JP7389376B2 - Positive electrode active material for non-aqueous electrolyte secondary batteries - Google Patents

Description

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

BACKGROUND ART In recent years, with the spread of portable electronic devices such as mobile phones and notebook computers, there is a strong desire to develop small, lightweight non-aqueous electrolyte secondary batteries with high energy density. There is also a strong desire to develop high-output secondary batteries for use in large batteries such as motor drive power supplies.

A lithium ion secondary battery is a secondary battery that meets these requirements. A lithium ion secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and the like, and uses a material capable of desorbing and inserting lithium as the positive electrode active material and negative electrode active material.

Research and development on lithium ion secondary batteries is currently being actively conducted. Among them, lithium ion secondary batteries using layered or spinel-type lithium metal composite oxides as positive electrode materials are being put into practical use as batteries with high energy density because they can obtain high voltages of the 4V class.

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

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

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

Japanese Patent Application Publication No. 2015-191847

By the way, in order to increase the output of lithium ion secondary batteries, it is effective to shorten the distance that lithium ions travel between the positive and negative electrodes, so porous particles with uniform pores are used. It is useful to use positive electrode materials that include particles.

However, although Patent Document 1 discloses the method for producing the precursor and the composition of the positive electrode active material produced using the precursor, it does not mention the structure of the particles of the positive electrode active material. In particular, no study has been made on the internal structure of the secondary particles.

Therefore, in view of the problems of the prior art described above, one aspect of the present invention provides 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. The purpose is to provide the body.

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

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

It is a figure showing an example of the flow of the manufacturing method of the cathode active material precursor for non-aqueous electrolyte secondary batteries of an embodiment of the present invention. It is a figure which shows another example of the flow of the manufacturing method of the positive electrode active material precursor for non-aqueous electrolyte secondary batteries of embodiment of this invention. FIG. 2 is an explanatory diagram of a cross-sectional configuration of a coin-type battery manufactured in Example 1 according to the present invention.

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 the following embodiments may be implemented without departing from the scope of the present invention. Various modifications and substitutions can be made to .

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

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

In addition, in this embodiment, the metal component Me contained in the precursor includes Ni, Mn, Co, and the additive element M listed in the above substance amount ratio.

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

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

The precursor of this embodiment will be specifically explained below.

(composition)
The nickel cobalt manganese carbonate complex and the hydrogen-containing functional group contained in the precursor of this embodiment will be explained.

As mentioned above, the nickel cobalt manganese carbonate composite is a nickel cobalt manganese composite in the form of a basic carbonate having a composition of Ni:Mn:Co:M=x:y:z:t in terms of substance amount ratio. be.

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

The precursors of this embodiment have general formula 1: xMn ₂ (CO ₃ ) ₃ ·yMn(OH) ₃ , general formula 2: xCo(CO ₃ ) ₂ ·yCo(OH) ₂ ·zH ₂ O, and General formula 3: It can contain a compound of indeterminate composition that is a mixture of carbonates and hydroxides represented by Ni ₄ CO ₃ (OH) ₆ (H ₂ O) ₄ and the like.

When the precursor of this embodiment is used as a precursor of a positive electrode active material of a nonaqueous electrolyte secondary battery, in order to further improve battery characteristics such as cycle characteristics and output characteristics, a nickel cobalt manganese carbonate composite is used. As mentioned above, one or more types of additive elements M can also be added to the oxide.

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

However, in the nickel cobalt manganese carbonate composite, if the mass ratio t of the additive element M exceeds 0.1, the metal elements that contribute to the redox reaction will decrease, and the battery capacity may decrease. There is.

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

Moreover, the precursor of this embodiment can contain the above-mentioned hydrogen-containing functional group. Examples of the hydrogen-containing functional group include a hydrogen group and a hydroxyl group. The hydrogen-containing functional group is mixed in the manufacturing process, and the material ratio H/Me of hydrogen H contained in the precursor of this embodiment and the metal component Me is set to 1.60 or more. This allows the particles to be porous when used as a positive electrode active material. Further, by setting H/Me to 1.70 or less, when the precursor of this embodiment is used as a positive electrode active material, the strength of the positive electrode active material can be particularly increased, and the shape can be reliably maintained.

In addition, in this embodiment, the metal component Me contained in the precursor includes Ni, Mn, Co, and the additive element M listed in the above substance amount ratio, as described above.

Further, the precursor of the present embodiment may contain components other than the nickel cobalt manganese carbonate complex and the hydrogen-containing functional group; It can also be constructed from groups. In this case, the precursor of the present embodiment does not exclude the inclusion of unavoidable components during the manufacturing process.

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

Specifically, in the method for producing the precursor of this embodiment, Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1 and 0.25<x <0.60, 0<y<0.70, 0<z<0.70, 0≦t≦0.10, M is Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and one or more additional elements selected from W. A method for producing a positive electrode active material precursor for a next battery, including the following steps.

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

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

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

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

The ammonium ion donor is not particularly limited, but is preferably one or more types selected from ammonium carbonate aqueous solution, aqueous ammonia, ammonium chloride aqueous solution, and ammonium sulfate aqueous solution.

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

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

During the crystallization step, it is preferred that the pH value of the mixed aqueous solution is also within the above range. In addition, since the pH value of the mixed aqueous solution changes slightly during the crystallization process, the maximum value of the pH value of the mixed aqueous solution during the crystallization process can be set as the pH value of the mixed aqueous solution in the crystallization process.

