JP7159589B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery, compact, and method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a molded body, and a method for producing a non-aqueous electrolyte secondary battery.

In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, there is a strong demand for the development of small, lightweight non-aqueous electrolyte secondary batteries with high energy density. In addition, there is a strong demand for the development of secondary batteries with excellent output characteristics and charge/discharge cycle characteristics as batteries for electric vehicles such as hybrid vehicles.

As a secondary battery that satisfies such requirements, there is a positive electrode active material for a non-aqueous electrolyte secondary battery, and a typical secondary battery is a lithium ion secondary battery. This lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and the active material of the negative electrode and the positive electrode is a material capable of desorbing and intercalating lithium.

Such lithium-ion secondary batteries are currently being actively researched and developed. Since a voltage as high as 4 V can be obtained, it is being put to practical use as a battery with high energy density.

Materials mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ), lithium-nickel-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 ), and the like.

Among these, lithium-nickel composite oxide (LiNiO ₂ ) has attracted attention from the viewpoint that nickel, which is cheaper than cobalt, is used and that it has a higher discharge capacity when used in the positive electrode of a secondary battery. there is

A lithium-nickel composite oxide can be obtained by mixing raw materials such as a nickel-containing compound (precursor) and a lithium-containing compound (lithium compound) to prepare a lithium mixture, and then firing the lithium mixture. Firing of the lithium mixture is usually performed at a temperature of about 700° C. or more and 900° C. or less for 10 hours or more. Then, during firing, the lithium compound and the precursor react with each other to obtain a lithium-nickel composite oxide having high crystallinity.

With the further increase in demand for lithium-ion secondary batteries in recent years, it is required to produce a lithium-nickel composite oxide having high crystallinity at low cost and with high productivity.

In the step of firing the lithium mixture, generally, the powder of the lithium mixture is placed in a container such as a sagger and fired in a firing furnace. In addition, several methods of obtaining a lithium-nickel composite oxide by granulating a lithium mixture to form a compact and then firing the compact have been disclosed.

For example, in Patent Document 1 below, a raw material mixture is prepared by mixing predetermined amounts of at least a nickel salt and a lithium salt, and the raw material mixture is granulated when synthesizing LiNiO ₂ by calcining the raw material mixture. A method for producing a LiNiO ₂ -based layered composite oxide is described, which is characterized by sintering the granulated material. According to Patent Document 1, it is possible to produce a compound having a desired crystal structure with high productivity including the working surface by the above production method. Further, in the examples of Patent Document 1, specifically, granules having a size of about 0.5 mm are placed in an alumina container, heated to 700° C., and held for 24 hours. It is described that it is fired at

In Patent Document 2 below, a raw material mixture containing a lithium raw material is formed into a molded body through a process such as granulation, and then held at a temperature of 700 ° C. to 1000 ° C. for 2 to 15 hours in an oxidizing atmosphere. The synthesis of complex oxides is described. Further, in the example of Patent Document 2, Ni main component raw material powder and Li raw material are mixed, formed into pellets by a mold press at a pressure of 2 t/cm ² , and the pellets are heated at 800 ° C. for 10 hours. It is described that it was fired in a pure oxygen atmosphere.

In Patent Document 3 below, when synthesizing LiCoO ₂ or a composition containing LiCoO ₂ as a main component, a mixed powder is press-molded under a pressure of 100 kg/cm ² to 1000 kg/cm ² and a press-molded body is obtained. It is described that the thickness is set to 2 to 10 mm, and the gap between the press-formed bodies is set to 1 mm or more, and the press-formed bodies are laminated and fired. Further, in the example of Patent Document 3, a mixed powder obtained by mixing raw materials is press-molded into a molded body having a diameter of 50 mm and a thickness of 5 mm at a press pressure of 500 kg/cm ² , and a fragment of an alumina spacer having a thickness of 1 mm is press-molded. It is described that it is sandwiched between appropriate parts of the body, held at 740° C. for 10 hours and 820° C. for 20 hours, and fired.

Patent Document 4 below describes slurring a raw material containing a lithium compound, spraying or freeze-drying the dried product, and then sintering the dried product after press molding. According to Patent Document 4, press molding is extremely useful in terms of shortening the intermolecular migration distance and promoting crystal growth during firing. Further, in the example of Patent Document 4, a dry gel is formed using a static compressor at a pressure of 2 t/cm ² to form pellets of φ14 and a thickness of 2 mm, placed in an alumina boat, and placed in a tubular furnace in an oxygen atmosphere. It is described that it was calcined at 750° C. for 48 hours.

JP-A-2000-72446 JP-A-11-135123 JP-A-06-290780 WO 98/06670

However, when the powder of the lithium mixture is placed in a container and fired as in the conventional method, a long firing time is required in order to produce a lithium-nickel composite oxide having poor heat conductivity and high crystallinity. Become. In addition, when the flow rate of the atmosphere gas in the firing furnace is increased in order to increase the firing efficiency, the powder may be blown up from the container and absorbed by the exhaust duct, resulting in a decrease in yield.

Moreover, in Patent Documents 1 to 4, granules or compacts are formed and then fired, and it is believed that the firing efficiency is improved to some extent. However, the firing conditions specifically disclosed as examples in Patent Documents 1 to 4 above require firing for 10 hours or more, and a highly crystalline lithium-nickel composite oxide can be produced with higher productivity. Need a way to do it.

In addition, in Patent Document 1, since the granules are packed in a container and fired, heat conduction is poor. Granules, as with powders discussed above, can float out of the container and reduce yield. On the other hand, Patent Document 3 describes that spacers are used to provide gaps between press-formed bodies, but in the firing process, two stages of firing are required, and in the example, a total of 30 hours is required. I am baking.

SUMMARY OF THE INVENTION In view of the above problems, the present invention aims to provide a method for producing a positive electrode active material having high crystallinity with higher productivity, and a molded article or the like that can be suitably used in the production method. and

A first aspect of the present invention comprises lithium (Li), nickel (Ni), cobalt (Co) and optionally other metals (M), wherein the molar ratio of each metal element is Li:Ni:Co: M = s: (1-xy): x: y (where 0.95 ≤ s ≤ 1.30, 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1-xy) ≤ 1.0, and M is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al.) Lithium represented by A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a nickel composite oxide,
A lithium mixture containing at least one of a nickel composite hydroxide and a nickel composite oxide and a lithium compound is molded to have a thickness of 10 mm or more and a major axis of a cross section perpendicular to the thickness direction of 30 mm or more. and to obtain a molded body having a density of 1.6 g/cm ³ or more, and to obtain a lithium nickel composite oxide by firing the molded body at 730 ° C. or higher and 930 ° C. or lower in an oxidizing atmosphere for less than 10 hours. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery is provided, comprising:

Moreover, it is preferable that the density of the compact is 1.8 g/cm ³ or more. Moreover, it is preferable that the compact is placed on a plate-like member placed in a firing furnace and fired. Moreover, it is preferable that the compact contains at least one of a nickel composite hydroxide and a nickel composite oxide, and lithium hydroxide, and does not contain a binder. Moreover, the lithium hydroxide is preferably anhydrous lithium hydroxide having a moisture content of 5% or less. In addition, it is preferable that the compact contains at least one of a nickel composite hydroxide and a nickel composite oxide, lithium carbonate, and a binder. Also, the binder is preferably one or more selected from polyvinyl alcohol, polyacrylamide, and carboxymethylcellulose. Further, it is preferable to calcine the lithium mixture at a temperature of 200° C. or higher and 800° C. or lower and lower than the sintering temperature in an oxidizing atmosphere. Further, it is preferable to include pulverizing the lithium-nickel composite oxide obtained by firing. Further, the lithium-nickel composite oxide preferably has a lithium site occupancy of 94.0% or more in the lithium-based layer obtained from Rietveld analysis of the X-ray diffraction pattern. In addition, 5 g of the lithium-nickel composite oxide is dispersed in 100 ml of pure water, and the amount of lithium eluted in the supernatant after standing for 10 minutes is 0.15% by mass or less with respect to the total amount of the lithium-nickel composite oxide. is preferred.

A second aspect of the invention comprises nickel (Ni), cobalt (Co), and optionally other metals (M), wherein the molar ratio of each element is Ni:Co:M=(1−x -y): x: y (where 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1-xy) ≤ 1.0, and M is Mn , V, Mo, Nb, Ti, Zr, W, and Al.) and nickel composite hydroxides obtained by oxidizing nickel composite hydroxides A molded body containing at least one of nickel composite oxides and lithium hydroxide, containing no binder, having a thickness of 10 mm or more, a major axis of a cross section perpendicular to the thickness direction of 30 mm or more, and a density of 1.6 g. /cm ³ or more and used for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery.

