JP7052806B2 - Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery and positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a positive electrode active material for a non-aqueous electrolyte secondary battery, which are made of a lithium nickel-manganese composite oxide. This application claims priority on the basis of Japanese Patent Application No. 2017-21139 filed in Japan on October 31, 2017, and is incorporated into this application by reference to this application. Will be done.

In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density and durability. Further, as a battery for electric vehicles such as electric tools and hybrid vehicles, the development of a high-output secondary battery is strongly desired.

As a secondary battery satisfying such a requirement, there is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. A non-aqueous electrolyte secondary battery using a layered or spinel-type lithium nickel-manganese composite oxide as a positive electrode material is being put into practical use as a battery having a high energy density because a high voltage of 4V class can be obtained.

In recent years, as a positive electrode active material for a non-aqueous electrolyte secondary battery, a lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having excellent thermal stability and high capacity has been used. Is attracting attention. Lithium-nickel-cobalt-manganese composite oxide is a layered compound like lithium-cobalt composite oxide and lithium-nickel composite oxide, and basically contains nickel, cobalt, and manganese at transition metal sites in a composition ratio of 1: 1: 1. It is included in the ratio of 1.

By the way, a technique of adding a metal such as tungsten, niobium, or zirconium to a positive electrode active material has been proposed for the purpose of obtaining a positive electrode having high performance (high cycle characteristics, high capacity, high output) as a non-aqueous electrolyte secondary battery. ing.

For example, Patent Document 1 proposes a positive electrode active material for a non-aqueous secondary battery, which comprises a composition composed of at least one compound composed of lithium, nickel, cobalt, element M, niobium, and oxygen. In this proposal, since the Li-Nb-O compound existing near or inside the surface of the particles has high thermal stability, a positive electrode active material having high thermal stability and a large discharge capacity can be obtained. Has been done.

Further, Patent Document 2 includes a mixing step of mixing a nickel-containing hydroxide, a lithium compound and a titanium compound to obtain a lithium mixture, and a firing step of firing the lithium mixture to obtain a lithium transition metal composite oxide. A positive electrode active material for a non-aqueous electrolyte secondary battery, which is composed of a lithium transition metal composite oxide composed of particles having a polycrystalline structure obtained by the method, has been proposed. This positive electrode active material is said to enable high thermal stability, charge / discharge capacity, and excellent cycle characteristics.

Further, Patent Document 3 is a positive electrode active material for a non-aqueous electrolyte secondary battery made of a lithium transition metal composite oxide obtained by a production method including a niobium coating step and a firing step, and has a porous structure. , A positive electrode active material having a specific surface area of 2.0 to 7.0 m ² / g has been proposed. By using this positive electrode active material, it is said that a non-aqueous electrolyte secondary battery having high safety, battery capacity and excellent cycle characteristics can be obtained.

Further, Patent Document 4 describes a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a layered structure of a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is a primary particle and an aggregate thereof. A non-aqueous electrolyte that exists in the form of particles consisting of one or both of certain secondary particles and has a compound having at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on at least the surface of the particles. Positive electrode active materials for secondary batteries have been proposed. It is said that the conductivity is improved by having the above compound on the surface of the particles.

Further, Patent Document 5 contains a lithium transition metal-based compound having a function of inserting and removing lithium ions as a main component, and contains at least one element selected from B and Bi as a main component raw material. Lithium transition metal compound powder for lithium secondary battery positive electrode material, which is obtained by adding one compound and a compound containing at least one element selected from Mo, W, Ti, Ta and Re in combination and then firing. The body is proposed. By firing after adding the additive element in combination, the rate and output characteristics are improved, and a lithium-containing transition metal compound powder that is easy to handle and prepare the electrodes can be obtained.

Further, Patent Document 6 proposes a positive electrode composition for a non-aqueous electrolytic solution secondary battery containing a lithium transition metal composite oxide and a boron compound containing at least a boron element and an oxygen element. By using a positive electrode composition containing a lithium transition metal composite oxide that requires nickel and tungsten and a specific boron compound, the output characteristics and cycle characteristics of the positive electrode composition using the lithium transition metal composite oxide are improved. It is said that it can be made to do.

Further, Patent Document 7 describes a positive electrode active material made of a lithium nickel-manganese composite oxide composed of a hexagonal lithium-containing composite oxide having a layered structure, having an average particle size of 2 to 8 μm and a particle size. An outer shell portion in which [(d90-d10) / average particle size], which is an index indicating the spread of distribution, is 0.60 or less and aggregated primary particles are sintered, and a hollow portion existing inside the outer shell portion. A positive electrode active material for a non-aqueous electrolyte secondary battery, which is characterized by having a hollow structure composed of the above, has been proposed. It is said that this positive electrode active material has a high capacity, good cycle characteristics, and high output when used in a non-aqueous secondary battery.

Further, in Patent Document 8, by adding zirconium to the lithium cobalt composite oxide at a molar ratio of 1 to 10% with respect to cobalt, the surface of the lithium cobalt composite oxide particles becomes zirconium oxide or a composite oxide of lithium and zirconium. By being covered, it is said that the decomposition reaction of the electrolytic solution and crystal destruction at high potential are suppressed, and a positive electrode active material exhibiting excellent cycle characteristics and storage characteristics can be obtained.

Japanese Unexamined Patent Publication No. 2002-151071 JP-A-2015-122298 International release WO2014 / 034430 Japanese Unexamined Patent Publication No. 2005-251716 Japanese Unexamined Patent Publication No. 2011-108554 Japanese Unexamined Patent Publication No. 2013-239434 International release WO2012 / 131881 Japanese Patent No. 2855877

However, although all of the above proposals have improved output characteristics, battery capacity, and durability, they are not sufficient for improving thermal stability, and development of a positive electrode active material that achieves both of these characteristics at a high level. Is desired. For example, in a lithium ion secondary battery, when a short circuit occurs inside the battery, heat is generated due to a sudden current. At this time, the positive electrode active material, which is unstable in the charged state, further generates heat due to rapid thermal decomposition, resulting in thermal runaway. Therefore, the positive electrode active material is required to have higher thermal stability.

As a method for improving thermal stability during overcharging, a method of adding a dissimilar element to the positive electrode active material to stabilize the crystal structure or oxidation of the surface of the positive electrode active material with SiO ₂ , Al ₂ O ₃ , ZrO ₂ , etc. A method of covering with an object has been proposed. However, with these methods, the initial capacity decrease is large, and it is difficult to achieve both thermal stability. In addition, it is often difficult to produce on an industrial scale because the process is complicated and it is difficult to scale up.

Therefore, the present invention has been made in view of these circumstances, and is a positive electrode capable of obtaining a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density and achieves both high thermal stability and excellent battery characteristics at a high level. The purpose is to provide an active material. Another object of the present invention is to provide a method capable of easily producing such a positive electrode active material in industrial scale production.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present invention contains lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and optionally element M, and has a plurality of elements. A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium nickel-manganese composite oxide composed of secondary particles in which primary particles are aggregated, the lithium nickel-manganese composite oxide is a material content ratio of each element. (Mole ratio) is Li: Ni: Mn: M: Zr = d: (1-a-bc): a: b: c [in the formula, a is 0.05≤a≤0.60, b. Is 0 ≦ b ≦ 0.60, c is 0.0003 ≦ c ≦ 0.06, d is 0.95 ≦ d ≦ 1.20, and (1-a-bc) is 0.30 ≦ (1-). abc) ≤ 0.95 is satisfied, and M is represented by at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb and Ta]. (However, the composition is Li _x (Ny Co _{2 (1-y) / 5 Mn} ( _{3-w) (1-y) / 5} ) _1-z Zr _z O ₂ (1.00 ≦ x ≦ 1.10 .) , 0.65 <y <0.82, excluding those represented by 0 ≦ z ≦ 0.05, 0 ≦ w ≦ 0.01) , at least a part of zirconium in the lithium nickel-manganese composite oxide. The variation index of the particle size calculated by D90 and D10 in the particle size distribution of the secondary particles by the laser diffraction scattering method and the volume average particle size (Mv) is shown [(D90-). D10) / Mv] is 0.80 or more and 1.20 or less, and the Li seat occupancy rate by the Rietbelt analysis is in the range of 94% or more and 97% or less.

By doing so, it is possible to provide a positive electrode active material capable of obtaining a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density and has both high thermal stability and excellent battery characteristics at a high level.

At this time, the minimum zirconium concentration in the primary particles may be 50% or more with respect to the average zirconium concentration in the primary particles.

By doing so, it is possible to provide a positive electrode active material that can obtain a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density, further improves thermal stability, and achieves both excellent battery characteristics at a high level. can.

At this time, the positive electrode active material for the non-aqueous electrolyte secondary battery may contain a compound containing lithium and zirconium in the positive electrode active material for the non-aqueous electrolyte secondary battery.

By doing so, it is possible to provide a positive electrode active material capable of obtaining a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density and has both high thermal stability and excellent battery characteristics at a high level.

At this time, in one aspect of the present invention, the compound containing lithium and zirconium may be at least one compound selected from Li ₂ ZrO ₃ , Li ₆ Zr ₂ O ₇ , Li ₄ ZrO ₄ , and Li ₈ ZrO ₆ . good.

In this way, the selection of the compound containing lithium and zirconium becomes the best, the decrease in tap density can be suppressed, the thermal stability can be further improved, and excellent battery characteristics can be achieved at a high level.

One aspect of the present invention is characterized in that the positive electrode active material for a non-aqueous electrolyte secondary battery is used for the positive electrode.

By doing so, it is possible to provide a positive electrode capable of obtaining a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density and has both high thermal stability and excellent battery characteristics at a high level.

