JP2014067645A - Method of manufacturing positive electrode active material for lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a positive electrode active material for a lithium ion battery, that can materialize further improvement of rate characteristics while having a high open pore ratio, by an extremely simple method.SOLUTION: Hydroxide material powder is prepared which comprises secondary particles formed by aggregation of a large number of primary particles having a composition expressed by NiM(OH)(in the formula, 0<y≤0.5, M is at least one or more kinds of metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn and Ga), and in which at least some of the primary particles are radially arranged outward from the center of the secondary particle. Ultrasonic waves are irradiated to the hydroxide material powder and/or the thermally decomposed oxide powder thereof. The hydroxide material powder and/or the thermally decomposed oxide powder thereof irradiated with ultrasonic waves are made to react with a single lithium compound, or a combination of a compound containing a metal element M and a lithium compound so as to give a prescribed composition, and the positive electrode active material for the lithium ion battery, that is provided with open pores, is thereby obtained.

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium ion battery.

  As a positive electrode active material in a lithium ion secondary battery, it consists of secondary particles in which a large number of primary particles such as lithium cobaltate are agglomerated, and the primary particles are arranged radially from the center of the secondary particles to the outside. Those having minute gaps (voids) through which electrolyte can permeate in the particles are known (see Patent Document 1 (Japanese Patent Laid-Open No. 2001-243951) and Patent Document 2 (Japanese Patent No. 4726896)). . As a method for producing such particles, a method is proposed in which spherical transition metal hydroxide and lithium hydroxide hydrate are wet-mixed and dehydrated, thermally decomposed in air, and then fired and reacted in an oxygen atmosphere. Has been.

  In addition, a method for producing a radially oriented spherical transition metal hydroxide is also known (for example, Patent Document 3 (Japanese Patent Laid-Open No. 9-17429) and Patent Document 4 (Japanese Patent Laid-Open No. 2002-304992). reference).

JP 2001-243951 A Japanese Patent No. 4726896 JP-A-9-17429 JP 2002-304992 A

  However, the charge / discharge characteristics at high rates of lithium ion secondary batteries using this positive electrode active material (hereinafter simply referred to as “rate characteristics”) are compared to random ones because primary particles are arranged radially. Although it was excellent in electron conductivity and ion conductivity, there was still room for improvement. In particular, in order to improve the rate characteristics, it is necessary to increase both the electronic conductivity and the lithium ion conductivity in the active material, but there are limitations in the conventional manufacturing method. In other words, increasing the number of minute voids in the secondary particles makes it easier for the electrolyte to penetrate, so that the ionic conductivity is improved. Will fall. On the other hand, when the voids are reduced, the electron conductivity is improved, but the penetration of the electrolytic solution into the active material is reduced and the diffusion distance of lithium ions is increased, so that the ion conductivity is lowered. Thus, electronic conductivity and ionic conductivity have a trade-off relationship, and it has been difficult to achieve both.

  In the production of a positive electrode active material for a lithium ion battery, the present inventors have recently developed an oxide powder having a high open pore ratio by irradiating a hydroxide raw material powder and / or its pyrolytic oxide powder with ultrasonic waves. As a result, it was found that a positive electrode active material for a lithium ion battery capable of further improving the rate characteristics was obtained.

  Therefore, an object of the present invention is to produce a positive electrode active material for a lithium ion battery having a high open pore ratio that can realize further improvement in rate characteristics by a very simple method.

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;
Irradiating the hydroxide raw material powder and / or the pyrolyzed oxide powder with ultrasonic waves;
The hydroxide raw material powder and / or its thermally decomposed oxide powder irradiated with the ultrasonic waves are combined with a lithium compound alone or a combination of a compound containing a metal element M and a lithium compound, and Li _x Ni _1-z M _z. A positive electrode active material for a lithium ion battery that is reacted so as to give a composition represented by O ₂ (wherein 0.96 ≦ x ≦ 1.09, 0 <z ≦ 0.5), thereby providing open pores And obtaining
A method is provided comprising.

It is a schematic cross section of the coin cell produced by Example A1-A4 and Example B1-B4. It is a SEM image of the complex oxide particle image | photographed before lithium introduction | transduction in Example A1 (with ultrasonic irradiation). It is a SEM image of the composite oxide particle image | photographed after lithium introduction | transduction in Example A1 (with ultrasonic irradiation). It is a SEM image of the complex oxide particle image | photographed before lithium introduction | transduction in Example A2 (no ultrasonic irradiation). It is a SEM image of the composite oxide particle image | photographed after lithium introduction | transduction in Example A2 (no ultrasonic irradiation).