In a third aspect of the present invention, there is provided a method for manufacturing a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the above manufacturing method There is provided a method for manufacturing a non-aqueous electrolyte secondary battery, comprising manufacturing a positive electrode using

According to the present invention, it is possible to provide a method for easily producing a positive electrode active material having high crystallinity with high productivity, and a molded article that can be suitably used in the production method.

FIG. 1 is a diagram showing an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a view showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIG. 3 is a view showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIG. 4 is a view showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIG. 5 is a view showing an example of a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the embodiment. FIG. 6A is a diagram showing an example of the arrangement of compacts in the firing furnace, and FIG. 6B is a diagram showing an example of the arrangement of lithium mixture powder in the firing furnace. FIG. 7 is a schematic explanatory diagram of a coin-type battery used in Examples.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. In the drawings, they may be represented schematically or may be represented by changing the scale as appropriate.

1. Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Batteries The present embodiment is a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter also referred to as "positive electrode active material") containing a lithium-nickel composite oxide. is. Lithium nickel composite oxide (hereinafter also simply referred to as "composite oxide") contains lithium (Li), nickel (Ni), cobalt (Co), and optionally other metals (M), and each metal element The molar ratio of Li: Ni: Co: M = s: (1-xy): x: y (where 0.95 ≤ s ≤ 1.30, 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40 and 0.55 ≤ (1-xy) ≤ 1.0, and M is at least one selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al is an element of ). Moreover, the lithium-nickel metal composite oxide may have a hexagonal crystal structure having a layered structure, and may contain secondary particles in which a plurality of primary particles are aggregated.

1 to 5 are diagrams showing an example of a method for producing a positive electrode active material according to this embodiment. As shown in FIG. 1 and the like, the method for producing a positive electrode active material includes, for example, obtaining a lithium mixture containing a nickel composite hydroxide and a lithium compound (step S10), molding the lithium mixture, Obtaining a compact (step S20), and firing the compact to obtain a lithium-nickel composite oxide (step S30). Each step will be described below.

[Step of obtaining a lithium mixture (step S10)]
A lithium mixture is obtained by mixing at least one of nickel composite hydroxide and nickel composite oxide with a lithium compound (step S10). The lithium mixture may contain a binder that binds the particles together, as described later (see FIG. 3). When the lithium mixture contains a binder, the strength of the resulting compact can be improved. In this specification, the nickel composite hydroxide and/or nickel composite oxide contained in the lithium mixture are also collectively referred to as "precursor".

(Nickel composite hydroxide)
The nickel composite hydroxide used in the present embodiment is not particularly limited, and a known nickel composite hydroxide can be used. For example, a nickel composite hydroxide (precursor) obtained by a crystallization method can be used. can be used. The nickel composite hydroxide obtained by the crystallization method has a uniform composition throughout the particles. A molded article containing a nickel composite hydroxide and a lithium compound obtained by a crystallization method can be sintered for a very short time to produce a lithium-nickel composite oxide having high crystallinity.

Nickel composite hydroxide can be prepared, for example, by using an alkaline aqueous solution in the presence of a complexing agent such as an ammonium ion donor while stirring an aqueous solution containing nickel (Ni), cobalt (Co), and optionally a metal M. It can be produced by performing a crystallization reaction, which is neutralized with Sulfates, nitrates, chlorides, and the like can be used as the metal salts of Ni, Co, and the metal element M used in preparing the aqueous solutions.

The nickel composite hydroxide obtained by the crystallization method is composed of secondary particles in which primary particles are agglomerated, and the positive electrode active material obtained by using the nickel composite hydroxide particles as a precursor also has agglomerated primary particles. It is composed of secondary particles. In addition, the nickel composite hydroxide may contain a small amount of independent primary particles in addition to the secondary particles.

Further, when the nickel composite hydroxide contains the metal element M, for example, in the crystallization reaction, it may be crystallized together with Ni and Co and uniformly dispersed in the nickel composite hydroxide. After the nickel composite hydroxide is formed by crystallization, a compound containing the metal element M is coated on the surface of the obtained nickel composite oxide particles, or added and mixed at the same time as the lithium compound is added. good too.

Nickel composite hydroxides can include, for example, nickel (Ni), cobalt (Co), and optionally other metals (M), where the molar ratio of each element is Ni:Co:W=( 1-xy): x: y (where 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1-xy) ≤ 1.0, M is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al.). Also, the nickel composite hydroxide may contain a small amount of metal elements other than the above.

Nickel composite hydroxide, for example, general formula (2): Ni _{1-x-y Co x} My (OH) _{2 + β} (in formula (2), 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0. 40, 0.55≦(1−x−y)≦1.0 and −0.2≦β≦0.2, and M is Mn, V, Mo, Nb, Ti, Zr, is at least one element selected from W and Al.).

The ratio of each metal element contained in the nickel composite hydroxide is inherited to the compact and the lithium-nickel composite oxide. Therefore, the composition of the nickel composite hydroxide as a whole can be the same as the composition of the metals other than lithium in the lithium-nickel composite oxide to be obtained.

The crystallization method is not particularly limited, and for example, a continuous crystallization method, a batch method, or the like can be used. For example, the continuous crystallization method is a method of continuously recovering the nickel composite hydroxide overflowing from the reaction vessel, and can easily produce a large amount of nickel composite hydroxide having the same composition. In addition, since the nickel composite oxide obtained by the continuous crystallization method has a wide particle size distribution, it is possible to improve the packing density of the compact obtained by using it.

For example, the batch method can obtain a nickel composite hydroxide having a more uniform particle size and a narrow particle size distribution. A molded body obtained using a nickel composite hydroxide obtained by a batch method can more uniformly react with a lithium compound during firing. In addition, the nickel composite hydroxide obtained by the batch method can reduce contamination of fine powder, which is one of the causes of deterioration of cycle characteristics and output characteristics when used in secondary batteries. In addition, the average particle size (D50) of the nickel composite hydroxide is, for example, 5 μm or more and 30 μm or less.

(Nickel composite oxide)
The nickel composite oxide used in this embodiment is not particularly limited, and known nickel composite oxides can be used. FIG. 2 is a diagram showing an example of a manufacturing method using a nickel composite oxide. As shown in FIG. 2, the nickel composite oxide may be obtained by subjecting the nickel composite hydroxide to oxidative roasting (heat treatment) (step S1). The types of metal elements contained in the nickel composite oxide and the molar ratio of each metal element are the same as those of the nickel composite hydroxide described above.

The oxidative roasting (step S1) is preferably carried out, for example, at 350° C. to 800° C. for 2 hours to 8 hours, and may be performed at 600° C. to 800° C. for 6 hours to 8 hours. If the oxidative roasting temperature is less than 350°C, a large amount of water may remain in the resulting precursor (mainly nickel composite oxide). On the other hand, if the oxidizing roasting temperature exceeds 800° C., the moisture in the precursor is removed, but it is not industrially suitable from the viewpoint of cost, processing time, etc., and the nickel composite oxide itself crystallizes. As the growth progresses, the reactivity with the lithium compound may decrease.

When the nickel composite oxide and the lithium compound are mixed (step S10), molded (step S20), and then fired (step S30), firing for a shorter time (for example, 1 hour or more and less than 10 hours) A lithium-nickel composite oxide having a sufficiently large crystallite size and high crystallinity can be obtained. In addition, in the production method of the present embodiment, even if oxidizing roasting is not performed, as described later, by appropriately adjusting the composition of the molded body, the flow rate of the atmosphere gas in the firing furnace, the arrangement of the molded body, etc., 10 A lithium-nickel composite oxide can be obtained by firing in less than an hour.

(lithium compound)
The lithium compound is not particularly limited, and a known lithium compound can be used. For example, lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate, a mixture containing two or more of these, and the like can be used. Among these, it is preferable to use lithium hydroxide or lithium carbonate.

When lithium hydroxide is used as the lithium compound, as will be described later, a compact having sufficient strength can be obtained without using a binder, and contamination of the positive electrode active material with impurities can be further suppressed. (See Figure 4). In addition, since lithium hydroxide has high reactivity, the molded body obtained by using it can be sintered earlier (sintered in a shorter time), and the firing time can be shortened.

