JP6616215B2 - Method for producing positive electrode active material for lithium ion battery - Google Patents

Description

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

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. A typical lithium-based metal oxide is obtained by substituting a part of cobalt atoms of LiCoO ₂ that is an initial positive electrode active material with Ni and further a trace amount of metal, and a transition metal composite hydroxide that is a precursor. It is obtained as a powder by firing a mixture of the product and the lithium compound. As the precursor, a precursor obtained by separating and drying a transition metal composite hydroxide obtained by introducing a transition metal salt into an aqueous solution whose pH is controlled is usually used.

  It is known that properties such as the particle size distribution of the precursor used for firing are largely involved in the performance of the lithium metal composite oxide powder as the positive electrode active material. 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 1 (Japanese Patent No. 5227306) discloses a nickel-cobalt composite hydroxide which is a so-called NC-based precursor having a spherical and regular particle shape using a reactor having an inclined plate settling device. Is described. The production method disclosed in Patent Document 1 is a highly versatile means for producing a composite hydroxide containing nickel and cobalt. However, the performance of the NCA-based positive electrode active material (element structure: Li (Ni, Co, Al) O ₂ ), which has attracted particular attention in recent years, greatly depends on the method of introducing aluminum into the NCA-based positive electrode active material. Nevertheless, it has not been fully optimized as a means for its production.

NCA-based positive electrode active materials have the advantage of being able to produce electrodes with a high energy density, and as a material for laminated batteries for mobile terminals and smartphones, and lithium-ion batteries for automobiles, which are rapidly becoming smaller and higher capacity in recent years. Expected. The NCA-based positive electrode active material is obtained by substituting a part of cobalt atoms of LiCoO ₂ with nickel and a small amount of aluminum, and adding an aluminum compound and a lithium compound to a nickel / cobalt composite hydroxide which is an NC precursor. Or a mixture obtained by adding a lithium compound to nickel-cobalt-aluminum composite hydroxide. In the production of nickel-cobalt-aluminum composite hydroxides, nickel sulfate is generally used as the nickel raw material, cobalt sulfate is used as the cobalt raw material, and aluminum sulfate or sodium aluminate is used as the aluminum raw material. Sodium aluminate is preferably used from the viewpoint that the amount of carbon dioxide brought in is small and the electrode density can be increased.

  In the precursor production apparatus and precursor production method disclosed in Patent Document 1, various conditions are optimized exclusively for producing nickel-cobalt composite hydroxide. These prior arts do not specifically consider the case where a small amount of sodium aluminate is added as a precursor raw material. Since it is necessary to strictly control requirements such as particle size distribution, which is known to affect battery performance even with NCA-based positive electrode active materials, it produces superior NCA-based positive electrode active materials using sodium aluminate as an aluminum raw material. In order to achieve this, it is necessary to re-examine the production conditions for nickel-cobalt-aluminum composite hydroxide and redesign the equipment and process.

  Patent Document 1 relates to an apparatus owned by the applicant himself, but is designed to be suitable for manufacturing a precursor of an NCA-based positive electrode active material only because it “expands the degree of freedom and creates a new degree of freedom”. I found out that it was not.

  Further, for example, in Patent Document 2 (Japanese Patent Laid-Open No. 2011-181193), for example, in the production of nickel-cobalt composite hydroxide particles containing an additive element M such as Al, the pH, temperature, and ammonia concentration of the reaction solution are controlled. Increasing the particle size and improving the uniformity of the particle size are described. However, Patent Document 2 does not specifically describe a production example of a nickel / cobalt / aluminum composite hydroxide which is a precursor of an NCA-based positive electrode active material. Even in the technique disclosed in Patent Document 2, optimization of the production of the precursor of the NCA-based positive electrode active material has not been sufficiently studied.

Japanese Patent No. 5227306 JP 2011-181193 A

  An object of the present invention is to produce a nickel-cobalt-aluminum composite hydroxide useful as an excellent precursor of an NCA-based positive electrode active material, and to produce an NCA-based positive electrode active material using such a precursor. In particular, the present invention aims to optimize the production of an NCA-based positive electrode active material using sodium aluminate as an aluminum raw material.

