JP7313112B2 - Positive electrode active material precursor for non-aqueous electrolyte secondary battery, positive electrode active material 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 relates to 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 method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries.

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-output secondary batteries as large-sized batteries for motor drive power sources 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 negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and intercalating lithium is used as a negative electrode active material and a positive 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.

Lithium-cobalt composite oxide (LiCoO₂) and lithium-nickel composite oxide (LiNiO₂), lithium nickel cobalt manganese composite oxide (LiNi_1/3Co_1/3Mn_1/3O.₂), lithium-manganese composite oxide using manganese (LiMn₂O.₄), lithium nickel manganese composite oxide (LiNi_0.5Mn_0.5O.₂), lithium-excess nickel-cobalt-manganese composite oxide (Li₂MnO₃-LiNi_xMn_yCo_zO.₂) and other lithium composite oxides have been proposed.

Among these positive electrode active materials, lithium-excess nickel-cobalt-manganese composite oxides, which have high capacity and excellent thermal stability, have been attracting attention in recent years. This composite oxide is a layered compound like lithium-cobalt composite oxide, lithium-nickel composite oxide, and the like (see, for example, Non-Patent Document 1).

A method for producing a precursor for obtaining such a lithium-excess nickel-cobalt-manganese composite oxide is disclosed in Patent Document 1 and Patent Document 2, for example.

JP 2011-028999 A JP 2011-146392 A

"High Performance Lithium Ion Batteries: On Solid Solution Cathode Materials," FB Technical News, No. 66, January 2011, pp. 3-10

By the way, in order to increase the output of a lithium ion secondary battery, it is effective to shorten the movement distance between the positive electrode and the negative electrode of lithium ions. However, in order to improve battery characteristics per unit volume, it is preferable to reduce pores as much as possible.

However, although Patent Documents 1 and 2 disclose the method for producing the precursor and the composition of the positive electrode active material produced using the precursor, they do not refer to the structure of the particles of the positive electrode active material, and in particular, the internal structure of the secondary particles is not examined.

Therefore, in view of the above-described problems of the prior art, one aspect of the present invention aims 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.

In order to solve the above problems, according to one aspect of the present invention,
General formula Ni _x Co _{y Mnz} M _t CO ₃ (where x + y + z + t = 1, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.55 ≤ z ≤ 0.8, 0 ≤ t ≤ 0.1 are satisfied, and M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W. ) and a nickel-cobalt-manganese carbonate composite represented by
a functional group containing hydrogen;
Provided is 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 and 1.65 or less, and the specific surface area is 30 m ² /g or more and 60 m ² /g or less.

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.

1 is a flow diagram of a method for manufacturing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; FIG. 1 is an SEM observation image of a positive electrode active material precursor for a non-aqueous electrolyte secondary battery obtained in Example 1 according to the present invention. 1 is an SEM observation image of a positive electrode active material for a non-aqueous electrolyte secondary battery obtained in Example 1 according to 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; 4 is an SEM observation image of the positive electrode active material for a non-aqueous electrolyte secondary battery obtained in Comparative Example 2. FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments, and various modifications and replacements can be made to the following embodiments without departing from the scope of the present invention.
[Positive electrode active material precursor for non-aqueous electrolyte secondary battery]
In the present embodiment, first, one structural example of the positive electrode active material precursor for non-aqueous electrolyte secondary batteries will be described.

The positive _electrode active material precursor for non-aqueous electrolyte secondary batteries of the present embodiment has the general formula _{NixCoyMnzMtCO3} (wherein x ₊ y+z+t=1, 0.05≦x≦0.3, 0.1≦y≦0.4, 0.55≦z≦0.8, 0≦t≦0.1, and M is Mg, Ca, Al, Ti, V, Cr, Zr, one or more additional elements selected from _Nb , Mo, and W. ₎ and a functional group containing hydrogen.

Further, H/Me, which is the substance amount ratio of the contained hydrogen H and the contained metal component Me, can be set to 1.60 or more and 1.65 or less. Moreover, the specific surface area can be 30 m ² /g or more and 60 m ² /g or less.

The positive electrode active material precursor for non-aqueous electrolyte secondary batteries of the present embodiment (hereinafter also simply referred to as "precursor") can contain a nickel-cobalt-manganese carbonate composite and a hydrogen-containing functional group, as described above. The precursor can also be composed of a nickel-cobalt-manganese carbonate compound and a functional group containing hydrogen.

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

The precursor of the present embodiment containing a nickel-cobalt-manganese carbonate composite and a hydrogen-containing functional group is highly uniform in particle size and fine crystals, and can be used as a raw material for a positive electrode active material for non-aqueous electrolyte secondary batteries, that is, as a precursor.

The precursor of this embodiment will be specifically described below.
(composition)
The nickel-cobalt _{- manganese} carbonate composite is, as described above _, a nickel-cobalt-manganese composite in the basic _carbonate form represented by the general formula: _{NixCoyMnzMtCO3} .

However, in the above general formula, x + y + z + t = 1, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.55 ≤ z ≤ 0.8, 0 ≤ t ≤ 0.1 are satisfied, and M is one or more additional elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W.

Note that the precursor of the present embodiment can include a _compound having an indefinite composition, which is a mixture of carbonates and hydroxides represented by general formula 1: _xMn2 ( _CO3 ) _3.yMn (OH) ₃ , general formula 2: xCo( _CO3 ) _2.yCo (OH) _2.zH2O , and _{general formula 3: Ni4CO3(OH)6 ( H2O ) 4.} is represented by the general formula of

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, one or more additional elements may be added to the nickel-cobalt-manganese carbonate composite as described above in order to further improve battery characteristics such as cycle characteristics and output characteristics.

One or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W are preferably distributed uniformly inside the secondary particles and/or uniformly covering the surfaces of the secondary particles within a predetermined atomicity ratio t.

However, in the nickel-cobalt-manganese carbonate composite, if the atomic ratio t of the additive element exceeds 0.1, the metal elements that contribute to the oxidation-reduction reaction (Redox reaction) may decrease, resulting in a decrease in battery capacity.

Further, even when the nickel-cobalt-manganese carbonate composite does not contain an additive element, the positive electrode active material produced using the precursor of the present embodiment has sufficient battery characteristics such as cycle characteristics and output characteristics. Therefore, it is not necessary to contain additional elements.

Therefore, it is preferable to adjust the additive element so that the atomic ratio t is within the range of 0≦t≦0.1.

As the additive element, one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W can be used as described above. In particular, the additive element preferably contains molybdenum. That is, it is preferable that the additive element M in the above general formula: Ni _x Co _{y Mnz} M _t CO ₃ contains Mo (molybdenum). This is because, according to studies by the inventors of the present invention, when the additive element contains molybdenum, the initial discharge capacity can be particularly increased in a non-aqueous electrolyte secondary battery using a positive electrode active material prepared using the precursor.

Further, the nickel-cobalt-manganese carbonate composite preferably contains molybdenum in a proportion of 0.5 at % or more and 5 at % or less among the metal components in the nickel-cobalt-manganese carbonate composite, that is, Ni, Co, Mn, and the additional element M. This is because when the content of molybdenum in the metal component of the nickel-cobalt-manganese carbonate composite is 0.5 at % or more, the above-described effect of increasing the initial discharge capacity can be particularly exhibited. In addition, molybdenum has the effect of promoting sintering during firing, but by setting the molybdenum content in the metal component of the nickel-cobalt-manganese carbonate composite to 5 at% or less, the formation of excessively large crystals can be prevented, and it is possible to reliably prevent an increase in resistance and a decrease in discharge capacity in a battery produced using the precursor, which is preferable.

