WO2015076323A1 - Positive electrode active material for nonaqueous electrolyte secondary batteries, method for producing same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

Provided are: a positive electrode active material for nonaqueous electrolyte secondary batteries, which has a good balance between thermal stability and charge/discharge capacity at high levels, while having excellent cycle characteristics; a simple and safe production method for this positive electrode active material for nonaqueous electrolyte secondary batteries; and a nonaqueous electrolyte secondary battery which uses this positive electrode active material. A method for producing a positive electrode active material for nonaqueous electrolyte secondary batteries, which is characterized by comprising: a crystallization step for obtaining a nickel-containing hydroxide represented by general formula Ni_1-a'-b'Co_a'M_b'(OH)₂ by adding, for crystallization, an aqueous alkaline solution to a mixed aqueous solution containing at least nickel and cobalt; a mixing step for obtaining a lithium mixture by mixing the thus-obtained nickel-containing hydroxide with a lithium compound and a niobium compound; and a firing step for obtaining a lithium-transition metal composite oxide by firing the lithium mixture in an oxidizing atmosphere at 700-840°C.

Description

Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery

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

In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, development of a small and lightweight non-aqueous electrolyte secondary battery with high energy density is strongly desired. As such a secondary battery, there is a lithium ion secondary battery. Lithium metal, a lithium alloy, a metal oxide, carbon or the like is used as a negative electrode material of a lithium ion secondary battery. These materials are materials capable of releasing and inserting lithium.

The research and development of such lithium ion secondary batteries is currently being actively conducted. Among them, a lithium ion secondary battery using a lithium transition metal complex oxide, particularly a lithium cobalt complex oxide (LiCoO ₂ ) relatively easy to synthesize, as a positive electrode material can obtain a high voltage of 4V grade, so it is high. It is expected and put to practical use as a battery having an energy density. In the lithium ion secondary battery using this lithium cobalt composite oxide (LiCoO ₂ ), many developments have been conducted to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.

However, since lithium cobalt compound oxide (LiCoO ₂ ) uses a rare and expensive cobalt compound as a raw material, it causes an increase in cost of the battery. Therefore, it is desirable to use materials other than lithium cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material.

Also, recently, not only small secondary batteries for portable electronic devices, but also expectations for using lithium ion secondary batteries as large secondary batteries for power storage, electric vehicles, etc. are increasing. . Therefore, reducing the cost of the active material and making it possible to manufacture a cheaper lithium ion secondary battery is expected to have a large ripple effect in a wide range of fields, and a positive electrode active material for lithium ion secondary batteries As lithium transition metal complex oxide newly proposed as lithium manganese complex oxide (LiMn ₂ O ₄ ) using manganese which is cheaper than cobalt, lithium nickel complex oxide (LiNiO ₂ ) using nickel Can be mentioned.

Lithium manganese complex oxide (LiMn ₂ O ₄ ) is a promising alternative to lithium cobalt complex oxide (LiCoO ₂ ) because it is inexpensive and has excellent thermal stability, particularly safety with regard to ignition etc. However, since the theoretical capacity is only about half that of lithium cobalt composite oxide (LiCoO ₂ ), it has a drawback that it is difficult to meet the demand for higher capacity of lithium ion secondary batteries, which is increasing year by year. In addition, at 45 ° C. or higher, self-discharge is severe, and the charge and discharge life is also reduced.

On the other hand, lithium nickel composite oxide (LiNiO ₂ ) has almost the same theoretical capacity as lithium cobalt composite oxide (LiCoO ₂ ), and exhibits a battery voltage slightly lower than that of lithium cobalt composite oxide. For this reason, since the decomposition | disassembly by oxidation of electrolyte solution does not become a problem easily, and a high capacity | capacitance can be anticipated, development is performed actively. However, when a lithium-ion secondary battery is manufactured using a lithium-nickel composite oxide consisting purely of nickel only as a positive electrode active material without replacing nickel with another element, the cycle is compared to a lithium-cobalt composite oxide. Poor in characteristics. In addition, it also has the disadvantage that it is relatively easy to impair battery performance when used or stored in a high temperature environment. Furthermore, when left in a fully charged state in a high temperature environment, it has the disadvantage of releasing oxygen from a lower temperature than cobalt-based composite oxides.

In order to solve such a drawback, it has been considered to add niobium, which is an element having a higher number of elements than nickel, to a lithium-nickel composite oxide. For example, Patent Document 1, for the purpose of improving the thermal stability at the time of an internal short circuit of the positive electrode active _{material, Li a Ni 1-x-} y-z Co x M y Nb z O b ( However, M is Mn At least one element consisting of Fe and Al, 1.0 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.05 And b) a particle having a composition composed of at least two or more kinds of compounds consisting of lithium, nickel, cobalt, element M, niobium and oxygen shown by 2 ≦ b ≦ 2.2), and the particles have a substantially spherical shape And has a substantially spherical shell layer containing at least one compound having a niobium concentration higher than the above composition in the vicinity of or inside the surface, and the positive electrode potential is in the range of 2 V to 1.5 V at the time of the first discharge. discharge capacity of mAh / g], and its layer in X-ray diffraction A lithium transition metal complex oxide in which α and β satisfy the conditions of 80 ≦ α ≦ 150 and 0.15 ≦ β ≦ 0.20 at the same time, where the half value width of (003) plane of crystal structure is β [deg]. Has been proposed.

Further, in Patent Document 2, Li _{1 + z} Ni _1-x-y Co _x Nb _y O ₂ (0.10 ≦ x ≦) for the purpose of improving the thermal stability of the positive electrode active material and enhancing the charge and discharge capacity. 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10), and in the measurement by the energy dispersive method, the peak intensity of the Nb L line is I _Nb , Ni L Lithium transition metal complex oxide is proposed in which the standard deviation of the intensity ratio I _Nb / I _Ni is within 1/2 of the average value of the intensity ratio I _Nb / I _Ni when the peak intensity of the line is I _Ni . .

Further, in Patent Document 3, for the purpose of obtaining a positive electrode active material having a large capacity and having improved thermal stability at the time of charging, the composition formula Li _x Ni _a Mn _b Co _c M 1 _d M 2 _e O ₂ (Wherein, M 1 is at least one element selected from the group consisting of Al, Ti and Mg, and M 2 is at least one element selected from the group consisting of Mo, W and Nb, 0.2 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.8, 0.05 ≦ b ≦ 0.3, 0.05 ≦ c ≦ 0.3, 0.02 ≦ d ≦ 0.04 The lithium transition metal complex oxide represented by 0.02 <= e <= 0.06, and a + b + c + d + e = 1.0 is proposed.

In Patent Document 4, Li _x Ni _(1-y-z-a) Co _y is used to achieve both the charge-discharge capacity characteristics and the safety of the lithium ion secondary battery and to suppress the deterioration of the cycle characteristics. Mn _z M _a O ₂ (M is at least one element selected from the group consisting of Fe, V, Cr, Ti, Mg, Al, Ca, Nb and Zr, and x, y and z are each 1 A on the surface of a lithium composite oxide represented by: 0 ≦ x ≦ 1.10, 0.4 ≦ y + z ≦ 0.7, 0.2 ≦ z ≦ 0.5, and 0 ≦ a ≦ 0.02) Lithium transition metal complex oxide is proposed having a structure coated with a substance (A is a compound consisting of at least one element selected from the group consisting of Ti, Sn, Mg, Zr, Al, Nb and Zn) ing.

Furthermore, in Patent Document 5, Li _{1 + z} Ni _1-x-y Co _x M _y O ₂ (in the formula, x, y) for the purpose of obtaining a positive electrode active material having excellent thermal stability and high charge / discharge capacity. , Z satisfies the requirements of 0.10 x x 0.2 0.21, 0.015 y y-0.08, -0.05 0.10 z 0.10 0.10, and M has an affinity for oxygen better than nickel Lithium transition metal complex oxide in which two kinds of M are impregnated or attached, which are represented by at least two kinds of elements selected from Al, Mn, Nb or Mo and whose average valence is more than 3 is proposed. It is done.

Recently, the demand for higher capacity for small secondary batteries such as portable electronic devices is increasing year by year. In addition, a movement to use a lithium ion secondary battery for a large secondary battery is also active, and among them, a power source for hybrid vehicles and electric vehicles, or a stationary storage battery for power storage is highly expected. Furthermore, these batteries are also required to have a long life, and it is important to have excellent cycle characteristics. In such applications, the positive electrode active material is required to have high charge and discharge capacity, and further improvement in thermal stability and cycle characteristics.

Japanese Patent Application Laid-Open No. 2002-151071 JP 2006-147500 A JP 2012-014887 A JP, 2008-153017, A JP, 2008-181839, A

The proposals disclosed in the above Patent Documents 1 to 5 are all aimed at achieving both the good thermal stability of the positive electrode active material and the high charge / discharge capacity. However, when the addition amount of niobium in the lithium transition metal complex oxide is small, although the charge / discharge capacity is large, sufficient thermal stability can not be obtained, and when the addition amount of niobium is large, the thermal stability is good. However, there is a problem that sufficient charge and discharge capacity can not be secured, and coexistence with good thermal stability and high charge and discharge capacity in a further higher dimension is required.

SUMMARY OF THE INVENTION In view of the above problems, the present invention achieves good thermal stability and high charge and discharge capacity in a high level, and further provides a positive electrode active material for a non-aqueous electrolyte secondary battery excellent in cycle characteristics and industrial production thereof. It is an object of the present invention to provide a simple and safe manufacturing method suitable for the above, and a non-aqueous electrolyte secondary battery using the same.