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material for a lithium ion battery, which includes a step of preparing a hydroxide raw material powder and, optionally, a hydroxide raw material. A process of thermally decomposing the powder by heating, a process of irradiating the hydroxide raw material powder and / or the pyrolyzed oxide powder with ultrasonic waves, and reacting the oxide powder with a lithium compound to produce a positive electrode active for a lithium ion battery. Obtaining a substance. Hereinafter, each step will be described.

(1) Preparation 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 is prepared, which is arranged radially from the center of the particle to the outside. Preferably, 0.15 ≦ y ≦ 0.4, and the preferred metal element M is at least two metal elements selected from the group consisting of Co, Al, Mg and Mn, more preferably Al, Mg and A particularly preferred combination of metal elements M is Co and Al, or Co and Mn, including at least one selected from the group consisting of Mn and Co.

  The hydroxide raw material powder preferably has a tap density of 1.80 g / cc or more, more preferably 1.9 g / cc or more, and further preferably 2.0 g / cc or more. The higher the tap density, the higher the density and the more likely to generate cracks, which is advantageous for the formation of open pores, but it is realistic that it is 2.3 g / cc or less. The hydroxide raw material powder preferably has a volume-based D50 average particle size of 10 to 30 μm as the secondary particle size, more preferably 10 to 25 μm, and still more preferably 15 to 20 μm. If the particle size is as large as this, cracks are likely to occur, which is advantageous for the formation of open pores.

  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) Thermal decomposition step Before the reaction with the lithium compound and before or after ultrasonic irradiation, a step of heating and hydrolyzing the hydroxide raw material powder to thereby generate an oxide powder is performed. Is preferred. This thermal decomposition step is more preferably performed before ultrasonic irradiation. In this thermal decomposition step, the hydroxide raw material powder is preferably heated by raising the temperature to a maximum temperature of 500 to 1000 ° C., and the temperature rise at that time is 30 ° C./min or higher. Or it is more preferable to carry out rapidly by spray pyrolysis. Thereby, an oxide powder having crack-like open pores can be generated. That is, the hydroxide raw material powder is pyrolyzed at the same time as it is heated rapidly to a maximum temperature of 500 to 1000 ° C., preferably at a heating rate of 30 ° C./min or more, and at the same time rapid thermal expansion. And it can make it easy to produce a crack resulting from volume contraction. Since the cracks thus formed easily form open pores communicating with the outside air, it contributes to a high open pore ratio to be realized in the subsequent ultrasonic irradiation process. A preferable maximum temperature is 600 to 1000 ° C, more preferably 700 to 1000 ° C, and still more preferably 750 to 950 ° C. The higher the rate of temperature rise, the easier the cracks are generated, so the rate of temperature rise may be 50 ° C./min or more, 100 ° C./min or more, 500 ° C./min or 1000 ° C./min or more. The hydroxide raw material powder that has been rapidly heated is preferably held at the above-mentioned maximum attained temperature for 0 to 10 minutes, more preferably 0 to 1 minute. The most preferable holding time is 0 minute, which means that the temperature is lowered immediately after reaching the maximum temperature without holding at the maximum temperature.

  The rapid heating method may be any method as long as it can realize a heating rate of 30 ° C./min or more, but the rapid heating is performed by heating in an infrared lamp heating furnace. This is preferable in that the temperature rate can be easily controlled. According to another preferred embodiment of the present invention, the rapid temperature increase may be performed by blowing the hydroxide raw material powder into the spray pyrolysis furnace together with the spray air. At this time, since the inside of the spray pyrolysis furnace is heated to the highest temperature of 500 to 1000 ° C., the particles constituting the raw material powder are instantaneously heated because of the spray state, thereby making it difficult to measure the temperature rising rate. A very high heating rate is realized. The temperature rising rate at this time is estimated to be 50 ° C./min or higher, and further 1000 ° C./min or higher. The crack-shaped open pores can be formed very efficiently, and a large amount of raw material powder can be processed in a short time, which is suitable for mass production. In any case, in the pyrolysis step of the present invention, the orientation of the hydroxide raw material powder in which at least part of the primary particles and voids (open pores) are arranged radially outward from the center of the secondary particles is As a result, it is inherited by oxides. As a result, it consists of secondary particles in which many primary particles are aggregated, and at least a part of the primary particles and voids (open pores) are arranged radially outward from the center of the secondary particles. An oxide powder is obtained.

