JP6988370B2 - Method for Producing Nickel Composite Hydroxide and Nickel Composite Hydroxide - Google Patents

Description

The present invention relates to a method for producing a nickel composite hydroxide and a nickel composite hydroxide.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density. Further, it is strongly desired to develop a high output secondary battery as a battery for electric vehicles such as hybrid vehicles. As a secondary battery satisfying such a requirement, there is a lithium ion secondary battery. The lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material for the negative electrode and the positive electrode.

Currently, research and development of lithium-ion secondary batteries are being actively carried out. Among them, lithium-ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode material have a high voltage of 4V class. Therefore, it is being put into practical use as a battery having a high energy density.

_{For batteries using lithium cobalt composite oxide (LiCoO 2} ), which is relatively easy to synthesize, as the positive electrode active material for lithium-ion secondary batteries, many developments have been made to obtain excellent initial capacity characteristics and cycle characteristics. It has been damaged, and various results have already been obtained. However, since the lithium cobalt composite oxide uses a rare and expensive cobalt compound as a raw material, it causes an increase in the cost of the positive electrode active material and the battery using the positive electrode active material, and it is desired to replace the positive electrode active material. ing.

Therefore, attention is being paid to _{lithium nickel composite oxide (LiNiO 2} ), which can be expected to have a higher capacity by using nickel, which is cheaper than cobalt. Lithium-nickel composite oxide shows not only cost but also lower electrochemical potential than lithium-cobalt composite oxide, so decomposition by oxidation of the electrolytic solution is less likely to be a problem, higher capacity can be expected, and cobalt. Since it shows a high battery voltage like the system, it is being actively developed.

However, lithium-nickel composite oxide is said to be inferior in cycle characteristics to cobalt-based batteries when a lithium-ion secondary battery is manufactured using a material obtained by synthesizing a metal component other than lithium purely with nickel as a positive electrode active material. There are drawbacks. In addition, there is a drawback that the battery performance is relatively easily impaired when used or stored in a high temperature environment.

In order to solve such a defect, for example, Patent Document 1 has a layered structure for the purpose of improving storage characteristics such as self-discharge characteristics and structural stability of a lithium ion secondary battery and cycle characteristics of a battery. Then, the following equation Li _x Ni _a Co _b M _c O ₂ (0.8 ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≤0.3, 0.8≤a + b + c≤1.2, M is composed of a lithium-containing composite oxide represented by at least one element selected from Al, V, Mn, Fe, Cu, and Zn). A positive electrode active material for a lithium secondary battery, which is characterized by the above, has been proposed.

In Patent Document 2, for the purpose of realizing a battery having a high capacity and good cycle characteristics and high rate discharge characteristics, LiNi _x M _1-x O ₂ (M is Co, Mn, M is Co, Mn, Any one or more of Cr, Fe, V, and Al, x: 1> x ≧ 0.5) has been proposed.

Lithium-nickel composite oxides such as those in Patent Documents 1 and 2 have higher charge capacity and discharge capacity than lithium cobalt composite oxides and have improved cycle characteristics, but they can be charged only for the first charge / discharge. There is a problem that the discharge capacity is smaller than the capacity and the so-called irreversible capacity defined by the difference between the two is large.

Lithium-nickel composite oxides are usually produced from the step of mixing a nickel composite hydroxide with a lithium compound and firing it. The nickel composite hydroxide contains impurities such as sulfuric acid roots derived from the raw material in the manufacturing process of the nickel composite hydroxide. These impurities often inhibit the reaction with lithium in the step of mixing and firing the lithium compound, and lower the crystallinity of the lithium nickel composite oxide having a layered structure.

Lithium-nickel composite oxides with low crystallinity have a problem that when a battery is formed as a positive electrode material, the capacity is reduced by inhibiting Li diffusion in the solid phase. Further, the impurities contained in the nickel composite hydroxide are mixed with the lithium compound and remain in the lithium nickel composite oxide even after firing. Since these do not contribute to the charge / discharge reaction, when constructing the battery, the negative electrode material must be used for the battery by the amount corresponding to the irreversible capacity of the positive electrode material. As a result, the capacity per unit weight and unit volume of the battery as a whole becomes small. Further, the excess lithium accumulated in the negative electrode as an irreversible capacity is required to be suppressed from the viewpoint of enhancing safety.

Therefore, a lithium nickel composite oxide having a lower impurity content is required, but for that purpose, a nickel composite hydroxide having a lower impurity content is required.

As a method for producing a nickel composite hydroxide having a low impurity content, Patent Document 3 describes in Patent Document 3 for a non-aqueous electrolyte secondary battery composed of nickel cobalt manganese composite hydroxide particles represented by the following general formula (1). A method for producing a precursor of a positive electrode active material, which comprises washing nickel-cobalt-manganese composite hydroxide particles with a carbonate aqueous solution having a carbonate concentration of 0.1 mol / L or more. A method for producing a precursor of a positive electrode active material for a battery is disclosed.

The general _{formula: Ni x Co y Mn z M} t (OH) 2 ··· (1)
(In the formula, M represents at least one element selected from Mg, Ca, Ba, Sr, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W, and 0.3 ≦ x. ≤0.4, 0.3≤y≤0.4, 0.3≤z≤0.4, 0≤t≤0.1, x + y + z + t = 1)
However, according to the method for producing a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 3, the nickel-cobalt-manganese composite hydroxide particles used for cleaning have impurities when viewed locally. There is concern that the content will be high.

For this reason, for example, there is a risk that a nickel composite hydroxide in which the content of sulfuric acid root and chlorine, which are particularly problematic as impurities, is uniformly reduced cannot be obtained.

Japanese Unexamined Patent Publication No. 08-21301 Japanese Unexamined Patent Publication No. 09-129230 Japanese Patent Application Laid-Open No. 2015-162322

Therefore, in view of the problems of the prior art, one aspect of the present invention is to provide a nickel composite hydroxide in which the contents of sulfuric acid root and chlorine are uniformly suppressed to be low.

According to one aspect of the present invention in order to solve the above problems.
In one aspect of the present invention, the general formula _{Ni 1-x-y Co x} Al y (OH) 2 + α (0.05 ≦ x ≦ 0.35,0.01 ≦ y ≦ 0.2, x + y <0.4, Represented by −0.2 ≦ α ≦ 0.2)
Contains spherical secondary particles formed by agglomeration of multiple primary particles,
The secondary particles have an average particle size of 3 μm or more and 20 μm or less, and the secondary particles have an index [(d90-d10) / average particle size] larger than 0.55, which is an index indicating the spread of the particle size distribution. .20 or less,
0.4 mass% or less content of sulfate radical, and Ri der chlorine content of less than 0.05 wt%,
When evaluated by sampling at five, the content of sulfate ion, and the content of chlorine to provide a median ± 20% or less of the range near Ru nickel composite hydroxide.

According to one aspect of the present invention, it is possible to provide a nickel composite hydroxide in which the contents of sulfuric acid root and chlorine are uniformly suppressed to be low.

Hereinafter, a configuration example of a method for producing a nickel composite hydroxide and a nickel composite hydroxide will be described in detail. The present invention is not limited to the following detailed description unless otherwise specified. The embodiments according to the present invention will be described in the following order.

1. 1. Nickel composite hydroxide 2. Manufacturing method of nickel composite hydroxide 3. Non-aqueous electrolyte Positive electrode active material for secondary batteries 4. 4. Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary batteries. Non-aqueous electrolyte secondary battery

1. 1. Nickel Nickel composite hydroxide of the composite hydroxide present embodiment, the general formula _{Ni 1-x-y Co x} Al y (OH) 2 + α (0.05 ≦ x ≦ 0.35,0.01 ≦ y ≦ 0 .2, x + y <0.4, −0.2 ≦ α ≦ 0.2). The content of sulfuric acid root is preferably 0.4% by mass or less, and the content of chlorine is preferably 0.05% by mass or less.

Further, the nickel composite hydroxide of the present embodiment contains spherical secondary particles formed by aggregating a plurality of primary particles, and the secondary particles have an average particle size of 3 μm or more and 20 μm or less. For the secondary particles, it is preferable that [(d90-d10) / average particle size], which is an index showing the spread of the particle size distribution, is larger than 0.55 and 1.20 or less.
[Composition of Nickel Composite Hydroxide]
Nickel composite hydroxide of the present embodiment, the general formula _{Ni 1-x-y Co x} Al y (OH) 2 + α (0.05 ≦ x ≦ 0.35,0.01 ≦ y ≦ 0.2, x + y < It can have a composition represented by 0.4, −0.2 ≦ α ≦ 0.2).

In the above general formula, x indicating the cobalt content is 0.05 ≦ x ≦ 0.35. A non-aqueous electrolyte secondary battery using a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “positive electrode active material”) obtained from the nickel composite hydroxide by appropriately containing cobalt. It is possible to reduce the expansion / contraction behavior of the crystal lattice due to the cycle characteristics of (hereinafter, also simply referred to as “battery”) and the deinsertion / insertion of Li due to charging / discharging.

When the cobalt content x is 0.05 or more, the positive electrode active material obtained from the nickel composite hydroxide can sufficiently exert the above-mentioned effects, which is preferable. However, if the cobalt content is too high and x exceeds 0.35, the initial discharge capacity of the battery using the positive electrode active material obtained from the nickel composite hydroxide may be significantly reduced, which further increases the cost. There is also a disadvantageous problem.

