect the growing particles at the same time as the overflow liquid. Product particles can be easily obtained. In the method for producing composite hydroxide particles used in the process of producing the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, it is necessary to appropriately control the reaction atmosphere during the crystallization reaction. Therefore, it is preferable to use a closed crystallizer.

2. 2. Positive electrode active material for lithium ion secondary battery 2-1. Cathode active material for a lithium ion secondary battery according to an embodiment of the positive electrode active material present invention for lithium ion secondary batteries, 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 represents one or more additive elements selected from Nb, Mo, Ta, Zr, and W), and is composed of lithium transition metal composite oxide particles having a hexagonal crystal structure having a layered structure. Features. Further, the lithium transition metal composite oxide particles constituting the positive electrode active material for the lithium ion secondary battery of the present embodiment are formed of secondary particles formed by aggregating a plurality of primary particles, and the positive electrode active material is scanned. When observed with a scanning electron microscope, the proportion of aggregated particles in which 5 or more secondary particles aggregate is characterized by the proportion of the number of secondary particles in the visual field being 0.7% or less .

(1) Particle Structure The positive electrode active material for a lithium ion secondary battery according to an 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, the secondary particles preferably include an outer shell portion and a hollow portion in which the inner primary particles of the outer shell portion are not present. In the positive electrode active material having a hollow structure, the electrolyte enters from the grain boundaries or voids between the primary particles, and lithium is inserted and desorbed at the reaction interface on the surface of the primary particles on the hollow side inside the particles. Electron movement is not hindered, and output characteristics can be improved.

  In the positive electrode active material having a hollow structure, the thickness of the outer shell portion is preferably 5 to 45%, more preferably 8 to 38%, in the ratio to the particle size of the secondary particles. Further, the absolute value is more preferably in the range of 0.5 to 2.5 μm, and particularly preferably in the range of 0.5 to 2.0 μm. When the ratio of the thickness of the outer shell is less than 5%, the strength of the secondary particles is reduced, so that the particles are broken and fine particles are generated when handling the powder and when making the positive electrode of the battery. make worse. On the other hand, when the thickness ratio 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. For this reason, the positive electrode resistance increases and the output characteristics deteriorate. In addition, the ratio of the thickness of the outer shell part to the secondary particle diameter can be obtained in the same manner as the composite hydroxide particles.

(2) Average particle diameter The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is adjusted so that the average particle diameter is preferably 3 μm to 15 μm, more preferably 3 μm to 10 μm. If the average particle diameter of the positive electrode active material is in such a range, not only can the battery capacity per unit volume of the secondary battery using this positive electrode active material be increased, but also the safety and output characteristics are improved. can do. On the other hand, when the average particle size is less than 3 μm, the filling property of the positive electrode active material is lowered, and the battery capacity per unit volume may not be sufficiently increased. On the other hand, if the average particle size exceeds 15 μm, the reaction area of the positive electrode active material is reduced and the interface with the electrolytic solution is reduced, so that the output characteristics may not be sufficiently improved. Note that 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. For example, the volume integration measured with a laser light diffraction scattering particle size analyzer It can be obtained from the value.

(3) Particle size distribution In the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, five or more secondary particles aggregated when observed at a magnification of 1000 using a scanning electron microscope. The ratio of the aggregated particles is 0.7% or less of the number of secondary particles in the visual field. By reducing the agglomerated particles in this way, 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. it can. When the aggregated particles increase, the distribution of the positive electrode active material particles in the positive electrode becomes non-uniform, and it is difficult to improve the battery characteristics.

  Furthermore, [(d90−d10) / average particle size], which is an index indicating the spread of the particle size distribution, is preferably 0.52 or less, more preferably 0.50 or less, and is composed of particles having a very narrow particle size distribution. . Such a positive electrode active material has a small proportion of fine particles and coarse particles, and a secondary battery using the positive electrode active material has more excellent safety, cycle characteristics, and output characteristics.

  On the other hand, when [(d90−d10) / average particle diameter] exceeds 0.52, 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 local reaction of fine particles, which not only decreases safety but also reduces fineness. Cycle characteristics may be inferior due to selective deterioration of the particles. In addition, 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 inferior.

  On the other hand, on the premise of production on an industrial scale, it is not practical to use a material having an excessively small [(d90-d10) / average particle size] as the positive electrode active material. Therefore, in consideration of cost and productivity, the lower limit of [(d90−d10) / average particle diameter] is preferably about 0.25. In addition, since the meaning of d10 and d90 in the index [(d90−d10) / average particle size] indicating the spread of the particle size distribution and how to obtain these are the same as those of the composite hydroxide particles described above, Description of is omitted.

