JP2006147500A - Positive electrode active material for non-aqueous electrolyte secondary battery, its manufacturing method, and non-aqueous electrolyte secondary battery using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an hydroxide of nickel, cobalt, and niobium superior in heat stability and having high charge and discharge capacity by means that the hydroxides of nickel, cobalt, and niobium are co-precipitated, and obtain a positive electrode active material for a nonaqueous electrolyte secondary battery superior in heat stability and having high discharge capacity by using the hydroxide as a raw material. <P>SOLUTION: As for the positive electrode material for the nonaqueous electrolyte secondary battery, a complex hydroxide Ni<SB>1-x-y</SB>Co<SB>x</SB>Nb<SB>y</SB>(OH)<SB>2</SB>obtained by adding an alkaline solution to an aqueous mixture solution of an aqueous mixture solution of nickel salt and cobalt salt, and a niobium salt solution under a condition of the temperature of 50°C or more 80°C or less and pH of 10 or more 12.5 or less and co-precipitating the hydroxides of nickel, cobalt, and niobium, and a lithium compound are mixed, and the mixture is heat-treated at the temperature of 650°C or more and 850°C or less, and this is obtained as powders of a lithium metal complex oxide expressed by a general formula Li<SB>1+z</SB>Ni<SB>1-x-y</SB>Co<SB>x</SB>Nb<SB>y</SB>O<SB>2</SB>(wherein 0.10≤x≤0.21, 0.01≤y≤0.08, and -0.05≤z≤0.10). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  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 using the same.

  In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. 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 a negative electrode material for a lithium ion secondary battery. These materials are materials capable of removing and inserting lithium.

Research and development of such lithium ion secondary batteries is being actively conducted. Among these, a lithium ion secondary battery using a lithium metal composite oxide, in particular, a lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, as a positive electrode material can obtain a high voltage of 4 V, and thus has high energy. It is expected as a battery having a high density and is being put to practical use. In the lithium ion secondary battery using this lithium cobalt composite oxide (LiCoO ₂ ), many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. ing.
However, since lithium cobalt complex oxide (LiCoO ₂ ) uses a rare and expensive cobalt compound as a raw material, it causes an increase in battery cost. For this reason, it is desired to use materials other than lithium cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material.

In addition, recently, not only small secondary batteries for portable electronic devices but also expectations for applying lithium ion secondary batteries as large-sized secondary batteries for power storage and electric vehicles are increasing. . For this reason, 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. The positive electrode active material for lithium ion secondary batteries As newly proposed materials, lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, and lithium nickel composite oxide (LiNiO ₂ ) using nickel can be cited. it can.

Lithium-manganese composite oxide (LiMn ₂ O ₄ ) is a powerful alternative to lithium-cobalt composite oxide (LiCoO ₂ ) because it is inexpensive and has excellent thermal stability, in particular, safety with respect to ignition. Although it can be said that 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. Further, at 45 ° C. or higher, there is a drawback that self-discharge is intense and the charge / 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 shows a slightly lower battery voltage than lithium cobalt composite oxide. For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance. However, when a lithium-ion secondary battery is made using a lithium-nickel composite oxide composed solely of nickel as a positive electrode active material without replacing nickel with other elements, the cycle is higher than that of lithium-cobalt composite oxide. The characteristics are inferior. In addition, there is a disadvantage that battery performance is relatively easily lost when used or stored in a high temperature environment.

In order to solve such drawbacks, for example, in Patent Document 1, Li _w Ni _x Co _y B _z O _{2 is} used as a positive electrode active material capable of maintaining good battery performance during storage and use in a high temperature environment. Lithium nickel composite oxide represented by (0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, x + y + z = 1), that is, boron is added. Lithium-containing composite oxides have been proposed.

In Patent Document 2, in order to improve the self-discharge characteristics and cycle characteristics of the lithium ion secondary _{battery, Li x Ni a Co b M} c O 2 (0.8 ≦ x ≦ 1.2,0. 01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al, V, Mn, Fe, Cu and A lithium nickel composite oxide represented by at least one element selected from Zn has been proposed.

  However, in the lithium nickel composite oxide obtained by the above-described conventional manufacturing method, both the charge capacity and discharge capacity are higher and the cycle characteristics are improved as compared with the lithium cobalt composite oxide. If left in the environment, there is a problem that oxygen is released from a temperature lower than that of the cobalt-based composite oxide.