Further, according to the studies by the inventors of the present invention, it has been confirmed that the addition element containing molybdenum has the effect of reducing the specific surface area of the positive electrode active material produced using the precursor. This is because the addition of molybdenum structurally changes fine pores in the positive electrode active material into large pores. Furthermore, according to the study by the inventors of the present invention, it is possible to easily manufacture the positive electrode mixture paste by controlling the specific surface area of the positive electrode active material in the range of 1.5 m ² /g or more and 15.0 m ² /g or less. Therefore, from the viewpoint of controlling the specific surface area within the above range, the additive element preferably contains molybdenum.

The additive element is preferably distributed uniformly inside the secondary particles contained in the precursor (hereinafter also simply referred to as "precursor particles") and/or uniformly coated on the surfaces of the secondary particles.

In the nickel-cobalt-manganese carbonate composite, the state of the additive element is not particularly limited. However, it is preferable that the additive element is uniformly distributed inside the nickel-cobalt-manganese carbonate composite and/or uniformly coated on the surface as described above. This is because the additive element is distributed (coated) inside and/or on the surface of the nickel-cobalt-manganese carbonate composite, so that the battery characteristics can be particularly improved when the precursor of the present embodiment is used as the precursor of the positive electrode active material.

In the nickel-cobalt-manganese carbonate composite, even if the amount of one or more additive elements added is particularly small, it is preferable to increase the concentration of the one or more additive elements on the surface of the carbonate complex rather than on the inside in order to sufficiently enhance the effect of improving battery characteristics.

As described above, in the nickel-cobalt-manganese carbonate composite, even if the amount of one or more additive elements added is small, the effect of improving the battery characteristics can be obtained and the decrease in battery capacity can be suppressed.

In addition, the precursor of this embodiment can contain the functional group containing hydrogen as described above. Functional groups containing hydrogen include, for example, hydrogen groups and hydroxyl groups. The functional group containing hydrogen is mixed in the manufacturing process, and it is preferable that the 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 contained, is 1.60 or more, so that the positive electrode active material can be made into porous particles. Further, by setting H/Me to 1.65 or less, the precursor of the present embodiment can be used as a positive electrode active material, and when applied to a secondary battery, the battery characteristics per unit volume can be improved, which is preferable.

Here, the metal component Me contained in the precursor includes Ni, Co, and Mn mentioned in the above general formula, and M as an additional element.

In addition, the precursor of the present embodiment can contain components other than the nickel-cobalt-manganese carbonate composite and the hydrogen-containing functional group, but it can also be composed of the nickel-cobalt-manganese carbonate composite and the hydrogen-containing functional group. Even when the precursor of the present embodiment is composed of a nickel-cobalt-manganese carbonate composite and a hydrogen-containing group, it does not exclude the inclusion of inevitable components in the manufacturing process or the like.

Furthermore, the specific surface area of the precursor of the present embodiment is preferably 30 m ² /g or more and 60 m ² /g or less. This is because by setting the specific surface area of the precursor to 30 m ² /g or more, it is possible to obtain a positive electrode active material containing porous particles having uniform pores inside the particles when such a precursor is used as a positive electrode active material. In addition, by setting the specific surface area of the precursor to 60 m ² /g or less, when such a precursor is used as a positive electrode active material, it is possible to prevent the pores in the particles contained in the positive electrode active material from becoming excessively large, and to increase the energy density.
[Method for producing positive electrode active material precursor for non-aqueous electrolyte secondary battery]
Next, one structural example of the 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 addition, since the precursor described above can be manufactured by the method for manufacturing a precursor according to the present embodiment, the description of the already described contents is partially omitted.

In the method for producing a precursor of the present embodiment, a precursor can be obtained by a crystallization reaction, and the obtained precursor can be washed and dried as necessary.

_Specifically , the method for producing the _precursor of the present embodiment uses the general _{formula NixCoyMnzMtCO3} (where x ₊ y + z + t = 1, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.55 ≤ z ≤ 0.8, 0 ≤ t ≤ 0.1, and M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo and one or more additional elements selected from W.) and a hydrogen-containing functional group.

A nucleation step of generating nuclei in a mixed aqueous solution in which an initial aqueous solution containing an alkaline substance and/or an ammonium ion donor, an aqueous solution containing nickel as a metal component, an aqueous solution containing cobalt as a metal component, and an aqueous solution containing manganese as a metal component are mixed in the presence of carbonate ions.
A grain growth step for growing the nuclei formed in the nucleation step.
In the nucleation step, the pH value of the mixed aqueous solution can be controlled to 7.5 or less at a reaction temperature of 40°C.

In addition, in the grain growth process, an oxygen-free atmosphere with an oxygen content of less than 0.1% by volume can be switched to an oxygen-containing atmosphere with an oxygen content of 2% by volume or more in the middle of the process.

One structural example of the flow of the method for producing a precursor according to the present embodiment shown in FIG. 1 will be described below. As shown in FIG. 1, the method for producing a precursor of the present embodiment includes (A) a nucleation step and (B) a particle growth step of forming precursor particles by a coprecipitation method after performing the nucleation step.

In the conventional continuous crystallization method, since the nucleation reaction and the particle growth reaction proceed simultaneously in the same reaction tank, the resulting compound particles have a wide particle size distribution.

In contrast, in the method for producing a precursor according to the present embodiment, 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) are clearly separated. As a result, even if both steps are performed in the same reactor, precursor particles having a narrow particle size distribution can be obtained. A nuclear disintegration step in which addition of raw materials is stopped and only stirring is performed can be included between the two steps.

Each step of the method for producing a precursor according to the present embodiment will be specifically described below.
(1) Nucleation Step The nucleation step will be described with reference to FIG.

As shown in FIG. 1, in the nucleation step, first, ion-exchanged water (water) is mixed with an alkaline substance and/or an ammonium ion donor in a reaction tank to prepare an initial aqueous solution.

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.

The alkaline substance is also not particularly limited, but is preferably one or more selected from sodium carbonate, sodium hydrogencarbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

In the nucleation step, the mixed aqueous solution obtained by adding an aqueous solution containing a metal component such as an aqueous solution containing nickel 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. This is because by keeping the pH value of the mixed aqueous solution low, the nuclei in the mixed aqueous solution can be made smaller and the number can be increased, and the particle size of the secondary particles contained in the resulting precursor can be made smaller.

Therefore, it is preferable to add an acidic substance to the initial aqueous solution to adjust the pH value (based on 40° C.) to 5.4 or more and 7.5 or less, more preferably 6.4 or more and 7.4 or less. In particular, it is more 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 set as the pH value of the mixed aqueous solution in the nucleation step, and the pH value of the mixed aqueous solution is preferably within the above range.

The acidic substance is not particularly limited, and sulfuric acid, for example, 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.

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

In the nucleation step, it is preferable to first blow an oxygen-free gas having an oxygen content of less than 0.1% by volume, such as nitrogen gas, into the reaction tank in which the initial aqueous solution is prepared to control the atmosphere so as to suppress the contamination of oxygen. After that, an aqueous solution containing a metal component such as an aqueous solution containing nickel as the metal component, which will be described later, is supplied at a constant flow rate, for example, so that the pH value of the mixed aqueous solution can be controlled to fall within a predetermined range.

In this way, by blowing an oxygen-free gas such as nitrogen gas into the reaction vessel to suppress the contamination of oxygen and performing the nucleation step in an environment in which oxygen is blocked, the reaction between oxygen and the crystallized product is suppressed, and fine particles close to single crystals of carbonate are produced.

In the nucleation step, while an aqueous solution containing a metal component such as an aqueous solution containing nickel as a metal component is being added to the initial aqueous solution, an oxygen-free gas such as nitrogen gas can be continuously supplied into the reaction vessel. As the oxygen-free gas, the same gas as that blown into the reaction vessel in which the initial aqueous solution was prepared can be used.