(4) Composition cathode active material for a lithium ion secondary battery according to an embodiment 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 Nb, It can be suitably applied to a positive electrode active material represented by one or more additive elements selected from Mo, Ta, Zr, and W.

  In this positive electrode active material, the value of u indicating an excess amount of lithium (Li) is preferably −0.05 or more and 0.50 or less, more preferably 0 or more and 0.50 or less, and further preferably 0 or more and 0.35 or less. And By 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 the positive electrode active material can be improved. On the other hand, if the value of u is less than −0.05, the positive electrode resistance of the secondary battery is increased, and the output characteristics cannot be improved. On the other hand, if it exceeds 0.50, not only the initial discharge capacity is lowered but also the positive electrode resistance is increased, which is not preferable.

  Nickel (Ni) is an element that contributes to increasing the potential and capacity of the secondary battery, and the value of x indicating the content thereof is 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 battery capacity of a secondary battery using this positive electrode active material cannot be improved, which is not preferable. On the other hand, if the value of x exceeds 0.80, the content of other elements decreases, and the effect cannot be obtained.

  Manganese (Mn) is an element contributing to the improvement of thermal stability, and the value of y indicating the content thereof is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. And If the value of y is less than 0.05, it is not preferable because the thermal stability of a secondary battery using this positive electrode active material cannot be improved. On the other hand, if the value of y exceeds 0.55, Mn is eluted from the positive electrode active material during high temperature operation, and the charge / discharge cycle characteristics deteriorate, which is not preferable.

  Cobalt (Co) is an element contributing to the improvement of charge / discharge cycle characteristics, and the value of z indicating the content thereof is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.35 or less. To do. If the value of z exceeds 0.4, the initial discharge capacity of a secondary battery using this positive electrode active material is significantly reduced, which is not preferable.

  In the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, in order to further improve the durability and output characteristics of the secondary battery, the additive element M may be included in addition to the metal element described above. Good. Examples of the additive element M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum. One or more selected from (Mo), hafnium (Hf), tantalum (Ta), lanthanum (La), and tungsten (W) can be used. The value of t indicating the content of the additive element M is preferably 0 or more and 0.1 or less, more preferably 0.001 or more and 0.05 or less. If the value of t exceeds 0.1, the metal element contributing to the Redox reaction is decreased, which is not preferable because the battery capacity is decreased.

(6) an exemplary cathode active material for a lithium ion secondary battery according to an embodiment of the specific surface area present invention, the specific surface area is preferably a 0.7m ² /g~5.0m ² / g, 1.8m and more preferably ^{2 /g~5.0m 2} / g. The positive electrode active material having a specific surface area in such a range has a large contact area with the electrolyte, and can greatly improve the output characteristics of a secondary battery using the positive electrode active material. On the other hand, when the specific surface area of the positive electrode active material is less than 0.7 m ² / g, when the secondary battery is configured, the reaction area with the electrolytic solution cannot be secured, and the output characteristics are sufficiently improved. It is not preferable because it becomes difficult to do so. On the other hand, if the specific surface area of the positive electrode active material exceeds 5.0 m ² / g, the reactivity with the electrolytic solution becomes too high, and the thermal stability may be lowered. In addition, the specific surface area of a positive electrode active material can be measured by the BET method by nitrogen gas adsorption, for example.

(7) Tap density Increasing the capacity of secondary batteries is an important issue in order to increase the usage time of portable electronic devices and the travel distance of electric vehicles. On the other hand, the thickness of the electrode of the secondary battery is required to be about a few microns due to problems of packing of the whole battery and electronic conductivity. For this reason, it is necessary not only to use a high-capacity positive electrode active material but also to increase the filling capacity of the positive electrode active material and to increase the capacity of the secondary battery as a whole. From such a point of view, in the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the tap density, which is an index of filling property, is preferably 1.0 g / cm ³ or more. More preferably 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 represents the bulk density after tapping the sample powder collected in a container 100 times based on JIS Z-2504, and can be measured using a shaking specific gravity measuring instrument.

2-2. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery FIG. 1 is a flowchart showing an outline of a method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. A method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery comprising lithium transition metal composite oxide particles. As shown, it has a heat treatment step S1, a mixing step S2, a calcining step S3, a pre-firing crushing step S4, a baking step S5, and a post-firing crushing step S6. By manufacturing a positive electrode active material by such a manufacturing method, the positive electrode active material mentioned above, especially the positive electrode active material represented by the general formula (B) described above can be easily obtained. Hereinafter, each step will be described in detail.

