JP5830178B2 - Method for producing positive electrode active material for lithium secondary battery and active material precursor powder used therefor - Google Patents

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery having a layered rock salt structure and an active material precursor powder used therefor.

  As a positive electrode active material in a lithium secondary battery (sometimes called a lithium ion secondary battery), a material using a lithium composite oxide (lithium transition metal oxide) having a layered rock salt structure is widely known. (For example, see Patent Document 1 (Japanese Patent Laid-Open No. 5-226004) and Patent Document 2 (Japanese Patent Laid-Open No. 2003-132877)).

In this type of positive electrode active material, the diffusion of lithium ions (Li ⁺ ) therein is performed in the in-plane direction of the (003) plane (that is, any direction in a plane parallel to the (003) plane). It is known that lithium ions enter and exit from crystal planes other than the (003) plane (for example, the (101) plane or the (104) plane).

  Therefore, in this type of positive electrode active material, the crystal plane (surface other than the (003) plane, for example, the (101) plane or the (104) plane) on which lithium ions can be satisfactorily entered and exited, is brought into contact with the electrolyte. Attempts have been made to improve the battery characteristics of lithium secondary batteries by exposing them (see, for example, Patent Document 3 (International Publication No. 2010/074304)).

  In addition, this type of positive electrode active material is known in which pores (also referred to as pores or voids) are formed inside (for example, Patent Document 4 (Japanese Patent Laid-Open No. 2002-75365)). 5 (Japanese Unexamined Patent Application Publication No. 2004-083388) and Patent Document 6 (Japanese Unexamined Patent Application Publication No. 2009-117241).

JP-A-5-226004 JP 2003-132877 A International Publication No. 2010/074304 JP 2002-75365 A JP 2004-083388 A JP 2009-117241 A

  As one of the methods for realizing the desired porosity and average pore diameter, it is conceivable to mix a pore-forming agent (void forming material) as an additive with respect to the raw material. As an example of such a pore-forming agent, a particulate or fibrous substance made of an organic synthetic resin, which is decomposed (mainly evaporated or carbonized) in a temporary firing step, can be considered. However, according to the knowledge of the present inventors, when the pore-forming agent is reduced in order to increase the volume energy density and the amount of voids is reduced, the voids are difficult to communicate with each other, and closed pores are formed. May not be able to enter the pores, which may reduce the output characteristics. Therefore, it is advantageous if a desired porosity and average pore diameter can be realized without using such a pore-forming agent.

  The present inventors now use a pore-forming agent by granulating and spheroidizing a substantially spherical secondary particle raw material powder to include voids (hereinafter sometimes referred to as “tertiary granulation”). Thus, it was found that a positive electrode active material having a desired porosity and a high open pore ratio can be produced, which provides high battery characteristics.

  Accordingly, an object of the present invention is to produce a positive electrode active material having a desired porosity and a high open pore ratio, which provides high battery characteristics without using a pore-forming agent.

According to one aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium ion battery,
Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga) Consisting of secondary particles in which a large number of primary particles having a composition represented by a metal element of a species or more are aggregated, and at least a part of the primary particles are arranged radially outward from the center of the secondary particles. Preparing a hydroxide raw material powder or an aggregate thereof;
Using the hydroxide raw material powder or pulverizing the aggregate to prepare a slurry containing the hydroxide raw material powder; and
Producing a substantially spherical granulated powder using the slurry;
Mixing the lithium compound with the granulated powder to obtain a lithium mixed powder;
Firing the lithium mixed powder to react the granulated powder with a lithium compound, thereby obtaining a positive active material for a lithium secondary battery having open pores;
A method comprising is provided.

According to another aspect of the present invention, a method for producing a positive electrode active material for a lithium ion battery, comprising:
Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga) Consisting of secondary particles in which a large number of primary particles having a composition represented by a metal element of a species or more are aggregated, and at least a part of the primary particles are arranged radially outward from the center of the secondary particles. Preparing a hydroxide raw material powder or an aggregate thereof;
Using the hydroxide raw material powder or pulverizing the aggregate to prepare a slurry containing the hydroxide raw material powder and lithium hydroxide;
Producing a substantially spherical granulated powder using the slurry;
Calcining the granulated powder to react the granulated powder with the lithium hydroxide, thereby obtaining a positive electrode active material for a lithium secondary battery having open pores;
A method comprising is provided.

According to still another aspect of the present invention, there is provided an active material precursor powder used for manufacturing a positive electrode active material for a lithium ion battery,
Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga) Consisting of secondary particles in which a large number of primary particles having a composition represented by a metal element of a species or more are aggregated, and at least a part of the primary particles are arranged radially outward from the center of the secondary particles. Hydroxide raw material powder,
A raw material having the same composition as the hydroxide raw material powder and a particle size smaller than that of the hydroxide raw material powder, in an amount of 0 to 25% by mass or less based on the total amount of the hydroxide raw material powder and the raw material fine particles Fine particles,
A water-soluble lithium compound interposed between the secondary particles and / or between the secondary particles and the raw material fine particles;
When the active material precursor powder is deagglomerated by ultrasonic irradiation in water, the proportion of particles having a particle size of 1.0 μm or less is 0 to 40% on a volume basis. And having a particle size distribution in which the proportion of particles having a particle size of 1.0 to 5.0 μm is 60 to 100%, and a volume of 10 to 40 μm when a positive electrode active material is obtained through lithium introduction by firing. An active material precursor powder having a reference D50 average particle size is provided.

It is a schematic diagram for demonstrating formation of the open pore in the method of this invention. 4 is a SEM image of a positive electrode active material produced in Example 2 under conditions within the scope of the present invention.

Definitions Listed below are definitions for some terms used in this specification.

  “Primary particles” refer to unit particles that do not contain crystal grain boundaries inside. On the other hand, those in which primary particles are aggregated and those in which a plurality (large number) of single-crystal primary particles are aggregated are referred to as “secondary particles”. The term “tertiary particles” is sometimes used in the present specification, but this is a term used for convenience to express particles of agglomerated powder in which a large number of secondary particles are aggregated. The above is included in the category of “secondary particles”. The “average particle diameter” is an average value of particle diameters. The “diameter” is typically a diameter of the sphere when the particle is assumed to be a sphere having the same volume or the same cross-sectional area. The “average value” is preferably calculated on the basis of the number. The average particle diameter of the primary particles can be determined, for example, by observing the surface or cross section of the secondary particles with a scanning electron microscope (SEM). The average particle diameter of the secondary particles is a volume-based D50 average particle measured using water as a dispersion medium using a laser diffraction / scattering particle size distribution measuring device (for example, model number “MT3000-II” manufactured by Nikkiso Co., Ltd.). It is evaluated by the diameter (median diameter).

  “Voidage” is the volume ratio of voids (including pores: including open pores and closed pores) in the positive electrode active material of the present invention. “Porosity” is sometimes referred to as “porosity”. This “porosity” is calculated from, for example, the bulk density and the true density. “Open pores” are pores communicating with the outside among the pores. “Closed pores” are pores which are not communicated with the outside among the pores.

  The “open pore ratio” is a ratio of open pores communicating with outside air in all pores in the secondary particles. That is, the open pore ratio is (area of open pore portion) / (area of open pore portion + area of closed pore portion). Since the open pores communicate with the outside, the resin can be injected from the outside, and the closed pores do not communicate with the outside, so the resin cannot be injected from the outside. Therefore, the open pore ratio is determined by performing resin filling in which a resin is injected into the gap (and thus in the open pore) while sufficiently removing the air present in the open pore using a vacuum impregnation device. The impregnated portion is treated as an open pore, the portion of the void not impregnated with resin is treated as a closed pore, and these areas are obtained from, for example, image processing of a SEM photograph of the cross-section of the secondary particle, , (Area of open pore portion) / (area of open pore portion + area of closed pore portion).

  “Average open pore diameter” means the average pore diameter of the open pores, and is the average value of the diameters of the open pores in the secondary particles. This “diameter” is typically the diameter of the spherical shape when the open pores are assumed to be spherical with the same volume or the same cross-sectional area. The “average value” is preferably calculated on a volume basis. Further, the average open pore diameter can be determined by a known method such as image processing of an SEM photograph of the cross section of the secondary particle or mercury intrusion method.

  “Tap density” is the increased bulk density obtained after mechanically tapping a container containing a powder sample. The tap density is obtained by mechanically tapping a measuring graduated cylinder or container containing a powder sample. The tap density is measured by measuring the initial volume or mass of the powder and then mechanically tapping the measuring graduated cylinder or container and reading the volume or mass until almost no change in volume or mass is observed. .

  The “press density” is a bulk density obtained when a powder sample is tableted with a constant press pressure in a mold or the like.