When an oxygen-free gas is supplied into the reaction tank, the amount of the oxygen-free gas supplied can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. Since the dissolved oxygen in the mixed aqueous solution is consumed during the nucleation step, if the dissolved oxygen amount in the mixed aqueous solution is 5% or less of the saturated amount, the mixing of oxygen can be sufficiently suppressed.

As the oxygen-free gas, for example, an inert gas such as nitrogen gas or argon gas, carbon dioxide gas, or the like can be used.

In the nucleation step, an aqueous solution containing nickel as a metal component, an aqueous solution containing cobalt as a metal component, and an aqueous solution containing manganese as a metal component are added and mixed to the initial aqueous solution in a reaction vessel to form a mixed aqueous solution.

When an aqueous solution or the like containing nickel 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, more preferably 7.4 or less, and even more preferably 7.0 or less at a reaction temperature of 40°C. Therefore, the aqueous solution containing the metal component, such as the aqueous solution containing nickel, is preferably added dropwise to the initial aqueous solution rather than 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 nickel as a metal component. The pH-adjusting aqueous solution in this case is not particularly limited, but for example, an aqueous solution containing an alkaline substance and/or an ammonium ion donor can be used. Although the alkaline substance and the ammonium ion donor are not particularly limited, the same substances as those described for the initial aqueous solution 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, the mixed aqueous solution may be added so that the pH value of the mixed aqueous solution is maintained within a predetermined range using a pump capable of controlling the flow rate, such as a metering pump.

Then, as described above, by adding an aqueous solution containing a metal component, such as an aqueous solution containing nickel as a metal component, to the initial aqueous solution, particles that serve as cores of the precursor can be generated in the mixed aqueous solution. Whether or not a predetermined amount of nuclei has been generated in the mixed aqueous solution can be determined from the amount of metal salt contained in the mixed aqueous solution.

Here, the aqueous solution containing nickel as a metal component, the aqueous solution containing cobalt as a metal component, and the aqueous solution containing manganese as a metal component, which are added to the initial aqueous solution in the nucleation step, will be described.

The aqueous solution containing nickel as a metal component, the aqueous solution containing cobalt as a metal component, and the aqueous solution containing manganese as a metal component can contain metal compounds containing each metal component. That is, for example, an aqueous solution containing cobalt as a metal component can contain a metal compound containing cobalt.

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

The aqueous solution containing nickel as a metal component, the aqueous solution containing cobalt as a metal component, and the aqueous solution containing manganese as a metal component are partially or entirely mixed in advance, and a metal component-containing mixed aqueous solution can be added to the initial aqueous solution.

The composition ratio of each metal in the resulting precursor is substantially the same as the composition ratio of each metal in the mixed aqueous solution containing metal components. For this reason, it is preferable to prepare the mixed aqueous solution containing the metal component by adjusting the proportion of the dissolved metal compound, for example, so that the composition ratio of each metal contained in the mixed aqueous solution containing the metal component added to the initial aqueous solution in the nucleation step is equal to the composition ratio of each metal in the precursor to be generated.

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

When the aqueous solutions containing each metal component are not mixed but individually added to the initial aqueous solution, it is preferable to prepare an aqueous solution containing each metal component so that the composition ratio of each metal contained in the entire aqueous solution containing the metal component to be added is equal to the composition ratio of each metal in the precursor to be generated.

As described above, the precursor produced by the _precursor production method of the present embodiment has the general formula _{NixCoyMnzMtCO3} (where x+y+z+t=1, 0.05≤x≤0.3, 0.1≤y≤0.4, 0.55≤z≤0.8, 0≤t≤0.1, and _M is _Mg , _Ca , Al, Ti, V, Cr, one or more additional elements selected from Zr, Nb, Mo, and W.) and a functional group containing hydrogen.

In other words, in addition to nickel, cobalt, and manganese, additional elements can also be contained.

Therefore, in the nucleation step, an aqueous solution containing one or more additional elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W (hereinafter simply referred to as "additional element") (hereinafter simply referred to as "additional element-containing aqueous solution") can also be added to the initial aqueous solution, if necessary. Since the additive element preferably contains Mo (molybdenum) as described above, it is preferable to use an aqueous solution containing at least molybdenum as a metal component as the aqueous solution containing the additive element.

When an aqueous solution or the like containing nickel as a metal component is mixed to form a mixed aqueous solution containing a metal component and then added to the initial aqueous solution, an aqueous solution containing additional elements may be added to and mixed with the mixed aqueous solution containing the metal component.

When an aqueous solution or the like containing nickel as a metal component is added individually to the initial aqueous solution without being mixed, an aqueous solution containing additional elements can also be added separately to the initial aqueous solution.

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

As described above, the additive element 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 additive element described above to the mixed aqueous solution, the additive element 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, for example, after the particle growth process, which will be described later, is finished, a coating step of coating the secondary particles with the additive element can be carried out. The coating process will be described later in the grain growth process.

In the nucleation step, an aqueous solution containing nickel as a metal component is added to the initial aqueous solution in the presence of carbonate ions and 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 (carbon dioxide gas) together with or as oxygen-free gas 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.

As described above, in the nucleation step, in the presence of carbonate ions, an aqueous solution or the like containing nickel as a metal component is added to the initial aqueous solution and mixed to form a mixed aqueous solution, and nuclei can be generated in the mixed aqueous solution.

At this time, the concentration of the metal compound in the mixed aqueous solution is preferably 1 mol/L or more and 2.6 mol/L or less, more preferably 1.5 mol/L or more and 2.2 mol/L or less.

This is because if the concentration of the metal compound in the mixed aqueous solution is less than 1 mol/L, the amount of crystallized product per reaction tank is small, which is not preferable because the productivity is lowered. On the other hand, if the concentration of the metal compound in the mixed aqueous solution exceeds 2.6 mol/L, it may exceed the saturated concentration at room temperature, and crystals may re-precipitate to clog the pipes of the equipment.

The concentration of the metal compound means the concentration of the metal compound derived from the aqueous solution containing nickel as the metal component, the aqueous solution containing cobalt as the metal component, the aqueous solution containing manganese as the metal component, and, in some cases, the aqueous solution containing the added additive element added to the mixed aqueous solution.

In the nucleation step, 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 in the nucleation step is not particularly limited, it is preferably 70° C. or lower, more preferably 50° C. or lower.

This is because, in the nucleation step, when the temperature of the mixed aqueous solution is lower than 20° C., nucleation tends to occur due to the low solubility, which may make control difficult.

On the other hand, in the nucleation step, if the temperature of the mixed aqueous solution exceeds 70° C., the primary crystal may be distorted and the tap density may be lowered.

In the nucleation step, the ammonium ion concentration in the mixed aqueous solution is not particularly limited.

The pH value in the mixed aqueous solution, the concentration of ammonium ions, the amount of dissolved oxygen, and the like can be measured with a general pH meter, ion meter, and dissolved oxygen meter, respectively.

After the nucleation step is finished, that is, after the metal component-containing mixed aqueous solution has been added to the initial aqueous solution, it is preferable to continue stirring the mixed aqueous solution and crush the generated nuclei (nuclear disintegration step). 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.
(2) Particle Growth Step Next, the particle growth step will be described with reference to FIG.

In the grain growth step, the nuclei generated in the nucleation step can be grown.

Specifically, for example, as shown in FIG. 1, 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. At this time, 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 a pH adjusting liquid to be described later.

This is because the remaining impurity cations can be suppressed by setting the pH value of the mixed aqueous solution to 6.0 or more and 9.0 or less.