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

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

  Note that in the heat treatment step, it is only necessary to remove moisture to such an extent that the amount of each metal component in the positive electrode active material and the proportion of the amount of Li do not vary. There is no need to convert to physical particles. However, in order to reduce the variation in the amount of each metal component and the amount of Li, the composite hydroxide particles are converted into composite oxide particles by heating to 400 ° C. or higher. It is preferable to do. In addition, the above-mentioned dispersion | variation can be suppressed more by calculating | requiring previously the metal component contained in the composite hydroxide particle by heat processing conditions by analysis, and determining the mixing ratio with a lithium compound.

  The atmosphere in which the heat treatment is performed is not particularly limited and may be a non-reducing atmosphere, but is preferably performed in an air stream that can be easily performed. The heat treatment time is not particularly limited, but is preferably at least 1 hour and more preferably 5 hours to 15 hours from the viewpoint of sufficiently removing excess water in the composite hydroxide particles.

(2) Mixing step The mixing step is represented by the general formula (A) described above, and [(d90-d10) / MV] is 0.65 or less, and the lithium compound is added to the transition metal composite hydroxide particles or heat-treated particles. It is a step of mixing to obtain a lithium mixture. In the mixing step, the ratio (Me) of the substance amount of metal atoms other than lithium in the lithium mixture, specifically, nickel, cobalt, manganese, and additive element M (Me) to the substance amount of lithium (Li) ( Li / Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, and even more preferably 1.0 to 1.2. It is necessary to mix the composite hydroxide particles or heat-treated particles and the lithium compound. That is, since Li / Me does not change before and after the firing step, the composite hydroxide particles or heat-treated particles and the lithium compound are mixed so that Li / Me in the mixing step becomes Li / Me of the target positive electrode active material. It is necessary to mix.

  The lithium compound used in the mixing step is not particularly limited, but it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate or a mixture thereof from the viewpoint of availability. In particular, lithium hydroxide or lithium carbonate is preferably used in consideration of ease of handling and quality stability. In the present embodiment, it is preferable that the transition metal composite hydroxide particles and the lithium compound are sufficiently mixed so that no fine powder is generated. Insufficient mixing is not preferable because Li / Me varies among individual particles, and sufficient battery characteristics may not be obtained. For mixing, for example, a general mixer such as a shaker mixer, a Laedige mixer, a Julia mixer, or a V blender can be used.

(3) Calcination step In the calcination step, the lithium mixture formed in the mixing step is calcined at 750 ° C to 900 ° C, preferably 750 ° C to 850 ° C in an oxidizing atmosphere. Thereby, lithium can be sufficiently diffused and reacted in the composite hydroxide particles or the heat-treated particles, and the secondary particles can be prevented from being sintered and aggregated in the firing step. That is, by calcining, the lithium compound is consumed by reaction with the composite hydroxide particles or the heat-treated particles, and the lithium compound remaining after calcining is greatly reduced. Further, in the firing step, it is necessary to keep the lithium transition metal composite oxide particles at a high temperature in order to increase the crystallinity of the lithium transition metal composite oxide particles. Aggregation proceeds rapidly.

  For this reason, in this embodiment, sintering aggregation of secondary particles can be suppressed by significantly reducing the lithium compound by calcination. Moreover, in this embodiment, since calcination is performed at a high temperature of 750 ° C. to 900 ° C., the TC (Total-Carbon) quality is lowered, so that aggregation in the subsequent firing step is suppressed. Become. The holding time at the above temperature in the calcination step is preferably 1 hour to 10 hours, and more preferably 3 hours to 6 hours. The atmosphere in the calcination step is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume, as in the baking step described later.

(4) Crushing step before firing The crushing step before firing crushes the lithium mixture calcined in the calcining step before the firing step. In this embodiment, since the calcining step is performed in an oxidizing atmosphere at a high temperature of 750 ° C. to 900 ° C., the lithium composite oxide particles obtained by the calcining step loosen coarse LiOH and the like sufficiently. In some cases, a portion having a high lithium concentration is likely to aggregate, and thus aggregation or mild sintering may occur. In such a case, if the baking is performed at a high temperature as it is, the sintering becomes strong, and the aggregated particles remain through the post-calcination crushing step performed after the baking step. For this reason, in this embodiment, the average particle diameter and particle size distribution of the positive electrode active material obtained by pulverizing the aggregate or sintered body of the lithium composite oxide particles after calcining generated in the calcining step It can be adjusted to a suitable range.