Therefore, x indicating the cobalt content of the nickel composite hydroxide of the present embodiment is preferably 0.05 ≦ x ≦ 0.35, and a positive electrode active material obtained from the nickel composite hydroxide is used. Considering the battery characteristics and cost of the battery, 0.07 ≦ x ≦ 0.25 is more preferable, and 0.10 ≦ x ≦ 0.20 is even more preferable.

In the above general formula, y indicating the aluminum content is 0.01 ≦ y ≦ 0.2, and preferably 0.01 ≦ y ≦ 0.1. When the aluminum content is in the above range, the durability and safety of the battery using the positive electrode active material obtained from the nickel composite hydroxide can be improved.

In particular, it is preferable that aluminum is uniformly distributed inside the particles of the nickel composite hydroxide. When aluminum is uniformly distributed inside the particles of the nickel composite hydroxide, a greater effect can be obtained with the same aluminum content as compared with the case where the distribution of aluminum is low, and the nickel composite water is obtained. A battery using a positive electrode active material obtained from an oxide has an advantage that a decrease in battery capacity can be suppressed.

As described above, it is preferable to set the aluminum content y to 0.01 or more because the above-mentioned effects can be particularly sufficiently obtained. Further, when the aluminum content y is 0.2 or less, when the positive electrode active material obtained from the nickel composite hydroxide is used as the positive electrode material of the battery, the positive electrode active material undergoes a redox reaction in the battery. This is because the battery capacity can be particularly increased because the metal element that contributes is particularly sufficiently contained, which is preferable. Therefore, as described above, y indicating the aluminum content is preferably 0.01 ≦ y ≦ 0.2.

Further, the total atomic ratio of the cobalt content x and the aluminum content y can be x + y <0.4. This is because when the total atomic ratio of the cobalt content and the aluminum content is 0.4 or more, the capacity of the battery using the positive electrode active material obtained from the nickel composite hydroxide may decrease.

The method for analyzing the composition of the nickel composite hydroxide of the present embodiment is not particularly limited, but can be obtained by using chemical analysis by ICP emission spectroscopy.
[Particle structure]
The nickel composite hydroxide of the present embodiment can contain spherical secondary particles formed by agglomeration of a plurality of primary particles, and can also be composed of such spherical secondary particles. The shape of the primary particles constituting the secondary particles is not particularly limited, and various forms such as a plate shape, a needle shape, a rectangular parallelepiped shape, an ellipse shape, and a rhombohedral shape can be adopted. In particular, it is preferable that the primary particles constituting the secondary particles have one or more shapes selected from a plate shape and a needle shape. Further, the agglomeration state of a plurality of primary particles constituting the secondary particles is not particularly limited, and may be a form of agglomeration in a random direction, a form of aggregating radially from the center in the major axis direction of the primary particles, or the like. You may.

As the agglomerated state, it is preferable that the primary particles having one or more types selected from the plate shape and the needle shape are aggregated in a random direction to form the secondary particles. This is because, in the case of such a structure, voids are formed almost uniformly between the primary particles, and when the lithium compound is mixed with the lithium compound and fired in order to form a positive electrode active material, the molten lithium compound is the secondary particles. This is because the lithium is sufficiently diffused inward.

The method for observing the shapes of the primary particles and the secondary particles is not particularly limited, but the cross section of the nickel composite hydroxide can be observed by observing it with a scanning electron microscope.
[Average particle size]
The nickel composite hydroxide of the present embodiment preferably contains secondary particles having an average particle size of 3 μm or more and 20 μm or less. This is because when the average particle size of the contained secondary particles is 3 μm or more, a positive electrode active material is generated from the nickel composite hydroxide, and the packing density of the particles can be sufficiently increased when the positive electrode is used. This is because the battery capacity per unit volume can be increased. On the other hand, by setting the average particle size of the secondary particles contained in the nickel composite hydroxide of the present embodiment to 20 μm or less, the specific surface area of the positive electrode active material produced from the nickel composite hydroxide is sufficiently increased. Can be done. Therefore, by using the positive electrode active material for the positive electrode of the battery, it is possible to sufficiently secure the interface between the positive electrode active material and the electrolytic solution of the battery, suppress the reaction resistance, and improve the output characteristics of the battery. It is possible and preferable. Therefore, it is preferable that the average particle size of the secondary particles contained in the nickel composite hydroxide is 3 μm or more and 20 μm or more.

In particular, when the average particle size of the secondary particles contained in the nickel composite hydroxide of the present embodiment is 7 μm or more and 15 μm or less, a battery using the positive electrode active material obtained from the nickel composite hydroxide as the positive electrode has a unit volume. It is more preferable because the battery capacity per particle can be made particularly large and the output characteristics of the battery can be made particularly good.

The method for measuring the average particle size is not particularly limited, but can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering type particle size analyzer.
[Impurity content]
Nickel composite hydroxides are usually contained as impurities such as sulfate roots and chlorine due to the manufacturing process and the like. Sulfuric acid root and chlorine are derived from, for example, the raw materials used in the crystallization step described later.

On the other hand, the nickel composite hydroxide of the present embodiment preferably has a sulfuric acid root content of 0.4% by mass or less and preferably 0.3% by mass or less. Further, the nickel composite hydroxide of the present embodiment has a chlorine content of 0.05% by mass or less, preferably 0.03% by mass or less.

This is because the content of sulfate roots in the nickel composite hydroxide is 0.4% by mass or less to generate a positive electrode active material. Therefore, the nickel composite hydroxide and the lithium compound are mixed and fired. This is because the reaction between lithium and the nickel composite hydroxide can proceed without being hindered. Further, it is possible to sufficiently increase the crystallinity of the lithium nickel composite oxide having a layered structure, which is a positive electrode active material obtained by the reaction of the nickel composite hydroxide and the lithium compound.

Further, in order to generate a positive electrode active material by setting the chlorine content in the nickel composite hydroxide to 0.05% by mass or less, when the nickel composite hydroxide and the lithium compound are mixed and fired. This is because the reaction between lithium and the nickel composite hydroxide can proceed without being hindered. Further, it is possible to sufficiently increase the crystallinity of the lithium nickel composite oxide having a layered structure, which is a positive electrode active material obtained by the reaction of the nickel composite hydroxide and the lithium compound.

When a battery is constructed by using a highly crystalline lithium-nickel composite oxide as a positive electrode active material, Li diffusion is sufficiently promoted in the solid phase, and the battery capacity can be increased.

Further, the impurities contained in the nickel composite hydroxide also remain in the lithium nickel composite oxide obtained by mixing and firing the nickel composite hydroxide and the lithium compound. Since these impurities do not contribute to the charge / discharge reaction, when constructing the battery, the negative electrode material must be used in the battery as much as the irreversible capacity of the positive electrode material. As a result, the capacity per unit weight and unit volume of the battery as a whole becomes small. Further, it is preferable to suppress excess lithium accumulated in the negative electrode as an irreversible capacity from the viewpoint of enhancing safety. Therefore, the sulfuric acid root content of the nickel composite hydroxide of the present embodiment is 0.4% by mass or less from the viewpoint of increasing the battery capacity per unit weight or unit volume and from the viewpoint of enhancing safety. The chlorine content is preferably 0.05% by mass or less.

Further, chlorine in the nickel composite hydroxide is contained in the lithium nickel composite oxide mainly in the form of LiCl or NaCl when the lithium nickel composite oxide which is a positive electrode active material is produced from the nickel composite hydroxide. Remains. Since LiCl and NaCl have high hygroscopicity, when the positive electrode active material is used in a battery, it causes moisture to be brought into the battery and further causes deterioration of the battery. Therefore, the chlorine content in the nickel composite hydroxide of the present embodiment is preferably 0.05% by mass or less.

Further, the nickel composite hydroxide of the present embodiment can be a nickel composite hydroxide in which the contents of sulfuric acid root and chlorine are uniformly suppressed to be low. Therefore, when the nickel composite hydroxide of the present embodiment is sampled at a plurality of locations, it is preferable that the sulfuric acid root content and the chlorine content satisfy the above-mentioned ranges at all the locations, and the plurality of locations. It is preferable that the variation in the sulfuric acid root content and the chlorine content is ± 20% or less, respectively, when the sample is sampled and evaluated.

When the nickel composite hydroxide is sampled at a plurality of locations and the content of sulfuric acid root and chlorine is evaluated, the number of the sampling locations is not particularly limited, but for example, sampling is performed at 2 or more and 10 or less locations. It is preferable to do.
[Particle size distribution]
The secondary particles contained in the nickel composite hydroxide of the present embodiment have an index [(d90-d10) / average particle size] that indicates the spread of the particle size distribution of the particles, which is larger than 0.55 and 1.20 or less. It is preferable to have.

When the positive electrode active material obtained from the nickel composite hydroxide of the present embodiment is used as the positive electrode material of the battery, it is preferable that the particle size distribution of the positive electrode active material has a certain spread. This is because when the particle size distribution of the positive electrode active material has a certain spread, the electrode plate of the battery manufactured by using the positive electrode active material can sufficiently secure the particle density per electrode plate, and the unit weight of the battery. This is because the battery capacity per unit volume can be increased.