TECHNICAL FIELD The present invention of the positive electrode active material for a lithium secondary battery, a method for producing a cathode active material for a lithium secondary battery having a layered rock salt structure. “Layered rock salt structure” means a crystal structure in which lithium layers and transition metal layers other than lithium are alternately stacked with oxygen layers in between (typically α-NaFeO ₂ type structure: cubic rock salt type structure) [111] A structure in which transition metals and lithium are regularly arranged in the axial direction. The method of the present invention produces a hydroxide raw material powder comprising substantially spherical secondary particles in which a large number of primary particles are aggregated, wherein at least a part of the primary particles are arranged outward from the center of the secondary particles. The slurry containing the hydroxide raw material powder is used to produce a substantially spherical granulated powder containing voids, which is mixed with a lithium compound and then subjected to firing to cause the granulated powder to react with the lithium compound. Comprising. Thus, in the method of the present invention, the substantially spherical secondary particle raw material of the raw material powder is granulated and spheroidized (tertiary granulated) so as to include voids, without using a pore forming agent. Thus, a positive electrode active material having a desired porosity and a high open pore ratio can be produced, which provides high battery characteristics.

  That is, in the method of the present invention, first, an aqueous metal element solution, an aqueous caustic solution, and an ammonium ion supplier are continuously supplied into a tank adjusted in pH and temperature while controlling the concentration and flow rate. Thus, a hydroxide raw material powder composed of substantially spherical secondary particles in which a large number of primary particles are aggregated and in which at least a part of the primary particles are arranged outward from the center of the secondary particles is produced. Next, as schematically shown in FIG. 1, a slurry containing raw material secondary particles is prepared and dried by spray drying or the like to obtain a substantially spherical granulated powder. The granulated powder thus obtained can be expressed as a tertiary particle powder in that many secondary particles are aggregated. In such a granulated powder, a large number of gaps are formed between the particles of the raw material secondary particle powder constituting the granulated powder due to the substantially spherical shape of the raw material powder. When such a granulated powder is fired, a large number of gaps provide a large number of voids that are easily communicated with the outside of the positive electrode active material as a fired body, and open pores are easily formed even when the amount of voids is reduced. As described above, a method of forming voids by utilizing melting or vaporization of the pore-forming agent during firing or calcination by incorporating a pore-forming agent is also conceivable, but in that case, it is necessary to increase the volume energy density. If the amount of voids is reduced by reducing the amount of the pore agent, there is a problem in that the voids are difficult to communicate with each other and closed pores are formed, so that the output characteristics are deteriorated because the electrolyte and the conductive additive cannot enter the pores. Further, although pores can be formed by adjusting the firing temperature or the like, there is a problem that closed pores are formed in a region where the amount of voids is small. Even if the pores are not closed, the open pores are not through-holes (there is only one entrance / exit to the surface), and it is difficult for the gas in the pores to escape when the electrolyte is injected. There was also a problem that it was difficult to penetrate. When the open pores are desired to be through-holes, the pores derived from the pore-forming agent are three-dimensionally formed by suppressing densification during firing and forming fine pores (for example, 0.1 μm or less) between the primary particles. Although a method of connection is conceivable, there is a problem that the volume energy density is lowered and a problem that the grain boundary resistance is increased and the resistance of electron conduction and lithium ion diffusion is also increased. Such a problem is effectively eliminated or reduced by the method of the present invention.

  Hereafter, each process in the method of this invention is demonstrated concretely.

(1) Production of hydroxide raw material powder In the method of the present invention, Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is Co, Al, Mg, Mn, Ti , Fe, Cr, Zn, and Ga, at least one metal element selected from the group consisting of secondary particles in which a large number of primary particles are aggregated, and at least part of the primary particles are secondary. A hydroxide raw material powder or an aggregate thereof is prepared, which is arranged radially outward from the center of the particle. Preferably, 0.15 ≦ y ≦ 0.4, and the preferred metal element M is at least one or two metal elements selected from the group consisting of Co, Al, Mg and Mn, more preferably Al. , Mg and Mn and at least one selected from the group consisting of Co and Co, and particularly preferred combinations of metal elements M are Co and Al, or Co and Mn.

  However, among these metal elements M, a predetermined element such as Al may not be included or made insufficient in the hydroxide raw material powder, and may be added in an arbitrary subsequent step. In this case, it is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn and Ga and is not included in the hydroxide raw material powder or hydroxide raw material powder It is preferable to add a compound (for example, an oxide, a hydroxide and a hydrate thereof) containing an element deficient in the slurry and / or the granulated powder in a subsequent slurrying step and / or a lithium mixing step. In this respect, the slurrying step is more preferable because the additive element compound can be easily mixed. Thus, as long as a positive electrode active material having a desired composition is finally obtained, a part of the metal element M may be added at any stage. In particular, it is preferable that a part of the metal element M added in any subsequent step is not a main additive element (for example, Co or Mn) but a small amount of additive element (for example, an element other than Co and Mn). This is because, when producing a hydroxide raw material powder that is a composite hydroxide, control of the particle shape and composition becomes easier when the number of types of elements is smaller. That is, at the time of preparing the hydroxide raw material powder, the type of the metal element M is reduced to only the main additive element (for example, Co or Mn) to facilitate the control of the particle shape and composition, while the hydroxide raw material powder is prepared. By adding a trace amount of an additive element (for example, an element other than Co and Mn) that is difficult to control in the solution process, a desired positive electrode active material composition can be obtained more accurately.

  The hydroxide raw material powder preferably has a tap density of 1.40 g / cc or more, more preferably 1.5 g / cc or more, and still more preferably 1.6 g / cc or more. The higher the tap density, the larger the difference in density between the voids and the particles in the tertiary particle powder described later, so that a high open pore ratio can be achieved even with a small porosity, but at 1.9 g / cc or less. It is realistic. The hydroxide raw material powder preferably has a volume-based D50 average particle size of 1 to 5 μm as the secondary particle size, more preferably 2 to 4 μm, and even more preferably 2 to 3 μm. When the particle size is about this level, a large number of gaps of an appropriate size are formed in the tertiary powder, which is advantageous for achieving a high open pore ratio even with a small porosity. The powder having a secondary particle size in the above range is composed of secondary particles having a volume-based D50 average particle size of 5 μm or more in which many primary particles are aggregated, and at least a part of the primary particles is outward from the center of the secondary particles. It is also possible to use a lightly pulverized hydroxide raw material powder arranged radially toward the surface. Alternatively, agglomerates of the hydroxide raw material powder having the radial orientation described above may be used, and such agglomerates preferably have a volume-based D50 average particle diameter of 5 to 30 μm, more preferably 10 to 20 μm. It is.

  Such hydroxide raw material powder can be produced according to a known technique (for example, see Patent Documents 3 and 4). For example, a method in which a nickel salt aqueous solution, a metal element M-containing aqueous solution, a caustic alkaline aqueous solution, and an ammonium ion supplier are continuously supplied and controlled while controlling the concentration and flow rate in a tank adjusted in pH and temperature. Is mentioned. At this time, in order to satisfy the tap density and the D50 average particle diameter, it is preferable that the pH in the tank is 10.0 to 12.0 and the temperature is 40 to 70 ° C.

(2) Slurry process A slurry is formed using the said hydroxide raw material powder or aggregate. This slurry can be prepared, for example, by mixing a hydroxide raw material powder (substantially spherical secondary particles) with a dispersion medium such as water, and agglomeration of the hydroxide raw material powder having the radial orientation described above. In the case of using a product, it is preferable to use the product in the slurry preparation after crushing the agglomerate and desirably forming the above-mentioned hydroxide raw material powder having the radial orientation. Furthermore, for the purpose of controlling the porosity and the void diameter, raw material fine particles having a diameter smaller than that of the raw material powder may be mixed with the raw material powder. The raw material fine particles preferably have the same composition as the hydroxide raw material powder, and may be obtained by pulverizing the hydroxide raw material powder, or prepared separately from the hydroxide raw material powder. It may be. The raw material fine particles may have a radial orientation similar to that of the hydroxide raw material powder, but may not have an orientation. For the raw material fine particles, the porosity and the void diameter can be appropriately changed by controlling the particle size ratio and the mixing ratio of the raw material powder and the raw material fine particles in the slurry. In addition, since the raw material fine particles have high cohesion, the granulated powder can be made difficult to break. The volume-based D50 average particle diameter of the raw material fine particles is preferably 10 nm to 700 nm, and more preferably 50 nm to 500 nm. The ratio of the raw material fine particles to the total amount of the raw material powder and the raw material fine particles is preferably 25% by mass or less, more preferably 20% by mass or less. In addition, a binder or a dispersant may or may not be added.

