JP5967264B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

  2. Description of the Related Art Conventionally, with the widespread use of portable devices such as mobile phones and notebook personal computers, small and lightweight secondary batteries having high energy density are required. As a secondary battery suitable for such an application, there is a lithium ion secondary battery, and research and development are actively performed.

  In the field of automobiles, demand for electric vehicles has increased due to resource and environmental issues. As a power source for electric vehicles and hybrid vehicles, lithium ion secondary batteries with small size, light weight, large discharge capacity, and good cycle characteristics are available. It has been demanded. Particularly in a power source for automobiles, output characteristics are important, and a lithium ion secondary battery with good output characteristics is required.

A lithium ion secondary battery using a lithium-containing composite oxide, particularly a lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, as a positive electrode active material can obtain a high voltage of 4V, and therefore has a high energy density. The battery has been put into practical use. In addition, lithium ion secondary batteries using this type of lithium cobalt composite oxide have been developed to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.

  However, since the lithium cobalt composite oxide uses an expensive cobalt compound as a raw material, the cost of the active material and the battery is increased, and improvement of the active material is desired. Since the unit price per capacity of the battery using this lithium cobalt composite oxide is significantly higher than that of the nickel metal hydride battery, the application to which it is applied is considerably limited. Therefore, not only for small secondary batteries for portable devices that are now widely used, but also for large-sized secondary batteries for power storage and electric vehicles, the cost of the active material is reduced, and cheaper lithium ion secondary batteries are used. The expectation for enabling the production of batteries is great, and the realization of this can be said to have great industrial significance.

As a new material for a positive electrode active material for a lithium ion secondary battery, a 4V class positive electrode active material that is cheaper than a lithium cobalt composite oxide, that is, a lithium nickel cobalt composite oxide has attracted attention. As the lithium nickel cobalt composite oxide, for example, Li [Ni _1/3 Co _1/3 Mn _1/3 ] O containing manganese and having an atomic ratio of nickel, cobalt and manganese of substantially 1: 1: 1. Lithium nickel cobalt manganese composite oxide etc. which have the composition of ₂ are mentioned. Lithium nickel cobalt manganese composite oxide is not only inexpensive, but also has higher thermal stability than lithium ion secondary batteries using lithium cobalt composite oxide or lithium nickel composite oxide as the positive electrode active material. Is actively performed.

  In order for a lithium ion secondary battery to exhibit good battery characteristics, the lithium nickel cobalt composite oxide, which is a positive electrode active material, has an appropriate particle size and particle size distribution, and has a crystallinity that affects the specific surface area and particle density. It must be an appropriate value. The particle size and particle size distribution affect the slurry properties and coating properties during electrode plate manufacturing, and the density of the electrode plate, which contributes to determining the volume capacity of the manufactured secondary battery, and each particle during charge and discharge This is important because it affects variations in the depth of charge and discharge. The crystallinity is generally expressed by the size of the crystallite and the primary crystal particle. However, when the crystallite and the primary crystal particle are small, the specific surface area of the secondary particle is large and the particle density is small, and the crystallite and the primary crystal particle are small. When the crystal particles are large, the specific surface area of the secondary particles is small and the particle density is large.

  A common method for producing nickel-cobalt composite hydroxide is to mix a mixed aqueous solution containing each metal salt with an aqueous solution containing an ammonium ion supplier and maintain a pH within a certain range. Is continuously supplied to form a reaction solution, and nickel cobalt composite hydroxide particles are continuously crystallized in the reaction solution. In this production method, nickel cobalt composite hydroxide having a particle size distribution close to a normal distribution can be efficiently obtained by continuously performing the reaction.

  When nickel-cobalt composite hydroxide is obtained by continuous crystallization, the particle size can be controlled by adjusting pH. In the method for producing nickel cobalt composite hydroxide by continuous crystallization reaction, the precipitated nucleation and the growth reaction of individual particles proceed simultaneously.

  Specifically, crystals produced by the neutralization reaction of the raw material solution can be classified into those that cause nucleation alone and those that cause particle growth of nuclei generated elsewhere. If particle growth does not occur only by nucleation, particles having a target particle size cannot be obtained, and particles having a larger particle size can be obtained as the particle growth becomes dominant.

  Moreover, if nucleation does not occur only by particle growth, it is impossible to obtain a constant particle continuously. When producing particles continuously, it is necessary to take out the obtained particles continuously, so continuous nucleation is necessary to keep the number of particles in the reaction system constant and allow the reaction to proceed continuously. is necessary.

  However, if nucleation occurs continuously and particle growth proceeds in parallel, particles with different particle growth progress, that is, particles having different particle sizes are obtained. Therefore, a nickel-cobalt composite hydroxide having a target particle size can be obtained by controlling the pH and controlling the ratio of nucleation and particle growth. In general, when the pH during the crystallization reaction is high, the nucleation is superior to the particle growth, and the particle size becomes smaller as the number of nucleation increases. Conversely, when the pH during the crystallization reaction is low, the particle growth becomes superior to the nucleation and the particle size becomes large.

  On the other hand, the controlled pH during the crystallization reaction greatly affects the crystallinity of the particles represented by the size of the crystallites and primary crystal particles. When the control pH is high, the number of nuclei generated is large, that is, fine crystallites are easily generated, and the crystals used for particle growth are also fine, so that the secondary crystallites and primary crystal grains to be generated are small. . On the other hand, when the control pH is low, the particle growth is preferential, so that the generated crystallites and primary crystal particles of the secondary particles are large.

