JP7001081B2 - A method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery, and a method for manufacturing a non-aqueous electrolyte secondary battery. - Google Patents

Description

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

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density. As such a secondary battery, there is a lithium ion secondary battery. Lithium metal, lithium alloy, metal oxide, carbon or the like is used as the negative electrode material of the lithium ion secondary battery. These materials are materials capable of desorbing and inserting lithium.

Currently, research and development of such lithium-ion secondary batteries is being actively carried out. Among these, the lithium ion secondary battery using the lithium transition metal composite oxide, particularly the lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, as the positive electrode material is high because a high voltage of 4V class can be obtained. It is expected and put into practical use as a battery with energy density. In the lithium ion secondary battery using this lithium cobalt composite oxide (LiCoO ₂ ), many developments have been made to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.

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

Recently, there are increasing expectations for the application of lithium-ion secondary batteries not only as small secondary batteries for portable electronic devices but also as large secondary batteries for power storage and electric vehicles. .. 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 great ripple effect in a wide range of fields, and is expected to have a large ripple effect on the positive-sided active material for the lithium-ion secondary battery. Examples of the newly proposed materials include lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, and lithium nickel composite oxide (LiNi O ₂ ) using nickel. can.

Lithium-manganese composite oxide (LiMn ₂ O ₄ ) is a promising alternative to lithium cobalt composite oxide (LiCoO ₂ ) because it is inexpensive as a raw material and has excellent thermal stability, especially safety against ignition. However, since the theoretical capacity is only about half that of the lithium cobalt composite oxide (LiCoO ₂ ), it has the disadvantage that it is difficult to meet the increasing demand for higher capacity lithium ion secondary batteries. Further, at 45 ° C. or higher, there is a drawback that self-discharge is severe and the charge / discharge life is shortened.

On the other hand, the lithium nickel composite oxide (LiNiO ₂ ) has almost the same theoretical capacity as the lithium cobalt composite oxide (LiCoO ₂ ), and exhibits a slightly lower battery voltage than the lithium cobalt composite oxide. For this reason, decomposition due to oxidation of the electrolytic solution is less likely to be a problem, and higher capacity can be expected, so that development is being actively carried out. However, when a lithium ion secondary battery is manufactured using a lithium nickel composite oxide composed purely of nickel without replacing nickel with another element as a positive electrode active material, the cycle is higher than that of the lithium cobalt composite oxide. The characteristics are inferior. It also has the disadvantage that the battery performance is relatively easily impaired when used or stored in a high temperature environment. Further, if it is left in a high temperature environment in a fully charged state, it has a drawback that oxygen is released from a lower temperature than that of a cobalt-based composite oxide.

In order to solve these drawbacks, it has been considered to add niobium, which is an element more expensive than nickel, to the lithium nickel composite oxide. For example, in Patent Document 1, for the purpose of improving the thermal stability of a lithium ion secondary battery at the time of internal short circuit, Li _a Ni _{1-x-y-z Co x} My Nb _{z Ob} (however, M). Is one or more elements composed of Mn, Fe and Al, 1.0 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0 It is composed of particles having a composition composed of at least two kinds of compounds composed of lithium, nickel, cobalt, element M, niobium and oxygen represented by 0.05, 2 ≦ b ≦ 2.2), and the particles are substantially spheres. It has a substantially spherical shell layer having a shape and containing at least one kind of compound having a niobium concentration higher than the above composition in the vicinity of or inside the surface thereof, and the positive potential is within the range of 2 V to 1.5 V at the time of initial discharge. When the discharge capacity of α [mAh / g] is shown and the half-value width of the (003) plane of the layered crystal structure in the X-ray diffraction is β [deg], α and β are 80 ≦ α ≦ 150 and 0, respectively. A positive electrode active material for a non-aqueous secondary battery that simultaneously satisfies the condition of 15 ≦ β ≦ 0.20 has been proposed.

Further, in Patent Document 2, for the purpose of improving the thermal stability and increasing the charge / discharge capacity, Li _{1 + z} Ni _{1-xy Co x} Nby O ₂ (0.10 ≦ x ≦ 0.21, 0.01 ≤ y ≤ 0.08, -0.05 ≤ z ≤ 0.10), and the peak intensity of the L line of Nb is the peak intensity of the L line of _Nb and Ni in the measurement by the energy dispersion method. A positive electrode active material for a non-aqueous electrolyte secondary battery has been proposed in which the standard deviation of the intensity ratio I _Nb / I _Ni when I _Ni is within 1/2 of the average value of the intensity ratio In _Nb / I _Ni . ..

Further, in Patent Document 3, for the purpose of having a large capacity and improving the thermal stability during charging, the composition formula Li _x Ni _a Mn _b Co _c M1 _d M2 _e O ₂ (however, M1 is At least one element selected from the group consisting of Al, Ti and Mg, M2 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, 0.02≤e ≤0.06, a + b + c + d + e = 1.0), and a positive electrode active material has been proposed.

On the other hand, in Patent Document 4, in order to achieve both charge / discharge capacity and safety and suppress deterioration of cycle characteristics, Li _x Ni _{(1-y-z-a) Coy} Mn _z M _a O ₂ (M is Fe). , V, Cr, Ti, Mg, Al, Ca, Nb and Zr represent at least one element selected from the group, x, y and z are 1.0 ≦ x ≦ 1.10 and 0, respectively. A substance (A is Ti, Sn, Mg) on the surface of the lithium composite oxide represented by (4 ≦ y + z ≦ 0.7, 0.2 ≦ z ≦ 0.5, 0 ≦ a ≦ 0.02). , Zr, Al, Nb and Zn) have been coated with a compound composed of at least one element selected from the group), and a positive electrode active material for a non-aqueous electrolytic solution secondary battery has been proposed.

In Patent Document 5, in order to obtain excellent thermal stability and high charge / discharge capacity, Li _{1 + z} Ni _{1-xy Co x} My O ₂ (x, y, z in the formula is 0.10 ≦ x ≦). Satisfying the requirements of 0.21, 0.015 ≤ y ≤ 0.08, -0.05 ≤ z ≤ 0.10, M is from Al, Mn, Nb or Mo, which has better affinity for oxygen than nickel. A positive electrode active material for a secondary battery for a non-aqueous electrolyte, which is composed of at least two selected elements and is impregnated or adhered with two types of M represented by (with an average valence of more than 3), has been proposed.
The proposals disclosed in Patent Documents 1 to 5 are all aimed at achieving both thermal stability and charge / discharge capacity, but when the amount of niobium added is small, the charge / discharge capacity is large, but sufficient heat is obtained. Stability could not be obtained, and if the amount of niobium added was large, the thermal stability was good, but there was a problem that the charge / discharge capacity could not be secured. There is also a problem that it is difficult to secure excellent cycle characteristics.

