JP7119302B2 - Positive electrode active material precursor for non-aqueous electrolyte secondary battery, method for producing positive electrode active material precursor for non-aqueous electrolyte secondary battery, method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

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

In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, there is a strong demand for the development of small, lightweight non-aqueous electrolyte secondary batteries with high energy density. There is also a strong demand for the development of high-power secondary batteries as large-sized batteries for power sources for driving motors and the like.

As a secondary battery that meets these requirements, there is a lithium ion secondary battery. A lithium-ion secondary battery is composed of a positive electrode, a negative electrode, an electrolytic solution, and the like, and a material capable of desorbing and intercalating lithium is used as a positive electrode active material and a negative electrode active material.

Lithium ion secondary batteries are currently being vigorously researched and developed. Among them, a lithium-ion secondary battery using a layered or spinel-type lithium metal composite oxide as a positive electrode material can obtain a high voltage of 4V class, and is being put to practical use as a battery having a high energy density.

Currently, lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ) using nickel, which is cheaper than cobalt, and lithium-nickel, are currently used as positive electrode materials for lithium-ion secondary batteries. Cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ ), lithium-rich nickel-cobalt-manganese composite oxide ( _{Li 2 MnO 3 —LiNixMnyCozO 2} ), and other lithium composite oxides have been proposed.

Among these positive electrode active materials, inexpensive lithium-nickel-cobalt-manganese composite oxides have been attracting attention in recent years. This composite oxide is a layered rock salt type compound like the lithium cobalt composite oxide.

A method for producing a precursor for obtaining such a lithium-nickel-cobalt-manganese composite oxide is disclosed in Patent Document 1, for example.

JP 2015-191847 A

By the way, in order to increase the output of lithium ion secondary batteries, it is effective to shorten the migration distance between the positive electrode and the negative electrode of lithium ions. It is useful to use cathode materials that contain particles.

However, although Patent Document 1 discloses the method for producing the precursor and the composition of the positive electrode active material produced using the precursor, it does not mention the structure of the particles of the positive electrode active material. In particular, the internal structure of secondary particles has not been investigated.

Therefore, in view of the above-described problems of the prior art, in one aspect of the present invention, a positive electrode active material precursor for non-aqueous electrolyte secondary batteries capable of forming a positive electrode active material for non-aqueous electrolyte secondary batteries containing porous particles is provided. The purpose is to provide the body.

In order to solve the above problems, according to one aspect of the present invention,
Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1, 0.25<x<0.60, 0<y<0.70, 0<z <0.70, 0 ≤ t ≤ 0.10, and M is one selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W The above additive elements.) A nickel-cobalt-manganese carbonate composite composed of
and a functional group containing hydrogen,
Provided is a positive electrode active material precursor for a non-aqueous electrolyte secondary battery in which H/Me, which is the ratio of the amount of hydrogen H contained and the metal component Me contained, is 1.60 or more.

According to one aspect of the present invention, it is possible to provide a positive electrode active material precursor for non-aqueous electrolyte secondary batteries that can form a positive electrode active material for non-aqueous electrolyte secondary batteries containing porous particles.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of the flow of the manufacturing method of the positive electrode active material precursor for non-aqueous electrolyte secondary batteries of embodiment of this invention. FIG. 4 is a diagram showing another example of the flow of the method for producing a positive electrode active material precursor for non-aqueous electrolyte secondary batteries according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a cross-sectional structure of a coin-type battery manufactured in Example 1 according to the present invention;

Hereinafter, the embodiments for carrying out the present invention will be described with reference to the drawings. Various modifications and substitutions can be made to.

[Positive electrode active material precursor for non-aqueous electrolyte secondary battery]
A configuration example of the positive electrode active material precursor for a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "precursor") of the present embodiment will be described. The precursor of this embodiment has a material amount ratio (molar ratio) of Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1 and 0.25<x<0.60 , 0<y<0.70, 0<z<0.70, 0≤t≤0.10, and M is Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, one or more additional elements selected from Nb, Mo, and W.) and a functional group containing hydrogen.

In the precursor of the present embodiment, H/Me, which is the substance amount ratio of the contained hydrogen H and the contained metal component Me, is set to 1.60 or more.

In the present embodiment, the metal component Me contained in the precursor includes Ni, Mn, Co, and the additional element M mentioned in the above substance amount ratio.

The precursor of the present embodiment can contain substantially spherical secondary particles formed by aggregation of a plurality of fine primary particles. The precursor of this embodiment can also be composed of the secondary particles.

The precursor of the present embodiment has a highly uniform particle size and is a fine crystal, and can be used as a raw material for a positive electrode active material for a non-aqueous electrolyte secondary battery.

The precursor of this embodiment will be specifically described below.

(composition)
The nickel-cobalt-manganese carbonate composite and the functional group containing hydrogen contained in the precursor of the present embodiment will be described.

The nickel-cobalt-manganese carbonate composite is, as described above, a nickel-cobalt-manganese composite in the form of a basic carbonate having a composition of Ni:Mn:Co:M=x:y:z:t in terms of mass ratio. be.

However, in the above substance amount ratio, x + y + z + t = 1, satisfying 0.25 < x < 0.60, 0 < y < 0.70, 0 < z < 0.70, 0 ≤ t ≤ 0.10, M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W;

The precursors of the present embodiment have general formula 1: _xMn2 ( _CO3 )3.yMn(OH) ₃ , general formula ₂ : _xCo ( _CO3 ) _2.yCo (OH) _2.zH2O , and General formula 3: It is possible to include a compound having an indefinite composition, which is a mixture of carbonates and hydroxides represented by Ni ₄ CO ₃ (OH) ₆ (H ₂ O) ₄ and the like.

When the precursor of the present embodiment is used as a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery, in order to further improve battery characteristics such as cycle characteristics and output characteristics, a nickel-cobalt-manganese carbonate composite can also be doped with one or more additive elements M, as described above.

One or more additive elements M selected from Mg, Ca, Al, Ti, V, Fe, Cr, Cu, Zn, Zr, Nb, Mo, and W are within the range of the predetermined substance amount ratio t, It is preferable that the particles are uniformly distributed inside the secondary particles and/or that the surfaces of the secondary particles are uniformly coated.

However, in the nickel-cobalt-manganese carbonate composite, if the substance amount ratio t of the additive element M exceeds 0.1, the metal element that contributes to the oxidation-reduction reaction (redox reaction) decreases, and the battery capacity may decrease. There is

Further, even when the nickel-cobalt-manganese carbonate composite does not contain the additive element M, the positive electrode active material produced using the precursor of the present embodiment has sufficient battery characteristics such as cycle characteristics and output characteristics. It has characteristics. Therefore, the additive element M does not have to be contained. Therefore, the additive element M is adjusted so that the substance amount ratio t is within the range of 0≦t≦0.1.

In addition, the precursor of this embodiment can contain the above-described hydrogen-containing functional groups. Functional groups containing hydrogen include, for example, hydrogen groups and hydroxyl groups. The functional group containing hydrogen is mixed in the manufacturing process, and H/Me, which is the substance amount ratio between the hydrogen H contained in the precursor of the present embodiment and the metal component Me, is set to 1.60 or more. Thus, when used as a positive electrode active material, porous particles can be obtained. Further, by setting H/Me to 1.70 or less, when the precursor of the present embodiment is used as a positive electrode active material, the strength of the positive electrode active material can be particularly increased, and the shape can be reliably maintained.

In the present embodiment, the metal component Me contained in the precursor includes Ni, Mn, Co, and the additional element M, which are listed in terms of the above substance amount ratios, as described above.

The precursors of the present embodiments can also contain components other than the nickel-cobalt-manganese-carbonate complex and the hydrogen-containing functional group, although the nickel-cobalt-manganese-carbonate complex and the hydrogen-containing functional group It can also be constructed from the base. In this case, the precursor of this embodiment does not exclude the inclusion of unavoidable components in the manufacturing process and the like.

[Method for producing positive electrode active material precursor for non-aqueous electrolyte secondary battery]
Next, an example of a method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also simply referred to as "precursor production method") will be described. In the method for producing a precursor of the present embodiment, a precursor can be obtained by a crystallization reaction, and the obtained precursor is washed and dried as necessary.

Specifically, in the method for producing the precursor of the present embodiment, the material amount ratio is Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1 and 0.25<x <0.60, 0<y<0.70, 0<z<0.70, 0≤t≤0.10, and M is Mg, Ca, Al, Ti, V, Cr, Fe, Cu, one or more additional elements selected from Zn, Zr, Nb, Mo, and W), and a non-aqueous electrolyte having a functional group containing hydrogen. A method for producing a positive electrode active material precursor for a next battery, comprising the following steps.

In the presence of carbonate ions, an initial aqueous solution containing at least one of an ammonium ion donor and an alkaline substance, an aqueous solution containing nickel (Ni) as a metal component, an aqueous solution containing cobalt (Co) as a metal component, and a metal Crystallization in which nuclei are generated in a mixed aqueous solution in which an aqueous solution containing manganese (Mn) as a component (hereinafter also simply referred to as "an aqueous solution containing Ni as a metal component, etc.") is mixed, and the generated nuclei are grown. process.

In the method for producing a precursor according to the present embodiment, the crystallization step is performed in an oxygen-containing atmosphere by controlling the pH value of the mixed aqueous solution to 9.0 or less at a reaction temperature of 40°C.

FIG. 1 shows an example of the flow of the method for producing a precursor according to this embodiment. As shown in FIG. 1, the method for producing a precursor of this embodiment includes a crystallization step.

(1) Crystallization step As shown in Fig. 1, in the crystallization step, first, ion-exchanged water (water) is mixed with at least one of an ammonium ion donor and an alkaline substance in a reaction tank to prepare an initial aqueous solution. can.

Although the ammonium ion donor is not particularly limited, it is preferably one or more selected from an aqueous ammonium carbonate solution, an aqueous ammonia solution, an aqueous ammonium chloride solution, and an aqueous ammonium sulfate solution.