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

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

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

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

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

Furthermore, by blowing in an oxygen-containing gas, it is possible to more easily mix hydrogen-containing functional groups into the precursor than in the case of an inert gas atmosphere. Thereby, the obtained precursor can have a substance amount ratio of H/Me of the hydrogen H contained and the metal component Me contained, of 1.60 or more.

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

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

The amount of dissolved oxygen in the mixed aqueous solution can be measured using a known dissolved oxygen meter.

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

Next, in the crystallization step, an aqueous solution containing the metal component, such as an aqueous solution containing Ni as a metal component, is added to the initial aqueous solution and mixed. As a result, fine particles (primary particles) that become the core (core particles) of the precursor are generated in the initial aqueous solution containing the metal component. As a result, a mixed aqueous solution containing primary particles serving as core particles is obtained. Whether or not a predetermined amount of core particles have been generated can be determined based on the amount of metal salt contained in the mixed aqueous solution.

When adding an aqueous solution containing a metal component, such as an aqueous solution containing Ni as a metal component, to the initial aqueous solution, the pH value of the resulting mixed aqueous solution is preferably controlled within a predetermined range as described above. For this reason, it is preferable that the aqueous solution containing the metal component is not added all at once, but gradually dropped into the initial aqueous solution. Thereby, the solution containing the metal component or the metal component-containing mixed aqueous solution described below can be supplied to the reaction tank at a constant flow rate, for example.

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

Here, in the crystallization step, the aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component in the aqueous solution containing the metal component added to the initial aqueous solution. The aqueous solution will be explained.

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

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

These aqueous solutions containing Ni as a metal component, Co as a metal component, and Mn as a metal component are mixed in part or in whole in advance to form an initial mixed aqueous solution containing a metal component. It may also be added to an aqueous solution.

The composition ratio of each metal in the obtained precursor is the same as the composition ratio of each metal in the metal component-containing mixed aqueous solution. For this reason, the composition ratio of each metal contained in the metal component-containing mixed aqueous solution added to the initial aqueous solution in the crystallization step is adjusted to be equal to the composition ratio of each metal in the precursor to be produced, for example, It is preferable to prepare a metal component-containing mixed aqueous solution by adjusting the ratio.

In addition, when mixing multiple metal compounds, if certain metal compounds react with each other and create unnecessary compounds, add aqueous solutions containing each metal component to the initial aqueous solution at the same time in a predetermined ratio. May be added.

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

As described above, the precursor produced by the precursor production method of this embodiment has a material ratio of Ni:Mn:Co:M=x:y:z:t (where x+y+z+t=1). , 0.25<x<0.60, 0<y<0.70, 0<z<0.70, 0≦t≦0.10, and M is Mg, Ca, Al, Ti, V, one or more types of additive elements selected from Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W); a nickel cobalt manganese carbonate composite consisting of a hydrogen-containing functional group; has.

That is, the precursor of the present embodiment may further contain an additive element M in addition to Ni, Mn, and Co.

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

In addition, when adding the metal component-containing mixed aqueous solution to the initial aqueous solution after mixing an aqueous solution containing Ni as a metal component to form a metal component-containing mixed aqueous solution, the metal component-containing aqueous solution containing the additive element M is added. A mixed aqueous solution may be added to the initial aqueous solution.

Furthermore, when aqueous solutions containing Ni as a metal component are individually added to the initial aqueous solution, an aqueous solution containing the additive element M may be individually added to the initial aqueous solution.

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

As mentioned above, it is preferable that the additive element M is uniformly distributed inside the core particle contained in the precursor and/or uniformly coated on the surface of the core particle.

Then, by adding the above-mentioned aqueous solution containing the additive element M to the precursor particle-containing aqueous solution, the additive element M can be uniformly dispersed inside the core particles contained in the precursor.

Further, in order to uniformly coat the surface of the secondary particles of the precursor with the additive element M, for example, after the crystallization process is completed, a coating process of coating the secondary particles with the additive element M can be performed. The coating process will be described later.

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

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

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

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

By completing the addition to the initial aqueous solution such as the metal component-containing mixed aqueous solution, the mixed aqueous solution can be turned into a precursor particle-containing aqueous solution containing sufficiently grown precursor particles.

In this way, in the crystallization step, fine particles (primary particles) that are the cores (nucleus particles) of the precursor can be generated and grown in the aqueous solution containing the precursor particles. Then, by continuing to perform the crystallization step until the core particles grow to a desired particle size, and growing the core particles, it is possible to obtain a precursor having porous secondary particles of the desired particle size. can.

In addition, in order to uniformly coat the surface of the porous secondary particles, which are the precursors, with the additive element M, for example, after the crystallization process is completed, a coating process of coating with the additive element M is performed. You can. The coating process will be described later.

(Other aspects of crystallization process)
In the precursor manufacturing method of this embodiment, as shown in FIG. 1, the crystallization step consists of one step, but the method is not limited thereto. For example, the crystallization step can also include a nucleation step and a particle growth step.

Specifically, in the precursor manufacturing method of this embodiment, the crystallization step can include the following steps.
In the presence of carbonate ions, an initial aqueous solution containing at least one of an ammonium ion donor and an alkaline substance, an aqueous solution containing Ni as a metal component, an aqueous solution containing Co as a metal component, and an aqueous solution containing Mn as a metal component. A nucleation process in which nuclei are generated in a mixed aqueous solution mixed with an aqueous solution.
A particle growth step of growing the nucleus generated in the nucleation step.