Recently, the demand for higher capacity for small secondary batteries such as portable electronic devices has been increasing year by year, and sacrificing capacity to ensure safety has the advantage of high capacity of lithium nickel composite oxide. You will lose. In addition, there is a growing movement to use lithium-ion secondary batteries for large secondary batteries, and there are high expectations for them as power sources for hybrid vehicles and electric vehicles, or stationary storage batteries for power storage. Further, these batteries are also required to have a long life, and it is important to have excellent cycle characteristics. In such applications, solving the problem of lithium-nickel composite oxide, which is inferior in safety, and achieving both safety and high capacity and long life are major issues.

Japanese Unexamined Patent Publication No. 2002-151071 Japanese Unexamined Patent Publication No. 2006-147500 Japanese Unexamined Patent Publication No. 2012-014887 Japanese Unexamined Patent Publication No. 2008-153017 Japanese Unexamined Patent Publication No. 2008-181839

In view of the above problems, the present invention uses a positive electrode active material for a non-aqueous electrolytic solution secondary battery capable of achieving both thermal stability, charge / discharge capacity, and cycle characteristics at a high level, and the positive electrode active material. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having excellent safety, high capacity and excellent cycle characteristics.
Furthermore, it is an object of the present invention to provide an industrial method for producing a positive electrode active material for a non-aqueous electrolytic solution secondary battery.

The present inventors diligently studied the addition of niobium to the lithium metal composite oxide in order to improve the thermal stability, and found that the niobium compound having a predetermined particle size was mixed with the lithium compound and the nickel-containing hydroxide. It was found that the positive electrode active material for non-aqueous electrolyte secondary batteries produced by firing can be a positive electrode active material that can uniformly add niobium, has good thermal stability, and has a high charge / discharge capacity. This led to the completion of the present invention.

That is, the method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is the general formula Lid Ni _{1-abc Co a} M _b Nb _c O ₂ (where M is Mn, V, At least one element selected from Ti and Al, 0.03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05, 0.95 ≦ d ≦ 1. 20), which is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is composed of a lithium transition metal composite oxide composed of particles having a polycrystalline structure, and is a mixture containing at least nickel and cobalt. An alkaline aqueous solution is added to the aqueous solution to crystallize it, and the general formula Ni _{1-a'-b'Co a'M b' (} OH) ₂ (where M is at least 1 selected from Mn, V, Mg, Ti and Al. A crystallization step for obtaining a nickel-containing hydroxide represented by 0.03 ≤ a'≤ 0.35, 0 ≤ b'≤ 0.10, which is a seed element, and the obtained nickel-containing water. A mixing step of mixing an oxide, a lithium compound, and a niobium compound having an average particle size 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 to oxidize a lithium transition metal composite. It is characterized by including a firing step of obtaining an object.
The niobium compound is preferably niobate acid or niobium oxide.

Further, it is preferable that the manufacturing step includes a heat treatment step of heat-treating the nickel-containing hydroxide at a temperature of 105 to 800 ° C. before the mixing step. Further, after the firing step, it is preferable to include a water washing step in which the lithium transition metal composite oxide is made into a slurry at a ratio of 100 to 2000 g / L with respect to 1 L of water and washed with water. Further, the lithium transition metal composite oxide preferably has a specific surface area of 0.9 to 3.0 m ² / g. Further, the lithium transition metal composite oxide preferably has a crystallite diameter of 10 to 180 nm.

Further, it is preferable that the lithium transition metal composite oxide has niobium dissolved in it and has an alkali metal content other than lithium of 20% by mass or less.

The method for producing a non-aqueous electrolyte secondary battery of the present invention is to obtain a positive electrode by using the positive electrode active material for a non-aqueous electrolyte secondary battery produced by the above method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. , The positive electrode, the negative electrode, and the non-aqueous electrolyte secondary battery are obtained by using the non-aqueous electrolyte.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention enables high thermal stability, charge / discharge capacity, and excellent cycle characteristics, and by using the active material, high safety is achieved. And a non-aqueous electrolyte secondary battery with battery capacity and excellent cycle characteristics can be obtained. Therefore, the non-aqueous electrolyte secondary battery according to the present invention satisfies the recent demands for high capacity and long life for small secondary batteries such as portable electronic devices, and is a storage battery for hybrid vehicles, electric vehicles, or stationary storage batteries. It is suitable as a power source used for a large secondary battery for electric vehicles.
Further, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery is easy and suitable for production on an industrial scale, and is extremely useful industrially.

Cross-sectional view of the coin battery used for battery evaluation

1. 1. Method for Producing Positive Active Material for Non-Aqueous Electrolyte Secondary Battery The method for producing positive electrode active material for non-aqueous electrolyte secondary battery, which is composed of the lithium transition metal composite oxide of the present invention, is (A) a mixed aqueous solution containing at least nickel and cobalt. A crystallization step of adding an alkaline aqueous solution to the mixture to obtain a nickel-containing hydroxide represented by a specific general formula, (B) mixing a niobium compound, a nickel-containing hydroxide and a lithium compound to prepare a lithium mixture. It includes a mixing step of obtaining, and (C) a firing step of firing the lithium mixture at 700 to 840 ° C. in an oxidizing atmosphere. Hereinafter, each process will be described in detail.

(A) Crystallization step The crystallization step is a general formula Ni _{1-a'-b'Co a'M b' (} OH) ₂ (where M is at least 1 selected from Mn, V, Mg, Ti and Al. It is an additive element of the seed, and is represented by 0.03 ≤ a'≤ 0.35, 0 ≤ b'≤ 0.10), and is a nickel-containing hydroxide composed of secondary particles composed of primary particles. To get.

The a'indicating the cobalt content is 0.03 ≤ a'≤ 0.35, preferably 0.05 ≤ a'≤ 0.35, and 0.07 ≤ a'≤ 0.20. It is more preferable that there is, and it is further preferable that 0.10 ≦ a ′ ≦ 0.20.
Further, in order to exhibit excellent cycle characteristics, it is preferable that 0 <b'≤ 0.10, which is a range in which not only Ni and Co but also M are always included, and 0.01 ≤ b'≤ 0. It is more preferably .07.

