JP6605390B2 - Lithium metal composite oxide powder - Google Patents

Description

  The present invention relates to a lithium metal composite oxide powder and a lithium ion battery using this as a positive electrode.

  Lithium ion batteries have a long history and their commercial production began in the 1990s. However, it can be said that the development of lithium-ion batteries has been developed in earnest with the spread of mobile terminals, smartphones, electric vehicles and the like since 2000. Lithium ion batteries, like other batteries, have a positive electrode, a negative electrode, an electrolyte, and an outer package as the main components. Among them, the positive electrode active material used for the positive electrode is an important material that affects the battery performance of the lithium ion battery. is there. Various lithium metal oxides have already been found as positive electrode active materials used in lithium ion batteries.

  So far, positive electrode active materials for high-power lithium-ion batteries have been proposed in order to achieve low cost and long-time use of portable terminals, smartphones, and electric vehicles. On the other hand, since safety and durability are also required for mobile terminals, smartphones, and electric vehicles equipped with lithium ion batteries, the positive electrode active material is required to have high heat resistance and the property of not causing deformation of the battery body. The In order to satisfy such requirements, various positive electrode active materials for lithium ion batteries have been proposed. So far, a cobalt-based positive electrode active material represented by lithium cobaltate and a nickel-based positive electrode active material using a composite oxide containing Li, Ni, and Co have been used.

  Among the nickel-based positive electrode active materials, the NCA-based positive electrode active material using a composite oxide containing Li, Ni, Co, and Al has an advantage that an electrode having a high energy density can be manufactured. Compared to the cobalt-based positive electrode active material, the NCA-based positive electrode active material exhibits a higher discharge capacity, and the discharge capacity generally exceeds 190 mAh / g. However, since the density of the NCA-based positive electrode active material itself is low and it is difficult to increase the electrode density, the discharge capacity per unit volume of the NCA-based positive electrode active material has not been sufficiently improved. In addition, in the case of the NCA-based positive electrode active material, there is a problem that sufficient rate characteristics and cycle characteristics cannot be obtained.

  It is common practice to improve cycle characteristics and stability by adding elements other than constituent elements to a nickel-based positive electrode active material. Patent Document 1 describes a composite oxide containing titanium in nickel-cobalt-aluminum as a positive electrode active material for a non-aqueous secondary battery having high capacity, high stability, and excellent output characteristics. However, this method has a problem in terms of manufacturing cost because the discharge capacity is not sufficient and an expensive titanium compound is used. In Patent Document 2, a powder comprising a lithium metal composite oxide is mixed with water and stirred to obtain a slurry, and an aqueous solution containing a cobalt salt is added while stirring the obtained slurry. A second step of attaching fine particles of a cobalt compound to the surface of primary particles of a lithium metal composite oxide, and a heat treatment at 300 to 700 ° C. to convert the cobalt compound into a lithium cobalt composite oxide. Although the positive electrode active material having a high discharge capacity and excellent thermal stability is described by including the third step, there is no description regarding cycle characteristics.

  By the way, a nickel-based positive electrode active material is generally obtained by firing a mixture comprising a nickel-cobalt composite hydroxide as a precursor and a compound containing a trace element such as aluminum to be used if necessary, and a lithium compound. Obtained. It is known that the properties of the nickel-based positive electrode active material are largely related to properties such as the particle size distribution of the precursor used for firing. Therefore, various methods for producing a nickel-cobalt composite hydroxide effective as a precursor of a better positive electrode active material have been proposed. For example, Patent Document 3 describes that a nickel-cobalt composite hydroxide composite hydroxide having a spherical and regular particle shape is produced using a reactor having an inclined plate settling device. The production method disclosed in Patent Document 3 is a highly versatile means for producing a composite hydroxide containing nickel and cobalt. However, there has been no optimization specializing in the production of a precursor of an NCA-based positive electrode active material that has attracted particular attention in recent years.

JP 2012-28163 A JP 2008-103181 A Japanese Patent No. 5227306

  An object of the present invention is to obtain an NCA-based positive electrode active material having a low pH and excellent cycle characteristics.

  The inventors of the present invention have a lithium metal composite oxide powder having a specific average particle size and specific surface area, which is treated with an aqueous solution of an organic metal salt, has a small residual alkali component, and has a high discharge capacity and a high cycle retention rate. It was found to be effective as a lithium ion battery positive electrode active material. That is, the present invention is as follows.

(Invention 1) Composition Li _a Ni _b Co _c Al _d O ₂ (where a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005 to 0.1, and b + c + d = 1)).
The powder has an average particle diameter (volume average diameter) of more than 13.1 μm and less than 21 μm;
The specific surface area of the BET method according to nitrogen adsorption of the powder exceeds 0.2 m ² / g, less than 0.9 m ² / g,
It is treated with an organic metal salt aqueous solution by contacting an aqueous solution in which an organic metal salt is dissolved in the lithium metal composite oxide, filtering, and drying .
Lithium metal composite oxide powder for lithium ion battery positive electrode active material.

  (Invention 2) The lithium metal composite oxide powder for a lithium ion battery positive electrode active material of Invention 1, wherein the organic metal salt is sodium paratoluenesulfonate.