  A preferred slurry is an aqueous slurry containing water as a dispersion medium. In this case, it is more preferable to further include a water-soluble lithium compound in the aqueous slurry to form an aqueous lithium compound solution. The water-soluble lithium compound not only functions as a lithium source, but can also function as a binder for binding secondary particles of the hydroxide raw material powder to form tertiary particles in the subsequent granulation step. Therefore, the use of a water-soluble lithium compound in an aqueous slurry makes it easy to stably obtain a granulated powder having a desired particle size, and it is possible to eliminate the need for a subsequent lithium mixing step if necessary. . In addition, since the use of an organic binder can be eliminated, a degreasing process for eliminating the organic binder can be eliminated. Preferable examples of the water-soluble lithium compound include lithium hydroxide, lithium nitrate, lithium chloride, lithium oxide, and lithium peroxide. More preferably, the binder effect is high, the reactivity is high, and lithium can be easily introduced. In terms of lithium hydroxide.

The aqueous slurry preferably contains a water-soluble lithium compound in a molar ratio of Li / (Ni + M) of 0.01 to 0.20, more preferably 0.02 to 0.15, and even more preferably. Is 0.04 to 0.10. When the molar ratio is in this range, the capacity increases in battery characteristics. The reason is not necessarily clear, but it is presumed that the reactivity with the water-soluble lithium compound added in the above range is improved. That is, when the Li / (Ni + M) ratio is 0.01 or more, lithium is also present in the granulated powder in advance, so that lithium can be sufficiently supplied to the reaction at the time of firing, whereby the active material It is considered that it is difficult to form a lithium-deficient region inside. That is, when there is no lithium in the granulated powder, it is necessary to diffuse lithium over a relatively long distance from the outside of the granulated powder to the central portion in order to sufficiently react the central portion of the granulated powder with lithium. However, if lithium is pre-existing in the granulated powder, it can reach the center with a relatively short diffusion distance, so that it can sufficiently react with lithium even in the vicinity of the center where an insufficiently reactive region is likely to occur. be able to. Further, if the Li / (Ni + M) ratio is 0.10% or less, a gas that is generated during the reaction of the water-soluble lithium compound and can stay in the granulated powder (in the case of lithium hydroxide, water vapor is It is considered that the amount of generation) is reduced to suppress the relative decrease in the concentration of oxygen necessary for the reaction, thereby making it difficult to form a region deficient in oxygen.
<Example of reaction between lithium hydroxide and hydroxide raw material powder>
(NiCoAl) (OH) ₂ + LiOH.H ₂ O + 1 / 4O ₂
→ Li (NiCoAl) O ₂ + 5 / 2H ₂ O

  Further, as described above, it is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga, and is not included in the hydroxide raw material powder or hydroxylated. A compound of an element lacking in the raw material powder may be added to the slurry.

(3) Drying / granulating (tertiary granulation) step By drying and granulating the slurry by spray drying or the like, a substantially spherical granulated powder containing voids can be obtained as a tertiary granulated powder. The particle size of the granulated powder is a direct factor that determines the average particle size of the positive electrode active material particles, and is appropriately set according to the intended use of the particles. Tap density, press density, electrode film thickness In view of the above, the volume-based D50 average particle diameter is generally 5 to 40 μm, preferably 7 to 40 μm. The drying / granulation method is not particularly limited as long as the raw material powder is filled and formed into a substantially spherical shape.

  The atmosphere at the time of drying is not particularly limited, and may be an air atmosphere or an inert gas atmosphere. However, when a water-soluble lithium compound is used in the slurrying step described above, nitrogen, argon, etc. It is preferable to use an inert gas atmosphere. This is because it is liable to react with lithium compounds in the firing step (lithium introduction step), because lithium carbonate, which is inferior in reactivity due to carbon dioxide in the air, can be precipitated when spray drying is performed in the air. This is because it may take time. In addition, at the time of drying, the added water-soluble lithium compound may precipitate between secondary particles constituting the granulated powder and function as a binder.

  The granulated powder as the tertiary powder obtained in this manner is an active material precursor powder, and may be directly subjected to the subsequent lithium mixing step (can be omitted in some cases) and the firing step (lithium introduction step). Alternatively, it may be traded as an active material precursor powder or as a mixed powder with a lithium compound under the premise that the subsequent process is performed by the purchaser.

(4) Lithium mixing step The granulated powder is mixed with a lithium compound to form a lithium mixed powder. As the lithium compound, any lithium-containing compound that can finally give the composition LiMO _{2 of the} positive electrode active material can be used, and preferable examples include lithium hydroxide and lithium carbonate. Prior to the reaction, the pulverized powder is preferably mixed with the lithium compound by a method such as dry mixing or wet mixing. The average particle size of the lithium compound is not particularly limited, but is preferably 0.1 to 5 μm from the viewpoint of ease of handling and reactivity from the viewpoint of hygroscopicity. In order to increase the reactivity, the lithium amount may be excessive by about 0.5 to 40 mol%. In addition, it may be calcined before the lithium mixing step or may not be calcined. By calcining, a thermal decomposition component such as a hydroxide group contained in the precursor can be removed, and the reactivity with lithium can be increased in the subsequent firing step. The calcining temperature is preferably 400 ° C to 1000 ° C. When the temperature is 400 ° C. or higher, a sufficient thermal decomposition effect can be obtained. On the other hand, when the temperature is 1000 ° C. or lower, rapid progress of grain growth can be suppressed and a decrease in reactivity with lithium in the firing step can be avoided. The calcination atmosphere is not particularly limited, and may be an air atmosphere or an oxygen atmosphere.

  Further, as described above, it is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga, and is not included in the hydroxide raw material powder or hydroxylated. A compound of an element lacking in the raw material powder may be added to the granulated powder.

  In addition, when the above-mentioned water-soluble lithium compound is used as a binder, it is possible to make the lithium mixing step unnecessary. In this case, all the required amount of water-soluble lithium compound may be added to the aqueous slurry in the slurrying step. However, a necessary amount of a part of the water-soluble lithium compound may be added to the aqueous slurry, and the remaining insufficient amount of the water-soluble lithium compound may be compensated in the lithium mixing step.

(5) Firing step (introducing lithium)
The lithium mixed powder is fired to react the granulated powder with a lithium compound, thereby obtaining a positive electrode active material for a lithium secondary battery having open pores. At this time, lithium is introduce | transduced into positive electrode active material precursor particle | grains by baking the above-mentioned mixture before baking by a suitable method, and, thereby, positive electrode active material particle | grains are obtained. For example, firing can be performed by putting a sheath containing the mixture before firing into a furnace. By this firing, the synthesis of the positive electrode active material, the sintering of the particles, and the grain growth are performed, and at the same time, open pores due to the gaps between the substantially spherical raw material powder secondary particles are formed.

  The firing temperature is preferably 600 ° C. to 1100 ° C. When the temperature is within this range, grain growth is sufficient, and the desired composition can be easily realized by suppressing decomposition of the positive electrode active material and volatilization of lithium. The firing time is preferably 1 to 50 hours, and if it is within this range, excessive increase in energy consumed for firing can be prevented.

  In addition, for the purpose of increasing the reactivity between the lithium and the precursor mixed in the temperature raising process, the temperature may be maintained for 1 to 20 hours at a temperature lower than the firing temperature (for example, 400 to 600 ° C.). Since lithium is melted through the temperature holding step, the reactivity can be increased. In addition, the same effect is acquired also by adjusting the temperature increase rate of a certain temperature range (for example, 400-600 degreeC) in this baking (lithium introduction | transduction) process.

  The firing atmosphere must be set as appropriate so that decomposition does not proceed during firing. When the volatilization of lithium proceeds, it is preferable to arrange lithium carbonate or the like in the same sheath to create a lithium atmosphere. When oxygen release or further reduction proceeds during firing, firing is preferably performed in an atmosphere having a high oxygen partial pressure. In addition, after firing, crushing and classification may be appropriately performed for the purpose of releasing adhesion and aggregation between the positive electrode active material particles or adjusting the average particle diameter of the positive electrode active material particles.

  In addition, post-heat treatment may be performed at 100 to 400 ° C. in the positive electrode material active material after firing or after being crushed or classified. By performing such a post heat treatment step, the surface layer of the primary particles can be modified, thereby improving the rate characteristics and output characteristics. In addition, the positive electrode active material may be subjected to a water washing treatment after firing or after being crushed or classified. By performing this water washing treatment step, the unreacted lithium raw material remaining on the surface of the positive electrode active material powder or the lithium carbonate produced by the adsorption of moisture and carbon dioxide in the atmosphere on the surface of the positive electrode active material powder is removed. Thereby, the high-temperature storage characteristics (especially gas generation suppression) are improved.