  However, as long as the positive electrode active material having a desired open pore ratio can be obtained through the subsequent ultrasonic irradiation step and the lithium introduction step, the thermal decomposition step and the rapid temperature increase need not be performed.

(3) Ultrasonic irradiation process Ultrasonic is irradiated to the hydroxide raw material powder and / or its pyrolytic oxide powder. By irradiating with ultrasonic waves, open pores can be formed at a high ratio in the hydroxide raw material powder and / or its pyrolytic oxide powder. The reason is not clear, but due to cavitation generated by ultrasonic irradiation, a large number of primary particles fall off from the surface of secondary particles constituting the powder and open pores such as cracks that may already exist, and new open pores It is presumed that this may be due to the promotion of the formation of open pores and the expansion of the existing open pores. Since the open pores formed or expanded in this way are easy to communicate with the outside air, voids having a high open pore ratio are mainly removed from the center of the secondary particles in the secondary particle matrix in which many primary particles are closely bonded. It can be formed radially toward the direction. Therefore, the electrolyte solution easily penetrates into the secondary particles through the open pores formed radially, so that the ionic conductivity is improved, and at the same time, the portions other than the open pores are caused by the dense bonding of many primary particles. As a result, a sufficiently large number of bonding portions between primary particles serving as electron conduction paths can be secured, and a 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 long as the above phenomenon is expected, the ultrasonic conditions are not particularly limited, but the preferable amplitude of the ultrasonic wave is 20 to 50 μm and the preferable frequency is 16 to 30 kHz. The irradiation time of ultrasonic waves is not particularly limited, but is preferably 3 minutes or more, and more preferably 5 to 60 minutes.

  According to a preferred embodiment of the present invention, before the ultrasonic irradiation, the hydroxide raw material powder and / or the thermally decomposed oxide powder is dispersed in a solvent such as water to produce a slurry, and ultrasonic waves are applied to the slurry. After irradiation, the slurry is dried before reaction with the lithium compound. As a result, an increase in the open pore ratio by ultrasonic irradiation can be realized efficiently. But even if it is a case where a slurry is not used, you may dry the hydroxide raw material powder and / or its thermal decomposition oxide powder with which the ultrasonic wave was irradiated before reaction with a lithium compound. In any case, drying is preferably performed at a temperature of 300 to 600 ° C, more preferably 350 to 550 ° C. Battery characteristics are improved by performing such drying.

(4) Lithium introduction process The hydroxide raw material powder and / or its thermally decomposed oxide powder irradiated with ultrasonic waves are a lithium compound alone, or a combination of a compound containing a metal element M and a lithium compound, and Li _x Ni _1. (wherein, 0.96 ≦ x ≦ 1.09,0 <z ≦ 0.5) -z M z O 2 are reacted to give a composition represented by lithium-ion battery thus with open pores A positive electrode active material is obtained. Any lithium-containing compound capable of providing the above composition can be used as the lithium compound, and preferred examples include lithium hydroxide and lithium carbonate. Prior to the reaction, the hydroxide raw material powder and / or its pyrolytic oxide powder is preferably mixed with the lithium compound by a technique 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%. At that time, it is also possible to realize a composition represented by Li _x Ni _1-z M _z O ₂ by reacting together a compound containing a metal element M such as Al ₂ O ₃ . However, when the required amount of the metal element M is already contained in the hydroxide raw material powder, it is not necessary to use a compound containing the metal element M in the lithium introduction step.

  The positive electrode active material obtained as described above comprises substantially spherical secondary particles having a porosity of 5 to 25% by volume, preferably 10 to 25% by volume, in which a large number of primary particles are aggregated, and at least one of primary particles and voids. It is preferable that the portions are arranged radially from the center of the secondary particle toward the outside. The positive electrode active material preferably has an open pore ratio of 80% or more, preferably 90% or more, more preferably 95% or more. The higher the open porosity, the better, and ideally 100%.