As a method for obtaining a nickel-containing hydroxide, the following production method is preferable.
For example, an alkaline solution is added to a mixed aqueous solution containing at least nickel and cobalt in the reaction vessel to prepare a reaction aqueous solution, and the pH of the reaction aqueous solution is controlled by stirring at a constant rate to control the pH of the reaction aqueous solution. The hydroxide is co-precipitated and crystallized so as to have an atomic ratio. Here, as the mixed aqueous solution, a sulfate solution, a nitrate solution, or a chloride solution can be used. Further, as the alkaline solution, for example, sodium hydroxide, potassium hydroxide and the like can be used.

For the pH range in the co-precipitation, when no complexing agent is used, pH = 10 to 11 is selected, and the temperature of the mixed aqueous solution is in the range of more than 60 ° C and 80 ° C or less. In the case of no complexing agent, when crystallized at a pH exceeding 11, fine particles are formed, the filterability is deteriorated, and spherical particles cannot be obtained. Further, when the pH is smaller than 10, the rate of hydroxylation formation becomes significantly slow, Ni remains in the filtrate, the amount of Ni precipitate deviates from the target composition, and the desired ratio of mixed hydroxide cannot be obtained. It ends up. Therefore, by setting the pH to 10 to 11 and keeping the temperature of the mixed aqueous solution above 60 ° C., the phenomenon that the amount of Ni precipitation deviates from the target composition and does not coprecipitate is caused by raising the reaction temperature and increasing the solubility of Ni. It is avoided by raising it. At this time, if the temperature of the mixed aqueous solution exceeds 80 ° C., the slurry concentration becomes high due to the large amount of water evaporation, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate, resulting in an impurity concentration. It is not preferable because there is a problem that the charge / discharge capacity of the positive electrode material is lowered, such as an increase in the amount of water.

On the other hand, when an ammonium ion feeder such as ammonia is used as a complexing agent in addition to the reaction aqueous solution, the solubility of Ni increases, so that the pH range is pH 10 to 12.5 and the temperature range is 50 ° C to 80 ° C. Can be expanded. In the reaction vessel, the ammonia concentration in the reaction aqueous solution is preferably kept constant within the range of 3 to 25 g / L in order not to cause the following problems. First, ammonia acts as a complexing agent, and if the ammonia concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, so plate-shaped hydroxide primary with a uniform shape and particle size. Since particles are not formed and gel-like nuclei are likely to be formed, the particle size distribution is likely to spread. On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of the metal ions becomes too large, the amount of the metal ions remaining in the reaction aqueous solution increases, and the composition shifts. Further, when the ammonia concentration fluctuates, the solubility of the metal ion fluctuates and uniform hydroxide particles are not formed. Therefore, it is preferable to keep the value constant. For example, the ammonia concentration is preferably maintained at a desired concentration with the upper and lower limits set to about 5 g / L. The ammonium ion feeder is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used.

Then, after the steady state is reached, the precipitate is collected, filtered and washed with water to obtain a nickel-containing hydroxide. Alternatively, a mixed aqueous solution and an alkaline solution, and in some cases, an aqueous solution containing an ammonium ion feeder are continuously supplied and overflowed from the reaction vessel to collect a precipitate, which is then filtered and washed with water to obtain a nickel-containing hydroxide. You can also.

The nickel-containing hydroxide after crystallization is preferably washed thoroughly with water in order to reduce the residual amount of impurities, particularly alkali metals such as sodium.

The method for blending at least one additive element selected from M = Mn, V, Mg, Ti and Al (hereinafter, also referred to as “additive element M”) with the nickel-containing hydroxide is particularly limited. Instead, a conventionally known method can be used, but from the viewpoint of increasing the productivity of the crystallization step, an aqueous solution containing the additive element M is added to the above-mentioned mixed aqueous solution containing nickel and cobalt, and a nickel-containing hydroxide (addition) is added. A method of co-precipitating (including element M) is preferable.
As the aqueous solution containing the additive element M, for example, aluminum sulfate, sodium aluminate, titanium sulfate, ammonium peroxotitanium, titanium potassium oxalate, manganese sulfate, magnesium sulfate, magnesium chloride, vanadium sulfate, ammonium vanadate and the like are used. Can be done.
The metal element M is at least one element selected from Mn, V, Mg, Ti and Al, and may be arbitrarily added in order to improve thermal stability, storage characteristics, battery characteristics and the like. can.

Further, in order to optimize the crystallization conditions and facilitate the control of the composition ratio, a coating step of coating M after adding an alkaline aqueous solution to a mixed aqueous solution containing at least nickel and cobalt may be provided. good.
The coating method is not particularly limited, and conventionally known methods can be used. For example, 1) an alkaline aqueous solution is added to a mixed aqueous solution containing nickel and cobalt (however, the additive element M is excluded) to crystallize the mixture. A method of coating the nickel-containing hydroxide with the additive element M, or 2) a mixed aqueous solution containing nickel, cobalt and a part of the additive element M is prepared, and the nickel-containing hydroxide (including the additive element M) is prepared. Then, the co-precipitate is coated with the additive element M to adjust the content of M.

(A)'Heat treatment step The mixing step is a step of mixing a niobium compound, a nickel-containing hydroxide and a lithium compound to obtain a lithium mixture, but in the production method of the present invention, before mixing with the lithium compound, For example, a heat treatment step for heat-treating the nickel-containing hydroxide can be provided, and the heat-treated nickel-containing hydroxide may be mixed with the lithium compound. Further, a compound containing the element M may be added in this step.

By the heat treatment step, the water content contained in the nickel-containing hydroxide can be removed, and the water content remaining in the nickel-containing hydroxide until the firing step can be reduced. The ratio of the number of atoms (Me) of metals other than lithium to the number of atoms of lithium (Li) (Li) in the positive electrode active material produced by sufficiently removing the water remaining in the nickel-containing hydroxide. / Me) can be prevented from fluctuating. It should be noted that it is not always necessary to convert all the composite hydroxides into composite oxides as long as the water can be removed to the extent that the Li / Me of the positive electrode active material does not vary. However, in order to further reduce the variation in Li / Me, it is preferable to convert the composite hydroxide in the nickel-containing hydroxide to the composite oxide. In the heat treatment step, the temperature may be such that residual water in the nickel-containing hydroxide is removed, and the temperature is preferably 105 to 800 ° C. For example, residual water can be removed by heating the composite hydroxide to 105 ° C. or higher. If the temperature is lower than 105 ° C, it takes a long time to remove the residual water, which is not industrially suitable. If the temperature exceeds 800 ° C., the particles converted into the composite oxide may be sintered and aggregated. When converting the composite hydroxide to the composite oxide, it is preferable to heat it at a temperature of 350 to 800 ° C.