  As described above, the size of the crystallite and the primary crystal particle affects the specific surface area which is an important physical property of the nickel cobalt composite hydroxide. If the crystallite and primary crystal are large, the specific surface area is small. That is, generally, when the control pH during the crystallization reaction is low, the particle size distribution of the obtained nickel-cobalt composite hydroxide tends to increase and the specific surface area tends to decrease.

  In producing nickel-cobalt composite hydroxide, the relationship between pH, particle size distribution, and specific surface area varies depending on the composition of the target nickel-cobalt composite hydroxide, the crystallization reaction apparatus, temperature, and stirring method. I take the. For this reason, the control pH at the time of the crystallization reaction for obtaining the nickel cobalt composite hydroxide having the target particle size distribution and specific surface area cannot be uniquely determined. In general, in order to obtain a nickel cobalt composite hydroxide having a particle size distribution with an average particle size exceeding 20 μm, it is necessary to lower the control pH during the crystallization reaction.

  In general, when the proportion of cobalt or the like is increased, cobalt and the like are oxidized during the crystallization reaction and the solubility is lowered. Therefore, the particle size is likely to be reduced even at the same control pH during the crystallization reaction. In that case, it is necessary to lower the control pH during the crystallization reaction in order to obtain a nickel-cobalt composite hydroxide having a target particle size.

  Here, when the control pH during the crystallization reaction was lowered, the solubility of the transition metal-ammine complex in the reaction solution was increased, and the outflow of the transition metal into the waste liquid in the solid-liquid separation process was increased and used. The yield of nickel cobalt composite hydroxide from a raw material and a product yield will fall. In addition, wastewater in which a large amount of transition metal is dissolved has a large environmental load, and costs are required to perform the treatment.

JP 2003-59490 A

  Then, an object of this invention is to provide the manufacturing method of the positive electrode active material of the nonaqueous electrolyte secondary battery which suppresses the outflow of a transition metal and has a target composition and particle size distribution.

The manufacturing method of the positive electrode active material of the aqueous electrolyte secondary battery according to the present invention that achieves the above-described object is a general formula obtained by a manufacturing method including the following (1) to (4): Ni _{1-xy z} Co _x Mn _y M _z (OH) ₂ (0 <x <1/2, 0 ≦ y <1/2, 0 ≦ z ≦ 0.1, M is Mg, Al, Ca, Ti, V, Cr And one or more elements selected from Zr, Nb, Mo, and W), and an average particle diameter D50 by laser scattering particle size distribution measurement is 4.0 to 25.0 μm. There, and nitrogen adsorption specific surface area measured by BET method is 1.0 m ² / g or more, the precursor of the positive electrode active material of the nonaqueous electrolyte secondary battery is less than 8.0m ² / g, 500~1000 ℃ after heat treatment at a temperature, to calcination at 800 to 1000 ° C. is mixed with a lithium compound It is characterized in.
(1) A mixed aqueous solution containing at least a nickel salt and a cobalt salt is mixed with an aqueous solution containing an ammonium ion supplier, and a caustic aqueous solution is continuously supplied to obtain a reaction solution. The pH of the reaction solution is adjusted to a liquid temperature. A crystallization step of continuously crystallizing the nickel cobalt composite hydroxide particles by maintaining the temperature within a range of 10.0 to 12.0 on a 25 ° C. basis.
(2) A caustic aqueous solution is continuously supplied to the reaction solution containing the nickel-cobalt composite hydroxide particles continuously discharged in the crystallization step, and the pH of the reaction solution is 12 on the basis of a liquid temperature of 25 ° C. PH adjustment step of raising the concentration to be 5 or more and lowering the transition metal ion concentration in the reaction solution.
(3) A solid-liquid separation step in which the reaction solution containing the nickel-cobalt composite hydroxide particles whose pH has been adjusted is subjected to solid-liquid separation to wash the nickel-cobalt composite hydroxide particles.
(4) A drying step of drying the nickel cobalt composite hydroxide particles washed with water.

  INDUSTRIAL APPLICATION This invention can suppress the outflow of a transition metal, and can obtain the positive electrode active material of the nonaqueous electrolyte secondary battery which has a target composition and particle size distribution with a high yield.

Below, the manufacturing method of the nickel cobalt composite hydroxide used as a precursor is demonstrated in detail about the manufacturing method of the positive electrode active material of the non-aqueous electrolyte secondary battery to which this invention is applied. Note that the present invention is not limited to the following detailed description unless otherwise specified. The embodiment according to the present invention will be described in the following order.
1. 1. Nickel-cobalt composite hydroxide 2. Manufacturing method of nickel cobalt composite hydroxide 2-1. Crystallization step 2-2. pH adjustment step 2-3. Solid-liquid separation step 2-4. Drying process

<1. Nickel-cobalt composite hydroxide>
The nickel-cobalt composite hydroxide is Ni _1-xyz Co _x Mn _y M _z (OH) ₂ (0 <x ≦ 1/3, 0 ≦ y ≦ 1/3, 0 ≦ z ≦ 0.1. , M is represented by one or more elements selected from Mg, Al, Ca, Ti, V, Cr, Zr, Nb, Mo, and W). This nickel-cobalt composite hydroxide has an average particle diameter D50 by laser scattering particle size distribution measurement of 4.0 to 25.0 μm, and a specific surface area measured by a nitrogen adsorption BET method of 1.0 m ² / g or more, It is preferably less than 8.0 m ² / g. As the nickel-cobalt composite hydroxide, nickel-cobalt-manganese composite hydroxide (0 <y) containing nickel, cobalt and manganese exhibiting high thermal stability is preferable.