In order to solve such a problem, for example, in Patent Document 3, Li _{a Mb} Ni _c Co _d O _e (M is Al) for the purpose of improving the thermal stability of the positive electrode material of the lithium ion secondary battery. , Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, and at least one metal selected from the group consisting of 0 <a <1.3, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1) has been proposed. In this case, for example, when aluminum is selected as the additive element M, it is confirmed that if the amount of substitution from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved. However, replacing nickel with aluminum, which is effective to ensure sufficient stability, reduces the amount of nickel that contributes to the oxidation-reduction reaction associated with the charge / discharge reaction, so the initial capacity, which is the most important for battery performance, is large. It had the problem of decreasing. Since Al is trivalent and stable, Ni is also matched to charge, and if it is stabilized with trivalent, a portion that does not contribute to the Redox reaction is generated, and it is considered that the capacity decreases.

In Patent Document 4, the general formula ^{_{Li a Ni 1-b-c}} M 1 b M 2 c O 2 ( however, 0.95 ≦ a ≦ 1.05,0.01 ≦ b ≦ 0.10,0. 10 ≦ c ≦ 0.20, M ¹ is an element composed of at least one of Al, B, Y, Ce, Ti, Sn, V, Nb, W, and Mo, and M ² is Co, Mn, and Fe the lithium-containing composite oxide represented by one or more elements) selected, first, using a reaction vessel, to which the salt concentration is adjusted nickel - cobalt -M ² salt solution, complexing to form an aqueous solution and complex The nickel-cobalt-M ² complex salt is formed by continuously supplying each of the agent and the alkali metal hydroxide, and then the complex salt is decomposed with the alkali metal hydroxide to form the nickel-cobalt-M ² hydroxide. Precipitate and circulate the formation and decomposition of the complex salt in the tank. Repeatedly, nickel - taken by bar flow - cobalt -M ² hydroxides Oh. A mixture of nickel-cobalt-M ¹ -M ² having a substantially spherical particle shape is obtained by mixing the resulting hydroxide and an oxide such as Nb ₂ O ₅ and wet-pulverizing the mixture, followed by spray drying. It is described that the lithium salt is mixed and calcined.

  According to the above method, by reducing the conductivity of the active material, it is possible to prevent the short-circuit current when the battery is short-circuited from passing through the active material particles, and the active material itself is thermally decomposed by the Joule heating of the short-circuit current. It is described that the thermal stability is improved.

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, a movement to use a lithium ion secondary battery for a large-sized secondary battery is also prominent. In particular, there is a great expectation as a power source for a hybrid vehicle and an electric vehicle. When used as a power source for automobiles, solving the problem of the lithium nickel composite oxide that is inferior in safety is a big problem.
JP-A-8-45509 Japanese Patent Laid-Open No. 8-213015 Japanese Patent Laid-Open No. 5-242891 JP 2000-323143 A

  The present invention has been made in view of such a problem, and niobium as the additive element M is preferable for improving the thermal stability in a charged state, and a mixed aqueous solution of nickel salt and cobalt salt and a niobium salt solution are preferable. Then, an alkaline solution is added to coprecipitate a uniform nickel, cobalt and niobium hydroxide, and the resulting positive electrode active material for a nonaqueous electrolyte secondary battery is used as the positive electrode of the nonaqueous electrolyte secondary battery. An object of the present invention is to provide a positive electrode active material having good thermal stability and high charge / discharge capacity when used.

Inventors have general formula _{Li 1 + Z Ni 1-x} -y Co x M y O 2 ( where, 0.10 ≦ x ≦ 0.21,0.01 ≦ y ≦ 0.08, -0.05 ≦ z As a result of intensive studies on the powder of lithium-metal composite oxide represented by ≦ 0.10), niobium as the additive element M is preferable for improving the thermal stability in the charged state, and in particular, uniform nickel-cobalt. -It discovered that it was necessary to use a niobium salt solution from the point of producing niobium hydroxide. Composite hydroxide obtained by co-precipitation of uniform nickel, cobalt and niobium hydroxide by adding alkaline solution to nickel salt and cobalt salt mixed aqueous solution and niobium salt solution prepared in desired composition ratio Positive electrode active for non-aqueous electrolyte secondary battery obtained by mixing Ni _1-xy Co _x Nb _y (OH) ₂ and a lithium compound and heat-treating the mixture at a temperature of 650 ° C. or higher and 850 ° C. or lower. It has been found that the substance becomes a positive electrode active material having good thermal stability and high charge / discharge capacity, and the present invention has been completed.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, a lithium metal composite oxide _{Li 1 + Z Ni 1-x} -y Co x Nb y O 2 ( where, 0.10 ≦ x ≦ 0. 21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10), a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a nickel salt and a cobalt salt A composite obtained by adding an alkaline solution to a mixed aqueous solution and a niobium salt solution, and co-precipitating nickel, cobalt and niobium hydroxide under the conditions of 50 to 80 ° C. and pH of 10 to 12.5 Hydroxide Ni _1-xy Co _x Nb _y (OH) ₂ and a lithium compound are mixed, and the mixture is heat-treated at a temperature of 650 ° C. or higher and 850 ° C. or lower.