The atmosphere in which the heat treatment is performed is not particularly limited, and it is preferable to perform the heat treatment in an air stream that can be easily performed. The heat treatment time is not particularly limited, but if it is less than 1 hour, the residual water in the composite hydroxide may not be sufficiently removed. Therefore, it is preferably at least 1 hour or more, and more preferably 5 to 15 hours. 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 dryer and an electric furnace that does not generate gas can be preferably used.

(B) Mixing Step In the mixing step, the nickel-containing hydroxide obtained in the crystallization step or the heat-treated nickel-containing hydroxide is mixed with the lithium compound and the niobium compound.
Conventionally, when Nb is blended with an active material, generally, niobium is added to the nickel-containing hydroxide by a wet coprecipitation / coating method such as coating or spray drying, and then fired with a lithium compound. Has been used. However, in the coating method such as wet co-precipitation / coating or spray drying, impurities derived from the solution that dissolves Nb (for example, KOH solution, oxalic acid solution, etc.) and the solution that adjusts the pH at the time of coating (for example, sulfuric acid, hydrochloric acid, nitrate) Etc.) Derived impurities will remain together with the coated Nb. In particular, alkali metals such as potassium and sodium contained in the solution adversely affect the battery capacity and cycle characteristics, and therefore need to be sufficiently reduced.

The present invention is characterized in that, in the mixing step of mixing the nickel-containing hydroxide and the lithium compound, the niobium compound is mixed and solid-phase added. The solid phase addition of Nb is a process having a low load and excellent productivity, which does not require a chemical solution or the like, as compared with the method of coprecipitating and coating Nb in a wet process. In addition, when coprecipitating and coating Nb in the wet process, it is necessary to control the pH, and in some cases it may not be possible to add the desired form and amount of Nb, which is an advantage from the viewpoint of quality stability. be. Further, if Nb is added in a solid phase, an alkali metal other than lithium (hereinafter, simply referred to as an alkali metal) entrapped in the lithium transition metal composite oxide, particularly potassium or sodium, etc., depends on the Nb compound to be added. The amount of impurities can be reduced.

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

On the other hand, when washing with water after firing as described later, Li / Me is reduced by washing with water. Therefore, when washing with water, it is preferable to mix the nickel-containing hydroxide and the lithium compound in anticipation of a decrease in Li / Me. The decrease in Li / Me varies depending on the firing conditions and washing conditions, but it is about 0.05 to 0.1, and the decrease can be confirmed by producing a small amount of positive electrode active material as a preliminary test. .. The lithium compound is not particularly limited, but for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferable in that it is easily available. In particular, considering the ease of handling and the stability of quality, it is more preferable to use lithium hydroxide.

Since the content of niobium does not change before and after the firing step, a niobium compound corresponding to the amount of niobium added to the positive electrode active material is added. Since the reactivity changes depending on the particle size in solid phase addition, the particle size of the niobium compound to be added is one of the important factors, and the average particle size of the niobium compound is 0.1 to 10 μm, preferably 0. .5 to 8 μm. If the average particle size is smaller than 0.1 μm, there is a problem that it becomes very difficult to handle the powder. If the average particle size is larger than 10 μm, the reactivity at the time of firing is lowered and the powder is into the lithium transition metal composite oxide. This is because there is a problem that the diffusion of Nb is insufficient and thermal stability cannot be ensured. It is considered that the obtained lithium transition metal composite oxide has a porous structure by solid-phase addition of the niobium compound having the above particle size. That is, although the details are unknown, the nickel-containing hydroxide obtained by crystallization is a secondary particle formed by agglomeration of primary particles, and when niob is diffused from the surface of the secondary particle and reacts, it is primary. Since the velocity is not uniform among the particles, it is presumed that the shrinkage of the primary particles becomes non-uniform and fine voids are generated.

As the niobium compound, niobium acid, niobium oxide, niobium nitrate, niobium pentachloride, niobium nitrate and the like can be used. Among these, niobium acid or niobium oxide is preferable from the viewpoint of easy availability and avoiding contamination of calcined lithium transition metal composite oxides with impurities that cause deterioration of thermal stability, capacity, and cycle characteristics.
In order to obtain a niobium compound having the above average particle size range, the niobium compound as a raw material can be pulverized using various pulverizers such as a ball mill, a planetary ball mill, a jet mill, a bead mill, and a pin mill. If necessary, the product may be classified by a dry classifier or a sieve.
The particle size of the nickel-containing hydroxide used in the mixing step is preferably about 5 to 20 μm, more preferably 10 to 15 μm.
The average particle size is a value measured by a laser scattering diffraction method as a volume reference average diameter (MV).

It is preferable that the lithium mixture is sufficiently mixed before firing. If the mixing is not sufficient, Li / Me may vary among the individual particles, and problems such as insufficient battery characteristics may occur. In addition, a general mixer can be used for mixing, for example, a shaker mixer, a Ladyge mixer, a Julia mixer, a V blender, or the like can be used, and the skeleton of nickel-containing hydroxide or the like is not destroyed. It suffices to sufficiently mix the nickel-containing hydroxide, the lithium compound, and the niobium compound.

(C) Firing step In the calcining step, the lithium mixture obtained in the mixing step is calcined in an oxidizing atmosphere at 700 to 840 ° C., preferably 700 to 830 ° C., more preferably 700 to 800 ° C. to have a polycrystalline structure. This is a step of forming a lithium transition metal composite oxide composed of particles. When the lithium mixture is calcined in the calcining step, niobium in the niobium compound is diffused together with lithium in the lithium compound in the nickel-containing hydroxide, so that a lithium transition metal composite oxide is formed. If the calcination temperature is less than 700 ° C., lithium and niob are not sufficiently diffused into the nickel-containing hydroxide, excess lithium and unreacted particles remain, and the crystal structure is not sufficiently arranged. Therefore, there arises a problem that sufficient battery characteristics cannot be obtained. Further, when the firing temperature exceeds 840 ° C., severe sintering occurs between the formed lithium transition metal composite oxide particles, and abnormal grain growth may occur. When abnormal grain growth occurs, the particles after firing may become coarse and the particle morphology may not be maintained, and when the positive electrode active material is formed, the specific surface area decreases and the resistance of the positive electrode increases. The problem of low battery capacity arises.