Lithium hydroxide may be lithium hydroxide hydrate such as lithium hydroxide monohydrate (LiOH.H ₂ O), or may be anhydrous lithium hydroxide (LiOH). Anhydrous lithium hydroxide can be obtained, for example, by heat-treating lithium hydroxide hydrate. When anhydrous lithium hydroxide is used, it is possible to further suppress the generation of moisture in the firing process, which not only promotes the synthesis reaction of the lithium-nickel composite oxide, but also reduces the moisture content of the metal components in the compact. An increase in productivity is also expected due to an increase of 10%. As the anhydrous lithium hydroxide, it is preferable to use lithium hydroxide having a moisture content of 5% or less.

When lithium carbonate is used as the lithium compound, lithium carbonate is cheaper than lithium hydroxide, so it is more advantageous from the viewpoint of cost. The temperature required for high crystallization of the lithium-nickel composite oxide is about 760° C. or higher, which is close to the melting temperature of lithium carbonate (melting point: 723° C.). Therefore, when lithium carbonate is used as the lithium compound, it is more difficult to achieve high crystallization of the lithium-nickel composite oxide than when lithium hydroxide (melting point: 462° C.) is used. Furthermore, the difficulty in achieving high crystallization of the lithium-nickel composite oxide becomes more pronounced as the Ni ratio contained in the precursor (nickel composite hydroxide/nickel composite oxide) increases. However, in the production method of the present embodiment, by firing the compact under appropriate conditions as described later, the reactivity of the lithium compound can be increased more than in the conventional production method. Even when lithium is used, it is possible to produce a lithium-nickel composite oxide having high crystallinity by firing for a short period of time.

(lithium mixture)
The precursor (nickel composite hydroxide/nickel composite oxide) and the lithium compound are the ratio (Li /Me ratio) is 0.95 or more and 1.30 or less, preferably 1.00 or more and 1.10 or less, more preferably more than 1.00 and 1.05 or less, and a lithium mixture becomes. Since Li/Me does not substantially change before and after firing (step S30), which will be described later, the Li/Me ratio in the lithium mixture is substantially maintained even in the lithium-nickel composite oxide. Therefore, the precursor and the lithium compound can be mixed so as to have the same Li/Me ratio in the lithium-nickel composite oxide particles to be obtained. If the Li/Me ratio is less than 0.95, a part of the nickel composite oxide may remain unreacted, resulting in insufficient battery performance. When the Li/Me ratio exceeds 1.30, sintering is accelerated, and the particle size and crystallite size of the positive electrode active material become large, and sufficient battery performance may not be obtained.

In addition, it is preferable that the lithium mixture is sufficiently mixed before firing. If the mixture is not sufficiently mixed, the Li/Me ratio varies among individual particles, which may cause problems such as insufficient battery characteristics. For mixing, a general mixer (mixing device) can be used, and for example, a mixer such as a shaker mixer, Loedige mixer, Julia mixer, V-blender, etc. can be used. Moreover, this mixing should be sufficiently mixed so as not to destroy the skeleton of the precursor.

(binder)
The lithium mixture may contain a binder. When a binder is included, the moldability of the lithium mixture is improved, and molded bodies of various shapes can be easily formed. As shown in FIG. 3, for example, when lithium carbonate is used as the lithium compound, the lithium mixture preferably contains a binder. Incidentally, as shown in FIG. 3, the nickel composite oxide in the case where the lithium mixture contains the binder may be the nickel composite oxide obtained by the oxidation roasting in step S1 shown in FIG. By molding a lithium mixture containing a binder, a molded article having sufficient strength can be easily obtained. As the binder, known binders can be used, for example, polyvinyl alcohol (PVA), polyacrylamide (PAM), carboxymethyl cellulose (CMC) and the like can be used. Among these, carboxymethyl cellulose is preferably used.

The content of the binder in the lithium mixture is, for example, 0.05% by mass or more and 2.0% by mass or less, preferably 0.08% by mass or more and 1.0% by mass or less with respect to the entire lithium mixture (total mass). be. When the content of the binder is within the above range, a molded article having appropriate strength can be produced. If the binder content is too high, the adhesive strength of the particles that make up the compact becomes too strong, reducing the efficiency of exhausting the gas produced by the reaction between lithium and nickel composite oxide, or decomposing the binder. The amount of carbon dioxide generated as a result of heating increases, and the generated gas cannot be discharged from the interior of the molded body, and the internal pressure of the molded body increases, which may result in crushing of the molded body.

Note that the lithium mixture may not contain a binder. As shown in FIG. 4, for example, when lithium hydroxide is used as the lithium compound, a compact can be formed from the precursor and lithium hydroxide alone without using a binder. In particular, when anhydrous lithium hydroxide having a moisture content of 5% or less is used as the lithium compound, the lithium mixture can provide a molded article having good strength even if the lithium mixture does not contain a binder. When no binder is used, the content of impurities (for example, carbon) in the resulting lithium-nickel composite oxide can be reduced.

[Temporary Firing (Step S15)]
As shown in FIG. 5, before firing, the lithium mixture may be calcined at a temperature of 200° C. or more and 800° C. or less in an air atmosphere (under an oxidizing atmosphere) and at a temperature lower than the firing temperature described later ( step S15). For example, calcination is performed before molding the lithium mixture (before step S20). The calcination may be performed when the lithium mixture as shown in FIG. 5 does not contain a binder, or may be performed when the lithium mixture as shown in FIG. 3 contains a binder. For example, when the lithium mixture as shown in FIG. 3 contains a binder, the lithium compound and the nickel composite hydroxide are mixed and then calcined, and after calcining, the binder is mixed to obtain a lithium mixture, and the lithium mixture may be molded (step S20). That is, calcination may be performed during preparation of the lithium mixture when the lithium mixture contains a binder. The calcination is preferably carried out at a temperature of 250° C. to 800° C., preferably 300° C. to 600° C., for about 1 hour to 8 hours, preferably 2 hours to 6 hours. Note that the oxidizing atmosphere refers to an air atmosphere or an atmosphere having an oxygen concentration higher than that of the air, and the air atmosphere is preferable from the viewpoint of cost.

When calcined before firing, lithium is sufficiently diffused, and a more uniform lithium-nickel composite oxide can be obtained. In the manufacturing method of the present embodiment, even if calcination is not performed, as will be described later, by appropriately adjusting the composition of the molded body, the flow rate of the atmosphere gas in the firing furnace, the arrangement of the molded body, etc., it can be fired for 10 hours. A lithium-nickel composite oxide can be obtained with less than sintering.

[Molding of compact (step S20)]
Next, the lithium mixture is molded to obtain a molded body (step S20). For example, the lithium mixture is pressure-molded to obtain a compact. FIG. 6A is a diagram showing an example of the molded body 20. FIG. The compact 20 has a thickness t of 10 mm or more, a major axis l of a cross section perpendicular to the thickness direction of 30 mm or more, and a density of 1.6 g/cm ³ or more. The compact 20 has a higher density than the conventional lithium mixture powder 10 (see FIG. 6B). Therefore, when the compact 20 is sintered, the heat transfer coefficient increases, so that a lithium-nickel composite oxide can be obtained in a very short sintering time.

In addition, when the molded body 20 is molded without using a binder, it contains nickel (Ni), cobalt (Co), and optionally other metals (M), and the molar ratio of each element is Ni:Co : M = (1-xy): x: y (where 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1-xy) ≤ 1.0 and M is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al.) Nickel composite hydroxide and nickel composite oxide represented by and lithium hydroxide, does not contain a binder, and preferably has a thickness of 10 mm or more, a major axis of 30 mm or more, and a density of 1.6 g/cm ³ or more.

When the compact 20 is molded using a binder, it contains nickel (Ni), cobalt (Co), and optionally other metals (M), and the molar ratio of each element is Ni:Co: M = (1-xy): x: y (where 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1-xy) ≤ 1.0 and M is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al.) Nickel composite hydroxide and nickel composite oxide It preferably contains at least one of them and lithium carbonate, and has a thickness of 10 mm or more, a length of 30 mm or more, and a density of 1.6 g/cm ³ or more.

(Thickness of compact)
The thickness t of the molded body 20 is 10 mm or more, and from the viewpoint of productivity, preferably 10 mm or more and 200 mm or less, more preferably 10 mm or more and 100 mm or less, more preferably 10 mm or more and 50 mm or less. It is preferably 20 mm or more and 40 mm or less. When the thickness t of the molded body 20 is within the above range, a positive electrode active material having high crystallinity can be easily produced with high productivity. In this embodiment, the thickness t of the molded body 20 is the maximum thickness in the direction of pressure. For example, in the case of a shape in which the thickness t of the molded body 20 is not constant, the thickness t of the molded body 20 is the maximum thickness. If the pressurizing direction is not fixed in one direction or is unknown, the maximum thickness in the direction perpendicular to the mounting surface during firing may be used.