One aspect of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium nickel-manganese composite oxide, which crystallizes nickel-manganese composite hydroxide particles by a continuous crystallization method. A step, a zirconium mixing step of at least a mixture containing nickel-manganese composite hydroxide particles, a zirconium compound, and a lithium compound, and a firing step of calcining the mixture to obtain the lithium nickel-manganese composite oxide. The nickel-manganese composite hydroxide particles having and added in the zirconium mixing step have a general formula (2): Ni _1-ab Mn _a M _b (OH) _{2 + α} (in the above formula (2), M. Is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb and Ta, and 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0. It is represented by .60, 0.30 ≦ (1-ab) ≦ 0.95, 0 ≦ α ≦ 0.4), and the firing step is carried out at 750 ° C. or higher and 1000 ° C. or lower in an oxidizing atmosphere. In the lithium nickel-manganese composite oxide obtained in the firing step, the substance amount ratio (molar ratio) of each element is Li: Ni: Mn: M: Zr = d :( 1-a-bc) :. a: b: c [in the formula, a is 0.05 ≦ a ≦ 0.60, b is 0 ≦ b ≦ 0.60, c is 0.0003 ≦ c ≦ 0.06, and d is 0.95 ≦ d. ≤ 1.20, (1-a-bc) satisfies 0.30 ≤ (1-a-bc) ≤ 0.95, and M is Co, W, Mo, V, Mg, Ca, It is represented by [at least one element selected from Al, Ti, Cr, Nb and Ta] (provided that the composition is Li _x (Ny Co 2 (1- _{y ) / 5} Mn _{(3-w) (1-w)). y) / 5} ) _1-z Zr _z O ₂ (Table with 1.00 ≦ x ≦ 1.10, 0.65 <y <0.82, 0 ≦ z ≦ 0.05, 0 ≦ w ≦ 0.01 It is characterized in that it is composed of secondary particles in which a plurality of primary particles are aggregated, and at least a part of zirconium is solidly dissolved in the primary particles.

By doing so, it is possible to provide a positive electrode active material capable of obtaining a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density and has both high thermal stability and excellent battery characteristics at a high level.

At this time, in one aspect of the present invention, in the zirconium mixing step, the nickel-manganese composite hydroxide particles obtained in the crystallization step have an average particle size of 0.01 μm or more and 10 μm or less with the lithium compound. A mixture of zirconium compounds may be mixed to obtain a lithium zirconium mixture.

By doing so, the handling of the powder becomes very easy, the zirconium compound is scattered in the firing step, and the desired composition can be added to the active material. In addition, a positive electrode active material that can uniformly distribute zirconium in the lithium transition metal composite oxide after firing and can obtain a non-aqueous electrolyte secondary battery that achieves both high thermal stability and excellent battery characteristics at a high level. Can be provided.

At this time, in one aspect of the present invention, the zirconium mixing step further includes a slurry step of mixing the nickel-manganese composite hydroxide particles obtained in the crystallization step with water to obtain a slurry, and the slurry. A zirconium coating step of coating the nickel-manganese composite hydroxide particles with a zirconium compound to obtain zirconium-coated nickel-manganese composite hydroxide particles by adding a zirconium salt solution and an alkali as necessary, and the zirconium coating. It may have a lithium mixing step of mixing the zirconium-coated nickel-manganese composite hydroxide particles obtained in the step with the lithium compound.

By doing so, it is possible to optimize the crystallization conditions and facilitate the control of the composition ratio, and a non-aqueous electrolyte secondary battery that achieves both high thermal stability and excellent battery characteristics at a high level can be obtained. The obtained positive electrode active material can be provided.

At this time, in one aspect of the present invention, the lithium-zirconium mixing step further includes a heat treatment step of heat-treating the nickel-manganese composite hydroxide particles or the zirconium-coated nickel-manganese composite hydroxide particles, and the heat treatment step comprises a heat treatment step. It may be performed at a temperature of 105 ° C. or higher and 700 ° C. or lower.

By doing so, it is possible to prevent the Li / Me of the positive electrode active material obtained in the firing step from being dispersed by removing at least a part of the water remaining in the composite hydroxide particles.

According to the present invention, it is possible to provide a positive electrode active material capable of obtaining a non-aqueous electrolyte secondary battery that suppresses a decrease in tap density and has both high thermal stability and excellent battery characteristics at a high level. Further, according to the present invention, such a positive electrode active material can be easily produced in industrial scale production, and it can be said that the industrial value is extremely large.

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 of the present invention. FIG. 2 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 of the present invention. FIG. 3 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 of the present invention. FIG. 4 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 of the present invention. FIG. 5 is a schematic cross-sectional view of a coin-type secondary battery used for battery evaluation. FIG. 6 is a diagram showing an example of a Nyquist plot. FIG. 7 is a diagram showing an equivalent circuit used for impedance evaluation.

As a result of diligent studies to solve the above problems, the present inventor added a specific amount of manganese to the lithium nickel-manganese composite oxide containing a specific amount of manganese while maintaining the battery characteristics. The present invention has been completed based on the finding that it is possible to achieve both electron conductivity and high thermal stability by suppressing oxygen release during overcharging. Hereinafter, preferred embodiments of the present invention will be described.

The embodiments described below do not unreasonably limit the content of the present invention described in the claims, and can be modified without departing from the gist of the present invention. Moreover, not all of the configurations described in the present embodiment are indispensable as the means for solving the present invention. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described in the following order.
1. 1. Positive electrode active material for non-aqueous electrolyte secondary batteries 2. Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary battery 2-1. Crystallization step 2-2. Zirconium mixing step 2-2-1. Slurry process 2-2-2. Zirconium coating process 2-2-3. Lithium mixing process 2-2-4. Heat treatment process 2-3. Baking process 3. Non-aqueous electrolyte secondary battery 3-1. Positive electrode 3-2. Negative electrode 3-3. Separator 3-4. Non-aqueous electrolyte solution 3-5. Shape and composition of secondary battery

<1. Positive electrode active material for non-aqueous electrolyte secondary batteries>
The positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter referred to as “positive electrode active material”) according to an embodiment of the present invention is composed of particles having a polycrystalline structure, and secondary particles in which a plurality of primary particles are aggregated. It contains a lithium nickel-manganese composite oxide composed of (hereinafter referred to as "lithium metal composite oxide").
In the above lithium metal composite oxide, the substance amount ratio (molar ratio) of each element is Li: Ni: Mn: M: Zr = d: (1-a-bc): a: b: c [in the formula]. , A is 0.05 ≦ a ≦ 0.60, b is 0 ≦ b ≦ 0.60, c is 0.0003 ≦ c ≦ 0.06, d is 0.95 ≦ d ≦ 1.20, (1- abc) satisfies 0.30 ≦ (1-abc) ≦ 0.95, and M is Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb and It is a layered compound represented by [at least one element selected from Ta]. Further, the lithium metal composite oxide has a general formula (1): Lid Ni _{1-ab-c Mn a} M _b Zr _c O _{2 + α} (in the general formula (1), M is Co, W, Mo. , V, Mg, Ca, Al, Ti, Cr, Nb and Ta, which is at least one element, 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0.60, 0.0003 ≦ c ≤ 0.06, 0.95 ≤ d ≤ 1.20, 0.30 ≤ (1-a-bc) ≤ 0.95, -0.5 ≤ α ≤ 0.5) It is a layered compound to be formed. In addition, α in the general formula may be 0.

Then, at least a part of zirconium in the lithium nickel-manganese composite oxide is dissolved in the primary particles, and D90 and D10 in the particle size distribution of the secondary particles by the laser diffraction scattering method and the volume average particle size (Mv). ] And [(D90-D10) / Mv] indicating the particle size variation index calculated by) is 0.80 or more and 1.20 or less, and the Li seat occupancy rate by the Rietbelt analysis is 94% or more and 97. It is characterized in that it is in the range of% or less.

Since a non-aqueous electrolyte secondary battery uses a flammable non-aqueous electrolyte as a battery material, high thermal stability is required. For example, it is known that a lithium ion secondary battery causes thermal runaway by releasing oxygen from a positive electrode active material crystal when heat is applied to it in a charged state and reacting with an electrolytic solution. Methods for improving thermal stability during overcharging include a method of adding dissimilar elements to the positive electrode active material to stabilize the crystal structure, and oxidation of the surface of the positive electrode active material with SiO ₂ , Al ₂ O ₃ , ZrO ₂ , etc. A method of covering with an object has been proposed. However, in these methods, the initial charge / discharge capacity is greatly reduced, and it is difficult to achieve both battery capacity and thermal stability. In addition, industrial scale production is often difficult due to the complexity of the process and the difficulty of scaling up.

Therefore, according to the present invention, by adding a specific amount of zirconium to a lithium nickel-manganese composite oxide containing a specific amount of manganese, a decrease in tap density is suppressed, and high thermal stability and excellent battery characteristics are achieved. It is compatible in terms of dimension and can be easily manufactured in industrial scale production. This will be described in detail below.

The positive electrode active material according to the embodiment of the present invention is made of a lithium metal composite oxide containing a specific amount of zirconium (Zr), and a non-aqueous electrolyte secondary battery (hereinafter, “secondary battery”) using this positive electrode active material. The reaction resistance in the positive electrode is low, and the secondary battery has extremely high thermal stability when the positive electrode active material is overcharged, as compared with the case where the positive electrode active material containing no zirconium is used. Further, since the variation index is 0.80 or more and 1.20 or less and the particle size distribution width is broad, the filling property of the active material is high, and the secondary battery shows a high volume energy density.

Further, the positive electrode active material of the present embodiment is characterized in that the Li seat occupancy rate is in the range of 94% or more and 97% or less, and the Li seat occupancy rate is lower than that in the case where zirconium is not contained. Since the Li-seat occupancy rate decreases as the amount of zirconium added increases, it is considered that this decrease in the Li-seat occupancy rate is caused by the solid solution of the added zirconium in the Li-seat. Although the details are not clear, it is thought that the solid solution of zirconium in the Li seat makes it difficult for the crystal structure to collapse even in an overcharged state, and exhibits high thermal stability.

In the above Patent Document 8, a technique for adding zirconium to a lithium cobalt composite oxide is proposed, but there is no description about the Li seat occupancy, the composition does not contain nickel and manganese, and zirconium oxide (ZrO) is used. It is a technique different from the present invention because it is premised on the formation of ₂ ) or a lithium zirconium compound (Li ₂ ZrO ₃ ).

In the above molar ratio and the general formula (1), the range of a indicating the Mn content is 0.05 ≦ a ≦ 0.60, preferably 0.05 ≦ a ≦ 0.50, and more preferably 0. 05 ≦ a ≦ 0.40. When the value of a is in the above range, a high capacity and excellent reaction resistance can be obtained, and further, high thermal stability can be obtained. On the other hand, when the value of a is less than 0.05, the effect of improving the thermal stability cannot be obtained. Further, when the value of a exceeds 0.60, the capacity decreases.

In the above molar ratio and the general formula (1), the range of c indicating the Zr content is 0.0003 ≦ c ≦ 0.06, preferably 0.005 ≦ c ≦ 0.04. When the range of c is in the above range, oxygen release can be suppressed when used for the positive electrode of a secondary battery, high thermal stability can be obtained, and the reaction resistance is reduced by the solid-dissolved zirconium, which is excellent. Output characteristics can be obtained. On the other hand, when the value of c is less than 0.0003, the amount of zirconium dissolved is not sufficient, so that the effect of improving thermal stability is not observed. Further, when the value of c exceeds 0.06, a large amount of lithium zirconium compound is generated, so that the battery capacity is significantly reduced. The composition of the lithium metal composite oxide can be measured by quantitative analysis by inductively coupled plasma (ICP) emission spectrometry.