Here, according to the studies by the inventors of the present invention, the positive electrode active material and the secondary particles contained in the nickel composite hydroxide as the raw material of the positive electrode active material have the same particle size distribution spread. is doing. When the [(d90-d10) / average particle size], which is an index showing the spread of the particle size distribution of the secondary particles contained in the nickel composite hydroxide, is larger than 0.55, it is generated from the nickel composite hydroxide. In the electrode plate of the battery using the positive electrode active material, the particle density per electrode plate can be sufficiently increased, which is preferable.

However, when [(d90-d10) / average particle size] is larger than 1.20, fine particles having a very small particle size with respect to the average particle size or particles having a very large particle size with respect to the average particle size. There will be an excessively large number of (large diameter particles). When the positive electrode active material produced from the nickel composite hydroxide is used, it is possible to increase the battery capacity per unit weight or unit volume.

However, when a positive electrode is formed using a positive electrode active material containing a large amount of fine particles, heat may be generated due to a local reaction of the fine particles, the fine particles are selectively deteriorated, and the cycle characteristics are deteriorated. It is not preferable because it may cause a problem. On the other hand, when the positive electrode is formed by using the positive electrode active material in which many large-diameter particles are present, the reaction area between the electrolytic solution and the positive electrode active material may not be sufficiently obtained, and the battery output may decrease due to the increase in reaction resistance. It is not preferable because it exists.

Therefore, the secondary particles contained in the nickel composite hydroxide of the present embodiment have an index [(d90-d10) / average particle size] that indicates the spread of the particle size distribution of the particles, which is larger than 0.55 and 1.20. The following is preferable. When the secondary particles contained in the nickel composite hydroxide of the present embodiment have such a particle size distribution, the battery using the positive electrode active material obtained from the nickel composite hydroxide is per unit weight or per unit volume. It is preferable because the battery capacity of the battery can be increased and the cycle characteristics and the battery output can be increased.

In the index [(d90-d10) / average particle size] indicating the spread of the particle size distribution, d10 has the cumulative volume of all particles when the number of particles in each particle size is accumulated from the smaller particle size. It means a particle size that is 10% of the total volume. Further, d90 means a particle size in which the cumulative volume is 90% of the total volume of all the particles when the number of particles in each particle size is accumulated from the smaller particle size.

The method for obtaining the average particle size and d90 and d10 is not particularly limited, but can be obtained from, for example, the volume integration value measured by a laser light diffraction / scattering type particle size analyzer. The average particle size and d90 and d10 in other parts of the present specification can be obtained in the same manner.

According to the nickel composite hydroxide of the present embodiment, the contents of sulfuric acid root and chlorine can be uniformly suppressed to a low level. Therefore, when a non-aqueous electrolyte secondary battery is manufactured using the positive electrode active material obtained from the nickel composite hydroxide, the battery can be a battery having a large battery capacity and excellent safety. Therefore, the nickel composite hydroxide of the present embodiment is a battery material for an electric vehicle driven only by electric energy, or a non-aqueous electrolyte for a plug-in hybrid vehicle that can directly charge the battery from an outlet using a plug. It can be suitably used as a precursor of a positive electrode active material in a secondary battery.

2. 2. Method for Producing Nickel Composite Hydroxide An example of the configuration of the method for producing a nickel composite hydroxide of the present embodiment will be described. Since the nickel composite hydroxide described above can be produced by the method for producing a nickel composite hydroxide of the present embodiment, some overlapping description will be omitted.

The method for producing a nickel composite hydroxide of the present embodiment can have the following steps.

A supply process in which a nickel composite hydroxide slurry is supplied into a pressing means via a supply pipe.
A filtration step of filtering the nickel composite hydroxide slurry by a pressing means to obtain a nickel composite hydroxide cake.
A cleaning process in which a nickel composite hydroxide cake is washed in a squeezing means.

The cleaning step can further include the following steps.

With the nickel composite hydroxide cake squeezed by the squeezing means, an alkaline liquid is supplied to the nickel composite hydroxide cake via the cleaning liquid pipe connected to the squeezing means to wash the nickel composite hydroxide cake. First cleaning step.
A second cleaning step in which the nickel composite hydroxide cake is not squeezed, an alkaline liquid is supplied into the squeezing means via a supply pipe, and then the nickel composite hydroxide cake is re-squeezed.

Hereinafter, each step will be described.
[Supply process, filtration process]
Since the nickel composite hydroxide obtained by various methods contains impurities, the impurities can be removed by carrying out a filtration step and a cleaning step described later.

As a method for cleaning the nickel composite hydroxide, for example, a method in which the nickel composite hydroxide is added to an alkaline liquid, slurried, washed, and then filtered can be considered. Further, a method of supplying a slurry containing a nickel composite hydroxide produced by the coprecipitation step to a filter to form a cake, and then transporting the cake to another cleaning means for cleaning is also conceivable.

However, it is preferable to carry out filtration and washing by using a squeezing means capable of continuously performing filtration and washing in the same equipment. Therefore, in the supply step, it is preferable to supply the nickel composite hydroxide slurry into the squeezing means via the supply pipe connected to the squeezing means.

Then, in the filtration step, the nickel composite hydroxide slurry supplied in the pressing means can be filtered by the pressing means to obtain a nickel composite hydroxide cake.

The squeezing means is not particularly limited as long as it is a means capable of performing filtration and washing of the nickel composite hydroxide slurry as described above. As a squeezing means capable of performing filtration and washing, for example, one or more selected from a filter press, a belt filter and the like can be preferably used.
[Washing process]
The cleaning step can have two cleaning steps, the following first cleaning step and the second cleaning step. Each step will be described in detail below.
(First cleaning step)
In the first cleaning step, after the above-mentioned filtration step, the nickel composite hydroxide cake is squeezed by the squeezing means, and the nickel composite hydroxide cake is used as a cleaning liquid via the cleaning liquid pipe connected to the squeezing means. An alkaline liquid can be supplied to wash the nickel composite hydroxide cake.

When an alkaline liquid, which is a cleaning liquid, is passed through the filtered nickel composite hydroxide cake under pressure, the cleaning liquid is evenly passed through the cake, improving cleaning efficiency and reducing the amount of cleaning liquid. The amount of impurities in the nickel composite hydroxide can be uniformly reduced to the desired concentration.

As the cleaning liquid used in the first cleaning step, an alkaline liquid can be preferably used. The alkaline liquid used as the cleaning liquid is not particularly limited, but is preferably at least one aqueous solution selected from sodium carbonate, potassium carbonate, sodium sesquicarbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and sodium hydroxide.

The concentration of the alkaline liquid is also not particularly limited, but for example, the lower limit is preferably 0.10 mol / L or more, more preferably 0.15 mol / L or more, and 0. It is more preferably 20 mol / L or more. The upper limit is preferably 2.00 mol / L or less, and more preferably 1.50 mol / L or less.

By using an alkaline liquid with a concentration of 0.10 mol / L or more as the cleaning liquid, impurities in the particles of the nickel composite hydroxide, especially sulfate roots and chlorine, can be removed by the ion exchange action of the ions contained in the cleaning liquid. This is because it can be removed efficiently, which is preferable. However, even if the concentration exceeds 2.00 mol / L, there is no significant difference in the effect of removing impurities in the particles of the nickel composite hydroxide, so the concentration is preferably 2.00 mol / L or less.

The liquid temperature (water temperature) of the alkaline liquid used as the cleaning liquid is also not particularly limited, but is preferably 15 ° C. or higher and 50 ° C. or lower, for example. This is because when the liquid temperature of the cleaning liquid is within the above range, the ion exchange reaction becomes active and the removal of impurities proceeds efficiently.

The supply amount of the alkaline liquid used as the cleaning liquid in the first cleaning step is also not particularly limited, but is preferably 1000 mL or more, more preferably 2000 mL or more, for example, with respect to 1000 g of the nickel composite hydroxide. preferable. The upper limit of the supply amount of the alkaline liquid used as the cleaning liquid in the first cleaning step is also not particularly limited, but is preferably 5000 mL or less with respect to 1000 g of the nickel composite hydroxide, for example.

This is because the amount of the alkaline liquid used as the cleaning liquid in the first cleaning step is 1000 mL or more with respect to 1000 g of the nickel composite hydroxide, so that the impurity ions contained in the nickel composite hydroxide are sufficiently removed. Because it can be done. Further, even if an alkaline liquid of more than 5000 mL is supplied to 1000 g of the nickel composite hydroxide, there is not much difference in the effect of removing impurities.

In the first cleaning step, the alkaline liquid used as the cleaning liquid is supplied, and the cleaning time is not particularly limited, but may be, for example, 0.2 hours or more and 1 hour or less.

In the first cleaning step, it is preferable to perform cleaning with pure water after cleaning with an alkaline liquid as the cleaning liquid, and then switching the cleaning liquid to pure water as needed. This is to remove cationic impurities such as sodium derived from the alkaline liquid used as the cleaning liquid. The method of cleaning with pure water is not particularly limited, but for example, it is preferable to switch the cleaning liquid to pure water and continuously perform water-passing cleaning with pure water after water-passing cleaning using an alkaline liquid as the cleaning liquid. That is, in a state where the nickel composite hydroxide cake is squeezed by the squeezing means, pure water is supplied to the nickel composite hydroxide cake via the cleaning liquid pipe connected to the squeezing means to wash the nickel composite hydroxide cake. be able to.