  When the particle size distribution of nickel-cobalt composite hydroxide, especially the average particle size represented by the D50 particle size, is smaller than 4.0 μm, the specific surface area increases and sufficient battery safety cannot be obtained. The tap density of the hydroxide, and hence the tap density of the lithium nickel cobalt composite oxide obtained after synthesis, is reduced, and the battery capacity is reduced.

  On the other hand, when the D50 particle size is larger than 25.0 μm, the smoothness of the surface of the electrode plate deteriorates during the manufacture of the electrode plate during battery manufacture, the filling property into the battery deteriorates, and the output of the lithium ion secondary battery Characteristics deteriorate. Therefore, by setting the D50 particle size to 4.0 to 25.0 μm, sufficient safety and output characteristics of the battery can be obtained, and the process load at the time of manufacturing the battery can be reduced.

When the specific surface area of the nickel-cobalt composite hydroxide exceeds 8.0 m ² / g, the specific surface area of the positive electrode active material finally obtained becomes too large, and sufficient safety cannot be obtained. On the other hand, when the specific surface area is less than 1.0 m ² / g, the specific surface area of the positive electrode active material becomes too small, and when used in a battery, the contact with the electrolytic solution becomes insufficient, and a sufficient output cannot be obtained. Therefore, sufficient safety and output of the battery can be obtained by setting the specific surface area to 1.0 to less than 8.0 m ² / g.

  The additive element M is added to improve battery characteristics such as cycle characteristics and output characteristics. If the atomic ratio z of the additive element M exceeds 0.1, the metal element contributing to the redox reaction (Redox reaction) decreases, and the battery capacity decreases, which is not preferable. Therefore, the additive element M is adjusted so that the atomic ratio z is in the range of 0 ≦ z ≦ 0.1.

  By uniformly distributing the additive element M to the particles of the nickel-cobalt composite hydroxide, it is possible to obtain the effect of improving the battery characteristics over the entire particles. For this reason, even if the addition amount of the additive element M is small, an effect can be obtained and a decrease in capacity can be suppressed. Furthermore, in order to obtain the effect with a smaller addition amount, it is preferable to increase the concentration of the additive element M on the particle surface from the inside of the nickel cobalt composite hydroxide particle.

The nickel-cobalt composite hydroxide as described above is suitable as a precursor of the positive electrode active material of the non-aqueous electrolyte secondary battery, has an average particle diameter D50 by laser scattering measurement of 4.0 to 25.0 μm, and To produce a positive electrode active material that exhibits excellent thermal stability, high density, and high battery characteristics by having a specific surface area measured by a nitrogen adsorption BET method of 1.0 to 10.0 m ² / g. Can do.

  When manufacturing the positive electrode active material of a non-aqueous electrolyte secondary battery using nickel cobalt composite hydroxide, it can be made into a positive electrode active material by the manufacturing method of a normal positive electrode active material. For example, after the nickel-cobalt composite hydroxide is left as it is or heat-treated at a temperature of 500 to 1000 ° C. or less, the lithium compound is preferably 0.95 by atomic ratio of lithium to the metal element of the composite hydroxide. What is necessary is just to mix and bak at 800-1000 degreeC so that it may become -1.5. The non-aqueous electrolyte secondary battery using the obtained positive electrode active material can have a high capacity, good cycle characteristics, and excellent safety.

<Method for producing nickel-cobalt composite hydroxide>
The method for producing a nickel-cobalt composite hydroxide as described above mixes an aqueous solution containing at least a nickel salt and a cobalt salt with an aqueous solution containing an ammonium ion supplier, and the pH is maintained within a certain range. In this way, a crystallization step is performed in which a solution supplied with a caustic aqueous solution is used as a reaction solution, and nickel cobalt composite hydroxide particles are crystallized in the reaction solution.

  Then, a caustic aqueous solution is continuously supplied to the reaction solution containing the nickel cobalt composite hydroxide particles generated in the crystallization step, and the pH of the reaction solution containing the nickel cobalt composite hydroxide particles is set to the liquid temperature. A pH adjustment step is performed in which the temperature is raised to 12.5 or higher on a 25 ° C. basis to lower the transition metal ion concentration in the reaction solution.

  After the pH adjustment step, the nickel-cobalt composite hydroxide particles are subjected to solid-liquid separation and washed with water, and the drying step of drying the washed nickel-cobalt composite hydroxide particles. Hereinafter, each process will be described in detail.

(2-1. Crystallization step)
In the crystallization step, a mixed aqueous solution containing at least a nickel salt and a cobalt salt, and optionally a manganese salt and a salt of an added metal element, and an aqueous solution containing an ammonium ion supplier are mixed, and the pH of the reaction solution is within a certain range. Among them, preferably, a caustic aqueous solution is supplied so that the pH is maintained in the range of 10.0 to 12.0 on the basis of a liquid temperature of 25 ° C. to obtain a reaction solution, and nickel cobalt composite hydroxide particles are formed in the reaction solution. Crystallize.

  In the crystallization step, the temperature of the reaction solution is preferably maintained at 20 to 70 ° C. Thereby, the crystal of nickel cobalt compound hydroxide grows. When the temperature of the reaction solution is less than 20 ° C., the solubility of the salt in the reaction solution is low and the salt concentration is low, so that the crystals of the nickel cobalt composite hydroxide do not grow sufficiently. On the other hand, when the temperature of the reaction solution exceeds 70 ° C., the generation of crystal nuclei is increased and the number of fine particles increases, so that the nickel cobalt composite hydroxide particles do not become high density. Therefore, it is preferable that the temperature of the reaction solution is 20 to 70 ° C. so that the crystals can grow sufficiently and the particles can have a high density.