  The introduction of lithium by reaction with the lithium compound can be preferably carried out by appropriately firing a mixture of oxide powder, lithium compound, and optionally a compound containing the metal element M. For example, firing can be preferably performed by putting a sheath containing the mixture before firing into a furnace. By this firing, synthesis of the positive electrode active material, and further, particle sintering and particle growth are performed. At this time, the orientation of the oxide powder in which at least a part of the primary particles and voids (open pores) are arranged radially outward from the center of the secondary particles is directly inherited by the calcined powder after lithium introduction. As a result, the positive electrode active material is composed of secondary particles in which a large number of primary particles are aggregated, and at least a part of the primary particles and voids (open pores) are arranged radially outward from the center of the secondary particles. A powder can be obtained.

  The firing temperature at the time of introducing lithium is preferably 600 ° C. to 1100 ° C. If the temperature is within this range, the grain growth is sufficient and the primary particles are easily arranged in a radial pattern (ie, easily oriented), and the positive electrode active material is decomposed. In addition, the volatilization of lithium and lithium can be suppressed and a desired composition can be easily realized. Moreover, even if it is the hydroxide raw material powder which did not pass through a pyrolysis process, after making it thermally decompose by hold | maintaining the temperature for 1 to 20 hours at low temperature (for example, 400-600 degreeC) from baking temperature, it is lithium at baking temperature. By introducing, thermal decomposition and lithium introduction can be performed efficiently. The firing time is preferably 1 to 50 hours. When the firing time is within this range, the orientation rate increases, and an excessive increase in energy consumed for firing can be prevented.

  In addition, for the purpose of increasing the reactivity between the lithium mixed with the precursor oxide powder in the temperature raising process, the temperature may be maintained at a temperature lower than the firing temperature (for example, 400 to 600 ° C.) for 1 to 20 hours. 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 is preferably set as appropriate so that the lithium does not escape from the lithium composite oxide once decomposed during firing and introduced once (reacted with lithium). 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 the adhesion and aggregation between the positive electrode active material particles or adjusting the average particle diameter of the positive electrode active material particles.

  Moreover, you may heat-process at 100-400 degreeC with respect to the positive electrode material active material which passed the crushing and the classification process as needed after baking. By performing such a post-heat treatment step, the surface layer of the primary particles can be modified, thereby further improving rate characteristics and output characteristics.

  Hereinafter, the present invention will be specifically described based on the following examples, but the present invention is not limited to these examples. In the examples, “parts” and “%” are based on mass unless otherwise specified. Moreover, the measuring method of various physical-property values and the evaluation method of various characteristics are shown below.

<Secondary particle size (μm)>
Using a particle size distribution measuring device ("Microtrack MT3300", manufactured by Nikkiso Co., Ltd.), the median diameter (D50) based on the volume of the positive electrode active material was measured using water as a dispersion medium, and this value was measured as the value of the positive electrode active material. The secondary particle size was taken.

<Alignment state of primary particles>
The positive electrode active material powder was filled with a resin and polished with a cross section polisher (CP) so that the cross-section polished surface of the positive electrode active material could be observed. Using the SEM (Scanning Microscope “JSM-6390LA”, manufactured by JEOL Ltd.), the array of primary particles is confirmed in the field where one secondary particle can be seen. did. The observation was performed under the condition (WD: 6 to 8 mm) in which the contrast (channeling contrast) due to the crystal orientation was high so that the grain boundaries of the primary particles became clearer.

<Tap density>
5 g or more of the powder was dried at 100 ° C. for 3 hours or more, filled into a 100 cc graduated cylinder, and then the volume after tapping 600 times was determined. The value obtained by dividing the weight of the powder after drying by the volume was taken as the tap density.

<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), and then SEM (scanning microscope, “JSM-6390LA”, manufactured by JEOL Ltd.) A cross-sectional image was acquired. This image was subjected to image processing to separate the void portion and the positive electrode material portion in the cross section, and (area of void portion) / (area of void portion + area of positive electrode material) was obtained. This was performed on 10 secondary particles, and the average value thereof was determined 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 part + area of the closing mechanism part). 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 (manufactured by Struers, device name “Citback”) to expel the air present in the pores sufficiently so that the open pores are sufficiently impregnated with the resin. Resin filling was performed.