  The present inventors reviewed the enormous conditions in the production of nickel-cobalt-aluminum composite hydroxide. As a result, it has been found that a nickel / cobalt / aluminum composite hydroxide that provides an excellent positive electrode active material can be obtained by limiting the supply method of the raw material nickel compound, cobalt compound, and aluminum compound. In the present invention, the initial charge / discharge efficiency and the rate are maintained by using a precursor of a positive electrode active material synthesized by supplying nickel compounds, cobalt compounds, and aluminum compounds to the reactor through different channels in the precipitation step. We have succeeded in producing an NCA-based positive electrode active material having a high rate and suppressed gas generation.

That is, the present invention is as follows.
(Invention 1) Precipitation step for producing nickel / cobalt / aluminum coprecipitated hydroxide by sucking, separating and circulating the composite hydroxide slurry using a reactor equipped with stirring means, nickel / cobalt / aluminum composite hydroxide In the above precipitation step, an aqueous nickel sulfate solution as a nickel raw material and an aqueous cobalt sulfate solution as a cobalt raw material are fed into a reactor in independent and separate flow paths. A composition Li _a Ni _b Co _c Al _d O ₂ (provided by supplying sodium aluminate, an aqueous sodium hydroxide solution, and aqueous ammonia as an aluminum raw material to the reactor through different independent channels, respectively) 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)), wherein the reactor used in the precipitation step is an inclined plate. Having a settling device, adapted for intimate mixing of the starting material solution upon introduction into the reaction zone of the reactor, wherein the inclined plate settling device is connected directly to the reaction zone And is connected to at least one circulation vessel via at least one pump and draws a turbid liquid from the product suspension in the reactor to the at least one circulation vessel. After removing the solid fines from the liquid through the filter element, the liquid is removed from the circulation vessel and directly pumped back to the reactor. A method for producing a lithium / nickel / cobalt / aluminum oxide powder for a positive electrode active material for a lithium ion battery, wherein the particle size distribution of the product suspension in the reactor is shifted to a higher D50 value.

  According to the present invention, a lithium ion battery having high initial charge / discharge efficiency and rate maintenance rate and suppressed gas generation is provided.

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

[Preparation of Precursor Raw Material] The present invention provides a 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). 0.2, d = 0.005 to 0.1, and b + c + d = 1.) A method for producing a lithium / nickel / cobalt / aluminum oxide powder. In the production method of the present invention, first, a nickel / cobalt / aluminum composite hydroxide which is a precursor of the lithium / nickel / cobalt / aluminum oxide powder is produced.

  In this invention, nickel sulfate aqueous solution (henceforth "a liquid") is used as a nickel raw material. The concentration of solution a is preferably as high as possible, but considering the precipitation of nickel sulfate crystals due to temperature fluctuations, it is preferably adjusted to a concentration of 15 wt% to 30 wt%, more preferably 20 wt% to 25 wt%. Is done. In the present invention, an aqueous cobalt sulfate solution (hereinafter “b solution”) is used as the cobalt raw material. The higher the concentration of solution b, the better. However, the concentration is preferably 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. Liquid a and liquid b are prepared separately and stored in separate containers.

  Sodium aluminate is used as the aluminum raw material. Sodium aluminate is supplied as an aqueous solution (hereinafter “liquid c”) having a concentration of 1% by weight to 50% by weight, preferably 1% by weight to 20% by weight.

  In the coprecipitation reaction, an aqueous sodium hydroxide solution as a pH regulator and ammonia water as a complexing agent are supplied. These are supplied to the reactor through a different flow path from the liquid a, liquid b, and liquid c.

  [Precipitation step] Liquids a, b and c, which are precursor raw materials, are supplied to a reactor to produce a nickel / cobalt / aluminum composite hydroxide (hereinafter referred to as “composite hydroxide”). 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. Although there will be no restriction | limiting if the temperature of a reaction liquid is a temperature which a composite hydroxide produces | generates, The range of 40 to 60 degreeC is common on production efficiency. 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.

  The reactor is connected to different supply paths for liquid a, liquid b and liquid c. The reactor is further provided with a pH regulator (aqueous sodium hydroxide solution), a complexing agent (ammonia water), and a pure water supply path. Each supply path is composed of a normal pipe, a pump, and a flow rate sensor, and the supply amount is controlled. These feed lines are generally connected to the top of the reactor.