The squeezing pressure when squeezing the nickel composite hydroxide cake in the first washing step may be lower than the re-squeezing pressure when re-squeezing the nickel composite hydroxide cake in the second washing step of the next step. preferable. This is because if the squeezing pressure in the first washing step is higher than the re-squeezing pressure in the second washing step, a portion where the cake is locally compacted may be formed and the washing liquid may be difficult to flow.

In the first washing step, the pressing pressure when squeezing the nickel composite hydroxide cake is not particularly limited, but is preferably 0.2 MPa or more and 0.5 MPa or less, for example.

By setting the pressing pressure in the first cleaning step to 0.2 MPa or more, the nickel composite hydroxide cake can be sufficiently squeezed as a whole, and by performing ion exchange, the cleaning liquid containing impurities is nickel-composited. This is because it can be sufficiently removed from the hydroxide cake and the amount of impurities can be sufficiently reduced. On the other hand, if the squeezing pressure in the first washing step becomes too high, the nickel composite hydroxide cake may be squeezed too much and a portion where the washing liquid may not flow easily may occur. However, when the squeezing pressure is 0.5 MPa or less, It is preferable because the cleaning liquid is surely distributed over the entire nickel composite hydroxide cake and can be washed uniformly.

Even when the nickel composite hydroxide cake is washed with pure water as described above after washing with the washing liquid, it is preferable that the nickel composite hydroxide cake is squeezed. The pressing pressure when washing the nickel composite hydroxide cake with pure water is also not particularly limited, but is preferably 0.2 MPa or more and 0.5 MPa or less for the same reason as in the above case.
(Second cleaning step)
The squeezing means is usually connected to a cleaning liquid pipe for supplying the cleaning liquid, a supply pipe for supplying the squeezed material to the squeezing means, and a drainage pipe for discharging the squeezed liquid to the outside. There is.

When cleaning is performed by a pressing means, the cleaning liquid is generally supplied only from the cleaning liquid pipe for cleaning. That is, it is common to supply the cleaning liquid only from the cleaning liquid pipe and perform cleaning as in the first cleaning step.

However, according to the study by the inventors of the present invention, a second cleaning step is carried out in addition to the first cleaning step, and in the second cleaning step, the cleaning liquid is discharged from the supply pipe which is a pipe different from the cleaning liquid pipe. It was found that by supplying the mixture, impurities in the nickel composite hydroxide cake can be significantly and uniformly reduced.

According to the study by the inventors of the present invention, the nickel composite hydroxide cake in the supply pipe and in the vicinity of the outlet of the supply pipe is difficult to be cleaned by supplying the cleaning liquid from the cleaning liquid pipe. Therefore, there is a possibility that a nickel composite hydroxide cake that has not been sufficiently washed may be mixed in only by carrying out the first washing step described above. Therefore, by carrying out the second cleaning step and supplying the cleaning liquid from the supply pipe in the second cleaning step, it becomes possible to sufficiently clean the supply pipe and the nickel composite hydroxide cake near the outlet thereof. , The concentration of impurities in the nickel composite hydroxide cake can be significantly and uniformly reduced.

As the cleaning liquid used in the second cleaning step, an alkaline liquid can be preferably used. The alkaline liquid used as the cleaning liquid is not particularly limited, but the alkaline liquid described as the alkaline liquid that can be suitably used in the first cleaning step can be preferably used.

The concentration of the alkaline liquid is also not particularly limited, but for example, the lower limit is preferably 0.10 mol / L or more, more preferably 0.15 mol / L or more, and 0. It is more preferably 20 mol / L or more. The upper limit is preferably 2.00 mol / L or less, and more preferably 1.50 mol / L or less.

By using an alkaline liquid with a concentration of 0.10 mol / L or more as the cleaning liquid, impurities in the particles of the nickel composite hydroxide, especially sulfate roots and chlorine, can be removed by the ion exchange action of the ions contained in the cleaning liquid. This is because it is preferable that it can be removed efficiently. However, even if the concentration exceeds 2.00 mol / L, there is no significant difference in the effect of removing impurities in the particles of the nickel composite hydroxide, so the concentration is preferably 2.00 mol / L or less.

The liquid temperature (water temperature) of the alkaline liquid used as the cleaning liquid is also not particularly limited, but is preferably 15 ° C. or higher and 50 ° C. or lower, for example. This is because when the liquid temperature of the cleaning liquid is within the above range, the ion exchange reaction becomes active and the removal of impurities proceeds efficiently.

The supply amount of the alkaline liquid used as the cleaning liquid in the second cleaning step is also not particularly limited, but is preferably 150 mL or more, more preferably 250 mL or more, for example, with respect to 1000 g of the nickel composite hydroxide. preferable. The upper limit of the supply amount of the alkaline liquid used as the cleaning liquid in the second cleaning step is also not particularly limited, but is preferably 5000 mL or less with respect to 1000 g of the nickel composite hydroxide, for example.

This is because the amount of the alkaline liquid used as the cleaning liquid in the second cleaning step is 150 mL or more with respect to 1000 g of the nickel composite hydroxide, so that the impurity ions contained in the nickel composite hydroxide are sufficiently removed. Because it can be done. Further, even if an alkaline liquid of more than 5000 mL is supplied to 1000 g of the nickel composite hydroxide, there is not much difference in the effect of removing impurities.

The alkaline liquid used as the cleaning liquid in the first cleaning step and the alkaline liquid used as the cleaning liquid in the second cleaning step may be the same, but may be different. However, in order to prevent different types of cations derived from the cleaning liquid from remaining in the nickel composite hydroxide cake, it is preferable to use the same alkaline liquid as the cleaning liquid in the first cleaning step and the second cleaning step. ..

In the second cleaning step, the time for supplying an alkaline liquid as a cleaning liquid and cleaning is not particularly limited, but may be, for example, 0.05 hours or more and 1 hour or less.

Also in the second cleaning step, as described in the first cleaning step, it is preferable to perform cleaning with pure water by switching the cleaning liquid to pure water as needed after cleaning using an alkaline liquid as the cleaning liquid. This is to remove cationic impurities such as sodium derived from the alkaline liquid used as the cleaning liquid. The method of cleaning with pure water is not particularly limited, but for example, it is preferable to switch the cleaning liquid to pure water and continuously perform water-passing cleaning with pure water after water-passing cleaning using an alkaline liquid as the cleaning liquid. That is, in a state where the nickel composite hydroxide cake is not squeezed, pure water is supplied to the nickel composite hydroxide cake via a supply pipe connected to the squeezing means to wash the nickel composite hydroxide cake. Can be done.

Then, in the second washing step, it is preferable to re-squeeze the nickel composite hydroxide cake after passing an alkaline liquid or further pure water. By re-squeezing, cation impurities and the like remaining in the nickel composite hydroxide cake can be removed together with water, and the amount of impurities in the nickel composite hydroxide cake can be further reduced. Further, by lowering the water content of the nickel composite hydroxide cake, for example, the amount of hot air used when carrying out a drying step or the like after the second washing step can be reduced.

In the second washing step, the re-squeezing when the nickel composite hydroxide cake is re-squeezed is not particularly limited, but is preferably 0.25 MPa or more and 0.8 MPa or less, for example. By setting the re-squeeze to 0.25 MPa or more, the nickel composite hydroxide cake can be sufficiently re-squeezed, and the nickel composite hydroxide cake can be sufficiently re-squeezed with a cleaning liquid containing impurities and cleaning water. Because it can be removed. Further, as will be described later, for example, when the drying step or the like is carried out after the second washing step, the cake can be easily dried, and the washing liquid and the washing water containing impurities can be sufficiently removed at that time as well. Therefore, the impurity concentration can be particularly reduced.

However, if it exceeds 0.8 MPa, the pressure applied to the pressed rubber and the filter cloth becomes high, which may cause tearing of the filter cloth. Therefore, the re-pressurized pressure is preferably 0.8 MPa or less.

After the washing step is completed, when the obtained nickel composite hydroxide cake is subjected to a drying step or the like, the nickel is used so that the drying can be carried out efficiently and the nickel can be easily recovered from the pressing means. The composite hydroxide cake is preferably dehydrated so that the water content is 10% or more and 30% or less.

The method for producing a nickel composite hydroxide of the present embodiment may have an arbitrary step in addition to the above-mentioned supply step, filtration step, and washing step.

For example, it can have a coprecipitation step to produce a nickel composite hydroxide.

A configuration example of the coprecipitation process will be described below.
[Coprecipitation process]
In the coprecipitation step, the nickel composite hydroxide slurry to be supplied to the pressing means can be produced in the above-mentioned supply step.

The coprecipitation step can have, for example, the following steps.

An initial aqueous solution preparation step of preparing an initial aqueous solution containing a Ni / Co-containing mixed aqueous solution containing nickel and cobalt, an ammonium ion feeder, and an aluminum source in a reaction vessel.

Then, an alkaline solution supply step of continuously supplying an alkaline solution, a Ni / Co-containing mixed aqueous solution, an ammonium ion feeder, an aluminum source, etc. to the initial aqueous solution to form a mixed aqueous solution.
In the alkaline solution supply step, it is preferable to control the pH value of the mixed aqueous solution measured with the liquid temperature of 25 ° C. as a reference so as to be 11.0 or more and 12.8 or less.