Positive electrode active material for lithium secondary battery According to the production method of the present invention described above, a positive electrode active material for a lithium secondary battery having a layered rock salt structure having voids with a high open pore ratio that provides high battery characteristics can be obtained. . Typically, in the positive electrode active material obtained by the present invention, secondary particles composed of a large number of primary particles form tertiary particles having a porosity of 1 to 30% and an open pore ratio of 50% or more. . By making the porosity within this range, the effect of improving the charge / discharge characteristics can be obtained without impairing the capacity. The open pore ratio in the positive electrode active material particles is preferably 50% or more, more preferably 60% or more, still more preferably 70%, particularly preferably 80% or more, and most preferably 90% or more. It is. Thus, since an open pore ratio is so high that it is preferable, an upper limit is not set in particular. By increasing the open pore ratio with a porosity in such a range, the electrolyte solution easily penetrates into the tertiary particles through the open pores, so that the ion conductivity is improved and at the same time, there are many portions other than the open pores. Due to the dense bonding between the primary particles, a sufficiently large number of bonding portions between the primary particles serving as electron conduction paths can be secured, and the decrease in electron conductivity associated with void formation can be suppressed. As a result, it is considered that both the electron conductivity and the ionic conductivity which are originally in a trade-off relationship can be achieved, and an improved rate characteristic can be obtained.

As the lithium composite oxide having a layered rock salt structure constituting the positive electrode active material of the present invention, lithium cobaltate (LiCoO ₂ ) can be typically used. However, it is also possible to use a solid solution containing nickel or manganese in addition to cobalt as the lithium composite oxide constituting the positive electrode active material of the present invention. Specifically, as the lithium composite oxide constituting the positive electrode active material of the present invention, the following composition formula:
_{Li x Ni 1-z M z} O 2
(Wherein 0.96 ≦ x ≦ 1.09, 0 <z ≦ 0.5) (where 0 <y ≦ 0.5, M is Co, Al, Mg, Mn, Ti, Fe, Cr, Those represented by at least one metal element selected from the group consisting of Zn and Ga are preferably usable. A preferable value of x is 0.98 to 1.06, and more preferably 1.00 to 1.04. A preferable value of z is 0.15 to 0.4, and more preferably 0.15 to 0.25. Preferred metal element M is at least one or two metal elements selected from the group consisting of Co, Al, Mg and Mn, more preferably at least one selected from the group consisting of Al, Mg and Mn. A particularly preferred combination of metal elements M containing Co is Co and Al, or Co and Mn.

  Furthermore, the surface of the positive electrode active material (including the pore inner wall) contains a compound containing a metal element not included in the active material, for example, a transition metal that can take an expensive number such as W, Mo, Nb, Ta, Re, etc. May be present. Such a compound may be a compound of a transition metal capable of taking an expensive number such as W, Mo, Nb, Ta, and Re and Li. The compound containing a metal element may be dissolved in the positive electrode active material or may exist as the second phase. By doing so, it is considered that the interface between the positive electrode active material and the non-aqueous electrolyte is modified, the charge transfer reaction is promoted, and the output characteristics and rate characteristics are improved.

  In consideration of the promotion of grain growth or the volatilization of lithium during firing, a large amount of lithium compound may be added to the raw material powder so that the lithium is in an excess of 0.1 to 40 mol%. For the purpose of promoting grain growth, low melting point oxide (bismuth oxide, vanadium oxide, etc.), low melting point glass (borosilicate glass, etc.), lithium fluoride lithium chloride, boron oxide, etc. are used as the raw material powder. -30 mass% may be added.

  The positive electrode active material according to a preferred embodiment of the present invention is a secondary particle comprising a large number of primary particles (preferably a single crystal primary particle of a lithium composite oxide having a layered rock salt structure) having an average primary particle size of 0.01 to 5 μm. Form tertiary particles, and the tertiary particles have a volume-based D50 average particle size of 1 to 100 μm, a porosity of 1 to 30%, an open pore ratio of 50% or more, and an average open pore size of 0.1 to 5 μm. And the value obtained by dividing the average particle diameter of the primary particles by the average open pore diameter is 0.1 to 5. In the positive electrode active material having such a configuration, a large number of primary particles exist around the pores in the tertiary particles, and the direction of electron conduction and lithium ion diffusion between the adjacent primary particles (particularly the direction of electron conduction). Is well aligned. For this reason, the path | route (especially path | route of electronic conduction) of the electronic conduction and lithium ion diffusion in a tertiary particle is ensured favorable. Therefore, according to the present invention, it is possible to further improve the battery characteristics as compared with the prior art. In particular, it is possible to improve the discharge voltage at high rate (hereinafter simply referred to as “output characteristics”) and the discharge capacity at high rate (hereinafter simply referred to as “rate characteristics”).

  The value of “average primary particle diameter / average open pore diameter” is preferably 0.1 or more and 5 or less, more preferably 0.2 or more and 3 or less, and further preferably 0.3 or more and 1 or less, as described above. In addition, the lithium ion conductivity and the electron conductivity in the tertiary particles are maximized. That is, when the value of “average primary particle diameter / average open pore diameter” is 0.1 or more, excessive increase in grain boundary resistance due to excessive number of primary particles present around the pores is prevented. Thus, it is possible to prevent the output characteristics and rate characteristics from being deteriorated. Further, when the value of “average primary particle diameter / average open pore diameter” is 5 or less, the number of contact points between the primary particles existing around the pores is increased, and electron conduction and lithium ion diffusion paths (especially electrons) Sufficient conduction path) can be secured to prevent degradation of output characteristics.

  The positive electrode active material particles have a large number of pores, preferably open pores. That is, in the positive electrode active material particles, the porosity is 1% or more and 30% or less, and the average open pore diameter is 0.1 μm or more and 5 μm or less. Furthermore, in this positive electrode active material particle, the value obtained by dividing the average particle size of the single crystal primary particles by the average open pore size is 0.1 or more and 5 or less.

  In the positive electrode active material particles of the present embodiment, a large number of single crystal primary particles exist around the pores (to the extent that the grain boundary resistance does not become too large), and electron conduction occurs between a plurality of adjacent single crystal primary particles. In addition, it is preferable that the direction of lithium ion diffusion is well aligned. Thereby, the path | route of electronic conduction and lithium ion diffusion is ensured favorably. Therefore, the resistance of electron conduction and lithium ion diffusion between single crystal primary particles is reduced, and lithium ion conductivity and electron conductivity are improved. Therefore, according to the positive electrode active material particles of this embodiment, the charge / discharge characteristics (particularly rate characteristics and output characteristics) of the lithium secondary battery can be significantly improved.

  Further, the secondary particles constituting the positive electrode active material particles (tertiary particles) are derived from the used hydroxide raw material, and the (003) plane where electron conduction and lithium ion diffusion are performed is outside the center of the secondary particles. They are lined up towards. For this reason, the exposure of the lithium ion entrance / exit surface and the electron conduction surface on the inner surface formed by the outer surface and open pores that are in contact with the electrolytic solution is increased, and the electron conduction in the secondary particles and the resistance of lithium ion diffusion are also increased. Can be reduced. In particular, since the secondary particles are typically substantially spherical, the radial orientation is likely to be aligned in substantially the same direction at the contact point between adjacent secondary particles, and the direction of electron conduction and lithium ion diffusion (especially the direction of electron conduction) is accordingly increased. It is easy to arrange well between secondary particles. From this point of view, it can be said that it is easy to ensure the path of electron conduction and lithium ion diffusion (particularly the path of electron conduction) in the tertiary particles.

  The average particle size of the single crystal primary particles is preferably from 0.01 μm to 5 μm, more preferably from 0.01 μm to 3 μm, and still more preferably from 0.01 μm to 1.5 μm. By setting the average particle diameter of the single crystal primary particles within the above range, the crystallinity of the single crystal primary particles is ensured. In this respect, if the average particle size of the single crystal primary particles is less than 0.1 μm, the crystallinity of the single crystal primary particles may be reduced, and the output characteristics and rate characteristics of the lithium secondary battery may be reduced. However, in the positive electrode active material particles of this embodiment, even if the average particle diameter of the single crystal primary particles is 0.1 to 0.01 μm, no significant reduction in output characteristics or rate characteristics is observed.

  The average particle diameter (volume-based D50 average particle diameter) of the positive electrode active material particles as the tertiary particles is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 70 μm or less, and further preferably 3 μm or more and 50 μm or less. Particularly preferably 5 μm to 40 μm, and most preferably 10 μm to 20 μm. By setting the average particle diameter of the positive electrode active material particles within this range, the filling property of the positive electrode active material in the positive electrode active material particles is ensured (the filling rate is improved). In addition, a flat electrode surface can be formed while maintaining the output characteristics and rate characteristics of the lithium secondary battery. On the other hand, when the average particle diameter of the positive electrode active material particles is within the above range, the filling rate of the positive electrode active material can be increased, and the output characteristics and rate characteristics of the lithium secondary battery are deteriorated and the flatness of the electrode surface is increased. Can be prevented. The distribution of the average particle diameter of the positive electrode active material particles may be sharp, broad, or have a plurality of peaks. For example, when the average particle size distribution of the positive electrode active material particles is not sharp, the packing density of the positive electrode active material in the positive electrode active material layer is increased, or the adhesion between the positive electrode active material layer and the positive electrode current collector is increased. can do. Thereby, charge / discharge characteristics can be further improved. In particular, when a slurry containing a water-soluble lithium compound is used as a binder and lithium source, it becomes easy to stably obtain a positive electrode active material having an average particle size within the above range (particularly 5 μm to 40 μm).