Although the alkaline substance is not particularly limited, it is preferably one or more selected from sodium carbonate, sodium hydrogencarbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

If necessary, an acidic substance is added to the initial aqueous solution to adjust the reaction temperature to 9.0 or less at a reaction temperature of 40°C. By setting the pH value of the initial aqueous solution within the above range, it is possible to suppress the remaining impurities, so that a precursor with a small residual amount of impurities can be obtained. At this time, the pH value of the initial aqueous solution is preferably adjusted to 5.4 or more and 9.0 or less, more preferably 6.4 or more and 8.0 or less, and 7.1. It is more preferable to adjust the ratio to be 7.4 or less. The pH at this time can be adjusted, for example, by adding a pH-adjusting aqueous solution described later.

During the crystallization process, it is preferable that the mixed aqueous solution also has a pH value within the above range. Since the pH value of the mixed aqueous solution slightly fluctuates during the crystallization step, the maximum pH value of the mixed aqueous solution during the crystallization step can be used as the pH value of the mixed aqueous solution in the crystallization step.

During the crystallization process, it is preferable that the fluctuation range of the pH value of the mixed aqueous solution is controlled to be within 0.2 above and below the central value (set pH value), for example. This is because when the pH value of the mixed aqueous solution fluctuates widely, the growth of the particles contained in the precursor of the present embodiment is not uniform, and uniform particles with a narrow particle size distribution range may not be obtained. Because there is

The pH values in the initial aqueous solution and the mixed aqueous solution can be measured with a known pH meter.

The acidic substance is not particularly limited, and for example, sulfuric acid can be preferably used. As the acidic substance, it is preferable to use the same kind of acid as the metal salt used when preparing the aqueous solution containing the metal component to be added to the initial aqueous solution.

In the crystallization step, the inside of the reaction tank is made to exist in the presence of carbonate ions. The method of supplying carbonate ions is not particularly limited. For example, carbonate ions can be supplied to the mixed aqueous solution by supplying carbon dioxide gas together with an oxygen-containing gas described later into the reaction tank. Carbonate ions can also be supplied by using a carbonate when preparing the initial aqueous solution or the pH-adjusted aqueous solution.

In the crystallization step, the atmosphere is controlled so as to create an oxygen-containing atmosphere by blowing an oxygen-containing gas into the reaction tank in which the initial aqueous solution has been prepared. After that, as will be described later, an aqueous solution containing a metal component such as an aqueous solution containing Ni as the metal component is supplied into the reaction vessel at a constant flow rate, for example, and the pH value of the mixed aqueous solution is controlled to fall within a predetermined range. is doing. The metal component reacts with dissolved oxygen contained in the mixed aqueous solution, oxygen contained in the oxygen-containing gas supplied to the reaction tank, and the like. As a result, amorphous fine particles (primary particles) that are not single crystals of carbonate are produced. This particle becomes the nucleus (nuclear particle) of the precursor. These core particles aggregate and grow to generate large secondary particles. The particle size of secondary particles can be controlled by the reaction time of the crystallization step.

In addition, by blowing in the oxygen-containing gas, the functional group containing hydrogen can be easily mixed into the precursor as compared with the case of the inert gas atmosphere. As a result, the resulting precursor can have a H/Me ratio of the amount of hydrogen H to the metal component Me of 1.60 or more.

As the oxygen-containing gas, for example, various gases containing oxygen such as air can be used.

When the oxygen-containing gas is supplied into the reaction tank, the amount of the oxygen-containing gas supplied can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. Since dissolved oxygen in the mixed aqueous solution is consumed during the crystallization process, if the dissolved oxygen amount in the mixed aqueous solution is at least half of the saturated amount, sufficient oxygen is supplied for the reaction.

The dissolved oxygen content in the mixed aqueous solution can be measured with a known dissolved oxygen meter or the like.

In the crystallization step, the oxygen-containing gas may be continuously supplied into the reaction vessel even while an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component is being added to the initial aqueous solution.

Next, in the crystallization step, an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component is added to and mixed with the initial aqueous solution in a reaction tank. As a result, fine particles (primary particles) that serve as nuclei (nuclear particles) of the precursor are produced in the initial aqueous solution containing the metal component. As a result, a mixed aqueous solution containing primary particles serving as core particles is obtained. Whether or not a predetermined amount of core particles has been generated can be determined from the amount of metal salt contained in the mixed aqueous solution.

When adding an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component to the initial aqueous solution, the pH value of the resulting mixed aqueous solution is preferably controlled within a predetermined range as described above. For this reason, the aqueous solution containing the metal component is preferably added dropwise to the initial aqueous solution rather than added all at once. As a result, the solution containing the metal component or the mixed aqueous solution containing the metal component, which will be described later, can be supplied to the reaction tank at a constant flow rate, for example.

In order to maintain the pH of the mixed aqueous solution within a predetermined range, it is preferable to drop the pH-adjusting aqueous solution when supplying the aqueous solution containing the metal component or the mixed aqueous solution containing the metal component described later. The pH-adjusting aqueous solution is not particularly limited, but for example, an aqueous solution containing at least one of an ammonium ion donor and an alkaline substance can be used. The method of supplying the pH-adjusted aqueous solution into the reaction vessel is not particularly limited. For example, while sufficiently stirring the obtained mixed aqueous solution, a pump capable of controlling the flow rate such as a metering pump is used to feed the mixed aqueous solution. It may be added so that the pH value is kept within a predetermined range.

Here, in the crystallization step, the aqueous solution containing the metal components, which is added to the initial aqueous solution, contains an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component. An aqueous solution to be used will be described.

The aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component can contain metal compounds containing each metal component. For example, an aqueous solution containing Mn as a metal component can contain a metal compound containing manganese.

As the metal compound, it is preferable to use a water-soluble metal compound, and examples of water-soluble metal compounds include nitrates, sulfates, and hydrochlorides. Specifically, for example, nickel sulfate, cobalt sulfate, manganese sulfate, and the like can be suitably used.

The aqueous solution containing Ni as the metal component, the aqueous solution containing Co as the metal component, and the aqueous solution containing Mn as the metal component are preliminarily mixed in part or in whole to form a mixed aqueous solution containing the metal component. It may be added to an aqueous solution.

The composition ratio of each metal in the resulting precursor is the same as the composition ratio of each metal in the mixed aqueous solution containing metal components. For this reason, the composition ratio of each metal contained in the metal component-containing mixed aqueous solution added to the initial aqueous solution in the crystallization step should be equal to the composition ratio of each metal in the precursor to be generated. It is preferable to prepare the mixed aqueous solution containing the metal component by adjusting the ratio.

In addition, when mixing a plurality of metal compounds, specific metal compounds react with each other to generate unnecessary compounds, etc., an aqueous solution containing each metal component is added to the initial aqueous solution at a predetermined ratio at the same time. may be added.

The aqueous solutions containing each metal component may be added individually to the initial aqueous solution without being mixed. In this case, the aqueous solution containing each metal component so that the composition ratio of each metal component contained in the aqueous solution is equal to the composition ratio of each metal component in the precursor to be generated in the entire aqueous solution containing the metal component to be added. is preferably prepared.

As described above, the precursor manufactured by the method for manufacturing a precursor of the present embodiment has a material amount ratio of Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1). , 0.25<x<0.60, 0<y<0.70, 0<z<0.70, 0≤t≤0.10, and M is Mg, Ca, Al, Ti, V, one or more additive elements selected from Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W.) and a functional group containing hydrogen; have

That is, the precursor of this embodiment can further contain the additional element M in addition to Ni, Mn, and Co.

Therefore, in the crystallization step, one or more additive elements M selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W are optionally added. (hereinafter simply referred to as "aqueous solution containing additional element M") can also be added to the initial aqueous solution.

In the case where an aqueous solution containing Ni as a metal component is mixed to form a mixed aqueous solution containing a metal component and then the mixed aqueous solution containing the metal component is added to the initial aqueous solution, the aqueous solution containing the additive element M is added to the aqueous solution containing the metal component. The mixed aqueous solution may be added to the initial aqueous solution.

Further, when an aqueous solution containing Ni as a metal component is individually added to the initial aqueous solution, the aqueous solution containing the additional element M may be individually added to the initial aqueous solution.

Here, the aqueous solution containing the additive element M can be prepared using a compound containing the additive element M, for example. Examples of compounds containing additive element M include magnesium sulfate, calcium sulfate, sodium aluminate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, and potassium chromate. , iron sulfate, copper sulfate, zinc sulfate, zirconium sulfate, zirconium nitrate, niobium oxalate, ammonium molybdate, sodium tungstate, or ammonium tungstate, and the compound can be selected according to the element to be added. .

As described above, the additive element M is preferably uniformly distributed inside the core particles contained in the precursor and/or uniformly coated on the surface of the core particles.

By adding an aqueous solution containing the additional element M to the precursor particle-containing aqueous solution, the additional element M can be uniformly dispersed inside the core particles contained in the precursor.

In order to uniformly coat the surfaces of the secondary particles of the precursor with the additional element M, for example, a coating step of coating with the additional element M can be performed after the crystallization step is finished. The coating process will be described later.

The temperature of the mixed aqueous solution is preferably maintained at 20°C or higher, more preferably at 30°C or higher. Although the upper limit of the temperature of the mixed aqueous solution is not particularly limited, it is preferably 70° C. or lower, more preferably 50° C. or lower, for example. This is because when the temperature of the mixed aqueous solution in the crystallization step is less than 20° C., the solubility is low, so nucleation is likely to occur, and control may become difficult. On the other hand, if the temperature of the mixed aqueous solution exceeds 70° C. in the crystallization step, the primary crystal may be distorted and the tap density may be lowered.

The ammonium ion concentration in the mixed aqueous solution in the crystallization step is not particularly limited, but is preferably, for example, 0 g/L or more and 20 g/L or less, and particularly preferably kept at a constant value. By setting the ammonium ion concentration to 20 g/L or less, fine particles (primary particles), which are the nuclei (nuclear particles) of the precursor, can be uniformly grown. In addition, since the ammonium ion concentration is kept at a constant value, the solubility of metal ions can be stabilized, and uniform particle growth of precursor nuclei (nuclear particles) can be promoted.