(major diameter of compact)
The major axis l of the molded body 20 is 30 mm or more, preferably 70 mm or more, more preferably 140 mm or more from the viewpoint of productivity. In addition, the upper limit of the major axis l of the molded body 20 can be appropriately adjusted depending on the size of the inside of the firing furnace, etc., and is preferably 400 mm or less, more preferably 300 mm or less, and even if it is 200 mm or less. good. If the major axis is 30 mm or more, a large amount of lithium mixture can be processed in the firing process.

In addition, the "major axis" of the molded body 20 means the length at which the distance between any two points is maximum in a cross section (usually a pressure surface) perpendicular to the thickness direction, and the molded body 20 has a special The maximum diameter of the circle circumscribing the outer edge of the cross section perpendicular to the thickness direction when the shape is uniform. In addition, when the shape of the cross section perpendicular to the thickness direction is not constant, it refers to the diameter of the circle that circumscribes the outer edge of the largest cross section. The shape of the cross section perpendicular to the thickness direction is not particularly limited, and may be circular, elliptical, rectangular, polygonal, or other shapes (eg, irregular).

(L/t ratio of compact)
In addition, the ratio of the length l to the thickness t of the molded body 20 (l/t ratio) is preferably 1.5 or more and 20 or less, more preferably 2 or more and 15 or less, and more preferably 3 or more and 11 or less. is.

(Shape of compact)
In addition, the shape of the molded body 20 is not particularly limited as long as it satisfies the above size (major axis, thickness) range, and a plate shape, a columnar shape, or the like can be used. From the viewpoint of productivity, a plate-like shape is preferable as shown in FIG. 6(A). Further, when the shape of the compact 20 is a rectangular plate shape, it is possible to increase the filling density in the furnace during firing.

(Density of compact)
The density of the compact 20 is 1.6 g/cm ³ or more, preferably 1.8 g/cm ³ or more, more preferably 1.8 g/cm ³ or more and 2.6 g/cm ³ or less. It is preferably 1.8 g/cm ³ or more and 2.3 g/cm ³ or less, more preferably 2.0 g/cm ³ or more and 2.2 g/cm ³ or less. When the density of the molded body 20 is within the above range, a positive electrode active material having high crystallinity can be produced with high productivity. On the other hand, if the density of the molded body 20 is less than 1.6 g/cm ³ , the strength of the molded body decreases, the molded body collapses during handling or firing, and the heat transfer coefficient decreases and the yield increases. may lead to aggravation of Moreover, when the density of the molded body 20 exceeds 2.6 g/cm ³ , sintering during firing proceeds too much, and the yield in the later-described crushing step may deteriorate significantly. In addition, it is preferable that the density inside the molded body 20 and the density between the plurality of molded bodies 20 are uniform as a whole. When the densities inside and between the molded bodies are uniform, the occurrence of so-called uneven baking caused by the difference in heat transfer rate due to the difference in density is suppressed, and the variation in quality can be suppressed.

(pressure)
The molded body 20 is manufactured, for example, by pressure-molding a lithium mixture. The pressure (surface pressure) in producing the molded article is not particularly limited, and the surface pressure may be controlled so as to achieve the target density. The surface pressure is preferably 300 kgf/cm ² (29.4 MPa) or more and 1000 kgf/cm ² (98.1 MPa) or less, more preferably 500 kgf/cm ² (49.0 MPa) or more and 800 kgf/cm ² (78.5 MPa). ) below. When the surface pressure is within the above range, it is possible to easily form a compact having the above density while the precursor particles retain their shape. If the surface pressure is less than 300 kgf/cm ² (29.4 MPa), the lithium mixture may not be molded. On the other hand, when the surface pressure exceeds 1000 kgf/cm ² (98.1 MPa), the compact 20 can be formed, but the particles of the precursor are destroyed, and the quality of the obtained positive electrode active material may deteriorate. .

(slide cutting)
The molded body 20 is manufactured, for example, by putting a lithium mixture into a predetermined form (mold) and then press-molding it. In this case, after the raw material (lithium mixture) is put into the mold, the material may be leveled before pressure molding, or the mold may be vibrated after the leveling. As a result, the lithium mixture can be more uniformly and stably filled in the mold, and as a result, the density inside the molded body 20 becomes more uniform as a whole. Also, when manufacturing a plurality of molded bodies 20, the amount of the lithium mixture put into the mold may be measured. As a result, the amount of the lithium mixture charged into the mold becomes uniform, and variations in density among the compacts 20 can be suppressed.

(Molded body manufacturing equipment)
The apparatus for manufacturing the molded body 20 is not particularly limited, and any apparatus capable of pressurizing (pressure molding) the lithium mixture may be used. , a roller compactor, a hydraulic press, and the like can be used, and a hydraulic press is preferably used. In addition, by using a lubricant such as stearic acid when manufacturing the molded body 20, adhesion of the raw material to the mold for manufacturing the molded body 20 can be prevented, and mass production is possible.

[Firing (step S30)]
Next, the obtained compact is fired at 730° C. or higher and 930° C. or lower in an oxidizing atmosphere (step S30). By firing the compact 20, the precursor reacts with the lithium compound to produce a lithium-nickel composite oxide. If the firing temperature is less than 730° C., the diffusion of lithium is not sufficiently performed, and particles of unreacted lithium compound remain, or the crystal structure of the lithium-nickel composite oxide is not sufficiently arranged. A secondary battery using a positive electrode active material may not have sufficient battery characteristics. On the other hand, if the firing temperature is higher than 930° C., intense sintering may occur between the lithium-nickel composite oxide particles and abnormal grain growth may occur, resulting in a decrease in the specific surface area. In addition, due to the decrease in the specific surface area of the positive electrode active material, the resistance of the positive electrode may increase and the battery capacity may decrease.

During firing, the temperature is gradually raised from room temperature, and the temperature is maintained in the temperature range of 730° C. or higher and 930° C. or lower for less than 10 hours. The firing temperature can be appropriately adjusted within the range of 730° C. or higher and 930° C. or lower depending on the composition of the precursor, the type of lithium compound, the shape of the compact, and the like. 800° C. or higher and 900° C. or lower. Moreover, the temperature increase rate of the firing furnace is not particularly limited, and is, for example, 3° C./min or more, preferably 5° C./min or more, more preferably 8° C./min or more. Further, the upper limit of the heating rate of the firing furnace is 15° C./min or less, preferably 10° C./min or less. When the heating rate of the firing furnace is within the above range, the firing efficiency is more excellent. When the heating rate of the firing furnace exceeds 15° C./min, the temperature variation in the compact becomes large, and local sintering may occur. Note that the firing temperature and the heating rate of the firing furnace may not be constant, and may be changed stepwise, for example.

The firing time is less than 10 hours, preferably 8 hours or less, more preferably 7.5 hours or less, still more preferably 6 hours or less, and may be 2.2 hours or less. In this specification, the term "firing time" refers to the time during which the above firing temperature is maintained. Conventionally, when firing the above lithium mixture, firing was performed in an air atmosphere or an oxidizing atmosphere for about 15 to 20 hours. As a result, a highly crystalline lithium-nickel composite oxide can be obtained in a very short period of time (for example, less than half the conventional baking time). The lower limit of the firing time may be a range in which the reaction between the precursor and the lithium compound is sufficiently performed, and may be, for example, 1 hour or longer, or 2 hours or longer.

The atmosphere during firing is an oxidizing atmosphere, and preferably has an oxygen concentration higher than that of the air atmosphere (air flow). In this embodiment, the ratio of nickel (Ni) in the obtained lithium metal composite oxide is 55 atomic % or more, and the ratio of nickel is relatively high. As the proportion of nickel increases, the valence of Ni increases, and more oxygen is required to form a layered compound with Li. It is necessary to allow oxygen to permeate into the interior of the compact 20 for reaction. .

The atmosphere during firing preferably has an oxygen concentration of 25% by volume or more, more preferably an atmosphere with an oxygen concentration of 30% by volume or more and 100% by volume, and more preferably an oxygen concentration of 100% by volume. preferable. When the atmosphere during firing has an oxygen concentration within the above range, oxygen can sufficiently permeate into the compact 20, and the lithium-nickel composite oxide having a layered crystal structure can be more reliably formed.