  The porosity (volume ratio of pores) in the positive electrode active material particles is preferably 1% or more and 30% or less. By making the porosity within this range, the effect of improving the charge / discharge characteristics can be obtained without impairing the capacity. In particular, according to the method of the present invention, there is an advantage that a high open pore ratio can be realized even with a low porosity (for example, 10% or less). The open pore ratio in the positive electrode active material particles is preferably 50% or more, more preferably 60% or more, still more preferably 70% or more, particularly preferably 80% or more, and most preferably 90%. That's it. The average open pore diameter in the positive electrode active material particles (average diameter of open pores in the positive electrode active material particles) is preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm or more and 3 μm or less. Is 0.4 μm or more and 3 μm or less. Within such a range, generation of relatively large pores can be prevented, and a sufficient amount per volume of the positive electrode active material contributing to charge / discharge can be secured. Further, it is possible to prevent the stress concentration from occurring locally in such large pores and to release the stress uniformly inside. Furthermore, it becomes easy to contain a conductive material and an electrolyte, and the stress releasing effect by the pores can be made sufficient. For this reason, the effect of improving the charge / discharge characteristics while maintaining a high capacity can be expected.

  The positive electrode active material preferably has a tap density of 2.5 to 3.1 g / cc, more preferably 2.6 to 3.0 g / cc. A tap density in such a range means that the positive electrode active material has a high density, and thus a positive electrode active material having a high volumetric energy density is brought about.

The positive electrode active material preferably has a press density of 3.0 to 3.5 g / cc, more preferably 3.2 to 3.4 g / cc when uniaxially pressed at a pressure of 1.0 kgf / cm ^2. It is. A press density in such a range means that a high density is obtained when the electrode is formed, resulting in a positive electrode active material having a high volumetric energy density. This press density is obtained by weighing 1.5 g of the positive electrode active material on a cylindrical die having a diameter of 20 mm, uniaxially pressing with a load of 1.0 kgf / cm ² , and then (powder weight) / (bulk volume of pressed powder). It can be determined by calculating.

Active Material Precursor Powder According to one embodiment of the present invention, there is provided an active material precursor powder that is used in the production of a positive electrode active material for a lithium ion battery. This active material precursor powder is a powder comprising the hydroxide raw material powder, the water-soluble lithium compound, and optionally aggregated particles containing the raw material fine particles as described above with respect to the production method. That is, the hydroxide raw material powder is Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga). At least one metal element selected from the group consisting of secondary particles in which a large number of primary particles are aggregated, and at least part of the primary particles are directed outward from the center of the secondary particles. Are arranged in a radial pattern. The raw material fine particles have the same composition as the hydroxide raw material powder and a particle size smaller than the hydroxide raw material powder in an amount of 0 to 25% by mass or less with respect to the total amount of the hydroxide raw material powder and fine particles. It is an ingredient. The water-soluble lithium compound is interposed between the secondary particles and / or between the secondary particles and the raw material fine particles, and not only functions as a lithium source but also binds the secondary particles of the hydroxide raw material powder to the tertiary particles. It also functions as a binder. Thus, the active material precursor powder corresponds to the granulated powder obtained in the “(3) drying / granulation (tertiary granulation) step” in the method for producing a positive electrode active material described above. Therefore, the description regarding the hydroxide raw material powder, the water-soluble lithium compound, and the raw material fine particles described in “Method for producing positive electrode active material for lithium secondary battery” is also incorporated into the active material precursor powder of this embodiment as it is. Shall.

  Moreover, the active material precursor powder of this embodiment has a volume-based D50 average particle diameter of 10 to 40 μm, preferably 10 to 20 μm, when converted into a positive electrode active material through lithium introduction by firing. The method of introducing lithium by firing may be in accordance with general lithium introduction and firing methods. However, for more accurate evaluation, after adding a lithium compound as necessary, a crucible made of high-purity alumina is used. It is preferable to carry out heat treatment in an oxygen atmosphere (0.1 MPa) at a rate of 50 ° C./h and heat treatment at 765 ° C. for 24 hours. What is necessary is just to measure the volume reference | standard D50 average particle diameter of the positive electrode active material obtained in this way by a laser diffraction / scattering type particle size distribution measuring apparatus by using water as a dispersion medium.

  Furthermore, when the active material precursor powder of this embodiment is deaggregated in water by ultrasonic irradiation, the proportion of particles having a particle size of 1.0 μm or less is 0 to 40%, preferably 10 to 30 on a volume basis. The particle size distribution is such that the proportion of particles having a particle size of 1.0 to 5.0 μm is 60 to 100%, preferably 70 to 90%. This deagglomeration may be carried out in accordance with a general deagglomeration technique by ultrasonic irradiation in water. However, in order to perform a more accurate evaluation, after putting the active material precursor powder into water, it is 600 W using an ultrasonic homogenizer. It is preferable to carry out by irradiating with ultrasonic waves for 3 minutes to loosen the hydroxide raw material powder and raw material fine particles. The particle size distribution of the sample slurry thus obtained may be measured using a laser diffraction / scattering particle size distribution measuring device.

  The reason why the particle size distribution characteristics are evaluated by firing or deaggregating as described above is that the active material precursor powder is the precursor powder before being subjected to firing, so the average particle size and particle size in the form as they are. Since it is not easy to determine the distribution uniquely, it is based on the idea that a more objective evaluation method is desirable. And the active material precursor powder of this embodiment characterized by the particle size distribution characteristics within the above range can be obtained by simply introducing lithium by firing (after mixing with a lithium compound as desired) without using a pore-forming agent, A positive electrode active material having a desired porosity and a high open pore ratio that provides high battery characteristics can be obtained very simply.

  Preferable examples of the water-soluble lithium compound include lithium hydroxide, lithium nitrate, lithium chloride, lithium oxide, and lithium peroxide. More preferably, the binder effect is high, the reactivity is high, and lithium can be easily introduced. In terms of lithium hydroxide.

  The agglomerated particles preferably contain a water-soluble lithium compound in an amount of 0.01 to 0.20 in terms of a molar ratio of Li / (Ni + M), more preferably 0.02 to 0.15, still more preferably. 0.04 to 0.10. As described above, when the molar ratio is within this range, the capacity increases in battery characteristics.

  The active material precursor powder preferably has a porosity of 1 to 30% and an open pore ratio of 50% or more when it is converted into a positive electrode active material through the introduction of lithium by firing. A more preferable porosity is 3 to 20%, and further preferably 5 to 15%. A more preferable open pore ratio is 60% or more, further preferably 70% or more, particularly preferably 80% or more, and most preferably 90% or more. The active material precursor powder preferably has an average open pore size of 0.2 to 3 μm, more preferably 0.4 to 3 μm, when converted into a positive electrode active material through the introduction of lithium by firing. The active material precursor powder preferably has a value obtained by dividing the average particle size of the primary particles constituting the positive electrode active material by the average open pore size of 0.2 to 3, more preferably 0.3 to 1. . The advantages of being within these numerical ranges are as described above for the positive electrode active material.

  The present invention is more specifically described by the following examples. Moreover, the measuring method of various physical-property values and the evaluation method of various characteristics are as showing below.

<D50 particle size>
The average particle size of the hydroxide raw material powder, granulated powder (active material precursor powder) and positive electrode active material is determined using a laser diffraction / scattering type particle size distribution measuring device (for example, model number “MT3000-II” manufactured by Nikkiso Co., Ltd.). The volume-based D50 average particle diameter (median diameter) measured using water as a dispersion medium was measured.

<Percentage of particles having a particle size of 1.0 μm or less>
After putting the granulated powder (active material precursor powder) into water, ultrasonic irradiation is performed at 600 W for 3 minutes with an ultrasonic homogenizer (Nippon Seiki Seisakusho, US-600T), hydroxide raw material powder and raw material fine particles I relaxed to the state of. The particle size distribution of the sample slurry thus obtained was measured using a laser diffraction / scattering particle size distribution measuring apparatus (for example, model number “MT3000-II” manufactured by Nikkiso Co., Ltd.). The proportion of particles below 0 μm was determined.

<Porosity>
The positive electrode material active material is filled with resin and polished so that the cross-section polished surface of the positive electrode active material can be observed with a cross section polisher (CP). By SEM (scanning microscope, “JSM-6390LA” manufactured by JEOL Ltd.), Get a cross-sectional image. This image is subjected to image processing to divide the void portion and the positive electrode material portion in the cross section, and obtain (area of void portion) / (area of void portion + area of positive electrode material). This was performed with respect to ten secondary particles, and the average value thereof was obtained as the porosity (%).