  As described above, in this embodiment, the lithium mixture calcined in the calcining process is crushed to suppress the sintering aggregation of the secondary particles constituting the positive electrode active material after the sintering process. In addition, the crushing mentioned here refers to agglomeration composed of a plurality of secondary particles generated by sintering necking between secondary particles during calcination, and mechanical energy is applied to the secondary particles themselves. It means an operation of separating the aggregates with little destruction and loosening the aggregates. Moreover, as a crushing method, a well-known means can be used, for example, a pin mill, a hammer mill, etc. can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

(5) Firing step In the firing step, the lithium mixture is calcined under predetermined conditions to increase the crystallinity of the composite hydroxide particles or particles that are diffused and reacted in the heat-treated particles, and the lithium transition metal composite This is a step of obtaining oxide particles. In this embodiment, the lithium mixture calcined in the calcining step is fired at 760 ° C. to 1050 ° C. in an oxidizing atmosphere at a temperature higher than the calcining temperature.

  The composite hydroxide particle is a secondary particle having a central part formed by agglomerating fine primary particles and having an outer peripheral part formed by aggregating plate-like primary particles outside the central part. In this case, in the firing step and the calcining step, the center portion and the high-density layer of the composite hydroxide particles and the heat-treated particles are sintered and contracted to form aggregated portions of primary particles in the positive electrode active material. On the other hand, since the low-density layer is composed of fine primary particles, the low-density layer starts to be sintered at a lower temperature than the center portion or the high-density layer composed of plate-like single particles larger than the fine primary particles. In addition, the low-density layer has a larger shrinkage than the central portion and the high-density layer.

  For this reason, the fine primary particles constituting the low-density layer shrink to the center part where the progress of the sintering is slow or to the high-density layer side, and a space part of an appropriate size is formed. At this time, the high-density part in the low-density layer shrinks and shrinks while maintaining the connection with the center part and the high-density layer. Therefore, in the obtained positive electrode active material, the outer shell part and the agglomerated part are electrically connected. And the cross-sectional area of the path can be sufficiently secured. As a result, the internal resistance of the positive electrode active material is greatly reduced, and when a secondary battery is configured, the output characteristics can be improved without deteriorating 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 particle as a precursor, but may be affected by its composition, firing conditions, and the like. It is preferable to appropriately adjust each condition so as to obtain a desired structure after conducting a preliminary test. The furnace used in the firing step is not particularly limited as long as it can heat the lithium mixture in the atmosphere or in an oxygen stream. However, from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace can be suitably used. This also applies to the furnace used in the heat treatment step and the calcining step.

  As described above, in the present embodiment, the firing temperature of the lithium mixture is higher than the calcining temperature and needs to be 760 ° C to 1050 ° C, preferably 790 ° C to 1000 ° C. When the firing temperature is less than 760 ° C., lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, and surplus lithium, unreacted composite hydroxide particles or heat-treated particles remain, or the resulting lithium composite This is not preferable because the crystallinity of the oxide particles becomes insufficient. On the other hand, if the firing temperature exceeds 1050 ° C., the lithium composite oxide particles are vigorously sintered, abnormal grain growth is caused, and the proportion of irregular coarse particles increases, which is not preferable.

  Moreover, it is preferable that the temperature increase rate in a baking process shall be 2 degree-C / min-10 degree-C / min, and it is more preferable to set it as 5 to 10 degree-C / min. Further, during the firing step, it is preferably maintained at a temperature near the melting point of the lithium compound for 1 hour to 5 hours, more preferably 2 hours to 5 hours. Thereby, the composite hydroxide particles or the heat-treated particles and the lithium compound can be reacted more uniformly.

  In the present embodiment, of the firing time in the firing step, the holding time at the firing temperature described above is preferably at least 2 hours, and more preferably 4 to 24 hours. When the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the composite hydroxide particles or heat-treated particles, and excess lithium, unreacted composite hydroxide particles or heat-treated particles remain or may be obtained. This is not preferable because the lithium composite oxide particles may have insufficient crystallinity.

  In the present embodiment, after the holding time, the cooling rate from the firing temperature to at least 200 ° C. is preferably 2 ° C./min to 10 ° C./min, and preferably 3 ° C./min to 7 ° C./min. It is more preferable. By controlling the cooling rate within such a range, it is possible to prevent equipment such as a mortar from being damaged by rapid cooling while securing productivity.