The flow rate of the atmosphere gas is not particularly limited, and from the viewpoint of cost, it may be, for example, less than 20 L/min or less than 10 L/min. Even if the flow rate of the atmosphere gas is within the above range, the lithium compound and the precursor can be reacted. Note that the flow rate of the atmosphere gas may exceed 20 L/min. For example, in the case of a batch-type firing furnace, the atmosphere gas flow rate within the above range can be suitably used. The lower limit of the flow rate of the atmosphere gas can be appropriately adjusted depending on the size of the inside of the firing furnace, the shape of the compact 20, and the like, but is, for example, 2 L/min or more.

The furnace used for firing is not particularly limited as long as it can heat in an oxygen stream, and a vertical furnace or a horizontal furnace may be used. Among these, an electric furnace that does not generate gas is preferable. Moreover, a batch-type furnace may be used, and a continuous-type furnace may be used. Among these, it is preferable to use a horizontal furnace such as a rotary hearth furnace or a roller hearth kiln from the viewpoint that more compacts can be efficiently transported and fired.

FIG. 6(A) is a diagram showing a state in which a compact 20 is placed on the plate-like member 1 during firing, and FIG. It is a figure which shows the state which inserted. Conventionally, when firing powder 10 of a lithium mixture or granules, the powder or granules are placed in a container 2 such as a sagger and fired as shown in FIG. 6B.

At the time of sintering, the compact 20 may be placed in the container 2 and sintered as in the conventional case, but as shown in FIG. , the compact 20 may be placed thereon and fired. The setter is a member (furnace material) with which the compact comes into contact in the firing furnace, and as shown in FIG. is preferred. When the plate-like member 1 is used without using the container 2, the contact area between the compact 20 and the atmospheric gas can be increased to further promote the reaction between the precursor and the lithium compound. At the time of firing, the plate-shaped compact 20 may be placed alone on the plate-shaped member 1 and fired as shown in FIG. 7A, or a plurality of plate-shaped compacts 20 may be stacked. A stack (aggregate) may be placed on the plate member 1 and fired.

(Processing amount of lithium mixture)
In the manufacturing method of the present embodiment, by firing the molded body 20 obtained by molding the lithium mixture, the density is higher than when the powder 10 of the lithium mixture is fired. can increase the production of For example, in the manufacturing method of the present embodiment, when firing the molded body 20 according to the present embodiment, compared with the case of firing the lithium mixture powder 10, for example, the processing amount of the lithium mixture calculated by the following formula However, it can be 2 times or more, preferably 2.5 times or more, more preferably 3 times or more, and still more preferably 5 times or more.
Processing amount: (T _(powder) / T _{(molded body)} ) × (L _{(molded body)} / L _(powder) × loss coefficient) (formula)
(In the above formula, T _{(molded body)} is the length of the retention time in the furnace during firing of the molded body (the time when the temperature is raised to the firing temperature (heating time) and the retention time at the firing temperature (firing time). T _(powder) is the retention time in the furnace during firing of the powder (the sum of the time (heating time) when raising the temperature to the firing temperature and the retention time at the firing temperature (firing time)) , and L _{(molded body)} indicates the weight of the molded body per unit volume during firing (the value obtained by multiplying the "unit volume during firing" by the "density of the molded body"), and L _(powder) indicates the weight of the lithium mixture of the powder per unit volume during firing (the value obtained by multiplying the "unit volume during firing" by the "powder density". The loss coefficient is the powder as 1.0. It is the relative filling rate of the molded body at the time of firing, and is a value corresponding to the volume ratio of the lithium mixture (molded body) to the above-mentioned "unit volume during firing".)
The above processing amount is a value when the processing amount of the powder described in Comparative Example 3 is set to 1.0 in the case of the compact 20 according to the present embodiment (eg, Examples 1 to 23).
(T _(powder) / T _{(molded body)} ) in the above throughput indicates the total time of the heating time and firing time of the lithium mixture powder (powder) with respect to the firing time of the shaped body 20, in other words, It shows the effect of firing time when firing compact 20 against powder.
In addition, (L _{(molded body)} / L _(powder) × loss coefficient) in the above processing amount is the amount of the molded body 20 when firing the molded body 20 with respect to the input weight per unit volume when firing the lithium mixture powder (powder) The input weight per unit volume is shown, in other words, the effect of the input weight per unit volume when firing the molded body 20 with respect to the powder is shown.
The unit volume for firing is a value that is arbitrarily set. may be set. For example, when the unit volume during firing is set to a value larger than the volume of one molded body 20, the weight of the molded body 20 charged per unit volume during firing is the same as that of a plurality of molded bodies in that unit volume. 20 (aggregate 30) (that is, L _{(molded body)} x loss coefficient).
The loss coefficient is a value that varies depending on the shape of the molded body 20 or the mode of arrangement of the molded bodies 20 (the mode of arrangement of each molded body 20 in the assembly 30 composed of a plurality of molded bodies 20). It is not particularly limited and can be set arbitrarily. The loss coefficient can be adjusted to any desired value by changing the shape of the molded body 20, the mode of arrangement of the molded body 20, or the like. For example, in the case of the assembly 30 made up of the compacts 20 (rectangular columnar shape) shown in the example of the present embodiment, the loss coefficient is set to 0.9, but the loss coefficient is not limited to these examples.
In the production method of the present embodiment, (T _(powder) /T _{(molded body)} )>1 and (L _{(molded body)} /L _(powder) × loss coefficient)>1 in the above throughput. , the sintering time and the weight per unit volume during sintering can be improved compared to the case of sintering powder.

[Crushing]
The lithium-nickel composite oxide after firing (step S30) may retain the shape of the compact 20 before firing. Also, particles of the lithium-nickel composite oxide obtained by firing (step S30) may be aggregated or slightly sintered. In such a case, the production method of the present embodiment may include a crushing step of crushing the aggregates or sintered bodies of the lithium-nickel composite oxide particles. By crushing, the average particle size and particle size distribution of the positive electrode active material to be obtained can be adjusted to a suitable range. Crushing means applying mechanical energy to agglomerates consisting of a plurality of secondary particles generated by sintering necking between secondary particles during firing, without almost destroying the secondary particles themselves. It refers to the operation of separating and loosening aggregates.

As a crushing method, known means can be used, for example, a pin mill or a hammer mill can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

2. Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Batteries According to the production method according to the present embodiment described above, a lithium-nickel composite oxide (positive electrode active material) with excellent crystallinity can be obtained with high productivity in a short period of time. The characteristics of the lithium-nickel composite oxide obtained by the production method according to this embodiment will be described below.

(composition)
The lithium-nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and optionally other metals (M), and the molar ratio of each metal element is Li:Ni:Co:M= s: (1-xy): x: y (where 0.95 ≤ s ≤ 1.30, 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1 -xy)≦1.0, and M is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al.).

Lithium-nickel composite oxides, for example, have a hexagonal crystal structure having a layered structure, and are represented by the general formula (1): Li _s Ni _{1-x-y Co x} My O _2+α (in formula (1), 0.95≦s≦1.30, 0≦x≦0.40, 0≦y≦0.40, 0.55≦(1−x−y)≦1.0, and M is is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al). Also, (1-xy) corresponding to the content of nickel (Ni) may be less than one.

(Lithium seat occupancy rate)
The lithium nickel composite oxide has, for example, a lithium site occupancy of 94% or more, preferably 95% or more, more preferably 95% or more, which is a lithium-based layer obtained from Rietveld analysis of an X-ray diffraction pattern. 96% or more. When the lithium seat occupancy is within the above range, the sintering reaction between the precursor and the lithium compound is sufficiently performed in the firing step (step S30), and the lithium-nickel composite oxide has high crystallinity. show. When a highly crystalline lithium-nickel composite oxide is used as a positive electrode active material for a secondary battery, it exhibits excellent battery characteristics (high battery capacity, etc.).

(Amount of eluted lithium)
The lithium-nickel composite oxide is prepared by dispersing the lithium-nickel composite oxide in pure water, and the amount of lithium eluted in the supernatant liquid after standing (the amount of eluted lithium) is 0.15 mass with respect to the total amount of the lithium-nickel composite oxide. % or less, preferably 0.14 mass % or less, more preferably 0.13 mass % or less, and still more preferably 0.12 mass % or less. The amount of eluted lithium can be measured by a neutralization titration method. For example, 10 g of lithium nickel composite oxide powder is added to 100 mL of ultrapure water and stirred to disperse the powder, and the supernatant after standing for 10 minutes is titrated with hydrochloric acid at a concentration of 1 mol / L. and measure to the second neutralization point, the alkali content neutralized with hydrochloric acid is taken as the lithium eluted from the lithium-nickel composite oxide, and the mass ratio of lithium to the lithium-nickel composite oxide is obtained from the titration result, and this value is It can be defined as the amount of eluted lithium.