<Open pore ratio>
In the porosity evaluation method described above, the portion of the void portion that is impregnated with the resin is the open pore, and the portion of the void portion that is not impregnated with the resin is the closed pore (area of the open pore portion) / (open pore) (Area of the portion + area of the closing mechanism portion). This was performed on 10 secondary particles, and the average value thereof was obtained as the open pore ratio. When filling the resin, use a vacuum impregnation device (device name “Sitback” manufactured by Struers) to sufficiently impregnate the open pores with the resin while sufficiently expelling the air present in the pores. Filled.

<Average open pore size>
The average open pore diameter (average open pore diameter) was measured by a mercury intrusion method using a mercury intrusion pore distribution measuring apparatus (manufactured by Shimadzu Corporation, apparatus name “Autopore IV9510”).

<Primary particle size / average open pore size>
Using a FE-SEM (field emission scanning electron microscope: manufactured by JEOL Ltd., product name “JSM-7000F”), a magnification at which 10 or more single crystal primary particles enter the field of view is selected, and an SEM image Was taken. In this SEM image, for each of the 10 primary particles, the diameter of the circumscribed circle when the circumscribed circle was drawn was determined. And the average value of the obtained 10 diameter was made into the primary particle diameter. The primary particle size was divided by the average open pore size to obtain a ratio of primary particle size / average open pore size.

<Tap density>
After tapping a graduated cylinder containing a powder sample of positive electrode active material particles 200 times using a commercially available tap density measuring device, the tap density was determined by calculating (powder weight) / (bulk volume of powder). .

<Discharge capacity and SOC 10% voltage>
In order to evaluate the battery characteristics, a coin cell type battery was produced as follows. Specifically, the obtained tertiary particle powder, acetylene black, and polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 90: 5: 5 and dispersed in N-methyl-2-pyrrolidone. Thus, a positive electrode active material paste was prepared. This paste was applied on an aluminum foil having a thickness of 20 μm as a positive electrode current collector so as to have a uniform thickness (thickness after drying: 50 μm), and punched out into a disk shape having a diameter of 14 mm from the dried sheet. A positive electrode plate was produced by pressing the product at a pressure of 2000 kg / cm ² . A coin cell was manufactured using the positive electrode plate thus manufactured. The electrolytic solution was prepared by dissolving LiPF ₆ in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at an equal volume ratio to a concentration of 1 mol / L.

  Using the battery for characteristic evaluation (coin cell) produced as described above, the output characteristic was evaluated by performing a charge / discharge operation as follows. Specifically, constant current charging was performed until the battery voltage reached 4.3 V at a current value of 0.1 C rate. Thereafter, constant voltage charging was performed until the current value decreased to 1/20 under the current condition of maintaining the battery voltage at 4.3V. After resting for 10 minutes, the battery was discharged at a constant current at a current value of 5C until the battery voltage reached 2.5 V, and then rested for 10 minutes. These charging / discharging operations were defined as 1 cycle, and the cycle was repeated for 2 cycles under the condition of 25 ° C. The value of the discharge capacity at the second cycle was adopted as the measurement result. The discharge voltage at 90% when the discharge capacity at the second cycle was assumed to be 100% (SOC 10% voltage: SOC is an abbreviation for “State Of Charge” and means a state of charge) was read from the discharge curve. This value was used as an index of output characteristics. The higher this value, the higher the output characteristics, which is preferable.

Example 1 : Comparative example using a pore-forming agent (1) Preparation of hydroxide raw material powder The composition is (Ni _0.844 Co _0.156 ) (OH) ₂ and the secondary particles are almost spherical and primary particles. A nickel-cobalt composite hydroxide powder having a secondary particle diameter (D50) shown in Table 1 in which some of the particles are arranged radially outward from the center of the secondary particles was prepared. This nickel-cobalt composite hydroxide powder can be produced according to a known technique. For example, it was produced as follows. That is, a mixed aqueous solution of nickel sulfate and cobalt sulfate having a molar ratio of Ni: Co = 84.4: 15.6 in a molar ratio of 1 mol / L to a reaction vessel containing 20 L of pure water at a charging rate of 50 ml / min. Ammonium sulfate having a concentration of 3 mol / L was continuously continuously fed at a feeding rate of 2 ml / min. On the other hand, an aqueous sodium hydroxide solution having a concentration of 10 mol / L was added so that the pH in the reaction vessel was automatically maintained at 12.5. The temperature in the reaction vessel was maintained at 70 ° C., and was always stirred with a stirrer. The produced nickel / cobalt composite hydroxide was taken out by overflowing from the overflow tube, washed with water, dehydrated, and dried.

(2) Slurry preparation step After adding boehmite which is an Al raw material to the hydroxide raw material powder produced as described above so that the molar ratio is Ni: Co: Al = 81: 15: 4, a dispersion medium is added. As a primary particle, 400 parts of pure water was added and ground with a ball mill for 24 hours. On the other hand, a pore-forming agent (spherical: manufactured by Air Water Co., Ltd., trade name “Bellpearl R100”) was added so that the ratio to the total powder weight after addition was 2%, and a binder (polyvinyl alcohol: product number VP) -18, 1 part by Nippon Vinegar Poval Co., Ltd., 1 part by dispersant (product name “Marialim KM-0521”, manufactured by NOF Corporation), and antifoaming agent (1-octanol: Wako Pure Chemical Industries, Ltd.) After adding 0.5 part), the mixture was mixed with a ball mill for 24 hours. The mixture was degassed by stirring under reduced pressure, and a slurry was prepared by adjusting the viscosity to 0.5 Pa · s (measured using an LVT viscometer manufactured by Brookfield).

(3) Drying and granulating step The slurry prepared as described above is dried and granulated with a spray dryer (Okawara Chemical Co., Ltd., model “FOC-16”, hot air inlet temperature 120 ° C., atomizer rotational speed 24000 rpm). By doing so, a substantially spherical secondary granulated powder was produced. The D50 particle size after drying was 17 μm. The granulated powder was heated to 50 ° C./h up to 500 ° C., and held at 500 ° C. for 3 hours to carry out temporary firing.

(4) Mixing with Lithium Compound The calcined powder and LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) in a molar ratio of Li / (Ni _0.81 Co _0.15 Al _0.04 ) = 1.04.

(5) Firing step (lithium introduction step)
The above mixed powder is put into a crucible made of high-purity alumina, heated at 50 ° C./h in an oxygen atmosphere (0.1 MPa), and heat-treated at 765 ° C. for 24 hours to obtain Li (Ni _0.81 Co _0.15 Al _0.04 ) O ₂ powder was obtained. When various measurements were performed on the positive electrode active material thus obtained, the results shown in Table 1 were obtained.

Examples 2 to 7 : Examples not using a pore-forming agent (tertiary granulation)
(1) Preparation of hydroxide raw material powder The composition is (Ni _0.844 Co _0.156 ) (OH) ₂ by appropriately changing various conditions in accordance with the same method as in Example 1, and the secondary particles Prepared various nickel-cobalt composite hydroxide powders with secondary particle size (D50) shown in Table 1 in which the particles are almost spherical and some of the primary particles are arranged radially outward from the center of the secondary particles. did.

(2) Slurry Preparation Step In Examples 2 to 4, 100 parts of powder obtained by adding boehmite as an Al raw material to the obtained hydroxide raw material powder, 300 parts of pure water as a dispersion medium, and secondary particles are not pulverized. Were mixed with stirring. On the other hand, in Examples 5 to 7, 100 parts of powder obtained by adding boehmite as an Al raw material to a mixed powder containing the obtained hydroxide raw material powder and the raw material fine powder at a mixing ratio shown in Table 1 was dispersed. Mixed with 300 parts of pure water as a medium. In addition, the raw material fine powder used in Examples 5 to 7 was obtained by pulverizing hydroxide raw material powder with a ball mill for 24 hours in the same manner as in Example 1. In Examples 2 to 7, the amount of boehmite added was such that the molar ratio in the mixed powder was Ni: Co: Al = 81: 15: 4. The mixture thus obtained was defoamed by stirring under reduced pressure, and the viscosity was adjusted to 0.5 Pa · s (measured using a Brookfield LVT viscometer) to prepare a slurry. .

(3) Drying / granulating process (tertiary granulating process)
The slurry prepared as described above was dried and granulated in the same manner as in Example 1 to obtain a substantially spherical tertiary granulated powder. The D50 particle size after drying was 17 μm.

(4) Mixing with the lithium compound and (5) calcination step (lithium introduction step) were carried out in the same manner as in Example 1. When various measurements were performed on the positive electrode active material thus obtained, the results shown in Table 1 were obtained.