(Invention 3) Composition Li _a Ni _b Co _c Al _d O ₂ (where a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005 to 0.1, and b + c + d = 1)).
The powder has an average particle diameter (volume average diameter) of more than 13.1 μm and less than 21 μm;
The specific surface area of the BET method according to nitrogen adsorption of the powder exceeds 0.2 m ² / g, less than 0.9 m ² / g,
The residual LiOH amount determined by the following method is 0.5% by weight or less,
(LiOH amount: 2 g of the calcined lithium metal composite oxide was added to 100 ml of pure water at 25 ° C., stirred for 3 minutes with a magnetic stirrer, and then suction filtered. 10 ml of the obtained filtrate was pipetted, The lithium hydroxide content was quantified by titrating with 0.1N hydrochloric acid.)
Moreover, a battery including a positive electrode active material made of the powder achieves an initial discharge capacity and a cycle maintenance ratio measured under the following conditions.
Lithium metal composite oxide powder for lithium ion battery positive electrode active material.
Initial discharge capacity: The capacity (initial discharge capacity) when performing 0.1 C discharge between 4.3 V and 3.0 V is 180 mAh / g or more.
-Cycle maintenance rate: The ratio of the capacity of the 50th cycle to the capacity of the first cycle after 50 cycles of the battery after confirming the initial discharge capacity are repeated at 1.0C charge and 0.5C discharge. The cycle maintenance ratio calculated by the formula is 95% or more.
Cycle maintenance ratio (%) = (discharge capacity at 50th cycle / discharge capacity at 1st cycle) × 100
(However, the batteries whose initial discharge capacity and cycle retention rate were measured were obtained by the following method.
-Battery production: Prepared to be 1 part by weight of acetylene black, 5 parts by weight of graphite carbon, and 4 parts by weight of polyvinylidene fluoride with respect to 100 parts by weight of the lithium metal composite oxide for the positive electrode active material of the lithium ion battery, -A slurry was prepared using methylpyrrolidone as a dispersion solvent. This slurry was applied to an aluminum foil as a current collector, dried and pressed as a positive electrode, a lithium metal foil as a negative electrode as a negative electrode, and 1 mol / L LiPF ₆ ethylene carbonate and ethyl as the electrolyte. A CR2032-type coin battery according to the International Electrotechnical Commission (IEC) standard was prepared using a solution of an equal amount mixture of methyl carbonate. )

  (Invention 4) A lithium ion battery using a positive electrode active material containing the lithium metal composite oxide powder according to any one of Inventions 1 to 3.

  The present invention provides a lithium nickel metal-based positive electrode active material having a low pH and excellent cycle characteristics and a lithium ion battery using the same.

The example of the inclined plate sedimentation apparatus which can be used by manufacture of this invention is represented typically. The example of the inclined plate sedimentation apparatus which can be used by manufacture of this invention is represented typically. The schematic diagram for understanding the function of the inclined plate sedimentation apparatus which can be used by manufacture of this invention. The reactor which can be used by manufacture of this invention and its attachment apparatus are represented typically.

The lithium metal composite oxide powder of the present invention is obtained by firing a fired product obtained by mixing an aluminum compound and a lithium compound with a nickel-cobalt composite hydroxide as a precursor, and washing the fired product with water. Hereinafter, the manufacturing method will be described in detail.

[1 Production of precursor]
Composition Li _a Ni _b Co _c Al _d O ₂ (where a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005) (B + c + d = 1)), a nickel-cobalt composite hydroxide, which is a precursor of a lithium metal composite oxide, is produced by a coprecipitation method.

  (1-1 Raw Material Preparation) In the present invention, nickel sulfate is used as the nickel raw material, and cobalt sulfate is used as the cobalt raw material. Nickel sulfate and cobalt sulfate are prepared in advance as a mixed aqueous solution and supplied to the reactor. The nickel sulfate concentration in the mixed aqueous solution is preferably adjusted to 15 to 30% by weight, more preferably 20 to 25% by weight. The cobalt sulfate concentration in the mixed aqueous solution is adjusted to 15% by weight or more and 25% by weight or less, more preferably 18% by weight or more and 23% by weight or less. In the coprecipitation reaction, an aqueous caustic soda (NaOH) solution as an alkali control agent and aqueous ammonia as a complexing agent are supplied. These are supplied to the reactor through a flow path different from the mixed aqueous solution of nickel nitrate and cobalt nitrate.

  (1-2 Precipitation step) A mixed aqueous solution of nickel nitrate and cobalt nitrate, an alkali regulator, and a complexing agent are supplied to the reactor to co-precipitate a nickel-cobalt composite hydroxide (hereinafter "composite hydroxide"). Manufactured as a product. The pH of the aqueous solution in the reactor is controlled to a range suitable for the coprecipitation reaction, generally 7 to 14, preferably 9 to 12. The temperature of the reaction solution is not limited as long as it is a temperature at which a composite hydroxide is produced, but it is generally 40 ° C. or higher from the range of the average particle size required for the produced particles. There is no particular limitation on the shape and material of the reactor main body, and so-called tank-shaped stainless steel containers are used without limitation. When the temperature of the reaction solution is high, the solubility of the metal component in water increases and the fine particles disappear, so that the growth of the composite hydroxide proceeds and a composite hydroxide having a relatively large particle size is generated. When the temperature of the reaction solution is low, a composite hydroxide having a relatively small particle size is formed.

  Stirring means is provided inside the reactor. There is no particular limitation on the stirring means. As long as the stirring blade is controlled by the motor, it can be used in various shapes such as a propeller, paddle, flat paddle, turbine, cone, screw, and ribbon. The size of the composite hydroxide particles can be adjusted by controlling the stirring intensity. When the stirring strength is high, the average particle size of the composite hydroxide is reduced, and when the stirring strength is low, the average particle size of the composite hydroxide is increased.

  The reactor is provided with an outlet for the produced composite hydroxide slurry. The position of the outlet may be any position from the top to the bottom of the reactor. A pipe for guiding the slurry to the outside of the reactor and a pump connected to the pipe are connected to the outlet. When the precipitation reaction reaches a steady state, the nickel-cobalt composite hydroxide slurry is taken out from the reactor at a constant flow rate by a pump and transferred to the next drying step.