The eluted lithium is considered to originate from unreacted lithium compounds existing on the surface of the particles of the positive electrode active material, lithium existing excessively in the crystals, and the like. That is, the amount of eluted lithium can be used as one of the indicators of the remaining amount of unreacted lithium compound derived from the raw material. It can be said that the sintering reaction between the body and the lithium compound is progressing. In addition, gelation of the positive electrode mixture paste, which will be described later, can be suppressed as the amount of eluted lithium is smaller.

(Initial charge/discharge efficiency)
The initial charge-discharge efficiency (initial discharge capacity/initial charge capacity) of the evaluation 2032-type coin-type battery CBA (see FIG. 7) produced using a lithium-nickel composite oxide as a positive electrode active material is, for example, 87%. or more, preferably 88% or more, more preferably 90% or more. When the initial charge-discharge efficiency is within the above range, the sintering reaction between the precursor and the lithium compound is sufficiently performed in the firing step (step S30), and the lithium-nickel composite oxide has high crystallinity. show. For the initial discharge capacity efficiency, the coin-type battery CBA used in the example was left for about 24 hours after it was manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA. It is a value obtained by measuring the capacity when charging to a cutoff voltage of 4.3 V at 2/cm ² , discharging to a cutoff voltage of 3.0 V after resting for 1 hour.

3. Non-aqueous electrolyte secondary battery A method for manufacturing a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also referred to as a “method for manufacturing a secondary battery”) comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte using a non-aqueous electrolyte. obtaining an electrolyte secondary battery, wherein the positive electrode is obtained using the positive electrode active material obtained by the manufacturing method described above. A secondary battery obtained by the manufacturing method according to the present embodiment may include, for example, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution, or may include a positive electrode, a negative electrode, and a solid electrolyte. Also, the secondary battery may be composed of components similar to those of a known lithium-ion secondary battery.

Hereinafter, as an example of a method of manufacturing a secondary battery according to the present embodiment, constituent materials of a secondary battery using a non-aqueous electrolytic solution and a method of manufacturing the same will be described. It should be noted that the embodiments described below are merely examples, and the manufacturing method of the secondary battery is based on the embodiments described herein, and various changes and improvements are made based on the knowledge of those skilled in the art. It can be implemented in the form of Moreover, the secondary battery obtained by the manufacturing method according to the present embodiment is not particularly limited in its application.

(positive electrode)
The positive electrode contains the positive electrode active material described above. A positive electrode can be manufactured, for example, as follows. Note that the method for producing the positive electrode is not limited to the following, and other methods may be used.

First, the above positive electrode active material, conductive material, and binder (binder) are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment, etc. are added, and this is kneaded to obtain a positive electrode mixture. Make a paste. The constituent material of the positive electrode mixture paste is not particularly limited, and materials equivalent to known positive electrode mixture pastes may be used.

The mixing ratio of each material in the positive electrode mixture paste is not particularly limited, and is appropriately adjusted according to the required performance of the secondary battery. The mixture ratio of the materials can be in the same range as the positive electrode mixture paste for known secondary batteries. The content of the active material may be 60 to 95 parts by mass, the content of the conductive material may be 1 to 20 parts by mass, and the content of the binder may be 1 to 20 parts by mass.

Examples of conductive agents that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

Binders (binders) play a role in binding active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. , polyacrylic acid, etc. can be used.

If necessary, a solvent for dispersing the positive electrode active material, the conductive material, and the activated carbon and dissolving the binder (binder) may be added to the positive electrode mixture paste. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) may be used. In addition, activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.

Next, the obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil, dried, and the solvent is dispersed to prepare a sheet-like positive electrode. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery, and used for manufacturing the battery.

(negative electrode)
Metallic lithium, a lithium alloy, or the like may be used for the negative electrode. For the negative electrode, a negative electrode active material capable of intercalating and deintercalating lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste. It may be applied to a surface, dried, and optionally compressed to increase electrode density.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. Similar to the positive electrode, a fluorine-containing resin such as PVDF can be used as the negative electrode binder. Further, organic solvents such as N-methyl-2-pyrrolidone can be used as solvents for dispersing these active materials and binders.

(separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

(Non-aqueous electrolyte)
The non-aqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, and the like, or a mixture of two or more thereof is used. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ and the like, and composite salts thereof can be used. Furthermore, the non-aqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(Battery shape and configuration)
The shape of the non-aqueous electrolyte secondary battery of the present embodiment, which is composed of the positive electrode, the negative electrode, and the non-aqueous electrolyte described above, can be various shapes such as cylindrical and laminated. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and sealed in the battery case to complete the non-aqueous electrolyte secondary battery. . Note that when a solid electrolyte is employed, the solid electrolyte may also serve as a separator.

EXAMPLES The present invention will be specifically described below using Examples, but the present invention is not limited to these Examples. Hereinafter, a method for evaluating the characteristics of the obtained positive electrode active material and a non-aqueous electrolyte secondary battery using this positive electrode active material will be described. In addition, in the production of the nickel composite hydroxide and the production of the positive electrode active material and the secondary battery in the present examples, special grade reagent samples manufactured by Wako Pure Chemical Industries, Ltd. were used.

[Drop strength]
The drop strength of the compact was evaluated by the following method.
The obtained compact was dropped from a height of 100 cm onto an iron plate having a thickness of 0.5 mm, and the presence or absence of cracks was observed. A case where no cracking of the molded body was observed was evaluated as "◯", and a case where cracking of the molded body was observed was evaluated as "X".

[Processing amount of lithium mixture]
The treated amount (burned amount) of the lithium mixture was determined by the following formula, and evaluated by converting the value of Comparative Example 3 to 1.0.
The throughput (sometimes abbreviated as "throughput") of the lithium mixture was evaluated. The processing amount of the lithium mixture was determined by the following formula.
Processing amount: (T _(powder) / T _{(molded body)} ) × (L _{(molded body)} / L _(powder) × loss coefficient) (formula)
(In the above formula, T _{(molded body)} is the length of the retention time in the furnace during firing of the molded body (the time when the temperature is raised to the firing temperature (heating time) and the retention time at the firing temperature (firing time). T _(powder) is the retention time in the furnace during firing of the powder (the sum of the time (heating time) when raising the temperature to the firing temperature and the retention time at the firing temperature (firing time)) , and L _{(molded body)} indicates the weight of the molded body per unit volume during firing (the value obtained by multiplying the "unit volume during firing" by the "density of the molded body"), and L _(powder) indicates the weight of the lithium mixture of the powder per unit volume during firing (the value obtained by multiplying the "unit volume during firing" by the "powder density". The loss coefficient is the powder as 1.0. It is the relative filling rate of the molded body at the time of firing, and is a value corresponding to the volume ratio of the lithium mixture (molded body) to the above-mentioned "unit volume during firing".)
In the examples of the molded bodies (Examples 1 to 23, Comparative Examples 1, 4 to 5), in the above formula, the processing amount of Comparative Example 3 (powder, retention time in the furnace: 15 hours) was set to 1.0, and "firing A compact or powder in a rectangular parallelepiped space of 100 cm long, 100 cm wide and 30 mm thick (height) (30 mm height in a unit hearth area (1 m ² ) of 100 cm long and 100 cm wide). The volume (100 cm×100 cm×3 cm=30000 [cm ³ ]) when the body was put in was taken as 0.9 and the loss coefficient of the molded body was set at 0.9.
For example, the processing amount of Example 3 is, in the above formula, T _(powder) (Comparative Example 3) = 15 hours (heating time: 2.7 hours, firing time: 12.3 hours), T _{(molded body )} = 8 hours (heating time: 2.8 hours, firing time: 5.2 hours), L _{(molded body)} × loss coefficient = 30000 cm ³ (unit volume) × 1.74 (density) × 0.9 ( Loss coefficient) = 47.0 [kg], L _(powder) (Comparative Example 3) = 30000 cm ³ (unit volume) × 1.00 (density) = 30.0 [kg], and these values 2.9 is calculated as the processing amount from the above. It should be noted that the loss coefficients of the examples and comparative examples are values calculated and set as average values in the examples and comparative examples.