The firing time is preferably at least 3 hours or more, more preferably 6 to 24 hours. This is because the formation of the lithium transition metal composite oxide may not be sufficiently performed in less than 3 hours. 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, firing is preferably performed in the atmosphere or an oxygen stream. This is because if the oxygen concentration is less than 18% by volume, it cannot be sufficiently oxidized, and the crystallinity of the lithium transition metal composite oxide may be insufficient. In particular, considering the battery characteristics, it is preferable to perform the operation in an oxygen stream.

In the firing step, before firing at a temperature of 700 to 840 ° C., it is preferable to perform calcining at a temperature lower than the firing temperature at which the lithium compound and the nickel-containing hydroxide can react. By holding the lithium mixture at such a temperature, lithium and niobium are sufficiently diffused into the nickel-containing hydroxide, and a uniform lithium transition metal composite oxide can be obtained. For example, when lithium hydroxide is used, it is preferable to hold it at a temperature of 400 to 550 ° C., which is higher than the melting point of lithium hydroxide, for about 1 to 10 hours for calcining.

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

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

(D) Water washing step The water washing step is a step of washing the lithium transition metal composite oxide with water. Further, it is preferable to wash with water, then filter and dry.
The lithium transition metal composite oxide obtained by the above firing step is used as a positive electrode active material as it is, but by removing excess lithium on the particle surface, the surface area that can be contacted with the electrolytic solution is increased and filled. Since the discharge capacity can be improved, it is preferable to wash with water after firing. Further, since the fragile portion formed on the particle surface is sufficiently removed, the contact with the electrolytic solution is increased and the charge / discharge capacity can be improved.

Further, since the surplus lithium causes a side reaction in the non-aqueous secondary battery and causes the battery to expand due to gas generation, it is preferable to wash it with water from the viewpoint of improving safety.

As the slurry concentration at the time of washing with water, the amount (g) of the lithium transition metal composite oxide with respect to 1 L of water contained in the slurry is preferably 100 to 2000 g / L. That is, the higher the slurry concentration, the larger the amount of powder, and if it exceeds 2000 g / L, not only is it difficult to stir because the viscosity is very high, but also because the alkali in the liquid is high, the dissolution rate of the deposits is due to equilibrium. Even if it slows down or peels off, it becomes difficult to separate it from the powder. On the other hand, when the slurry concentration is less than 100 g / L, the amount of lithium elution is large because it is too dilute, and the amount of lithium on the surface is small. Not only does it easily collapse, but the high-pH aqueous solution absorbs the carbon dioxide gas in the atmosphere and reprecipitates lithium carbonate.

The water used is not particularly limited, and pure water is preferable. By using pure water, it is possible to prevent deterioration of battery performance due to adhesion of impurities to the positive electrode active material.
It is preferable that the amount of water adhering to the particle surface during the solid-liquid separation of the slurry is small. When the amount of adhering water is large, the lithium dissolved in the liquid is reprecipitated, and the amount of lithium present on the surface of the lithium transition metal composite oxide particles after drying increases.

Further, the washing step preferably includes a step of filtering and drying after washing with water.
As the filtration method, a commonly used method may be used, and for example, a suction filter, a filter place, a centrifuge or the like can be used.
The drying temperature after filtration is not particularly limited, and is preferably 80 to 350 ° C. If the temperature is lower than 80 ° C., the drying of the positive electrode active material after washing with water is delayed, so that a gradient of lithium concentration occurs between the surface of the particles and the inside of the particles, which may deteriorate the battery characteristics. On the other hand, near the surface of the positive electrode active material, it is expected that the ratio is very close to the stoichiometric ratio, or that lithium is slightly desorbed and the state is close to the state of charge. There is a risk that the crystal structure close to that of the battery will collapse, leading to deterioration of battery characteristics.

2. 2. Positive Active Material for Non-Aqueous Electrolyte Secondary Battery The positive positive active material for non-aqueous electrolyte secondary battery according to the present invention is the general formula Lid Ni _{1-abc Co a} M _b Nb _c O ₂ (provided that 0). .03 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05, 0.95 ≦ d ≦ 1.20, M is selected from Mn, V, Mg, Ti and Al. It is composed of a lithium transition metal composite oxide composed of particles having a polycrystalline structure, has a porous structure, and has a specific surface area of 0.8 to 3.0 m ² / g. It is characterized by having an alkali metal content other than lithium of 20 mass ppm or less.

The a indicating the cobalt content is 0.03 ≦ a ≦ 0.35, preferably 0.05 ≦.
a ≦ 0.35, more preferably 0.07 ≦ a ≦ 0.20, still more preferably 0.10 ≦ a ≦ 0.20. Cobalt is an additive element that contributes to the improvement of cycle characteristics, but if the value of a is less than 0.03, sufficient cycle characteristics cannot be obtained and the capacity retention rate also decreases. Further, when the value of a exceeds 0.35, the decrease in the initial discharge capacity becomes large.

The c indicating the amount of niobium added is 0.001 ≦ c ≦ 0.05, preferably 0.001 ≦ c ≦ 0.02. Niobium is an additive element that is thought to contribute to the suppression of the thermal decomposition reaction due to deoxidation of the lithium transition metal composite oxide and is effective in improving safety. If the value of c is less than 0.001, the amount added is too small and the improvement in safety is insufficient. On the other hand, the safety is improved according to the addition amount, but the crystallinity tends to decrease, so that the charge / discharge capacity decreases when the value of c exceeds 0.05. In addition, the cycle characteristics are also reduced. Further, within the above range, when the value of c is 0.005 or more, the thermal stability of the obtained positive electrode active material becomes better. On the other hand, if the value of c is 0.01 or less within the above range, the charge / discharge capacity of the obtained positive electrode active material becomes larger.
The existence form of niob may be either solid solution in the lithium transition metal composite oxide or present as a lithium niobium composite oxide on the grain boundaries or the particle surface of the lithium transition metal composite oxide, but is solid. It is preferably melted. Here, the solid solution means a state in which niobium compounds are hardly detected by EDX measurement with a transmission electron microscope.

Further, in the case of solid solution, the ratio of the grain boundary to the Nb concentration in the grain is preferably 4 times or less, and more preferably 3 times or less. The ratio of the grain boundary to the Nb concentration in the grain (grain boundary / intragrain) can be obtained from the EDX measurement result of the transmission electron microscope. By solid solution, the effect of suppressing the thermal decomposition reaction can be enhanced even if a small amount is added.

The additive element 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, which indicates the amount of M added, exceeds 0.10, the battery characteristics are further improved, but the initial discharge capacity is significantly reduced, which is not preferable. Further, since 0 <b ≦ 0.10 that always contains M as well as Ni and Co can exhibit excellent cycle characteristics, b is preferably in this range, and 0.01 ≦ b. It is more preferable that there is ≦ 0.07.