  In the crystallization step, the pH of the reaction solution is preferably controlled in the range of 10.0 to 12.0 on the basis of the liquid temperature of 25 ° C. When the pH is less than 10.0, the nickel-cobalt composite hydroxide particles become coarse and it becomes difficult to obtain dense secondary particles. Also, if the pH of the reaction solution is low, the solubility of the transition metal-ammine complex in the reaction solution becomes too high, and remains in the reaction vessel when the nickel-cobalt composite hydroxide and the reaction solution are separated in the solid-liquid separation process. The amount of transition metal to increase increases the yield of nickel-cobalt composite hydroxide from the metal salt of the raw material, and the cost for separating and recovering the transition metal component from the reaction solution to be discarded increases.

  On the other hand, when the pH of the reaction solution in the crystallization step exceeds 12.0, the crystallization rate of the nickel cobalt composite hydroxide increases, and fine particles increase. When there are too many fine particles, there exists a problem that these will sinter and produce agglomerated powder at the time of positive electrode active material manufacture.

  Therefore, in order to reduce the loss of transition metal, the nickel cobalt composite hydroxide particles are not coarse or fine, have an appropriate size, and suppress the generation of agglomerated powder, the pH of the reaction solution is based on a liquid temperature of 25 ° C. It is preferable to make it into the range of 10.0-12.0, and also the solubility of the transition metal-ammine complex in a reaction solution is made small by adjusting pH to 12.5 or more by a pH adjustment process.

  The pH of the reaction solution can be controlled by supplying a caustic aqueous solution. The aqueous caustic solution is not particularly limited, and for example, an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the reaction solution, but it is preferably added as an aqueous solution in view of easy pH control. The method of adding the caustic aqueous solution is not particularly limited, and the pH is in the range of 10.0 to 12.0 with a pump capable of controlling the flow rate such as a metering pump while sufficiently stirring the reaction solution. It may be added to.

  Furthermore, in the crystallization step, it is preferable that nickel cobalt composite hydroxide particles are produced by coprecipitation in an environment with a low oxygen content. When crystallization is performed in an inert atmosphere or in the presence of a reducing agent, cobalt and manganese are not oxidized, but the solubility of cobalt and manganese in the reaction solution increases under the above-mentioned temperature and pH conditions of the reaction solution. In some cases, plate-like primary particles develop, spherical secondary particles do not grow, and nickel-cobalt composite hydroxide particles having a high tap density cannot be obtained. Therefore, the crystallization step is preferably performed in an environment having a low oxygen content, not in an inert atmosphere or in the presence of a reducing agent.

In the crystallization process described above, the fine powder is not too little or too much, and the density is high, preferably the tap density is 2.0 g / cm ³ or more, more preferably the tap density is 2.0 to 3.0 g / cm. ³ nickel cobalt composite hydroxide particles are obtained. When the tap density is larger than 3.0 g / cm ^3, the area where the positive electrode active material obtained when the particle size becomes too large is brought into contact with the electrolytic solution is lowered, so that preferable battery characteristics may not be obtained. Therefore, the tap density of 2.0 g / cm ³ or more, preferably a tap density of 2.0 to 3.0 g / cm ^3, by further preferably 2.0~2.5g / cm ^3, high density Battery performance can be improved.

As described above, the obtained nickel-cobalt composite hydroxide has a general formula: Ni _1-xyz Co _x Mn _y M _z (OH) ₂ (0 <x ≦ 1/3, 0 ≦ y ≦ 1 / 3, 0 ≦ z ≦ 0.1, M is represented by one or more elements selected from Mg, Al, Ca, Ti, V, Cr, Zr, Nb, Mo, and W), It almost coincides with the atomic ratio of the supplied mixed aqueous solution. Therefore, by adjusting the atomic ratio of the mixed aqueous solution to the atomic ratio of the above general formula, the atomic ratio of nickel, cobalt, manganese, and the additive element M can be in the range shown in the above general formula.

  The salt concentration in the mixed aqueous solution in which nickel, cobalt salt, and manganese salt are mixed is preferably 1 mol / L to 2.6 mol / L in total for each salt. When the concentration is less than 1 mol / L, the salt concentration is low, and the nickel-cobalt composite hydroxide crystals do not grow sufficiently. On the other hand, if it exceeds 2.6 mol / L, the saturated concentration at room temperature is exceeded, so there is a risk that crystals will re-precipitate and clog the piping, and there will be many crystal nuclei and many fine particles. End up. Accordingly, the salt concentration in the mixed aqueous solution is such that the total of each salt is 1 mol / L to 2.6 mol / L in order to suppress the generation of fine particles without growing and reprecipitation of nickel cobalt composite hydroxide crystals. It is preferable to do so. However, since the saturation concentration at room temperature varies depending on the ratio of each transition metal salt, the upper limit cannot be generally determined to be 2.6 mol / L.

  The nickel salt, cobalt salt, and manganese salt that can be used here are not particularly limited, but are preferably at least one of sulfate, nitrate, and chloride.

  The ammonium ion supplier is not particularly limited, but is preferably at least one of ammonia, ammonium sulfate, or ammonium chloride.

  The addition amount of the ammonium ion supplier is preferably in the range of 5 to 20 g / L in terms of the ammonium ion concentration in the reaction solution. When the ammonium ion concentration is less than 5 g / L, the solubility of nickel, cobalt and manganese in the reaction solution is low, and the crystal growth is insufficient, so that a high-density nickel-cobalt composite hydroxide cannot be obtained. On the other hand, when the ammonium ion concentration exceeds 20 g / L, the crystallization rate is lowered and the productivity is deteriorated, and the metal ions such as nickel remaining in the liquid are increased, thereby increasing the cost. Therefore, the addition amount of the ammonium ion supplier is preferably in the range of 5 to 20 g / L in order to obtain good productivity and high density nickel cobalt composite hydroxide.