[Amount of eluted lithium]
The amount of eluted lithium (Li) refers to the amount of lithium dissolved in water when the positive electrode active material is dispersed in water, and was measured by the following method. First, 100 ml of ultrapure water was added to 10 g of the powder of the obtained positive electrode active material (composite oxide) and stirred to disperse the powder. Measurements were taken up to the neutral point. Using the alkali content neutralized with hydrochloric acid as lithium on the surface of the composite oxide powder, the mass ratio of lithium to the composite oxide was obtained from the titration results, and this value was taken as the amount of eluted lithium. Tables 1 to 3 show the amount of lithium eluted into pure water (the amount of eluted lithium) with respect to the entire positive electrode active material.

[Lithium seat occupancy]
The obtained positive electrode active material was subjected to X-ray diffraction measurement. The X-ray diffraction measurement was performed by a powder X-ray diffraction method using Cu—Kα rays using a powder X-ray diffraction apparatus (X'Prt PRO manufactured by PANalytical). The obtained powder X-ray diffraction pattern was subjected to Rietveld analysis to obtain the lithium site occupancy at the 3a site.

[Production and Evaluation of Secondary Battery for Evaluation]
A 2032-type coin-type battery CBA (see FIG. 7) was produced by the following method, and battery characteristics of the positive electrode active material were evaluated.

(Production of coin-type battery)
52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa to prepare a positive electrode PE (evaluation electrode). did. The produced positive electrode PE was dried in a vacuum dryer at 120° C. for 12 hours. Using the dried positive electrode PE, negative electrode NE, separator SE, and electrolytic solution, the coin-type battery CBA shown in FIG.

Lithium metal is used for the negative electrode NE, and an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiPF ₆ as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) is used as the electrolyte. board. A polyethylene porous film having a film thickness of 25 μm was used as the separator SE. Also, the coin-type battery CBA has a gasket GA and a wave washer WW, and is assembled into a coin-shaped battery with a positive electrode can PC and a negative electrode can NC.

(Evaluation of initial charge/discharge capacity)
The prepared coin-type battery CBA was left for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA / cm ² and charged to a cutoff voltage of 4.3 V. The capacity was defined as the initial charge capacity, and the capacity when discharged to a cutoff voltage of 3.0 V after resting for 1 hour was defined as the initial discharge capacity.

[Battery efficiency]
Battery efficiency (initial charge/discharge efficiency) was calculated from the ratio of initial discharge capacity to initial charge capacity [(initial discharge capacity/initial charge capacity)×100]. In addition, when the battery efficiency (initial charge/discharge efficiency) was 87% or more, it was evaluated as "◯", and when the battery efficiency was less than 87%, it was evaluated as "x".

[Example 1]
(Manufacturing process of lithium mixture)
As precursors, a nickel composite hydroxide represented by Ni _0.70 Co _0.15 Mn _0.15 (OH) ₂ obtained by a crystallization method, and Li/Me ratio = 1.05 The weighed lithium hydroxide was sufficiently mixed using a shaker mixer (TURBULA Type T2C manufactured by Willie & Bacchofen (WAB)) to obtain a lithium mixture. Table 1 shows the composition of the resulting lithium mixture.

(Molding process)
The resulting lithium mixture was put into a mold and pressurized at a surface pressure of 600 kgf/cm ² (58.8 MPa) using a pressing machine (“Table Press” model number: TB-50H, AS ONE Corporation). Thus, compacts having densities and sizes (length, width, thickness, length, etc.) shown in Table 6 were obtained. Table 1 shows the properties of the obtained compact. The shape of the molded body was a rectangular plate (rectangular parallelepiped) of length x width: 30 mm x 30 mm and thickness: 10 mm. The major axis is the length of the diagonal of a square in a cross section of a square of length x width: 30 mm x 30 mm as the length that maximizes the distance between any two points in the cross section (pressure surface) perpendicular to the thickness direction. It was calculated as (30 ² +30 ² ) ^1/2 mm = 42.4 mm.

(Baking process)
The obtained compact was fired using a roller hearth kiln manufactured by NGK Insulators, Ltd. as a firing furnace. An aggregate composed of a plurality of molded bodies was formed, the formed aggregate was placed on an alumina setter, introduced into a firing furnace, and fired. The aggregate is formed by arranging and stacking a plurality of compacts in the vertical and horizontal directions so that the atmosphere gas passes through the inside of the aggregate to form a rectangular parallelepiped outer shape of the aggregate. It was formed so that the “loss coefficient” indicating the degree of filling per unit volume (length×width×height: 100 cm×100 cm×3 cm=30000 [cm ³ ]) was about 0.9. Firing is carried out by raising the temperature from room temperature to the firing temperature (heating time: 2.8 hours) in an oxygen atmosphere (oxygen concentration: 100% by volume), and firing at 870°C (firing temperature) for 5.2 hours (firing time). and then pulverized to obtain particles of a lithium-nickel composite oxide (positive electrode active material). The holding time in the furnace was 8 hours, which is the sum of the heating time (2.8 hours) and the firing time (5.2 hours). Table 1 shows the production conditions and the evaluation results of the obtained positive electrode active material.

[Examples 2 to 6]
In the molding step, the molded body and the positive electrode active material were produced under the same conditions as in Example 1 except that the surface pressure (pressure), the density of the obtained molded body, and the size (thickness, major diameter) were as shown in Table 1. Materials were obtained and evaluated. Table 1 shows the production conditions and the evaluation results of the obtained molded body and positive electrode active material.

[Example 7]
As the metal M, the metal elements shown in Table 1 are used, and in the molding process, the surface pressure (pressure) is adjusted so that the density of the obtained compact is as shown in Table 1, and the size of the compact is adjusted. A positive electrode active material was obtained and evaluated under the same conditions as in Example 1, except that the thickness (thickness, major axis) was as shown in Table 1 and the firing was performed at 850°C. Table 1 shows the production conditions and the evaluation results of the obtained positive electrode active material.

[Comparative Example 1]
In the molding process, the surface pressure (pressure) is adjusted so that the density of the obtained compact is less than 1.6 g/ ^cm3 , and the size (thickness, major axis) of the compact is as shown in Table 1. A compact and a positive electrode active material were obtained and evaluated under the same conditions as in Example 1, except that the sintering was performed at 850° C. for 9.8 hours. Table 1 shows the production conditions and the evaluation results of the obtained molded body and positive electrode active material.

[Comparative Examples 2 and 3]
A lithium mixture (powder) is put into a bowl of 100 mm long, 100 mm wide and 100 mm high, with a thickness of 30 mm so that the weight is almost the same, and baked at the baking temperature and baking time shown in Table 1. A molded body and a positive electrode active material were obtained and evaluated in the same manner as in Example 1 except that they were obtained. Table 1 shows the production conditions and the evaluation results of the obtained molded body and positive electrode active material.

[Evaluation result 1]
In the examples, a lithium mixture was used to produce a compact having a thickness of 10 mm or more, a major axis of 30 mm or more, and a density of 1.6 g/cm ³ or more, followed by firing to obtain a positive electrode active material. . The positive electrode active material obtained in the example has a small amount of eluted lithium and a high lithium site occupancy with a baking time of less than 10 hours. Moreover, it was shown that the secondary batteries using the positive electrode active materials obtained in the examples had high battery efficiency. In addition, in the examples, it was shown that the processing amount in the baking process was large and the production efficiency was high. Moreover, in the examples, it was shown that a molded body with high strength can be produced even when a lithium mixture containing no binder is used.

On the other hand, in Comparative Example 1, in which the density of the compact was less than 1.6 g/cm ³ , the amount of eluted lithium in the obtained positive electrode active material was large, and the lithium site occupancy was low compared to Examples. In addition, the secondary battery using the positive electrode active material obtained in the comparative example had low battery efficiency. In addition, the processing amount in the baking process was also small.

In addition, in Comparative Example 2, in which the lithium mixture was not molded and was fired in a powder state for less than 10 hours in the same manner as in the prior art, the amount of eluted lithium in the obtained positive electrode active material was lower than that of the Examples. , the lithium site occupancy rate was low, and the battery efficiency was also low. In addition, the processing amount in the baking process was also small.

In addition, in Comparative Example 3 in which the powder was fired for 12.3 hours in the same manner as in Comparative Example 2, the amount of eluted lithium in the obtained positive electrode active material, the lithium site occupancy, and the battery efficiency were evaluated. Similar to the example. In addition, the amount of treatment in the firing process was small compared to the examples.