The particle growth step can be a step of adding and mixing an aqueous solution containing nickel as a metal component, an aqueous solution containing cobalt as a metal component, and an aqueous solution containing manganese as a metal component in the presence of carbonate ions to the mixed aqueous solution after the nucleation step.

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, the aqueous solution containing nickel as a metal component, the aqueous solution containing cobalt as a metal component, and the aqueous solution containing manganese as a metal component may be partially or wholly mixed in the same manner as in the nucleation step, and added to the mixed aqueous solution as a mixed aqueous solution containing the metal component. In addition, when a plurality of metal compounds are mixed to generate an unnecessary compound due to a reaction between specific metal compounds, an aqueous solution containing each metal component may be individually added to the mixed aqueous solution.

Furthermore, when adding an aqueous solution or the like containing nickel as a metal component to the mixed aqueous solution, an aqueous solution containing additional elements can also be added, as in the case of the nucleation step. As described above, an aqueous solution containing additional elements 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 can also be individually added to the mixed aqueous solution.

As the aqueous solution containing nickel as a metal component, the aqueous solution containing cobalt as a metal component, and the aqueous solution containing manganese as a metal component, the same aqueous solutions as in the nucleation step can be used. Also, the density and the like may be adjusted separately.

When adding an aqueous solution or the like containing nickel 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. Therefore, the aqueous solution or the like containing nickel 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, an aqueous solution containing a metal component such as an aqueous solution containing nickel as a metal component can be added to the mixed aqueous solution after adjusting the pH value as described above. In this case as well, for the same reason as when the pH value was adjusted before the start of the particle growth step, the pH value of the mixed aqueous solution is maintained in the same range as in the case of the mixed aqueous solution after pH value adjustment, that is, at a reaction temperature of 40° C., preferably 6.0 or more and 9.0 or less, more preferably 6.4 or more and 8.0 or less, and even more preferably 7.1 or more and 8.0 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 residual amount of impurities can be obtained.

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 set as the pH value of the mixed aqueous solution in the particle growth process, and the pH value of the mixed aqueous solution is preferably within the above range.

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

When supplying an aqueous solution containing metal components or a mixed aqueous solution containing metal components as described above, it is preferable to add a pH-adjusting aqueous solution so that the pH of the mixed aqueous solution can be maintained within a predetermined range. As the pH-adjusted aqueous solution, the same pH-adjusted aqueous solution as in the nucleation step can be used, and the pH-adjusted aqueous solution in this case is not particularly limited, but for example, an aqueous solution containing an alkaline substance and/or an ammonium ion donor can be used. Although the alkaline substance and the ammonium ion donor are not particularly limited, the same substances as those described for the initial aqueous solution 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, the mixed aqueous solution may be added so that the pH value of the mixed aqueous solution is maintained within a predetermined range using a pump capable of controlling the flow rate, such as a metering pump.

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. Further, in the particle growth step, the ammonium ion concentration is kept constant, so that 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 preferably adjusted to 0 g/L or more and 20 g/L or less by using an ammonium ion donor in, for example, the initial aqueous solution or the pH-adjusted aqueous solution and adjusting the supply amount.

In the particle growth step, an aqueous solution containing a metal component such as an aqueous solution containing nickel 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-free gas or 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 initial aqueous solution or the pH-adjusted aqueous solution.

In the particle growth process, an oxygen-free gas having an oxygen content of less than 0.1% by volume is blown into the reaction vessel at the start of the particle growth process, thereby controlling the atmosphere so as to suppress the contamination of oxygen. In addition, after a certain period of time has elapsed after the start of supply of the oxygen-free gas, the oxygen-free gas is switched to an oxygen-containing gas having an oxygen content of 2% by volume or more, and an aqueous solution containing a metal component such as an aqueous solution containing nickel as a metal component can be supplied, for example, at a constant flow rate while blowing the oxygen-containing gas.

That is, in the grain growth step, an oxygen-free atmosphere with an oxygen content (oxygen concentration) of less than 0.1% by volume can be switched to an oxygen-containing atmosphere with an oxygen content (oxygen concentration) of 2% by volume or more during the process.

By supplying an oxygen-free gas for a certain period after the start of the particle growth process, it is possible to suppress oxidation of the growing precursor particles by oxygen. In addition, fine crystals can be further aggregated to form large secondary particles.

By supplying an oxygen-containing gas instead of the oxygen-free gas after a certain period of time has elapsed after the start of the particle growth process, the surfaces of the growing precursor particles can react with oxygen contained in the oxygen-containing gas supplied to the reaction vessel. Then, amorphous fine particles that are not single crystals of carbonate are further aggregated, and larger secondary particles can be generated.

As described above, by switching from an oxygen-free gas to an oxygen-containing gas in the middle of the particle growth process, it is possible to obtain a positive electrode active material precursor that has uniform pores inside the particles and has as few pores as possible so as to increase the energy density.

In addition, by blowing the oxygen-containing gas in the middle of the particle growth process, it is possible to make it easier to mix the functional group containing hydrogen into the precursor compared to the case of an inert gas atmosphere, and the H / Me, which is the substance amount ratio between the hydrogen contained in the obtained precursor and the contained metal component Me, can be 1.60 or more and 1.65 or less.

The timing of switching from the oxygen-free gas to the oxygen-containing gas is not particularly limited, and can be arbitrarily selected according to the energy density and the like required for the positive electrode active material. For example, when the time of the grain growth step is T, it is preferable that the oxygen-free atmosphere time is 1/5T or more and 1/2T or less. This is because the energy density of the positive electrode active material produced from the obtained precursor can be sufficiently increased by setting the oxygen-free atmosphere time to 1/5 T or longer. Also, by setting the time of the oxygen-free atmosphere to 1/2 T or less, uniform pores can be formed inside the particles.

The time T of the particle growth step refers to the time during which an aqueous solution or the like containing nickel as a metal component is dripped into the mixed aqueous solution.

When an oxygen-free gas or an oxygen-containing gas is supplied into the reaction tank in the particle growth step, the amount of the oxygen-free gas or oxygen-containing gas supplied can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. For example, when an oxygen-free gas is supplied, if the amount of dissolved oxygen in the mixed aqueous solution is 5% or less of the saturated amount, the mixing of oxygen can be sufficiently suppressed.

Further, when oxygen-containing gas is supplied, if the amount of dissolved oxygen in the mixed aqueous solution is half or more of the saturated amount, sufficient dissolved oxygen/oxygen for the reaction can be supplied.

As the oxygen-free gas, for example, an inert gas such as nitrogen gas or argon gas, carbon dioxide gas, or the like can be used.

For example, air or the like can be used as the oxygen-containing gas.

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 the desired particle size, a precursor having secondary particles of the desired particle size can be obtained.

After the precursor is obtained in the particle growth step, the surface of the precursor particles obtained as described above may be further coated with an additive element. That is, the method for producing a precursor of the present embodiment can further include a coating step of coating the precursor particles (secondary particles) obtained in the particle growth step with an additive element.

The coating step can be, for example, one of the following steps.

For example, first, an aqueous solution containing the additional element is added to the slurry in which the precursor particles are suspended, and the additional element is precipitated on the surfaces of the precursor particles by a crystallization reaction.

The slurry in which the precursor particles are suspended is preferably prepared by slurrying the precursor particles using an aqueous solution containing an additive element. Further, when adding the aqueous solution containing the additive element 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 is preferably controlled to 6.0 or more and 9.0 or less. This is because the surface of the precursor particles can be particularly uniformly coated with the additive element by controlling the pH of the mixed aqueous solution of the slurry and the aqueous solution containing the additive element within the above range.