In the above molar ratio and the general formula (1), M indicating an additive element is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb and Ta. Yes, the range of b indicating the content of M is 0 ≦ b ≦ 0.60. When b is 0 or more, thermal stability, storage characteristics, battery characteristics, and the like can be improved. If b exceeds 0.60, the structure may become unstable and the layered compound may not be formed, or the ratio of Ni and Mn may be relatively lowered, so that the battery capacity may be lowered. For example, when M contains Co, it is superior in battery capacity and output characteristics. When M is Co, it is preferably 0.05 ≦ b ≦ 0.5, more preferably 0.05 ≦ b ≦ 0.4.

In the above molar ratio and the general formula (1), the range of d indicating the Li content is 0.95 ≦ d ≦ 1.20. When the range of d is the above range, the reaction resistance of the positive electrode is lowered and the output of the battery is improved. If the value of d is less than 0.95 or more than 1.20, the reaction resistance may increase and the output of the battery may decrease.

In the positive electrode active material according to the embodiment of the present invention, at least a part of zirconium is dissolved in the primary particles, and the Li seat occupancy rate (site occupancy rate of Li ions at 3a sites of the layered compound) is 94% or more. The range is preferably 97% or less, and more preferably 94.5% or more and 97% or less. The effect of improving thermal stability and reaction resistance is considered to be due to the solid solution of zirconium into the Li seat.

Here, the solid dissolution of zirconium means that, for example, zirconium is detected by ICP emission analysis method, and zirconium is found by surface analysis of the primary particle cross section using EDX in a scanning transmission electron microscope (S-TEM). It refers to a state in which zirconium is detected in the primary particles, and it is preferable that zirconium is detected over the entire surface of the primary particles. The Li seat occupancy was obtained from Rietveld analysis of the powder X-ray diffraction pattern using Cu Kα rays. When the Li seat occupancy rate exceeds 97%, the amount of zirconium dissolved in the Li seat is not sufficient, so that the effect of improving thermal stability is not observed. Further, when the Li seat occupancy rate is less than 94%, the proportion of Li ions contributing to the charge / discharge reaction is small, so that the battery capacity is significantly reduced.

Further, if there is a portion of the primary particle having an extremely low zirconium concentration, a sufficient effect of improving thermal stability cannot be obtained. Therefore, the minimum zirconium concentration in the primary particle is set to the average zirconium concentration in the primary particle. On the other hand, it is preferably 50% or more. The minimum zirconium concentration is the concentration of the portion of the primary particle where the zirconium concentration is locally lowest. The average zirconium concentration means the average zirconium concentration in the primary particles.

Fluctuations in the zirconium concentration in the primary particles can be confirmed by analyzing the composition of the cross section of the primary particles by EDX analysis of a scanning transmission electron microscope (S-TEM). The ratio of the minimum zirconium concentration to the average zirconium concentration in the primary particles (minimum zirconium concentration / average zirconium concentration) is, for example, arbitrarily selected 20 or more primary particles from a plurality of secondary particles, and each primary particle cross section. The inside can be obtained by analyzing the composition with EDX of S-TEM. Since the fluctuation of the zirconium concentration is a value within the primary particle, if a zirconium compound is confirmed on the surface of the primary particle by prior surface analysis or the like, the presence of the zirconium compound causes the surface of the primary particle. EDX analysis is performed at a position where the measured value of the zirconium concentration in the vicinity is not affected, and the fluctuation of the zirconium concentration is measured.

As described above, in the secondary battery using the positive electrode active material according to the embodiment of the present invention, the zirconium is dissolved in the Li seat in the primary particles, so that the crystal structure at the time of overcharging is less likely to collapse. Thermal stability can be improved. Furthermore, the reaction resistance is reduced by the solid-dissolved zirconium, and excellent output characteristics can be obtained. Therefore, it is possible to achieve both high thermal stability and excellent battery characteristics at a high level.

Further, it is preferable that the positive electrode active material according to the embodiment of the present invention contains a compound containing lithium and zirconium. The lithium zirconium compound may be present alone separately from the positive electrode active material, or may be present on at least a part of the surface of the primary particles. Further, the entire surface of the primary particles may be covered. Since the lithium zirconium compound has relatively high chemical stability with respect to the positive electrode active material, the presence of the lithium zirconium compound can further enhance the thermal stability of the obtained secondary battery.

The lithium zirconium compound preferably contains at least one selected from Li ₂ ZrO ₃ , Li ₆ Zr ₂ O ₇ , Li ₄ ZrO ₄ , and Li ₈ ZrO ₆ , and Li ₆ Zr has a high effect of improving thermal stability. ₂ O ₇ is more preferred. Further, an amorphous phase may be contained as a part of the lithium zirconium compound.

The positive electrode active material preferably has a volume average particle diameter (Mv) of 5 μm or more and 20 μm or less, and more preferably 6 μm or more and 15 μm or less. When the volume average particle size (Mv) is in the above range, when the positive electrode active material is used for the positive electrode of the secondary battery, it is possible to achieve both high output characteristics and battery capacity and high filling property to the positive electrode. If the average particle size of the secondary particles is less than 5 μm, high filling property to the positive electrode may not be obtained, and if the average particle size exceeds 20 μm, high output characteristics and battery capacity may not be obtained. The average particle size can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering type particle size distribution meter.

In addition, it is calculated by D90 and D10 (particle size at 90% and particle size at 10% in the volume integration of the particle size in the particle size distribution curve) and volume average particle size (Mv) in the particle size distribution by the laser light diffraction scattering method. It is preferable that [(D90-D10) / Mv] indicating the variation index of the particle size to be obtained is 0.80 or more and 1.20 or less.

When the particle size distribution of the positive electrode active material is wide, there are many fine particles having a small particle size with respect to the average particle size and coarse particles having a large particle size with respect to the average particle size in the positive electrode active material. It will be. If these fine particles and coarse particles are mixed, the packing density becomes high, and the energy density per volume can be increased. Therefore, if the particle size variation index is less than 0.80, the volumetric energy density may decrease. If the manufacturing method described later is used, the upper limit is 1.20. If the firing temperature, which will be described later, exceeds 1000 ° C, the particle size variation index may exceed 1.20, but when the positive electrode active material is formed, the specific surface area decreases, the resistance of the positive electrode increases, and the battery capacity increases. May decrease.

The tap density is preferably 2.0 g / cm ³ , more preferably 2.2 g / cm ³ or more. If the tap density is less than 2.0 g / cm ³ , the filling property of the secondary battery may deteriorate, which may cause a decrease in the volumetric energy density.

According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, a decrease in tap density (less than 2.0 g / cm ³ ) is suppressed, and high thermal stability and excellent battery characteristics are achieved. It is possible to provide a positive electrode active material that can obtain a non-aqueous electrolyte secondary battery that is compatible in terms of dimensions.

<2. Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary battery ＞
Next, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing an outline of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention contains a lithium nickel-manganese composite oxide and comprises the crystallization step S10, the zirconium mixing step S20, and the firing step S30 shown in FIG. At least, it has a zirconium mixing step S20 and a firing step S30. Hereinafter, each step will be described in detail. The following description is an example of the manufacturing method, and does not limit the manufacturing method.

<2-1. Crystallization step S10>
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention improves thermal stability by containing manganese and also contains manganese and zirconium in combination to provide a positive electrode active material. It relates to a positive electrode active material having further improved thermal stability.

Therefore, the crystallization step S10 can be carried out by a known method as long as nickel-manganese composite hydroxide particles having the above manganese content (hereinafter, may be referred to as “composite hydroxide particles”) can be obtained. For example, in a reaction vessel, a mixed aqueous solution containing at least nickel and manganese is stirred at a constant rate, and a neutralizing agent is added to neutralize the mixed aqueous solution to control the pH. Hydroxide particles can be produced by co-precipitation.

The production method in the crystallization step S10 includes 1) a production method by batch-type crystallization, and 2) a production method by continuous crystallization. However, in order to obtain an active material having a high variation index, a broad particle size distribution width, a high filling property, and a high volumetric energy density when used as a secondary battery, it is necessary to use a continuous crystallization manufacturing method. The optimum production method by the continuous crystallization method will be described below. In addition, the continuous crystallization method has higher productivity than the batch type crystallization and is suitable for production on an industrial scale.

As the mixed aqueous solution containing nickel and manganese, for example, a sulfate solution, a nitrate solution, or a chloride solution of nickel and manganese can be used. Further, as described later, the mixed aqueous solution may contain the additive element M. The composition of the metal element contained in the mixed aqueous solution is almost the same as the composition of the metal element contained in the obtained composite hydroxide particles. Therefore, the composition of the metal element in the mixed aqueous solution can be adjusted so as to have the same composition as the metal element of the target composite hydroxide particles. As the neutralizing agent, an alkaline aqueous solution can be used, and for example, sodium hydroxide, potassium hydroxide and the like can be used.

Further, it is preferable to add a complexing agent to the mixed aqueous solution together with the neutralizing agent. The complexing agent is not particularly limited as long as it can combine with nickel ions or other metal ions to form a complex in the aqueous solution in the reaction vessel (hereinafter referred to as "reaction aqueous solution"), and known ones are used. It can be used, for example, an ammonium ion feeder can be used. The ammonium ion feeder is not particularly limited, and for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used. By adding a complexing agent, the solubility of metal ions in the reaction aqueous solution can be adjusted.

When no complexing agent is used in the crystallization step S10, the temperature of the reaction aqueous solution is preferably in the range of more than 60 ° C. and 80 ° C. or lower, and the reaction aqueous solution at the above temperature. The pH of is preferably 10 or more and 12 or less (based on 25 ° C.). When the pH of the reaction aqueous solution exceeds 12, the obtained composite hydroxide particles become fine particles, the filterability is deteriorated, and spherical particles may not be obtained. On the other hand, when the pH of the reaction aqueous solution is smaller than 10, the formation rate of the composite hydroxide particles becomes significantly slow, Ni remains in the filtrate, the amount of Ni precipitate deviates from the target composition, and the composite has the desired ratio. Hydroxides may not be obtained.

Further, when the temperature of the reaction aqueous solution exceeds 60 ° C., the solubility of Ni increases, the amount of precipitation of Ni deviates from the target composition, and the phenomenon that coprecipitation does not occur can be avoided. On the other hand, when the temperature of the reaction aqueous solution exceeds 80 ° C., the slurry concentration (reaction aqueous solution concentration) becomes high due to the large amount of water vaporized, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate. However, there is a possibility that the charge / discharge capacity of the positive electrode active material may decrease, such as an increase in the concentration of impurities.