From the above, when the powder of the lithium mixture is fired as in the conventional method, the firing time of 10 hours or more is required. It was shown that a lithium-nickel composite oxide (cathode active material) with high crystallinity can be obtained with high productivity within the firing time.

Next, examples and comparative examples in which mainly the kind of lithium compound and the mixing amount (Li/Me ratio) are different from those of Example 7 and the like will be described below.

[Examples 8 to 12, Comparative Examples 4 and 5]
A compact and a positive electrode active material were obtained and evaluated under the same conditions as in Example 7 except that the production conditions shown in Table 2 were used. Table 2 shows the manufacturing conditions and the evaluation results of the obtained molded body and positive electrode active material.

In Example 8, dry lithium hydroxide having a moisture content of 4.8% (anhydrous lithium hydroxide was used) was used as the lithium compound.

Moreover, in Examples 9 and 10 and Comparative Example 4, as shown in Table 2, a lithium mixture containing a binder was used. Polyvinyl alcohol (PVA), polyacrylamide (PAM), and carboxymethyl cellulose (CMC) were used as binders. In Example 9 and Comparative Example 4, carboxymethyl cellulose (CMC) was included as a binder in an amount of 2.0% by mass with respect to the total mass of the lithium mixture. 0.5% by weight of polyvinyl alcohol (PVA), 0.5% by weight of polyacrylamide (PAM), and 1.0% by weight of carboxymethylcellulose (CMC).

[Evaluation result 2]
In Example 8, lithium hydroxide (anhydrous lithium hydroxide) having a moisture content of 5% or less was used as the lithium compound to form a molded body. A positive electrode active material was obtained that was reduced and had excellent battery efficiency. Therefore, it was shown that the sintering efficiency is greatly improved when anhydrous lithium hydroxide is used. again,

Further, in Examples 9 and 10, lithium carbonate was used as a lithium compound to form a molded body, and the amount of eluted lithium was small, the lithium site occupancy was high, and the sintering time was less than 10 hours. It was shown to have high cell efficiency. Therefore, even when using lithium carbonate, which is more cost-effective than lithium hydroxide but difficult to obtain a lithium-nickel composite oxide having high crystallinity, a lithium-nickel composite oxide having high crystallinity can be obtained. was shown to be obtained.

Examples 11 and 12 in which the Li/Me ratio was 0.95 or more and 1.30 or less showed that the amount of eluted lithium was reduced and a positive electrode active material with excellent battery efficiency was obtained. On the other hand, in Comparative Example 4 in which the Li/Me ratio was less than 0.95, the lithium site occupancy was low, the amount of eluted lithium was large, and the battery efficiency was low. In addition, in Comparative Example 5 in which the Li/Me ratio exceeded 1.30, the lithium site occupancy was low, the amount of eluted lithium was large, and the battery efficiency was low.

Next, an example in which the composition of the nickel composite hydroxide is mainly different from that of Example 7, etc., and an example in which a calcination step is added will be described below.

[Examples 13 to 23]
A compact and a positive electrode active material were obtained and evaluated under the same conditions as in Example 7, except that the manufacturing conditions shown in Table 3 were used.

In addition, in Examples 14, 15, 17, and 23, as shown in Table 3, a lithium mixture containing a binder was used. The binder content in Examples 13, 15 and 17 is the same as in Example 9, and in Example 23 is the same as in Example 10.

Further, in Examples 21 to 23, calcination was performed under the conditions of 250° C. (8 hours), 500° C. (4 hours), and 800° C. (1 hour) in an air atmosphere before firing. Table 3 shows the production conditions and the evaluation results of the obtained compact and positive electrode active material.

[Evaluation result 3]
In Examples 13 to 23, the nickel content was in the range of 55 atomic % to 100 atomic %, and all of them had a small amount of eluted lithium and a high lithium site occupancy with a baking time of less than 10 hours. , and a positive electrode active material having high battery efficiency can be obtained.

In addition, in Examples 21 to 23 in which calcination was performed before firing, the amount of eluted lithium was greatly reduced, and it was found that a positive electrode active material having a high lithium site occupancy and excellent battery efficiency was obtained. shown.

As described above, in the positive electrode active material obtained by the production method according to the present embodiment, the sintering reaction between the precursor and the lithium compound in the compact (lithium mixture) proceeds very efficiently in the firing step. , it is clear that a positive electrode active material with high crystallinity and excellent battery characteristics can be obtained even by calcination for a short period of time.

It should be noted that the technical scope of the present invention is not limited to the aspects described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. Also, the requirements described in the above-described embodiments and the like can be combined as appropriate. In addition, as long as it is permitted by laws and regulations, the disclosure of all the documents cited in the above-described embodiments and the like is used as part of the description of the text.

DESCRIPTION OF SYMBOLS 1... Plate-shaped member 2... Container 10... Lithium mixture (powder)
20 Molded body 30 Assembly CBA Coin battery NC Negative electrode can NE Negative electrode PC Positive electrode can PE Positive electrode SE Separator GA Gasket WW Wave washer

Claims (13)

Lithium (Li), Nickel (Ni), Cobalt (Co) and optionally other metals (M), wherein the molar ratio of each metal element is Li:Ni:Co:M=s:(1-x- y): x: y (where 0.95 ≤ s ≤ 1.30, 0 ≤ x ≤ 0.40, 0 ≤ y ≤ 0.40, and 0.55 ≤ (1-xy) ≤ 1 .0, and M is at least one element selected from Mn, V, Mo, Nb, Ti, Zr, W, and Al.) A non-aqueous electrolyte containing a lithium-nickel composite oxide represented by A method for producing a positive electrode active material for a secondary battery, comprising:
A lithium mixture containing at least one of a nickel composite hydroxide and a nickel composite oxide and a lithium compound is molded to have a thickness of 10 mm or more and a major axis of a cross section perpendicular to the thickness direction of 30 mm. Obtaining a molded body having the above and having a density of 1.6 g/cm ³ or more and 2.6 g/cm ³ or less ;
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: sintering the molded body in an oxidizing atmosphere at 730° C. or higher and 930° C. or lower for less than 10 hours to obtain a lithium-nickel composite oxide. . The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the molded body has a density of 1.8 g/ ^cm3 or more. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the compact is placed on a plate-shaped member placed in a firing furnace and fired. The molded body according to any one of claims 1 to 3, wherein the molded body contains at least one of the nickel composite hydroxide and the nickel composite oxide, lithium hydroxide, and does not contain a binder. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. 5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein said lithium hydroxide is anhydrous lithium hydroxide having a moisture content of 5% or less. The molded body contains at least one of the nickel composite hydroxide and the nickel composite oxide, lithium carbonate, and a binder, non-aqueous system according to any one of claims 1 to 3 A method for producing a positive electrode active material for an electrolyte secondary battery. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the binder is one or more selected from polyvinyl alcohol, polyacrylamide, and carboxymethyl cellulose. The lithium mixture according to any one of claims 1 to 7, comprising calcining the lithium mixture at a temperature of 200 ° C. or higher and 800 ° C. or lower and lower than the firing temperature in an oxidizing atmosphere. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, comprising pulverizing the lithium-nickel composite oxide obtained by firing. The lithium nickel composite oxide has a lithium site occupancy of 94% or more in the lithium-based layer obtained from Rietveld analysis of an X-ray diffraction pattern. A method for producing a positive electrode active material for an aqueous electrolyte secondary battery. Claims 1 to 3, wherein the lithium-nickel composite oxide is dispersed in pure water, and the amount of lithium eluted in the supernatant after standing is 0.15% by mass or less with respect to the total amount of the lithium-nickel composite oxide. Item 11. A method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Items 10 to 11. Nickel (Ni), Cobalt (Co), and optionally other metals (M), wherein the molar ratio of each element is Ni:Co:M=(1-xy):x:y, where , 0≦x≦0.40, 0≦y≦0.40, and 0.55≦(1-xy)≦1.0, and M is Mn, V, Mo, Nb, Ti, at least one element selected from Zr, W, and Al.) and at least one of a nickel composite hydroxide represented by and a nickel composite oxide obtained by oxidizing the nickel composite hydroxide. , and lithium hydroxide,
without binder
a thickness of 10 mm or more, a major axis of a cross section perpendicular to the thickness direction of 30 mm or more, and a density of 1.6 g/cm ³ or more and 2.6 g/cm ³ or less ;
A molded body used for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery. A method for manufacturing a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising manufacturing a positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the manufacturing method according to any one of claims 1 to 11. manufacturing method.

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