  Each of the positive electrode active materials obtained in Examples 2 to 7 includes tertiary particles composed of a large number of primary particles having an average primary particle diameter of 0.01 to 5 μm, and the tertiary particles are based on a volume of 10 to 40 μm. D50 has an average particle size, a porosity of 1 to 30%, an open pore ratio of 50% or more, and an average open pore size of 0.2 to 3 μm, and the average particle size of primary particles is divided by the average open pore size. The value was 0.2 to 3, and the tap density was 2.5 g / cc or more.

Examples 8 and 9 : Example in which no pore-forming agent was used (addition of lithium compound in tertiary granulation and slurry preparation process)
(1) Preparation of hydroxide raw material powder The composition is (Ni _0.844 Co _0.156 ) (OH) ₂ by appropriately changing various conditions in accordance with the same method as in Example 1, and the secondary particles Prepared various nickel-cobalt composite hydroxide powders with secondary particle size (D50) shown in Table 1 in which the particles are almost spherical and some of the primary particles are arranged radially outward from the center of the secondary particles. did.

(2) Slurry preparation process After stirring and mixing 100 parts of powder obtained by adding boehmite which is an Al raw material to the obtained hydroxide raw material powder, so that secondary particles are not pulverized with 300 parts of pure water as a dispersion medium, LiOH · H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) was mixed and dissolved. The amount of boehmite added was such that the molar ratio in the mixed powder was Ni: Co: Al = 81: 15: 4. In Example 8, Li / (Ni _0.81 Co _0.15 Al _0.04 ) = 0.40 in terms of mol ratio, and in Example 9, Li / (Ni _{0.81 in terms of} mol ratio). LiOH · H ₂ O powder was used so that Co _0.15 Al _0.04 ) = 1.04. The mixture thus obtained was defoamed by stirring under reduced pressure, and the viscosity was adjusted to 0.5 Pa · s (measured using a Brookfield LVT viscometer) to prepare a slurry. .

(3) Drying / granulating process (tertiary granulating process)
The slurry prepared as described above was dried and granulated in the same manner as in Example 1 to obtain a substantially spherical tertiary granulated powder. The D50 particle size after drying was 17 μm.

(4) Mixing with Lithium Compound In Example 8, Li / (Ni ₀ .2) in a mol ratio after mixing dried granulated powder and LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) _{. It} was mixed at a ratio of Li / (Ni _0.81 Co _0.15 Al _0.04 ) = 0.64 so that ₈₁ Co _0.15 Al _0.04 ) = 1.04. In Example 9, since LiOH.H ₂ O powder was mixed in the slurry preparation step so that the molar ratio was Li / (Ni _0.81 Co _0.15 Al _0.04 ) = 1.04, dry granulation was performed. The powder and the lithium compound were not mixed.

(5) The firing step (lithium introduction step) was performed in the same manner as in Example 1. When various measurements were performed on the positive electrode active material thus obtained, the results shown in Table 1 were obtained.

  Each of the positive electrode active materials obtained in Examples 8 and 9 includes tertiary particles composed of a large number of primary particles having an average primary particle diameter of 0.01 to 5 μm, and the tertiary particles are based on a volume of 10 to 40 μm. D50 has an average particle size, a porosity of 1 to 30%, an open pore ratio of 50% or more, and an average open pore size of 0.2 to 3 μm, and the average particle size of primary particles is divided by the average open pore size. The value was 0.2 to 3, and the tap density was 2.5 g / cc or more.

Examples 10 to 13 : Examples using no pore-forming agent (addition of lithium compound in the tertiary granulation and slurry preparation process)
In Example 8, in “(2) Slurry preparation process”, the mixing amount of LiOH · H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) was expressed in terms of a molar ratio of Li / (Ni _0.81 Co _0.15 Al _{0. 04} ) becomes 0.01 (Example 10), 0.05 (Example 11), 0.10 (Example 12) or 0.15 (Example 13), and further "(4) Mixing with lithium compound" , Dried granulated powder and LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.), Li / (Ni _0.81 Co _0.15 Al _0.04 ) 1.03 (Example 10) ), 0.99 (Example 11), 0.94 (Example 12) or 0.89 (Example 13), except that the positive electrode active material was prepared and evaluated in the same manner as in Example 8. . The results were as shown in Table 1.

  Each of the positive electrode active materials obtained in Examples 10 to 13 includes tertiary particles composed of a large number of primary particles having an average primary particle diameter of 0.01 to 5 μm, and the tertiary particles are based on a volume of 10 to 40 μm. D50 has an average particle size, a porosity of 1 to 30%, an open pore ratio of 50% or more, and an average open pore size of 0.2 to 3 μm, and the average particle size of primary particles is divided by the average open pore size. The value was 0.2 to 3, and the tap density was 2.5 g / cc or more.

Example 14 : Comparative example using a pore-forming agent (1) Preparation of hydroxide raw material powder The composition is (Ni _0.5 Co _0.2 Mn _0.3 ) (OH) ₂ and the secondary particles are almost spherical. In addition, a nickel / cobalt / manganese composite hydroxide powder having a secondary particle diameter (D50) shown in Table 2 in which some of the primary particles are arranged radially outward from the center of the secondary particles was prepared. This nickel-cobalt-manganese composite hydroxide powder can be produced according to a known technique, and for example, produced as follows. That is, a mixed aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate having a concentration of 1 mol / L in a molar ratio of Ni: Co: Mn = 50: 20: 30 is charged into a reaction vessel containing 20 L of pure water at a rate of 50 ml / min. In addition, ammonium sulfate having a concentration of 3 mol / L was continuously charged simultaneously at a charging rate of 2 ml / min. On the other hand, an aqueous sodium hydroxide solution having a concentration of 10 mol / L was added so that the pH in the reaction vessel was automatically maintained at 12.5. The temperature in the reaction vessel was maintained at 70 ° C., and was always stirred with a stirrer. The produced nickel-cobalt-manganese composite hydroxide was taken out by overflowing from the overflow tube, washed with water, dehydrated and dried. In addition, all of a series of steps (i.e., a series of steps excluding water washing, dehydration and drying treatment) from the introduction of each compound into the reaction vessel to the removal of the hydroxide was performed in an inert atmosphere.

(2) Slurry Preparation Step 400 parts of pure water was added as a dispersion medium to the hydroxide raw material powder produced as described above, and pulverized with a ball mill for 24 hours to obtain primary particles. On the other hand, a pore-forming agent (spherical: manufactured by Air Water Co., Ltd., trade name “Bellpearl R100”) was added so that the ratio to the total weight of the powder after addition was 2%, and further a binder (polyvinyl alcohol: product number VP). -18, 1 part by Nippon Vinegar Poval Co., Ltd., 1 part by dispersant (product name “Marialim KM-0521”, manufactured by NOF Corporation), and antifoaming agent (1-octanol: Wako Pure Chemical Industries, Ltd.) After adding 0.5 part), the mixture was mixed with a ball mill for 24 hours. The mixture was degassed by stirring under reduced pressure, and a slurry was prepared by adjusting the viscosity to 0.5 Pa · s (measured using an LVT viscometer manufactured by Brookfield).

(3) Drying and granulating step The slurry prepared as described above is dried and granulated with a spray dryer (Okawara Chemical Co., Ltd., model “FOC-16”, hot air inlet temperature 120 ° C., atomizer rotational speed 24000 rpm). By doing so, a substantially spherical secondary granulated powder was produced. The granulated powder was heated to 50 ° C./h up to 500 ° C., and held at 500 ° C. for 3 hours to carry out temporary firing.

(4) Mixing with Lithium Compound The calcined powder and LiOH · H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) are in a molar ratio of Li / (Ni _0.5 Co _0.2 Mn _0.3 ) = 1.04.

(5) Firing step (lithium introduction step)
The above mixed powder is put into a crucible made of high-purity alumina, heated at 50 ° C./h in an air atmosphere, and heat-treated at 850 ° C. for 24 hours, whereby Li ((Ni _0.5 Co _{0 .2} Mn _0.3 ) O ₂ powder was obtained, and various measurements were performed on the positive electrode active material thus obtained, and the results shown in Table 2 were obtained.

Examples 15 to 20 : Examples not using a pore-forming agent (tertiary granulation)
(1) Preparation of hydroxide raw material powder The composition is (Ni _0.5 Co _0.2 Mn _0.3 ) (OH) ₂ by appropriately changing various conditions in accordance with the same method as in Example 14. Various nickel-cobalt-manganese composites having secondary particle diameters (D50) shown in Table 2 in which the secondary particles are substantially spherical and part of the primary particles are arranged radially outward from the center of the secondary particles. A hydroxide powder was prepared.

(2) Slurry Preparation Step In Examples 15 to 17, 100 parts of the obtained hydroxide raw material powder was stirred and mixed with 300 parts of pure water as a dispersion medium so that secondary particles were not pulverized. On the other hand, in Examples 18 to 20, 100 parts of mixed powder comprising the obtained hydroxide raw material powder and the raw material fine powder in the mixing ratio shown in Table 2 was mixed with 300 parts of pure water as a dispersion medium. . The raw material fine powder used in Examples 18 to 20 was obtained by pulverizing hydroxide raw material powder with a ball mill for 24 hours in the same manner as in Example 14. The mixture thus obtained was defoamed by stirring under reduced pressure, and the viscosity was adjusted to 0.5 Pa · s (measured using a Brookfield LVT viscometer) to prepare a slurry. .