  An apparatus (separation mechanism) for separating the composite hydroxide slurry into the high solid concentration slurry and the low solid concentration slurry is connected to the reactor. As the separation mechanism, a centrifugal separator or a filter is used. A certain amount of composite hydroxide slurry is sucked from the reactor using a pump and a suction pipe and sent to a separation mechanism. By the separation mechanism, the composite hydroxide slurry is separated into a high solid concentration slurry composed of nickel-cobalt composite hydroxide particles and a low solid concentration slurry composed of aqueous solution and nickel-cobalt composite hydroxide fine particles. . A part of the separated low solid concentration slurry is discharged out of the reactor, and the remaining low solid concentration slurry and high solid concentration slurry are returned to the reactor. In this way, the slurry circulates inside and outside the reactor through the separation mechanism. The concentration of the composite hydroxide in the reactor can be controlled by such circulation of the slurry. If the solid concentration of the slurry in the reactor is controlled to 50 g / L or more, there is no problem in production efficiency. By removing solid particles having an average particle diameter in a certain range by the separation mechanism, the average particle diameter of the obtained composite hydroxide can be controlled.

  In the precipitation step, it is necessary to generate the composite hydroxide as a solid having a solid particle size close to that of the lithium metal composite oxide particles of the present invention. That is, in the precipitation step, a composite hydroxide having an average particle size of more than 10 μm and not more than 30 μm, preferably not less than 10 μm and not more than 25 μm, is prepared by adjusting the temperature, stirring strength, and slurry concentration of the reaction solution.

  (1-3 Reactor) It is efficient to perform such suction, separation and circulation of the composite hydroxide slurry by using the inclined plate settling device disclosed in Japanese Patent No. 5227306. Inclined plate settling devices are used in devices and methods for producing compounds by precipitating solids from solution. Using a settling device with a tilted plate settling device, the physical and chemical properties of the solid particles formed during the precipitation can be adjusted very flexibly and independently of each other, tailor-made products Is produced with a very high space-time yield.

  The inclined plate settling device is connected to a reactor in which composite hydroxide is generated, and separates a high solid concentration slurry, a low solid concentration slurry consisting of an aqueous solution and fine particles from the slurry in the reactor, and a part of the slurry. Is a reactor-filter system (IRKS) that can be returned to the reactor. By using IRKS with an inclined plate settling device, the product slurry consisting of product and mother liquor after precipitation of the compound removes the mother liquor and particulates through the inclined plate settling device, thus increasing the solids concentration of the slurry.

  The reactor may be provided with an opening through which the slurry may be removed, optionally with a pump or by overflow, and pumped back to the reactor. In order to obtain a homogeneous precipitation product, it is important that the starting materials are well mixed when charged into the reactor. This reactor can also be operated as a stirred reactor. In the precipitation process in IRKS in which the inclined plate settling device is installed, the temperature can be adjusted according to the object. The process temperature in IRKS is controlled by heating or cooling via a heat exchanger, if necessary.

  In order to enhance the separation performance of the inclined plate settling device, one or more lamellae can be mounted on which the solid particles move down the lamella after they reach the surface of the lamella by settling. Return to the slip-down reaction slurry. The lamella provided in the inclined plate settling device is schematically represented in FIGS.

The lamellae (2, 5) are arranged in a plane parallel to the floor surface in the inclined plate settling device (1, 4). A lamella is a rectangular plate that may be made of plastic, glass, wood, metal or ceramic. The thickness of the lamellae (2, 5) can be up to 10 cm, depending on the material and the product. Preferably, lamellae having a thickness of 0.5 cm to 5 cm, particularly preferably 0.5 cm to 1.5 cm are used. The lamellae (2, 5) are fixedly mounted in the inclined plate settling device (1, 4). These may be removable. In this case, they are put into the inclined plate settling device (1, 4) via a rail system (6) or groove (3) mounted on the side inside the inclined plate settling device (1, 4). It is done. The height of the rail system (6) may be designed to be adjustable, which gives the inclined plate settling device (1, 4) great flexibility with regard to the selection of the lamella (2, 5) spacing. The The inclined plate settling device may be configured in a cylindrical shape having a round cross section or a parallelepiped shape having a square cross section. In order for the particle slippage to function without obstruction of the inclined plate settling device, the angle of the inclined plate settling device is 20 ° to 85 °, preferably 40 ° to 70 ° and particularly preferably 50 ° to 60 ° with respect to the horizontal plane. It is. The inclined plate settling device may be attached to the reactor via a flexible joint. In this embodiment, the angle can be variably adjusted during the process.

  In order to better understand the functional mode of IRKS by the inclined plate settling device, it will be described in detail with reference to FIG. The solid particles (7) settle down at a constant rate in the inclined plate settling device, depending on their shape and size. For example, assuming Stokes friction, the settling velocity of spherical particles caused by effective gravity is proportional to the square of the particle diameter. This velocity overlaps with the upper component of the laminar flow velocity in the inclined plate settling device. All solid particles whose settling velocity is less than or equal to the upper component of the liquid stream cannot settle down to the surface of the lamella (8) or the floor of the tilted plate settling device, and eventually tilt It is discharged with the overflow of the plate settling device.

  If the particle settling velocity is greater than the upper component of the liquid stream, the downward movement of the particles occurs at a constant settling velocity. Whether the particles are discharged from the inclined plate settling device together with the fluid flow is determined by the constant flow rate of the liquid, the vertical distance between the particles and the lamella when entering the inclined plate settling device, and the inclination of the inclined plate settling device. Depends on length and tilt angle. Since it is easy to see that there is a critical particle radius r0, all particles with r> r0 are completely retained by the inclined plate settling device. A straight line (9) in FIG. 3 shows the trajectory of the particle having the limit radius r0. The trajectories of all particles with larger radii have a smaller angle with respect to the horizontal plane and thus reliably impinge on the lamella or floorboard. This means that these particles are retained. By adjusting the ratio in the inclined plate settling device, particularly the flow rate of the liquid, the upper limit of the particle diameter of the fine particles removed by overflow from the inclined plate settling device can be adjusted.

  As long as the overflow of the inclined plate settling device is returned to the stirred reactor via the circulation vessel, nothing changes in the entire system. When a part of the diluted slurry containing fine particles is taken out from the circulation container using the pump, a set part of the fine particles is discharged, and the particle size distribution can be directly controlled. Thereby the particle size as well as the particle size distribution can be controlled independently of other plant parameters.