In addition, the lower limit of the ammonium ion concentration is not particularly limited, and can be appropriately adjusted as necessary. Therefore, the ammonium ion concentration in the mixed aqueous solution is adjusted to 0 g/L or more and 20 g/L or less by, for example, using an ammonium ion donor in the initial aqueous solution or the pH-adjusted aqueous solution and adjusting the supply amount. preferably.

The ammonium ion concentration in the precursor particle-containing aqueous solution can be measured with a known ion meter or the like.

By completing the addition of the metal component-containing mixed aqueous solution to the initial aqueous solution, the mixed aqueous solution can be converted to a precursor particle-containing aqueous solution containing sufficiently grown precursor particles.

Thus, in the crystallization step, fine particles (primary particles), which are the nuclei (nuclear particles) of the precursor, can be generated and grown in the precursor particle-containing aqueous solution. Then, the crystallization step is continued until the core particles grow to a desired particle size, and by growing the core particles, it is possible to obtain a precursor having porous secondary particles with a desired particle size. can.

Further, in order to uniformly coat the surfaces of the porous secondary particles, which are precursors, with the additive element M, for example, after the crystallization process is finished, a coating process of coating with the additive element M is performed. may The coating process will be described later.

(Other aspects of the crystallization step)
In the method for producing a precursor of the present embodiment, as shown in FIG. 1, the crystallization step is composed of one step, but the present invention is not limited to this. For example, a crystallization step can also include a nucleation step and a grain growth step.

Specifically, in the method for producing the precursor of the present embodiment, the crystallization step can include the following steps.
An initial aqueous solution containing at least one of an ammonium ion donor and an alkaline substance in the presence of carbonate ions, an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component. A nucleation step of generating nuclei in a mixed aqueous solution mixed with an aqueous solution.
a grain growing step for growing the nuclei generated in the nucleating step;

The nucleation step is preferably carried out in an oxygen-containing atmosphere by controlling the pH value of the mixed aqueous solution to 7.5 or less at a reaction temperature of 40°C.

FIG. 2 shows another example of the flow of the method for producing a precursor according to this embodiment. As shown in FIG. 2, in the method for producing a precursor according to the present embodiment, the crystallization step includes a nucleation step and, after the nucleation step, a particle growth step of forming precursor particles by a coprecipitation method. including. The nucleation step is a step in which a nucleation reaction mainly occurs, and the grain growth step is a step in which a grain growth reaction mainly occurs. Precursor particles having a narrower particle size distribution can be obtained by having the crystallization process include the nucleation process and the particle growth process.

Each step of the method for producing a precursor according to the present embodiment shown in FIG. 2 will be specifically described below. In addition, the description of the contents common to the crystallization step of the method for producing the precursor of the present embodiment shown in FIG. 1 is partially omitted.

(1-1) Nucleation Step The nucleation step will be described with reference to FIG. As shown in FIG. 2, in the nucleation step, first, ion-exchanged water (water) is mixed with at least one of an ammonium ion donor and an alkaline substance in a reaction vessel to prepare an initial aqueous solution.

As the ammonium ion donor and alkaline substance, the same ammonium ion donor and alkaline substance as in the above-described crystallization step can be preferably used.

In the nucleation step, the mixed aqueous solution obtained by adding an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component to the initial aqueous solution is preferably maintained at a pH value lower than that in the particle growth step described later. By keeping the pH value of the mixed aqueous solution low, the number of nuclei in the mixed aqueous solution can be reduced and the number of nuclei can be increased, and the particle size of the secondary particles contained in the resulting precursor can be reduced. Because it becomes

Therefore, it is preferable to add an acidic substance to the initial aqueous solution as necessary to adjust the pH value to 7.5 or less, more preferably 5.4 or more and 7.5 or less, and 6.4. More preferably, it should be adjusted to 7.4 or less. It is particularly preferable to adjust the pH value to 6.4 or more and 7.0 or less.

During the nucleation step, it is preferred that the mixed aqueous solution also has a pH value in the above range. Since the pH value of the mixed aqueous solution slightly fluctuates during the nucleation step, the maximum value of the pH value of the mixed aqueous solution during the nucleation step can be used as the pH value of the mixed aqueous solution in the nucleation step.

During the nucleation step, the pH value of the mixed aqueous solution is preferably controlled within 0.2 above and below the center value (set pH value), for example.

As for the acidic substance, the acidic substance described in the above crystallization step can be preferably used.

In the nucleation step, an oxygen-containing gas is blown into the reaction tank in which the initial aqueous solution is prepared, and the atmosphere is controlled. can be controlled to fall within the range of As a result, the dissolved oxygen contained in the mixed aqueous solution and the oxygen contained in the oxygen-containing gas supplied to the reaction tank react with each other to generate fine irregular-shaped carbonate particles that are not single crystals. In addition, by blowing in the oxygen-containing gas, the functional group containing hydrogen can be more easily mixed into the precursor than in the case of an inert gas atmosphere. Thereby, H/Me, which is the substance amount ratio of hydrogen H contained in the obtained precursor and metal component Me contained, can be made 1.60 or more.

In the nucleation step, the oxygen-containing gas can be continuously supplied into the reaction vessel even while adding an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component to the initial aqueous solution.

When the oxygen-containing gas is supplied into the reaction tank, the amount of the oxygen-containing gas supplied can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. Since dissolved oxygen in the mixed aqueous solution is consumed during the nucleation step, if the dissolved oxygen amount in the mixed aqueous solution is at least half of the saturated amount, sufficient oxygen is supplied for the reaction.

As the oxygen-containing gas, for example, various gases containing oxygen such as air can be used.

In the nucleation step, an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component are added and mixed to the initial aqueous solution in the reaction tank. , can form a mixed aqueous solution.

When an aqueous solution containing Ni as a metal component is added to the initial aqueous solution, the pH value of the resulting mixed aqueous solution is preferably controlled to 7.5 or less at a reaction temperature of 40°C. It is more preferably controlled to 4 or less, and even more preferably 7.0 or less. Therefore, the aqueous solution containing the metal component such as the aqueous solution containing Ni as the metal component is preferably added dropwise to the initial aqueous solution rather than being added all at once.

In addition, in order to control the pH of the mixed aqueous solution, a pH-adjusting aqueous solution can also be dropped together with dropping an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component. As the pH-adjusted aqueous solution, the same pH-adjusted aqueous solution as in the crystallization step described above can be suitably used.

Then, in the mixed aqueous solution obtained by adding an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component to the initial aqueous solution as described above, it becomes the nucleus (nuclear particle) of the precursor in the mixed aqueous solution. Fine particles (primary particles) can be generated. Whether or not a predetermined amount of core particles is generated in the mixed aqueous solution can be determined by the amount of metal salt contained in the mixed aqueous solution.

The aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component, which are added to the initial aqueous solution in the nucleation step, are the same as in the crystallization step described above. An aqueous solution containing Ni as a metal component similar to that of can be preferably used.

As described above, the precursor manufactured by the method for manufacturing a precursor of the present embodiment has a material amount ratio of Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1). , 0.25<x<0.60, 0<y<0.70, 0<z<0.70, 0≤t≤0.10, and M is Mg, Ca, Al, Ti, V, one or more additive elements selected from Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W.) and a functional group containing hydrogen; have

That is, in addition to Ni, Mn, and Co, the additional element M can also be included.

Therefore, in the nucleation step, one or more additional elements M selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W, if necessary (aqueous solution containing additive element M) can also be added to the initial aqueous solution. As for the method of adding the aqueous solution containing the additive element M and the method of adding the aqueous solution containing the additive element M to the initial aqueous solution, the same method as in the above-described crystallization step can be used.

As described above, the additive element M is preferably uniformly distributed inside the core particles contained in the precursor and/or uniformly coated on the surfaces of the core particles.

By adding the aqueous solution containing the additive element M described above to the mixed aqueous solution, the additive element M can be uniformly dispersed inside the core particles contained in the precursor.

Further, in order to uniformly coat the surfaces of the secondary particles of the precursor with the additive element M, for example, after the particle growth process, which will be described later, is finished, a coating process of coating the secondary particles with the additive element M may be performed. . The coating process will be described later.

In the nucleation step, as in the crystallization step of the precursor production method of the present embodiment shown in FIG. 1, an aqueous solution containing Ni as a metal component is added to the initial aqueous solution in the presence of carbonate ions. They can be mixed to form a mixed aqueous solution, and nuclei can be generated in the mixed aqueous solution.

At this time, the method of supplying carbonate ions is not particularly limited. For example, carbonate ions can be supplied to the mixed aqueous solution by supplying carbon dioxide gas together with the oxygen-containing gas described later into the reaction tank. . Carbonate ions can also be supplied by using a carbonate when preparing the initial aqueous solution or the pH-adjusted aqueous solution.

The temperature of the mixed aqueous solution in the nucleation step is preferably maintained at 20°C or higher, more preferably at 30°C or higher. Although the upper limit of the temperature of the mixed aqueous solution in the nucleation step is not particularly limited, it is preferably 70° C. or lower, more preferably 50° C. or lower, for example. This is because when the temperature of the mixed aqueous solution in the nucleation step is less than 20° C., the solubility is low, so nucleation is likely to occur, and control may become difficult. On the other hand, if the temperature of the mixed aqueous solution exceeds 70° C. in the nucleation step, the primary crystal may be distorted and the tap density may be lowered.

The range of the ammonium ion concentration in the mixed aqueous solution in the nucleation step is preferably the same range as in the above-described crystallization step, for example. As for the methods for measuring the pH value, the ammonium ion concentration, and the dissolved oxygen content in the mixed aqueous solution, the same methods as in the above-described crystallization step can be suitably used.

After the nucleation step is completed, that is, after the addition of the mixed aqueous solution containing the metal component to the initial aqueous solution is completed, it is preferable to continue stirring the mixed aqueous solution and disintegrate the generated nuclei (nuclear disintegration process). When the nuclear disintegration step is performed, the time is preferably 1 minute or longer, more preferably 3 minutes or longer. By performing the nucleus disintegration step, it is possible to more reliably suppress the aggregation of the generated nuclei, the coarsening of the particle size, and the decrease in the density inside the particle.