D indicating Li / Me is 0.95 ≦ d ≦ 1.20. When the value of d is less than 0.95, the charge / discharge capacity decreases. On the other hand, the charge / discharge capacity increases as the value of d increases, but if d exceeds 1.20, the safety deteriorates.

The lithium transition composite metal oxide is characterized by having an alkali metal content other than lithium of 20% by mass or less, preferably 10% by mass or less. When the content of the alkali metal other than lithium is 20% by mass or less and c indicating the addition amount of niobium is 0.001 ≦ c ≦ 0.05, excellent cycle characteristics can be obtained. Even if either the content of an alkali metal other than lithium or the amount of niobium added exceeds the above range, good cycle characteristics cannot be obtained.

The positive electrode active material is made of a lithium transition metal composite oxide composed of particles having a polycrystalline structure and has a porous structure.
In the present specification, the porous structure means that the distance between any two points on the outer edge of the void is 0.3 μm by observing the positive electrode active material particles on an arbitrary cross section (observation surface) of a scanning electron microscope (magnification of 5000 times). The above-mentioned plurality of voids are present in the cross section of the positive electrode active material particles.

Further, the maximum length of the void is preferably 50% or less, more preferably 40% or less of the cross-sectional major axis of the particle by observing the cross section of the scanning electron microscope, and it is preferable that the void is present at least at the grain boundary. By having the above-mentioned porous structure, the particle surface that can come into contact with the electrolytic solution when used for the positive electrode of the battery is greatly increased, and the decrease in charge / discharge capacity due to the addition of niobium is compensated for to ensure safety. However, a sufficient charge / discharge capacity can be obtained.

Further, the number of the voids in the cross-sectional observation is obtained for any 20 or more particles, and the total number of voids is divided by the total particle cross-sectional major axis (μm) of the particles to obtain an index (hereinafter, “”. The number of voids (also referred to as)) is preferably 0.2 to 10 / μm, and more preferably 0.5 to 3 / μm. Here, the particle cross-sectional major axis is the maximum distance between any two points on the outer circumference of the particle on the observation surface of the particle. Further, in the cross-sectional observation, particles having a particle size of 20% or less of the volume standard average diameter (MV) of the positive electrode active material in the subsequent stage are excluded from the judgment of the porous structure. This is because particles having a particle size of 20% or less of the average particle size are small in quantity in the positive electrode active material and have little effect on the charge / discharge capacity, and the observation surface is a cross section of the particle end, which is an evaluation of the particles. Because it may not be suitable. When the number of voids is 0.2 to 10 / μm, excessive contact with the electrolytic solution is suppressed and deterioration of thermal stability is suppressed, and a high charge / discharge capacity is obtained with a sufficient contact area. Can be done.

The specific surface area of the positive electrode active material is 0.9 to 3.0 m ² / g, preferably 0.9 to 2.8 m ² / g. When the specific surface area is less than 0.8 m ² / g, the number of particle surfaces that can come into contact with the electrolytic solution is reduced, and a sufficient charge / discharge capacity cannot be obtained. On the other hand, if the specific surface area exceeds 3.0 m ² / g, the number of particle surfaces that come into contact with the electrolytic solution becomes too large, and the safety is lowered.

The crystallite diameter of the lithium transition metal oxide is preferably 10 to 180 nm, more preferably 10 to 150 nm. If the crystallite diameter is less than 10 nm, the crystal grain boundaries become too large and the resistance of the active material increases, so that a sufficient charge / discharge capacity may not be obtained. On the other hand, when the crystallite diameter exceeds 150 nm, crystal growth proceeds too much, and cation mixing in which nickel is mixed in the lithium layer of the lithium transition metal composite oxide which is a layered compound occurs, and the charge / discharge capacity decreases.

The average particle size of the positive electrode active material is preferably 5 to 20 μm, more preferably 10 to 15 μm, as D50 having a volume integrated 50% diameter measured by a laser scattering method. If it is less than 5 μm, the filling density may decrease when used for the positive electrode of a battery, and a sufficient charge / discharge capacity per volume may not be obtained. On the other hand, if it exceeds 20 μm, a sufficient contact area with the electrolytic solution may not be obtained, and the charge / discharge capacity may decrease.

3. 3. Non-aqueous electrolyte secondary battery An embodiment of the lithium ion secondary battery according to the present invention will be described in detail for each component. The lithium ion secondary battery according to 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 carried out in various modifications and improvements based on the knowledge of those skilled in the art, including the following embodiments. can do. Further, the non-aqueous electrolyte secondary battery of the present invention is not particularly limited in its use.

(1) Positive Electrode A positive electrode mixture forming a positive electrode and each material constituting the same material 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, a solvent for viscosity adjustment, etc. is added, and the mixture is kneaded to form a positive electrode mixture paste. To make. The mixing ratio of each in the positive electrode mixture is also an important factor in determining the performance of the lithium secondary battery.

When the total mass of the 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 conductive material is the same as the positive electrode of a general lithium secondary battery. It is desirable that the content is 1 to 20% by mass and the content of the binder is 1 to 20% by mass.

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

In producing the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, and Ketjen black can be used as the conductive agent. The binder plays a role of binding the active material particles, and for example, a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, a thermoplastic resin such as polypropylene, or polyethylene can be used. If necessary, the positive electrode active material, the conductive material, and the activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(2) Negative electrode For the negative electrode, a negative electrode mixture made into a paste by mixing a binder with a negative electrode active material that can occlude and desorb lithium ions, such as metallic lithium and lithium alloy, and adding an appropriate solvent. , Copper and other metal foils are applied to the surface of a current collector, dried, and if necessary, compressed to increase the electrode density.

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

(3) Separator A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode to retain the electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of minute holes, can be used.

(4) Non-aqueous electrolyte solution The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and moreover, tetrahydrofuran and 2-. One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethyl sulfone and butane sulton, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. is used alone or in combination of two or more. be able to.

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

(5) Shape and configuration of the 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 solution described above, may be various, such as a cylindrical type and a laminated type. be able to.
Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolytic solution. 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 by using a current collector lead or the like. The battery can be completed by sealing the above configuration in a battery case.