The coating step can also be a step of spraying an aqueous solution or slurry containing the additive element onto the precursor particles and drying the precursor particles.

Alternatively, the coating step can be a step of spray-drying a slurry in which the precursor particles and the compound containing the additive element are suspended.

Alternatively, the step of mixing the precursor particles and the compound containing the additive element by a solid phase method may be employed.

As for the aqueous solution containing the additive element described here, the same aqueous solution as that described in the nucleation step can be used. Also, in the coating step, an alkoxide solution containing the additive element may be used instead of the aqueous solution containing the additive element.

As described above, when an aqueous solution containing an additional element is added to the mixed aqueous solution in the nucleation step, and the surfaces of the precursor particles are coated with the additional element in the particle growth step, it is preferable to reduce the amount of additive element ions added to the mixed aqueous solution in the nucleation step by the amount to be coated. This is because, by reducing the amount of the aqueous solution containing the additive element added to the mixed aqueous solution by the coating amount, the atom number ratio between the additive element contained in the obtained precursor and other metal components can be set to a desired value.

The coating step of coating the surfaces of the precursor particles with the additive element as described above may be performed on the precursor particles after the heating after the particle growth step.

In the method for producing a precursor according to the present embodiment, it is preferable to use an apparatus that does not recover the precursor, which is the product, until the reaction from the nucleation step to the particle growth step is completed. Such an apparatus includes, for example, a commonly used batch reactor equipped with a stirrer. By adopting such an apparatus, unlike a continuous crystallizer in which a product is recovered by general overflow, the problem of growing particles being recovered simultaneously with the overflow liquid does not occur, so particles with a narrow particle size distribution and 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, so particles with excellent particle size distribution, that is, particles with a narrow range of 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 so as to fall within a predetermined range, and an aqueous solution containing a metal component such as an aqueous solution containing nickel as a metal component is added to the mixed aqueous solution, whereby uniform precursor particles can be obtained.

By carrying out the above particle growth step, a precursor particle aqueous solution, which is a slurry containing precursor particles, is obtained. After finishing the particle growth process, a washing process and a drying process can be carried out.
(3) Washing step In the washing step, the slurry containing the precursor particles obtained in the particle growth step 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 carried out by a commonly used method as long as the surplus raw materials 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.
(4) Drying Step In the drying step, the particles of the precursor 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, a precursor can be obtained.

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

Further, according to the method for producing a precursor of the present embodiment, by clearly separating 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), precursor particles (secondary particles) having a narrow particle size distribution can be obtained even if both steps are performed in the same reaction vessel.

In addition, in the method for producing the precursor of the present embodiment, the crystal size of the precursor particles obtained during 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 primary particles with a small particle size, secondary particles with high particle size uniformity, and high density (tap density).

In addition, in the method for producing a precursor according to the present embodiment, the nucleation step and the particle growth step can be performed separately in one reaction tank only by mainly adjusting the pH of the reaction solution. 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 configuration example of the positive electrode active material for a non-aqueous electrolyte secondary battery (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.
The lithium metal _composite oxide has the general formula Li1 _{+αNixCoyMnzMtO2 (} 0.25≦α≦0.55, x+ _y +z+t= ₁ , 0.05≦x≦0.3, 0.1≦y≦0.4, 0.55≦z≦0.8, 0≦t≦0.1, M is an additive element, Mg, Ca, Al, Ti, V, Cr, Z one or more elements selected from _r , 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 inside the secondary particles of 10% or more and 20% or less can be 80% or more. Furthermore, the positive electrode active material of the present embodiment can have an energy density of 580 mAh/cc or more, which is the product of the tap density and the initial discharge capacity.

The positive electrode active material of the present embodiment can contain a lithium metal composite oxide in which two types of layered compounds represented by Li ₂ M1O ₃ and LiM2O ₂ are solid-dissolved, more specifically a lithium-excess 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 formula, M1 is a metal element containing at least Mn adjusted to have a valence of 4 on average, and M2 is a metal element containing at least Ni, Co, and Mn adjusted to have a valence of 3 on average.

It is assumed that the composition ratio of Ni, Co, and Mn shown in the precursor described above is M1+M2. Also, since the abundance ratio of Li ₂ M1O ₃ and LiM2O ₂ is lithium excess, it is assumed that Li ₂ M1O ₃ is not 0%.

As described above, the lithium metal composite oxide can contain one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W, 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. For the reason described above in the precursor, it is preferable to adjust the content of the additive element so that the atomic ratio t is within the range of 0≦t≦0.1.

As described above, the additive element may be one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W. In particular, the additive element preferably contains molybdenum. That is, it is preferable that the _{additive element} M in _the above general formula: Li1 _{+ αNixCoyMnzMtO2} contains _Mo (molybdenum). This is because, according to studies by the inventors of the present invention, when the positive electrode active material contains molybdenum as an additive element, the initial discharge capacity can be particularly increased in a battery using the positive electrode active material.

Furthermore, it is more preferable that the content of molybdenum in the lithium metal composite oxide is 0.5 at % or more and 5 at % or less among the metal components other than Li, that is, Ni, Co, Mn, and the additive element M in the lithium metal composite oxide. This is because when the content of molybdenum in the metal components other than Li in the lithium metal composite oxide is 0.5 at % or more, the above-described effect of increasing the initial discharge capacity can be particularly exhibited. In addition, molybdenum has the effect of promoting sintering during firing, but by setting the content of molybdenum in the metal components other than Li in the lithium metal composite oxide to 5 at% or less, it is preferable because it is possible to prevent the formation of large crystals and reliably prevent an increase in resistance and a decrease in discharge capacity in a battery produced using the lithium metal composite oxide.

Further, according to the studies by the inventors of the present invention, it was confirmed that the addition of molybdenum has the effect of reducing the specific surface area of the positive electrode active material. This is because the addition of molybdenum structurally changes fine pores in the positive electrode active material into large pores. Furthermore, according to the studies of the inventors of the present invention, by controlling the specific surface area of the positive electrode active material in the range of 1.5 m ² /g or more and 15.0 m ² /g or less, the production of the positive electrode mixture paste can be facilitated and the output characteristics can be increased. Therefore, from the viewpoint of controlling the specific surface area within the above range, the additive element preferably contains molybdenum.

The positive electrode active material of the present embodiment can have porous secondary particles having a structure with uniform pores up to the center of the secondary particles, and by having such a porous structure, the reaction surface area can be increased. In addition, since the electrolytic solution penetrates through the grain boundaries or pores between the primary particles of the outer shell, and lithium is inserted and detached even at the reaction interface inside the particles, the movement of Li ions and electrons is not hindered, and the output characteristics can be increased.

The positive electrode active material of the present embodiment can contain porous secondary particles as described above, and the porous secondary particles preferably contain porous secondary particles having an internal porosity of 10% or more and 20% or less. Further, the positive electrode active material of the present embodiment preferably contains 80% or more of secondary particles having a porosity of 10% or more and 20% or less inside the secondary particles among the porous secondary particles contained. The porosity of the 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 or the like. In addition, for example, particles having a calculated porosity exceeding 3% can be treated as porous secondary particles, that is, porous particles. The ratio of the porous secondary particles contained in the positive electrode active material is not particularly limited, but can be, for example, 85% or more and 100% or less in number ratio.

In addition, the number ratio of porous secondary particles and the number ratio of secondary particles having a porosity of 10% or more and 20% or less inside the secondary particles among the porous secondary particles can be obtained, for example, by observing the cross-sectional structure of a plurality of, for example, 100 or more secondary particles of the positive electrode active material, and counting the ratio of the secondary particles having a porosity within a predetermined range.