The inventors of the present invention conducted intensive studies on the method of adding niobium to the lithium transition metal complex oxide in order to achieve both good thermal stability and high charge and discharge capacity, and found that nickel-containing water having a specific composition. The positive electrode active material obtained by the manufacturing method in which an oxide, a lithium compound and a niobium compound having a specific particle diameter are mixed and fired can be uniformly added with niobium, and the thermal stability is good and high. It discovered that it became a positive electrode active material which has discharge capacity and cycle characteristics improved, and completed the present invention.

That is, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention can be performed according to the general formula Li _d Ni _{1 -a-b-c} Co _a M _b Nb _c O ₂ (however, 0.03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05, 0.95 ≦ d ≦ 1.20, M is at least one selected from Mn, V, Mg, Ti and Al And a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide composed of particles of a polycrystalline structure, the mixed aqueous solution containing at least nickel and cobalt. An alkaline aqueous solution is added to cause crystallization, and the general formula Ni _{1-a'-b '} Co _a' M _{b '} (OH) ₂ (0.03 a a' 0.35 0.35, 0 b b '0.10 0.10) M is represented by at least one element selected from Mn, V, Mg, Ti and Al) Crystallization process for obtaining a nickel-containing hydroxide, mixing process for obtaining a lithium mixture by mixing the obtained nickel-containing hydroxide, lithium compound and niobium compound having an average particle diameter of 0.1 to 10 μm, and the lithium mixture Are fired at 700 to 840 ° C. in an oxidizing atmosphere to obtain a lithium transition metal composite oxide.

In the crystallization step, an aqueous alkaline solution is added to the mixed aqueous solution containing at least nickel and cobalt to crystallize, and then the obtained crystallized product can be coated with M to obtain the nickel-containing hydroxide. .

The niobium compound is preferably niobic acid or niobium oxide.

Further, before the mixing step, the method includes a heat treatment step of heat treating the nickel-containing hydroxide at a temperature of 105 to 800 ° C., and in the mixing step, nickel-containing hydroxide and / or nickel obtained by the heat treatment. A lithium mixture can be obtained by mixing the contained oxide, the lithium compound, and the niobium compound.

Moreover, it is preferable that the said lithium compound is lithium hydroxide, and it is more preferable that the said lithium hydroxide is anhydrous lithium hydroxide with a moisture content of 5 mass% or less.

Moreover, it is preferable to dry the lithium mixture obtained by the said mixing process before the said baking process, and to include the drying process of making the lithium hydroxide in a lithium mixture into anhydrous lithium hydroxide with a moisture content of 5 mass% or less.

Furthermore, it is preferable to include a water washing step of slurrying the lithium transition metal complex oxide at a ratio of 100 to 2000 g / L to 1 L of water after the baking step to wash with water.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a general formula Li _d Ni ₁ -ab _c Co _a M _b Nb _c O ₂ (where 0.03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05, 0.95 ≦ d ≦ 1.20, M is at least one element selected from Mn, V, Mg, Ti and Al) A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide composed of particles of a polycrystalline structure, wherein the specific surface area of the positive electrode active material is 0.9 to 3.0 m ² / g, and the content of alkali metals other than lithium is 20 mass ppm or less.

The crystallite diameter of the positive electrode active material is preferably 10 to 180 nm.

In the particles of the positive electrode active material, the maximum diameter of the niobium compound observed by EDX measurement with a transmission electron microscope is preferably 200 nm or less.

The sulfate group content of the positive electrode active material is preferably 0.2% by mass or less, and the positive electrode active material preferably has a porous structure.

Furthermore, the non-aqueous electrolyte secondary battery according to the present invention uses the above-mentioned positive electrode active material for non-aqueous electrolyte secondary battery as a positive electrode.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention achieves high thermal stability and high charge / discharge capacity in a high level, and further provides a positive electrode for a non-aqueous electrolyte secondary battery having excellent cycle characteristics. An active material can be obtained. Furthermore, the production method of the present invention is simple and safe, is suitable for production on an industrial scale, and is extremely useful industrially also in terms of cost. Further, by using the obtained positive electrode active material, it is possible to obtain a non-aqueous electrolyte secondary battery with high safety, high battery capacity and high lifetime.

FIG. 1 is a cross-sectional view of a coin battery used for battery evaluation.

1. Method of producing positive electrode active material for non-aqueous electrolyte secondary battery According to the method of producing a positive electrode active material for non-aqueous electrolyte secondary battery of the present embodiment, (A) aqueous alkali solution is added to mixed aqueous solution containing at least nickel and cobalt to crystallize Crystallization step to obtain nickel-containing hydroxide, (C) mixing nickel-containing hydroxide, lithium compound, and niobium compound having an average particle diameter of 0.1 to 10 μm to obtain lithium mixture The method further comprises the step of mixing, (D) calcining the lithium mixture at 700 to 840 ° C. in an oxidizing atmosphere to obtain a lithium transition metal composite oxide.
Further, after the firing step (D), the step of (E) lithium transition metal complex oxide may be made into a slurry at a ratio of 100 to 2000 g / L per 1 L of water, and the step of washing with water may be included.
In addition, before the mixing step (C), the nickel-containing hydroxide may be heat-treated at a temperature of 105 to 800 ° C. to include a heat treatment step (B).
The details of each manufacturing process will be described below.

(A) Crystallization Step The nickel-containing hydroxide obtained in this step has a general formula Ni _{1-a′-b ′} Co _{a ′} M _{b ′} (OH) ₂ (however, 0.03 ≦ a ′ ≦ 0. 35, 0 ≦ b ′ ≦ 0.10, M represents at least one element selected from Mn, V, Mg, Ti and Al). The content of cobalt a ′ is 0.03 ≦ a ′ ≦ 0.35, preferably 0.05 ≦ a ′ ≦ 0.35, and more preferably 0.07 ≦ a ′ ≦ 0.20. is there. Further, b ′ indicating the content of the element M is 0 ≦ b ′ ≦ 0.10, preferably 0.01 ≦ b ′ ≦ 0.07. The nickel-containing hydroxide is preferably composed of secondary particles composed of primary particles.

The nickel-containing hydroxide is obtained by adding an alkaline aqueous solution to a mixed aqueous solution containing at least nickel (Ni) and cobalt (Co) to crystallize. The production method is not particularly limited as long as it is a method by which the nickel-containing hydroxide represented by the above general formula can be obtained. For example, it can be produced by the following method.

First, an alkaline aqueous solution is added to a mixed aqueous solution containing at least nickel and cobalt in the reaction vessel to obtain a reaction aqueous solution. Next, the reaction aqueous solution is stirred at a constant speed to control the pH to coprecipitate and crystallize the nickel-containing hydroxide in the reaction vessel.

As the mixed aqueous solution containing at least nickel and cobalt, a sulfate solution of nickel and cobalt, a nitrate solution, and a chloride solution can be used. Further, since the composition ratio of the metal element contained in the mixed aqueous solution and the composition ratio of the metal element contained in the obtained nickel-containing hydroxide coincide with each other, the composition ratio of the metal element in the mixed aqueous solution is the target nickel-containing water It can be prepared to have the same composition ratio as the metal element of the oxide.

The aqueous alkali solution is not particularly limited, and, for example, sodium hydroxide, potassium hydroxide and the like can be used.

Further, a complexing agent may be added to the mixed aqueous solution in combination with the alkaline aqueous solution.
The complexing agent is not particularly limited, and any complexing agent that can form a complex by combining with nickel ion or cobalt ion in an aqueous solution can be used. As the complexing agent, for example, an ammonium ion donor can be used. Specifically as an ammonium ion donor, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride etc. are mentioned.

When a complexing agent is not used, the temperature of the reaction aqueous solution is preferably in the range of 60 ° C. to 80 ° C. or less, and in the above temperature range, the pH of the reaction aqueous solution is 10 to 11 (based on 25 ° C.) It is preferable to do.

In the above temperature range, if the pH of the reaction aqueous solution exceeds 11, the nickel-containing hydroxide may become fine particles during crystallization, the filterability may be deteriorated, and spherical particles may not be obtained. On the other hand, if the pH of the reaction aqueous solution is less than 10, the formation rate of the nickel-containing hydroxide becomes extremely slow, Ni remains in the filtrate, and the precipitation amount of Ni deviates from the target composition and the nickel-containing water of the target ratio In some cases, oxides can not be obtained.

When the temperature of the reaction aqueous solution is in the above range, the solubility of nickel is increased, and the precipitation amount of nickel deviates from the target composition, and the phenomenon in which coprecipitation does not occur can be avoided. On the other hand, when the temperature of the reaction aqueous solution exceeds 80 ° C., the amount of evaporation of water increases, the slurry concentration increases, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate and the impurity concentration For example, there is a possibility that the charge and discharge capacity of the positive electrode material may be reduced.

On the other hand, when using an ammonium ion donor such as ammonia as the complexing agent, the pH of the reaction aqueous solution is preferably 10 to 12.5, and the temperature is 50 to 80 ° C., because the solubility of Ni increases. Is preferred.

The ammonia concentration in the reaction aqueous solution is preferably kept at a constant value within the range of 3 to 25 g / L. When the ammonia concentration is less than 3 g / L, the solubility of metal ions can not be kept constant, so that plate-like primary hydroxide particles having a uniform shape and particle size can not be formed, and gel-like nuclei are formed. Since it is easy to form, the particle size distribution also spreads easily. On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of metal ions becomes too large, the amount of metal ions remaining in the reaction aqueous solution increases, and the composition tends to shift. In addition, when the concentration of ammonia fluctuates, the solubility of metal ions fluctuates, and uniform hydroxide particles are not formed, so it is preferable to keep the value constant. For example, it is preferable to maintain the ammonia concentration at a desired concentration with the width between the upper limit and the lower limit being about 5 g / L.