  According to another method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, the niobium salt solution is a niobium caustic potash aqueous solution or a niobium hydrochloric acid solution, The lithium compound is lithium carbonate, lithium hydroxide, or a hydrate thereof.

Moreover, the positive electrode active material for nonaqueous electrolyte secondary batteries according to the present invention is a lithium metal composite oxide Li _{1 + Z} Ni _1-x obtained by the method for producing a positive electrode active material for nonaqueous electrolyte secondary batteries described above. _-Y Co _x Nb _y O ₂ (where 0.10 ≤ x ≤ 0.21, 0.01 ≤ y ≤ 0.08, -0.05 ≤ z ≤ 0.10) In addition, the other positive electrode active material for non-aqueous electrolyte secondary battery according to the present invention is the result of measuring the positive electrode active material for non-aqueous electrolyte secondary battery by an energy dispersion method. In any case, the standard deviation of the intensity ratio I _Nb / I _Ni is the intensity ratio when the peak intensity of the _Nb L-line is I _Nb and the peak intensity of the Ni L-line is I _Ni. It is within 1/2 of the average value of I _Nb / _{I Ni,} always, the composition formula _{i 1 + Z Ni 1-x} -y Co x Nb y O 2 ( where, 0.10 ≦ x ≦ 0.21,0.01 ≦ y ≦ 0.08, -0.05 ≦ z ≦ 0.10) satisfy It is characterized by this.

  The non-aqueous electrolyte secondary battery according to the present invention is characterized in that the positive electrode active material for a non-aqueous electrolyte secondary battery described above is used for a positive electrode.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a general formula Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10), the powder comprising a mixed aqueous solution of nickel salt and cobalt salt, and niobium caustic potash as a niobium salt solution. A composite hydroxide Ni _1-xy Co _x obtained by coprecipitation of nickel, cobalt and niobium hydroxide by adding an alkaline solution to these mixed solutions using an aqueous solution or niobium hydrochloric acid solution A positive electrode active material for a non-aqueous electrolyte secondary battery obtained by mixing Nb _y (OH) ₂ and a lithium compound and heat-treating the mixture at a temperature of 650 ° C. or higher and 850 ° C. or lower. Niobium to Ni By substituting, a part of Ni is stabilized from trivalent to divalent, so that it is possible to prevent a decrease in the initial capacity of the battery due to the replacement of nickel with another element. Further, by replacing with niobium having strong oxidizing power, when used as a positive electrode of a lithium ion battery, the thermal stability of the battery can be improved without deteriorating the battery capacity.

  By using the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, a large capacity for a hybrid vehicle and an electric vehicle can be satisfied. A non-aqueous electrolyte secondary battery capable of ensuring the safety required as a power source used for the secondary battery can be obtained and is industrially useful.

  The charge / discharge reaction of the secondary battery according to the present invention proceeds by reversibly entering and exiting lithium ions in the positive electrode active material. The positive electrode active material from which lithium has been extracted by charging is unstable at high temperatures, and when heated, the active material decomposes and releases oxygen, which causes combustion of the electrolyte and an exothermic reaction. To improve the thermal stability of the positive electrode material means to suppress the decomposition reaction of the positive electrode active material from which lithium has been extracted. As a method for suppressing the decomposition reaction of the positive electrode active material disclosed heretofore, it has been generally performed that a part of nickel is substituted with an element having strong covalent bond with oxygen such as aluminum. Certainly, if the amount of substitution from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved, but the amount of nickel contributing to the redox reaction accompanying the charge / discharge reaction is reduced. In order to reduce the charge / discharge capacity, the amount of substitution with aluminum had to be limited to a certain extent. As a result, a sufficient reversible capacity could not be obtained when sufficient thermal stability was ensured, and thermal stability had to be sacrificed in order to obtain a certain level of capacity.

Therefore, in order to solve the above problems, the general formula _{Li 1 + Z Ni 1-x} -y Co x M y O 2 ( where, 0.10 ≦ x ≦ 0.21,0.01 ≦ y ≦ 0.08, - 0.05 ≦ z ≦ 0.10), and by replacing the additive element M with pentavalent and stable niobium, a part of Ni can be changed from trivalent. It is possible to stably reduce the initial capacity of the battery due to divalent and stable replacement of nickel with another element, and in particular to improve thermal stability in a charged state.