  Stirring means is provided inside the reactor. There is no particular limitation on the stirring means. As long as the impeller is controlled by a motor, various shapes such as a propeller, a paddle, a flat paddle, a turbine, a cone, a screw, and a ribbon can be used. The particle shape of the composite hydroxide can be adjusted by controlling the stirring speed. The stirring rotation speed is not particularly limited as long as the composite hydroxide is formed in the form of fine particles, but is generally controlled within a range of 300 rpm to 800 rpm, preferably 400 rpm to 700 rpm when a paddle blade is used. .

  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 / aluminum 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 apparatus) for separating the composite hydroxide slurry into a solid fraction and a liquid fraction 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. The separation mechanism separates the composite hydroxide slurry into a solid fraction composed of nickel / cobalt / aluminum composite hydroxide particles and a liquid fraction composed of aqueous solution and nickel / cobalt / aluminum composite hydroxide particles. The A part of the separated liquid fraction is discharged out of the reactor, and the remaining liquid fraction and solid fraction 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.

  It is efficient to perform such suction, separation and circulation of the composite hydroxide slurry 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 target of the inclined plate settling device is connected to a reactor where composite hydroxide is generated, and the slurry in the reactor is separated, the liquid fraction composed of the solid fraction, aqueous solution and fine particles is separated, and the slurry is separated. It is a body-type reactor / clarifier system (IRKS) that can be partially returned to the reactor.

  The use of IRKS with a tilted plate settling device increases the solids concentration as the mother liquor and particles are removed via the tilted plate settling device in the formation of a product suspension consisting of the product and the mother liquor after compound precipitation. Is achieved.

  The reactor may be provided with an opening through which the suspension can be removed, optionally using a pump, and pumped back to the reactor. In order to obtain a homogeneous precipitation product, it is important that the starting materials are well mixed upon charging into the reactor. This reactor can also be operated as a stirred reactor. The precipitation process in IRKS equipped with an inclined plate settling device can adjust the temperature depending on the product. The process temperature in IRKS is controlled by heating or cooling via a heat exchanger, if necessary.

  IRKS is used for the separation of compounds from the slurry. In the inclined plate settling device, the mother liquor is separated from the product suspension along with the fines fraction. This turbid liquid containing trace amounts of solids is mostly returned to the reactor and recombined with the product suspension. By removing a portion of this turbid liquid, the fines fraction is removed from the product suspension and the particle size distribution is shifted to a higher D50 value. A further purpose of the inclined plate settling device is to provide a liquid with a pre-cleaned slurry and a low solids content, from which a clear mother liquor can be separated by a simple method such as filtration.

  To enhance the separation performance of the inclined plate settling device, one or more lamellae can be attached, on which the solid particles move downward after they reach the surface of the lamella by settling. Slide down into the homogeneously mixed suspension. 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 to 5 cm, particularly preferably 0.5 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 slip-off 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. 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 along with the overflow 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 leaving the inclined plate settling device in the overflow 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 using a pump to remove from the circulation vessel a part of the turbid liquid volume due to the fine content of solids, a defined fraction of fines is discharged and can directly interfere with the particle size distribution. Thereby the particle size as well as the particle size distribution can be influenced independently of other plant parameters.

  Of course, at the same time, the solids concentration of the suspension in the reactor is simultaneously with this removal of a turbid stream with a solids concentration of 0.5-5% solids in the reactor as it enters the circulation vessel. This is because, with the intentional removal of the fines content, a large amount of mother liquor is unbalanced from the entire system. This is usually desirable, but is not desirable when the solids concentration in the reactor is to be kept at a low level and when the increase in solids concentration cannot be satisfactorily countered by regulating the flow of other materials. Depending on the quantity and specification, this fine content can subsequently be mixed again with the product suspension. Separation in the reactor-clarifier-system is critical.

  In this case, in order to increase the solid concentration of the turbid material, it is conceivable that the mother liquor is taken out of the circulation vessel through the filter element and directly pumped back to the reactor. Less mother liquor is removed when discharging the same amount of granules. Particles whose 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 simultaneously removing an equal volume of mother liquor 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 dissolved salt 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 precipitation carried out batchwise. Preferably, however, this IRKS is suitably used for precipitation processes in continuous operation.