Then, after the inside of the reaction layer is in a steady state, the precipitate is collected, filtered and washed with water to obtain a nickel-containing hydroxide. Alternatively, a mixed aqueous solution, an aqueous alkaline solution, and optionally an aqueous solution containing an ammonium ion supplier may be continuously supplied to cause the reactor to overflow and the precipitate is collected, filtered and washed with water to obtain a nickel-containing hydroxide. You can also.
The nickel-containing hydroxide after crystallization is preferably sufficiently washed with water in order to reduce the residual amount of impurities, particularly alkali metals such as sodium.

At least one additive element (hereinafter, also referred to as “additive element M”) selected from M = Mn, V, Mg, Ti and Al can be optionally blended with the nickel-containing hydroxide. The additive element M can improve the thermal stability, the storage characteristics, and the battery characteristics.

The method of blending the additive element M is not particularly limited, and various conventionally known methods can be used. For example, an aqueous solution containing the additional element M is added to a mixed aqueous solution containing nickel and cobalt, and coprecipitation can be performed to obtain a nickel-containing hydroxide (including the additional element M). This method can increase the productivity of the crystallization process.

As an aqueous solution containing the additional element M, for example, an aqueous solution containing aluminum sulfate, sodium aluminate, titanium sulfate, ammonium peroxotitanate, titanium potassium oxalate, manganese sulfate, magnesium sulfate, magnesium chloride, vanadium sulfate, ammonium vanadate and the like Can be used.

In addition, in order to optimize the crystallization conditions and facilitate control of the composition ratio, after adding an alkaline aqueous solution to a mixed aqueous solution containing nickel and cobalt for crystallization, the surface of the obtained crystallized material is added as an additive element M may be coated.

The coating method of the additive element M is not particularly limited, and a known method can be used, for example, 1) adding an alkaline aqueous solution to a mixed aqueous solution containing nickel and cobalt (except for the additive element M) A method of coating the additive element M on the crystallized nickel-containing hydroxide, or 2) preparing a mixed aqueous solution containing nickel, cobalt and part of the additive element M, the nickel-containing hydroxide (additive element M And co-precipitate the co-precipitate with the additional element M to adjust the content of M.

Hereinafter, an example of a method for coating the nickel-containing hydroxide with the additive element M will be described.
The nickel-containing hydroxide is dispersed in pure water to form a slurry. A solution containing M at the target coverage amount is mixed with this slurry, and an acid is dropped and adjusted so as to obtain a predetermined pH. At this time, sulfuric acid, hydrochloric acid, nitric acid or the like may be used as the acid. After mixing for a predetermined time, filtration and drying are performed to obtain a nickel-containing hydroxide coated with M. As another method of coating M, a solution containing the compound of M may be spray-dried or impregnated.
In the present embodiment, niobium coating is not performed because solid phase addition of the niobium compound is performed in the mixing step.

(B) Heat Treatment Step Although the nickel-containing hydroxide obtained in the crystallization step can be used as it is in the mixing step, it includes a heat treatment step of heat-treating the obtained nickel-containing hydroxide before the mixing step. be able to. By the heat treatment, the water contained in the nickel-containing hydroxide is removed, and the water remaining in the nickel-containing hydroxide in the lithium mixture is sufficiently reduced during the firing step described later. Thereby, it is possible to prevent variation in the ratio (Li / Me) of the number of atoms (Me) of metals other than lithium in the lithium transition metal complex oxide obtained by firing and the number of atoms of lithium (Li). Further, a compound containing the element M may be added in this heat treatment step.

The heat treatment may be heated to a temperature at which residual water in the nickel-containing hydroxide is removed, and is preferably 105 to 800.degree. For example, the residual moisture can be removed by heating the nickel-containing hydroxide to 105 ° C. or higher. If the temperature is lower than 105 ° C., it takes a long time to remove the residual water, and therefore, it is not industrially suitable. If the temperature is higher than 800 ° C., the particles converted to the composite oxide may be sintered and agglomerated. When converting a nickel-containing hydroxide to a nickel-containing oxide, heating at a temperature of 350 to 800 ° C. is preferable.

In order to further reduce the variation of Li / Me, the composite hydroxide in the nickel-containing hydroxide can be converted to a composite oxide to form a nickel-containing oxide. In addition, it is not necessary to convert all the nickel-containing hydroxides to the nickel-containing oxides because it is sufficient if the water can be removed to such an extent that no variation occurs in Li / Me of the positive electrode active material.

The atmosphere in which the heat treatment is performed is not particularly limited, and the heat treatment is preferably performed in an air stream that can be easily performed. The heat treatment time is not particularly limited, but residual water in the composite hydroxide may not be sufficiently removed in less than 1 hour, so at least 1 hour or more is preferable, and 5 to 15 hours is more preferable. The equipment used for the heat treatment is not particularly limited as long as it can heat the composite hydroxide in an air stream, and a blower drier and an electric furnace without gas generation can be suitably used.

(C) Mixing Step The mixing step is a step of mixing the nickel-containing hydroxide, niobium compound and lithium compound obtained in the crystallization step to obtain a lithium mixture. When heat treatment is performed after the crystallization step, the nickel-containing oxide and / or hydroxide after heat treatment, the niobium compound, and the lithium compound are mixed to obtain a lithium mixture.

The present embodiment is characterized in that in the mixing step, a niobium compound having a specific particle diameter is added in a solid phase and mixed with a nickel-containing hydroxide and a lithium compound. Conventionally, as a method of blending niobium into an active material, generally, niobium is added to a nickel-containing hydroxide by a coating method such as wet coprecipitation / coating or spray drying, and then mixed with a lithium compound and fired Methods have been used (eg, Patent Document 5). However, coating methods such as wet coprecipitation / coating and spray drying have problems such as increase in the number of steps and cost as described above, safety, etc., and also a solution for dissolving niobium (for example, KOH solution, oxalic acid There is a problem that an impurity derived from a solution or the like, or an impurity derived from a solution (for example, sulfuric acid, hydrochloric acid, nitric acid or the like) adjusted in pH at the time of coating remains with the coated niobium.

Further, as another method of adding niobium, there is known a method in which a niobium-containing solution is added to a mixed solution containing nickel to co-precipitate in a step of crystallizing a nickel-containing hydroxide (for example, patent documents 1 to 3). However, when a niobium-containing solution is added during crystallization, a fine niobium hydroxide is formed, and the resulting nickel-containing hydroxide becomes a form of secondary particles in which finer primary particles are aggregated, and the inside of the secondary particles The amount of impurities such as alkali metals such as potassium and sodium and sulfates increases and it is difficult to reduce the impurities even by washing after crystallization. In addition, since the primary particles of this nickel-containing hydroxide are fine and the crystallinity is low, the crystallite diameter of the positive electrode active material obtained after firing is fine.

On the other hand, as in the present embodiment, solid phase addition of the niobium compound in the mixing step does not require a chemical solution or the like compared to the method of coprecipitation / coating niobium by the wet step, and the load is low and productivity is low. It is an excellent process. In addition, when coprecipitation / coating niobium by a wet process, it is necessary to control the pH, and in some cases, it may not be possible to add a targeted form or amount of niobium. Therefore, solid phase addition of the niobium compound is also excellent in quality stability. In addition, in the case of solid phase addition of niobium, it is incorporated into a lithium transition metal complex oxide by adding a niobium compound substantially free of alkali metals other than lithium (for example, sodium, potassium) and sulfur. The amount of impurities such as alkali metals and sulfates other than lithium can be reduced.

The niobium compound is not particularly limited, and niobium oxide, niobium oxide, niobium nitrate, niobium pentachloride, niobium nitrate and the like can be used. Among these, it is preferable to use niobic acid and niobium oxide from the viewpoint of easy availability and reduction of impurities in the lithium transition metal complex oxide. When the impurities are mixed, the battery characteristics such as the thermal stability, the charge and discharge capacity, and the cycle characteristics are degraded.

Since the reactivity changes depending on the particle size in solid phase addition, controlling the particle size of the added niobium compound is one of the important factors. In this embodiment, the average particle diameter of the niobium compound is 0.1 μm to 10 μm, preferably 0.5 to 8 μm, more preferably 0.1 to 3.0 μm, and still more preferably 0.1 to 1.0 μm. . If the average particle size is smaller than 0.1 μm, handling of the powder becomes very difficult. For example, the niobium compound is scattered during the mixing / baking step, and the target composition can not be added to the active material. There is. On the other hand, when the average particle size is larger than 10 μm, the reactivity at the time of firing is reduced, and the diffusion of niobium into the lithium transition metal composite oxide is insufficient, and the niobium is uniform in the lithium transition metal composite oxide after firing. It is not possible to ensure thermal stability. The average particle diameter is a value measured by a laser scattering diffraction method as a volume-based average diameter (MV).

As a method of adjusting the average particle diameter of the niobium compound to the above range, a method of pulverizing to a predetermined particle diameter using various pulverizers such as a ball mill, a planetary ball mill, a jet mill / nano jet mill, a beads mill and a pin mill There is. In addition, if necessary, classification may be performed by a dry classifier or a sieve.

The solid phase addition of the niobium compound having the above-mentioned average particle diameter is considered to make the obtained lithium transition metal complex oxide to have a porous structure. That is, although the details are unknown, the nickel-containing hydroxide obtained by the crystallization process is a secondary particle formed by aggregation of primary particles, and in the firing process, niobium is diffused from the surface of the secondary particle. When reacting, since the reaction rate is not uniform among primary particles, shrinkage of the primary particles is not uniform and fine voids are generated, which is presumed to have a porous structure suitable as a positive electrode active material.