  In the present embodiment, the firing atmosphere in the firing step is preferably an oxidizing atmosphere, more preferably an oxygen concentration of 18% by volume to 100% by volume, and oxygen having the above oxygen concentration. It is particularly preferable to use an inert gas mixed atmosphere. That is, firing is preferably performed in the air or in an oxygen stream. An oxygen concentration of less than 18% by volume is not preferable because the crystallinity of the lithium composite oxide particles may be insufficient.

(6) Crushing step after firing The lithium composite oxide particles obtained by the firing step may be agglomerated or slightly sintered. In such a case, it is preferable to crush the aggregate or sintered body of the lithium composite oxide particles after firing. Thereby, the average particle diameter and particle size distribution of the positive electrode active material obtained can be adjusted to a suitable range. Crushing means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and the secondary particles themselves are hardly destroyed. It means an operation of separating and loosening the aggregates. Moreover, as a crushing method, a well-known means can be used, for example, a pin mill, a hammer mill, etc. 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. Lithium ion secondary battery Although the positive electrode active material for lithium ion secondary batteries which concerns on one Embodiment of this invention is not limited to the secondary battery to be used, For example, it can be used suitably for a lithium ion secondary battery. A lithium ion secondary battery is provided with the same structural members as a general lithium ion secondary battery, such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The embodiment described below is merely an example, and a lithium ion secondary battery using a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention as a positive electrode active material is described in this specification. It is also possible to apply to various modified and improved embodiments based on each embodiment.

(1) Constituent Member Using the positive electrode active material described above, for example, a positive electrode of a nonaqueous electrolyte secondary battery is produced as follows. First, a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is mixed with a conductive material and a binder, and activated carbon or a solvent such as viscosity adjustment is added as necessary. A positive electrode mixture paste is prepared by kneading. At that time, each mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the lithium ion secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass to 95 parts by mass, like the positive electrode of a general lithium ion secondary battery, The content of the conductive material can be 1 part by mass to 20 parts by mass, and the content of the binder can be 1 part by mass to 20 parts by mass.

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

  As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), and carbon black materials such as acetylene black and ketjen black can be used. The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin or polyacrylic. An acid can be used.

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

  On the other hand, metallic lithium, a lithium alloy, or the like can be used for the negative electrode. In addition, a negative electrode active material capable of occluding and desorbing lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste of the negative electrode mixture on the surface of a metal foil current collector such as copper. It is possible to use one that is dried and compressed to increase the electrode density as necessary. Examples of the negative electrode active material include lithium-containing materials such as metallic lithium and lithium alloys, natural compound capable of occluding and desorbing lithium ions, fired organic compounds such as artificial graphite and phenol resin, and carbon materials such as coke. A powdery body can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder as in the positive electrode, and an organic material such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing these active materials and the binder. A solvent can be used.

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

The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include 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, and tetrahydrofuran, 2-methyltetrahydrofuran. And one kind selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, or a mixture of two or more of them. it can. As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used. The non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  In this embodiment, it is also possible to configure a lithium ion secondary battery using a solid electrolyte instead of a non-aqueous electrolyte. When a solid electrolyte is used, the state of charge of the lithium ion secondary battery Safety and charge / discharge characteristics at a high rate are improved. That is, the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention can exhibit the above-described objects and effects of the present invention even for a lithium ion secondary battery using a solid electrolyte. Become.

(2) Lithium ion secondary battery The lithium ion secondary battery according to an embodiment of the present invention composed of the above positive electrode, negative electrode, separator, and non-aqueous electrolyte has various shapes such as a cylindrical shape and a laminated shape. can do. Whichever shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode terminal communicates with the positive electrode current collector and the outside And a negative electrode current collector and a negative electrode terminal communicating with the outside are connected by a current collecting lead or the like and 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 an embodiment of the present invention uses the positive electrode active material according to the embodiment of the present invention as the positive electrode active material. Excellent battery capacity, output characteristics and cycle characteristics. Moreover, it can be said that it is excellent in thermal stability and safety in comparison with a secondary battery using a positive electrode active material made of conventional lithium nickel composite oxide particles.

(4) Applications The lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention as the positive electrode active material is excellent in battery capacity, output characteristics, and cycle characteristics as described above. Therefore, the present invention can be suitably used as a power source for small portable electronic devices such as notebook personal computers and mobile phones, which require these characteristics at a high level. Further, the lithium ion secondary battery according to one embodiment of the present invention is excellent in safety, and not only can be downsized and increased in output, but also can simplify an expensive protection circuit. It can also be suitably used as a power source for transportation equipment that is restricted by the mounting space.