(Example 1)
A mixed aqueous solution of nickel sulfate and cobalt sulfate, an aqueous solution of sodium aluminate, a 25 mass% sodium hydroxide solution, and 25 mass so that the molar ratio of nickel: cobalt: aluminum is 81.5: 15.0: 3.5. % Ammonia water was added to the reaction vessel at the same time, the pH was maintained at 11.8 based on the solution temperature of 25 ° C, the reaction temperature was maintained at 50 ° C, and the ammonia concentration was maintained at 10 g / L. Nickel-cobalt-aluminum composite hydroxide was formed. After the inside of the reaction tank becomes stable, the hydroxide slurry is collected from the overflow port, filtered, washed with water, and dried to dry nickel-cobalt-aluminum composite hydroxide (nickel-containing hydroxide: Ni _0.815 Co _0.150 Al ₀ . _.035 (OH) ₂ ) was obtained. (Crystalization process)

Next, the above nickel-cobalt-aluminum composite hydroxide (nickel-containing hydroxide), commercially available lithium hydroxide, and a nano-grinding mill (nano-grinding mill manufactured by Sunlex Industries, Ltd.) have an average particle size of 0.6 μm. After weighing the niobic acid (Nb ₂ O ₅ · xH ₂ O) powder crushed so as to have a Li / Me of 1.10, the skeleton of the nickel-containing hydroxide is maintained. A lithium mixture was obtained by mixing sufficiently with a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)) at a strength. The target niobium addition amount c'was set to 0.01. (Mixing process)

This lithium mixture is inserted into a magnesia baking vessel and heated to 500 ° C. at a heating rate of 2.77 ° C./min in an oxygen stream with a flow rate of 6 L / min using a closed electric furnace at 500 ° C. It was held for 3 hours. Then, the temperature was raised to 780 ° C. at the same heating rate and held for 12 hours, and then the mixture was cooled to room temperature to obtain a lithium transition metal composite oxide. (Baking process)
The obtained lithium transition metal composite oxide was mixed with pure water so that the slurry concentration became 1500 g / L to prepare a slurry, washed with water using a stirrer for 30 minutes, and then filtered. After filtration, the mixture was kept at 210 ° C. for 14 hours using a vacuum dryer and cooled to room temperature to obtain a positive electrode active material. (Washing process)

[Evaluation of positive electrode active material]
Crystal calculated from Scatter's equation using the composition of the positive electrode active material obtained by quantitative analysis by the ICP emission analysis method, the 2θ of the (003) plane and the half-value width in the diffraction pattern obtained by the XRD measurement of the positive electrode active material. Tables show the child diameter, the specific surface area measured by the BET method, the volume-based average diameter (MV) measured by the laser scattering diffraction method, and the number of voids, which are indicators of porosity obtained by observing the particle cross section with an inspection electron microscope. Shown in 1.
The amount of alkali metals other than lithium was measured by atomic absorption spectroscopy and is also shown in Table 1.
When the cross section of the obtained positive electrode active material was observed with a transmission electron microscope, no heterogeneous phase was observed, and by EDX analysis, niobium was uniformly distributed in the positive electrode active material particles, and the crystal grain boundaries and grains were observed. It was confirmed that the Nb concentration ratio in the inside was 3 times or less.

[Evaluation of initial discharge capacity]
The initial volume evaluation of the obtained positive electrode active material was performed as follows. 20% by mass of acetylene black and 10% by mass of PTFE were mixed with 70% by mass of the active material powder, and 150 mg was taken out from this to prepare pellets and used as a positive electrode. Lithium metal was used as the negative electrode, and an equal amount mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) having 1 M of LiClO ₄ as a supporting salt (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used as the electrolytic solution. A 2032 type coin battery as shown in FIG. 2 was manufactured in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C.

The prepared battery was left to stand for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) became stable, the current density with respect to the positive electrode was set to 0.5 mA / cm ² and the battery was charged to a cutoff voltage of 4.3 V to obtain the initial charge capacity. The capacity when discharged to a cutoff voltage of 3.0 V after a one-hour rest was defined as the initial discharge capacity.

[Evaluation of cycle characteristics]
The cycle characteristics were evaluated as follows. For each battery, CC charge to 4.4V at a rate of 1C at a temperature of 25 ° C (charge voltage must be confirmed), pause for 10 minutes, then CC discharge to 3.0V at the same rate and pause for 10 minutes. The charging / discharging cycle was repeated for 200 cycles. The discharge capacities of the 1st cycle and the 200th cycle were measured, and the percentage of the 200th cycle 2C discharge capacity with respect to the 1st cycle 2C discharge capacity was determined as the capacity retention rate (%).

[Evaluation of positive electrode safety]
To evaluate the safety of the positive electrode, a 2032 type coin battery manufactured by the same method as above is charged with CCCV up to a cutoff voltage of 4.5V (constant current-constant voltage charging. First, the charging operates at a constant current. Then, after charging using the two-phase charging process of ending charging at a constant voltage), the positive electrode was taken out by disassembling while being careful not to short-circuit. 3.0 mg of this electrode
Weigh, add 1.3 mg of electrolyte, seal in an aluminum measuring container, and use a differential scanning calorimeter (DSC) PTC-10A (manufactured by Rigaku) at a heating rate of 10 ° C / min from room temperature to 300 ° C. The heat generation behavior was measured up to.
Table 1 shows the evaluation results of the initial capacity, cycle characteristics and safety of the positive electrode active material.
Niobium acid (Nb ₂ O ₅ · xH ₂ O) is also referred to as niobium hydroxide, and niobate is described as niobium hydroxide in Table 1.

(Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the average particle size of niobic acid was 8 μm. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Example 3)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the niobium compound was niobium oxide and the average particle size of the niobium compound was 1 μm. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Example 4)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the target niobium addition amount c'was 0.05. Table 1 shows the evaluation results of the obtained positive electrode active material.
(Example 5)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the target niobium addition amount c'was 0.005. Table 1 shows the evaluation results of the obtained positive electrode active material.
(Example 6)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the target niobium addition amount c'was 0.001. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Example 7)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the firing temperature was 700 ° C. Table 1 shows the evaluation results of the obtained positive electrode active material.