In the present invention, the general formula Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ The lithium nickel cobalt niobium composite oxide having a layered structure represented by 0.10) is first composed of nickel salt and cobalt salt so that the atomic ratio of cobalt, nickel and niobium is the atomic ratio of the above general formula. Add alkaline solution to mixed aqueous solution and niobium salt solution, stir them at a constant speed, and co-precipitate in reaction tank so that atomic ratio of cobalt, nickel and niobium is the atomic ratio of the above general formula Let After the steady state is reached, the precipitate is collected, filtered and washed with water to obtain nickel cobalt niobium composite hydroxide. Thereafter, this is mixed with a lithium compound and subjected to a heat treatment to obtain a lithium nickel cobalt niobium composite oxide useful as a positive electrode active material for a lithium ion secondary battery in a desired ratio.

  Next, embodiments 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 those of a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolyte. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention is implemented in various modifications and improvements based on the knowledge of those skilled in the art, including the following embodiment. can do. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.

(1) Positive electrode active material, positive electrode The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a general formula Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ (where 0.10 ≦ x ≦ 0 .21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10).
In the present invention, a composite aqueous solution of nickel salt and cobalt salt and a niobium caustic potash aqueous solution or niobium-dissolved hydrochloric acid as a niobium salt solution are prepared, and simultaneously added together with an alkaline aqueous solution so that the three elements are uniformly dispersed. It is characterized by getting things. In order to prepare a mixed aqueous solution of nickel salt, cobalt salt and niobium salt, ortho niobate (M ₃ NbO ₄ : M is monovalent), meta niobate (MNbO ₃ : M is divalent) ) Is used in order to obtain a niobium salt solution, the oxidation proceeds during hydrolysis or dissolution, and niobium hydroxide or insoluble niobium oxide may be generated or hardly dissolved.
Even when niobium metal is added to a hydrofluoric acid / sulfuric acid mixed solution to obtain a mixed solution, niobium oxide or niobium hydroxide will precipitate if the nickel salt and cobalt salt are mixed first. Then, even if an alkaline aqueous solution is added thereafter, a uniform hydroxide coprecipitate cannot be obtained, and even if a lithium nickel cobalt niobium compound is synthesized using this, niobium segregation occurs.
Therefore, it is industrially necessary to use a niobium salt solution having high solubility in water as the niobium salt to be used. In the present invention, the above-mentioned niobium salt dissolved in caustic potash aqueous solution or hydrochloric acid is preferable because it is stable in the solution, but it is necessary to prepare it separately from the composite aqueous solution of nickel salt and cobalt salt and add it together with the alkaline aqueous solution. By performing this operation, a composite hydroxide in which the three elements are uniformly dispersed is obtained.

Next, the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries which concerns on this invention is demonstrated.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is prepared by adding an alkaline solution to a mixed aqueous solution of nickel salt and cobalt salt and an aqueous niobium salt solution and stirring them at a constant speed. Coprecipitation is performed so that the atomic ratio of cobalt, nickel, and niobium is the atomic ratio of the above general formula. After reaching a steady state, the precipitate is collected, filtered and washed with water to obtain nickel cobalt niobium composite hydroxide. Thereafter, nickel cobalt niobium composite hydroxide obtained by coprecipitation of nickel, cobalt and niobium hydroxide and a lithium compound are mixed, and the mixture is heat-treated at a temperature of 650 ° C. or higher and 850 ° C. or lower. is required.

As the niobium salt solution, it is preferable to use an aqueous solution in which niobium hydroxide, niobium metal and niobium pentachloride are dissolved in a caustic potash aqueous solution or a solution in which niobium hydroxide and niobium pentachloride are dissolved in hydrochloric acid. Unlike the conventional method, the niobium salt solution is added separately because niobium segregation may occur because a neutralization reaction occurs partly when niobium caustic potash aqueous solution and other sulfuric acid mixed aqueous solution are mixed first. is there.
The reaction conditions vary depending on the presence or absence of the use of a complexing agent, but the mixed aqueous solution of nickel salt and cobalt salt and the mixed aqueous solution of niobium salt have a pH of 10 to 12.5 in the temperature range of more than 50 ° C. and 80 ° C. or less. It is preferable to add an alkali solution to cause coprecipitation so that the above range is satisfied.