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

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

Each step of the method for producing a precursor according to the present embodiment shown in FIG. 2 will be specifically described below. Note that some descriptions of the contents common to the crystallization step of the precursor manufacturing method of this embodiment shown in FIG. 1 will be omitted.

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

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

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

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

During the nucleation step, it is preferred that the pH value of the mixed aqueous solution is also within the above range. Since the pH value of the mixed aqueous solution varies slightly 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.

Note that during the nucleation step, the pH value of the mixed aqueous solution is preferably controlled within 0.2 above or below the central value (set pH value), for example.

As for the acidic substance, the acidic substance explained in the above-mentioned crystallization step can be suitably used.

In the nucleation step, an oxygen-containing gas is blown into the reaction tank in which the initial aqueous solution has been prepared, the atmosphere is controlled, and then the aqueous solution containing the metal component described above is supplied at a constant flow rate to adjust the pH value of the mixed aqueous solution to a predetermined value. can be controlled to fall within the range of This reacts with dissolved oxygen contained in the mixed aqueous solution, oxygen contained in the oxygen-containing gas supplied to the reaction tank, and amorphous fine particles, which are not single crystals of carbonate, are generated. Furthermore, by blowing in an oxygen-containing gas, it is possible to more easily mix hydrogen-containing functional groups into the precursor than in the case of an inert gas atmosphere. Thereby, H/Me, which is the ratio of the amount of hydrogen H contained in the obtained precursor to the metal component Me contained, can be set to 1.60 or more.

In addition, in the nucleation step, the oxygen-containing gas may be continuously supplied into the reaction tank while an aqueous solution containing a metal component, such as an aqueous solution containing Ni as a metal component, is added to the initial aqueous solution.

When supplying oxygen-containing gas into the reaction tank, the amount of oxygen-containing gas supplied can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. Since dissolved oxygen in the mixed aqueous solution is consumed during the nucleation process, if the amount of dissolved oxygen in the mixed aqueous solution is more than half of the saturated amount, it means that sufficient oxygen is being supplied for the reaction.

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

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

Note that when adding an aqueous solution containing Ni as a metal component to the initial aqueous solution, the pH value of the resulting mixed aqueous solution is preferably controlled to 7.5 or less based on the reaction temperature of 40°C. It is more preferable to control it to 4 or less, and even more preferably to control it to 7.0 or less. For this reason, it is preferable that an aqueous solution containing a metal component, such as an aqueous solution containing Ni as a metal component, is not added all at once, but is gradually dropped into the initial aqueous solution.

Further, in order to control the pH of the mixed aqueous solution, a pH adjusting aqueous solution can be added dropwise at the same time as an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component. As the pH-adjusted aqueous solution, the same pH-adjusted aqueous solution as in the crystallization step described above can be suitably used.

Then, as mentioned above, the nucleus of the precursor (nucleus particle) becomes in the mixed aqueous solution obtained by adding an aqueous solution containing a metal component, such as an aqueous solution containing Ni as a metal component, to the initial aqueous solution. Can generate fine particles (primary particles). Whether or not a predetermined amount of core particles have been generated in the mixed aqueous solution can be determined based on the amount of metal salt contained in the mixed aqueous solution.

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

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

That is, in addition to Ni, Mn, and Co, an additional element M may be further contained.

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

As mentioned above, it is preferable that the additive element M is uniformly distributed inside the core particle contained in the precursor and/or that the surface of the core particle is uniformly coated.

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

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

In addition, in the nucleation step, as in the crystallization step of the precursor manufacturing method of the present embodiment shown in FIG. 1, an aqueous solution containing Ni as a metal component is added to the initial aqueous solution in the presence of carbonate ions. They are 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, and for example, carbonate ions can be supplied to the mixed aqueous solution by supplying carbon dioxide gas together with the oxygen-containing gas described below into the reaction tank. . Furthermore, carbonate ions can be supplied by using a carbonate when preparing the initial aqueous solution or the pH-adjusted aqueous solution.

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

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

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

(1-2) Particle Growth Process Next, the particle growth process will be explained using FIG. 2. In the particle growth step, the nuclei generated in the nucleation step can be grown. Specifically, for example, as shown in FIG. 2, in the particle growth step, the pH value of the mixed aqueous solution obtained in the nucleation step can be adjusted first.

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

In addition, since the pH value of the mixed aqueous solution changes slightly during the particle growth process, the maximum value of the pH value of the mixed aqueous solution during the particle growth process can be taken as the pH value of the mixed aqueous solution in the particle growth process, It is preferable that the pH value of the mixed aqueous solution is within the above range.

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

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

Note that the mixed aqueous solution after the nucleation step here is preferably a mixed aqueous solution whose pH has been adjusted after the nucleation step, as described above.

In addition, the aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component are mixed in part or in whole as in the case of the nucleation step, It may be added to the mixed aqueous solution as a metal component-containing mixed aqueous solution. In addition, if mixing multiple metal compounds causes certain metal compounds to react with each other and produce unnecessary compounds, add the aqueous solutions containing each metal component individually to the mixed aqueous solution. Good too.

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

As the aqueous solution containing Ni as a metal component, the aqueous solution containing Co as a metal component, and the aqueous solution containing Mn as a metal component, the same aqueous solutions as in the case of the nucleation step described above can be used. Further, the concentration etc. may be adjusted separately.