When an ammonium ion feeder (complexing agent) is used in the crystallization step S10, the temperature of the reaction aqueous solution is preferably 30 ° C. or higher and 60 ° C. or lower because the solubility of Ni in the reaction aqueous solution increases. Moreover, the pH of the reaction aqueous solution is preferably 10 or more and 13 or less (based on 25 ° C.), and more preferably 12 or more and 13 or less.

Further, it is preferable to keep the ammonia concentration in the reaction aqueous solution at a constant value within the range of 3 g / L or more and 25 g / L or less. When the ammonia concentration is less than 3 g / L, the solubility of the metal ion cannot be kept constant, so that the primary particles of the composite hydroxide having a uniform shape and particle size may not be formed. In addition, since gel-like nuclei are easily generated, the particle size distribution of the obtained composite hydroxide particles is also easy to spread. On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of the metal ions becomes too large, the amount of the metal ions remaining in the reaction aqueous solution increases, and the composition of the obtained composite hydroxide particles tends to shift. .. When the ammonia concentration fluctuates, the solubility of the metal ion fluctuates and uniform hydroxide particles are not formed. Therefore, it is preferable to keep the value constant. For example, the ammonia concentration is preferably maintained at a desired concentration with the upper and lower limits set to about 5 g / L.

Further, the composite hydroxide particles are at least one selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb and Ta as shown in the general formula (2) described later. (Hereinafter referred to as “additive element M”) may be contained. The method for blending the additive element M in the composite hydroxide particles is not particularly limited, and a known method can be used. For example, from the viewpoint of increasing productivity, a mixed aqueous solution containing nickel and manganese can be used. A method of adding an aqueous solution containing the additive element M to co-precipitate the composite hydroxide particles containing the additive element M is preferable.

Examples of the aqueous solution containing the additive element M include cobalt sulfate, sodium tungstate, tungsten oxide, molybdenum oxide, molybdenum sulfide, vanadium pentoxide, magnesium sulfate, magnesium chloride, calcium chloride, aluminum sulfate, sodium aluminate, and titanium sulfate. An aqueous solution containing ammonium peroxotitanate, potassium titanium oxalate, niobium oxide, niobic acid, chromium chloride, sodium aluminate, tantalic acid and the like can be used.

Further, from the viewpoint of optimizing the crystallization conditions and facilitating the control of the composition ratio, a step of coating the obtained composite hydroxide particles with M after obtaining the composite hydroxide particles by crystallization is performed. It may be provided. The method for coating the additive element M is not particularly limited, and a known method can be used.

An example of the coating method of the additive element M will be described below. First, the composite hydroxide particles obtained by crystallization are dispersed in pure water to form a slurry. Next, a solution containing M corresponding to the target coating amount is mixed with this slurry, and an acid or an alkali is added dropwise to adjust the pH to a predetermined pH. As the acid, for example, sulfuric acid, hydrochloric acid, nitric acid and the like are used. As the alkali, for example, sodium hydroxide, potassium hydroxide and the like are used. Then, after mixing the slurry for a predetermined time, the slurry can be filtered and dried to obtain composite hydroxide particles coated with the additive element M. Other coating methods include a spray-drying method in which a solution containing a compound containing M is sprayed on the composite hydroxide particles and then dried, and a solution containing a compound containing M is impregnated in the composite hydroxide particles. The method etc. can be mentioned.

The method of blending the additive element M into the composite hydroxide particles is one or both of mixing the additive element M with the above-mentioned mixed aqueous solution and coating the composite hydroxide particles with the additive element M. For example, 1) a nickel-containing hydroxide crystallized by adding an alkaline aqueous solution to a mixed aqueous solution containing nickel and manganese (excluding the additive element M) may be coated with the additive element M. Often, 2) a mixed aqueous solution containing nickel, manganese and a part of the additive element M is prepared, nickel-manganese composite hydroxide particles (including the additive element M) are co-precipitated, and the additive element M is further added to the co-precipitate. The content of M may be adjusted by coating.

<2-2. Zirconium mixing step S20>
Next, the zirconium mixing step S20 will be described. As shown in FIG. 1, in the zirconium mixing step S20, a mixture containing the nickel-manganese composite hydroxide particles obtained in the above crystallization step S10, a zirconium compound, and a lithium compound (hereinafter referred to as “zirconium mixture”). It may be done.)

Further, as shown in FIG. 2, in the zirconium mixing step S20, for example, a mixture of a lithium compound and a zirconium compound is added as a powder (solid phase) to the composite hydroxide particles and mixed to obtain a zirconium mixture. Can be done.

Further, as shown in FIG. 3, in the zirconium mixing step S20, further, a slurry step S21 for obtaining a slurry by mixing the nickel-manganese composite hydroxide particles obtained in the crystallization step S10 with water, and the above. The zirconium coating step S22 for obtaining zirconium-coated nickel-manganese composite hydroxide particles by coating the nickel-manganese composite hydroxide particles with a zirconium compound by adding a zirconium salt solution and, if necessary, an alkali to the slurry, and the above. It is possible to have a lithium mixing step S23 in which the zirconium-coated nickel-manganese composite hydroxide particles obtained in the zirconium coating step S22 and the above lithium compound are mixed. Hereinafter, the zirconium mixing step S20 will be described in detail with reference to FIGS. 1 to 3.

The composite hydroxide particles used in the zirconium mixing step S20 have a general formula (2): Ni _1-ab Mn _a M _b (OH) _{2 + α} (where M is Co, W, Mo, V, Mg, It is at least one element selected from Ca, Al, Ti, Cr, Nb and Ta, and is 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0.60, 0.30 ≦ (1-a-). b) ≤0.95, 0≤α≤0.4). Since the content (composition) of the metal (Ni, Mn, M) in the composite hydroxide particles is almost maintained even in the lithium metal composite oxide, the content of each metal (Ni, Mn, M) is described above. It is preferably in the same range as the content in the lithium metal composite oxide.

As the composite hydroxide particles, nickel composite hydroxide particles containing at least manganese in the above range are used. As a result, manganese can be uniformly distributed in the plurality of primary particles of the obtained positive electrode active material. A positive electrode active material containing (solid-dissolved) manganese and zirconium in a plurality of primary particles has high thermal stability and a decrease in conductivity.

Further, the inclusion of manganese in the primary particles makes it possible to calcin the lithium zirconium mixture at a relatively high temperature. Then, by firing at a high temperature, the zirconium in the zirconium compound can be more uniformly dissolved in the primary particles. The method for producing the composite hydroxide particles is not particularly limited, but as shown in FIGS. 2, 3 and 4, it is preferable to use the composite hydroxide particles obtained by the crystallization step S10.

The composite hydroxide particles contain nickel and manganese uniformly in the particles, and are, for example, coated with a mixture of nickel hydroxide particles and a manganese compound or a manganese compound. In the case of nickel hydroxide particles or the like, the distribution of manganese in the obtained positive electrode active material becomes non-uniform, and the effect obtained by containing manganese may not be sufficiently obtained.

As shown in FIG. 2, in the zirconium mixing step S20, for example, the nickel-manganese composite hydroxide particles obtained in the crystallization step S10 are mixed with a mixture of the lithium compound and the zirconium compound to obtain a zirconium mixture. It is preferable to obtain. By doing so, in the firing step S30 described later, a lithium nickel-nickel-manganese composite oxide in which zirconium is dissolved in at least primary particles can be obtained.

The zirconium compound is preferably mixed with particles (solid phase). When zirconium is added in solid phase, the reactivity in the subsequent firing step S30 changes depending on the particle size of the zirconium compound, so the particle size of the zirconium compound used is one of the important factors. The average particle size of the zirconium compound is preferably 0.01 μm or more and 10 μm or less, more preferably 0.05 μm or more and 3.0 μm or less, and further preferably 0.08 μm or more and 1.0 μm or less. If the average particle size is smaller than 0.01 μm, it becomes very difficult to handle the powder, and in the zirconium mixing step S20 and the firing step S30, the zirconium compound is scattered and the desired composition is added to the active material. There may be problems that cannot be done. On the other hand, when the average particle size is larger than 10 μm, zirconium may not be uniformly distributed in the lithium nickel-manganese composite oxide after firing, and thermal stability may not be ensured. The average particle size is a volume average particle size Mv, and can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering type particle size distribution meter.

The zirconium compound may be pulverized in advance using various pulverizers such as a ball mill, a planetary ball mill, a jet mill / nano jet mill, a bead mill, and a pin mill so as to have a particle size in the above range. Further, the zirconium compound may be classified by a dry classifier or sieving, if necessary. For example, sieving can be performed to obtain particles close to 0.01 μm.

As the zirconium compound mixed in the zirconium mixing step S20, a known compound containing zirconium can be used, and for example, zirconium oxide, zirconium hydroxide, zirconium sulfate, zirconium trichloride, zirconium tetrachloride and the like can be used. .. Among these, zirconium oxide, zirconium hydride, or a mixture thereof is preferable from the viewpoint of easy availability and avoiding contamination of lithium metal composite oxide with impurities. If impurities are mixed in the lithium metal composite oxide, the thermal stability, battery capacity, and cycle characteristics of the obtained secondary battery may be deteriorated.

The lithium compound is not particularly limited, and a known compound containing lithium can be used, and for example, lithium carbonate, lithium hydroxide, lithylium nitrate, or a mixture thereof can be used. Among these, lithium carbonate, lithium hydroxide, or a mixture thereof is preferable from the viewpoint of being less affected by residual impurities and dissolving at the firing temperature.

The method of mixing the composite hydroxide particles, the lithium compound, and the zirconium compound is not particularly limited, and the composite hydroxide particles, the lithium compound, and the zirconium compound are sufficient to the extent that the skeletons such as the composite hydroxide particles are not destroyed. It may be mixed with. As a mixing method, for example, a general mixer can be used for mixing, and for example, a shaker mixer, a Ladyge mixer, a Julia mixer, a V blender, or the like can be used for mixing. It is preferable that the zirconium mixture is sufficiently mixed before the firing step S30 described later. When the mixing is not sufficient, the atomic% ratio (Li / Me, general formula (1)) of Li and the metal element Me other than Li (Me = Ni + Mn + added element M + Zr in this embodiment) between the individual particles of the positive electrode active material. And the same as d of the general formula (3) described later) may vary, and problems such as insufficient battery characteristics may occur.