Further, the lithium compound used in the mixing step is not particularly limited as long as it does not contain a sulfate group as a composition, and, for example, lithium hydroxide, carbonate, oxide and the like can be used. Among them, the lithium compound is preferably lithium hydroxide. In addition, in this specification, lithium hydroxide shall include the form of a hydrate and an anhydrate.

Furthermore, 1) the lithium compound used for mixing is anhydrous lithium hydroxide having a moisture content of 5% by mass or less, or 2) the obtained lithium mixture is dried before the calcination step, and lithium in the lithium mixture is More preferably, the compound is anhydrous lithium hydroxide having a water content of 5% by mass or less. By using anhydrous lithium hydroxide having a water content of 5% by mass or less, in the firing step, the reactivity of the solid phase reaction between the lithium compound, the nickel-containing hydroxide and the niobium compound becomes high, and the manufactured positive electrode Variations in the grade of the ratio of the number of atoms of lithium (Li) of the active material to a metal (Me) other than lithium (hereinafter referred to as “Li / Me”) become smaller, and more stable charge / discharge capacity and heat A positive electrode active material having stability can be obtained.

The preparation method of anhydrous lithium hydroxide which has a moisture content of the said range is not specifically limited, For example, it can obtain by vacuum-drying or air-baking lithium hydroxide monohydrate. Among them, vacuum drying is preferable from the viewpoint of the number of steps and the quality.

In addition, the moisture content of anhydrous lithium hydroxide makes the moisture content of lithium hydroxide monohydrate 100%, and the moisture content of anhydrous lithium hydroxide obtained by vacuum-drying lithium hydroxide for 8 hours at 200 ° C. It can be calculated from the relative proportion (mass) when the amount is 0%.

When the lithium compound in the lithium mixture is anhydrous lithium hydroxide, for example, a lithium mixture obtained by mixing a nickel-containing hydroxide, lithium hydroxide and a niobium compound is dried by vacuum drying or air baking. Anhydrous lithium hydroxide having a water content of 5% by mass or less can also be obtained in the process. In this drying step, drying is preferably performed at 150 to 250 ° C., preferably for 10 to 20 hours. The moisture content of anhydrous lithium hydroxide obtained by drying in the drying step is measured by measuring the moisture content when lithium hydroxide used in mixing is dried under the same conditions as in this drying step. It can be determined as a value similar to the value.

After mixing the nickel-containing hydroxide, the lithium hydroxide and the niobium compound, a step of drying is performed in the furnace for performing the baking step as it is, at the same temperature and for the same time as the drying step. The compound may be anhydrous lithium hydroxide having a water content of 5% by mass or less.

The nickel-containing hydroxide used in the mixing step preferably has an average particle diameter of about 5 to 20 μm, and more preferably 10 to 15 μm. The particle size of the nickel-containing hydroxide can be controlled by adjusting the conditions at the time of crystallization and the like. The average particle diameter is a value measured by a laser scattering diffraction method as a volume-based average diameter (MV).

The nickel-containing hydroxide, the lithium compound and the niobium compound are mixed such that Li / Me in the lithium mixture is 0.95 to 1.20. That is, Li / Me in the lithium mixture is mixed to be the same as Li / Me in the positive electrode active material. This is because Li / Me does not change before and after the firing step, so Li / Me mixed in this mixing step becomes Li / Me in the positive electrode active material.

In addition, when performing a water washing process after a baking process so that it may mention later, Li / Me reduces by water washing. Therefore, in the case of washing with water, it is preferable to mix the nickel-containing hydroxide, the lithium compound and the niobium compound in anticipation of the decrease in Li / Me. Although the decrease due to water washing of Li / Me varies depending on the baking conditions and the water washing conditions, it is about 0.05 to 0.1, and it is necessary to confirm the decrease by producing a small amount of positive electrode active material as a preliminary test. Can.

A common mixer can be used to mix the nickel-containing hydroxide, the lithium compound and the niobium compound, and for example, a shaker mixer, a lodige mixer, a Julia mixer, a V blender, or the like can be used. The mixing conditions may be such that the nickel-containing hydroxide, the lithium compound and the niobium compound are sufficiently mixed to such an extent that the shape of the nickel-containing hydroxide particles and the like is not broken.

The lithium mixture is preferably sufficiently mixed before firing. If mixing is not sufficient, Li / Me may vary among individual particles, which may cause problems such as when sufficient battery characteristics can not be obtained.

(D) Firing Step In the firing step, the lithium mixture obtained in the mixing step is fired in an oxidizing atmosphere at 700 to 840 ° C., preferably 700 to 820 ° C., more preferably 700 to 800 ° C. It is a process of obtaining a thing.

The calcination temperature is 700 to 840 ° C., preferably 700 to 820 ° C., more preferably 710 to 810 ° C. in an oxidizing atmosphere. When the firing temperature is less than 700 ° C., the diffusion of lithium and niobium into the nickel-containing hydroxide is not sufficiently performed, excess lithium or unreacted particles remain, or the crystal structure is not sufficiently aligned. As a result, there arises a problem that sufficient battery characteristics can not be obtained. In addition, when the firing temperature exceeds 840 ° C., severe sintering may occur between the formed lithium transition metal complex oxide particles, and abnormal grain growth may occur. When abnormal grain growth occurs, the particles after firing may become coarse and may not retain the particle form, and when the positive electrode active material is formed, the specific surface area decreases and the resistance of the positive electrode increases to cause the battery There is a problem that battery characteristics such as capacity decrease.

When the lithium mixture is fired in the firing step, the lithium in the niobium compound is diffused into the nickel-containing hydroxide together with the lithium in the lithium compound, so that a lithium transition metal complex oxide composed of particles of a polycrystalline structure is formed. Here, from the viewpoint of uniform distribution of the niobium compound, it is preferable that Ni, Co and the additional element M in the lithium mixture be in the form of a composite hydroxide (nickel-containing hydroxide). In the lithium compound mixed with the nickel-containing hydroxide, the reaction of lithium and these elements proceeds almost simultaneously with the reaction in which the niobium compound is decomposed and diffused in the composite hydroxide, so that in the lithium transition metal composite oxide Distribution of niobium is more uniform. In the form of a nickel-containing oxide, the reaction between lithium and these elements proceeds first, so that the diffusion of niobium into the composite hydroxylated part becomes insufficient, resulting in the form of niobium oxide or the like. In some cases, niobium is segregated in the lithium transition metal complex oxide.

The baking time is preferably at least 3 hours or more, more preferably 6 to 24 hours. If less than 3 hours, formation of lithium transition metal complex oxide may not be sufficiently performed. Further, the atmosphere at the time of firing is preferably an oxidizing atmosphere, and more preferably an atmosphere having an oxygen concentration of 18 to 100% by volume. That is, the firing is preferably performed in the air or an oxygen stream. This is because if the oxygen concentration is less than 18% by volume, the oxygen can not be sufficiently oxidized, and the crystallinity of the lithium transition metal complex oxide may be insufficient. In particular, in consideration of the battery characteristics, it is preferable to carry out in an oxygen stream.

In the firing step, before firing at a temperature of 700 to 840 ° C., the lithium mixture is calcined at a temperature lower than the firing temperature and at which the lithium compound and the nickel-containing hydroxide can react. it can. The calcination sufficiently diffuses lithium into the nickel-containing hydroxide in the lithium mixture, and a uniform lithium transition metal complex oxide can be obtained. For example, in the case of using lithium hydroxide, it is preferable to carry out calcination by holding at a temperature of 400 to 550 ° C. which is equal to or higher than the melting point of lithium hydroxide for about 1 to 10 hours.

The furnace used for the firing is not particularly limited as long as it can fire the lithium mixture in the atmosphere or an oxygen stream, but an electric furnace free of gas generation is preferable, and a batch type or continuous type furnace is preferable. Either can be used.

Although the sintering between particles is suppressed, the lithium transition metal complex oxide obtained by firing may form coarse particles due to weak sintering or aggregation. In such a case, sintering and aggregation can be eliminated by crushing to adjust the particle size distribution.

(E) Water Washing Step The lithium transition metal complex oxide obtained in the firing step can be used as a positive electrode active material even in the as-is state, but after the firing step, a slurry is used at a ratio of 100 to 2000 g / L per liter of water. It is preferable to carry out a water washing step of washing with water.

By performing the water washing step, it is possible to remove excess lithium on the particle surface of the lithium transition metal complex oxide, to increase the surface area which can be in contact with the electrolytic solution, and to improve the charge and discharge capacity. Further, the fragile portion formed on the particle surface can be sufficiently removed, and the contact with the electrolytic solution can be increased to improve the charge and discharge capacity. Furthermore, since excess lithium causes a side reaction in the non-aqueous secondary battery and causes expansion of the battery due to gas generation and the like, it is preferable to perform the water washing step also from the viewpoint of safety improvement.

The slurry concentration at the time of washing with water is preferably such that the amount (g) of the lithium transition metal complex oxide to 1 L of water contained in the slurry is 100 to 2000 g / L. That is, as the slurry concentration increases, the amount of powder increases, and when it exceeds 2000 g / L, the viscosity is also very high and stirring becomes difficult, and since the alkali in the liquid is high, the dissolution rate of the attached matter from the equilibrium relationship May be difficult to separate from the powder even if exfoliation occurs. On the other hand, if the slurry concentration is less than 100 g / L, the amount of lithium eluted is too large and the amount of lithium on the surface decreases, but lithium is also released from the crystal lattice of the positive electrode active material. In addition, the aqueous solution of high pH absorbs carbon dioxide gas in the atmosphere and reprecipitates lithium carbonate.