  As described above, when a secondary battery is configured by using the positive electrode active material for a lithium ion secondary battery as a positive electrode active material, the method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, a precursor When the mixture of lithium and lithium compound is fired, it is fired after calcining at a higher temperature than before, so that sintering aggregation of secondary particles constituting the positive electrode active material is suppressed. For this reason, since the output characteristics such as the battery capacity and the positive electrode resistance when used in the secondary battery can be further improved and improved, the cycle characteristics of the secondary battery are further improved. That is, by providing a positive electrode active material that can improve output characteristics such as battery capacity and positive electrode resistance, the output characteristics and cycle characteristics of a secondary battery using the positive electrode active material can be greatly improved. Has significant significance.

  Hereinafter, a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention and a method for producing the same will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to these Examples. It is not limited to. In the following Examples and Comparative Examples, Wako Pure Chemical Industries, Ltd. reagent grade samples were used for the production of composite hydroxide particles and a positive electrode active material, unless otherwise specified. Further, through the nucleation step and the particle growth step, the pH value of the reaction aqueous solution is measured by a pH controller (manufactured by Nisshin Rika, NPH-690D), and the supply amount of the sodium hydroxide aqueous solution is adjusted based on this measurement value. Thus, the fluctuation range of the pH value of the aqueous reaction solution in each step was controlled within a range of ± 0.2.

(Example 1)
[Production of composite hydroxide particles]
(Nucleation process)
First, the temperature inside the tank was set to 40 ° C. while stirring by adding half the amount of water into the reaction tank (34 L). The inside of the reaction tank at this time was an air atmosphere (oxygen concentration: 21% by volume). Appropriate amounts of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water are added to the water in the reaction tank, and the pH value of the reaction liquid in the tank is adjusted to 13.0 based on the liquid temperature of 25 ° C. did. Furthermore, the ammonia concentration in the reaction solution was adjusted to 10 g / L to obtain a pre-reaction aqueous solution. At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate are mixed with water so that the molar ratio of each metal element is Ni: Mn: Co: Zr = 33.1: 33.1: 33.1: 0.2. The raw material aqueous solution of 1.8 mol / L was prepared.

  Next, this mixed aqueous solution was added to the pre-reaction aqueous solution in the reaction vessel at a rate of 88 mL / min to obtain a reaction aqueous solution. At the same time, 25% by mass aqueous ammonia and 25% by mass aqueous sodium hydroxide solution are also added to this reaction aqueous solution at a constant rate, and the ammonia concentration in the reaction aqueous solution (nucleation aqueous solution) is maintained at the above value. While controlling the value to 13.0 (nucleation pH value), nucleation was performed by crystallization for 2 minutes and 30 seconds.

(Particle growth process)
After the nucleation is completed, the supply of all aqueous solutions is once stopped, and sulfuric acid is added to adjust the pH value to 11.6 based on the liquid temperature of 25 ° C. Formed. To the reaction aqueous solution (particle growth aqueous solution), the supply of the raw material aqueous solution and the 25% by mass sodium hydroxide aqueous solution is restarted, and the sodium tungstate aqueous solution is additionally supplied as the raw material aqueous solution. The value was maintained, the pH value was maintained at the above value, and crystallization was continued to perform particle growth. The concentration and flow rate of the aqueous solution of sodium tungstate were adjusted so as to match the composition. After the particle growth for 30 minutes, the liquid supply was temporarily stopped, and nitrogen gas was circulated at 5 L / min until the oxygen concentration in the reaction vessel space became a non-oxidizing atmosphere of 0.2% by volume or less. Thereafter, the supply of the raw material aqueous solution and the sodium tungstate aqueous solution was restarted, and the crystallization was carried out for 2 hours while maintaining the ammonia concentration and the pH value and starting the growth.

  When the reaction vessel became full, crystallization was stopped, and stirring was stopped and the mixture was allowed to stand to promote precipitation of the product. Then, after extracting half amount of the supernatant from the reaction tank, crystallization was resumed, and after crystallization for 2 hours (4 hours in total), crystallization was terminated. Then, 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 a point of 12.5% with respect to the entire particle growth process time from the start of the particle growth process. At this time, in the crystallization, the pH was controlled by adjusting the supply flow rate of the sodium hydroxide aqueous solution with 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 dissolved in an inorganic acid and then subjected to chemical analysis by ICP emission spectroscopy. The composition was Ni _0.331 Mn _0.331 Co _0.331 Zr _{0. 002} W _0.005 (OH) _{2 + a} (0 ≦ a ≦ 0.5). Moreover, about this composite hydroxide, the value [(d90-d10) / average particle diameter] which shows an average particle diameter and a particle size distribution was measured using the laser diffraction scattering type particle size distribution measuring apparatus (the Nikkiso Co., Ltd. Microtrac HRA). It was calculated from the volume integrated value measured in the above. As a result, the average particle size was 5.2 μm, and the [(d90−d10) / average particle size] value was 0.48.