The specific surface area of the positive electrode active material of the present embodiment can be increased by having secondary particles with a porous structure. The specific surface area of the positive electrode active material of the present embodiment can be arbitrarily selected according to the properties required for the positive electrode active material, and is not particularly limited, but is preferably 1.5 m ² /g or more, for example. This is because by setting the specific surface area of the positive electrode active material of the present embodiment to 1.5 m ² /g or more, the production of the positive electrode mixture paste can be facilitated, and the output characteristics can be enhanced.

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 15.0 m ² /g or less, more preferably 13.0 m ² /g or less.

However, when particularly increasing the reaction surface area and particularly increasing the output characteristics are required, the specific surface area of the positive electrode active material of the present embodiment is preferably 5.0 m ² /g or more and 15.0 m ² /g or less. Moreover, when particularly easy production of the positive electrode mixture paste is desired, the specific surface area of the positive electrode active material of the present embodiment is preferably 1.5 m ² /g or more and 5.0 m ² /g or less.

In addition, according to the positive electrode active material of the present embodiment, the secondary particles contain porous secondary particles, and the porosity inside the secondary particles is 10% or more and 20% or less.

The tap density of the positive electrode active material of the present embodiment is not particularly limited, but is preferably 1.7 g/cc or more, more preferably 2.0 g/cc or more.

The positive electrode active material of the present embodiment preferably has a high initial discharge capacity of 250 mAh/g or more when used for the positive electrode of a 2032 type coin battery, for example. Also, the discharge capacity under high discharge rate conditions (2C) is preferably 195 mAh/g 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.

Further, when the positive electrode active material of the present embodiment is used for the positive electrode of a 2032 type coin battery, for example, it is preferable that the energy density is high. Specifically, for example, 550 mAh/cc or more is preferable, and 600 mAh/cc or more is more preferable. Since a higher energy density is preferable, the upper limit is not particularly limited.

The energy density can be calculated by multiplying the tap density and the initial discharge capacity.

The initial discharge capacity is the capacity obtained by constructing a 2032-type coin-type battery using the positive electrode active material of the present embodiment for the positive electrode, setting the current density to the positive electrode to 0.05 C (270 mA / g is 1 C), charging to a cutoff voltage of 4.65 V, and discharging to a cutoff voltage of 2.35 V after resting for 1 hour.
[Method for producing positive electrode active material for non-aqueous electrolyte secondary battery]
Next, one configuration example of the 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 the "production method for 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, but the following method is preferable because the positive electrode active material can 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 precursor described above 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 variation may not be suppressed.

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.

It is also possible to analyze the metal components contained in the precursor particles obtained when heat treatment is performed under predetermined heat treatment conditions, and to determine the correspondence between the heat treatment conditions and the metal components in the precursor particles obtained thereby. By determining the ratio between the precursor particles obtained under predetermined heat treatment conditions and the lithium compound, the 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, excess water in 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.

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 preferably used.
(2) Mixing Step The mixing step is a step of adding and mixing a lithium compound to the heat-treated particles obtained by heating in the heat treatment step 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 preferably mixed so that the ratio (Li/Me) of the number of metal atoms other than lithium in the lithium mixture, that is, the sum of the number of atoms of nickel, cobalt, manganese and additional elements (Me), and the number of lithium atoms (Li) is 1.1 or more and 1.8 or less. At this time, it is more preferable to mix so that Li/Me is 1.3 or more and 1.5 or less.

That is, since Li/Me hardly changes 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 mixed so as to be the same as Li/Me in the positive electrode active material to be obtained.

The lithium compound used to form the lithium mixture is not particularly limited, but since it is easily available, for example, one or more selected from lithium hydroxide, lithium nitrate, and lithium carbonate can be preferably 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.

For mixing, a general mixer can be used, for example, a shaker mixer, Loedige mixer, Julia mixer, V-blender, or the like.
(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 sufficient battery characteristics are obtained when used in batteries.

However, if the firing temperature exceeds 1000° C., intense sintering may occur between the composite oxide particles, and abnormal grain growth may occur, and the particles after firing may become coarse and fine pores may not be formed inside the particles. Since such a positive electrode active material has a reduced specific surface area, when it is used in a battery, the problem arises that the resistance of the positive electrode increases and the battery capacity decreases.

Since the firing temperature of the lithium mixture also affects the specific surface area of the obtained positive electrode active material, it can be selected from the temperature range described above according to the specific surface area required for the positive electrode active material. For example, when it is required to particularly suppress the specific surface area of the positive electrode active material, it is preferable to set the firing temperature to a higher temperature, for example, 900° C. or higher and 950° C. or lower. According to the study of the inventor of the present invention, the specific surface area of the obtained positive electrode active material can be made 1.5 m ² /g or more and 5.0 m ² /g or less by firing in such a temperature range, and the production of the positive electrode mixture paste can be particularly facilitated. Moreover, when the positive electrode active material is used to form a non-aqueous electrolyte secondary battery, the battery capacity can be kept high, which is preferable.

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 more.

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 and 10 ° C./min or less in order to suppress deterioration of the sagger. It is preferable to cool the atmosphere to 200 ° C. 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 having the oxygen concentration. 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 crystallinity of the lithium-nickel-cobalt-manganese composite oxide can be sufficiently improved by setting the oxygen concentration to 18% by volume or more.

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, but from the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferable. 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.

Note that crushing is an operation in which mechanical energy is applied to an agglomerate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing to separate the secondary particles without almost destroying the secondary particles themselves, thereby loosening the agglomerates.
[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 the present 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 can have substantially the same structure as a general non-aqueous electrolyte secondary battery, except that the positive electrode active material described above is used as the positive electrode material.

The secondary battery of this 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 that communicates with the outside, and between the negative electrode current collector of the negative electrode and the negative electrode terminal that communicates with the outside, respectively.

Needless to say, 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 positive electrode active material described above 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 with 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 this positive electrode mixture is not particularly limited, but for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic acid, etc. 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 can be 60 parts by mass or more and 95 parts by mass or less, the content of the conductive material can be 1 part by mass or more and 20 parts by mass or less, and the binder content can be 1 part by mass or more and 20 parts by mass or less, like the positive electrode of a general nonaqueous electrolyte secondary battery.

(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, and various treatments are performed as necessary in the same manner as the positive electrode.

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 substance is employed 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, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing the negative electrode active material in the binder.

(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, having 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 the organic solvent 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 tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butanesultone; One type can be used alone, or two or more types can be mixed and used.

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, a flame retardant, and the like in order 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 it has a high energy density, a high initial discharge capacity, and a low positive electrode resistance. High capacity and high output can be obtained.

(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. However, since the secondary battery of this embodiment has excellent safety, it not only facilitates safety assurance, but also simplifies the expensive protection circuit and lowers the cost. 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 samples in Examples and Comparative Examples are described below.
[Example 1]
1. Production and Evaluation of Precursor First, a precursor was produced by the following procedure.

In all examples and comparative examples, special grade reagent 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.
(Nucleation step)
(1) Preparation of Initial Aqueous Solution First, about 1.2 L of water was put into a reaction tank (5 L), and the temperature in the tank was set to 40° C. while stirring, and the mixed aqueous solution was controlled to 40° C. in the following nucleation step, nuclear disintegration step, and particle growth step. 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.

Further 64% sulfuric acid was added to the initial aqueous solution to adjust the pH to 6.4.