  Of course, the solid concentration of the slurry in the reactor is simultaneously increased by extracting a dilute slurry whose solid concentration when entering the circulation vessel is usually 0.5 to 5% of the solid concentration in the reactor. . That is, the mother liquor is extracted together with the extraction of the fine particle content. This is usually desirable, but is not desirable when the solids concentration in the reactor should be kept at a low level and when the increase in solids concentration cannot be satisfactorily countered by adjusting the flow of other materials. Depending on the quantity and specification, this fines content can subsequently be mixed again with the product slurry. Separation in the reactor-filter-system is critical.

  In this case, in order to increase the solid concentration of the slurry, it is conceivable that the mother liquor is taken out of the circulation container through the filter element and directly pumped back to the reactor. Less mother liquor is removed when discharging the same amount of granules. At this time, particles whose particle size does not exceed 30% of the D50 value of the particle size distribution are called fine particles. It may also be advantageous to remove the mother liquor from the system in the circulation vessel via a filter element. This allows the solids content in the reactor to be increased, firstly to several times the stoichiometric solids concentration, and secondly the neutral salt concentration and solids concentration that may occur during the precipitation reaction. Can be achieved. The concentration ratio of solid to salt in the reactor depends on the possibility of removal of the mother liquor, e.g. not only by increasing the solid concentration at a constant salt concentration, but also by the presence of salt-free solvent in the reactor at a constant solid concentration. It can also be increased by adding and at the same time an equal volume of mother liquor is removed from the system via the filter element.

  The increase in IRKS flexibility with the inclined plate settling device and the achievement of additional degrees of freedom are explained in more detail for the general reaction AX + BY → AY solid + BX dissolution in both parameter salt concentration and solid content examples. The AX and BY represent the starting material in the starting material solution, and BX represents the salt dissolved in the mother liquor. AY represents the product that occurs as an insoluble solid. IRKS with an inclined plate settling device can be used for batch-type precipitation. Preferably, however, this IRKS is suitably used for precipitation processes in continuous operation.

  The inclined plate settling device further relates to a method for producing a compound by precipitation, wherein individual process parameters such as (concentration of starting material, solid content in the slurry, salt concentration in the mother liquor) are settling. Tailor-made products that are adjusted independently of each other in this way, and thus control the particle size distribution during the precipitation process, and finally have the defined physical properties, especially economically and very high space-time yields Manufactured by.

The object of the inclined plate settling device is therefore a process for the production of compounds by precipitation comprising the following steps:
Providing at least a first, second and third starting material solution;
Combining at least the first, second and third starting material solutions in the reactor;
Generating a reaction zone that is homogeneously mixed in the reactor;
-Precipitating the compound in the reaction zone to produce a product slurry consisting of insoluble product and mother liquor,
A step of partially separating the mother liquor from the precipitated product via an inclined plate settling device;
A step of producing a precipitated product slurry in which the concentration of the precipitated product is higher than the stoichiometric concentration;
-Removing the product slurry from the reactor;
-Filtering, washing and drying the precipitated product.

  The starting material solution in the inclined plate settling process is conducted into the reactor using a pump system. If this is IRKS with a tilted plate settling device equipped with a stirred reactor, the starting materials are mixed using a stirrer. If IRKS is designed in the form of a jet reactor, the starting materials are mixed by a jet coming out of the nozzle. In order to achieve even better mixing of the starting materials, additionally air or inert gas may be passed into the reactor. Already during the mixing or homogenization of the starting material, a precipitation reaction is initiated in which product and mother liquor are generated. The product slurry is concentrated to the desired concentration at the bottom of the reactor. In order to achieve an intentionally high concentration of the product slurry, in the method with the inclined plate settling device, the mother liquor is partially removed via the inclined plate settling device. Preferably, the partial separation of the mother liquor by removing the overflow from the inclined plate settling device is performed using a pump.

  According to the method with the inclined plate settling device, a concentration of the precipitated product slurry is achieved which can be several times the stoichiometrically possible concentration of the precipitated product. This can be up to 20 times higher than the possible stoichiometric value. In order to achieve a particularly high product concentration in the slurry, it is necessary to partially remove a large amount of mother liquor. On the contrary, up to 95% of the mother liquor can be partially separated. The amount of mother liquor to be partially separated depends on the process parameters selected, such as starting material concentration, mother liquor salt concentration, and slurry solids concentration.

  In the precipitation step of the present invention, such an inclined plate settling device can be combined with a reactor as shown schematically in FIG. 4 to produce a composite hydroxide.

  An independent pipe and pumps (23) to (27) are installed in a reactor (13) equipped with a paddle blade (10), a heat exchanger (11), and an inclined plate settling device (12) as a stirring device capable of controlling the rotation speed. ) Is connected. An integrated reactor in which a mixed aqueous solution (metal aqueous solution) of nickel sulfate and cobalt sulfate, an alkali regulator (caustic soda aqueous solution), a complexing agent (ammonia water), and pure water are continuously provided from each of the pumps (23) to (26). -Conveyed into the reaction zone of the filter-(IRKS). Slurry generated in the reactor (13) is taken out via a liquid level regulator using a pump (14). It may be advantageous to operate the circulation pump (16) to prevent the risk of settling when large particles are produced.

  The pump (17) can carry the slurry with very low concentrations of fine particles into a circulation vessel (18) equipped with a stirrer and from there back into the reactor (13). Only particles below the separation size depending on the liquid volume flow rate and the sizing of the inclined plate settling device are conveyed into the circulation vessel (18). As long as all the turbid stream removed using the pump (17) is returned via the slurry stream (19), nothing changes for the reactor (13).