The lithium compound is mixed so that Li / Me in the lithium zirconium mixture is 0.95 or more and 1.20 or less. That is, the Li / Me in the zirconium mixture is mixed so as to be the same as the Li / Me in the obtained positive electrode active material. This is because the molar ratio of Li / Me and each metal element does not change around the firing step S30 described later, so that Li / Me of the lithium zirconium mixture at the time of the above mixing becomes Li / Me of the positive electrode active material. Is. Further, the zirconium compound has a zirconium content in the lithium zirconium mixture of 0.03 atomic% or more with respect to the total of metal elements (Ni, Mn, additive elements M, Zr) other than Li in the lithium zirconium mixture. It is mixed so as to be atomic% or less.

<2-2-1. Slurry process S21>
In the zirconium mixing step S20, as shown in FIG. 3, the surface of the nickel-manganese composite hydroxide particles may be coated with a zirconium compound to obtain a zirconium mixture. In this case, it is more preferable to have the slurry step S21. In the slurry step S21, the nickel-manganese composite hydroxide particles obtained in the crystallization step S10 and water are mixed to obtain a slurry. By forming a slurry, the zirconium compound can be crystallized on the surface of the nickel-manganese composite hydroxide particles in the zirconium coating step S22 described later, and the zirconium compound can be easily coated. The mixing method is not particularly limited, and a known method may be used.

<2-2-2. Zirconium coating step S22>
As shown in FIG. 3, the zirconium mixing step S20 preferably further includes a zirconium coating step S22. In the zirconium coating step S22, a zirconium salt solution and, if necessary, an alkali are added to the slurry obtained in the slurry step S21, and the composite hydroxide particles obtained in the crystallization step S10 are coated with the zirconium compound. A zirconium-coated nickel-manganese composite hydroxide particle is obtained.

The method for coating the zirconium compound is not particularly limited, and a known method can be used. However, from the viewpoint of low cost and industrial ease of use, for example, composite hydroxide particles and water are mixed. A method of adding a zirconium salt solution and, if necessary, an alkali to the obtained slurry to crystallize a zirconium compound (for example, zirconium hydroxide) on the surface of the composite hydroxide particles is preferable. When the surface of the nickel-manganese composite hydroxide particles is coated with the zirconium compound, the reaction of zirconium that dissolves in the lithium nickel-manganese composite oxide particles is promoted in the firing step S30 described later. Since the slurry obtained by mixing the composite hydroxide particles and water is basic, the pH at which the zirconium compound crystallizes may be reached when the zirconium salt solution is small. In some cases, no alkali is added.

<2-2-3. Lithium mixing step S23>
As shown in FIG. 3, the zirconium mixing step S20 preferably further includes a lithium mixing step S23. In the lithium mixing step S23, the zirconium-coated nickel-manganese composite hydroxide particles obtained in the zirconium-coated step S22 are mixed with the lithium compound. The mixing method is not particularly limited, and a known method may be used.

<2-2-4. Heat treatment step S24>
As shown in FIG. 4, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is a heat treatment for further heat-treating the nickel-manganese composite hydroxide particles in the zirconium mixing step S20. It may have a step S24. The heat treatment step S24 is a step of removing at least a part of the water content contained in the composite hydroxide particles by the heat treatment. By having the heat treatment step S24, at least a part of the water remaining in the composite hydroxide particles is removed to prevent the Li / Me of the positive electrode active material obtained in the firing step S30 described later from being dispersed. Can be done.

From the viewpoint of further reducing the variation in Li / Me, it is preferable that the heat treatment in the heat treatment step S24 sufficiently oxidizes the composite hydroxide particles and converts them into the composite oxide particles. Since it is sufficient that water can be removed to the extent that the Li / Me of the positive electrode active material does not vary, it is necessary to convert the hydroxide (composite hydroxide) in all the composite hydroxide particles to the composite oxide. There is no.

Further, when the heat treatment step S24 is performed, as shown in FIG. 4, in the zirconium mixing step S20, the composite hydroxide particles are heat-treated before preparing the zirconium mixture, and then the composite hydroxide particles after the heat treatment are performed. And / or the composite oxide particles, the lithium compound, and the zirconium compound can be mixed to prepare a zirconium mixture. When the composite hydroxide particles contain the additive element M, the composite hydroxide particles may be coated with the compound containing the additive element M and then heat-treated, and the composite hydroxide particles and / or the heat-treated composite hydroxide particles may be subjected to heat treatment. The composite oxide particles may be coated with a compound containing the additive element M. Further, when the above-mentioned composite hydroxide particles are coated with a zirconium compound (see FIG. 3), the obtained zirconium-coated composite hydroxide particles may be heat-treated. In this case, as described in FIG. 3, the zirconium coating step S22 is followed by the heat treatment step S24 and the lithium mixing step S23 (not shown).

The heat treatment in the heat treatment step S24 may be performed by heating to a temperature at which the residual water content in the composite hydroxide particles is removed. For example, the heat treatment temperature is preferably 105 ° C. or higher and 700 ° C. or lower. When the composite hydroxide particles are heated at 105 ° C. or higher, at least a part of the residual water can be removed. If the heat treatment temperature is less than 105 ° C., it takes a long time to remove the residual water, which is not industrially suitable. On the other hand, when the temperature of the heat treatment exceeds 700 ° C., the particles converted into the composite oxide particles may be sintered and aggregated. For example, when converting most of the composite hydroxide particles to the composite oxide particles, the heat treatment temperature is preferably 350 ° C. or higher and 700 ° C. or lower.

The atmosphere in which the heat treatment is performed is not particularly limited, and is preferably performed in an air stream from the viewpoint of easy operation, for example. The heat treatment time is not particularly limited, and may be, for example, one hour or more. If the heat treatment time is less than 1 hour, the residual water content in the composite hydroxide particles may not be sufficiently removed. The heat treatment time is preferably 5 hours or more and 15 hours or less. The equipment used for the heat treatment is not particularly limited as long as it can heat the composite hydroxide particles in an air stream, and for example, a blower dryer, an electric furnace that does not generate gas, or the like can be preferably used. ..

<2-3. Firing step S30>
In the firing step S30, the mixture obtained in the zirconium mixing step S20 is fired to obtain the lithium nickel-manganese composite oxide. The firing step S30 is performed at 750 ° C. or higher and 1000 ° C. or lower in an oxidizing atmosphere.

When the lithium zirconium mixture is fired, lithium in the lithium compound diffuses into the composite hydroxide particles or the zirconium-coated composite hydroxide particles described later, so that a lithium metal composite oxide composed of particles having a polycrystalline structure is formed. To. The lithium compound melts at the temperature at the time of firing and permeates into the composite hydroxide particles to form a lithium metal composite oxide. At this time, the zirconium compound penetrates into the secondary particles together with the molten lithium compound. In addition, even in the primary particles, if there are crystal grain boundaries, they permeate. By permeating, diffusion inside the primary particles is promoted and zirconium is uniformly dissolved in the primary particles. In this study, depending on the amount of zirconium, the solid solution limit in the primary particles may be exceeded, and the zirconium that exceeds the solid solution limit reacts with the excess lithium content, and the lithium zirconium compound is applied to the surface of the primary particles, grain boundaries, and grain boundaries. Alternatively, it is formed by itself.

The firing temperature is 750 ° C. or higher and 1000 ° C. or lower, preferably 750 ° C. or higher and 950 ° C. or lower in the oxidizing atmosphere. When firing at the above temperature, the lithium compound melts and the permeation and diffusion of the zirconium compound are promoted. Further, the lithium zirconium mixture contains manganese, so that the firing temperature can be increased. By increasing the firing temperature, the diffusion of zirconium is promoted and the formation of the lithium zirconium compound is promoted. Further, the crystallinity of the lithium nickel-manganese composite oxide is increased, and the battery capacity can be further improved.

On the other hand, when the firing temperature is less than 750 ° C., the diffusion of lithium and zirconium into the nickel-manganese composite hydroxide particles is not sufficiently performed, excess lithium and unreacted particles remain, and the crystal structure is sufficient. There is a problem that sufficient battery characteristics cannot be obtained due to improper alignment. In addition, the Li seat occupancy rate may become too high, and sufficient thermal stability may not be obtained. Further, when the firing temperature exceeds 1000 ° C., severe sintering occurs between the formed lithium transition metal composite oxide particles, and abnormal grain growth may occur. When abnormal grain growth occurs, not only the particles after firing become coarse and the particle morphology cannot be maintained, but also the ratio of coarse particles becomes high and the particle size variation index exceeds 1.20, and the positive electrode active material. When the particles are formed, there arises a problem that the specific surface area decreases, the resistance of the positive electrode increases, and the battery capacity decreases.

The firing time is preferably at least 3 hours or more, more preferably 6 hours or more and 24 hours or less. If the calcination time is less than 3 hours, the lithium transition metal composite oxide may not be sufficiently produced. Further, it is more preferable that the atmosphere at the time of firing is an oxidizing atmosphere, and in particular, an atmosphere having an oxygen concentration of 3 to 100% by volume. That is, firing is preferably performed in an air or oxygen stream. This is because if the oxygen concentration is less than 3% by volume, it cannot be sufficiently oxidized, and the crystallinity of the lithium transition metal composite oxide may be insufficient. In particular, considering the battery characteristics, it is preferable to perform the operation in an oxygen stream. The furnace used for firing is not particularly limited as long as it can fire the lithium zirconium mixture in an air or oxygen stream, but it is preferable to use an electric furnace that does not generate gas, and a batch type or a continuous type is preferable. Any of the furnaces can be used.

The firing step S30 may further include a step of calcining at a temperature lower than this firing temperature before firing at a temperature of 750 ° C. or higher and 1000 ° C. or lower. The calcining is preferably performed at a temperature at which the lithium compound and / or the zirconium compound in the lithium zirconium mixture can be melted and reacted with the composite hydroxide particles. The calcining temperature can be, for example, 350 ° C. or higher and lower than the firing temperature. The lower limit of the calcining temperature is preferably 400 ° C. or higher. By holding (temporarily burning) the lithium-zirconium mixture in the above temperature range, the lithium compound and / or the zirconium compound permeates the composite hydroxide particles, and lithium and zirconium are sufficiently diffused to obtain uniform lithium. A metal composite oxide can be obtained. For example, when lithium hydroxide is used, it is preferable to carry out the calcining at a temperature of 400 ° C. or higher and 550 ° C. or lower for about 1 hour or more and 10 hours or less.

The lithium transition metal composite oxide obtained by firing suppresses sintering between particles, but may form coarse particles due to weak sintering or aggregation. In such a case, the particle size distribution can be adjusted by eliminating the sintering and aggregation by crushing.