Water to be used is not particularly limited, and pure water is preferable. By using pure water, it is possible to prevent a decrease in battery performance due to the adhesion of impurities to the positive electrode active material.
It is preferable that the amount of adhering water remaining on the particle surface at the time of solid-liquid separation of the above-mentioned slurry is small. When the amount of adhering water is large, lithium dissolved in the solution is reprecipitated, and the amount of lithium present on the surface of the lithium transition metal composite oxide particles after drying is increased.

Moreover, it is preferable that the water washing process includes the process of filtering and drying after water washing.
The filtration method may be a commonly used method, for example, a suction filter, a filter press, a centrifuge or the like.

The temperature of drying after filtration is not particularly limited, and is preferably 80 to 350 ° C. If the temperature is less than 80 ° C., drying of the positive electrode active material after washing with water is delayed, so that a lithium concentration gradient may occur between the particle surface and the inside of the particle, and battery characteristics may be degraded. On the other hand, near the surface of the positive electrode active material, it is expected that the stoichiometry is very close to the stoichiometric ratio or lithium is desorbed to be in a state close to the charged state. It may trigger the collapse of the near crystalline structure, which may lead to the deterioration of the battery characteristics.
The drying time is not particularly limited, but preferably 2 to 24 hours.

2. Cathode Active Material for Nonaqueous Electrolyte Secondary Battery (1) Composition The cathode active material of the present embodiment has a general formula Li _d Ni ₁ -ab _c Co _a M _b Nb _c O ₂ (where M is Mn And at least one element selected from V, Mg, Ti and Al, 0.03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05, 0.95 It consists of lithium transition metal complex oxide represented by <= <= <= 1.20.

A representing the cobalt content is 0.03 ≦ a ≦ 0.35, preferably 0.05 ≦ a ≦ 0.35, more preferably 0.07 ≦ a ≦ 0.20, more preferably Is 0.10 ≦ a ≦ 0.20. Cobalt contributes to the improvement of cycle characteristics. When the value of a is less than 0.03, sufficient cycle characteristics can not be obtained, and the capacity retention rate also decreases. On the other hand, when the value of a exceeds 0.35, the decrease in initial discharge capacity becomes large.

B indicating the content of M is 0 ≦ b ≦ 0.10, preferably 0 <b ≦ 0.10, and more preferably 0.01 ≦ b ≦ 0.07. M is at least one element selected from Mn, V, Mg, Ti and Al, and can be added to improve battery characteristics such as cycle characteristics and safety. When b exceeds 0.10, the battery characteristics are further improved, but the decrease in initial discharge capacity becomes large, which is not preferable. Furthermore, excellent cycle characteristics can be expressed by satisfying 0 <b ≦ 0.10.

The c indicating the niobium content is 0.001 ≦ c ≦ 0.05, preferably 0.002 ≦ c ≦ 0.05, more preferably 0.002 ≦ c ≦ 0.04, further preferably 0 . 003 c c 0.02 0.02. Niobium is considered to contribute to the suppression of the thermal decomposition reaction due to the deoxidation of lithium transition metal complex oxide, and is effective in improving safety, and is also effective in improving cycle characteristics because the crystal is stabilized. . When the value of c is less than 0.001, the added amount is too small, and the improvement of safety becomes insufficient. On the other hand, the safety is improved according to the addition amount of niobium, but when the value of c exceeds 0.05, the crystallinity is lowered and the charge / discharge capacity and the cycle characteristics are lowered.

D represents the ratio (Li / Me) of the number of moles of metal other than lithium (Me) to lithium. d is 0.95 ≦ d ≦ 1.20, preferably 0.98 ≦ d ≦ 1.10. When the value of d is less than 0.95, the charge and discharge capacity is reduced. On the other hand, although the charge / discharge capacity increases as the value of d increases, the safety decreases if d exceeds 1.20.

In addition, content of said each component is the value measured by the quantitative analysis by an inductively coupled plasma (ICP) method.

(2) Internal Structure The positive electrode active material of the present embodiment is made of a lithium transition metal composite oxide composed of particles of a polycrystalline structure, and preferably has a porous structure. In the present specification, the porous structure means the distance between any two points on the outer edge of the void by observation (a magnification of 5000) of an arbitrary cross section (observation surface) of the positive electrode active material particle using a scanning electron microscope. This refers to a structure in which a plurality of voids having a diameter of 0.3 μ or more are observed in the cross section of the positive electrode active material particles.

Further, the voids in the particles preferably have a maximum length of 50% or less, more preferably 40% or less of the above-mentioned particle cross section major axis by cross-sectional observation with a scanning electron microscope, and preferably exist at least at grain boundaries. . By having the above-described porous structure, the particle surface which can be brought into contact with the electrolytic solution when used for the positive electrode of the battery greatly increases, compensates for the decrease in charge / discharge capacity due to the addition of niobium, and secures safety. Therefore, sufficient charge and discharge capacity can be obtained.

Furthermore, the number of voids in the cross-sectional observation is determined for any 20 or more particles, and the index obtained by dividing the total of the number of voids by the total of the particle cross section major axis (μm) of the particles (hereinafter referred to as “void (Also referred to as “number”) is preferably 0.2 to 10 / μm, and more preferably 3 to 8 / μm. Here, the particle cross-sectional major axis is the maximum distance between any two points on the particle periphery in the particle observation surface. Moreover, in the said cross-sectional observation, the particle | grains which have a particle size of 20% or less of the volume based average diameter (MV) of the latter stage positive electrode active material are excluded from judgment of porous structure. This is because particles having a particle diameter of not more than 20% of the average particle diameter are small in the positive electrode active material and have little influence on charge and discharge capacity, and the observation surface is the cross section of the particle end. It may not be appropriate. When the number of voids is in the above range, it is possible to obtain a high charge / discharge capacity with a sufficient contact area, while suppressing excessive contact with the electrolytic solution and suppressing a decrease in thermal stability.

(3) Specific Surface Area The positive electrode active material of the present embodiment has a specific surface area of 0.9 to 4.0 m ² / g, preferably 0.9 to 3.0 m ² / g, more preferably 0.9 to It is 2.8 m ² / g, more preferably 1.0 to 2.8 m ² / g, and particularly preferably 1.0 to 2.6 m ² / g. When the specific surface area is less than 0.9 m ² / g, the particle surface which can be in contact with the electrolytic solution decreases, and a sufficient charge and discharge capacity can not be obtained. On the other hand, when the specific surface area exceeds 4.0 m ² / g, the particle surface in contact with the electrolytic solution becomes too large, and the safety is lowered. A specific surface area can be made into the said range by adjusting Li / Me ratio, baking conditions, and water washing conditions.

(4) Impurity Content The positive electrode active material of the present embodiment has an alkali metal content other than lithium of 20 mass ppm or less, preferably 10 mass ppm or less. When c indicating the niobium content is in the above range and the alkali metal content other than lithium is 20 mass ppm or less, more excellent cycle characteristics can be obtained. If either the content of an alkali metal other than lithium or the addition amount of niobium exceeds the above range, good cycle characteristics can not be obtained. The alkali metal content other than lithium can be made into the above-mentioned range by using the above-mentioned manufacturing method in which niobium is solid-phase added.

Furthermore, in the lithium transition composite metal oxide, the amount of sulfate radical (SO ₄ ) contained is preferably 0.2% by mass or less, more preferably 0.01 to 0.2% by mass, and still more preferably 0.02 It is ̃0.1 mass%. By the sulfate radical being 0.2 mass% or less, more excellent cycle characteristics are obtained.

Here, at least a part of the sulfate groups contained in the lithium transition metal complex oxide is derived from a metal salt such as nickel or cobalt at the time of crystallization, and, for example, when a sulfate is used as the metal salt, Since the content of sulfate groups tends to increase when the pH in the solution decreases, the amount of sulfate groups can be made to fall in the above range by appropriately adjusting the pH and sufficiently washing with water. In the crystallization step, using a sulfate as the metal salt is effective to increase the metal concentration in the aqueous solution to enhance the productivity and reduce the environmental load.

In the present embodiment, in the mixing step (C), by adding the niobium compound in the solid phase, it is possible to prevent the mixing of the sulfate radical when the niobium is wet coated, and to reduce the sulfate radical content. Moreover, the amount of sulfuric acid radicals can be reduced by excluding the sulfur compound mixed from the niobium compound used in the (C) mixing step.

(5) Existing Form of Niobium In the positive electrode active material of the present embodiment, as the existing form of niobium, niobium may be solid-solved in the lithium transition metal complex oxide, and grain boundaries in the lithium transition metal complex oxide Alternatively, it may be present on the particle surface as a lithium niobium composite oxide. Among these, niobium is preferably in solid solution. Here, the solid solution means a state in which no hetero phase is recognized in the observation by EDX measurement of the transmission electron microscope within the particles of the lithium transition metal complex oxide.
That is, the maximum diameter of the niobium compound observed in the lithium transition metal complex oxide particles is preferably 200 nm or less by EDX measurement with a transmission electron microscope. A high battery capacity can be obtained by setting the maximum diameter of the niobium compound in the above-mentioned range and suppressing the formation of the coarse niobium compound.

Furthermore, the ratio of the grain boundary to the concentration of niobium in the grain (grain boundary / within grain) is preferably 4 times or less, more preferably 3 times or less. The ratio of the niobium concentration in the grain boundaries and in the grains can be determined from the EDX measurement result of the transmission electron microscope. By reducing the ratio of the niobium concentration, the effect of suppressing the thermal decomposition reaction can be enhanced even with a small amount.