When adding an aqueous solution containing Ni as a metal component to the mixed aqueous solution, the pH value of the resulting mixed aqueous solution is preferably controlled within a predetermined range as described below. Therefore, an aqueous solution containing Ni as a metal component can be gradually dropped into 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 tank at a constant flow rate, for example.

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

Note that during the particle growth process, the pH value of the mixed aqueous solution after pH value adjustment slightly fluctuates, so the maximum pH value of the mixed aqueous solution after pH value adjustment during the particle growth process is used as the mixing value for the particle growth process. It is preferable that the pH value of the mixed aqueous solution after adjusting the pH value is within the above range.

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

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

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

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

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

In the particle growth step, an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component is fed at a constant flow rate while controlling the atmosphere to create an oxygen-containing atmosphere by blowing an oxygen-containing gas into the reaction tank. can be supplied by As a result, the irregularly shaped fine particles, which are not single crystals of carbonate, react with the dissolved oxygen contained in the mixed aqueous solution and the oxygen contained in the oxygen-containing gas supplied to the reaction tank, causing further aggregation. can generate large secondary particles. Moreover, by blowing in an oxygen-containing gas, it is possible to mix hydrogen-containing functional groups into the precursor more easily than in the case of an inert gas atmosphere. Thereby, H/Me, which is the substance amount ratio between hydrogen H contained in the obtained precursor and metal component Me contained, can be more reliably set to 1.60 or more.

In addition, when supplying oxygen-containing gas into the reaction tank in the particle growth step, the supply amount of the oxygen-containing gas can be confirmed by measuring the dissolved oxygen concentration in the mixed aqueous solution. Since dissolved oxygen in the mixed aqueous solution is consumed during the particle growth process, if the amount of dissolved oxygen in the mixed aqueous solution is half or more of the saturated amount, it means that sufficient oxygen is being supplied for the reaction.

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

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

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

In the method for producing a precursor of the present embodiment, it is preferable to use an apparatus that does not collect the precursor product until the reaction in the crystallization step is completed. Such an apparatus includes, for example, a commonly used batch reaction tank equipped with a stirrer. By adopting such a device, there is no problem that growing particles are collected at the same time as the overflow liquid, which is the case with general continuous crystallizers that collect products by overflow, resulting in a narrow particle size distribution. This is preferable because particles with uniform particle sizes can be obtained.

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

By using a device that can control the atmosphere of the reaction tank, the particles contained in the precursor can be made to have the structure described above, and the coprecipitation reaction can proceed almost uniformly, so the particle size can be adjusted. Particles with excellent 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 to be within a predetermined range, and an aqueous solution containing a metal component such as an aqueous solution containing Ni as a metal component is added to the mixed aqueous solution. By doing so, uniform precursor particles can be obtained.

(Coating process)
Further, in the method for producing the precursor of this embodiment, after obtaining particles (secondary particles) of the precursor of this embodiment in the crystallization step, the surface of the obtained precursor particles of this embodiment is , it may further include a coating step of coating with the additive element M.

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

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

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

As described above, the surfaces of the precursor particles can be coated with the additive element M by adding an aqueous solution containing the additive element M to the initial aqueous solution or mixed aqueous solution in the crystallization step, and performing the coating step. In this case, the amount of additional element ions added to the initial aqueous solution or mixed aqueous solution in the crystallization step is preferably reduced by the amount to be coated. This can be done by reducing the amount of the aqueous solution containing the additive element M added to the mixed aqueous solution by the amount required for coating, thereby increasing the atomic ratio between the additive element M and other metal components contained in the resulting precursor. This is because it is possible to set the value to a desired value.

As described above, the coating step of coating the surfaces of the precursor particles with the additive element M may be performed on the heated precursor particles after the crystallization step is completed.

Next, after completing the crystallization step shown in FIG. 1 or 2, a washing step or a drying step may be performed. The washing process and drying process will be explained below.

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

In the washing step, first, the slurry containing particles of the precursor is filtered, then washed with water, and then filtered again.

Filtration may be performed by a commonly used method, such as a centrifuge or a suction filter.

Further, washing with water may be carried out by a commonly used method, as long as it can remove excess raw materials contained in the particles of the precursor.

In order to prevent contamination of impurities, it is preferable to use water that contains as few impurities as possible, and it is more preferable to use pure water as the water used for washing.

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

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

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

Furthermore, in the method for producing a precursor of the present embodiment, the crystal size of the particles of the precursor obtained by the crystallization reaction can be controlled. Therefore, according to the method for producing a precursor of the present embodiment, it is possible to obtain a precursor in which the primary particles have a small particle size, the secondary particles have high uniformity in particle size, and have a high density (tap density). I can do it.

Furthermore, according to the method for producing a precursor of the present embodiment shown in FIG. 2, the time during which the nucleation reaction primarily occurs (nucleation step) and the time during which the particle growth reaction primarily occurs (particle growth step) can be separated. I can do it. Thereby, even if both steps are performed in the same reaction tank, precursor particles (secondary particles) having a narrow particle size distribution can be obtained.

Furthermore, in the precursor manufacturing method of this embodiment shown in FIG. 2, the nucleation step and the particle growth step can be performed separately in one reaction tank by simply adjusting the pH of the reaction solution. can.

Therefore, since the method for producing the precursor of this embodiment is easy and suitable for large-scale production, it can be said to have extremely high industrial value.