As described above, the lithium nickel-manganese composite oxide obtained in the firing step S30 has a substance amount ratio (molar ratio) of each element of Li: Ni: Mn: M: Zr = d: (1-a-). bc): a: b: c [In the formula, a is 0.05 ≦ a ≦ 0.60, b is 0 ≦ b ≦ 0.60, c is 0.0003 ≦ c ≦ 0.06, and d is. 0.95 ≦ d ≦ 1.20, (1-a-bc) satisfies 0.30 ≦ (1-a-bc) ≦ 0.95, and M is Co, W, Mo, V. , Mg, Ca, Al, Ti, Cr, Nb and at least one element selected from Ta], which is composed of secondary particles in which a plurality of primary particles are aggregated, and at least a part of zirconium is described above. It is characterized by being solidly dissolved in primary particles. Further, the lithium nickel-manganese composite oxide has a general formula (3): Lid Ni _{1-ab-c Mn a} M _b Zr _c O _{2 + α} (in the above formula (3), M is Co, W, It is at least one element selected from Mo, V, Mg, Ca, Al, Ti, Cr, Nb and Ta, and is 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0.60, 0.0003. ≤c ≤ 0.06, 0.95 ≤ d ≤ 1.20, 0.30 ≤ (1-a-bc) ≤ 0.95, -0.5 ≤ α ≤ 0.5) expressed.

Further, in the lithium nickel-manganese transition metal composite oxide obtained in the firing step S30, sintering between particles is suppressed, but coarse particles may be formed by weak sintering or aggregation. In such a case, the particle size distribution can be adjusted by eliminating the sintering and aggregation by crushing.

According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, a decrease in tap density is suppressed, and high thermal stability and excellent battery characteristics are achieved at a high level. It is possible to provide a positive electrode active material from which an aqueous electrolyte secondary battery can be obtained. Further, according to the present invention, such a positive electrode active material can be easily produced in industrial scale production, and it can be said that the industrial value is extremely large.

<3. Non-aqueous electrolyte secondary battery ＞
The non-aqueous electrolyte secondary battery (hereinafter, also referred to as “secondary battery”) according to the embodiment of the present invention uses the above-mentioned positive electrode active material as the positive electrode. Hereinafter, the secondary battery according to the embodiment of the present invention will be described for each component. The secondary battery according to the embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolytic solution, and is composed of the same components as a general lithium ion secondary battery. It should be noted that the embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery may be implemented in a form in which various changes and improvements have been made based on the knowledge of those skilled in the art, including the following embodiments. can. Further, the secondary battery is not particularly limited in its use.

<3-1. Positive electrode>
The positive electrode of the secondary battery is manufactured by using the positive electrode active material for the non-aqueous electrolyte secondary battery according to the embodiment of the present invention described above. An example of a method for manufacturing a positive electrode will be described below. First, the above-mentioned positive electrode active material (powder), conductive material and binder (binder) are mixed, and if necessary, activated carbon or a solvent of interest such as viscosity adjustment is added, and the mixture is kneaded to form a positive electrode. Make a mixture paste.

Since the mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium secondary battery, it can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium secondary battery. For example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the positive electrode active material is 60. It can contain up to 95% by mass, a conductive material in an amount of 1 to 20% by mass, and a binder in an amount of 1 to 20% by mass.

The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent to produce a sheet-shaped positive electrode. If necessary, pressurization may be performed by a roll press or the like in order to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the target battery and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the above-exemplified one, and other methods may be used.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and Ketjen black, and the like can be used.

The binder (binder) plays a role of binding the active material particles, and is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based. Resins, polyacrylic acid and the like can be used.

If necessary, the positive electrode active material, the conductive material and the activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. Specifically, as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

<3-2. Negative electrode>
As the negative electrode, metallic lithium, a lithium alloy, or the like can be used. For the negative electrode, a negative electrode mixture made into a paste by mixing a binder with a negative electrode active material capable of occluding and desorbing lithium ions and adding an appropriate solvent is applied to the surface of a metal foil current collector such as copper. It may be coated, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, a calcined body of an organic compound such as natural graphite, artificial graphite and a phenol resin, and a powdery body of a carbon substance such as coke can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and the solvent for dispersing these active substances and the binder is an organic substance such as N-methyl-2-pyrrolidone. A solvent can be used.

<3-3. Separator>
A separator is sandwiched between the positive electrode and the negative electrode. As the separator, a positive electrode and a negative electrode are separated to retain an electrolyte, and a known one can be used. For example, a thin film such as polyethylene or polypropylene, which has a large number of fine pores, may be used. can.

<3-4. Non-aqueous electrolyte>
The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Further, as the non-aqueous electrolyte solution, one in which a lithium salt is dissolved in an ionic liquid may be used. The ionic liquid is a salt composed of cations and anions other than lithium ions and showing a liquid state even at room temperature. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2-. Use one selected from ether compounds such as methyl tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethyl sulfone and butane sulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, alone or in combination of two or more. Can be done.

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

It is also possible to construct a secondary battery by using a solid electrolyte instead of the non-aqueous electrolyte solution. Since the solid electrolyte does not decompose even at a high potential, it has high thermal stability because there is no gas generation or thermal runaway due to decomposition of the electrolyte during charging as seen in non-aqueous electrolytes. Therefore, when used in a lithium ion secondary battery using the positive electrode active material according to the present invention, a secondary battery with higher thermal stability can be obtained. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like is used.

The oxide-based solid electrolyte is not particularly limited as long as it contains oxygen (O) and has lithium ion conductivity and electron insulation. Examples of the oxide-based solid electrolyte include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _X , LiBO ₂ N _X , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , and Li ₄ SiO ₄ -Li ₃ . PO ₄ , Li ₄ SiO ₄ -Li ₃ VO ₄ , Li ₂ O-B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O ₃ -ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0 ≤ X ≤ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≤ X ≤ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≤ X ≤ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ and the like can be mentioned.

The sulfide-based solid electrolyte is not particularly limited, and any sulfide-based solid electrolyte that contains sulfur (S) and has lithium ion conductivity and electron insulation can be used. Examples of the sulfide-based solid electrolyte include Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ . SB ₂ S ₃ , Li ₃ PO ₄ -Li ₂ S-Si ₂ S, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , LiPO ₄ -Li ₂ S-SiS, LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ and the like can be mentioned.

As the inorganic solid electrolyte, an electrolyte other than the above may be used, and for example, Li 3N, LiI, Li 3N _- LiI _- LiOH or the like may be used.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

<3-5. Shape and configuration of secondary battery>
The non-aqueous electrolyte secondary battery of the present invention composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte solution described above can have various shapes such as a cylindrical shape and a laminated type. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolytic solution and communicates with the positive electrode current collector and the outside. Connect between the positive electrode terminal and the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead or the like, and seal the battery case to complete a non-aqueous electrolyte secondary battery. ..

The secondary battery according to the embodiment of the present invention can suppress a decrease in tap density and can achieve both high thermal stability and excellent battery characteristics at a high level. Further, the positive electrode active material used in the above-mentioned secondary battery can be obtained by the above-mentioned industrial manufacturing method. The secondary battery according to the embodiment of the present invention is suitable for a power source of a small portable electronic device (such as a notebook personal computer or a mobile phone terminal) that always requires a high capacity. Further, the secondary battery according to the embodiment of the present invention has not only capacity and electron conductivity but also a comparison with a conventional battery using a positive electrode active material of a lithium cobalt-based oxide or a lithium nickel-based oxide. It has excellent durability and thermal stability during overcharging. Therefore, since it is possible to reduce the size and increase the capacity, it is suitable as a power source for electric vehicles whose mounting space is limited. The secondary battery according to the embodiment of the present invention is used not only as a power source for an electric vehicle driven by purely electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine. Can also be used.

Next, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described in detail with reference to Examples. .. The methods for analyzing the metal contained in the positive electrode active material and various evaluation methods for the positive electrode active material in Examples and Comparative Examples are as follows.

(A) Composition analysis: Measured by ICP emission spectrometry.
(B) Average particle size Mv and variation index [(D90-D10) / average volume particle size]:
This was performed by a laser diffraction / scattering type particle size distribution measuring device (Microtrac HRA manufactured by Nikkiso Co., Ltd.).
(C) Qualitative evaluation of crystal structure and lithium zirconium compound, and evaluation of Li seat occupancy: XRD diffractometer (X'Pert PRO manufactured by PANalytical Co., Ltd.). The Rietveld analysis of the XRD diffraction pattern using Cu-Kα rays was used to determine the Li seat occupancy of the 3a site.
(D) Zirconium concentration: The positive electrode active material was processed so that the cross-sectional analysis of the primary particles by S-TEM was possible. Arbitrarily 30 primary particles were selected from a plurality of secondary particles contained in the positive electrode active material, and the composition of 5 points at arbitrary points on each primary particle cross section was analyzed by S-TEM EDX. The zirconium concentration ratio (minimum zirconium concentration / average zirconium concentration) was calculated for each primary particle, and the average value of the zirconium concentration ratios of the obtained 30 primary particles was taken as the zirconium concentration ratio of the positive electrode active material.
(E) Initial charge capacity and initial discharge capacity:
The initial charge capacity and initial discharge capacity are set to 0.1 mA with respect to the positive electrode after the coin-type battery 1 shown in FIG. 5 is manufactured and left to stand for about 24 hours to stabilize the open circuit voltage OCV (open circuit voltage). The initial charge capacity was defined as the initial charge capacity when the battery was charged to a cutoff voltage of 4.3 V at / ^cm2 , and the capacity when the battery was discharged to a cutoff voltage of 3.0 V after 1 hour of rest was defined as the initial discharge capacity. A multi-channel voltage / current generator (R6741A, manufactured by Advantest Co., Ltd.) was used to measure the discharge capacity.
(F) Reaction resistance:
For the reaction resistance, the coin-type battery 1 whose temperature was adjusted to the measured temperature was charged with a charging potential of 4.1 V, and the resistance value was measured by the AC impedance method. For the measurement, a frequency response analyzer and a potential galvanostat (Solartron, 1255B) were used to create the Nyquist plot shown in FIG. 6, and the fitting calculation was performed using the equivalent circuit shown in FIG. The value of reaction resistance) was calculated.
(G) Thermal stability evaluation The thermal stability evaluation of the positive electrode was performed by quantifying the amount of oxygen released by heating the positive electrode active material in an overcharged state. A coin-type battery was produced in the same manner as in (E), and CCCV charging (constant current-constant voltage charging) was performed at a cutoff voltage of 4.5 V at a rate of 0.2 C. Then, the coin battery was disassembled, only the positive electrode was carefully taken out so as not to cause a short circuit, washed with DMC (dimethyl carbonate), and dried. Approximately 2 mg of the dried positive electrode was weighed, and the temperature was raised from room temperature to 450 ° C. at a heating rate of 10 ° C./min using a gas chromatograph mass spectrometer (GCMS, Shimadzu Corporation, QP-2010plus). Helium was used as the carrier gas. The generation behavior of oxygen (m / z = 32) generated during heating was measured, and the amount of oxygen generated was semi-quantified from the obtained maximum oxygen generation peak height and peak area, and these were used as evaluation indexes for thermal stability. .. The semi-quantitative value of oxygen evolution was calculated by injecting pure oxygen gas into GCMS as a standard sample and extrapolating the calibration curve obtained from the measurement results.