(3) Drying / granulating process (tertiary granulating process)
The slurry prepared as described above was dried and granulated by the same method as in Example 14 to obtain a substantially spherical tertiary granulated powder.

(4) Mixing with the lithium compound and (5) calcination step (lithium introduction step) were carried out in the same manner as in Example 14. When various measurements were performed on the positive electrode active material thus obtained, the results shown in Table 2 were obtained.

Examples 21 to 26 : Examples in which no pore-forming agent is used (lithium compound is added in the tertiary granulation and slurry preparation process)
(1) Preparation of hydroxide raw material powder The composition is (Ni _0.5 Co _0.2 Mn _0.3 ) (OH) ₂ by appropriately changing various conditions in accordance with the same method as in Example 14. Various nickel-cobalt-manganese composites having secondary particle diameters (D50) shown in Table 2 in which the secondary particles are substantially spherical and part of the primary particles are arranged radially outward from the center of the secondary particles. A hydroxide powder was prepared.

(2) Slurry preparation process After stirring and mixing 100 parts of the obtained hydroxide raw material powder and 300 parts of pure water as a dispersion medium and secondary particles are not crushed, LiOH · H ₂ O powder (Wako Pure Chemical Industries, Ltd.) Kogyo Co., Ltd.) was mixed and dissolved. At this time, the molar ratio of Li / (Ni _0.5 Co _0.2 Mn _0.3 ) = 0.01 (Example 21), 0.05 (Example 22), 0.10 (Example 23), 0.15 LiOH.H ₂ O powder was used so as to be (Example 24), 0.40 (Example 25), or 1.04 (Example 26). The mixture thus obtained was defoamed by stirring under reduced pressure, and the viscosity was adjusted to 0.5 Pa · s (measured using a Brookfield LVT viscometer) to prepare a slurry. .

(3) Drying / granulating process (tertiary granulating process)
The slurry prepared as described above was dried and granulated by the same method as in Example 14 to obtain a substantially spherical tertiary granulated powder.

(4) Mixing with Lithium Compound Dry granulated powder and LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed in a molar ratio (Li / (Ni _0.5 Co _0.5 ) _{. 2} Mn _0.3 ) = 1.04 Li / (Ni _0.5 Co _0.2 Mn _0.3 ) = 1.03 (Example 21), 0.99 (Example 22), 0. 94 (Example 23), 0.89 (Example 24) or 0.64 (Example 25) were mixed at a ratio of 26. In Example 26, LiOH.H ₂ O powder was mixed at a molar ratio of Li / (H / O) in the slurry preparation step. Ni _0.5 Co _0.2 Mn _0.3 ) = 1.04 was mixed so that the dried granulated powder and the lithium compound were not mixed.

(5) The firing step (lithium introduction step) was performed in the same manner as in Example 14. When various measurements were performed on the positive electrode active material thus obtained, the results shown in Table 2 were obtained.

  Each of the positive electrode active materials obtained in Examples 15 to 26 includes tertiary particles composed of a large number of primary particles having an average primary particle diameter of 0.01 to 5 μm, and the tertiary particles are based on a volume of 10 to 40 μm. D50 has an average particle size, a porosity of 1 to 30%, an open pore ratio of 50% or more, and an average open pore size of 0.2 to 3 μm, and the average particle size of primary particles is divided by the average open pore size. The value was 0.2 to 3, and the tap density was 2.5 g / cc or more.

Claims (18)

A method for producing a positive electrode active material for a lithium ion battery,
Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga) Consisting of secondary particles in which a large number of primary particles having a composition represented by a metal element of a species or more are aggregated, and at least a part of the primary particles are arranged radially outward from the center of the secondary particles. Preparing a hydroxide raw material powder or an aggregate thereof;
Using the hydroxide raw material powder or pulverizing the aggregate to prepare a slurry containing the hydroxide raw material powder; and
Producing a granulated powder formed by agglomerating a number of the secondary particles using the slurry; and
Mixing the lithium compound with the granulated powder to obtain a lithium mixed powder;
Firing the lithium mixed powder to react the granulated powder with a lithium compound, thereby obtaining a positive active material for a lithium secondary battery having open pores;
Ri name contains,
The method in which the granulated powder and the lithium mixed powder do not contain a pore forming agent .   The method according to claim 1, wherein the hydroxide raw material powder has a volume-based D50 average particle diameter of 1 to 5 μm. The slurry further includes raw material fine particles having a composition similar to that of the hydroxide raw material powder and a particle size smaller than that of the hydroxide raw material powder and having a volume-based D50 average particle size of 10 nm to 700 nm. The method according to 1 or 2.   The method according to claim 3, wherein a ratio of the raw material fine particles to a total amount of the raw material powder and the raw material fine particles is 25% by mass or less. The positive electrode active material for a lithium secondary battery comprises secondary particles composed of a large number of primary particles, and the secondary particles have a porosity of 1 to 30% and an open pore ratio of 50% or more. Item 5. The method according to any one of Items 1 to 4 . The method according to any one of claims 1 to 5 , wherein the slurry is an aqueous slurry. The method according to claim 6 , wherein the aqueous slurry further contains a water-soluble lithium compound. The method according to claim 7 , wherein the water-soluble lithium compound is lithium hydroxide. The method according to claim 7 or 8 , wherein the aqueous slurry contains the water-soluble lithium compound in an amount of 0.01 to 0.10 in terms of a molar ratio of Li / (Ni + M). The positive active material has a volume-based D50 average particle size of 10 to 40 [mu] m, method according to any one of claims 1-9. A method for producing a positive electrode active material for a lithium ion battery,
Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga) Consisting of secondary particles in which a large number of primary particles having a composition represented by a metal element of a species or more are aggregated, and at least a part of the primary particles are arranged radially outward from the center of the secondary particles. Preparing a hydroxide raw material powder or an aggregate thereof;
Using the hydroxide raw material powder or pulverizing the aggregate to prepare a slurry containing the hydroxide raw material powder and lithium hydroxide;
Producing a granulated powder formed by agglomerating a number of the secondary particles using the slurry; and
Calcining the granulated powder to react the granulated powder with the lithium hydroxide, thereby obtaining a positive electrode active material for a lithium secondary battery having open pores;
Ri name contains,
A method wherein the granulated powder does not contain a pore former . At least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga, which is not included in the hydroxide raw material powder or in the hydroxide raw material powder compounds containing missing element, wherein is added to the slurry and / or the granulated powder, the method according to any one of claims 1 to 11. An active material precursor powder that does not contain a pore-forming agent and is used for manufacturing a positive electrode active material for a lithium ion battery,
Ni _1-y M _y (OH) ₂ (where 0 <y ≦ 0.5, M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga) Consisting of secondary particles in which a large number of primary particles having a composition represented by a metal element of a species or more are aggregated, and at least a part of the primary particles are arranged radially outward from the center of the secondary particles. Hydroxide raw material powder,
Arbitrary composition having the same composition as the hydroxide raw material powder and a particle size smaller than the hydroxide raw material powder, in an amount of 0 to 25% by mass or less with respect to the total amount of the hydroxide raw material powder and the raw material fine particles Raw material fine particles as components ,
A water-soluble lithium compound interposed between the secondary particles and / or between the secondary particles and the raw material fine particles;
When the active material precursor powder is deagglomerated by ultrasonic irradiation in water, the proportion of particles having a particle size of 1.0 μm or less is 0 to 40% on a volume basis. And having a particle size distribution in which the proportion of particles having a particle size of 1.0 to 5.0 μm is 60 to 100%, and a volume of 10 to 40 μm when a positive electrode active material is obtained through lithium introduction by firing. An active material precursor powder having a reference D50 average particle size. The active material precursor powder according to claim 13 , wherein the water-soluble lithium compound is lithium hydroxide. The active material precursor powder according to claim 13 or 14 , wherein the aggregated particles contain the water-soluble lithium compound in an amount of 0.01 to 0.10 in terms of a molar ratio of Li / (Ni + M). The active material precursor according to any one of claims 13 to 15 , which has a porosity of 1 to 30% and an open pore ratio of 50% or more when converted into a positive electrode active material through introduction of lithium by firing. Powder. The active material precursor powder according to any one of claims 13 to 16 , which has an average open pore diameter of 0.2 to 3 µm when a positive electrode active material is obtained through introduction of lithium by firing. The active material precursor powder according to claim 17 , wherein a value obtained by dividing an average particle diameter of primary particles constituting the positive electrode active material by the average open pore diameter is 0.2 to 3.