(6) Crystallite Diameter In the positive electrode active material of the present embodiment, the crystallite diameter of the lithium transition metal oxide is preferably 10 to 180 nm, more preferably 10 to 150 nm, still more preferably 50 to 150 nm, particularly preferably Is 50 to 130 nm. When the crystallite diameter is less than 10 nm, the number of crystal grain boundaries is too large, the resistance of the active material is increased, and sufficient charge and discharge capacity may not be obtained. On the other hand, when the crystallite diameter exceeds 180 nm, crystal growth proceeds too much, and there is a possibility that cation mixing in which nickel is mixed in the lithium layer of the lithium transition metal complex oxide which is a layered compound occurs, and the charge and discharge capacity is reduced. . The crystallite diameter can be made into the above-mentioned range by adjusting the crystallization conditions, the calcination temperature, the calcination time and the like. For example, the crystallite diameter can be increased by increasing the crystallinity of the nickel-containing hydroxide under crystallization conditions, and the crystallite diameter can be increased by increasing the firing temperature. The crystallite diameter is a value calculated from the peak of the (003) plane in X-ray diffraction (XRD).

(7) Average Particle Size The positive electrode active material of the present embodiment preferably has an average particle size of 5 to 20 μm, preferably 10 to 15 μm, as D50 which is 50% of volume integration by laser scattering measurement. More preferable. If it is less than 5 μm, the packing density may be lowered when used for the positive electrode of the battery, and the charge / discharge capacity per volume may not be sufficiently obtained. On the other hand, if it exceeds 20 μm, the contact area with the electrolytic solution may not be sufficiently obtained, and the charge and discharge capacity may be reduced.

3. Nonaqueous Electrolyte Secondary Battery An embodiment of the nonaqueous electrolyte secondary battery of the present invention will be described in detail for each component. The non-aqueous electrolyte secondary battery of the present invention is composed of the same components as a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolytic solution. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is embodied in various modifications and improvements based on the knowledge of those skilled in the art, including the following embodiments. can do. Moreover, the non-aqueous electrolyte secondary battery of this invention does not specifically limit the use.

(1) Positive Electrode A positive electrode composite material for forming a positive electrode and each material constituting the same will be described. The powdery positive electrode active material of the present invention is mixed with a conductive material and a binder, and if necessary, activated carbon and a solvent for adjusting viscosity etc. are added, and this is kneaded to prepare a positive electrode mixture paste. Make. In addition, each mixing ratio in positive mix can be adjusted suitably according to the performance of the secondary battery requested | required.

For example, assuming that the total solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass and the conductivity is the same as in the positive electrode of a general lithium secondary battery. The content of the material can be 1 to 20% by mass, and the content of the binder can be 1 to 20% by mass.

The obtained positive electrode mixture paste is applied, for example, on the surface of a current collector made of aluminum foil, and dried to disperse the solvent. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size according to the target battery, and can be used for battery production. However, the method of producing the positive electrode is not limited to the above-described one, and other methods can also be used.

The conductive agent is not particularly limited, and for example, carbon black-based materials such as graphite (natural graphite, artificial graphite, expanded graphite and the like), acetylene black, ketjen black and the like can be used.
The binder (binder) is not particularly limited. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine-containing resin such as fluororubber, styrene butadiene, cellulose resin, polyacrylic acid and polypropylene. And polyethylene can be used.

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

(2) Negative electrode In the negative electrode, metal lithium, lithium alloy, etc., or a negative electrode active material capable of absorbing and desorbing lithium ions, a binder is mixed, and an appropriate solvent is added to make a negative electrode composite material Is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density if necessary.

As the negative electrode active material, it is possible to use, for example, a calcined product of an organic compound such as natural graphite, artificial graphite, or a phenol resin, or a powder of a carbon material such as coke. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride can be used as in the positive electrode, and as a solvent for dispersing the active material and the binder, N-methyl-2-pyrrolidone or the like can be used. Organic solvents can be used.

(3) Separator A separator is interposed and arrange | positioned between a positive electrode and a negative electrode. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a thin film of polyethylene, polypropylene or the like, which has a large number of fine holes, can be used.

(4) Nonaqueous Electrolyte The nonaqueous electrolyte is a lithium salt as a support salt dissolved in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, tetrahydrofuran and 2-methyl tetrahydrofuran Or one or a combination of two or more selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. it can.
As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _{2 and the} like, and complex salts thereof can be used.
Furthermore, the non-aqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(5) Shape and Configuration of Battery The shape of the lithium secondary battery according to the present invention, which is composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above, may be various types such as cylindrical type and laminated type. be able to.
In any of the shapes, the positive electrode and the negative electrode are stacked via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolyte. The positive electrode current collector and the positive electrode terminal leading to the outside, and the negative electrode current collector and the negative electrode terminal leading to the outside are connected using a current collection lead or the like. The battery can be completed by sealing the above configuration in a battery case.

Hereinafter, the present invention will be described in more detail by way of examples of the present invention and comparative examples, but the present invention is not limited by these examples.

Example 1
[Method of producing positive electrode active material]
(A) Crystallization process A mixed aqueous solution of nickel sulfate, cobalt sulfate and a sodium aluminate aqueous solution so that the molar ratio of nickel: cobalt: aluminum is 81.5: 15.0: 3.5, and 25 mass% water A sodium oxide solution and 25% by weight aqueous ammonia were simultaneously added to the reaction vessel. At this time, the pH in the reaction layer is kept at 11.8 at a liquid temperature of 25 ° C., the reaction temperature at 50 ° C., the ammonia concentration at 10 g / L, and precipitation consisting of spherical secondary particles by crystallization reaction. It formed. After the inside of the reaction vessel is stabilized, the slurry of the precipitate is recovered from the overflow port, filtered, washed with water and then dried to obtain a nickel-containing hydroxide (Ni _0.815 Co _0.150 Al _0.035 (OH) ₂ ) Obtained.

(C) Mixing Step The obtained nickel-containing hydroxide, a commercially available lithium hydroxide monohydrate, and an average particle diameter of 0.6 μm with a nano-grinding mill (nano-grinding mill manufactured by Sunrex Industries Ltd.) Niobic acid (Nb ₂ O ₅ · x H ₂ O) powder, which has been pulverized to a certain weight, is weighed so that the target niobium addition amount c 'is 0.01 and Li / Me is 1.10. The lithium mixture was obtained by sufficiently mixing using a shaker mixer apparatus (TURBULA Type T2C manufactured by Willie-e-Bachkofen (WAB), with a strength sufficient to maintain the form of the hydroxide.

(E) Firing step The obtained lithium mixture is inserted into a magnesia firing vessel and heated to a temperature of 2.77 ° C./min up to 500 ° C. in an oxygen stream at a flow rate of 6 L / min using a closed electric furnace. The temperature was raised and maintained at 500 ° C. for 3 hours. Thereafter, the temperature was raised to 780 ° C. at the same temperature rising rate, and held at 780 ° C. for 12 hours, and then furnace cooled to room temperature to obtain a lithium transition metal composite oxide.

(F) Water Washing Step The obtained lithium transition metal complex oxide was mixed with pure water so that the slurry concentration was 1500 g / L to prepare a slurry, which was washed with water for 30 minutes using a stirrer and filtered. After filtration, it was kept at 210 ° C. for 14 hours using a vacuum dryer. Then, it cooled to room temperature and obtained the positive electrode active material.

[Evaluation of positive electrode active material]
The obtained positive electrode active material was evaluated by the following methods, and the obtained evaluation results are shown in Table 1 and (Evaluation 1).
(Composition and alkali metal content)
The composition of the obtained positive electrode active material was analyzed by quantitative analysis by ICP emission analysis. Further, the amount of alkali metal other than lithium in the positive electrode active material was measured by atomic absorption spectrometry.
(Crystallite diameter)
The crystallite diameter of the positive electrode active material was calculated from the formula of Scerrer using 2θ and the half width of the (003) plane in the diffraction pattern obtained by the XRD measurement of the positive electrode active material.
(Specific surface area)
The specific surface area of the positive electrode active material was measured by the BET method.
(Volume-based average diameter)
The volume based mean diameter (MV) was measured by the laser scattering diffraction method.
(Number of voids)
The number of voids and the particle cross-sectional major axis (μm) of any 20 particles are measured by observation of the particle cross section by a reverse electron microscope, and the number of voids [(the number of voids of the measured particles Of the total of the particle cross section major axis of the measured particles) was determined.

(Evaluation of initial discharge capacity)
The evaluation of the initial discharge capacity of the positive electrode active material was performed by the following method.
70% by mass of the obtained positive electrode active material powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg was taken out therefrom to prepare a pellet, which was used as a positive electrode. Lithium metal was used as the negative electrode, and an equal mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1 M LiClO ₄ as a supporting salt was used as the electrolytic solution. A 2032 type coin battery as shown in FIG. 1 was manufactured in a glove box under an Ar atmosphere controlled at a dew point of −80 ° C.
The prepared battery is allowed to stand for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) is stabilized, the current density to the positive electrode is set to 0.5 mA / cm ² and charged to a cutoff voltage of 4.3 V to obtain an initial charge capacity, The capacity when discharged to a cutoff voltage of 3.0 V after one hour of rest was taken as the initial discharge capacity.

(Evaluation of cycle characteristics)
The cycle characteristics were evaluated by the capacity retention rate (%) measured by the following method. For each battery, CC charge to 4.4 V at a rate of 1 C at a temperature of 25 ° C, pause for 10 minutes, then CC discharge to 3.0 V at the same rate, and charge and discharge cycles for 10 minutes of rest, 200 The cycle was repeated. Measure the discharge capacity at the 1st and 200th cycles, and calculate the percentage of 200th cycle 2C discharge capacity to the 1st cycle 2C discharge capacity ([200th cycle 2C discharge capacity / 1st cycle 2C discharge capacity] x 100) Maintenance rate (%).