  It is also possible to remove the mother liquor and / or solid particles from the system by removing the clear mother liquor from the circulation vessel (18) and transporting it into the second circulation vessel (20). The pump (21) takes the clear mother liquor from the first circulation vessel (18) and conveys it into the second circulation vessel (20). The pH value of the solution in the second circulation vessel (20) can be continuously analyzed, and the composition of the mother liquor can be controlled in the entire coprecipitation reactor. In addition, by discharging the clear mother liquor accumulated in the first circulation vessel (18) by the pump (22), it is possible to remove very fine precipitates contained in the clear mother liquor from the precipitation reactor.

  When producing a precursor that gives particles of the lithium metal composite oxide of the present invention using such an inclined plate settling device, the temperature of the reaction solution is set to 40 ° C to 70 ° C, preferably 45 ° C to 65 ° C. The rotational speed of the paddle blade is controlled to 450 rpm to 1000 rpm, preferably 500 rpm to 800 rpm, and the slurry concentration is controlled to 100 g / L or more, preferably 100 g / L to 400 g / L.

  (1-4 Separation and Drying of Composite Hydroxide) When the target amount of raw material has reacted in the reactor, the slurry is taken out from the outlet of the reactor and filtered. In this way, the solid fraction containing the composite hydroxide is separated. Further, this solid fraction is washed. Washing may be carried out in accordance with a conventional method, and washing is performed using an alkaline aqueous solution and pure water until the sulfate and alkali components contained in the composite hydroxide are sufficiently removed. In this way, the composite hydroxide containing moisture is separated.

  Next, the separated composite hydroxide containing moisture is dried. The drying method may be any of hot air drying under atmospheric pressure, infrared drying, high frequency drying, vacuum drying, and the like. Vacuum drying which can be dried in a short time is preferable. Dry until the water content in the composite hydroxide is about 1% by weight. Thus, a nickel-cobalt composite hydroxide powder as a precursor is obtained.

[2 Firing]
A lithium raw material and a raw material compound of aluminum as a trace element are added to the precursor powder and fired in the presence of oxygen. Aluminum hydroxide is generally used as the aluminum raw material. As the lithium raw material, lithium hydroxide powder or lithium carbonate powder is generally used. The precursor powder, the aluminum raw material, and the lithium raw material have an element ratio of Li, Ni, Co, and Al contained in these raw materials, the composition Li _a Ni _b Co _c Al _d O ₂ (where a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005 to 0.1, and b + c + d = 1). To do. Mixing is performed by applying shear force using various mixers. Although there is no restriction | limiting in the baking furnace used when baking, A tubular furnace, a muffle furnace, RK (rotary kiln), RHK (roller hearth kiln), etc. are preferable. A particularly preferred firing furnace is RHK.

  Firing can also be performed multiple times. In any of the firings, the reaction is completed by holding at the maximum temperature for 2 to 30 hours. In order to obtain particles of the lithium metal composite oxide of the present invention, the firing temperature is in the range of 450 ° C. to 900 ° C., preferably 600 ° C. to 850 ° C., and the total firing time is 2 hours to 20 hours, preferably 3 Bake for a period of time to 15 hours.

[3 Treatment with aqueous solution of organometallic salt]
The positive electrode active material used in the present invention can be obtained by treating the lithium metal composite oxide produced above with an aqueous solution of an organic metal salt. The “organometallic salt” as used in the present invention refers to a water-soluble salt of an organic acid and a metal, and such an organic metal salt is not particularly limited. For example, lithium acetate, sodium acetate, potassium acetate, magnesium acetate, acetic acid Calcium, ammonium acetate, aluminum acetate, sodium sorbate, potassium sorbate, calcium sorbate, sodium 2-ethylhexanoate, potassium 2-ethylhexanoate, calcium 2-ethylhexanoate, cobalt 2-ethylhexanoate, 2- Manganese ethylhexanoate, lithium butyrate, sodium butyrate, potassium butyrate, magnesium butyrate, calcium butyrate, ammonium butyrate, lithium benzoate, sodium benzoate, potassium benzoate, magnesium benzoate, calcium benzoate, ammonium benzoate, benzoate Aluminum, sodium para-toluene sulfonic acid, such as potassium p-toluenesulfonic acid is used. Among these, sodium paratoluenesulfonate is most preferably used.

  The treatment with the aqueous solution of the organic metal salt is performed by bringing the lithium metal composite oxide produced above and the aqueous solution in which the organic metal salt is dissolved into contact, filtering and drying. Specifically, a method in which a lithium metal composite oxide is added to an aqueous solution of an organic metal salt and agitated, a lithium metal composite oxide layer is formed on the filter medium, and an aqueous solution of the organic metal salt is poured on the lithium metal composite oxide layer. The method etc. are mentioned and the contact by stirring is used preferably.

  The concentration of the aqueous solution of the organic metal salt is not particularly limited, but is preferably more than 0.5 wt% and 20 wt% or less, more preferably more than 1 wt% and 20 wt% or less, particularly preferably more than 1 wt% and more than 10 wt%. % Or less. The weight ratio of the lithium metal composite oxide to the aqueous solution of the organic metal salt is 2 parts by weight or more and less than 30 parts by weight, preferably 3 parts by weight or more and 20 parts by weight with respect to 10 parts by weight of the lithium metal composite oxide. Less than 5 parts by weight, more preferably 5 parts by weight or more and less than 15 parts by weight, and particularly preferably 6 parts by weight or more and less than 13 parts by weight. After the treatment with an aqueous solution of an organic metal salt, filtration and drying are performed. For the filtration, a known method such as suction filtration or pressure filtration can be used, and for drying, in an air stream containing oxygen, preferably 200 ° C. to 800 ° C., more preferably 300 ° C. to 700 ° C., still more preferably 400 Dry at a temperature of from 600C to 600C.