(1-2) Particle Growth Step Next, the particle growth step will be described with reference to FIG. In the particle growth step, the nuclei generated in the nucleation step can be grown. Specifically, for example, as shown in FIG. 2, in the particle growth step, the pH value of the mixed aqueous solution obtained in the nucleation step can be adjusted.

At this time, the pH value of the mixed aqueous solution can be adjusted to, for example, 6.0 or more and 9.0 or less at a reaction temperature of 40°C. By setting the pH value of the mixed aqueous solution to 6.0 or more and 9.0 or less, it is possible to prevent impurity cations from remaining. The pH value of the mixed aqueous solution is more preferably adjusted to 6.4 or more and 8.0 or less, more preferably 7.1 or more and 8.0 or less. The pH at this time can be adjusted, for example, by adding the pH-adjusting aqueous solution described above.

Since the pH value of the mixed aqueous solution slightly fluctuates during the particle growth process, the maximum value of the pH value of the mixed aqueous solution during the particle growth process can be used as the pH value of the mixed aqueous solution in the particle growth process. The pH value of the mixed aqueous solution is preferably within the above range.

In particular, it is preferable to control the fluctuation range of the pH value of the mixed aqueous solution during the grain growth process so as to be within 0.2 above and below the center value (set pH value). This is because when the pH value of the mixed aqueous solution fluctuates widely, the growth of the particles contained in the precursor may not be uniform, and uniform particles with a narrow particle size distribution may not be obtained. .

In the particle growth step, the mixed aqueous solution after the nucleation step is added to an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component in the presence of carbonate ions. It can be a step of adding and mixing.

In addition, it is preferable that the mixed aqueous solution after the nucleation process here is the mixed aqueous solution which adjusted pH after the nucleation process as mentioned above.

Further, an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component are mixed in part or in whole, as in the nucleation step, It may be added to the mixed aqueous solution as a mixed aqueous solution containing a metal component. In addition, when mixing a plurality of metal compounds causes reactions between specific metal compounds to produce unwanted compounds, the aqueous solution containing each metal component can be added individually to the mixed aqueous solution. good too.

Furthermore, when adding an aqueous solution containing Ni as a metal component to the mixed aqueous solution, an aqueous solution containing the additive element M can be added together, as in the case of the nucleation step. As described above, an aqueous solution containing the additional element M can be mixed with the mixed aqueous solution containing the metal component and added. Moreover, when the aqueous solution containing each metal component is individually added to the mixed aqueous solution, the aqueous solution containing the additive element M can also be individually added to the mixed aqueous solution.

The aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component can be the same aqueous solutions as in the nucleation step described above. Also, the density and the like may be adjusted separately.

When adding an aqueous solution containing Ni as a metal component to the mixed aqueous solution, the pH value of the obtained mixed aqueous solution is preferably controlled within a predetermined range as described later. For this reason, the aqueous solution containing Ni as a metal component can be gradually added dropwise to the mixed aqueous solution instead of being added all at once. Therefore, a solution containing these metal components or a mixed aqueous solution containing the metal components can be supplied to the reaction vessel, for example, at a constant flow rate.

In the particle growth step, as described above, an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component can be added to the mixed aqueous solution after adjusting the pH value. Also in this case, for the same reason as adjusting the pH value before starting the particle growth process, the pH value of the mixed aqueous solution after the pH value adjustment is in the same range as in the case of the mixed aqueous solution, that is, 6.0 or more. It is preferably maintained at 9.0 or less. In the particle growth step, by controlling the pH value of the mixed aqueous solution within the range described above, a precursor with a small remaining amount of impurities can be obtained. The pH value of the mixed aqueous solution is more preferably maintained between 6.4 and 8.0, more preferably between 7.1 and 8.0.

Since the pH value of the mixed aqueous solution after pH value adjustment fluctuates slightly during the particle growth process, the maximum value of the pH value of the mixed aqueous solution after pH value adjustment during the particle growth process is It can be the pH value of the aqueous solution, and the pH value of the mixed aqueous solution after the pH value adjustment is preferably within the above range.

In particular, during the particle growth process, it is preferable to control the fluctuation range of the pH value of the mixed aqueous solution after adjusting the pH value to be within 0.2 above and below the center value (set pH value). This is because when the fluctuation range of the pH value of the mixed aqueous solution after adjusting the pH value is large, the growth of the particles contained in the precursor is not uniform, and uniform particles with a narrow particle size distribution cannot be obtained. because there is

As described above, when an aqueous solution containing a metal component or a mixed aqueous solution containing a metal component is supplied to a mixed aqueous solution, a pH-adjusting aqueous solution is also added so that the pH of the mixed aqueous solution can be maintained within a predetermined range. is preferred. As the pH-adjusted aqueous solution, the same pH-adjusted aqueous solution as in the above-described nucleation step can be used. As for the method of supplying the pH-adjusted aqueous solution into the reaction tank, the method described above in the above-described nucleation step can be suitably used.

In the particle growth step, the ammonium ion concentration in the mixed aqueous solution is preferably 0 g/L or more and 20 g/L or less, and particularly preferably kept at a constant value. This is because the nuclei of the precursor particles can be uniformly grown by setting the ammonium ion concentration to 20 g/L or less. Also, by keeping the ammonium ion concentration at a constant value in the particle growth step, the solubility of the metal ions can be stabilized, and uniform particle growth of the precursor particles can be promoted.

In addition, the lower limit of the ammonium ion concentration is not particularly limited, and can be appropriately adjusted as necessary. Therefore, the ammonium ion concentration in the mixed aqueous solution is adjusted to 0 g/L or more and 20 g/L or less by, for example, using an ammonium ion donor in the initial aqueous solution or the pH-adjusted aqueous solution and adjusting the supply amount. is preferred.

In the particle growth step, an aqueous solution containing a metal component, such as an aqueous solution containing Ni as a metal component, can be added to and mixed with the mixed aqueous solution in the presence of carbonate ions. At this time, the method of supplying carbonate ions is not particularly limited. For example, carbonate ions can be supplied to the mixed aqueous solution by supplying carbon dioxide gas together with an oxygen-containing gas, which will be described later, into the reaction tank. Carbonate ions can also be supplied by using a carbonate when preparing the above-described initial aqueous solution or pH-adjusted aqueous solution.

In the particle growth step, an oxygen-containing gas is blown into the reaction vessel to control the atmosphere so as to create an oxygen-containing atmosphere. can be supplied by As a result, the dissolved oxygen contained in the mixed aqueous solution and the oxygen contained in the oxygen-containing gas supplied to the reaction tank react with each other to further agglomerate amorphous fine particles that are not single crystals of carbonate. can generate large secondary particles. In addition, by blowing in the oxygen-containing gas, it is possible to easily mix the functional group containing hydrogen into the precursor as compared with the case of the inert gas atmosphere. Thereby, the H/Me, which is the substance amount ratio of the hydrogen H contained in the obtained precursor and the contained metal component Me, can be more reliably set to 1.60 or more.

In the particle growth step, when oxygen-containing gas is supplied into the reaction tank, the amount of oxygen-containing gas supplied can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. Since dissolved oxygen in the mixed aqueous solution is consumed during the particle growth process, if the dissolved oxygen amount in the mixed aqueous solution is at least half of the saturated amount, sufficient oxygen is supplied for the reaction.

As the oxygen-containing gas, for example, various gases containing oxygen such as air can be used.

The particle size of the secondary particles contained in the precursor can be controlled by adjusting the reaction time in the particle growth step. That is, in the particle growth step, if the reaction is continued until the particles grow to a desired particle size, a precursor having porous secondary particles with a desired particle size can be obtained.

As described above, by performing the crystallization step shown in FIG. 1 or 2, a precursor particle aqueous solution, which is a slurry containing precursor particles, is obtained.

In addition, in the method for producing a precursor of the present embodiment, it is preferable to use an apparatus that does not recover the precursor, which is a product, until the reaction in the crystallization step is completed. Such an apparatus includes, for example, a commonly used batch reactor equipped with a stirrer. By adopting such an apparatus, there is no problem that the growing particles are collected at the same time as the overflow liquid, unlike a continuous crystallizer that collects the product by general overflow, so that the particle size distribution is narrow and Particles having a uniform particle size can be obtained, which is preferable.

Moreover, in order to control the atmosphere of the reaction tank, it is preferable to use an apparatus capable of controlling the atmosphere, such as a closed type apparatus.

By using a device capable of controlling the atmosphere of the reaction vessel, the particles containing the precursor can have the structure as described above, and the coprecipitation reaction can proceed almost uniformly. Particles with an excellent distribution, ie particles with a narrow particle size distribution, can be obtained.

In the particle growth step, the pH value of the mixed aqueous solution obtained in the nucleation step is adjusted to a predetermined range, and an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component is added to the mixed aqueous solution. By doing so, uniform precursor particles can be obtained.

(Coating process)
Further, in the method for producing the precursor of the present embodiment, after obtaining the particles (secondary particles) of the precursor of the present embodiment in the crystallization step, the surfaces of the obtained particles of the precursor of the present embodiment are , a coating step of coating with an additive element M can be further included.

The coating step can be, for example, one of the following steps.
A step of adding an aqueous solution containing the additive element M to the slurry in which the precursor particles are suspended, and depositing the additive element M on the surfaces of the precursor particles by a crystallization reaction.
A step of spraying an aqueous solution or slurry containing the additional element M onto the precursor particles and drying them.
a step of spraying and drying the slurry in which the precursor particles and the compound containing the additional element M are suspended;
A step of mixing the precursor particles and the compound containing the additive element M by a solid-phase method.