Then, into the reaction tank, nitrogen gas having an oxygen concentration of 9 ppm was supplied from a nitrogen gas cylinder at 4 L/min as an oxygen-free gas that blocks oxygen, and the inside of the tank was purged to create an oxygen-free atmosphere with an oxygen concentration of 0.1% by volume or less. The nitrogen gas is continuously supplied until a certain period of time has elapsed after the start of the particle growth step, and the inside of the reaction vessel is maintained in a nitrogen gas atmosphere, which is the same atmosphere as the nitrogen gas, that is, an oxygen-free atmosphere in which contamination of oxygen is suppressed.
(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=0.165:0.165:0.67.
(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 vessel at a flow rate of 10.3 ml/min. was added at a ratio of , to form a mixed aqueous solution.

When adding the metal component-containing mixed aqueous solution, a pH-adjusted aqueous solution was added at the same time, and the nucleation step was performed by crystallization for 4 minutes while controlling the pH value of the mixed aqueous solution in the reaction tank so as not to exceed 6.4 (nucleation pH value).

In the nucleation step, the pH value was 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 was within the range of 0.2 above and below the central value (set pH value) of 6.2.
(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, the pH value was adjusted to 7.4 (based on liquid temperature of 40°C) by adding a pH-adjusted aqueous solution to the mixed aqueous solution obtained in the nucleation step while the same nitrogen gas as in the nucleation step was blown into the reaction tank.
(2) Addition and Mixing of Metal Component-Containing Mixed Solution to Mixed Solution Add 10.3 ml/min. was added at a ratio of

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 at a reaction temperature of 40°C.

After continuing this state for 50 minutes, the nitrogen gas blown into the reactor was replaced with air having an oxygen content of 21% by volume, and the reaction was continued for another 143 minutes, stirring was stopped, and crystallization was completed.

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 was 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 was within the range of 0.2 above and below the central value (set pH value) of 7.2.

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

(Precursor evaluation)
The obtained precursor was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. Furthermore, using an elemental analyzer (Model: FlashEA 1112, manufactured by Thermo Fisher Scientific), the element amount of hydrogen (H) was measured, and when the substance amount ratio with the metal (Ni + Co + Mn) was calculated, it was confirmed to contain a large amount of hydrogen, 1.61. In addition, it was confirmed to have 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 (Microtrac HRA manufactured by Nikkiso Co., Ltd.), and the average particle diameter was confirmed to be 10.7 μm.

Next, when the obtained precursor particles were observed by SEM (scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Corporation) (magnification: 3000 times), it was confirmed that the obtained precursor particles were substantially spherical and had a substantially uniform particle size. In the case of such a shape, the sphericity of the precursor particles shown in Table 2 is judged as ◯.

SEM observation results are shown in FIG.

Further, the specific surface area of the obtained precursor particles was evaluated using Mac Soap (manufactured by Mountec Co., Ltd.) and found to be 40.5 m ² /g.
2. Production and Evaluation of Positive Electrode Active Material Next, the obtained precursor was used to produce and evaluate a positive electrode active material.

(Manufacturing 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 1.5, 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 obtained lithium mixture was calcined at 500° C. for 5 hours in the air (oxygen: 21% by volume), then calcined at 950° C. for 2 hours, cooled, and pulverized to obtain a positive electrode active material.

_The composition _{of the obtained} positive electrode active material is expressed as _{Li1.5Ni0.158Co0.166Mn0.676O2} .

(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 9.8 μm.

Moreover, the cross-sectional SEM observation of the positive electrode active material was performed.

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.

3A and 3B show cross-sectional SEM observation results of the positive electrode active material. FIG. 3(B) is a partially enlarged view of FIG. 3(A), which is an enlarged view of the particle surrounded by the dotted line in FIG. 3(A).

As shown in FIGS. 3A and 3B, it was confirmed that the positive electrode active material obtained was substantially spherical. In this case, sphericity is evaluated as ◯ in Table 3. In addition, 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 porous particles was calculated using the above image analysis software, the percentage of porous particles was 100%. The porous particles mean particles in which the porosity of the secondary particles exceeds 3%. Non-porous secondary particles are dense particles with a porosity of 3% or less.

Moreover, the average porosity of the porous particles was 15%. Furthermore, among the porous particles, the proportion of porous particles having a porosity of 10% or more and 20% or less was 100%.

Table 3 shows the average porosity of the porous particles among the above arbitrarily selected particles as the porosity of the porous particles. In addition, the ratio of the porous particles to the observed particles is shown as the number ratio of the porous particles. Furthermore, the number ratio of porous particles having a porosity of 10% or more and 20% or less among the porous particles is also shown.

The same applies to Comparative Examples 1 and 2 below.

Furthermore, when the tap density was measured, it was confirmed to be 2.1 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 Co., Ltd., Multisorb), it was confirmed to be 2.5 m ² /g.

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

The configuration of the manufactured coin-type battery will be described with reference to FIG. FIG. 4 schematically shows a cross-sectional configuration diagram of a coin-type battery.

As shown in FIG. 4, 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 hollow positive electrode can 111 with one end open, and a negative electrode can 112 arranged in the opening of the positive electrode can 111. When the negative electrode can 112 is arranged in the opening of the positive electrode can 111, a space for accommodating 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 and housed in the case 11 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.

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 resin (PTFE) were mixed with a solvent (N-methyl-2-pyrrolidone), and press-molded at a pressure of 100 MPa to have a diameter of 11 mm and a thickness of 100 μm to prepare the positive electrode 121. 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, a 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.

For the initial discharge capacity, the coin-type battery 10 was left for about 24 hours after it was produced, and after the open circuit voltage OCV (open circuit voltage) was stabilized, the current density to the positive electrode was set to 0.05 C (270 mA / g is set to 1 C), charged to the cutoff voltage of 4.65 V, and after resting for 1 hour, the capacity when discharged to the cutoff voltage of 2.35 V was taken 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 290 mAh/g. In addition, in order to evaluate the high discharge rate characteristics, the charge/discharge capacity was measured at 0.01 C, then the charge/discharge capacity was measured three times each at 0.2 C, 0.5 C, and 1.0 C, and the average value of the three measurements at 2.0 C was taken as the high discharge rate discharge capacity. Its value was 205 mAh/g.

The energy density, which is the product of the initial discharge capacity and the tap density, was 609 mAh/cc.

Table 1 summarizes the production conditions of this example, Table 2 shows the properties of the precursor obtained in this example, and Table 3 shows the properties of the positive electrode active material and 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 the following comparative examples 1 and 2 as well.
[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 air gas having an oxygen concentration of 21% by volume was used as the gas blown into the reaction vessel during the production of the precursor, and that the time for the particle growth process was changed to 196 minutes. The results are shown in Tables 1-3.

A cross-sectional SEM image of the obtained positive electrode active material was observed 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 100%. Furthermore, the average porosity of the porous particles was 23%.

All of the observed secondary particles of the positive electrode active material were porous particles, but most of the porous particles had a porosity of more than 20%.
[Comparative Example 2]
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 nitrogen gas having an oxygen concentration of 9 ppm was used as the gas blown into the reaction vessel during the production of the precursor, the time for the particle growth process was changed to 196 minutes, and the firing temperature was set to 850°C. The results are shown in Tables 1-3.

Cross-sectional SEM observation was performed in the same manner as in Example 1 for the obtained positive electrode active material.

5A and 5B show cross-sectional images of representative particles. In addition, FIG. 5(A) shows an overall view, and FIG. 5(B) shows an enlarged view of the particle surrounded by the dotted line in FIG. 5(A).

Further, for the obtained positive electrode active material, the porosity of the secondary particles was calculated from the cross-sectional SEM image in the same manner as in Example 1 using image analysis software. Among 100 arbitrarily selected secondary particles, the number ratio of porous particles was 30%. Furthermore, the average porosity of the porous particles was 18%.

Furthermore, among the porous particles, the percentage of porous particles having a porosity of 10% or more and 20% or less was 30%.