[Cathode active material for nonaqueous electrolyte secondary batteries]
Next, a 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 this embodiment relates to a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium metal composite oxide. The lithium metal composite oxide has a material amount ratio of Li:Ni:Mn:Co:M=α:x:y:z:t (1.00≦α≦1.30, x+y+z+t=1, and 0 .25<x<0.60, 0<y<0.70, 0<z<0.70, 0≦t≦0.10, M is Mg, Ca, Al, Ti, V, Cr, Fe, One or more types of additive elements selected from Cu, Zn, Zr, Nb, Mo, and W.).

The positive electrode active material of this embodiment can include porous secondary particles in which a plurality of primary particles are aggregated. Among the porous secondary particles, the number ratio of secondary particles having an internal porosity of 10% by volume or more and 30% by volume or less can be 80% or more.

The positive electrode active material of this embodiment can include a lithium metal composite oxide with a layered rock salt crystal structure represented by LiAO ₂ , more specifically a lithium nickel cobalt manganese composite oxide. In addition, the positive electrode active material of this embodiment can also be comprised from the said lithium metal composite oxide.

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

In the precursor of this embodiment, as described above, in order to further improve battery characteristics such as cycle characteristics and output characteristics of the positive electrode active material of a non-aqueous electrolyte secondary battery, the lithium metal composite oxide is used as described above. In addition, one or more types of additive elements M selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, and W can be contained. The content of the additive element M in the precursor is preferably adjusted so that the substance amount ratio t falls within the range of 0≦t≦0.1 for the above-mentioned reasons.

As described above, the positive electrode active material of this embodiment can contain porous secondary particles, and the porous secondary particles have an internal porosity of 10% by volume or more and 30% by volume. % by volume or less of porous secondary particles. In the positive electrode active material of the present embodiment, among the porous secondary particles contained, 80% or more of the secondary particles have an internal porosity of 10% by volume or more and 30% by volume or less. contains. The porosity of the porous secondary particles contained in the positive electrode active material can be calculated, for example, by observing the cross-sectional structure of the positive electrode active material using a SEM and performing image processing. Note that, for example, particles having a calculated porosity of more than 3% are defined as porous secondary particles (porous particles). Porous particles can be particles that have pores down to the center. The proportion of porous secondary particles contained in the positive electrode active material is not particularly limited, but can be, for example, 30% or more and 100% or less in terms of number proportion.

Calculation of the number ratio of porous secondary particles and the number ratio of porous secondary particles whose internal porosity is 10 volume % or more and 30 volume % or less among porous secondary particles The method is not particularly limited. The calculation method includes, for example, first observing the cross-sectional structure of a plurality of secondary particles, for example, 100 or more secondary particles of a positive electrode active material using SEM, and counting the number ratio of secondary particles serving as a control among the secondary particles. You can find it by doing.

The positive electrode active material of this embodiment can have a large specific surface area by having porous secondary particles. The specific surface area of the positive electrode active material of this embodiment can be arbitrarily selected depending on the characteristics required of the positive electrode active material, and is not particularly limited, but for example, it should be 1.0 m ² /g or more. is preferred. This is because by setting the specific surface area of the positive electrode active material of this embodiment to 1.0 m ² /g or more, it is possible to easily manufacture the positive electrode composite material paste and to improve the output characteristics. It is.

The upper limit of the specific surface area of the positive electrode active material of this embodiment is not particularly limited, but is preferably, for example, 3.0 m ² /g or less, more preferably 2.0 m ² /g or less. However, if it is required to particularly increase the reaction surface area and particularly improve the output characteristics, the specific surface area of the positive electrode active material of this embodiment should be 1.0 m ² /g or more and 2.0 m ² /g or less. is preferred. In addition, especially when it is required to make the production of the positive electrode composite paste particularly easy, the specific surface area of the positive electrode active material of this embodiment is 0.5 m ² /g or more and 1.5 m ² /g or less. It is preferable.

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

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

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

Note that the discharge capacity under the above-mentioned high discharge rate condition (2C) can be measured at 2C multiple times, for example, three times, and can be taken as the average value of the multiple measurements.

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

The method for manufacturing the positive electrode active material of this embodiment is not particularly limited as long as the positive electrode active material can be manufactured to have the particle structure of the positive electrode active material described above. This is preferred because the substance can be manufactured more reliably.

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

Each step will be explained below.

(1) Heat Treatment Step In the heat treatment step, the above-mentioned precursor can be heat treated at a temperature of 80° C. or higher and 600° C. or lower. By performing heat treatment, water contained in the precursor can be removed and the ratio of the number of metal atoms and the number of lithium atoms in the finally obtained positive electrode active material can be prevented from varying.

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 an extent that does not cause variations in the ratio of the number of metal atoms and the number of lithium atoms in the positive electrode active material. However, in order to further reduce the above-mentioned variations, it is preferable to set the heating temperature to 500° C. or higher to convert all precursor particles into composite oxide particles.

In the heat treatment process, the heat treatment temperature is set at 80°C or higher because if the heat treatment temperature is lower than 80°C, excess moisture in the particles of the precursor cannot be removed and the above-mentioned variations may not be able to be suppressed. It is. On the other hand, the heat treatment temperature is set at 600°C or less because if the heat treatment temperature exceeds 600°C, the particles may sinter due to roasting and composite oxide particles with a uniform particle size may not be obtained. be.