  The residual LiOH contained in the lithium metal composite oxide powder for a lithium ion battery positive electrode active material of the present invention is reduced to 0.5% by weight or less. The treatment with the organic metal salt aqueous solution according to the present invention can be reduced without excessively removing the alkaline substance remaining on the surface of the positive electrode active material, which is a cause of gas generation. It has been found that the treatment suppresses gas generation accompanying charging / discharging and contributes to an increase in discharge capacity and improvement of cycle characteristics. In order to reduce the alkaline substance remaining on the surface of the positive electrode active material, it is common to carry out a water washing treatment using pure water. However, the treatment with the aqueous solution of the organometallic salt in the present invention is performed under milder conditions. Thus, damage to the positive electrode active material due to washing with water can be suppressed. This is because, in the case of washing with pure water, lithium ions present in the positive electrode active material crystals are exchanged with hydrogen ions, and the battery performance is lowered due to the destruction of the layered crystal structure accompanying dehydration in the subsequent drying process. On the other hand, in the treatment with the aqueous solution of the organic metal salt, it can be inferred that the ions contained in the aqueous solution suppress the exchange with hydrogen ions and suppress the destruction of the crystal structure. Furthermore, in the treatment with an aqueous solution of an organic metal salt, the ions contained in the salt change the composition of the positive electrode active material to a more stable composition, which is considered to contribute to the stabilization of the crystal structure during repeated charge and discharge. .

The average particle diameter (volume average diameter) of the particles of the lithium metal composite oxide of the present invention is more than 13.1 μm and less than 21 μm, preferably more than 13.1 μm and less than 20 μm, more preferably more than 13.1 μm. It is less than 18 μm. The specific surface area of the BET method according to nitrogen adsorption of the particles of the lithium-metal composite oxide of the present invention is 0.7m less than ² / g exceed 0.2 m ² / g, preferably greater than 0.25 m ² / g 0.65 m ² / g or less, more preferably 0.3 m ² / g and 0.6 m ² / g or less. When the powder comprising the lithium metal composite oxide particles of the present invention is used as the positive electrode active material because the average particle size and specific surface area are in the above ranges, a lithium ion battery having a high discharge capacity and excellent cycle characteristics can be obtained. It is done.

  The lithium metal composite oxide powder for a lithium ion battery positive electrode active material of the present invention has an average particle diameter (volume average diameter) and a specific surface area within a specific range, and as described above, compared with the examples described later. As can be seen from the examples, the treatment with the organic metal salt aqueous solution has at least a surplus alkaline substance removed from the surface thereof at an appropriate level in a state where the side effect is suppressed. Such a lithium metal composite oxide powder for a lithium ion battery positive electrode active material of the present invention is novel and exhibits performance as a positive electrode active material that is exceptionally superior to conventional products. However, how the chemical or physical characteristics of the lithium metal composite oxide powder change due to the treatment of the organic metal salt is expressed by an absolute or general index (for example, observation results by various general-purpose analytical instruments). This is difficult with the current technical level. Accordingly, the expression “treated with an aqueous solution of an organic metal salt” must be used as one of the characteristics defined by the lithium metal composite oxide powder for a positive electrode active material of the lithium ion battery of the present invention.

[Lithium ion battery positive electrode active material]
The obtained powder composed of lithium metal composite oxide particles can be used alone as a positive electrode active material of a lithium ion battery. Alternatively, a mixture of other positive electrode active materials for lithium ion batteries may be used as the positive electrode active material. Further, a plurality of types of lithium metal oxide powders having different particle sizes and compositions may be produced by the production method of the present invention, and a mixture thereof may be used as the positive electrode active material.

  When the lithium metal composite oxide powder for a lithium ion battery positive electrode active material of the present invention is used as a positive electrode active material, an initial discharge capacity of 180 mAh / g or more in a coin battery manufactured under the conditions used in Examples described later, A cycle retention rate of 95% or higher can be achieved.

[Example 1]
The following raw material solutions and other reaction liquids were prepared.
-(Metal salt aqueous solution) A mixed aqueous solution in which 84 parts by weight of nickel sulfate aqueous solution containing nickel at a concentration of 8.2% by weight and 16 parts by weight of cobalt sulfate aqueous solution containing cobalt at a concentration of 8.2% by weight were mixed.
(Complexing agent) Aqueous ammonia containing ammonia at a concentration of 25% by weight (pH adjusting agent) A sodium hydroxide aqueous solution containing sodium hydroxide at a concentration of 25% by weight.
・ Pure water A sodium sulfate aqueous solution having a concentration of 16% by weight was filled in the precipitation tank shown in FIG. 4, and the stirring rotation speed was maintained at 400 rpm and the temperature of the reaction liquid was maintained at 65 ° C. while circulating the aqueous solution through the inclined plate settling device. . The metal salt aqueous solution, the complexing agent, and the pH adjusting agent were separately supplied to initiate the coprecipitation reaction.

  The pH of the reaction solution was controlled within the range of 11.0 or more and 11.5 to advance the complex hydroxide formation reaction. The mother liquor and the slurry were extracted until the solid concentration reached 200 g / L and further stabilized. After continuous operation of the precipitation process equipment for 72 hours from the start of supply of raw materials, collection of the slurry containing the composite hydroxide was started. The slurry was extracted through the pump 14. The obtained composite hydroxide slurry was filtered and washed to obtain a composite hydroxide having an average particle size of 12.5 μm. This was dried in vacuum at 120 ° C. Thus, a nickel-cobalt composite hydroxide powder was obtained as a precursor.

100 g of aluminum hydroxide and 504.2 g of lithium hydroxide per 1900 g of the nickel-cobalt composite hydroxide were added and mixed while applying a shearing force twice. 4000 g of the above mixture was taken and filled in a ceramic sagger for firing. The mixture filled in the mortar was fired in oxygen at 750 ° C. for 11 hours. The fired product was crushed to obtain lithium metal composite oxide powder having a composition of Li _1.015 Ni _0.80 Co _0.15 Al _0.05 O ₂ .

  100 g of the above lithium metal composite oxide was immersed in 100 g of a 1 wt% aqueous solution of sodium paratoluenesulfonate (PTSNA), stirred for 3 minutes, filtered by suction, and dried at 500 ° C. in oxygen. In this way, a PTSNA-treated lithium metal composite oxide was obtained. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery. The active material powder and the coin battery were evaluated by the methods shown below.