(Example 1)
<Crystalization process>
A predetermined amount of pure water was put into the reaction tank (60 L), and the temperature inside the tank was set to 49 ° C. with stirring. At this time, _N2 gas was flowed into the reaction vessel so that the dissolved oxygen concentration in the reaction vessel liquid was 0.8 mg / L. In this reaction vessel, a mixed aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate of 2.0 M and an alkaline solution of 25% by mass hydroxylation so that the molar ratio of nickel: cobalt: manganese is 80:10:10. A sodium solution and 25% by mass aqueous ammonia as a complexing agent were continuously added to the reaction vessel at the same time.

At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, the pH in the reaction vessel was adjusted to 12.0 to 12.6, and the ammonia concentration was adjusted to 10 to 14 g / L. After the reaction vessel became stable, the slurry containing the nickel-cobalt-manganese composite hydroxide was recovered from the overflow port and then filtered to obtain a nickel-cobalt-manganese composite hydroxide cake (crystallization step). Impurities were washed by passing 1 L of pure water through 140 g of the nickel-cobalt-manganese composite hydroxide in the filtered Denver. The powder after filtration was dried to obtain nickel-cobalt-manganese composite hydroxide particles represented by Ni _0.80 Co _0.10 Mn _0.10 (OH) _{2 + α} (0 ≦ α ≦ 0.4). The average particle size Mv of the obtained composite hydroxide was 12.6 μm.

<Zirconium mixing process>
The obtained nickel-cobalt-manganese composite hydroxide particles, lithium hydroxide, and zirconium oxide (ZrO ₂ ) having an average particle size of 1.0 μm were used, and the molar ratio of nickel: cobalt: manganese: zirconium was 79.4 :. Atomic ratio of lithium amount (Li) to total metal amount (Me) of nickel, cobalt, manganese and zirconium (hereinafter referred to as Li / Me) so as to be 10.0: 9.8: 0.8. ) Was 1.01, and then sufficiently mixed using a shaker mixer device (TURBULA TypeT2C manufactured by Willy et Bacoffen (WAB)) to obtain a lithium mixture.

<Baking process>
The obtained lithium mixture was held in an air (oxygen: 21% by volume) air stream at 800 ° C. for 10 hours and fired, and then crushed to obtain a positive electrode active material composed of a lithium nickel cobalt manganese zirconium composite oxide. rice field.

Table 1 shows the volume average particle size Mv, the variation index and the tap density of the obtained positive electrode active material. As a result of XRD measurement, no particular phase was confirmed. In addition, an increase in the lattice constants a and c of the lithium nickel-cobalt-manganese composite oxide was observed. From the Rietveld analysis of the XRD diffraction pattern, it was confirmed that the Li seat occupancy rate decreased. Furthermore, from the results of STEM-EDX analysis, it was confirmed that zirconium was uniformly dissolved in the crystal structure. These results are shown in Table 1.

(Evaluation of electrochemical characteristics)
The obtained positive electrode active material (52.5 mg), acetylene black (15 mg), and polytetrafluoroethylene resin (PTFE) (7.5 mg) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. Evaluation electrode) 2 was produced. The prepared positive electrode 2 was dried in a vacuum dryer at 120 ° C. for 12 hours, and then the 2032 type coin battery 1 was manufactured using the positive electrode 2 in a glove box having an Ar atmosphere in which the dew point was controlled to −80 ° C.

A lithium (Li) metal having a diameter of 17 mm and a thickness of 1 mm is used for the negative electrode 3, and an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte (DEC) is used as the electrolytic solution. Tomiyama Pure Chemical Industries, Ltd.) was used. A polyethylene porous membrane having a film thickness of 25 μm was used for the separator 4. Further, the coin battery has a gasket 5 and a wave washer 6, and the positive electrode can 7 and the negative electrode can 8 are assembled into a coin-shaped battery. Table 2 shows the measurement results of the initial charge / discharge capacity and the positive electrode resistance value of the obtained positive electrode active material.

(Evaluation of thermal stability)
The thermal stability was evaluated by the procedure described in the above-mentioned evaluation method (G) for the positive electrode active material. A semi-quantitative value of oxygen evolution was obtained from the obtained maximum oxygen evolution peak intensity and peak area. These results are shown in Table 2.

The judgment method of the electrochemical property evaluation and the thermal stability evaluation of the battery obtained above was judged by the following three-step evaluation (1, 2, 3).
(I) Battery characteristic determination initial charge capacity (mAh / g)
Greater than 3: 195.0, 2: 170.0 to 195.0, less than 1: 170.0 (The larger the number on the three-point scale, the higher the performance. The same shall apply hereinafter).
Initial discharge capacity (mAh / g)
Greater than 3: 160.0, 2: 150.0 to 160.0, less than 1: 150.0 Reaction resistance (Ω)
Less than 3: 3.0, 2: 3.0 to 4.0, greater than 1: 4.0 (II) Thermal stability determination Oxygen evolution (wt%)
Less than 3: 3.5, 2: 3.5 to 5.5, greater than 1: 5.5 (III) Comprehensive judgment Then, the total of each evaluation is quantified, and the numerical value is 12 for ◎, 11 for ○, 8 to 10 were determined as Δ, and 7 or less was determined as x. The results are shown in Table 3.

(Example 2)
The nickel-cobalt-manganese composite hydroxide particles obtained in the lithium mixing step, lithium hydroxide, and zirconium oxide (ZrO ₂ ) having an average particle size of 1.0 μm are mixed with a nickel: cobalt: manganese: zirconium molar ratio of 78. A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the particles were weighed so as to be 0: 9.8: 9.6: 2.6. As a result of XRD measurement, a peak attributed to Li ₆ Zr ₂ O ₇ was confirmed. The evaluation results are shown in Tables 1 to 3.

(Example 3)
<Crystalization process>
Nickel cobalt manganese composite hydroxide particles represented by Ni _0.80 Co _0.10 Mn _0.10 (OH) _{2 + α} (0 ≦ α ≦ 0.4) are obtained in the same manner as in the crystallization step of Example 1. Obtained.

<Zirconium coating process in the zirconium mixing process>
Next, zirconium sulfate (Zr (SO ₄ ) _{2.nH 2 O} ) powder was adjusted to a zirconium concentration of 100 g / L in an aqueous solution, the dissolution temperature was kept constant at 50 ° C., and the mixture was stirred for 2 hours. After dissolution, the residue was filtered off to prepare a zirconium salt solution. A zirconium salt solution and a 25 mass% sodium hydroxide aqueous solution were simultaneously added dropwise to a slurry obtained by mixing the nickel-cobalt-manganese composite hydroxide with pure water so that the pH became 11.0 while maintaining the liquid temperature at 25 ° C. A nickel-cobalt-manganese composite hydroxide coated with a zirconium compound was obtained. The target amount of zirconium added was 0.8 (molar ratio).

<Lithium mixing process and firing process in zirconium mixing process>
The atomic ratio (hereinafter referred to as Li / Me) of the obtained zirconium-coated nickel-cobalt-manganese composite hydroxide particles and the total amount of metal of lithium hydroxide and nickel, cobalt, manganese, and zirconium is 1.01. After weighing, the mixture was sufficiently mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)) to obtain a lithium mixture. The firing step and subsequent steps were the same as in Example 1, and the positive electrode active material was obtained and evaluated. The evaluation results are shown in Tables 1 to 3.

(Example 4)
Nickel cobalt manganese composite hydroxide particles represented by Ni _0.80 Co _0.10 Mn _0.10 (OH) _{2 + α} (0 ≦ α ≦ 0.4) are obtained in the same manner as in the crystallization step of Example 1. After that, in the zirconium coating step, a positive electrode active material was obtained and evaluated in the same manner as in Example 3 except that the target amount of zirconium added was 2.6 (molar ratio). The evaluation results are shown in Tables 1 to 3.

(Example 5)
The nickel-cobalt-manganese composite hydroxide particles obtained in the lithium mixing step, lithium hydroxide, and zirconium oxide (ZrO ₂ ) having an average particle size of 1.0 μm are mixed with a nickel: cobalt: manganese: zirconium molar ratio of 76. The positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that it was weighed so as to be 6: 9.7: 9.5: 4.2. The evaluation results are shown in Tables 1 to 3.

(Comparative Example 1)
In the lithium mixing step, the positive electrode activity is the same as in Example 1 except that zirconium oxide is not prepared (the obtained nickel-cobalt-manganese composite hydroxide particles and lithium hydroxide are weighed so that Li / Me is 1.01). The substance was obtained and evaluated. The evaluation results are shown in Tables 1 to 3.

(Comparative Example 2)
The nickel-cobalt-manganese composite hydroxide particles obtained in the lithium mixing step, lithium hydroxide, and zirconium oxide (ZrO ₂ ) having an average particle size of 1.0 μm are mixed with a nickel: cobalt: manganese: zirconium molar ratio of 74. A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that it was weighed so as to be 5: 9.4: 9.1: 7.0. The evaluation results are shown in Tables 1 to 3.

(Comparative Example 3)
In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the lithium mixture was held and fired at 1020 ° C. for 10 hours in an air (oxygen: 21% by volume) air stream. The evaluation results are shown in Tables 1 to 3.

(Comparative Example 4)
In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the lithium mixture was held and fired at 700 ° C. for 10 hours in an air (oxygen: 21% by volume) air stream. The evaluation results are shown in Tables 1 to 3.

(Comparative Example 5)
In the crystallization step, the positive electrode active material was obtained and evaluated in the same manner as in Example 2 except that the crystallization method by the batch method was used. The evaluation results are shown in Tables 1 to 3.