  Next, SEM (manufactured by Hitachi High-Technologies Corporation, scanning electron microscope S-4700) observation (magnification: 1000 times) of the obtained composite hydroxide particles was performed. It was spherical and it was confirmed that the particle diameters were almost uniform. Moreover, when the sample of the obtained composite hydroxide particle was embedded in a resin and subjected to cross section polisher, an SEM observation result with a magnification of 10,000 times was performed. Is composed of secondary particles, and the secondary particles are larger than the fine primary particles on the outer side of the central part composed of needle-like and flaky fine primary particles (particle size approximately 0.3 μm). It was confirmed that it was composed of a plate-shaped primary particle (particle diameter: about 0.6 μm) and an outer peripheral portion. The thickness of the outer shell portion with respect to the secondary particle diameter obtained from the SEM observation result of this cross section was 12%.

[Production of positive electrode active material]
Lithium hydroxide was weighed and mixed with the composite hydroxide particles so that Li / Me = 1.12 to prepare a lithium mixture. Mixing was performed using a shaker mixer apparatus (manufactured by Willy et Bacofen (WAB), TURBULA Type T2C). The obtained lithium mixture was calcined at 780 ° C. for 4 hours in the air (oxygen: 21% by volume). The calcined lithium mixture was crushed, heated at 5 ° C./min, baked at 990 ° C. for 4 hours, cooled, and crushed to obtain a positive electrode active material.

[Analysis of cathode active material]
When the particle size distribution of the positive electrode active material obtained by the same method as that for the composite hydroxide particles was measured, the average particle size was 4.7 μm, and the [(d90−d10) / average particle size] value was 0. .48. Moreover, when SEM observation and 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 had a uniform particle size. Was confirmed. Furthermore, when observed at a magnification of 1000 using a scanning electron microscope, the proportion of aggregated particles in which 5 or more secondary particles aggregate is 0.32% or less of the number of secondary particles in the field of view. Aggregated particles obtained by aggregating 5 or more secondary particles were 3 / viewing field or less with respect to about 1000 secondary particles.

About the obtained positive electrode active material, the specific surface area is measured by a flow method gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb), and the tap density is respectively determined by a tapping machine (Kurachi Scientific Instruments, KRS-406) It was measured. As a result, it was confirmed that the specific surface area was 1.5 m ² / g and the tap density was 1.29 g / cm ³ . Moreover, when the obtained positive electrode active material was analyzed by powder X-ray diffraction using Cu-Kα rays using an X-ray diffractometer (manufactured by Panaltical, X'Pert PRO), the crystal structure of the positive electrode active material was It was confirmed to be composed of a hexagonal layered crystal lithium nickel manganese composite oxide single phase. Furthermore, this positive electrode active material is represented by the general formula: Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ by analysis using an ICP emission spectroscopic analyzer. It was confirmed that

[Manufacture of coin-type battery and evaluation of battery characteristics]
22.5 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 and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. The positive electrode 1 (electrode for evaluation) shown in FIG. The produced positive electrode 1 was dried at 120 ° C. for 12 hours in a vacuum dryer. Then, using this positive electrode 1, a 2032 type coin-type battery B was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.

  For the negative electrode 2, a negative electrode sheet in which graphite powder punched into a disk shape having a diameter of 14 mm and an average particle diameter of about 20 μm and polyvinylidene fluoride are applied to a copper foil is used, and 1 M LiPF 6 is used as a supporting electrolyte for the electrolyte. An equivalent mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. As the separator 3, a polyethylene porous film having a film thickness of 25 μm was used. The coin-type battery B has a gasket 4 and a wave washer 5, and the positive electrode can 6 and the negative electrode can 7 are assembled into a coin-shaped battery. The initial discharge capacity and positive electrode resistance showing the performance of the manufactured coin-type battery B were evaluated as follows.