The above-mentioned variations can be suppressed by determining the metal component contained in the particles of the precursor corresponding to the heat treatment conditions in advance by analysis and determining the ratio to the lithium compound.

The heat treatment atmosphere is not particularly limited as long as it is a non-reducing atmosphere, but it is preferable to carry out the heat treatment in an air stream because it can be easily carried out.

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

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

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

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

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

The lithium compound used to form the lithium mixture is not particularly limited, but is preferably one or more selected from lithium hydroxide, lithium nitrate, and lithium carbonate because it is easily available. Can be used. In particular, considering ease of handling and stability of quality, it is more preferable to use one or more types 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, such as a shaker mixer, Loedige mixer, Julia mixer, V blender, etc.

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

The firing temperature of the lithium mixture at this time is not particularly limited, but is preferably, for example, 600°C or more and 1000°C or less. By setting the firing temperature to 600°C or higher, the diffusion of lithium into the heat-treated particles is sufficiently promoted, and the remaining of excess lithium and unreacted particles is suppressed, so that when used in batteries, This is because sufficient battery characteristics can be obtained. However, if the firing temperature exceeds 1000°C, intense sintering may occur between the composite oxide particles, and abnormal grain growth may occur, resulting in coarse particles after firing and the formation of fine pores inside the particles. This is because there is a possibility that it will not be possible to do so. Since such a positive electrode active material has a reduced specific surface area, when used in a battery, the resistance of the positive electrode may increase and the battery capacity may decrease.

In addition, from the viewpoint of uniformly performing the 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.

Furthermore, the reaction can be carried out more uniformly 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.

Among the firing times, the holding time at the firing temperature is preferably 1 hour or more, and 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 holding the firing temperature for 2 hours or more.

After the holding time at the firing temperature is over, although it is not particularly limited, when loading the lithium mixture into a sagger and firing it, in order to prevent deterioration of the sagger, the lowering rate should be set at 2°C/min or more. It is preferable to cool the atmosphere to 200°C or less at a temperature of 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 at the above oxygen concentration and an inert gas. is particularly preferred. That is, the firing is preferably performed in the atmosphere or in an oxygen-containing gas.

As mentioned above, it is preferable to create an atmosphere with an oxygen concentration of 18% by volume or more because by setting the oxygen concentration to 18% by volume or more, the crystallinity of the lithium nickel cobalt manganese composite oxide can be sufficiently increased. Because you can.

Particularly in consideration of battery characteristics, it is preferable to carry out the process 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 oxygen-containing gas, but from the viewpoint of maintaining a uniform atmosphere in the furnace, it is necessary to avoid gas generation. Preferably, an electric furnace is used. Further, either a batch type or a continuous type furnace can be used.

In addition, when lithium hydroxide or lithium carbonate is used as the lithium compound, it is preferable to perform calcination after the mixing step and before the calcination step. The calcination temperature is lower than the firing temperature and is preferably 350°C or more and 800°C or less, more preferably 450°C or more and 780°C or less.

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

Note that the calcination is preferably performed by maintaining the calcination temperature at the calcination temperature. In particular, it is preferable to calcinate at the reaction temperature of lithium hydroxide or lithium carbonate and the heat-treated particles.

Calcining is preferable because lithium is sufficiently diffused into the heat-treated particles and a uniform lithium-nickel-cobalt-manganese composite oxide can be obtained.

The particles of the lithium nickel cobalt manganese composite oxide obtained by the firing process may be agglomerated or slightly sintered. In this case, it may be crushed. Thereby, the positive electrode active material of this embodiment containing the lithium nickel cobalt manganese composite oxide can be obtained.

Note that crushing is a process in which mechanical energy is applied to an aggregate consisting of multiple secondary particles that is generated due to sinter necking between secondary particles during firing, without destroying the secondary particles themselves. This is an operation to separate secondary particles and loosen aggregates.

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

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

The non-aqueous electrolyte secondary battery of this embodiment (hereinafter also simply referred to as "secondary battery") is a general non-aqueous electrolyte secondary battery, except that the above-mentioned positive electrode active material of this embodiment is used as the positive electrode material. It can have a structure substantially similar to an electrolyte secondary battery.

The secondary battery of this embodiment can have a structure including, for example, a case, a positive electrode, a negative electrode, a nonaqueous 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 nonaqueous electrolyte, and the current collector is connected between the positive electrode current collector of the positive electrode and the positive electrode terminal leading to the outside, and between the negative electrode current collector of the negative electrode and the negative electrode terminal leading to the outside, respectively. It can be connected using a lead or the like and sealed in a case.

Note that the structure of the secondary battery of this embodiment is not limited to the above example, and its outer shape can also adopt various shapes such as a cylindrical shape and a stacked shape.

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

Note that the positive electrode is appropriately treated according to the battery used. For example, a cutting process is performed to form the material into an appropriate size depending on the intended battery, and a pressurizing process using a roll press or the like is performed to increase the electrode density.

The positive electrode composite material paste can be formed by adding a solvent to the positive electrode composite material and kneading the mixture. The positive electrode composite material can be formed by mixing the above-mentioned positive electrode active material in powder form, a conductive material, and a binder.

The conductive material is added to give the electrode appropriate conductivity. This conductive material is not particularly limited, and 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 composite material is not particularly limited, but includes, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, Alternatively, polyacrylic acid or the like can be used.