<Rate capacity maintenance rate (%)>
The manufactured battery was charged with a constant current at a current value of 0.1 C rate until the battery voltage became 4.3V. 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, constant current discharge was performed until the battery voltage reached 3.0 V at a current value of 0.2 C rate. Then, it rested for 10 minutes. These charging / discharging operations were defined as one cycle, and repeated for a total of two cycles under the condition of 25 ° C., and the measured value of the discharge capacity at the second cycle was defined as “discharge capacity at 0.2 C rate”. Subsequently, the current value at the time of charging was fixed at the 0.1 C rate, the current value at the time of discharging was set to the 2 C rate, and two-cycle charge / discharge was repeated in the same manner as described above. The measured value of the discharge capacity at the second cycle was defined as “discharge capacity at 2C rate”. The value obtained by dividing the “discharge capacity at the 2C rate” by the “discharge capacity at the 0.2C rate” (actually, the value expressed as a percentage) was defined as the “rate capacity maintenance rate”.

Examples A1 to A3
Production and evaluation of a positive electrode active material composed of Li _1.02 (Ni _0.81 Co _0.15 Al _0.04 ) O ₂ and having various void ratios and open pores were performed as follows.

Example A1
Secondary particle diameter in which the composition is (Ni _0.844 Co _0.156 ) (OH) ₂ , the secondary particles are almost spherical, and a part of the primary particles are arranged radially outward from the center of the secondary particles A nickel-cobalt composite hydroxide powder having (d50) of 12 μm and a tap density of 1.9 g / cc was prepared. This nickel-cobalt composite hydroxide powder can be produced according to a known technique. For example, in Example 1, 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 5 mol / L was continuously continuously fed at a feeding rate of 5 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 11.6. The temperature in the reaction vessel was maintained at 50 ° C. and constantly 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.

<Thermal decomposition process>
Nickel-cobalt composite hydroxide powder Ni _0.844 Co _0.156 ) (OH) ₂ was heated from room temperature to 750 ° C. at a rate of temperature increase of 50 ° C./min by an infrared lamp heating furnace (MILA3000 manufactured by ULVAC-RIKO). The mixture was heated and thermally decomposed at 750 ° C. for 1 minute to obtain nickel / cobalt composite oxide powder (Ni _0.844 Co _0.156 ) O.

<Ultrasonic irradiation process>
Using an ultrasonic homogenizer (US-600AT, manufactured by Nippon Seiki Seisakusho Co., Ltd.), an ultrasonic wave having a frequency of 20 kHz and an amplitude of 40 μm is applied to the slurry in which 10 g of the nickel-cobalt composite oxide powder is dispersed in 20 g of pure water for 5 minutes. Irradiated. From the powder obtained by drying this slurry at 500 ° C. for 12 hours, fine powder of 5 μm or less generated by ultrasonic irradiation was removed using an airflow classifier (manufactured by Nissin Engineering Co., Ltd., product type TC-15). . Moreover, when the composite oxide particle after ultrasonic irradiation was observed with SEM, the image shown in FIG. 2 was obtained.

<Powder mixing process>
Heat-treated nickel / cobalt composite oxide powder (Ni _0.844 Co _0.156 ) O, LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) and Al ₂ O _{3 .H 2} O (manufactured by SASOL) _Were mixed so that the molar ratio was Li _1.02 (Ni _0.81 Co _0.15 Al _0.04 ) O ₂ .

<Baking process>
The mixed powder is placed in a crucible made of high-purity alumina and subjected to heat treatment at 750 ° C. for 24 hours in an oxygen atmosphere (0.1 MPa) using an atmospheric electric furnace (FT-201P manufactured by Fulltech) _{. 02} (Ni _0.81 Co _0.15 Al _0.04 ) O ₂ powder was obtained. Thus, when the complex oxide particle after lithium was introduce | transduced was observed by SEM, the image shown by FIG. 3 was obtained.

<Battery characteristics evaluation>
In order to evaluate the battery characteristics, a coin-type lithium secondary battery (coin cell) shown in FIG. 1 was prepared as follows. The coin cell 1 includes a positive electrode plate 2, a negative electrode plate 3, a separator 4, an electrolytic solution 5, and a battery case 6. The positive electrode plate 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22. It consists of an electric conductor 31 and a negative electrode active material layer 32. The Li _1.02 (Ni _0.81 Co _0.15 Al _0.04 ) O ₂ powder obtained above, acetylene black, and polyvinylidene fluoride (PVDF) are in a mass ratio of 75: 20: 5. To prepare a positive electrode material. A positive electrode active material layer was produced by press-forming 0.02 g of the prepared positive electrode material into a disk shape having a diameter of 20 mm at a pressure of 300 kg / cm ² . The produced positive electrode active material layer, negative electrode active material layer made of a lithium metal plate, stainless steel current collector plate, and separator were combined into a positive electrode current collector plate 21-a positive electrode active material layer 22-a separator 4-a negative electrode active material layer 31-a negative electrode current collector. The coin cell 1 is obtained by arranging the integrated body and the electrolyte 5 in a battery case 6 (including the positive electrode side container 61, the negative electrode side container 62, and the insulating gasket 63) in a liquid-tight manner. It was. The electrolytic solution 5 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 so as to have a concentration of 1 mol / L. Using the battery (coin cell) produced as described above, the rate capacity retention rate was evaluated. The evaluation results are as shown in Table 1.