  (Average particle diameter) The obtained lithium metal composite oxide was passed through a standard sieve having a nominal aperture of 53 μm as defined in JIS Z8801-1: 2006. However, when there was no aggregation of particles, it was sieved as it was, and when aggregation of particles was observed, it was sieved after pulverization with a mortar. The average particle diameter (D50) of the lithium metal composite oxide particles that passed through the sieve was measured using a laser scattering particle size distribution analyzer LA-950 manufactured by Horiba.

  (Specific surface area) About 10 g of the obtained lithium metal composite oxide was weighed and placed in a specific surface area measuring device (NOVA4200e manufactured by Cantachrome). After deaeration at 200 ° C., by nitrogen adsorption at liquid nitrogen temperature The specific surface area was measured by the BET method.

  (Measurement of pH) 2 g of the obtained lithium metal composite oxide was added to 100 ml of pure water at 25 ° C., stirred for 3 minutes with a magnetic stirrer, and then suction filtered. The pH of the obtained filtrate was measured with a pH meter manufactured by Horiba. The results are shown in Table 1.

  (Measurement of LiOH amount) 2 g of the obtained lithium metal composite oxide was added to 100 ml of pure water at 25 ° C., stirred for 3 minutes with a magnetic stirrer, and then suction filtered. 10 ml of the obtained filtrate was pipetted and titrated with 0.1N hydrochloric acid to quantify the lithium hydroxide content.

(Manufacture of battery) For 100 parts by weight of the obtained lithium metal composite oxide, 1 part by weight of acetylene black made by Denka, 5 parts by weight of graphite carbon made by Japanese graphite, and 4 parts by weight of polyvinylidene fluoride made by Kureha were prepared. A slurry was prepared using N-methylpyrrolidone as a dispersion solvent. This slurry was applied to an aluminum foil as a current collector, dried and pressed, a positive electrode, a lithium metal foil as a negative electrode as a negative electrode, and 1 mol / L LiPF ₆ ethylene carbonate and ethyl as an electrolyte. A CR2032-type coin battery was prepared using a solution of an equal amount mixture of methyl carbonate.

  (Initial discharge capacity) The capacity at the time of performing 0.1 C discharge between 4.3 V and 3.0 V was defined as the initial discharge capacity.

(Cycle maintenance rate) The ratio of the capacity of the 50th cycle to the capacity of the first cycle after 50 cycles of charge 1.0C and discharge 0.5C after confirming the initial discharge capacity is expressed by the following formula. The cycle maintenance rate was calculated.
Cycle maintenance ratio (%) = (discharge capacity at 50th cycle / discharge capacity at 1st cycle) × 100

[Example 2]
During the production of the positive electrode active material, the firing conditions of Example 1 were changed. That is, 100 g of aluminum hydroxide and 521.6 g of lithium hydroxide per 1900 g of nickel-cobalt composite hydroxide and mixing while applying shearing force were repeated twice. 4000 g of the above mixture was taken and filled in a ceramic sagger for firing. The mixture filled in the mortar was fired in oxygen at 730 ° C. for 9 hours. The fired product was pulverized to obtain a lithium metal composite oxide powder having a composition of Li _1.05 Ni _0.80 Co _0.15 Al _0.05 O ₂ . Otherwise, the same processing as in Example 1 was performed. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Example 3]
During the production of the positive electrode active material, the PTSNA treatment conditions of Example 1 were changed. That is, 100 g of the lithium metal composite oxide obtained in Example 1 was immersed in 100 g of a 4 wt% aqueous solution of PTSNa, stirred for 3 minutes, suction filtered and dried. In this way, a PTSNA-treated lithium metal composite oxide was obtained. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Example 4]
During the production of the positive electrode active material, the PTSNA treatment conditions of Example 2 were changed. That is, 100 g of the lithium metal composite oxide obtained in Example 2 was immersed in 100 g of a 4 wt% aqueous solution of PTSNa, stirred for 3 minutes, and then subjected to suction filtration and drying. In this way, a PTSNA-treated lithium metal composite oxide was obtained. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Example 5]
During the production of the positive electrode active material, the PTSNA treatment conditions of Example 1 were changed. That is, 100 g of the lithium metal composite oxide obtained in Example 1 was immersed in 100 g of an 8 wt% aqueous solution of PTSNa, stirred for 3 minutes, suction filtered and dried. In this way, a PTSNA-treated lithium metal composite oxide was obtained. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Example 6]
During the production of the positive electrode active material, the PTSNA treatment conditions of Example 2 were changed. That is, 100 g of the lithium metal composite oxide obtained in Example 2 was immersed in 100 g of an 8 wt% aqueous solution of PTSNa, stirred for 3 minutes, and then subjected to suction filtration and drying. Thus, a lithium metal composite oxide treated with PTSNa was obtained. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Comparative Example 1]
This is an example in which treatment with an aqueous solution of sodium paratoluenesulfonate was not performed. The stirring speed of the coprecipitation reaction of Example 1 was changed to 800 rpm, and the reaction temperature was changed to 50 ° C. to obtain a composite hydroxide having an average particle size of 5.0 μm. This was dried in vacuum at 120 ° C. Thus, a nickel-cobalt composite hydroxide powder was obtained as a precursor. Using this precursor, firing and pulverization of the fired product were performed under the same conditions as in Example 1, so that a lithium metal composite oxide having a composition of Li _1.015 Ni _0.80 Co _0.15 Al _0.05 O ₂ was obtained. A product powder was obtained. The lithium metal composite oxide was directly used as a positive electrode active material without being treated with an aqueous solution of sodium paratoluenesulfonate. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Comparative Example 2]
This is an example in which treatment with an aqueous solution of sodium paratoluenesulfonate was not performed. The stirring speed of the coprecipitation reaction of Example 1 was changed to 800 rpm, and the reaction temperature was changed to 50 ° C. to obtain a composite hydroxide having an average particle size of 5.0 μm. This was dried in vacuum at 120 ° C. Thus, a nickel-cobalt composite hydroxide powder was obtained as a precursor. Using this precursor, firing and pulverization of the fired product were performed under the same conditions as in Example 2 to obtain a lithium metal composite oxide having a composition of Li _1.05 Ni _0.80 Co _0.15 Al _0.05 O _2. A product powder was obtained. The lithium metal composite oxide was directly used as a positive electrode active material without being treated with an aqueous solution of sodium paratoluenesulfonate. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