実施例１の前駆体は、表２の結果から目的組成になっていることを確認できた。さらに、該前駆体から得られた正極活物質は多孔質粒子を含み、多孔質粒子のうち、空隙率が１０％以上２０％以下の多孔質粒子の個数割合も１００％となることが確認された。

It was confirmed from the results in Table 2 that the precursor of Example 1 had the target composition. Furthermore, it was confirmed that the positive electrode active material obtained from the precursor contained porous particles, and the number ratio of porous particles having a porosity of 10% or more and 20% or less among the porous particles was 100%.

It was confirmed that a battery using such a positive electrode active material can sufficiently increase the initial discharge capacity and the discharge capacity under high discharge rate conditions. In addition, it was confirmed that the energy density also increased to 609 mAh/cc.

On the other hand, in Comparative Example 1, the H/Me ratio of the precursor exceeded 1.65, and it was confirmed that the precursor having the target composition was not obtained. In addition, it was confirmed that the positive electrode active material obtained using such a precursor contained porous particles, but many of the porous particles had a porosity of more than 20%. Therefore, it was confirmed that the positive electrode active material had a low tap density and a low energy density.

In addition, in Comparative Example 2, the H/Me ratio of the precursor was less than 1.6, confirming that the precursor having the intended composition was not obtained. In addition, although the positive electrode active material obtained using such a precursor contains porous particles, the number ratio of porous particles having a porosity of 10% or more and 20% or less among the porous particles was as low as 30%. That is, it was confirmed that porous particles with a porosity of 10% or more and 20% or less were hardly obtained when a positive electrode active material was produced using the precursor.

It was also confirmed that the secondary battery manufactured using such a positive electrode active material was inferior to that of Example 1 in terms of initial discharge capacity, discharge capacity under high discharge rate conditions, and energy density.

Claims (15)

General formula Ni _x Co _{y Mnz} M _t CO ₃ (where x + y + z + t = 1, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.55 ≤ z ≤ 0.8, 0 ≤ t ≤ 0.1 are satisfied, and M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W. ) and a nickel-cobalt-manganese carbonate composite represented by
a functional group containing hydrogen;
H/Me, which is the substance amount ratio of the contained hydrogen H and the contained metal component Me, is 1.60 or more and 1.65 or less,
A positive electrode active material precursor for a non-aqueous electrolyte secondary battery, having a specific surface area of 30 m ² /g or more and 60 m ² /g or less. The additive element M in the general formula of the nickel-cobalt-manganese carbonate composite contains Mo,
2. The positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of Mo among the metal components in said nickel-cobalt-manganese carbonate composite is 0.5 at % or more and 5 at % or less. A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium metal composite oxide,
The lithium metal composite oxide has the general _formula Li1 _{+αNixCoyMnzMtO2 (} 0.25≦α≦0.55, x+ _y +z+t= ₁ , 0.05≦x≦0.3, 0.1≦y≦0.4, 0.55≦z≦0.8, 0≦t≦0.1, M is an additive element, _Mg , Ca, Al, Ti, V, Cr, Zr , Nb, Mo, and one or more elements selected from W),
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 secondary particles of 10% or more and 20% or less is 80% or more,
The energy density, which is the product of the tap density and the initial discharge capacity, is 580 mAh/cc or more,
The initial discharge capacity is obtained by mixing 52.5 mg of the positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) with N-methyl-2-pyrrolidone, pressing the mixture into a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa, and further drying in a vacuum dryer at 120° C. for 12 hours.
A negative electrode in which graphite powder and polyvinylidene fluoride are applied to a copper foil, which are punched into a disk shape with a diameter of 14 mm,
A separator that is a polyethylene porous membrane with a thickness of 25 μm;
Using a battery using an electrolytic solution that is an equal mixture of ethylene carbonate and diethyl carbonate with 1 M LiClO ₄ as the supporting electrolyte,
A positive electrode active material for a non-aqueous electrolyte secondary battery, which is the capacity when the positive electrode is charged to a cut-off voltage of 4.65 V at a current density of 0.05 C, rested for 1 hour, and then discharged to a cut-off voltage of 2.35 V. The additional element M in the general formula of the lithium metal composite oxide contains Mo,
4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the content of molybdenum among Ni, Co, Mn, and additive element M in said lithium metal composite oxide is 0.5 at % or more and 5 at % or less. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 3 or 4, having a specific surface area of 1.5 m ² /g or more. The positive electrode active material for non-aqueous electrolyte secondary batteries according to any one of claims 3 to 5, having a tap density of 2.0 g/cc or more. The positive electrode active material for non-aqueous electrolyte secondary batteries according to any one of claims 3 to 6, wherein the discharge capacity under high discharge rate conditions (2C) is 195 mAh/g or more. General formula Ni _x Co _{y Mnz} M _t CO ₃ (where x + y + z + t = 1, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.55 ≤ z ≤ 0.8, 0 ≤ t ≤ 0.1 are satisfied, and M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W. ) and a functional group containing hydrogen, a method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery,
a nucleation step of generating nuclei in a mixed aqueous solution in which an initial aqueous solution containing an alkaline substance and/or an ammonium ion donor, an aqueous solution containing nickel as a metal component, an aqueous solution containing cobalt as a metal component, and an aqueous solution containing manganese as a metal component are mixed in the presence of carbonate ions;
a particle growth step of growing the nuclei formed in the nucleation step;
In the nucleation step, the pH value of the mixed aqueous solution is controlled to be 7.5 or less at a reaction temperature of 40° C. and lower than the pH value of the mixed aqueous solution in the particle growth step ,
In the particle growth step, the pH value of the mixed aqueous solution obtained in the nucleation step is adjusted to 6.0 or more and 9.0 or less at a reaction temperature of 40 ° C., and the oxygen content is 0.1% by volume or less in the middle of the step. 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 method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 8, wherein the alkaline substance is one or more selected from sodium carbonate, sodium hydrogen carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide. The particle growth step is a step of adding and mixing an aqueous solution containing nickel as a metal component, an aqueous solution containing cobalt as a metal component, and an aqueous solution containing manganese as a metal component in the presence of carbonate ions to the mixed aqueous solution after the nucleation step,
The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to claim 8 or 9, wherein the ammonium ion concentration in the mixed aqueous solution is 0 g/L or more and 20 g/L or less during the particle growth step. The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 10, wherein the oxygen-free atmosphere is 1/5T or more and 1/2T or less in the time T of the particle growth step. The method for producing a positive electrode active material precursor for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 11, wherein in the nucleation step, the temperature of the mixed aqueous solution is maintained at 30°C or higher. The method for producing a positive electrode active material precursor for non-aqueous electrolyte secondary batteries according to any one of claims 8 to 12, further comprising a coating step of coating the positive electrode active material precursor for non-aqueous electrolyte secondary batteries obtained in the particle growth step with the additive element. The coating step includes
A step of adding an aqueous solution containing the additive element to the slurry in which the positive electrode active material precursor for non-aqueous electrolyte secondary batteries is suspended to deposit the additive element on the surface of the positive electrode active material precursor for non-aqueous electrolyte secondary batteries;
The method for producing a positive electrode active material precursor for non-aqueous electrolyte secondary batteries according to claim 13, wherein the positive electrode active material precursor for non-aqueous electrolyte secondary batteries and the step of spray drying a slurry in which the compound containing the additive element is suspended, and the positive electrode active material precursor for non-aqueous electrolyte secondary batteries and the step of mixing the compound containing the additive element by a solid phase method. A heat treatment step of heat-treating 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 8 to 14 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;
and a baking step of baking the lithium mixture at a temperature of 600° C. or higher and 1000° C. or lower in an oxidizing atmosphere.

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