As shown in Tables 1 and 2, the positive electrode active material obtained in Examples has extremely good thermal stability and excellent reaction resistance as compared with Comparative Example 1 to which zirconium is not added. .. In all of the positive electrode active materials obtained in the examples, zirconium is dissolved in the primary particles and the Li seat occupancy is lower than that in the case where zirconium is not added. Further, in all the examples, the decrease in tap density was suppressed and the value was high.

Further, as shown in Table 3, in all the examples, the overall judgment was ◯ or ⊚, and high thermal stability and excellent battery characteristics could be achieved at a high level. On the other hand, in the comparative example, the overall judgment was Δ or ×, and it was not possible to achieve both thermal stability and battery characteristics at a high level.

It is presumed that the solid solution of zirconium in the Li seat makes it difficult for the crystal structure to collapse even in an overcharged state, and exhibits high thermal stability. It is also considered that the solid-dissolved zirconium facilitates the movement of Li ions in the crystal and reduces the reaction resistance. Further, the method of adding Zr may be either solid phase addition or coating, and in the case of coating, the effect of improving thermal stability and the effect of reducing resistance are slightly higher than those of solid phase addition. From the viewpoint of productivity and the like, industrially, solid phase addition is superior.

On the other hand, the positive electrode active material of Comparative Example 1 is inferior in both thermal stability and reaction resistance because Zr is not added. In Comparative Example 2, since the amount of Zr added is large, the thermal stability is extremely good, but a large amount of Zr compound is precipitated due to excessive Zr addition, and the reaction resistance and the initial capacity are significantly deteriorated. The reduction in the amount of Ni that contributes to the redox also affects the capacity reduction, and it is presumed that the thermal stability is apparently improved due to the low electrochemical characteristics.

In Comparative Example 3, the crystal growth did not proceed sufficiently because the firing temperature was low, Zr remained alone and hardly solid-solved in the crystal structure, and the concentration difference between the particle surface and the central portion was large. Further, although the Li seat occupancy rate is high, it is presumed that this is also because the firing temperature is low and the solid solution of Zr is insufficient. Furthermore, since the crystal growth does not proceed sufficiently, the reaction resistance and the initial capacitance are low. In Comparative Example 4, since the firing temperature is high, the variation index of the particle size increases due to the progress of sintering and aggregation, and the initial capacity is low due to the occurrence of cation mixing. It is presumed that the thermal stability was apparently improved as in Comparative Example 2 due to the low capacity.

In Comparative Example 5, the variation index and the tap density of the active material are low because the composite hydroxide particles are obtained by the batch crystallization method. Similar to the examples, it exhibits high thermal stability and excellent battery characteristics, but it is considered that the low tap density causes deterioration of the filling property when the secondary battery is used, which causes a decrease in the volumetric energy density.

Based on the above, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery according to an embodiment of the present invention suppress a decrease in tap density. It is possible to provide a positive electrode active material capable of obtaining a non-aqueous electrolyte secondary battery having both high thermal stability and excellent battery characteristics at a high level. Further, according to the present invention, such a positive electrode active material can be easily produced in industrial scale production, and it can be said that the industrial value is extremely large.

In the present embodiment, a positive electrode active material for a non-aqueous electrolyte secondary battery that achieves both high thermal stability and excellent battery characteristics at a high level can be obtained by an industrial manufacturing method. This non-aqueous electrolyte secondary battery is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that are always required to have high capacity and long life.

Further, the secondary battery according to the embodiment of the present invention is excellent in safety even in comparison with a conventional battery using a positive electrode active material of lithium cobalt oxide or lithium nickel oxide, and further. Excellent in capacity and durability. Therefore, since it is possible to reduce the size and extend the service life, it is suitable as a power source for electric vehicles whose mounting space is limited.

Further, the positive electrode active material and the secondary battery using the positive electrode active material according to the embodiment of the present invention are used not only as a power source for an electric vehicle driven by purely electric energy but also as a combustion engine such as a gasoline engine or a diesel engine. It can also be used as a power source for so-called hybrid vehicles and as a stationary storage battery.

Although each embodiment and each embodiment of the present invention have been described in detail as described above, those skilled in the art will be able to make many modifications that do not substantially deviate from the new matters and effects of the present invention. , Will be easy to understand. Therefore, all such modifications are included in the scope of the present invention.

For example, in a specification or drawing, a term described at least once with a different term having a broader meaning or a synonym may be replaced with the different term in any part of the specification or the drawing. Further, the configuration and operation of the method for producing the positive electrode active material for the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery and the positive electrode active material for the non-aqueous electrolyte secondary battery are also described in each embodiment and each embodiment of the present invention. It is not limited to the one, and various modifications can be carried out.

S10 crystallization process, S20 zirconium mixing process, S21 slurry process, S22 zirconium coating process, S23 lithium mixing process, S24 heat treatment process, S30 firing process 1 coin-type battery, 2 positive electrode (evaluation electrode), 3 negative electrode (lithium metal) 4, Separator, 5 Gasket, 6 Wave washer, 7 Positive electrode can, 8 Negative electrode can

Claims (10)

A lithium nickel-nickel-manganese composite oxide composed of secondary particles containing lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and optionally the element M, in which a plurality of primary particles are aggregated. It is a positive electrode active material for non-aqueous electrolyte secondary batteries that contains it.
In the lithium nickel-manganese composite oxide, the substance amount ratio (molar ratio) of each element is Li: Ni: Mn: M: Zr = d: (1-a-bc): a: b: c [formula]. Among them, a is 0.05 ≦ a ≦ 0.60, b is 0 ≦ b ≦ 0.60, c is 0.0003 ≦ c ≦ 0.06, and d is 0.95 ≦ d ≦ 1.20, (1). -A-bc) satisfies 0.30 ≤ (1-a-bc) ≤ 0.95, and M is Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb. And at least one element selected from Ta] (however, the composition is Li _x (Ny Co _{2 (1-y) / 5 Mn} ( _{3-w) (1-y) / 5} ) _{1- z} Zr _z O ₂ (excluding those represented by 1.00 ≦ x ≦ 1.10, 0.65 <y <0.82, 0 ≦ z ≦ 0.05, 0 ≦ w ≦ 0.01) ,
At least a part of zirconium in the lithium nickel-manganese composite oxide is dissolved in the primary particles, and D90 and D10 in the particle size distribution of the secondary particles by the laser diffraction scattering method, and the volume average particle size (Mv). [(D90-D10) / Mv], which indicates the particle size variation index calculated by, is 0.80 or more and 1.20 or less, and the Li seat occupancy rate by the Rietbelt analysis is 94% or more and 97% or less. A positive electrode active material for a non-aqueous electrolyte secondary battery, which is characterized by being in the range of. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the minimum zirconium concentration in the primary particles is 50% or more with respect to the average zirconium concentration in the primary particles. The non-aqueous electrolyte according to claim 1, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery contains a compound containing lithium and zirconium in the positive electrode active material for the non-aqueous electrolyte secondary battery. Positive active material for secondary batteries. The third aspect of claim 3, wherein the compound containing lithium and zirconium is at least one compound selected from Li ₂ ZrO ₃ , Li ₆ Zr ₂ O ₇ , Li ₄ ZrO ₄ , and Li ₈ ZrO ₆ . Non-aqueous electrolyte Positive active material for secondary batteries. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the positive electrode active material for the non-aqueous electrolyte secondary battery is used for the positive electrode. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium nickel-manganese composite oxide.
A crystallization step for crystallization of nickel-manganese composite hydroxide particles by a continuous crystallization method,
At least, a zirconium mixing step of making a mixture containing nickel-manganese composite hydroxide particles, a zirconium compound, and a lithium compound.
It has a firing step of calcining the mixture to obtain the lithium nickel-manganese composite oxide.
The nickel-manganese composite hydroxide particles added in the zirconium mixing step have a general formula (2): Ni _1-ab Mn _a M _b (OH) _{2 + α} (in the formula (2), M is Co. , W, Mo, V, Mg, Ca, Al, Ti, Cr, Nb and Ta, which are at least one element, 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0.60, It is represented by 0.30 ≦ (1-ab) ≦ 0.95, 0 ≦ α ≦ 0.4).
The firing step is performed at 750 ° C. or higher and 1000 ° C. or lower in an oxidizing atmosphere.
In the lithium nickel-manganese composite oxide obtained in the firing step, the substance amount ratio (molar ratio) of each element is Li: Ni: Mn: M: Zr = d :( 1-a-bc) :. a: b: c [in the formula, a is 0.05 ≦ a ≦ 0.60, b is 0 ≦ b ≦ 0.60, c is 0.0003 ≦ c ≦ 0.06, and d is 0.95 ≦ d. ≤ 1.20, (1-a-bc) satisfies 0.30 ≤ (1-a-bc) ≤ 0.95, and M is Co, W, Mo, V, Mg, Ca, It is represented by [at least one element selected from Al, Ti, Cr, Nb and Ta] (provided that the composition is Li _x (Ny Co 2 (1- _{y ) / 5} Mn _{(3-w) (1-w)). y) / 5} ) _1-z Zr _z O ₂ (1.00 ≦ x ≦ 1.10, 0.65 <y <0.82, 0 ≦ z ≦ 0.05, 0 ≦ w ≦ 0.01 A positive electrode for a non-aqueous electrolyte secondary battery, which is composed of secondary particles in which a plurality of primary particles are aggregated, and at least a part of zirconium is solidly dissolved in the primary particles. Manufacturing method of active material. In the zirconium mixing step, a mixture of the lithium compound and the zirconium compound having an average particle size of 0.01 μm or more and 10 μm or less is mixed with the nickel-manganese composite hydroxide particles obtained in the crystallization step to form a zirconium mixture. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the present invention is obtained. In the zirconium mixing step, there is a heat treatment step of further heat-treating the nickel-manganese composite hydroxide particles.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6 or 7, wherein the heat treatment step is performed at a temperature of 105 ° C. or higher and 700 ° C. or lower. The zirconium mixing step further includes a slurry step of mixing the nickel-manganese composite hydroxide particles obtained in the crystallization step with water to obtain a slurry, and the slurry with a zirconium salt solution and, if necessary, an alkali. The nickel-manganese composite hydroxide particles are coated with a zirconium compound to obtain zirconium-coated nickel-manganese composite hydroxide particles, and the zirconium-coated nickel-manganese composite obtained in the zirconium-coating step. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, further comprising a lithium mixing step of mixing the hydroxide particles and the lithium compound. The zirconium mixing step further includes a heat treatment step of heat-treating the zirconium-coated nickel-manganese composite hydroxide particles.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 9, wherein the heat treatment step is performed at a temperature of 105 ° C. or higher and 700 ° C. or lower.

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