The coating step is, for example, a step of adding an aqueous solution containing the additional element M to the slurry in which the precursor particles are suspended, and depositing the additional element M on the surfaces of the precursor particles by a crystallization reaction. In this case, it is preferable that the precursor particles are slurried using an aqueous solution containing the additive element M for the slurry in which the precursor particles are suspended. Further, when the aqueous solution containing the additive element M is added to the slurry in which the precursor particles are suspended, the pH of the mixed aqueous solution of the slurry and the aqueous solution containing the additive element M is 6.0 or more and 9.0 or less. It is preferable to control This is because the surfaces of the precursor particles can be particularly uniformly coated with the additive element M by controlling the pH of the mixed aqueous solution of the slurry and the aqueous solution containing the additive element M within the above range.

As for the aqueous solution containing the additional element M used in the coating step, the same aqueous solution as in the above-described nucleation step can be used. Further, in the coating step, instead of the aqueous solution containing the additive element M, an alkoxide solution containing the additive element M may be used.

As described above, the surface of the precursor particles can be coated with the additive element M by adding an aqueous solution containing the additive element M to the initial aqueous solution or the mixed aqueous solution in the crystallization step and performing the coating step. In this case, the amount of additive element ions added to the initial aqueous solution or the mixed aqueous solution in the crystallization step is preferably reduced by the coating amount. This is because the addition amount of the aqueous solution containing the additional element M to be added to the mixed aqueous solution is reduced by the coating amount, and the atomic ratio of the additional element M contained in the obtained precursor and the other metal components is can be set to a desired value.

The coating step of coating the surface of the precursor particles with the additional element M as described above may be performed on the precursor particles after heating after the crystallization step is completed.

Next, after finishing the crystallization process shown in FIG. 1 or 2, a washing process or a drying process may be performed. The washing process and the drying process are described below.

(2) Cleaning process The cleaning process will be described. In the washing step, the slurry containing the precursor particles obtained in the crystallization step shown in FIG. 1 or 2 can be washed.

In the washing step, first, the slurry containing the precursor particles can be filtered, washed with water, and filtered again.

Filtration may be carried out by a commonly used method, for example, using a centrifuge or a suction filter.

Moreover, the washing with water may be performed by a commonly used method as long as the surplus raw material and the like contained in the precursor particles can be removed.

In order to prevent contamination of impurities, the water used for washing is preferably water containing as few impurities as possible, and more preferably pure water.

(3) Drying process The drying process will be explained. In the drying step, the particles of the precursor of the present embodiment that have been washed in the washing step can be dried. First, in the drying step, for example, the washed precursor particles can be dried at a drying temperature of 80° C. or higher and 230° C. or lower.

After the drying step, the precursor of this embodiment can be obtained.

According to the method for producing a precursor of the present embodiment, a precursor capable of forming a positive electrode active material for a non-aqueous electrolyte secondary battery containing porous particles can be obtained.

Moreover, in the method for producing a precursor of the present embodiment, the crystal size of the precursor particles obtained by the crystallization reaction can be controlled. Therefore, according to the method for producing a precursor of the present embodiment, it is possible to obtain a precursor having a small primary particle size, a highly uniform secondary particle size, and a high density (tap density). can be done.

Further, according to the method for producing the precursor of the present embodiment shown in FIG. 2, the time during which the nucleation reaction mainly occurs (nucleation step) and the time during which the particle growth reaction mainly occurs (particle growth step) can be separated. can be done. As a result, precursor particles (secondary particles) having a narrow particle size distribution can be obtained even if both steps are performed in the same reactor.

Furthermore, in the method for producing a precursor according to the present embodiment shown in FIG. 2, the nucleation step and the particle growth step can be performed separately in one reaction tank by mainly adjusting the pH of the reaction solution. can.

Therefore, the method for producing the precursor according to the present embodiment is easy and suitable for large-scale production, and is therefore of great industrial value.

[Positive electrode active material for non-aqueous electrolyte secondary battery]
Next, one structural example of the positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter also simply referred to as "positive electrode active material") of the present embodiment will be described.

The positive electrode active material of the present embodiment relates to a positive electrode active material for non-aqueous electrolyte secondary batteries containing a lithium metal composite oxide. Li: Ni: Mn: Co: M = α: x: y: z: t (1.00 ≤ α ≤ 1.30, x + y + z + t = 1, and 0 .25<x<0.60, 0<y<0.70, 0<z<0.70, 0≤t≤0.10, M is Mg, Ca, Al, Ti, V, Cr, Fe, one or more additional elements selected from Cu, Zn, Zr, Nb, Mo, and W).

The positive electrode active material of the present embodiment can contain porous secondary particles in which a plurality of primary particles are aggregated. Then, among the porous secondary particles, the number ratio of secondary particles having a porosity of 10% or more and 30% or less in the interior of the secondary particles can be 80% or more.

The positive electrode active material of the present embodiment may contain a lithium metal composite oxide having a layered rocksalt crystal structure represented by LiAO ₂ , more specifically a lithium nickel cobalt manganese composite oxide. The positive electrode active material of this embodiment can also be composed of the lithium metal composite oxide.

In the above substance amount ratio, A is a metal element containing at least Ni, Co, and Mn adjusted to be trivalent on average.

In the precursor of the present embodiment, as described above, in order to further improve the battery characteristics such as the cycle characteristics and output characteristics of the positive electrode active material of the non-aqueous electrolyte secondary battery, the lithium metal composite oxide is added as described above. may contain one or more additive elements M selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W. For the reason described above, the content of the additive element M is preferably adjusted so that the substance amount ratio t is within the range of 0≦t≦0.1 in the precursor.

As described above, the positive electrode active material of the present embodiment can contain porous secondary particles, and the porous secondary particles have a porosity of 10% or more and 30% inside the secondary particles. Contains porous secondary particles that are: Among the porous secondary particles contained in the positive electrode active material of the present embodiment, secondary particles having a porosity inside the secondary particles of 10% or more and 30% or less are contained in a number ratio of 80% or more. . The porosity of porous secondary particles contained in the positive electrode active material can be calculated, for example, by observing the cross-sectional structure of the positive electrode active material with an SEM and performing image processing. For example, particles with a calculated porosity exceeding 3% are defined as porous secondary particles (porous particles). Porous particles can be particles that have pores all the way to the center. The ratio of the porous secondary particles contained in the positive electrode active material is not particularly limited, but can be, for example, 30% or more and 100% or less in terms of number ratio.

How to calculate the number ratio of porous secondary particles and the number ratio of porous secondary particles in which the internal porosity of the secondary particles is 10% or more and 30% or less among the porous secondary particles , is not particularly limited. In the calculation method, for example, first, the cross-sectional structure of a plurality of, for example, 100 or more secondary particles of the positive electrode active material is observed by SEM, and the number ratio of the secondary particles to be the control among the secondary particles is counted. can be obtained by doing

The specific surface area of the positive electrode active material of the present embodiment can be increased by having porous secondary particles. The specific surface area of the positive electrode active material of the present embodiment can be arbitrarily selected depending on the properties required for the positive electrode active material, and is not particularly limited, but is, for example, 1.0 m ² /g or more. is preferred. This is because by setting the specific surface area of the positive electrode active material of the present embodiment to 1.0 m ² /g or more, the production of the positive electrode mixture paste can be facilitated, and the output characteristics can be enhanced. is.

Although the upper limit of the specific surface area of the positive electrode active material of the present embodiment is not particularly limited, it is preferably 3.0 m ² /g or less, more preferably 2.0 m ² /g or less. However, when it is required to particularly increase the reaction surface area and particularly improve the output characteristics, the specific surface area of the positive electrode active material of the present embodiment should be 1.0 m ² /g or more and 2.0 m ² /g or less. is preferred. In addition, when particularly easy production of the positive electrode mixture paste is required, the specific surface area of the positive electrode active material of the present embodiment is 0.5 m ² /g or more and 1.5 m ² /g or less. is preferred.

Further, according to the positive electrode active material of the present embodiment, the porous secondary particles contain porous secondary particles, and the porosity inside the secondary particles of the porous secondary particles is 10% or more and 30% or less. By having a certain ratio or more of the secondary particles, the output characteristics when used as a battery can be improved, and the tap density can also be increased.

The tap density of the positive electrode active material of the present embodiment is not particularly limited, but is preferably 1.5 g/cc or more, more preferably 1.7 g/cc or more.

For example, when the positive electrode active material of the present embodiment is used for the positive electrode of a 2032 type coin battery, when charged at a current of 0.05 C, the capacity at a discharge current of 2.0 C with respect to the capacity at a discharge current of 0.05 C (discharge capacity retention rate) is preferably 85% or more.

In addition, the discharge capacity under the high discharge rate condition (2C) can be measured at 2C a plurality of times, for example, three times, and the average value of the plurality of measurements can be obtained.

[Method for producing positive electrode active material for non-aqueous electrolyte secondary battery]
Next, an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also simply referred to as "a method for producing a positive electrode active material") will be described.

The method for producing the positive electrode active material of the present embodiment is not particularly limited as long as the positive electrode active material can be produced so as to have the particle structure of the positive electrode active material described above. This is preferred because it allows the material to be produced more reliably.

The manufacturing method of the positive electrode active material of this embodiment can have the following steps.
A heat treatment step of heat-treating the positive electrode active material precursor for non-aqueous electrolyte secondary batteries obtained by the above-described method for producing a positive electrode active material precursor for non-aqueous electrolyte secondary batteries at a temperature of 80° C. or higher and 600° C. or lower.
A mixing step of adding a lithium compound to the particles obtained by the heat treatment step and mixing them to form a lithium mixture.
A firing step of firing the lithium mixture at a temperature of 600° C. or higher and 1000° C. or lower in an oxidizing atmosphere.

Each step will be described below.

(1) Heat Treatment Step In the heat treatment step, the above precursor can be heat treated at a temperature of 80° C. or higher and 600° C. or lower. By performing the heat treatment, it is possible to remove the moisture contained in the precursor and prevent the ratio of the number of metal atoms and the number of lithium atoms from varying in the finally obtained positive electrode active material.

Note that it is not necessary to convert all the precursors to the nickel-cobalt-manganese composite oxide, as long as the moisture can be removed to the extent that the ratio of the number of metal atoms and the number of lithium atoms in the positive electrode active material does not vary. However, in order to further reduce the variation, it is preferable to set the heating temperature to 500° C. or higher to convert all the precursor particles into composite oxide particles.