Example A2
A positive electrode active material was prepared and evaluated in the same manner as in Example A1, except that ultrasonic irradiation was not performed. The evaluation results are as shown in Table 1. Further, FIG. 4 shows an SEM image of the composite oxide particles taken before introducing lithium, and FIG. 5 shows an SEM image of the composite oxide particles taken after introducing lithium.

Example A3
The thermal decomposition process was carried out using a spray pyrolysis apparatus (manufactured by Okawara Chemical Industries, RH-2), with an electric heater temperature of 950 ° C., an in-furnace temperature of 750 ° C., a powder carrier gas flow rate of 40 L / min, and an in-furnace carrier gas flow rate of 10 L / min. The positive electrode active material was prepared and evaluated in the same manner as in Example A1, except that the powder input was 10 g / min. The evaluation results are as shown in Table 1.

Examples B1-B3
Production and evaluation of a positive electrode active material composed of Li _1.02 (Ni _0.60 Co _0.20 Mn _0.20 ) O ₂ and having various void ratios and open pores were performed as follows.

Example B1
The composition is (Ni _0.6 Co _0.2 Mn _0.2 ) (OH) ₂ , the secondary particles are almost spherical, and some of the primary particles are arranged radially outward from the center of the secondary particles, A nickel / cobalt / manganese composite hydroxide powder having a secondary particle diameter (d50) of 13 μm and a tap density of 1.9 g / cc was prepared. This nickel / cobalt / manganese composite hydroxide powder can be produced according to a known technique, and various nickel / cobalt / manganese composite hydroxide powders were produced by appropriately changing the conditions of Example A1 described above.

<Thermal decomposition process>
Nickel / cobalt / manganese composite hydroxide powder (Ni _0.6 Co _0.2 Mn _0.2 ) (OH) ₂ is heated from room temperature to 750 ° C. with an infrared lamp heating furnace (MILA3000, ULVAC-RIKO) The temperature was raised at a rate of 50 ° C./min, and a thermal decomposition treatment was performed at 750 ° C. for 1 minute to obtain nickel / cobalt / manganese composite oxide powder (Ni _0.6 Co _0.2 Mn _0.2 ) O.

<Ultrasonic irradiation process>
Using an ultrasonic homogenizer (US-600AT, manufactured by Nippon Seiki Seisakusho Co., Ltd.), an ultrasonic wave having a frequency of 20 kHz and an amplitude of 40 μm is applied to a slurry in which 10 g of the nickel-cobalt-manganese composite oxide powder is dispersed in 20 g of pure water. Irradiated for 5 minutes. From the powder obtained by drying this slurry at 500 ° C. for 12 hours, fine powder of 5 μm or less generated by ultrasonic irradiation was removed using an airflow classifier (product model TC-15 manufactured by Nisshin Engineering Co., Ltd.).

<Powder mixing process>
The obtained nickel-cobalt-manganese composite hydroxide powder (Ni _0.6 Co _0.2 Mn _0.2 ) (OH) ₂ and LiOH · H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed such that _{Li 1.02 (Ni 0.6 Co 0.2 Mn} 0.2) O 2 in mol ratio.

<Baking process>
The mixed powder is put into a high-purity alumina crucible and subjected to heat treatment in an atmospheric atmosphere at 825 ° C. for 24 hours in an atmospheric electric furnace (manufactured by Fulltech, FT-201P), whereby Li _1.02 (Ni _{0 .6} Co _0.2 Mn _0.2 ) O ₂ powder was obtained.