Note that 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, etc. in the binder. This solvent is not particularly limited, but for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

Furthermore, the mixing ratio of each substance in the positive electrode composite paste is not particularly limited. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the conductive The content of the material can be 1 part by mass or more and 20 parts by mass or less, and the content of the binder can be 1 part by mass or more and 20 parts by mass or less.

(Negative electrode)
The negative electrode is a sheet-like member formed by applying a negative electrode composite paste to the surface of a metal foil current collector made of copper or the like and drying the paste. This negative electrode is formed by substantially the same method as the positive electrode, although the components and composition of the negative electrode composite paste, the material of the current collector, etc. are different, and like the positive electrode, various treatments are performed as necessary. will be held.

The negative electrode composite material paste is made into a paste by adding an appropriate solvent to a negative electrode composite material that is a mixture of a negative electrode active material and a binder.

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

The storage material is not particularly limited, but for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, and a powdered carbon material such as coke can be used. When such an occluding material is used as a negative electrode active material, a fluorine-containing resin such as PVDF can be used as a binder, similar to the positive electrode, and a solvent for dispersing the negative electrode active material in the binder can be Organic solvents such as N-methyl-2-pyrrolidone can be used.

(Separator)
The separator is placed 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. Such a separator may be, for example, a thin film made of polyethylene or polypropylene having many fine pores, but is not particularly limited as long as it has the above-mentioned functions.

(Non-aqueous electrolyte)
The non-aqueous electrolyte is one in which a lithium salt as a supporting salt is dissolved in an organic solvent.

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate; furthermore, tetrahydrofuran, 2- Ether compounds such as methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butane sultone; phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. may be used alone or in combination of two or more. I can do it.

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

Note that the nonaqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, or the like in order to improve battery characteristics.

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

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

The secondary battery of this embodiment is also suitable for use as a power source for driving a motor that requires high output. As batteries become larger, it becomes difficult to ensure safety, and an expensive protection circuit is essential. However, the secondary battery of this embodiment has excellent safety, so it is difficult to ensure safety. Not only is this easier, but expensive protection circuits can be simplified and costs lower. Since it can be made smaller and have higher output, it is suitable as a power source for transportation equipment that is limited in mounting space.

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

Below, conditions for preparing samples and evaluation results in each Example and Comparative Example will be described.

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

In addition, in all Examples and Comparative Examples, special reagent grade samples manufactured by Wako Pure Chemical Industries, Ltd. were used to prepare the precursor, positive electrode active material, and secondary battery, unless otherwise specified. .

(Crystallization process)
As shown in FIG. 2, the crystallization process included a nucleation process and a particle growth process. The nucleation step and particle growth step will be explained below.

(Nucleation process)
(1) Preparation of initial aqueous solution First, add water to approximately 1.2 L in a reaction tank (5 L), set the temperature inside the tank to 40°C while stirring, and perform the following nucleation process and nuclear decomposition. The mixed aqueous solution was controlled to have a temperature of 40° C. in the crushing step and the 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 ammonia water was added to the water in the reaction tank 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, air gas was supplied as an oxygen-containing gas into the reaction tank from an air compressor at a rate of 4 L/min, and the inside of the tank was purged to create an oxygen-containing atmosphere. Note that the supply of air gas is continued until the particle growth step is completed, and the interior of the reaction tank is maintained in an air atmosphere, that is, an oxygen-containing atmosphere.

(2) Preparation of mixed aqueous solution containing metal components Next, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water to prepare a mixed aqueous solution containing metal components with a metal ion concentration of 2.0 mol/L. In this mixed aqueous solution containing metal components, the elemental molar ratio of each metal was adjusted to be Ni:Co:Mn=0.334:0.333:0.333.

(3) Preparation of pH-adjusted aqueous solution Sodium carbonate and ammonium carbonate were dissolved in water to prepare a pH-adjusted aqueous solution with a carbonate ion concentration of 2.2 mol/L. Note that sodium carbonate and ammonium carbonate in the pH-adjusted aqueous solution were added at a molar ratio of 9:2.

(4) Adding and mixing the metal component-containing mixed aqueous solution to the initial aqueous solution The metal component-containing mixed aqueous solution was added to the initial aqueous solution in the reaction tank at a rate of 10.3 ml/min. were added at a ratio of 1 to 2 to form a mixed aqueous solution.

When adding the metal component-containing mixed aqueous solution, at the same time, a pH adjusting aqueous solution is added to control the pH value of the mixed aqueous solution in the reaction tank so as not to exceed 6.4 (nucleation pH value). The nucleation step was carried out by crystallizing for minutes. Further, during the nucleation step, the pH value of the mixed aqueous solution fluctuated within a range of 0.2 above and below the central value (set pH value) of 6.2. Note that the maximum pH value of the mixed aqueous solution in the nucleation step was 6.4.

(5) Nuclear disintegration step After that, stirring was continued for 5 minutes to disintegrate the nuclei.

(Particle growth process)
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 particle growth process will be explained below.
(1) Adjustment of pH of mixed aqueous solution In the particle growth step, first, a pH adjustment aqueous solution was added to the mixed aqueous solution obtained in the nucleation step to adjust the pH value to 7.4 (based on liquid temperature of 40° C.). Note that the maximum pH value of the mixed aqueous solution in the particle growth step was 7.4.
(2) Addition and mixing of metal component-containing mixed aqueous solution to mixed aqueous solution The metal component-containing mixed aqueous solution was added at a rate of 10.3 ml/min to the mixed aqueous solution after adjusting the pH value.