The reason why the heat treatment temperature is set to 80° C. or higher in the heat treatment step is that if the heat treatment temperature is lower than 80° C., excess moisture in the precursor particles cannot be removed, and the above variations may not be suppressed. is. On the other hand, the reason why the heat treatment temperature is set to 600° C. or less is that if the heat treatment temperature exceeds 600° C., the particles may be sintered by roasting and composite oxide particles having a uniform particle size may not be obtained. be.

By determining the metal component contained in the precursor particles corresponding to the heat treatment conditions in advance by analysis and determining the ratio to the lithium compound, the above variation can be suppressed.

The heat treatment atmosphere is not particularly limited, and may be a non-reducing atmosphere, but it is preferable to perform the heat treatment in an air stream, which can be easily performed.

In addition, the heat treatment time is not particularly limited, but if it is less than 1 hour, the excessive moisture of the precursor particles may not be sufficiently removed, so it is preferably at least 1 hour or more, and more preferably 2 hours or more and 15 hours or less. preferable.

The equipment used for the heat treatment is not particularly limited as long as it can heat the precursor particles in a non-reducing atmosphere, preferably in an air stream, and an electric furnace that does not generate gas is suitable. Used.

(2) Mixing Step The mixing step is a step of adding a lithium compound to the heat-treated particles obtained by heating in the heat treatment step and mixing them to form a lithium mixture.

The heat-treated particles obtained by heat treatment in the heat treatment step contain nickel-cobalt-manganese carbonate composite particles and/or nickel-cobalt-manganese composite oxide particles.

The heat-treated particles and the lithium compound are the number of atoms of the metal component Me other than lithium in the lithium mixture, that is, the sum of the number of atoms of Ni, Co, Mn and the additive element M (Me), and the number of lithium atoms (Li ) and (Li/Me) is preferably 1.0 or more and 1.3 or less. At this time, it is more preferable to mix so that Li/Me is 1.05 or more and 1.15 or less.

That is, since Li / Me does not change before and after the firing process, Li / Me mixed in this mixing process becomes Li / Me in the positive electrode active material, so Li / Me in the lithium mixture is the desired positive electrode active material are mixed to be the same as Li/Me in

The lithium compound used to form the lithium mixture is not particularly limited, but is easily available, so one or more selected from, for example, lithium hydroxide, lithium nitrate, and lithium carbonate are preferred. can be used. In particular, considering ease of handling and stability of quality, it is more preferable to use one or more selected from lithium hydroxide and lithium carbonate as the lithium compound used when forming the lithium mixture.

A general mixer can be used for mixing, and for example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, or the like may be used.

(3) Firing Step The firing step is a step of firing the lithium mixture obtained in the mixing step to obtain a positive electrode active material. When the mixed powder is fired in the firing step, lithium in the lithium compound diffuses into the heat-treated particles, forming a lithium-nickel-cobalt-manganese composite oxide.

Although the firing temperature of the lithium mixture at this time is not particularly limited, it is preferably 600° C. or higher and 1000° C. or lower, for example. This is because by setting the firing temperature to 600 ° C. or higher, the diffusion of lithium into the heat-treated particles is sufficiently promoted, the residual of excess lithium and unreacted particles is suppressed, and when used in a battery This is because sufficient battery characteristics can be obtained. However, if the sintering temperature exceeds 1000° C., intense sintering occurs between the composite oxide particles, and abnormal grain growth may occur. This is because it may become impossible to Since such a positive electrode active material has a reduced specific surface area, when it is used in a battery, the resistance of the positive electrode may increase and the battery capacity may decrease.

From the viewpoint of uniform reaction between the heat-treated particles and the lithium compound, it is preferable to raise the temperature to the above temperature at a rate of 3° C./min or more and 10° C./min or less.

Further, the reaction can be made more uniform by maintaining the temperature near the melting point of the lithium compound for about 1 hour or more and 5 hours or less. When the temperature is maintained near the melting point of the lithium compound, the temperature can then be raised to a predetermined firing temperature.

Of the firing time, the holding time at the firing temperature is preferably 1 hour or more, more preferably 2 hours or more and 24 hours or less. This is because the formation of the lithium-nickel-cobalt-manganese composite oxide can be sufficiently promoted by maintaining the firing temperature for two hours or longer.

After the end of the holding time at the firing temperature, although not particularly limited, when the lithium mixture is loaded in a sagger and fired, the descent rate is set to 2 ° C./min or more to suppress deterioration of the sagger. It is preferable to cool the atmosphere to 200° C. or less at a rate of ° C./min or less.

The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume or more and 100% by volume or less, and a mixed atmosphere of oxygen and an inert gas at the oxygen concentration. is particularly preferred. That is, it is preferable to carry out the calcination in the atmosphere or in an oxygen-containing gas.

As described above, an atmosphere with an oxygen concentration of 18% by volume or more is preferable because the oxygen concentration of 18% by volume or more can sufficiently improve the crystallinity of the lithium-nickel-cobalt-manganese composite oxide. Because you can.

In particular, considering battery characteristics, it is preferable to carry out in an oxygen stream.

The furnace used for firing is not particularly limited as long as it can heat the lithium mixture in the atmosphere or in an oxygen-containing gas. An electric furnace with no heat is preferred. Also, either batch or continuous furnaces can be used.

Further, when lithium hydroxide or lithium carbonate is used as the lithium compound, it is preferable to calcine after the mixing step and before performing the firing step. The calcining temperature is lower than the firing temperature, preferably 350° C. or higher and 800° C. or lower, more preferably 450° C. or higher and 780° C. or lower.

The calcining time is preferably about 1 hour or more and 10 hours or less, more preferably 3 hours or more and 6 hours or less.

In addition, it is preferable to calcine while maintaining the calcination temperature. In particular, it is preferable to calcine at the reaction temperature of lithium hydroxide or lithium carbonate and the heat-treated particles.

When calcination is performed, diffusion of lithium into the heat-treated particles is sufficiently performed, and a uniform lithium-nickel-cobalt-manganese composite oxide can be obtained, which is preferable.

Particles of the lithium-nickel-cobalt-manganese composite oxide obtained by the firing step may be aggregated or slightly sintered. In this case, it may be pulverized. Thereby, the positive electrode active material of the present embodiment containing the lithium-nickel-cobalt-manganese composite oxide can be obtained.

In addition, crushing refers to applying mechanical energy to aggregates composed of multiple secondary particles generated by sintering necking between secondary particles during firing, and almost without destroying the secondary particles themselves. It is an operation to separate secondary particles and loosen aggregates.

[Non-aqueous electrolyte secondary battery]
Next, one structural example of the non-aqueous electrolyte secondary battery of this embodiment will be described. The non-aqueous electrolyte secondary battery of this embodiment can have a positive electrode using the positive electrode active material described above.

First, the structure of the non-aqueous electrolyte secondary battery of this embodiment will be described.

The non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") of the present embodiment is a general non-aqueous system except that the positive electrode active material of the present embodiment is used as the positive electrode material. It can have substantially the same structure as the electrolyte secondary battery.

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

More specifically, the secondary battery of this embodiment can have an electrode body in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween. Then, the electrode body is impregnated with a non-aqueous electrolyte, and between the positive electrode current collector of the positive electrode and the positive electrode terminal connected to the outside, and between the negative electrode current collector of the negative electrode and the negative electrode terminal connected to the outside, respectively. A structure in which they are connected using a lead or the like and hermetically sealed in a case can be employed.

The structure of the secondary battery of this embodiment is not limited to the above example, and various shapes such as a cylindrical shape and a laminated shape can be adopted for the outer shape.

(positive electrode)
First, the positive electrode, which is a feature of the secondary battery of this embodiment, will be described. The positive electrode is a sheet-like member, and is formed by coating and drying the positive electrode mixture paste containing the above-described positive electrode active material on the surface of a current collector made of aluminum foil, for example.

In addition, the positive electrode is appropriately processed according to the battery to be used. For example, a cutting process to form the material into a suitable size according to the intended battery, and a pressure compression process such as a roll press to increase the electrode density are performed.

The positive electrode mixture paste can be formed by adding a solvent to the positive electrode mixture and kneading the mixture. The positive electrode mixture can be formed by mixing the powdery positive electrode active material described above, a conductive material, and a binder.

The conductive material is added in order to give suitable conductivity to the electrode. Although the conductive material is not particularly limited, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

The binder plays a role of binding the positive electrode active material particles. The binder used in the positive electrode mixture is not particularly limited, but examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, Alternatively, polyacrylic acid or the like can be used.

Activated carbon or the like may be added to the positive electrode mixture, and by adding activated carbon or the like, the electric double layer capacity of the positive electrode can be increased.

The solvent dissolves the binder and disperses the positive electrode active material, conductive material, activated carbon, and the like in the binder. Although this solvent is not particularly limited, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

Moreover, the mixing ratio of each substance in the positive electrode mixture paste is not particularly limited. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, similarly to the positive electrode of a general non-aqueous electrolyte secondary battery. The content of the material can be 1 part by mass or more and 20 parts by mass or less, and the content of the binder can be 1 part by mass or more and 20 parts by mass or less.

(negative electrode)
The negative electrode is a sheet-like member formed by applying a negative electrode mixture paste to the surface of a metal foil current collector such as copper and drying it. This negative electrode is formed by substantially the same method as the positive electrode, although the components constituting the negative electrode mixture paste, the composition thereof, the material of the current collector, etc. are different. is done.

The negative electrode mixture paste is obtained by adding an appropriate solvent to a negative electrode mixture obtained by mixing a negative electrode active material and a binder to form a paste.

As the negative electrode active material, for example, a lithium-containing material such as metallic lithium or a lithium alloy, or an occluding material capable of intercalating and deintercalating lithium ions can be employed.

The occluding substance is not particularly limited, but for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. When such an occluding material is used as the negative electrode active material, a fluorine-containing resin such as PVDF can be used as the binder in the same manner as the positive electrode. Organic solvents such as N-methyl-2-pyrrolidone can be used.