  The additive element M is one or more elements selected from Mg, Al, Ca, Ti, V, Cr, Zr, Nb, Mo, and W, and is added to the mixed aqueous solution during the crystallization process or individually. By adding to the reaction solution, the nickel-cobalt composite hydroxide can have a general formula composition. The additive element M is preferably added as a water-soluble compound. For example, titanium sulfate, ammonium peroxotitanate, potassium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, zirconium nitrate Niobium oxalate, ammonium molybdate, sodium tungstate, ammonium tungstate, and the like can be used.

  In the case where the additive element M is uniformly dispersed inside the nickel cobalt composite hydroxide particles, an additive containing the additive element may be added to the mixed aqueous solution, and the additive element is added inside the nickel cobalt composite hydroxide particles. Can be coprecipitated in a uniformly dispersed state.

  In addition to adding an additive element to the inside of the nickel cobalt composite hydroxide particles, the surface may be coated with the additive element. In this case, for example, the nickel cobalt composite hydroxide may be coated with an aqueous solution containing the additive element. If particles are slurried and controlled to have a predetermined pH, an aqueous solution containing one or more additive elements is added, and the additive elements are precipitated on the surface of nickel-cobalt composite hydroxide particles by a crystallization reaction. The surface can be uniformly coated with the additive element. In this case, an alkoxide solution of the additive element may be used instead of the aqueous solution containing the additive element.

  Another method is to coat the surface of the nickel cobalt composite hydroxide particles with the additive element by spraying the nickel cobalt composite hydroxide particles with an aqueous solution or slurry containing the additive element and drying it. Can do. Alternatively, the slurry in which the nickel cobalt composite hydroxide particles and the salt containing one or more additional elements are suspended is spray-dried, or the nickel cobalt composite hydroxide particles and the salt containing the one or more additional elements are solidified. It can coat | cover by methods, such as mixing by a phase method.

  In addition, when the additive element is coated on the surface of the nickel cobalt composite hydroxide particles, the composite water obtained can be obtained by reducing the atomic ratio of the additive element ions present in the mixed aqueous solution by an amount that covers the additive element ion. The atomic ratio of the metal ions of the oxide particles can be matched. Further, the step of coating the surface of the nickel cobalt composite hydroxide particles with the additive element may be performed on the heat-treated particles when the nickel cobalt composite hydroxide is heat-treated. By coating the surface of the nickel cobalt composite hydroxide particles with the additive element, the concentration of the additive element on the particle surface can be increased from the inside of the positive electrode active material particle.

  The reaction method in the crystallization step is not particularly limited, and a batch method may be adopted. However, a mixed aqueous solution, an aqueous solution containing an ammonium ion supplier, and a caustic aqueous solution are continuously supplied to the reaction tank. From the viewpoint of productivity and stability, it is preferable to continuously overflow the reaction solution containing nickel-cobalt composite hydroxide particles to recover the nickel-cobalt composite hydroxide particles.

  In the case of a continuous system, while keeping the temperature constant, while supplying a constant amount of the mixed aqueous solution and ammonium ion supplier to the reaction tank, the pH is controlled by adding a caustic aqueous solution, and the reaction tank is in a steady state. Then, it is preferable to continuously collect the generated particles from the overflow pipe. It is also possible to supply the reaction tank after mixing the mixed aqueous solution and the caustic aqueous solution in advance, but it prevents the formation of nickel-cobalt composite hydroxide in the mixed aqueous solution when mixed with the caustic aqueous solution. Therefore, the mixed aqueous solution and the caustic aqueous solution are preferably supplied to the reaction tank separately. In addition, the metal salt such as nickel or cobalt does not necessarily have to be supplied to the reaction vessel as a mixed aqueous solution. For example, when using a metal salt that reacts when mixed to produce a compound, Metal salt aqueous solutions may be individually prepared so that the concentration is in the range of 1 mol / L to 2.6 mol / L, and the aqueous solutions of the individual metal salts may be simultaneously supplied into the reaction tank at a predetermined ratio.

  Regardless of which reaction method is used, it is preferable to sufficiently stir in order to maintain a uniform reaction during crystallization. However, excessive stirring may involve a large amount of oxygen in the atmosphere and the salt in the aqueous solution may be excessively oxidized, so stirring is preferably performed to such an extent that the reaction can be maintained sufficiently uniformly. The water used in the crystallization process is preferably water having as little impurity content as possible, such as pure water, in order to prevent contamination with impurities. In order to suppress oxidation, the mixed aqueous solution is preferably inserted, for example, into an injection nozzle serving as a supply port in the reaction solution so that the mixed aqueous solution is directly supplied into the reaction solution.

(1-2) pH adjustment step Next, a pH adjustment step of adjusting the pH of the reaction solution containing the nickel cobalt composite hydroxide particles obtained by crystallization to 12.5 or more is performed. In the pH adjustment step, the pH is adjusted to be higher than the pH of the reaction solution in the crystallization step, and the solubility of transition metal ions in the reaction solution is lowered. By providing this pH adjustment step, the pH of the reaction solution can be adjusted so as to have a desired particle size in the crystallization step, and the solubility of transition metal ions can be increased by increasing the pH of the reaction solution in the subsequent pH adjustment step. The transition metal component contained in the reaction solution can be reduced and the transition metal can be prevented from flowing out in the subsequent solid-liquid separation step.