In the alkaline solution supply step, the nickel composite hydroxide can be co-precipitated in the reaction vessel so as to have the atomic ratio of the general formula of the nickel composite hydroxide described above, and the nickel composite is overflowed from the reaction vessel. Hydroxides can be recovered.

In the coprecipitation step, the nucleation reaction and the particle growth reaction proceed simultaneously in the same reaction vessel, so that the particle size distribution of the obtained nickel composite hydroxide can be widened.

Hereinafter, each step will be described.
(Initial aqueous solution preparation step)
In the initial aqueous solution preparation step of the coprecipitation step, an initial aqueous solution containing a Ni / Co-containing mixed aqueous solution containing nickel and cobalt, an ammonium ion feeder, and an aluminum source can be prepared in the reaction vessel. Hereinafter, each component contained in the initial aqueous solution will be described.
(1) Ni / Co-containing mixed aqueous solution The salt such as nickel salt and cobalt salt used in the Ni / Co-containing mixed aqueous solution containing nickel and cobalt is not particularly limited as long as it is a water-soluble compound. Sulfates, nitrates, chlorides and the like can be used. For example, nickel sulfate, cobalt sulfate and the like can be preferably used.

The concentration of the metal salt in the Ni / Co-containing mixed aqueous solution is preferably 1 mol / L or more and 2.6 mol / L or less in total, and more preferably 1 mol / L or more and 2.2 mol / L or less. .. This is because by setting the metal salt concentration of the Ni / Co-containing mixed aqueous solution to 1 mol / L or more, the slurry concentration of the obtained nickel composite hydroxide slurry can be sufficiently increased, so that the nickel composite water is highly productive. This is because oxides can be produced. However, if the metal salt concentration of the Ni / Co-containing mixed aqueous solution exceeds 2.6 mol / L, crystal precipitation or freezing may occur at -5 ° C or lower, which may clog the equipment piping, and keep the piping warm or warm. It is not preferable because it is necessary to do it and it is costly.

Further, the amount of the Ni / Co-containing mixed aqueous solution supplied to the reaction vessel is not particularly limited, but for example, the concentration of the crystallization product at the time when the crystallization reaction is completed is adjusted to be 30 g / L or more and 250 g / L or less. It is more preferable to adjust the concentration of the crystallized product to be 80 g / L or more and 150 g / L or less. This is because when the concentration of the crystallized product at the time when the crystallization reaction is completed is 30 g / L or more, the aggregation of the primary particles can proceed particularly sufficiently, and the concentration should be 250 g / L or less. This is because the Ni / Co-containing mixed aqueous solution to be added can be sufficiently diffused in the reaction vessel to obtain a nickel composite hydroxide slurry having a particularly uniform composition.
(2) Ammonium ion feeder The ammonium ion feeder is not particularly limited as long as it is a water-soluble compound, but is one selected from, for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like. The above can be preferably used. In particular, one or more selected from ammonia and ammonium sulfate can be more preferably used.

The ammonium ion feeder can function as a complexing agent. By adding the ammonium ion feeder, even if the pH value of the mixed aqueous solution is controlled within a wide range of 11.0 or more and 12.8 or less in the alkaline solution supply step described later, the nickel composite hydroxide is produced. This is because the generation speed can be kept sufficiently high. Further, even if the pH value of the mixed aqueous solution is controlled within the above range, the generation of fine particles that hinder the filtration when filtering the obtained nickel composite hydroxide is suppressed, and the nickel composite hydroxide is suppressed. This is because the secondary particles of can be spherical particles.

In the reaction vessel, the ammonia concentration in the initial aqueous solution and the mixed aqueous solution is preferably 3 g / L or more and 25 g / L or less.

As described above, the ammonium ion feeder acts as a complexing agent, and by setting the ammonia concentration in the initial aqueous solution and the mixed aqueous solution to 3 g / L or more, the solubility of metal ions is stabilized in the initial aqueous solution and the mixed aqueous solution. Can be kept constant. Therefore, primary particles of nickel composite hydroxide having a uniform shape and particle size can be formed. Furthermore, by setting the ammonia concentration to 3 g / L or more, it is possible to generate a nickel composite hydroxide containing secondary particles having an appropriate spread of particle size distribution suitable for use as a raw material for a positive electrode active material. ..

On the other hand, by setting the ammonia concentration in the initial aqueous solution and the mixed aqueous solution to 25 g / L or less, it is possible to prevent the solubility of metal ions from becoming too large, and the resulting nickel composite hydroxide may have a composition shift. Can be prevented.

As the ammonia concentration in the initial aqueous solution and the mixed aqueous solution fluctuates, the solubility of metal ions may fluctuate, and the uniformity of the internal composition of the nickel composite hydroxide particles may decrease. Therefore, it is preferable to control the fluctuation range of the ammonia concentration in the initial aqueous solution and the mixed aqueous solution to be small. For example, it is more preferable to control the ammonia concentration so that the width between the upper limit value and the lower limit value is 5 g / L and is within the width. Even in this case, the upper limit and the lower limit of ammonia are preferably 3 g / L or more and 25 g / L or less.
(3) Aluminum source The aluminum source is not particularly limited, but it is preferable to use an aqueous solution of sodium aluminate. The sodium aluminate aqueous solution can be obtained, for example, by dissolving a predetermined amount of sodium aluminate in water to form an aqueous solution, and adding a predetermined amount of sodium hydroxide. In order to uniformly disperse aluminum inside the particles of the nickel composite hydroxide, a mixed aqueous solution containing nickel and cobalt and a sodium aluminate aqueous solution may be added to the reaction vessel at the same time. At this time, it is preferable to adjust the metal concentrations of nickel, cobalt, and aluminum so as to match the target composition ratio represented by the general formula of the nickel composite hydroxide.
(Alkaline solution supply step)
Then, in the alkaline solution supply step, the alkaline solution, the Ni / Co-containing mixed aqueous solution, the ammonium ion feeder, the aluminum source, and the like can be continuously supplied to the initial aqueous solution to form the mixed aqueous solution.

The alkaline solution used in the alkaline solution supply step is not particularly limited, but it is preferable to use an aqueous solution of an alkali metal hydroxide. As the alkali metal hydroxide, it is preferable to use a compound that is easily dissolved in water because it is easy to control the amount of addition, and for example, one or more selected from lithium hydroxide, sodium hydroxide, and potassium hydroxide. Is preferable.

In the alkaline solution supply step, the method of adding the alkaline solution to the reaction vessel is not particularly limited, and it is preferable to add the alkaline solution with a pump capable of controlling the flow rate, such as a metering pump. When adding the alkaline solution, it is preferable to add the mixed aqueous solution so that the pH value of the mixed aqueous solution is maintained at 11.0 or more and 12.8 or less based on the liquid temperature of 25 ° C.

In the alkaline solution supply step, when supplying the Ni / Co-containing mixed aqueous solution and the aluminum source, the metal concentrations of nickel, cobalt, and aluminum in the mixed aqueous solution are the targets shown by the general formula of the nickel composite hydroxide. It is preferable to adjust the composition ratio to match the composition ratio.

As the Ni / Co-containing mixed aqueous solution, the ammonium ion feeder, and the aluminum source to be added to the initial aqueous solution in the alkaline solution supply step, the same ones as described in the initial aqueous solution can be preferably used. Then, the explanation is omitted.

The temperature of the mixed aqueous solution in the alkaline solution supply step is not particularly limited, but is preferably 50 ° C. or higher and 80 ° C. or lower, for example.

Further, the method for producing a nickel composite hydroxide of the present embodiment may include a drying step of drying the obtained nickel composite hydroxide cake after the washing step.
[Drying process]
In the drying step, the nickel composite hydroxide cake obtained by the washing step can be dried. The nickel composite hydroxide cake can be made into a powder by drying.

The drying means used in the drying step is not particularly limited, and various drying means can be used. For example, a drying method such as hot air drying can be used, and as the drying equipment, a stationary dryer, a batch type or continuous air flow dryer using hot air heated by steam or the like can be used. ..

3. 3. Positive electrode active material for non-aqueous electrolyte secondary battery The positive electrode active material for non-aqueous electrolyte secondary battery can be produced by using the above-mentioned nickel composite hydroxide as a precursor.

The positive electrode active material of the present embodiment is made of a lithium nickel composite oxide composed of a hexagonal lithium-containing composite oxide having a layered structure. Since the lithium nickel composite oxide uses the above-mentioned nickel composite hydroxide as a precursor, it can have a predetermined composition and average particle size, and can have a predetermined particle size distribution. Therefore, the positive electrode active material of the present embodiment is excellent in cycle characteristics and safety, and is suitable as a material for the positive electrode of a non-aqueous electrolyte secondary battery.

[composition]
The positive electrode active material of the present embodiment is made of lithium-nickel-cobalt-aluminum composite oxide, the composition has the general _{formula: Li t Ni 1-x-} y Co x Al y O 2 + β ( where in the formula, 0.97 ≦ t ≦ 1.20, 0.05 ≦ x ≦ 0.35, 0.01 ≦ y ≦ 0.2, x + y <0.4, −0.2 ≦ β ≦ 0.2). To.