<Battery characteristics evaluation>
In order to evaluate the battery characteristics, a coin-type lithium secondary battery (coin cell) shown in FIG. 1 was prepared as follows. The coin cell 1 includes a positive electrode plate 2, a negative electrode plate 3, a separator 4, an electrolytic solution 5, and a battery case 6. The positive electrode plate 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22. It consists of an electric conductor 31 and a negative electrode active material layer 32. Li _1.03 (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ powder obtained above, acetylene black, and polyvinylidene fluoride (PVDF) are in a mass ratio of 75: 20: 5. To prepare a positive electrode material. A positive electrode active material layer was produced by press-forming 0.02 g of the prepared positive electrode material into a disk shape having a diameter of 20 mm at a pressure of 300 kg / cm ² . The produced positive electrode active material layer, negative electrode active material layer made of a lithium metal plate, stainless steel current collector plate, and separator were combined into a positive electrode current collector plate 21-a positive electrode active material layer 22-a separator 4-a negative electrode active material layer 31-a negative electrode current collector. The coin cell 1 is obtained by arranging the integrated body and the electrolyte 5 in a battery case 6 (including the positive electrode side container 61, the negative electrode side container 62, and the insulating gasket 63) in a liquid-tight manner. It was. The electrolytic solution 5 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 so as to have a concentration of 1 mol / L. Using the battery (coin cell) produced as described above, the rate capacity retention rate was evaluated. The evaluation results were as shown in Table 2.

Example B2
A positive electrode active material was prepared and evaluated in the same manner as in Example B1, except that ultrasonic irradiation was not performed. The evaluation results were as shown in Table 2.

Example B3
The thermal decomposition process was carried out using a spray pyrolysis apparatus (manufactured by Okawara Chemical Industries, RH-2), with an electric heater temperature of 950 ° C., an in-furnace temperature of 750 ° C., a powder carrier gas flow rate of 40 L / min, and an in-furnace carrier gas flow rate of 10 L / min. The positive electrode active material was prepared and evaluated in the same manner as in Example B1 except that the powder input was 10 g / min. The evaluation results were as shown in Table 2.

Claims (13)

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;
Irradiating the hydroxide raw material powder and / or the pyrolyzed oxide powder with ultrasonic waves;
The hydroxide raw material powder and / or its thermally decomposed oxide powder irradiated with the ultrasonic waves are combined with a lithium compound alone or a combination of a compound containing a metal element M and a lithium compound, and Li _x Ni _1-z M _z. A positive electrode active material for a lithium ion battery that is reacted so as to give a composition represented by O ₂ (wherein 0.96 ≦ x ≦ 1.09, 0 <z ≦ 0.5), thereby providing open pores And obtaining
Comprising a method.   The method according to claim 1, wherein the ultrasonic wave has an amplitude of 20 to 50 μm.   The method according to claim 1, wherein the ultrasonic wave has a frequency of 16 to 30 kHz.   Before the ultrasonic irradiation, the hydroxide raw material powder and / or the pyrolyzed oxide powder thereof is dispersed in a solvent to prepare a slurry, and after the ultrasonic wave is irradiated to the slurry, the lithium compound The method according to any one of claims 1 to 3, wherein the slurry is dried prior to reaction with.   5. The method according to claim 1, further comprising a step of drying the hydroxide raw material powder and / or the thermally decomposed oxide powder irradiated with the ultrasonic wave before the reaction with the lithium compound. The method described.   The method of Claim 4 or 5 that the said drying is performed at the temperature of 300-600 degreeC.   The method according to any one of claims 1 to 6, wherein the hydroxide raw material powder has a tap density of 1.80 g / cc or more.   The method according to any one of claims 1 to 7, wherein the hydroxide raw material powder has a volume-based D50 average particle size of 10 to 30 µm as a secondary particle size.   The method further includes the step of heating and hydrolyzing the hydroxide raw material powder before the reaction with the lithium compound and before or after the ultrasonic irradiation, thereby generating the oxide powder. The method as described in any one of 1-8.   The method according to claim 9, wherein the thermal decomposition is performed by heating the hydroxide raw material powder to a maximum temperature of 500 to 1000 ° C.   The method according to claim 10, wherein the temperature increase is performed rapidly at a temperature increase rate of 30 ° C./min or more and / or by spray pyrolysis.   The positive electrode active material is composed of substantially spherical secondary particles having a porosity of 5 to 25% by volume in which a large number of primary particles are aggregated, and at least a part of the primary particles and voids outward from the center of the secondary particles. The method according to claim 1, wherein the methods are arranged in a radial pattern.   The method according to claim 12, wherein the positive electrode active material has an open pore ratio of 80% or more.