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

(Example 9)
A nickel-cobalt-aluminum composite hydroxide was heat-treated at 700 ° C. for 6 hours to obtain a composite oxide, and then a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that it was mixed with lithium hydroxide and niobic acid. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Comparative Example 1)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the average particle size of niobic acid was 15 μm. When the obtained positive electrode active material was observed with a scanning electron microscope, an unreacted niobium compound was confirmed. Therefore, the positive electrode active material was added to a 100 g / L potassium hydroxide aqueous solution, and the mixture was stirred at 80 ° C. for 10 minutes and not yet. After dissolving the niobium compound in the reaction and filtering to remove the niobium compound, the composition of the positive electrode active material was analyzed in the same manner as in Example 1. The Nb content was below the lower limit of analysis. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Comparative Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the target niobium addition amount c'was 0.07. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Comparative Example 3)
A mixed aqueous solution of nickel sulfate and cobalt sulfate, an aqueous solution of sodium aluminate, a 25 mass% sodium hydroxide solution, and 25 mass so that the molar ratio of nickel: cobalt: aluminum is 81.5: 15.0: 3.5. % Ammonia water was added to the reaction vessel at the same time, the niob compound was not added during the mixing step, and the firing temperature was set to 740 ° C. did. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Comparative Example 4)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the firing temperature was set to 850 ° C. Table 1 shows the evaluation results of the obtained positive electrode active material.

(Comparative Example 5)
A niobium salt solution (30 g / L) prepared by dissolving niobium acid (Nb ₂ O ₅ · xH ₂ O) in caustic potash in a slurry obtained by mixing nickel cobalt aluminum composite hydroxide obtained in the crystallization step with pure water. ) Is added dropwise together with sulfuric acid while adjusting the pH to 10.0 to prepare an Nb-coated nickel-cobalt-aluminum composite hydroxide (hereinafter, also referred to as “Nb-coated nickel hydroxide”) and a mixing step. The positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the niobium compound was not mixed and the Nb-coated nickel hydroxide (Nb amount c'was 0.01) was used. Table 1 shows the evaluation results of the obtained positive electrode active material.

(evaluation)
As shown in Table 1, in Examples 1 to 9 of the present invention, the initial discharge capacity of the obtained positive electrode active material exceeds approximately 185 mAh / g, and it can be seen that the material can be used as the positive electrode active material. The capacity retention rate is also 85% or more, and it can be seen that it has excellent cycle characteristics. In Example 4, since the amount of niobium added is large, the cycle characteristics are slightly lower than those in the other examples.
In addition, the maximum exothermic peak height measured by DSC is 4.0 cal / sec / g or less, and the calorific value is significantly suppressed as compared with the conventional positive electrode active material to which niobium is not added in Comparative Example 3. I understand.
In Comparative Example 1 in which the average particle size of the niobium compound was 15 μm, the reactivity of the niobium compound was low, so that the amount of unreacted niobium compound increased and Nb was not contained in the positive electrode active material. Therefore, the maximum heat generation peak height was as high as 7.1 cal / sec / g, and the thermal stability was not good.
In Comparative Example 2, since the amount of niobium added was as high as 0.07, the initial discharge capacity was significantly reduced to 182.6 mAh / g. The cycle characteristics are also low.
Comparative Example 3 is a conventional positive electrode active material to which niobium is not added, and although the initial discharge capacity is high and the cycle characteristics are excellent, the maximum heat generation peak height is as high as 7.0 cal / sec / g. The thermal stability was not good.
In Comparative Example 4, nickel is mixed in the lithium layer of the lithium transition metal composite oxide, which is a layered compound, due to firing at a high temperature, and cation mixing occurs, and the specific surface area is small, so that the initial discharge capacity is significantly reduced. did. In addition, the maximum heat generation peak height is high.
In Comparative Example 5, since niobium was added by the coating method, the content of the alkali metal as an impurity was high, and therefore the cycle characteristics were lower than those of the examples.

Small portable electronics that always require high capacity and long life in order to take advantage of the non-aqueous electrolyte secondary battery of the present invention, which has excellent safety, high initial capacity, and excellent cycle characteristics. It is suitable for use as a power source for equipment. In addition, in power supplies for electric vehicles and stationary storage batteries, it is indispensable to install an expensive protection circuit to ensure higher safety and difficulty in ensuring safety due to the increase in size of the battery. Since the lithium ion secondary battery of the present invention has excellent safety, not only the safety can be easily ensured, but also the expensive protection circuit can be simplified and the cost can be reduced. It is suitable as a power source for electric vehicles and a stationary storage battery. The power source for an electric vehicle can be used not only as a power source for an electric vehicle driven by purely electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

1 Lithium metal negative electrode 2 Separator (impregnated with electrolyte)
3 Positive electrode (evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector

Claims (8)

General formula Li _d Ni _1-ab-c Co _a M _b Nb _c O ₂ (where M is at least one element selected from Mn, V, Ti and Al, 0.03 ≦ a ≦ 0 .35, 0 ≦ b ≦ 0.10, 0.001 ≦ c ≦ 0.05, 0.95 ≦ d ≦ 1.20), and a lithium transition metal composed of particles having a polycrystalline structure. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery made of a composite oxide.
An alkaline aqueous solution is added to a mixed aqueous solution containing at least nickel and cobalt for crystallization, and the general formula Ni _{1-a'-b'Co a'M b' (} OH) ₂ (where M is Mn, V, Mg, Ti). And Al, which is at least one element and is represented by 0.03 ≤ a'≤ 0.35, 0 ≤ b'≤ 0.10), a crystallization step for obtaining a nickel-containing hydroxide. ,
A mixing step of mixing the obtained nickel-containing hydroxide, a lithium compound, and a niobium compound having an average particle size of 0.1 to 10 μm to obtain a lithium mixture, and firing the lithium mixture in an oxidizing atmosphere at 700 to 840 ° C. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a firing step of obtaining a lithium transition metal composite oxide. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the niobium compound is niobium acid or niobium oxide. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the mixing step includes a heat treatment step of heat-treating the nickel-containing hydroxide at a temperature of 105 to 800 ° C. Production method. The invention according to any one of claims 1 to 3, wherein after the firing step, the lithium transition metal composite oxide is made into a slurry at a ratio of 100 to 2000 g / L with respect to 1 L of water, and the washing step is included. A method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the lithium transition metal composite oxide has a specific surface area of 0.9 to 3.0 m ² / g. Manufacturing method. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the lithium transition metal composite oxide has a crystallite diameter of 10 to 180 nm. The secondary non-aqueous electrolyte according to any one of claims 1 to 6, wherein the lithium transition metal composite oxide has a solid solution of niobium and a content of an alkali metal other than lithium of 20% by mass or less. A method for manufacturing a positive electrode active material for a battery. Obtaining a positive electrode by using the positive electrode active material for a non-aqueous electrolyte secondary battery produced by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7 .
Using the positive electrode, the negative electrode, and the non-aqueous electrolyte to obtain a non-aqueous electrolyte secondary battery,
A method for manufacturing a non-aqueous electrolyte secondary battery.

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