(separator)
The separator is sandwiched between the positive electrode and the negative electrode, and has the function of separating the positive electrode and the negative electrode and retaining the electrolyte. The separator may be, for example, a thin film of polyethylene, polypropylene, or the like, which has a large number of fine pores, but is not particularly limited as long as it has the above functions.

(Non-aqueous electrolyte)
The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate; Ether compounds such as methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. can be done.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ and their composite salts can be used.

In addition, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, or a flame retardant to improve battery characteristics.

(Characteristics of non-aqueous electrolyte secondary battery of the present embodiment)
The non-aqueous electrolyte secondary battery of the present embodiment can have, for example, the above configuration and has a positive electrode using the positive electrode active material described above, so that high initial discharge capacity and low positive electrode resistance can be obtained. High capacity and high output.

(Use of secondary battery of the present embodiment)
Since the secondary battery of the present embodiment has the properties described above, it is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that always require high capacity.

In addition, the secondary battery of the present embodiment is also suitable as a battery for driving a motor that requires high output. As the size of the battery increases, it becomes difficult to ensure safety, and an expensive protection circuit is essential. not only is it easier, but it also simplifies the expensive protection circuitry and makes it less expensive. Further, since it is possible to reduce the size and increase the output, it is suitable as a power supply for transportation equipment, which is limited in mounting space.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

The preparation conditions and evaluation results of the samples in each example and comparative example will be described below.

[Example 1]
1. Precursor production and evaluation [precursor production]
First, a precursor was produced by the following procedure.

It should be noted that, throughout all the examples and comparative examples, reagent special grade samples manufactured by Wako Pure Chemical Industries, Ltd. are used for the preparation of precursors, positive electrode active materials, and secondary batteries, unless otherwise specified. .

(Crystallization step)
The crystallization process was performed in a process including a nucleation process and a grain growth process, as shown in FIG. The nucleation step and the grain growth step are described below.

(Nucleation step)
(1) Preparation of initial aqueous solution First, water was added to about 1.2 L in a reaction tank (5 L), and the temperature in the tank was set to 40°C while stirring. The mixed aqueous solution was controlled to 40° C. in the crushing process and the particle growth process. The temperatures of the initial aqueous solution and the mixed aqueous solution were controlled by adjusting the temperature of heated water for the reaction tank provided around the reaction tank.

Then, an appropriate amount of 25% by mass aqueous ammonia was added to the water in the reaction vessel to adjust the ammonium ion concentration in the initial aqueous solution to 5 g/L. Additional 64% sulfuric acid was added to the initial aqueous solution to adjust the pH to 6.4.

Then, an air gas was supplied from an air compressor at 4 L/min as an oxygen-containing gas into the reaction vessel to purge the inside of the vessel to create an oxygen-containing atmosphere. The supply of air gas is continued until the particle growth step is completed, and the inside of the reaction vessel is maintained in an air atmosphere, that is, an oxygen-containing atmosphere.

(2) Preparation of Metal Component-Containing Mixed Aqueous Solution Next, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water to prepare a metal component-containing mixed aqueous solution having a metal ion concentration of 2.0 mol/L. In this metal component-containing mixed aqueous solution, the element molar ratio of each metal was adjusted to Ni:Co:Mn=0.334:0.333:0.333.

(3) Adjustment of pH-adjusted aqueous solution Sodium carbonate and ammonium carbonate were dissolved in water to prepare a pH-adjusted aqueous solution having a carbonate ion concentration of 2.2 mol/L. In addition, sodium carbonate and ammonium carbonate in the pH-adjusted aqueous solution were added so that the molar ratio was 9:2.

(4) Addition and mixing of metal component-containing mixed aqueous solution to initial aqueous solution The metal component-containing mixed aqueous solution was added to the initial aqueous solution in the reaction tank at a flow rate of 10.3 ml/min. was added at a ratio of , to form a mixed aqueous solution.

In addition, when adding the metal component-containing mixed aqueous solution, a pH-adjusting aqueous solution is added at the same time, and the pH value of the mixed aqueous solution in the reaction tank is controlled so as not to exceed 6.4 (nucleation pH value). A nucleation step was carried out with a minute crystallization. Moreover, during the nucleation step, the fluctuation range of the pH value of the mixed aqueous solution was within the range of 0.2 above and below the central value (set pH value) of 6.2. The maximum pH value of the mixed aqueous solution in the nucleation step was 6.4.

(5) Nucleus Disintegration Step After that, stirring was continued for 5 minutes to disintegrate the nuclei.

(Particle growth step)
In the particle growth step, the same metal component-containing mixed aqueous solution and pH-adjusted aqueous solution as in the nucleation step were used. The experimental procedure for the grain growth process is described below.
(1) Adjustment of pH of Mixed Aqueous Solution In the particle growth step, first, a pH-adjusted aqueous solution was added to the mixed aqueous solution obtained in the nucleation step to adjust the pH value to 7.4 (based on liquid temperature of 40°C). The maximum pH value of the mixed aqueous solution in the particle growth step was 7.4.
(2) Addition and Mixing of Metal Component-Containing Mixed Aqueous Solution to Mixed Aqueous Solution A metal component-containing mixed aqueous solution was added at a rate of 10.3 ml/min to the mixed aqueous solution after adjusting the pH value.

At this time, the amounts of the metal component-containing mixed aqueous solution and the pH-adjusted aqueous solution added were controlled so that the pH value of the mixed aqueous solution did not exceed 7.4 based on the reaction temperature of 40°C.

After continuing this state for 196 minutes, the stirring was stopped to terminate the crystallization.

Then, the product obtained by the particle growth process was washed with water, filtered and dried to obtain particles of the precursor (washing and drying process).

In the particle growth process, the pH value is controlled by adjusting the supply flow rate of the pH-adjusted aqueous solution with a pH controller, and the fluctuation range of the pH value of the mixed aqueous solution is above and below the central value (set pH value) of 7.2. It was within the range of 0.2.

Also, the ammonium ion concentration in the mixed aqueous solution was maintained at 5 g/L in the nucleation step and the particle growth step.

[Precursor evaluation]
The resulting precursor was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. It was confirmed that it was salt. Furthermore, using an elemental analyzer (Model: FlashEA 1112, manufactured by Thermo Fisher Scientific), the element amount of hydrogen (H) was measured, and the amount ratio of hydrogen (H) to the metal (Ni + Co + Mn) was calculated to be 1.68. It was confirmed that a large amount of hydrogen was included. Moreover, it was confirmed that it had a functional group containing hydrogen.

In addition, the average particle diameter _D50 of the precursor particles was measured using a laser diffraction/scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., Microtrac HRA), and the average particle diameter was about 8.6 μm. I was able to confirm something.

Next, when the obtained precursor particles were observed by SEM (scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Corporation) (magnification: 3000 times), the obtained precursor particles were approximately It was confirmed that the particles were spherical and had almost uniform particle diameters.

2. Production and Evaluation of Positive Electrode Active Material Next, the obtained precursor was used to produce and evaluate a positive electrode active material.

[Production of positive electrode active material]
The above precursor was heat-treated at 500° C. for 2 hours in an air stream (oxygen: 21% by volume), converted to heat-treated composite oxide particles, and recovered. Next, the heat-treated particles and the lithium compound were mixed to obtain a lithium mixture. Specifically, lithium carbonate was weighed so that Li/Me in the resulting lithium mixture would be 1.10, and mixed with the heat-treated particles to prepare a lithium mixture. Mixing was performed using a shaker-mixer device (TURBULA Type T2C manufactured by Willie & Bachoffen (WAB)). The resulting lithium mixture was calcined at 500° C. for 5 hours in the air (oxygen: 21% by volume), then calcined at 910° C. for 10 hours, and cooled. After that, it was pulverized to obtain a positive electrode active material. The composition of the obtained positive electrode active material is expressed as Li:Ni:Co:Mn=1.10:0.334:0.333:0.333.

[Evaluation of Positive Electrode Active Material]
When the particle size distribution of the obtained positive electrode active material was measured in the same manner as for the precursor particles, it was confirmed that the average particle size was about 7.9 μm.

Moreover, the cross section of the positive electrode active material was observed by SEM. In performing SEM observation of the cross section of the positive electrode active material, secondary particles of a plurality of positive electrode active material particles were embedded in a resin, and the cross section of the particles was made possible by processing with a cross-section polisher, and then observed by SEM. . As a result, it was confirmed that the secondary particles had a structure with uniform pores up to the central part.

In addition, 100 or more particles in these cross-sectional SEM images were observed, and the porosity of the secondary particles was calculated using image analysis software (developed by the National Institutes of Health, ImageJ). When the porosity of each of 100 arbitrarily selected secondary particles was calculated using the above image analysis software, the number ratio of particles having pores up to the center (porous particles) was 100%. . The porous particles mean particles whose secondary particles have a porosity of more than 3%. Non-porous secondary particles are dense particles with a porosity of 3% or less. The average porosity of the porous particles was 22%. Among the porous particles, the number ratio of porous particles having a porosity of 10% or more and 30% or less inside the porous particles was 100%.

Table 2 shows the average porosity of the porous particles among the arbitrarily selected particles described above as the porosity of the porous particles. In addition, as the number ratio of porous particles, the ratio of porous particles to the observed particles is shown. Furthermore, among the porous particles, the number ratio of porous particles having an internal porosity of 10% or more and 30% or less is also shown. The same applies to Comparative Example 1 below.

Furthermore, when the tap density was measured, it was confirmed to be approximately 1.9 g/cc.

The tap density was measured after filling a 20 ml graduated cylinder with the obtained positive electrode active material, and then densely filling the graduated cylinder by a method in which free fall from a height of 2 cm was repeated 500 times.

Further, when the specific surface area of the obtained positive electrode active material was determined by a flow-type gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics, Multisorb), it was confirmed to be about 1.1 m ² /g. .

3. Manufacture and evaluation of secondary batteries [Manufacture of secondary batteries]
Using the obtained positive electrode active material, a 2032 type coin battery was produced and evaluated.