(Evaluation of safety of positive electrode)
The safety of the positive electrode was evaluated by the maximum exothermic peak height measured by the following method. CCCV charging (constant current-constant voltage charging up to a cutoff voltage of 4.5 V) of a 2032 type coin battery manufactured by the same method as the above. First, charging operates with a constant current and then charging ends with a constant voltage After charging using a two-phase charging process, the cathode was disassembled taking care not to short circuit. 3.0 mg of this electrode is weighed out, 1.3 mg of an electrolytic solution is added, the solution is sealed in an aluminum measurement container, and the temperature rising rate is 10 ° C./differential scanning calorimeter (DSC) PTC-10A (manufactured by Rigaku Corporation) The exothermic behavior was measured from room temperature to 300 ° C. in min.

(Example 2)
A positive electrode active material was obtained in the same manner as in Example 1 except that the average particle diameter of the niobic acid was changed to 8 μm, and the respective characteristics were evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Example 3)
A positive electrode active material was obtained in the same manner as in Example 1 except that the niobium compound was niobium oxide and the average particle diameter of the niobium compound was 1 μm, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Example 4)
A positive electrode active material was obtained in the same manner as in Example 1 except that the target niobium addition amount c ′ was set to 0.05, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.
(Example 5)
A positive electrode active material was obtained in the same manner as in Example 1 except that the target niobium addition amount c ′ was set to 0.005, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.
(Example 6)
A positive electrode active material was obtained in the same manner as in Example 1 except that the target niobium addition amount c ′ was set to 0.001, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Example 7)
A positive electrode active material was obtained in the same manner as in Example 1 except that the firing temperature was 700 ° C., and the respective characteristics were evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Example 8)
A positive electrode active material was obtained in the same manner as in Example 1 except that the firing temperature was set to 830 ° C., and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Example 9)
The nickel-containing hydroxide obtained in the crystallization step (A) was heat-treated at 700 ° C. for 6 hours to form a nickel-containing oxide (heat treatment step (B)). Thereafter, a positive electrode active material was obtained in the same manner as in Example 1 except that a nickel-containing oxide obtained by heat treatment, lithium hydroxide and niobic acid were mixed, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Comparative example 1)
A positive electrode active material was obtained in the same manner as in Example 1 except that the average particle diameter of the niobic acid was changed to 15 μm, and the respective characteristics were evaluated. The obtained positive electrode active material was observed with a scanning electron microscope, and an unreacted niobium compound was confirmed. Therefore, the positive electrode active material is added to a 100 g / L aqueous solution of potassium hydroxide and stirred at 80 ° C. for 10 minutes. After the reaction niobium compound was dissolved and filtered to remove the niobium compound, the composition of the positive electrode active material was analyzed in the same manner as in Example 1. The niobium content was below the lower limit of analysis. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Comparative example 2)
A positive electrode active material was obtained in the same manner as in Example 1 except that the target niobium addition amount c ′ was set to 0.07, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Comparative example 3)
A mixed aqueous solution of nickel sulfate, cobalt sulfate and an aqueous solution of sodium aluminate, and 25 mass% sodium hydroxide solution so that the molar ratio of nickel: cobalt: aluminum is 81.5: 15.0: 3.5 A positive electrode active material is obtained in the same manner as in Example 1 except that mass% ammonia water is simultaneously added to the reaction tank, that a niobium compound is not added in the mixing step, and that the firing temperature is 740 ° C. In addition, each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Comparative example 4)
A positive electrode active material was obtained in the same manner as in Example 1 except that the firing temperature was changed to 850 ° C., and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Comparative example 5)
A niobium salt solution (30 g / L) prepared by dissolving niobic acid (Nb ₂ O ₅ · x H ₂ O) in caustic potash in a slurry in which the nickel-containing hydroxide obtained in the crystallization step is mixed with pure water. Nb-coated nickel-containing hydroxide (hereinafter, also referred to as “Nb-coated nickel hydroxide”) is prepared by adding dropwise with the sulfuric acid while adjusting the pH to 10.0, and the niobium compound is added in the mixing step. A positive electrode active material was obtained in the same manner as in Example 1 except that the above Nb-coated nickel hydroxide (Nb amount c ′ is 0.01) was used without mixing, and each characteristic was evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 1.

(Evaluation 1)
As shown in Table 1, the positive electrode active materials obtained in Examples 1 to 9 have an initial discharge capacity of approximately 185 mAh / g, and have a good initial discharge capacity. In addition, the capacity retention rate after 200 cycles is 85% or more, and has excellent cycle characteristics. In Example 4, the cycle characteristics were slightly lower than those in the other examples because the niobium addition amount was large. In addition, the positive electrode active materials obtained in Examples 1 to 9 have a maximum exothermic peak height of 4.0 cal / sec / g or less as measured by DSC, and a conventional positive electrode active material in which no niobium is added (Comparative Example 3) The calorific value is greatly suppressed as compared with the above, and shows good thermal stability.

Further, when cross sections of the positive electrode active materials obtained in Examples 1 to 8 were observed with a transmission electron microscope, no hetero phase was recognized, and niobium was contained in the lithium transition gold complex oxide. Further, when the distribution of niobium in the positive electrode active material obtained in Examples 1 to 8 was analyzed by EDX analysis, the niobium was uniformly distributed in the particles of the positive electrode active material, and Nb in the grain boundaries and in the grains It was confirmed that the concentration ratio was 3 times or less.
When a cross section of the positive electrode active material obtained in Example 9 is observed by a transmission electron microscope, a heterophase having a maximum diameter of more than 200 nm is observed at grain boundaries, and EDX analysis confirms that the heterophase is a niobium compound It was done. In Example 9, the initial discharge capacity was slightly lower (186.5 mAh / g) as compared to the other examples. This is presumably because the use of the nickel-containing oxide in the mixing step reduces the reactivity with the niobium compound, and the niobium compound present in the grain boundaries affects the electrochemical reactivity.

On the other hand, in Comparative Example 1, the average particle diameter of the niobium compound was 15 μm, the reactivity of the niobium compound was low, the amount of unreacted niobium compound was large, and niobium was not contained in the positive electrode active material. Therefore, the maximum exothermic peak height becomes very high (7.1 cal / sec / g), and thermal stability is poor. In addition, in Comparative Example 2, the niobium addition amount was as high as 0.07, and the initial discharge capacity and the cycle characteristics were significantly reduced. Comparative Example 3 is a conventional positive electrode active material to which no niobium is added, and although the initial discharge capacity is high and the cycle characteristics are excellent, the maximum exothermic peak height is very high (7.0 cal / Sec / g), thermal stability was not good. In Comparative Example 4, sintering was performed at a high temperature, and while mixing of cations in which nickel was mixed in the lithium layer of the lithium transition metal complex oxide which is a layered compound occurred, the specific surface area was reduced and the initial discharge capacity was significantly reduced. . In addition, the maximum exothermic peak height also increased.
In Comparative Example 5, niobium was added by the coating method, the content of impurities (alkali metals other than lithium) was high, and the cycle characteristics were degraded.

(Example 10)
(A) Crystallization process A mixed aqueous solution of nickel sulfate, cobalt sulfate and a sodium aluminate aqueous solution so that the molar ratio of nickel: cobalt: aluminum is 81.5: 15.0: 3.5, and 25 mass% water A sodium oxide solution and 25% by mass aqueous ammonia are simultaneously added to the reaction vessel, and the pH is maintained at 11.8 with a liquid temperature of 25 ° C, the reaction temperature is maintained at 50 ° C, and the ammonia concentration is maintained at 10g / L. The reaction formed a precipitate consisting of spherical secondary particles. After the inside of the reaction vessel is stabilized, the slurry of the precipitate is recovered from the overflow port, filtered, washed with water and then dried to obtain a nickel-containing hydroxide (Ni _0.815 Co _0.15 Al _0.035 (OH) ₂ ) Obtained.

(B) Mixing step Commercially available lithium hydroxide monohydrate was vacuum dried at 150 ° C. for 12 hours to prepare anhydrous lithium hydroxide (water content: 0.4% by mass). The moisture content is 0% by mass of anhydrous lithium hydroxide after vacuum drying (150 ° C. for 12 hours), and the moisture content of anhydrous lithium hydroxide after vacuum drying for another 8 hours at 200 ° C. The water content of lithium monohydrate was 100% by mass, and it was determined as a relative value from the mass change before and after drying.
The above nickel-containing hydroxide, anhydrous lithium hydroxide, and niobium oxide powder (Nb ₂ O ₅ · xH ₂ O) with an average particle diameter of 0.6 μm pulverized by a nanogrinding jet mill, Li / Me After weighing each so that 1.10, niobium addition amount c becomes 0.01, using a shaker mixer device (TURBULA Type T2C manufactured by Willie et bachkofen (WAB)), the form of nickel-containing hydroxide The lithium mixture was obtained by thorough mixing at a maintained strength.

(C) Firing Step This lithium mixture is inserted into a magnesia firing vessel and heated to 500 ° C. at a heating rate of 2.77 ° C./min in an oxygen stream at a flow rate of 6 L / min using a closed electric furnace. And kept at 500 ° C. for 3 hours. Thereafter, the temperature was raised to 780 ° C. at the same temperature rising rate and held for 12 hours, and then furnace cooling was performed to room temperature to obtain a lithium transition metal composite oxide.

(D) Water Washing Step The obtained lithium transition metal complex oxide was mixed with pure water so that the slurry concentration was 1500 g / L to prepare a slurry, which was then washed with water for 30 minutes using a stirrer and filtered. After filtration, it was held at 210 ° C. for 14 hours using a vacuum dryer and cooled to room temperature to obtain a positive electrode active material.