In the positive electrode active material of the present embodiment, the atomic ratio t of lithium preferably satisfies 0.97 ≦ t ≦ 1.20. By setting the atomic ratio t of lithium to 0.97 or more, the reaction resistance of the positive electrode in the battery using the positive electrode active material can be sufficiently suppressed, so that the output of the battery can be particularly increased. However, when the atomic ratio t of lithium is more than 1.20, the initial discharge capacity of the battery using the positive electrode active material may decrease and the reaction resistance of the positive electrode may increase. Therefore, the atomic ratio t of lithium is preferably 0.97 ≦ t ≦ 1.20, and more preferably 1.05 or more is the lower limit of the atomic ratio t of lithium.

By containing cobalt in the positive electrode active material, good cycle characteristics can be obtained. This is because by substituting a part of nickel in the crystal lattice with cobalt, the expansion and contraction behavior of the crystal lattice due to the deinsertion and insertion of lithium due to charge and discharge can be reduced. The atomic ratio x of cobalt is preferably 0.05 ≦ x ≦ 0.35, more preferably 0.07 ≦ x ≦ 0.25, and 0.10 ≦ x in consideration of improving battery characteristics and safety. It is more preferable to set ≦ 0.20.

In the positive electrode active material, the atomic ratio y of aluminum to the atoms of all metals other than lithium is preferably 0.01 ≦ y ≦ 0.2, more preferably 0.01 ≦ y ≦ 0.1. .. By adding aluminum to the positive electrode active material, the durability and safety of the battery can be improved when used as the positive electrode active material of the battery. In particular, in the positive electrode active material, when aluminum is uniformly distributed inside the particles of the positive electrode active material, the effect of improving the durability and safety of the battery can be exhibited in the entire particles, and the same amount of addition can be used. Even if there is, there is an advantage that a larger effect can be obtained and a decrease in battery capacity can be suppressed.

As described above, in the positive electrode active material, the atomic ratio y of aluminum to the atoms of all metals other than lithium is preferably 0.01 or more. This is because when the atomic ratio y of aluminum to the atoms of all metals other than lithium is 0.01 or more, durability (cycle characteristics) and safety can be particularly improved.

Further, the atomic ratio y of aluminum to the atoms of all metals other than lithium in the positive electrode active material is preferably 0.2 or less. This is because when the atomic ratio y of aluminum to the atoms of all metals other than lithium is 0.2 or less, when the positive electrode active material is used as the positive electrode material of the battery, the positive electrode active material is redox in the battery. This is because the battery capacity can be particularly increased because the metal element that contributes to the reaction is particularly sufficiently contained, which is preferable.

The positive electrode active material inherits the properties of the above-mentioned nickel composite hydroxide as a precursor, and the sulfate root content is preferably 0.4% by mass or less, more preferably 0.3% by mass or less. And the chlorine content is preferably 0.05% by mass or less, more preferably 0.03% by mass or less.

Further, the average particle size of the particles (secondary particles) of the positive electrode active material is preferably 3 μm or more and 25 μm or less. By setting the average particle size of the particles of the positive electrode active material in the above range, the battery capacity per volume of the battery using the positive electrode active material can be increased, and the output characteristics of the battery can be particularly improved. can.

It is preferable that [(d90-d10) / average particle size], which is an index showing the spread of the particle size distribution of the positive electrode active material, is larger than 0.55 and 1.20 or less. By satisfying the range of [(d90-d10) / average particle size] of the positive electrode active material, the battery using this positive electrode active material as the positive electrode has a high capacity per unit weight or a high capacity per unit volume. Moreover, it is excellent in safety, and good cycle characteristics and battery output can be obtained.

4. Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery Next, a configuration example of the method for producing the positive electrode active material of the present embodiment will be described.

The method for producing the positive electrode active material of the present embodiment is not particularly limited as long as it can be produced from the nickel composite hydroxide described above, but it is more reliable if the following method for producing the positive electrode active material is adopted. It is preferable because it can produce a positive electrode active material.

The method for producing a positive electrode active material of the present embodiment can have the following steps.

A heat treatment process that heat-treats nickel composite hydroxide, which is the raw material for the positive electrode active material.
A mixing step of mixing a heat-treated nickel composite hydroxide and a lithium compound to form a mixture.

A firing step of firing the mixture formed in the mixing step.

After the firing step, the fired product can be crushed if necessary (crushing step).

Through the above steps, a lithium nickel composite oxide, that is, a positive electrode active material can be obtained. Hereinafter, each step will be described.

In the heat treatment step, the residual water content of the nickel composite hydroxide can be removed and the nickel composite hydroxide can be decomposed into a nickel composite oxide. The heat treatment temperature in the heat treatment step is not particularly limited, but the heat treatment temperature is preferably 300 ° C. or higher and 800 ° C. or lower. This is because by setting the heat treatment temperature to 300 ° C. or higher, the removal of water and the decomposition of the nickel composite hydroxide can be sufficiently proceeded. However, the heat treatment temperature is preferably 800 ° C. or lower from the viewpoint of suppressing aggregation due to sintering of the produced nickel composite oxide.

In the heat treatment step, the atmosphere in which the heat treatment is performed is not particularly limited, and it is preferable to perform the heat treatment in an air stream that can be easily performed.

In the mixing step, the nickel composite hydroxide after the heat treatment, that is, the nickel composite oxide and the lithium compound can be mixed.

The lithium compound used in the mixing step is not particularly limited, but for example, one or more selected from lithium hydroxide, lithium nitrate, and lithium carbonate can be preferably used. This is because the above-mentioned lithium compound is relatively easy to obtain. In particular, in consideration of ease of handling and stability of quality, it is more preferable to use lithium hydroxide as the lithium compound in the mixing step.

The mixing means for mixing the nickel composite oxide and the lithium compound in the mixing step is not particularly limited. For example, various mixers generally used in the mixing process can be used, and for example, one or more selected from a shaker mixer, a Ladyge mixer, a Julia mixer, a V blender and the like can be used. When these mixers are used, it is preferable to select the conditions so that the nickel composite oxide and the lithium compound can be sufficiently mixed without destroying the skeleton of particles such as the nickel composite oxide.

In the firing step, the mixture formed in the mixing step can be fired. The firing temperature in the firing step is not particularly limited, but is preferably 700 ° C. or higher and 850 ° C. or lower, and more preferably 720 ° C. or higher and 820 ° C. or lower.

By setting the firing temperature of the mixture formed in the mixing step to 700 ° C. or higher, lithium can be sufficiently diffused in the mixture, and excess lithium and unreacted particles are suppressed from remaining. However, the crystal structure of the obtained lithium-nickel composite oxide can be sufficiently prepared. Therefore, in a battery using the obtained lithium nickel composite oxide which is a positive electrode active material, sufficient battery characteristics can be exhibited.

However, if the temperature at which the mixture formed in the mixing step is calcined exceeds 850 ° C., the aggregation of the obtained lithium nickel composite oxide may be promoted. Therefore, the upper limit of the firing temperature of the mixture formed in the mixing step is preferably 850 ° C. or lower.

In the firing step, the firing time for firing the mixture formed in the mixing step is not particularly limited, but is preferably, for example, 3 hours or more, and more preferably 6 hours or more. The upper limit of the firing time is not particularly limited, but is preferably 24 hours or less, for example.

This is because the lithium nickel composite oxide can be sufficiently produced by setting the firing time for firing the mixture formed in the mixing step to 3 hours or more. That is, the reaction rate can be sufficiently increased.

Further, in the firing step, the atmosphere when firing the mixture formed in the mixing step is preferably an oxidizing atmosphere, and in particular, oxygen is contained in the range of oxygen concentration of 18% by volume or more and 100% by volume or less. It is more preferable to have an atmosphere that makes the atmosphere.

In the method for producing a positive electrode active material as described above, since the above-mentioned impurities sulfate root and nickel composite hydroxide having a uniform and low content of chlorine are used as raw materials, they are mixed with a lithium compound. The reaction with lithium is not hindered during firing, and the deterioration of the crystallinity of the lithium nickel composite oxide can be suppressed. As a result, the positive electrode active material obtained by this method for producing the positive electrode active material has few impurities remaining inside and has high crystallinity. Therefore, the non-aqueous electrolyte secondary battery using the positive electrode active material has a high battery capacity per unit weight and unit volume as a whole, has a higher capacity than the conventional one, and has excellent safety. It can be a secondary battery.

5. Non-aqueous electrolyte secondary battery An example of the configuration of the non-aqueous electrolyte secondary battery of the present embodiment will be described.

The non-aqueous electrolyte secondary battery of the present embodiment can be a non-aqueous electrolyte secondary battery using the above-mentioned positive electrode active material. The non-aqueous electrolyte secondary battery of the present embodiment can more specifically have a positive electrode using the above-mentioned positive electrode active material. The non-aqueous electrolyte secondary battery can have substantially the same structure as a general non-aqueous electrolyte secondary battery except that the positive electrode active material described above is used as the positive electrode material, and thus will be briefly described. ..

The non-aqueous electrolyte secondary battery of the present embodiment has a structure including a case and a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and a separator housed in the case.