The structure of the manufactured coin-type battery will be described with reference to FIG. FIG. 3 schematically shows a cross-sectional configuration diagram of a coin-type battery. As shown in FIG. 3, the coin-type battery 10 is composed of a case 11 and an electrode 12 housed in the case 11. As shown in FIG.

The case 11 has a positive electrode can 111 which is hollow and one end of which is open, and a negative electrode can 112 arranged in the opening of the positive electrode can 111 . The case 11 is configured such that when the negative electrode can 112 is placed in the opening of the positive electrode can 111 , a space for housing the electrode 12 is formed between the negative electrode can 112 and the positive electrode can 111 .

The electrode 12 is composed of a positive electrode 121, a separator 122 and a negative electrode 123, which are stacked in this order so that the positive electrode 121 is in contact with the inner surface of the positive electrode can 111 and the negative electrode 123 is in contact with the inner surface of the negative electrode can 112. is accommodated in the case 11.

The case 11 is provided with a gasket 113, and the positive electrode can 111 and the negative electrode can 112 are fixed by the gasket 113 so as to maintain an electrically insulated state. The gasket 113 also has the function of sealing the gap between the positive electrode can 111 and the negative electrode can 112 to airtightly and liquidtightly isolate the inside of the case 11 from the outside.

This coin-type battery 10 was produced as follows. First, 52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) were mixed with a solvent (N-methyl-2-pyrrolidone), and a pressure of 100 MPa was applied to a diameter of 11 mm and a thickness of 11 mm. A positive electrode 121 was produced by press molding to a thickness of 100 μm. The produced positive electrode 121 was dried at 120° C. for 12 hours in a vacuum dryer. Using the positive electrode 121, the negative electrode 123, the separator 122, and the electrolytic solution, the coin-type battery 10 was produced in an Ar atmosphere glove box with a controlled dew point of -80°C.

For the negative electrode 123, a negative electrode sheet in which graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride coated on a copper foil was used, which was punched into a disk shape of 14 mm in diameter. A polyethylene porous film having a film thickness of 25 μm was used for the separator 122 . As the electrolytic solution, an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiClO ₄ as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used.

[Battery evaluation]
The initial discharge capacity for evaluating the performance of the obtained coin-type battery 10 was defined as follows.

The initial discharge capacity is obtained by leaving the prepared coin-type battery 10 for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) is stabilized, the current density to the positive electrode is 0.05 C (270 mA / g is 1 C). , was charged to a cut-off voltage of 4.3V. After resting for 1 hour, it was discharged at 0.05C to a cut-off voltage of 3.0V. The discharge capacity at this time was defined as the initial discharge capacity. A coin battery having a positive electrode formed using the above positive electrode active material was evaluated, and the initial discharge capacity was about 167 mAh/g.

Next, in order to evaluate high discharge rate characteristics, first, charging and discharging were performed under the same conditions as above with a current density of 0.01 C, and the discharge capacity was measured. After that, charging and discharging were repeated three times under the same conditions as above at current densities of 0.2 C, 0.5 C, and 1.0 C, respectively, and the discharge capacity was measured three times. After that, the current density was set to 2.0 C, charging and discharging were repeated three times under the same conditions as above, and the discharge capacity was measured three times. This average value was taken as the high discharge rate discharge capacity. Its value was about 147 mAh/g.

The discharge capacity retention rate (discharge capacity retention rate) at this time was about 88%. The discharge capacity retention rate is the ratio of discharge capacity at a high discharge rate to initial discharge capacity, and was obtained by the following formula (1).
Discharge capacity retention rate (%) = Discharge capacity at high discharge rate/Initial discharge capacity x 100 (1)

Table 1 shows the properties of the precursor obtained in this example, Table 2 shows the properties of the positive electrode active material, and Table 3 shows the evaluation of the coin-type battery produced using this positive electrode active material. In addition, the same contents are shown in the same table for Comparative Example 1 below.

[Comparative Example 1]
A precursor, a positive electrode active material, and a secondary battery were produced and evaluated in the same manner as in Example 1, except that the gas blown into the reaction vessel during the production of the precursor was changed to nitrogen gas. . The results are shown in Tables 1-3.

Regarding the obtained positive electrode active material, the cross section of the positive electrode active material was observed by SEM in the same manner as in Example 1, and the porosity of the secondary particles was calculated using image analysis software. Among 100 arbitrarily selected secondary particles, the number ratio of porous particles was 29%. The average porosity of the porous particles was 7%. Among the porous particles, the number ratio of porous particles having a porosity of 10% or more and 30% or less inside the porous particles was 0%.

From the results in Table 1, it was confirmed that the precursors of Example 1 all had the target composition. Furthermore, it was confirmed that the positive electrode active material obtained from the precursor had a porosity of the porous particles of 10% or more, and a ratio of the number of porous particles of 100%. It was confirmed that a battery using such a positive electrode active material can have sufficiently high initial discharge capacity and discharge capacity under high discharge rate conditions.

On the other hand, in Comparative Example 1, the H/Me ratio of the precursor was less than 1.60, and it was confirmed that the precursor with the target composition was not obtained. Therefore, when the positive electrode active material was produced using the precursor, almost no porous particles were obtained, and it was confirmed that the porosity of the porous particles was small. It was also confirmed that the secondary battery manufactured using such a positive electrode active material was inferior to that of Example 1 in both the initial discharge capacity and the discharge capacity under high discharge rate conditions.

Claims (9)

Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1, 0.25<x<0.60, 0<y<0.70, 0<z <0.70, 0 ≤ t ≤ 0.10, and M is one selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W The above additive elements.) A nickel-cobalt-manganese carbonate composite composed of
and a functional group containing hydrogen,
A positive electrode active material precursor for a non-aqueous electrolyte secondary battery, wherein H/Me, which is the substance amount ratio of contained hydrogen H and contained metal component Me, is 1.60 or more. Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1, 0.25<x<0.60, 0<y<0.70, 0<z <0.70, 0 ≤ t ≤ 0.10, M is one or more selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W A method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery having a nickel-cobalt-manganese carbonate composite composed of an additive element) and a hydrogen-containing functional group,
An initial aqueous solution containing at least one of an ammonium ion donor and an alkaline substance in the presence of carbonate ions, an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component. A crystallization step of generating nuclei in a mixed aqueous solution mixed with an aqueous solution and growing the generated nuclei,
The crystallization step is carried out in an oxygen-containing atmosphere by controlling the pH value of the mixed aqueous solution to 9.0 or less at a reaction temperature of 40° C.,
A non-aqueous electrolyte secondary battery, wherein the positive electrode active material precursor for a non-aqueous electrolyte secondary battery has a substance amount ratio H/Me of hydrogen H contained and metal component Me contained of 1.60 or more. A method for producing a positive electrode active material precursor for The crystallization step is
In the presence of carbonate ions, the nuclei are formed in the mixed aqueous solution obtained by mixing the initial aqueous solution, the aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component. a nucleation step to produce;
a particle growth step of growing the nuclei generated in the nucleation step;
including
The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 2 , wherein the nucleation step controls the pH value of the mixed aqueous solution to 7.5 or less at a reaction temperature of 40°C. In the particle growth step, an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component are added to the mixed aqueous solution after the nucleation step in the presence of carbonate ions. A step of adding and mixing
4. The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 3 , wherein the ammonium ion concentration in said mixed aqueous solution is 0 g/L or more and 20 g/L or less during said particle growth step. The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 3 or 4 , wherein in the nucleation step, the temperature of the mixed aqueous solution is maintained at 30°C or higher. The ammonium ion donor is one or more selected from an aqueous ammonium carbonate solution, an aqueous ammonia solution, an aqueous ammonium chloride solution, and an aqueous ammonium sulfate solution,
The non-aqueous electrolyte secondary according to any one of claims 2 to 5 , wherein the alkaline substance is one or more selected from sodium carbonate, sodium hydrogen carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide. A method for producing a positive electrode active material precursor for a battery. The positive electrode active material precursor for non-aqueous electrolyte secondary batteries according to any one of claims 2 to 6 , further comprising a coating step of coating the positive electrode active material precursor for non-aqueous electrolyte secondary batteries with the additive element. body manufacturing method. The coating step includes
An aqueous solution containing the additive element is added to the slurry in which the positive electrode active material precursor for non-aqueous electrolyte secondary batteries is suspended, and the additive element is added to the surface of the positive electrode active material precursor for non-aqueous electrolyte secondary batteries. a step of depositing
a step of spraying and drying a slurry in which the positive electrode active material precursor for a non-aqueous electrolyte secondary battery and the compound containing the additive element are suspended, or the positive electrode active material precursor for a non-aqueous electrolyte secondary battery; 8. The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 7 , wherein the step of mixing with the compound containing the additive element by a solid-phase method. Li: Ni: Mn: Co: M = α: x: y: z: t (1.00 ≤ α ≤ 1.30, x + y + z + t = 1, 0.25 < x < 0.60 , 0<y<0.70, 0<z<0.70, 0≤t≤0.10, M is Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, One or more additional elements selected from Mo and W. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium metal composite oxide represented by
The positive electrode active material precursor for non-aqueous electrolyte secondary batteries obtained by the method for producing a positive electrode active material precursor for non-aqueous electrolyte secondary batteries according to any one of claims 2 to 8 is heated at 80 ° C. or higher and 600 ° C. A heat treatment step of heat-treating at a temperature of ° C. or less;
A mixing step of adding a lithium compound to the particles obtained by the heat treatment step and mixing them to form a lithium mixture;
a firing step of firing the lithium mixture at a temperature of 600° C. or more and 1000° C. or less in an oxidizing atmosphere;
including
The positive electrode active material for a non-aqueous electrolyte secondary battery is
Including porous secondary particles in which a plurality of primary particles are aggregated,
Among the porous secondary particles, the number ratio of secondary particles having a porosity inside the porous secondary particles of 10% by volume or more and 30% by volume or less is 80% or more. A method for producing a positive electrode active material for a secondary battery.

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