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

After this state was continued for 196 minutes, stirring was stopped to complete the crystallization.

Then, the product obtained in the particle growth step was washed with water, filtered, and dried to obtain precursor particles (washing and drying steps).

In addition, the pH value in the particle growth process is controlled by adjusting the supply flow rate of the pH adjustment aqueous solution using a pH controller, and the fluctuation range of the pH value of the mixed aqueous solution is above and below the center value (set pH value) of 7.2. It was within the range of 0.2.

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

[Evaluation of precursor]
After dissolving the obtained precursor in an inorganic acid, chemical analysis was performed by ICP emission spectroscopy, and the composition was found to be carbonic acid consisting of Ni:Co:Mn=0.334:0.333:0.333. It was confirmed that it was salt. Furthermore, the elemental amount of hydrogen (H) was measured using an elemental analyzer (manufactured by Thermo Fisher Scientific, model: FlashEA 1112), and the material amount ratio with metals (Ni + Co + Mn) was calculated to be 1.68. It was confirmed that it contained hydrogen. Furthermore, it was confirmed that it had a hydrogen-containing functional group.

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

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

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

[Manufacture of positive electrode active material]
The above precursor was heat-treated at 500° C. for 2 hours in a stream of air (oxygen: 21% by volume) to convert it into composite oxide particles, which were heat-treated particles, and were 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 of the resulting lithium mixture was 1.10, and mixed with the heat-treated particles to prepare a lithium mixture. The mixing was performed using a shaker mixer device (TURBULA Type T2C, manufactured by Willy & Backofen (WAB)). The obtained lithium mixture was calcined in the atmosphere (oxygen: 21% by volume) at 500°C for 5 hours, then at 910°C for 10 hours, and then cooled. Thereafter, it was crushed to obtain a positive electrode active material. The composition of the obtained positive electrode active material is expressed as Li:Ni:Co:Mn=1.10:0.334:0.333:0.333.

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

In addition, a cross section of the positive electrode active material was observed by SEM. In conducting SEM observation of the cross section of the positive electrode active material, the secondary particles of a plurality of positive electrode active material particles were embedded in the resin, and the particles were made into a state where the cross section of the particles could be observed by cross-section polishing, and then the SEM observation was performed. . As a result, it was confirmed that the secondary particles had a structure with uniform pores up to the center.

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

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

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

The tap density was measured after filling a 20 ml measuring cylinder with the obtained positive electrode active material, and then tightly filling the cylinder by repeating free fall from a height of 2 cm 500 times.

In addition, the specific surface area of the obtained positive electrode active material was determined using a fluidized gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics, Multisorb), and it was confirmed to be approximately 1.1 m ² /g. .

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

The structure of the produced coin-type battery will be explained using FIG. 3. FIG. 3 schematically shows a cross-sectional configuration diagram of a coin-type battery. As shown in FIG. 3, this coin-type battery 10 is comprised of a case 11 and an electrode 12 housed within this case 11.

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

The electrode 12 consists of a positive electrode 121, a separator 122, and a negative electrode 123, which are stacked in this order so that the positive electrode 121 contacts the inner surface of the positive electrode can 111 and the negative electrode 123 contacts the inner surface of the negative electrode can 112. It is housed in case 11.

Note that the case 11 includes a gasket 113, and the gasket 113 fixes the positive electrode can 111 and the negative electrode can 112 so as to maintain an electrically insulated state between them. Furthermore, the gasket 113 also has the function of sealing the gap between the positive electrode can 111 and the negative electrode can 112, thereby creating an airtight and liquid-tight seal between the inside of the case 11 and the outside.

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

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

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

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

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

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

The characteristics of the precursor obtained in this example are shown in Table 1, the characteristics of the positive electrode active material are shown in Table 2, and the evaluations of the coin type battery manufactured using this positive electrode active material are shown in Table 3. The same table also shows the same contents for Comparative Example 1 below.

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

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

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

On the other hand, in Comparative Example 1, the H/Me of the precursor was less than 1.60, and it was confirmed that a precursor with the desired composition was not obtained. Therefore, it was confirmed that when a positive electrode active material was produced using the precursor, hardly any porous particles were obtained, and the porosity of the porous particles was also reduced. It was also confirmed that in the secondary battery manufactured using such a positive electrode active material, both the initial discharge capacity and the discharge capacity under high discharge rate conditions were inferior to those of Example 1.

Claims (3)

A positive electrode active material for a nonaqueous electrolyte secondary battery containing a lithium metal composite oxide,
The lithium metal composite oxide has a material amount ratio of Li:Ni:Mn:Co:M=α:x:y:z:t (1.00≦α≦1.30, x+y+z+t=1, and 0 .25<x<0.60, 0<y<0.70, 0<z<0.70, 0≦t≦0.10, M is Mg, Ca, Al, Ti, V, Cr, Fe, One or more additive elements selected from Cu, Zn, Zr, Nb, Mo, and W.)
Contains porous secondary particles in which multiple primary particles aggregate,
The porous secondary particles have a porosity of more than 3%, which is calculated by observing the cross-sectional structure of the lithium metal composite oxide and performing image processing, and have pores up to the center,
Among the porous secondary particles, the number ratio of secondary particles having an internal porosity of 10% by volume or more and 30% by volume or less is 80% or more. Cathode active material for next-generation batteries. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, having a specific surface area of 1.0 m ² /g or more. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, having a tap density of 1.5 g/cc or more.

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