  In the pH adjusting step, for example, a slurry of a reaction solution containing nickel cobalt composite hydroxide particles is continuously supplied from the crystallization reaction tank of the crystallization apparatus to the pH adjustment tank of the pH adjustment apparatus. The pH adjuster is connected so that the reaction solution is continuously supplied from the crystallization reaction tank of the crystallizer to the pH adjuster. In addition, although this is a case of a continuous system, as a batch system, the same reaction tank is used as a crystallization apparatus and a pH adjustment apparatus, and the pH in the reaction tank may be adjusted to the pH of the pH adjustment step after crystallization. it can.

  In the pH adjustment step, the pH of the reaction solution is controlled by continuously supplying a caustic aqueous solution to the reaction solution supplied into the pH adjustment tank. The aqueous caustic solution is not particularly limited, and for example, an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the reaction solution, but it is preferably added as an aqueous solution in view of easy pH control. There is no particular limitation on the method of adding the caustic aqueous solution, and the reaction solution may be added so as to be within the target pH range with a pump capable of controlling the flow rate such as a metering pump while sufficiently stirring the reaction solution. .

  Specifically, in the pH adjustment step, the pH of the reaction solution is set to 12.5 or more on the basis of the liquid temperature of 25 ° C. in order to suppress the outflow of transition metals such as nickel. By setting the pH to 12.5 or more, the solubility of transition metal ions in the reaction solution becomes several ppm or less, and the transition metal component is contained in the reaction solution at the time of solid-liquid separation and can be almost eliminated. . At this time, the concentration of the transition metal-ammine complex generated by the ammonium ion supplier added during the crystallization reaction decreases as the pH increases, and decreases as the ammonium ion supplier concentration decreases. Therefore, the higher the ammonium ion supplier concentration, the higher the pH of the reaction solution in the pH adjustment step. Further, raising the pH more than necessary undesirably increases the amount of caustic used, which is undesirable in terms of cost. Therefore, in the pH adjustment step, the upper limit of the pH of the reaction solution is preferably 13.0.

(1-3) Solid-Liquid Separation Step Next, a solid-liquid separation step is performed in which the nickel cobalt composite hydroxide particles obtained by crystallization are subjected to solid-liquid separation and then washed with water. In this solid-liquid separation step, for example, nickel cobalt composite hydroxide particles are filtered and then washed with water to obtain a filtrate. In addition, you may filter after wash | cleaning nickel cobalt composite hydroxide particle.

  As a method of solid-liquid separation, a commonly used method may be used. For example, a centrifuge, a suction filter, or the like can be used. The washing with water may be performed by a normal method as long as it can remove excess base and ammonia contained in the nickel-cobalt composite hydroxide particles. The water used in the water washing is preferably water having as little impurity content as possible, and more preferably pure water, in order to prevent contamination of impurities.

(1-4) Drying process Next, the drying process which dries the nickel cobalt composite hydroxide particle after a solid-liquid separation process is performed. In the drying step, drying is performed at a drying temperature of 100 to 230 ° C.

When the drying temperature is less than 100 ° C., fine hydroxide particles are newly generated on the surface, so that the specific surface area exceeds 8.0 m ² / g, and the residual moisture content in the nickel-cobalt composite hydroxide May increase, and an unreacted part may be generated during the synthesis reaction of the lithium nickel cobalt composite oxide. On the other hand, when the drying temperature exceeds 230 ° C., the decomposition of the nickel-cobalt composite hydroxide proceeds and a mixture with the oxide is formed. When an oxide is mixed, the metal content such as nickel per mass varies depending on the mixed amount of the oxide, so that it is difficult to accurately mix with a lithium compound in the manufacturing process of the positive electrode active material, and the resulting positive electrode active material It is difficult to achieve sufficient battery characteristics. Therefore, the drying temperature needs to be 100 to 230 ° C. so that the oxide is not mixed and the specific surface area is 8.0 m ² / g or less.

  The drying apparatus may be a commonly used drying apparatus as long as the above drying conditions can be satisfied, and any of a stationary type, a fluid type, and an airflow type drying apparatus can be used. The heating method is preferably an electric heating method in which the carbon-containing gas in the atmosphere does not increase.

  As described above, in the method for producing nickel cobalt composite hydroxide, in the crystallization process, the aqueous solution of caustic alkali is supplied so that the pH of the reaction solution is maintained within a certain range, and the nickel cobalt composite hydroxide particles are continuously provided. Next, in the pH adjustment step, a caustic aqueous solution is added to the reaction solution to adjust the pH of the reaction solution to 12.5 or higher, which is higher than the pH in the crystallization step. That is, in this method for producing nickel-cobalt composite hydroxide, the pH of the reaction solution is maintained within a certain range in the crystallization step, and the pH of the reaction solution is increased in the next pH adjustment step, so that solid-liquid separation is achieved. The concentration of transition metal ions in the reaction solution is reduced before the separation, and the transition metal component is contained in the reaction solution during solid-liquid separation. A nickel cobalt composite hydroxide having a specific surface area measured by the diameter D50 and the nitrogen adsorption BET method can be obtained.

Further, in this method for producing nickel cobalt composite hydroxide, by adjusting the pH of the reaction solution in the crystallization step to a range of 10.0 to 12.0, while suppressing the outflow of transition metal, the laser scattering particle size distribution A nickel-cobalt composite hydroxide having an average particle diameter D50 of 4.0 to 25.0 μm and a specific surface area of 1.0 to 8.0 m ² / g measured by a nitrogen adsorption BET method can be obtained. . Such a nickel-cobalt composite hydroxide exhibits excellent thermal stability, and enables production of a positive electrode active material capable of increasing density and improving battery characteristics.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples. In addition, the evaluation method of the nickel cobalt hydroxide used by the Example and the comparative example is as follows.