(Evaluation of positive electrode active material)
Each characteristic was evaluated in the same manner as in Example 1. The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Example 11)
A positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that the water content of anhydrous lithium hydroxide was changed to 3.0% by mass. The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Example 12)
A positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that the lithium compound was changed to lithium hydroxide monohydrate (water content 99.7% by mass). The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Example 13)
A positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that the niobium addition amount c was set to 0.005. The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Example 14)
A positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that the niobium addition amount c was set to 0.001. The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Example 15)
A positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that a nickel-containing oxide obtained by heat-treating a nickel-containing hydroxide at 600 ° C. for 12 hours was used in the mixing step. The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Example 16)
The nickel-containing oxide obtained by subjecting the nickel-containing hydroxide to heat treatment oxidation calcination at 600 ° C. for 12 hours was used in the mixing step, and lithium hydroxide monohydrate (water content 99.7 mass) as a lithium compound The positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that%) was used. The evaluation results of the obtained positive electrode active material are shown in Table 2 and (Evaluation 2).

(Comparative example 6)
A positive electrode active material was obtained and evaluated in the same manner as in Example 10 except that no niobium compound was added. The evaluation results of the obtained positive electrode active material are shown in Table 2.

(Comparative example 7)
A niobium salt solution (30 g / L) prepared by dissolving niobic acid (Nb ₂ O ₅ · x H ₂ O) in caustic potash in a slurry in which the nickel-containing hydroxide obtained in the crystallization step is mixed with pure water. The Nb-coated nickel-containing hydroxide (Nb-coated nickel hydroxide) is prepared by adding dropwise with the sulfuric acid while adjusting the pH to 8.0, and the niobium compound is not mixed in the mixing step. The positive electrode active material was prepared in the same manner as in Example 10 except that the nickel hydroxide (Nb amount c was 0.01) was used and the lithium compound was changed to lithium hydroxide (water content 99.7 mass%). It acquired and evaluated about each characteristic. The evaluation results of the obtained positive electrode active material are shown in Table 2.

(Comparative example 8)
In the crystallization step, a niobium salt solution (72 g / L) prepared by dissolving niobic acid (Nb ₂ O ₅ · x H ₂ O) in caustic potash was added to prepare a nickel-containing hydroxide, in the mixing step A positive electrode active material was obtained in the same manner as in Example 10, except that the above-mentioned nickel-containing hydroxide (Nb amount c was 0.01) was used without mixing the niobium compound, and the respective characteristics were evaluated. The evaluation results of the obtained positive electrode active material are shown in Table 2.

(Evaluation 2)
As shown in Table 2, the positive electrode active materials obtained in Examples 10 to 16 had an initial discharge capacity of more than 183 mAh / g and had a good initial capacity. In addition, the capacity retention rate after 200 cycles was also about 90% or more, and had excellent cycle characteristics. In addition, the maximum exothermic peak height is 4 cal / sec / g or less, and the calorific value is largely suppressed as compared with the conventional positive electrode active material (comparative example 6) not containing niobium, and the cycle characteristics are also improved. Was shown.

Examples 10, 11 and 13 use anhydrous lithium hydroxide having a low moisture content, and compared with Example 12 using lithium hydroxide monohydrate, the initial discharge capacity, cycle characteristics and maximum heat generation are higher An improvement in peak height was observed. It is considered that this is because the use of anhydrous lithium hydroxide having a low water content makes it easy for the firing to proceed, and the reactivity between lithium and the nickel-containing hydroxide and niobium is increased. In Example 14, since the addition amount of niobium is small, the initial discharge capacity is high, but the maximum exothermic peak height is slightly high.

Moreover, when the cross section of the positive electrode active material obtained in Examples 10 to 14 was observed by a transmission electron microscope, in Examples 10 to 14, no hetero phase was recognized, and niobium was solid in the lithium transition gold complex oxide. I was forgiven. Furthermore, when the distribution of niobium of the positive electrode active material obtained in Examples 10 to 14 is analyzed by EDX analysis, the niobium is uniformly distributed in the positive electrode active material particles, and the Nb concentration in the grain boundaries and in the grains The ratio was confirmed to be less than 3 times.

The cross section of the positive electrode active material obtained in Examples 15 and 16 is observed by a transmission electron microscope, and a different phase having a maximum diameter of more than 200 nm is observed in the grain boundary, and the different phase is a niobium compound by EDX analysis. Was confirmed. Further, in Examples 15 and 16, the initial discharge capacity was slightly lower (about 183 to 187 mAh / g) as compared with the other examples. This is presumably because the use of the nickel-containing oxide in the mixing step lowers the reactivity with the niobium compound, and the niobium compound present in the grain boundaries affects the electrochemical reactivity.

In Comparative Example 7, niobium is coated on the nickel-containing hydroxide, and although the initial discharge capacity is as high as about 197 mAh / g and the maximum exothermic peak height is also low, the sulfate content is increased, and the cycle characteristics are examples. It was inferior compared with. In Comparative Example 8, niobium is added at the time of crystallization, the structure of the nickel-containing hydroxide particles becomes fine, the amount of alkali metals other than lithium and the content of sulfate groups increase, and the crystallite diameter also decreases. The cycle characteristics were inferior to those of Examples. Moreover, compared with Example 10 which used the same raw material except the addition method of niobium, initial stage discharge capacity became low, and the maximum exothermic peak height also became a little high.

The non-aqueous electrolyte secondary battery of the present invention is excellent in safety and has high initial capacity and excellent cycle characteristics, so it is suitable for use as a power source of small portable electronic devices that always require high capacity and long life. It is. In addition, in the power supply for electric vehicles and stationary storage batteries, it is difficult to ensure the safety by increasing the size of the battery, and it is necessary to attach an expensive protection circuit to ensure a higher degree of safety. The lithium-ion secondary battery has excellent safety, which not only makes it easy to ensure the safety of the battery but also simplifies the expensive protection circuit and makes it more inexpensive. It is suitable as a power source for stationary batteries and stationary storage batteries. The electric vehicles include not only electric vehicles that are purely driven by electric energy, but also so-called hybrid vehicles used in combination with combustion engines such as gasoline engines and diesel engines.

1 Lithium metal negative electrode 2 Separator (impregnated with electrolyte)
3 Positive electrode (electrode for evaluation)
4 gasket 5 negative electrode can 6 positive electrode can 7 current collector

Claims (14)

General formula Li _d Ni _1-a-b-c Co _a M _b Nb _c O ₂ (however, 0.03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05 , 0.95 ≦ d 20 1.20, M is at least one element selected from Mn, V, Mg, Ti and Al), and is a lithium transition metal complex oxide composed of particles of a polycrystalline structure A method of manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising:
An aqueous alkaline solution is added to a mixed aqueous solution containing at least nickel and cobalt for crystallization, and a general formula Ni _{1-a'-b '} Co _a' M _{b '} (OH) ₂ (however, 0.03 ≦ a' ≦ 0. 35, 0 ≦ b ′ ≦ 0.10, where M is at least one element selected from Mn, V, Mg, Ti, and Al) a nickel-containing hydroxide
Mixing the nickel-containing hydroxide, the lithium compound, and the niobium compound having an average particle diameter of 0.1 to 10 μm to obtain a lithium mixture, and firing the lithium mixture at 700 to 840 ° C. in an oxidizing atmosphere A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising the step of: calcining the lithium transition metal composite oxide. In the crystallization step, the aqueous alkali solution is added to the mixed aqueous solution containing at least nickel and cobalt for crystallization, and then the obtained crystallized product is coated with M to obtain the nickel-containing hydroxide. The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 1 characterized by these. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the niobium compound is niobic acid or niobium oxide. Before the mixing step, the method includes a heat treatment step of heat treating the nickel-containing hydroxide at a temperature of 105 to 800 ° C., and in the mixing step, the nickel-containing hydroxide and / or nickel-containing oxide obtained by the heat treatment A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, characterized in that a lithium mixture is obtained by mixing a lithium compound, the lithium compound and the niobium compound. . The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the lithium compound is lithium hydroxide. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the lithium hydroxide is anhydrous lithium hydroxide having a moisture content of 5% by mass or less. Before the firing step, the method includes drying the lithium mixture obtained by the mixing step to form lithium hydroxide in the lithium mixture as anhydrous lithium hydroxide having a water content of 5% by mass or less. The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 5. The method according to any one of claims 1 to 7, further comprising a water washing step of slurrying the lithium transition metal complex oxide at a ratio of 100 to 2000 g / L to 1 L of water after the firing step and washing with water. The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries as described in 4. General formula Li _d Ni _1-a-b-c Co _a M _b Nb _c O ₂ (however, 0.03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05 , 0.95 ≦ d 20 1.20, M is at least one element selected from Mn, V, Mg, Ti and Al), and is a lithium transition metal complex oxide composed of particles of a polycrystalline structure A positive electrode active material for a non-aqueous electrolyte secondary battery comprising
The positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the specific surface area of the positive electrode active material is 0.9 to 4.0 m ² / g and the content of alkali metals other than lithium is 20 mass ppm or less . 10. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 9, wherein a crystallite diameter of the positive electrode active material is 10 to 180 nm. 11. The positive electrode active for a non-aqueous electrolyte secondary battery according to claim 9, wherein the maximum diameter of the niobium compound observed by EDX measurement of a transmission electron microscope is 200 nm or less in particles of the positive electrode active material. material. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 9 to 11, wherein a sulfate group content of the positive electrode active material is 0.2 mass% or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 9 to 12, wherein the positive electrode active material has a porous structure. A non-aqueous electrolyte secondary battery comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 9 to 13 as a positive electrode.

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