Specifically, the non-aqueous electrolyte secondary battery of the present embodiment can have a structure in which an electrode body impregnated with a non-aqueous electrolyte solution is sealed in a battery case. The electrode body referred to here has a structure in which a positive electrode and a negative electrode are laminated via a separator, and can be impregnated with a non-aqueous electrolytic solution as described above. Hereinafter, each member constituting the non-aqueous electrolyte secondary battery will be described.

The positive electrode is a sheet-shaped member. For example, a positive electrode mixture paste made by mixing a positive electrode active material, a conductive material, and a binder is applied to the surface of a current collector made of aluminum foil, and dried to form the positive electrode. can do. Further, for example, a mixture of a positive electrode active material, a conductive material and a binder may be formed and dried if necessary to obtain a positive electrode.

The negative electrode is a sheet-like member formed by applying a negative electrode mixture paste containing a negative electrode active material to the surface of a metal foil current collector such as copper and drying the negative electrode. Further, a lithium metal processed into a desired shape can also be used as the negative electrode.

As the separator, for example, a thin film such as polyethylene or polypropylene, and a film having a large number of fine pores can be used. It should be noted that the present invention is not particularly limited as long as it has the function of a separator.

The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. As the organic solvent, ethylene carbonate, propylene carbonate, diethyl carbonate and the like can be used. As the electrolyte salt, LiPF ₆ , LiBF ₄ , LiClO _4, or the like can be used.

The non-aqueous electrolyte secondary battery of the present embodiment has the above-mentioned sulfate root and a positive electrode using a positive electrode active material having a nickel composite hydroxide having a suppressed chlorine content as a precursor. Therefore, the capacity per unit weight and unit volume of the battery as a whole is high, the irreversible capacity is small, and the safety can be high.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples.

Here, first, the evaluation method of the nickel composite hydroxide obtained in the present example and the comparative example will be described.
(Evaluation of composition of nickel composite hydroxide)
The composition of the nickel composite hydroxide was measured by a high frequency inductively coupled plasma (ICP) emission spectrophotometer (ICPS-8100, manufactured by Shimadzu Corporation) after dissolving the sample in nitric acid.
(Evaluation of sulfate root content of nickel composite hydroxide)
The sulfuric acid root content was measured by dissolving the obtained nickel composite hydroxide in nitric acid and then measuring the sulfur element content with an ICP emission spectrophotometer (ICPS-8100, manufactured by Shimadzu Corporation). the amount of elemental sulfur was determined by converting the SO _4.

For the evaluation of the sulfuric acid root content, samples were taken from arbitrary 5 locations for the nickel composite hydroxides obtained in each Example and Comparative Example, and each sample was subjected to the above evaluation.
(Evaluation of chlorine content of nickel composite hydroxide)
The chlorine content was measured with an automatic titrator (COM-1600, manufactured by Hiranuma Sangyo Co., Ltd.).

For the evaluation of the chlorine content, samples were taken from arbitrary 5 locations for the nickel composite hydroxides obtained in each Example and Comparative Example, and each sample was subjected to the above evaluation.
(Evaluation of average particle size and particle size distribution of nickel composite hydroxide)
For the secondary particles contained in the nickel composite hydroxide, d10, d90, and the average particle size were measured using a laser light diffraction / scattering type particle size analyzer (model: MT3300EXII manufactured by Microtrac Bell Co., Ltd.).

In addition, d10 means a particle size in which the cumulative volume becomes 10% of the total volume of all the particles when the number of particles in each particle size is accumulated from the smaller particle size. Further, d90 means a particle size in which the cumulative volume is 90% of the total volume of all the particles when the number of particles in each particle size is accumulated from the smaller particle size.

In addition, (d90-d10) / average particle size was calculated from the measured values.
(Evaluation method of battery characteristics)
In evaluating the battery characteristics, lithium nickel composite oxide, which is a positive electrode active material, was produced from the nickel composite hydroxides produced in each Example and Comparative Example. The method for producing the lithium nickel composite oxide will be described below.

The nickel composite hydroxide produced in Examples and Comparative Examples was heat-treated at a temperature of 700 ° C. for 6 hours in an air stream having an oxygen content of 21% by volume, and the nickel composite oxide was recovered (heat treatment step).

Subsequently, lithium hydroxide was weighed so that Li / Me = 1.025 and mixed with the recovered nickel composite oxide to form a mixture (mixing step). The Li / Me Me means the total amount of metals other than lithium in the mixture, that is, nickel, cobalt, and aluminum. Mixing was performed using a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)).

Next, the mixture obtained in the mixing step was calcined at 500 ° C. for 4 hours in an oxygen stream having an oxygen content of 100% by volume, and then calcined at 730 ° C. for 24 hours (firing step).

After firing, the mixture was cooled to room temperature and the recovered product was crushed (crushing step).

Through the above steps, a lithium nickel composite oxide as a positive electrode active material was obtained.

Next, a non-aqueous electrolyte secondary battery was produced using the obtained lithium-nickel composite oxide.

According to the above procedure, 70% by mass of the positive electrode active material powder obtained from the nickel composite hydroxide produced in each Example and Comparative Example, 20% by mass of acetylene black as a conductive material, and PTFE (PTFE) as a binder. (Polytetrafluoroethylene) was added and mixed in an amount of 10% by mass, and 150 mg thereof was taken out to prepare pellets and used as a positive electrode.

Lithium metal was used as the negative electrode.

As the non-aqueous electrolyte solution, an equal amount mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) having _{1M LiClO 4 as a supporting salt (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.}

Then, a 2032 type coin battery was manufactured using each of the above members in a glove box having an Ar atmosphere in which the dew point was controlled to −80 ° C.

The initial discharge capacity of the manufactured coin battery was evaluated, and the initial efficiency was calculated.

The produced coin battery is left to stand for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) stabilizes, the current density to the positive electrode is set to 0.5 mA / cm ² and the cutoff voltage is charged to 4.3 V to obtain the initial charge capacity. did. Then, after a one-hour rest, the capacity when discharged to a cutoff voltage of 3.0 V was defined as the initial discharge capacity. The initial efficiency was calculated as initial discharge capacity / initial charge capacity × 100 (%).

In Examples and Comparative Examples, a special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. is used for each sample for producing a nickel composite hydroxide.

The conditions for producing the nickel composite hydroxides of the Examples and Comparative Examples will be described below.
[Example 1]
The following coprecipitation step was carried out to produce a nickel composite hydroxide.

A Ni / Co-containing mixed aqueous solution containing nickel sulfate and cobalt chloride, 25% by mass of ammonia water, and aluminum so that the molar ratio of nickel: cobalt: aluminum is 81.5: 15.0: 3.5. An aqueous sodium acid solution was added to the reaction vessel at the same time to prepare an initial aqueous solution (initial aqueous solution preparation step). The concentration of the metal salt in the Ni / Co-containing mixed aqueous solution of nickel sulfate and cobalt chloride was 2.0 mol / L.

Then, with respect to the initial aqueous solution, 25 mass% sodium hydroxide aqueous solution, while controlling the pH to be 11.8 based on the solution temperature of 25 ° C., the reaction temperature to 50 ° C., and the ammonia concentration to be maintained at 10 g / L. A Ni / Co-containing mixed aqueous solution, 25% by mass of ammonia water, and an aqueous sodium aluminate solution were added (alkaline solution supply step).

At this time, the Ni / Co-containing mixed aqueous solution and sodium aluminate were added so that the molar ratio of nickel, cobalt, and aluminum in the obtained mixed aqueous solution maintained the molar ratio in the initial aqueous solution.

By carrying out the co-precipitation step having the above initial aqueous solution preparation step and alkaline solution supply step, a nickel composite hydroxide (nickel cobalt-aluminum composite) composed of spherical secondary particles in which plate-shaped primary particles are aggregated. Hydroxide) was produced. After the inside of the reaction vessel became stable, the nickel composite hydroxide slurry was recovered from the overflow port.

Next, 40 L of the obtained nickel composite hydroxide slurry having a slurry concentration of 100 g / L was put into a filter press (Nippon Filtration Equipment Co., Ltd. model: PFS-0.48-25) as a pressing means, and used as a pressing means. It was supplied via a connected supply pipe (supply process).

Next, the nickel composite hydroxide slurry was filtered using a filter press as a pressing means to obtain a nickel composite hydroxide cake (filtration step).

Then, the nickel composite hydroxide cake was washed and filtered by the following procedure (washing step).

While pressing the nickel composite hydroxide cake with the pressing pressure by the filter press set to 0.4 MPa, the liquid temperature, which is an alkaline liquid as the cleaning liquid, is 25 ° C. and 1.0 mol via the cleaning liquid pipe connected to the filter press. 8 L of / L sodium carbonate aqueous solution was supplied. The alkaline liquid, which is the cleaning liquid, was supplied over 0.3 hours. As a result, the nickel composite hydroxide cake was washed (first washing step).

After the completion of the first washing step, the squeezing by the filter press was temporarily stopped.

Next, in a state where the nickel composite hydroxide cake was not squeezed, the liquid temperature, which is an alkaline liquid as a cleaning liquid, was 25 ° C., 1.0 mol / 1 L of L sodium carbonate aqueous solution was supplied. The alkaline liquid, which is the cleaning liquid, was supplied over 0.1 hours.

Further, after supplying the alkaline liquid, 9 L of pure water was further flowed through the supply pipe as washing water. After that, the cake was dehydrated by flowing air for 20 minutes while re-squeezing the cake at 0.7 MPa (second washing step).