  The inclined plate settling device further relates to a process for the production of compounds by precipitation, in which the individual process parameters such as (concentration of starting material, solid content in suspension, salt concentration in mother liquor) are: Custom-made products that are regulated independently of one another during precipitation, thus providing controlled interference with the development of the particle size distribution during the precipitation process, and finally having defined physical properties are particularly economical And very high space-time yields.

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 the at least first, second and third starting material solutions in the reactor of claim 1;
Generating a reaction zone that is homogeneously mixed in the reactor;
The step of precipitating the compound in the reaction zone to produce a product suspension consisting of insoluble product and mother liquor,
-Partly separating the mother liquor from the precipitated product via an inclined plate settling device;
Producing a precipitation product suspension in which the concentration of the precipitation product is higher than the stoichiometric concentration,
Removing the product suspension 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. In order to achieve a uniform product quality, it is necessary that the starting materials are homogeneously mixed in the reaction zone of 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 suspension is enriched to the desired concentration in the lower reactor. In order to achieve the intentional enrichment of the product suspension, the mother liquor is partly removed via the inclined plate settling device in the method using 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 suspension is achieved which can be many 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 suspension, 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 selected process parameters, such as the starting material concentration, the salt concentration of the mother liquor, and the solids concentration of the suspension.

  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.

  A reactor (13) equipped with a stirrer (10) capable of controlling the number of revolutions, a heat exchanger (11), and an inclined plate settling device (12), and comprising independent pipes and pumps (23) to (27). Supply path is connected. Continuous reaction of nickel sulfate aqueous solution (liquid a), cobalt sulfate aqueous solution (liquid b), sodium aluminate aqueous solution (liquid c), sodium hydroxide aqueous solution, and aqueous ammonia from each of the pumps (23) to (27). Into the reactor-clarifier-system (IRKS) reaction zone. 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.

  [Separation / Drying of Composite Hydroxide] When the target amount of the raw material has been 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, the 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 / aluminum composite hydroxide powder as a precursor is obtained.

  [Baking] A lithium raw material is added to the precursor powder, and baking is performed in the temperature range of 450 to 900 ° C. in the presence of oxygen. As the lithium raw material, lithium hydroxide powder or lithium carbonate powder is generally used. Firing can also be performed multiple times. What is the maximum temperature for 2 hours in any firing? Hold for 30 hours to complete the reaction. 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. The fired product is appropriately washed with water, pulverized and dried to obtain the desired lithium / nickel / cobalt / aluminum composite oxide powder.

  [Positive electrode active material] The obtained lithium / nickel / cobalt / aluminum oxide powder can be used alone as a positive electrode active material. 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 / nickel / cobalt / aluminum 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.

  [Battery Production] The positive electrode active material thus obtained, carbon black as a conductive additive, a binder, and a solvent are mixed to prepare a positive electrode mixture, and this positive electrode mixture is applied to a current collector and dried. Thus, the positive electrode of the lithium ion battery can be manufactured. A laminated battery obtained by laminating and encapsulating a thin film positive electrode using an aluminum foil as a current collector together with a thin film negative electrode and an electrolyte is useful as a lithium ion battery that meets the demand for miniaturization.

[Example 1] The following raw material solutions and other reaction liquids were prepared.
Solution a: nickel sulfate aqueous solution containing nickel at a concentration of 8.2% by weight (nickel sulfate concentration: 21.6% by weight).
Liquid b: A cobalt sulfate aqueous solution containing cobalt at a concentration of 8.2% by weight (cobalt sulfate concentration: 21.6% by weight).
Liquid c: An aqueous sodium aluminate solution containing aluminum at a concentration of 3.3% by weight (sodium aluminate concentration: 10% by weight).
(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 The sodium sulfate aqueous solution with a concentration of 16% by weight was filled in the precipitation tank shown in FIG. 4, and the stirring rotation speed was maintained at 550 rpm and the reaction liquid temperature was maintained at 65 ° C. while circulating the aqueous solution through the inclined plate settling device. . The liquid a, liquid b, liquid c, and other materials were separately supplied so that the atomic ratio of nickel: cobalt: aluminum was 82: 16: 2, and the coprecipitation reaction was started.