The initial discharge capacity is left for about 24 hours after the coin-type battery 10 is manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The capacity when the battery was charged to 3 V, discharged after a pause of 1 hour to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

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

(Example 2)
In the particle growth process, except that the flow rate of the sodium tungstate aqueous solution is adjusted so that the concentration of tungsten in the non-oxidizing atmosphere is 20% with respect to the concentration of the additive element (tungsten) in the raw material aqueous solution in the oxidizing atmosphere. In the same manner as in Example 1, a positive electrode active material for a lithium ion secondary battery was obtained and evaluated. 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)
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 760 and the calcination temperature was 980 ° C.

(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 800 and the calcination temperature was 1000 ° C.

(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 840 and the firing temperature was 1020 ° C.

(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 calcining was not performed and the firing temperature was 980 ° C.

  Table 1 shows the characteristics of the composite hydroxides obtained in Examples 1 to 5 and Comparative Example 1 described above, and the characteristics of the positive electrode active material and each evaluation of the coin-type battery manufactured using this positive electrode active material. 2 respectively.

(Evaluation)
Since the composite hydroxide particles and the positive electrode active materials of Examples 1 to 5 were manufactured according to the method for manufacturing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, any positive electrode active material aggregated. It has a structure composed of an outer shell portion in which primary particles are sintered and a hollow portion inside thereof, and has a concentrated layer of additive elements on the surface of the primary particles. Further, [(d90−d10) / average particle diameter] values were all lower than those of Comparative Example 1, and the number and ratio of aggregated particles were also reduced. For this reason, coin-type batteries using these positive electrode active materials all have a higher initial discharge capacity and a lower positive electrode resistance than those of Comparative Example 1, and thus have excellent output characteristics. It was.

  Although the embodiments and examples of the present invention have been described in detail as described above, it will be understood by those skilled in the art that many modifications can be made without departing from the novel matters and effects of the present invention. It will be easy to understand. Therefore, all such modifications are included in the scope of the present invention.

  For example, a term described with a different term having a broader meaning or the same meaning at least once in the specification or the drawings can be replaced with the different term in any part of the specification or the drawings. 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 the embodiments and examples of the present invention, and various modifications can be made.

1 positive electrode (electrode for evaluation), 2 negative electrode, 3 separator, 4 gasket, 5 wave washer, 6 positive electrode can, 7 negative electrode can, 10 coin-type battery, S1 heat treatment process, S2 mixing process, S3 calcining process, S4 before firing Crushing step, S5 firing step, S6 crushing step after firing

Claims (8)

A method for producing a positive electrode active material for a lithium ion secondary battery comprising lithium transition metal composite oxide particles,
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, where M is one or more additive elements selected from Nb, Mo, Ta, Zr, and W) A mixing step of mixing a transition metal composite hydroxide particle having a [(d90−d10) / MV] of 0.65 or less and a lithium compound to form a lithium mixture;
A calcining step of calcining the lithium mixture formed in the mixing step at 750 ° C. to 900 ° C. in an oxidizing atmosphere;
A firing step of firing the lithium mixture calcined in the calcining step in an oxidizing atmosphere at a temperature higher than the calcining temperature and at 760 ° C. to 1050 ° C .;
The manufacturing method of the positive electrode active material for lithium ion secondary batteries which has this.   The manufacturing method of the positive electrode active material for lithium ion secondary batteries of Claim 1 which further has the crushing process of crushing the said lithium mixture calcined at the said calcining process before the said baking process.   In the mixing step, the lithium mixture is adjusted so that the ratio of the sum of the amount of metal other than lithium contained in the lithium mixture and the amount of lithium is 1: 0.95 to 1.5. The manufacturing method of the positive electrode active material for lithium ion secondary batteries of Claim 1 or 2.   4. The positive electrode active material for a 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. 5. Production method. A positive electrode active material for a lithium ion secondary battery comprising lithium transition metal composite oxide particles,
The 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 ≦ 0.80, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is one selected from Nb, Mo, Ta, Zr, and W The additive element), a hexagonal crystal structure having a layered structure, and secondary particles formed by aggregating a plurality of primary particles,
When observed with a scanning electron microscope, the proportion of aggregated particles in which 5 or more secondary particles aggregated is a lithium ion secondary that accounts for 0.7% or less of the number of secondary particles in the field of view. Positive electrode active material for batteries.   6. The positive electrode active material for a lithium ion secondary battery according to claim 5, wherein [(d90-d10) / MV], which is an index indicating the spread of the particle size distribution, is 0.52 or less.   The positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the secondary particles have an average particle size of 3 μm to 15 μm.   A positive electrode active material for a lithium ion secondary battery according to claim 5, comprising a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the positive electrode active material for the positive electrode is any one of claims 5 to 7. Lithium ion secondary battery.

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