The obtained nickel composite hydroxide cake was dried at 120 ° C. for 15 hours in a stationary dryer to obtain a nickel composite hydroxide.

The obtained nickel composite hydroxide was evaluated as described above. The evaluation results are shown in Table 1.

The evaluation of the sulfate root content and the chlorine content of the nickel composite hydroxide were carried out by collecting samples from any five locations of the nickel composite hydroxide obtained as described above. .. However, as for the evaluation results of the sulfuric acid root content and the chlorine content, since the evaluation results of the samples at the five locations were the same, only one value is shown in Table 1. The same was true for Examples 2 to 11.
[Example 2]
In the first washing step, a nickel composite hydroxide was prepared in the same manner as in Example 1 except that the pressing pressure of the nickel composite hydroxide cake was 0.2 MPa, and the evaluation described above was performed. The evaluation results are shown in Table 1.
[Example 3]
In the first washing step, a nickel composite hydroxide was prepared in the same manner as in Example 1 except that the pressing pressure of the nickel composite hydroxide cake was 0.5 MPa, and the evaluation described above was performed. The evaluation results are shown in Table 1.
[Example 4]
In the second washing step, a nickel composite hydroxide was prepared in the same manner as in Example 1 except that the re-squeeze of the nickel composite hydroxide cake was 0.5 MPa, and the evaluation described above was performed. The evaluation results are shown in Table 1.
[Example 5]
In the first washing step, a nickel composite hydroxide was prepared in the same manner as in Example 1 except that the pressing pressure of the nickel composite hydroxide cake was 0.1 MPa, and the above-mentioned evaluation was performed. The evaluation results are shown in Table 1.
[Example 6]
Except for the point that the squeezing pressure of the nickel composite hydroxide cake was set to 0.7 MPa in the first washing step and the point that the re-squeezing of the nickel composite hydroxide cake was set to 0.8 MPa in the second washing step. A nickel composite hydroxide was prepared in the same manner as in Example 1 and evaluated as described above. The evaluation results are shown in Table 1.
[Example 7]
It was carried out except that the squeezing pressure of the nickel composite hydroxide cake was 0.7 MPa in the first washing step and the re-squeezing of the nickel composite hydroxide cake was 0.4 MPa in the second washing step. A nickel composite hydroxide was prepared in the same manner as in Example 1 and evaluated as described above. The evaluation results are shown in Table 1.
[Example 8]
Except for the point that the squeezing pressure of the nickel composite hydroxide cake was 0.2 MPa in the first washing step and the re-squeezing of the nickel composite hydroxide cake was 0.3 MPa in the second washing step. A nickel composite hydroxide was prepared in the same manner as in Example 1 and evaluated as described above. The evaluation results are shown in Table 1.
[Example 9]
By reducing the supply rate of each supply liquid in the coprecipitation step as compared with Example 1, it is an index showing the expansion of the particle size distribution of the obtained nickel composite hydroxide [(d90-d10) / average grain. A nickel composite hydroxide was prepared in the same manner as in Example 1 except that the diameter] was 0.61, and the evaluation described above was performed.

The evaluation results are shown in Table 1.
[Example 10]
By increasing the supply rate of each supply liquid in the coprecipitation step as compared with Example 1, it is an index showing the expansion of the particle size distribution of the obtained nickel composite hydroxide [(d90-d10) / average grain. A nickel composite hydroxide was prepared in the same manner as in Example 1 except that the diameter] was 1.18, and the evaluation described above was performed.

The evaluation results are shown in Table 1.
[Example 11]
Nickel composite water in the same manner as in Example 1 except that in the first cleaning step and the second cleaning step, a potassium carbonate aqueous solution having a liquid temperature of 25 ° C. and 1.0 mol / L, which is an alkaline liquid, was used as the cleaning liquid. An oxide was prepared and evaluated as described above.

In the first washing step, 8 L of the potassium carbonate aqueous solution was supplied, and in the second washing step, 1 L of the potassium carbonate aqueous solution was supplied.

The evaluation results are shown in Table 1.
[Comparative Example 1]
After the first washing step was completed, the cake was dehydrated by flowing air for 20 minutes while re-squeezing the cake at 0.7 MPa without carrying out the second washing step. A nickel composite hydroxide was prepared in the same manner as in Example 1 and evaluated as described above. The evaluation results are shown in Table 1.

The evaluation of the sulfate root content and the chlorine content of the nickel composite hydroxide were carried out by collecting samples from any five locations of the obtained nickel composite hydroxide as described above. Table 1 shows the evaluation results of the lowest sulfate root content and chlorine content.

得られたニッケル複合水酸化物については、既述のニッケル複合水酸化物の組成の評価を実施したところ、実施例１〜１１、及び比較例１のいずれについても、Ｎｉ_{０．８１５}Ｃｏ_０．１５Ａｌ_{０．０３５}（ＯＨ）_２の組成になっていることが確認できた。

The composition of the nickel composite hydroxide described above was evaluated for the obtained nickel composite hydroxide _{. As a result , Ni 0.815} Co. 0. was carried out for both Examples 1 to 11 and Comparative Example 1. It was confirmed that the composition was ₁₅ Al _0.035 (OH) _2.

Further, when the cross section of the obtained nickel composite hydroxide was observed with a scanning electron microscope in Examples 1 to 11, a plurality of plate-shaped primary particles aggregated to form spherical secondary particles. I was able to confirm that.

According to the results shown in Table 1, in Examples 1 to 11, the sulfuric acid root content of the nickel composite hydroxide is 0.4% by mass or less, and the chlorine content is 0.05% by mass or less. Met. It was also confirmed that the contents of sulfuric acid root and chlorine could be suppressed uniformly and low.

Therefore, the initial discharge capacity of the non-aqueous electrolyte secondary battery using the positive electrode active material obtained from the nickel composite hydroxides of Examples 1 to 11 is 180 mAh / g or more, and the initial efficiency is 85% in each case. From the above, it was confirmed that the battery capacity was high.

On the other hand, in Comparative Example 1 in which the second washing step was not carried out, the sulfuric acid root was 0.42% by mass and the chlorine was 0.09% by mass. In addition, it was confirmed that the contents of sulfate roots and chlorine were not uniform in the same sample. Specifically, in Comparative Example 1, the evaluation results of the sulfuric acid root content and the chlorine content of the five evaluated samples had the maximum value and the minimum value of ± 20% of the median, respectively. It was confirmed that the range was exceeded.

The initial discharge capacity of the non-aqueous electrolyte secondary battery using the positive electrode active material obtained from the nickel composite hydroxide of Comparative Example 1 was 173 mAh / g, and the initial efficiency was 83% in each of Examples 1 to 1. It was confirmed that the value was lower than that of Example 11.

Claims (6)

General formula Ni _1-x-y Co _x Al _y (OH) _{2 + α} (0.05 ≦ x ≦ 0.35, 0.01 ≦ y ≦ 0.2, x + y <0.4, −0.2 ≦ α ≦ Represented by 0.2)
Contains spherical secondary particles formed by agglomeration of multiple primary particles,
The secondary particles have an average particle size of 3 μm or more and 20 μm or less, and the secondary particles have an index [(d90-d10) / average particle size] larger than 0.55, which is an index indicating the spread of the particle size distribution. .20 or less,
0.4 mass% or less content of sulfate radical, and Ri der chlorine content of less than 0.05 wt%,
When evaluated by sampling at five, content, and chlorine content of the median ± 20% or less of the range near Ru nickel composite hydroxide of the sulfate. The supply process of supplying the nickel composite hydroxide slurry into the pressing means via the supply pipe,
A filtration step of filtering the nickel composite hydroxide slurry by the pressing means to obtain a nickel composite hydroxide cake.
It has a cleaning step of cleaning the nickel composite hydroxide cake in the pressing means.
The cleaning step is
In a state where the nickel composite hydroxide cake is squeezed by the squeezing means, an alkaline liquid is supplied to the nickel composite hydroxide cake via a cleaning liquid pipe connected to the squeezing means to supply the nickel composite hydroxide cake. The first washing step to wash the thing cake,
A second washing step in which the alkaline liquid is supplied into the pressing means through the supply pipe in a state where the nickel composite hydroxide cake is not squeezed, and then the nickel composite hydroxide cake is re-squeezed. A method for producing a nickel composite hydroxide containing and. The method for producing a nickel composite hydroxide according to claim 2, wherein the alkaline liquid is at least one aqueous solution selected from sodium carbonate, potassium carbonate, sodium sesquicarbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and sodium hydroxide. .. In the first washing step, the squeezing pressure when squeezing the nickel composite hydroxide cake is
The method for producing a nickel composite hydroxide according to claim 2 or 3, which is lower than the re-squeeze when the nickel composite hydroxide cake is re-squeezed in the second washing step. The nickel composite hydroxide according to any one of claims 2 to 4, wherein in the first washing step, the squeezing pressure when squeezing the nickel composite hydroxide cake is 0.2 MPa or more and 0.5 MPa or less. Manufacturing method. The nickel composite water according to any one of claims 2 to 5, wherein the re-squeeze when the nickel-composite hydroxide cake is re-squeezed in the second washing step is 0.25 MPa or more and 0.8 MPa or less. Oxide production method.