  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. This was dried at 80 ° C. in the atmosphere. Thus, a nickel / cobalt / aluminum composite hydroxide powder was obtained as a precursor.

A mixture of 132 g of the obtained precursor and 27.6 g of lithium hydroxide was mixed while applying a shearing force, and 60 g of the obtained powder mixture was taken and filled in an alumina boat for firing. The mixture filled in the mortar was held in oxygen at 790 ° C. for 5 hours, then cooled to room temperature, further heated to 770 ° C. and held for 4 hours for firing. The fired product was crushed, washed with water, and dried. Thus, a lithium / nickel / cobalt / aluminum composite oxide powder having the composition Li _1.02 Ni _0.82 Co _0.16 Al _0.02 O ₂ was obtained.

  Using the lithium / nickel / cobalt / aluminum oxide powder as a positive electrode active material, a positive electrode and a laminate battery were produced and evaluated as follows. The results are shown in Table 1.

  (Production of Positive Electrode) 100 parts by weight of the obtained positive electrode active material, 1 part by weight of acetylene black as a conductive auxiliary agent and 5 parts by weight of graphite carbon, 4 parts by weight of polyvinylidene fluoride as a binder, N-methyl as a dispersion medium A positive electrode mixture was obtained by mixing with pyrrolidone. This positive electrode mixture was applied to an aluminum foil as a current collector in a thickness of 50 μm and dried to produce a positive electrode.

(Manufacture of laminate battery) 98 parts by weight of artificial graphite (MAG-D), 1 part by weight of carboxymethyl cellulose (CMC) as a binder and 1 part by weight of styrene butadiene copolymer (SBR) were mixed together with water as a dispersion medium. Thus, a negative electrode mixture was obtained. This negative electrode mixture was applied to a copper foil as a current collector and dried to produce a negative electrode. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinyl carbonate (VC) in which LiPF ₆ is dissolved at a concentration of 1 mol / L, the weight ratio (EC: EMC: VC) is 50: 50: 1. To prepare an electrolytic solution. A laminate battery was manufactured by laminating and enclosing the above positive electrode, negative electrode, and electrolyte.

(Initial Discharge Capacity and Initial Charge / Discharge Efficiency) The capacity when charging at a rate of 0.1 C between 3.0 and 4.2 V was defined as the initial charge capacity. The capacity when performing 0.1 C discharge between 4.2 V and 3.0 was defined as the initial discharge capacity. The initial charge / discharge efficiency was determined by the following formula.
Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) × 100

(Rate maintenance rate) After charging the battery after confirming the initial charge / discharge capacity at the 0.2C rate, the discharge capacity when discharging at the 0.2C rate was defined as the discharge capacity at 0.2C. Thereafter, after charging at a 0.2 C rate, the discharge capacity when discharging at a 2.0 C rate was defined as a discharge capacity at 2.0 C. The rate maintenance rate was calculated by the following formula.
Rate maintenance rate (%) = (2.0 C discharge capacity ÷ 0.2 C discharge capacity) × 100

(Gas generation amount) After charging to 4.2 V at a rate of 0.1 C, the volume of the laminate cell is measured by the Archimedes method (MDS300 type, manufactured by Alpha Mirage). The laminate cell was stored in a thermostatic bath at 85 ° C. for 72 hours, and then the volume was measured again by the Archimedes method, and the amount of gas generated was calculated from the degree of increase in the laminate cell volume.
Gas generation amount (cc / g) = (volume after storage−volume before storage) ÷ weight of positive electrode active material

[Example 2] A composite hydroxide as in Example 1 except that the coprecipitation reaction was started by supplying the raw materials separately such that the atomic ratio of nickel: cobalt: aluminum was 80: 15: 5. Manufactured. Through the same firing step as in Example 1, a lithium / nickel / cobalt / aluminum composite oxide powder having the composition Li _1.02 Ni _0.80 Co _0.15 Al _0.05 O ₂ was obtained. The results of analyzing and evaluating this in the same manner as in Example 1 are shown in Table 1.