(1) Analysis of metal components:
Using an ICP (Inductively Coupled Plasma) emission spectrometer (725 ES, manufactured by VARIAN), analysis was performed by ICP emission analysis.
(2) Analysis of ammonium ion concentration:
It measured by the distillation method by JIS-K0102 standard.
(3) Measurement of BET specific surface area:
Using a specific surface area measuring apparatus (manufactured by Yuasa Ionics Co., Ltd., Multisoap 16), the measurement was performed by the BET one-point method by nitrogen adsorption.
(4) Measurement of carbon content:
It measured by the high frequency combustion-infrared absorption method using the carbon sulfur analyzer (the product made by LECO, CS-600).
(5) Measurement of average particle size and evaluation of particle size distribution width:
Using a laser diffraction particle size distribution meter (manufactured by Nikkiso Co., Ltd., Microtrac HRA), the average particle size was measured and the particle size distribution width was evaluated.
(6) Observation evaluation of form:
Using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6360LA, hereinafter referred to as SEM), observation and evaluation of shape and appearance were performed.

[Sample 1]
In Sample 1, 32 L of industrial water and 1300 mL of 25% by mass ammonia water were put into a 34 L overflow crystallization reaction tank equipped with four baffle plates, and heated to 50 ° C. with a thermostatic bath and a heating jacket. The mixture was warmed and a 24 mass% sodium hydroxide solution was added to adjust the pH of the reaction solution in the reaction vessel to 10.9 to 11.1. Since this pH is a pH at 50 ° C., in order to accurately control the pH, the reaction solution is collected, cooled to 25 ° C., and the pH is measured. Thus, the pH at 50 ° C. was adjusted.

  Next, while stirring the reaction solution maintained at 50 ° C., using a metering pump, nickel sulfate and cobalt sulfate having a nickel concentration of 0.8 mol / L, a cobalt concentration of 0.8 mol / L, and a manganese concentration of 0.8 mol / L. And a mixed aqueous solution of manganese sulfate (in terms of metal element molar ratio, Ni: Co: Mn = 1: 1: 1, hereinafter referred to as a mixed aqueous solution) at 30 ml / min. While continuously supplying at 5 ml / min, a 24% by weight caustic soda solution was added to control the pH at 25 ° C. to be 11.7 to 11.9 and the ammonium ion concentration to be 5 to 15 g / L. The crystallization reaction was performed.

  Stirring at this time was performed by rotating horizontally at a rotational speed of 1200 rpm using a 6-blade turbine blade having a diameter of 10 cm. As a method of supplying the mixed aqueous solution into the reaction system, an injection nozzle serving as a supply port was inserted into the reaction solution so that the mixed aqueous solution was directly supplied into the reaction solution.

  The nickel-cobalt composite hydroxide particles produced by the crystallization reaction are continuously discharged from the discharge port by overflow and introduced into the pH adjustment tank. In the pH adjustment tank, the pH was adjusted by adding a 24 mass% sodium hydroxide solution and controlling the pH at 25 ° C. to be 12.7 to 12.9. Nickel-cobalt composite hydroxide particles were continuously discharged from the discharge port through the overflow from the pH adjustment tank. Nickel-cobalt composite hydroxide particles taken out from the pH adjustment tank over 48 to 72 hours after the start of the reaction when the crystallization reaction was stabilized were subjected to solid-liquid separation using a Buchner funnel and a suction bottle, and then washed with water to obtain a filtrate. . The nickel, cobalt, and manganese concentrations in the reaction solution separated into solid and liquid were measured and found to be 10 ppm or less. Moreover, it was 16.8 mass% when the moisture content of the filtrate was measured by the loss on drying method for 24 hours at 120 degreeC.

  This filtrate was transferred to a vat and set in an air dryer maintained at a drying temperature of 110 ° C. Drying was performed for 1 hour including the time to reach the drying temperature, and the resulting dried product was recovered.

In the obtained nickel-cobalt composite hydroxide, the nickel content was 19.1% by mass, the cobalt content was 19.1% by mass, the manganese content was 17.9% by mass, and each element ratio was 33. 4: 33: 2: 33.4, which was almost equal to the composition ratio of the raw material aqueous solution. The specific surface area was 7.1 m ² / g and the average particle diameter D50 was 14.6 μm. When the particles were observed with an SEM, they were substantially spherical particles. It was confirmed that the particles were composed of simple crystals. The pH of the crystallization reaction tank during the crystallization reaction, the pH of the adjustment tank during the pH adjustment, and the nickel concentration in the reaction solution after the solid-liquid separation are shown in Table 1, and the D50 particle size and ratio of the nickel cobalt composite hydroxide Table 2 shows element ratios of the surface area, nickel, cobalt, and manganese.

[Samples 2 to 10]
In Samples 2 to 5, the pH of the crystallization reaction tank and the pH adjustment tank were changed as shown in Table 1 in the same manner as in Sample 1. The nickel concentration in the reaction solution after each solid-liquid separation is as shown in Table 1, and the D50 particle size, specific surface area, nickel, cobalt, and manganese element ratios of the obtained nickel cobalt composite hydroxide are shown in Table 2. It was as shown.

  In Samples 6, 8, and 10, the pH adjustment step is not performed, and the nickel cobalt composite hydroxide particles obtained by overflow from the crystallizer are directly subjected to the treatment after the solid-liquid separation step to obtain the nickel cobalt composite hydroxide. I got a thing.