[Comparative Example 3]
The firing conditions were changed in Example 3. That is, 100 g of aluminum hydroxide and 499.3 g of lithium hydroxide per 1900 g of nickel-cobalt composite hydroxide and mixing while applying shearing force were repeated twice. 4000 g of the above mixture was taken and filled in a ceramic sagger for firing. The mixture filled in the mortar was fired in oxygen at 790 ° C. for 10 hours. The fired product was pulverized to obtain a lithium metal composite oxide powder having a composition of Li _1.005 Ni _0.80 Co _0.15 Al _0.05 O ₂ . Otherwise, the same processing as in Example 3 was performed. Table 1 shows the evaluation results of the obtained positive electrode active material and the evaluation results of the coin battery.

  As Table 1 shows, the lithium metal composite oxide powder of the present invention has low alkalinity, and the average particle diameter and specific surface area are controlled. A lithium ion battery using such a lithium metal composite oxide powder of the present invention as a positive electrode active material of a lithium ion battery has a large discharge capacity and excellent cycle characteristics.

  The lithium metal composite oxide powder of the present invention has a large discharge capacity and is useful as a positive electrode active material of a lithium ion battery excellent in cycle characteristics. The present invention can contribute to the manufacture of a lithium ion battery having a large discharge capacity and excellent cycle characteristics.

DESCRIPTION OF SYMBOLS 1 Inclined plate settling apparatus 2 Lamella 3 Groove 4 Inclined plate settling apparatus 5 Lamella 6 Rail system 7 Solid particle 8 Lamella 9 Straight line 10 Paddle blade 11 Heat exchanger 12 Inclined plate settling apparatus 13 Reactor 14 Pump 15 Slurry flow 16 Circulation pump 17 Pump 18 Circulating container 19 Slurry flow 20 Circulating container 21 Pump 22 Pump 23 Metal aqueous solution supply pump 24 Complexing agent supply pump 25 pH adjuster supply pump 26 Pure water supply pump

Claims (4)

Composition Li _a Ni _b Co _c Al _d O ₂ (where a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005) A lithium metal composite oxide powder for a lithium ion battery positive electrode active material having a value of ˜0.1 and b + c + d = 1.
The powder has an average particle diameter (volume average diameter) of more than 13.1 μm and less than 21 μm;
The specific surface area of the BET method according to nitrogen adsorption of the powder exceeds 0.2 m ² / g, less than 0.9 m ² / g,
It is treated with an organic metal salt aqueous solution by contacting an aqueous solution in which an organic metal salt is dissolved in the lithium metal composite oxide, filtering, and drying .
Lithium metal composite oxide powder for lithium ion battery positive electrode active material. The lithium metal composite oxide powder for a lithium ion battery positive electrode active material according to claim 1, wherein the organic metal salt is potassium sorbate or sodium benzoate. Composition Li _a Ni _b Co _c Al _d O ₂ (where a = 0.8 to 1.2, b = 0.7 to 0.95, c = 0.02 to 0.2, d = 0.005) A lithium metal composite oxide powder for a lithium ion battery positive electrode active material having a value of ˜0.1 and b + c + d = 1.
The powder has an average particle diameter (volume average diameter) of more than 13.1 μm and less than 21 μm;
The specific surface area of the BET method according to nitrogen adsorption of the powder exceeds 0.2 m ² / g, less than 0.9 m ² / g,
The residual LiOH amount determined by the following method is 0.5% by weight or less,
(LiOH amount: 2 g of the calcined lithium metal composite oxide was added to 100 ml of pure water at 25 ° C., stirred for 3 minutes with a magnetic stirrer, and then suction filtered. 10 ml of the obtained filtrate was pipetted, The lithium hydroxide content was quantified by titrating with 0.1N hydrochloric acid.)
Moreover, a battery including a positive electrode active material made of the powder achieves an initial discharge capacity and a cycle maintenance ratio measured under the following conditions.
Lithium metal composite oxide powder for lithium ion battery positive electrode active material.
Initial discharge capacity: The capacity (initial discharge capacity) when performing 0.1 C discharge between 4.3 V and 3.0 V is 180 mAh / g or more.
-Cycle maintenance rate: The ratio of the capacity of the 50th cycle to the capacity of the first cycle after 50 cycles of the battery after confirming the initial discharge capacity are repeated at 1.0C charge and 0.5C discharge. The cycle maintenance ratio calculated by the formula is 95% or more.
Cycle maintenance ratio (%) = (discharge capacity at 50th cycle / discharge capacity at 1st cycle) × 100
(However, the batteries whose initial discharge capacity and cycle retention rate were measured were obtained by the following method.
-Battery production: Prepared to be 1 part by weight of acetylene black, 5 parts by weight of graphite carbon, and 4 parts by weight of polyvinylidene fluoride with respect to 100 parts by weight of the lithium metal composite oxide for the positive electrode active material of the lithium ion battery, -A slurry was prepared using methylpyrrolidone as a dispersion solvent. This slurry was applied to an aluminum foil as a current collector, dried and pressed as a positive electrode, a lithium metal foil as a negative electrode as a negative electrode, and 1 mol / L LiPF ₆ ethylene carbonate and ethyl as the electrolyte. A CR2032-type coin battery according to the International Electrotechnical Commission (IEC) standard was prepared using a solution of an equal amount mixture of methyl carbonate. ) The lithium ion battery using the positive electrode active material containing the lithium metal complex oxide powder of any one of Claims 1-3.

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