Example 3 A composite hydroxide was produced under the same conditions as in Example 1. Firing was performed under the same conditions as in Example 1 except that a powder mixture composed of 132 g of the obtained composite hydroxide and 28.5 g of lithium hydroxide was used. A lithium / nickel / cobalt / aluminum composite oxide powder having the composition Li _1.05 Ni _0.82 Co _0.16 Al _0.02 O ₂ was obtained. The results of analyzing and evaluating this in the same manner as in Example 1 are shown in Table 1.

  [Comparative Example 1] Instead of the liquid a and liquid b used in Example 1, a mixed aqueous solution of nickel and cobalt was used. That is, a nickel sulfate aqueous solution having a nickel concentration of 8.2% by weight and a cobalt sulfate aqueous solution having a cobalt concentration of 8.2% by weight were mixed at a weight ratio of 84:16, and this mixed aqueous solution was supplied to the precipitation tank. Other conditions were the same as in Example 1 to obtain a nickel / cobalt / aluminum composite hydroxide powder. The results of analyzing and evaluating this in the same manner as in Example 1 are shown in Table 1.

  [Comparative Example 2] The supply of the liquid c in the example was changed. That is, liquid c and sodium hydroxide aqueous solution were mixed in advance, and this mixed aqueous solution was supplied to the precipitation tank. Other conditions were the same as in Example 1 to obtain a lithium / nickel / cobalt / aluminum oxide powder. The results of analyzing and evaluating this in the same manner as in Example 1 are shown in Table 1.

  As shown in the analysis and evaluation results of the examples and comparative examples, the lithium ion battery manufactured using the lithium / nickel / cobalt / aluminum composite oxide powder obtained by the manufacturing method of the present invention has an initial discharge efficiency and rate. The maintenance rate is high and gas generation is suppressed.

  The method for producing a lithium / nickel / cobalt / aluminum oxide powder of the present invention is useful as a method for producing an NCA-based positive electrode active material that provides a lithium ion battery with good initial discharge efficiency, rate characteristics, and suppressed gas generation. . According to the present invention, it is possible to provide a lithium ion battery that exhibits good initial discharge efficiency and rate characteristics and further suppresses gas generation.

DESCRIPTION OF SYMBOLS 1 Inclined plate settling device 2 Lamella 3 Groove 4 Inclined plate settling device 5 Lamella 6 Rail system 7 Solid particle 8 Lamella 9 Straight line 10 Stirrer 11 Heat exchanger 12 Inclined plate settling device 13 Reactor 14 Pump 15 Slurry flow 16 Circulation pump 17 Pump 18 Circulating vessel 19 Slurry flow 20 Circulating vessel 21 Pump 22 Pump 23 Nickel sulfate aqueous solution supply pump 24 Cobalt sulfate aqueous solution supply pump 25 Sodium aluminate aqueous solution supply pump 26 Sodium hydroxide aqueous solution supply pump 27 Ammonia water supply pump

Claims (1)

A precipitation step of producing a nickel / cobalt / aluminum coprecipitated hydroxide by sucking, separating and circulating the composite hydroxide slurry using a reactor equipped with a stirring means;
Firing a mixture of a precursor comprising a nickel-cobalt-aluminum composite hydroxide and a lithium compound,
In the above precipitation step,
Supply nickel sulfate aqueous solution as nickel raw material and cobalt sulfate aqueous solution as cobalt raw material to the reactor through independent different flow paths,
It is characterized by supplying sodium aluminate, sodium hydroxide aqueous solution, and ammonia water as an aluminum raw material to the reactor through independent and different flow paths,
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.) A method for producing a lithium-nickel-cobalt-aluminum oxide powder for a positive electrode active material for a lithium ion battery ,
The reactor used in the precipitation step has a tilted plate settling device and is adapted to intimately mix the starting material solution upon introduction into the reaction zone of the reactor;
The inclined plate settling device is integrated with the reactor so as to be directly connected to the reaction zone, and connected to at least one circulation vessel via at least one pump;
Aspirating turbid liquid from the product suspension in the reactor to the at least one circulation vessel, removing the solid fines from the turbid liquid through a filter element, and removing the liquid from the circulation vessel; And by pumping directly back to the reactor, the particle size distribution of the product suspension in the reactor is shifted to a higher D50 value,
A method for producing lithium / nickel / cobalt / aluminum oxide powder for a lithium ion battery positive electrode active material.

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