  From the results shown in Table 1 and Table 2, in Samples 1 to 5 in which the pH of the reaction solution was maintained in a certain range in the crystallization step, and then the pH of the reaction solution was adjusted to 12.5 or more in the pH adjustment step, The concentration of nickel in the reaction solution after liquid separation is less than 10 ppm, so that the outflow of nickel can be suppressed, and the element ratio of nickel, cobalt, and manganese is almost the same as the element ratio of the mixed aqueous solution, that is, the target element ratio. did. Samples 1 to 5 were obtained by adjusting the pH of the reaction solution to 12.5 or higher in the pH adjustment step performed after the crystallization step, thereby obtaining a nickel-cobalt composite hydroxide having the desired particle size distribution and specific surface area. It was.

Among samples 1 to 5, samples 1 to 4 are adjusted to a pH of 10.0 to 12.0 in the crystallization step, so that the nickel concentration in the reaction solution after solid-liquid separation is less than 10 ppm, The D50 particle size of the nickel cobalt composite hydroxide was in the range of 4.0 to 25 μm, and the specific surface area was in the range of 1.0 to 8.0 m ² / g.

  In sample 5, the pH of the reaction solution in the crystallization process is 12.3, which is slightly higher than 12.0. Therefore, the crystallization speed of the nickel cobalt composite hydroxide is slightly increased, and the number of fine particles is increased. The specific surface area was larger than those of Samples 1 to 4.

  In the samples 6 to 9 in which the pH of the reaction solution is lower than 12.5 or not adjusted in the pH adjustment step, the nickel concentration in the reaction solution after solid-liquid separation becomes very high, and nickel loss occurs. You can see that it ’s big. Further, the elemental ratio of nickel, cobalt, and manganese in the obtained nickel-cobalt composite hydroxide was greatly different from the elemental ratio of the mixed aqueous solution, that is, the intended elemental ratio. Among these, in Samples 8 and 9, the pH of the reaction solution in the crystallization step was lower than 10.0, and the nickel cobalt composite hydroxide particles became coarse.

  In addition, since the pH of the reaction solution in the crystallization step of Sample 10 was 12.8, the nickel concentration in the reaction solution was low, but the nickel-cobalt composite hydroxide particles became coarse and the specific surface area also increased. It was.

  From the above results, in the production of nickel-cobalt composite hydroxide, the crystallization step is performed with the pH of the reaction solution in a certain range, and then the pH in the reaction solution is set so that the solubility of transition metals such as nickel becomes low. By adjusting the pH to 12.5 or more, the nickel concentration in the reaction solution after solid-liquid separation can be lowered, the loss of nickel can be reduced, and the yield of nickel cobalt composite hydroxide can be increased. I understand. Furthermore, it turns out that the D50 particle size and specific surface area of a nickel cobalt composite hydroxide can be made into the target range by making pH of the reaction solution in a crystallization process into 10.0-12.0.

Claims (4)

Following (1) to (4) formulas obtained by the manufacturing method _{comprising: Ni 1-x-y-} z Co x Mn y M z (OH) 2 (0 <x <1 / 2,0 ≦ y < 1/2, 0 ≦ z ≦ 0.1, where M is one or more elements selected from Mg, Al, Ca, Ti, V, Cr, Zr, Nb, Mo, and W) 7. It is a composite hydroxide, the average particle diameter D50 by laser scattering particle size distribution measurement is 4.0-25.0 micrometers, and the specific surface area measured by nitrogen adsorption BET method is 1.0 m < ² > / g or more. A precursor of a positive electrode active material of a non-aqueous electrolyte secondary battery that is less than 0 m ² / g is heat-treated at a temperature of 500 to 1000 ° C., then mixed with a lithium compound and fired at 800 to 1000 ° C. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.
(1) A mixed aqueous solution containing at least a nickel salt and a cobalt salt is mixed with an aqueous solution containing an ammonium ion supplier, and a caustic aqueous solution is continuously supplied to obtain a reaction solution. The pH of the reaction solution is adjusted to a liquid temperature. A crystallization step of continuously crystallizing the nickel cobalt composite hydroxide particles by maintaining the temperature within a range of 10.0 to 12.0 on a 25 ° C. basis.
(2) A caustic aqueous solution is continuously supplied to the reaction solution containing the nickel-cobalt composite hydroxide particles continuously discharged in the crystallization step, and the pH of the reaction solution is 12 on the basis of a liquid temperature of 25 ° C. PH adjustment step of raising the concentration to be 5 or more and lowering the transition metal ion concentration in the reaction solution.
(3) A solid-liquid separation step in which the reaction solution containing the nickel-cobalt composite hydroxide particles whose pH has been adjusted is subjected to solid-liquid separation to wash the nickel-cobalt composite hydroxide particles.
(4) A drying step of drying the nickel cobalt composite hydroxide particles washed with water. 2. The non-aqueous electrolyte according to claim 1, wherein the lithium compound is mixed so that lithium is in an atomic ratio of 0.95 to 1.5 with respect to the metal element of the nickel-cobalt composite hydroxide. The manufacturing method of the positive electrode active material of a secondary battery. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the temperature of the reaction solution in the crystallization step is maintained in the range of 20 to 70 ° C and the ammonium ion concentration in the range of 5 to 20 g / L. Of manufacturing positive electrode active material. In the pH adjustment step, the non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, characterized in that the transition metal ion concentration in the reaction solution after pH adjustment and 100ppm or less A method for producing a positive electrode active material.