  As for the pH region, when there is no complexing agent, pH = 10 to 11 is selected, and the temperature of the mixed aqueous solution is over 60 ° C. and 80 ° C. or less. In the case of no complexing agent, when crystallization is performed at pH 11 to 13, fine particles are formed, filterability is deteriorated, and spherical particles cannot be obtained. On the other hand, if the pH is less than 10, the rate of hydroxide formation is remarkably slow, Ni remains in the filtrate, and the amount of precipitation of Ni deviates from the target composition, making it impossible to obtain a mixed hydroxide of the target ratio. End up. Therefore, by adjusting the pH to 10 to 11 and keeping the temperature of the mixed aqueous solution above 60 ° C., the reaction temperature is increased by increasing the reaction temperature to prevent the Ni precipitation amount from deviating from the target composition and causing coprecipitation. This is avoided by increasing the solubility of. At this time, if the temperature of the mixed aqueous solution exceeds 80 ° C., the slurry concentration becomes high due to a large amount of water evaporation, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration A problem that the charge / discharge capacity of the positive electrode material decreases, such as an increase in the positive electrode material, is not preferable. On the other hand, in the case of using a complexing agent such as ammonia, the solubility of Ni increases, so that the pH range can be expanded to pH 10 to 12.5 and the temperature range can be expanded to 50 ° C. to 80 ° C.

  As the lithium compound, lithium carbonate, lithium hydroxide, and hydrates thereof are preferable. Nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide, etc. can be used as the nickel compound, and oxides, carbonates, etc. can be used as the compound related to the additive element. It is more preferable to use an oxide or a complex oxide.

Stirring at a constant speed under predetermined conditions, and after the inside of the reaction vessel has reached a steady state, the overflowed precipitate is collected, filtered and washed to obtain nickel cobalt niobium composite hydroxide particles. Yes.
By this method, nickel cobalt niobium composite hydroxide particles can be obtained in which the atomic ratio of nickel, cobalt, and niobium is uniformly mixed to a desired ratio. The metal composite hydroxide is preferably composed of spherical secondary particles in which a plurality of primary particles of 1 μm or less are aggregated, and good particles with good filterability and good handleability can be obtained.

  The positive electrode active material of the present invention is prepared by mixing a predetermined amount of a lithium compound and the above nickel cobalt niobium composite hydroxide, and firing in an oxygen stream at a temperature of about 650 ° C. to 850 ° C. for about 10 to 20 hours. Can be synthesized. When the firing temperature is lower than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium nickel composite oxide having a desired layered structure. Further, when the temperature exceeds 850 ° C., Ni is mixed into the Li layer, Li is mixed into the Ni layer, and the layered structure is disturbed, and the site occupancy of metal ions other than lithium at the 3a site becomes larger than 2%. Since the mixing rate of metal ions at the 3a site, which is the site, is increased, the lithium ion diffusion path is hindered, and a battery using the positive electrode is not preferable because the initial capacity and output are reduced.

  Moreover, d50 of the particle size distribution of the obtained positive electrode active material is preferably 4.5 to 8.1 μm, and the tap density is preferably 1.2 to 1.76 g / ml. If it is out of the above range, it becomes unsuitable as a positive electrode material, for example, the positive electrode active material cannot be sufficiently filled when producing the positive electrode.

Next, the positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described.
General formula Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ (however, 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10) For example, the positive electrode using the lithium metal composite oxide represented by (2) is produced as follows.

  A powdered positive electrode active material, a conductive material, and a binder are mixed, and activated carbon and a target solvent such as viscosity adjustment are added as necessary, and these are kneaded to prepare a positive electrode mixture paste. The respective mixing ratios in the positive electrode mixture are also important factors that determine 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, respectively, as in the case of 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, for example, aluminum foil, and dried to scatter the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, 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 used for battery production. However, the manufacturing method of the positive electrode is not limited to the above-described examples, and may depend on other methods.

In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluororubber, styrene butadiene, cellulose resin, polyacrylic acid, and the like can be used.
The binder plays a role of holding the active material particles, and for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, and thermoplastic resins such as polypropylene and polyethylene can be used. If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that 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. Moreover, 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, metallic lithium, lithium alloy, or the like, and a negative electrode mixture made by mixing a binder with a negative electrode active material capable of occluding and desorbing lithium ions and adding an appropriate solvent to form a paste. In addition, it is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.
As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride can be used as in the case of the positive electrode, and the active material and the solvent for dispersing the binder include N-methyl-2-pyrrolidone. Organic solvents can be used.

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

(4) Non-aqueous electrolyte The non-aqueous electrolyte 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, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture 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 , or a composite salt thereof can be used.
Furthermore, the non-aqueous electrolyte 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 composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above is various, such as a cylindrical type and a laminated type. be able to.
In any case, 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 electrolyte. The positive electrode current collector and the positive electrode terminal communicating with the outside, and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like. The battery having the above structure can be sealed in a battery case to complete the battery.
[Example]

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the preferred drawings. Table 1 summarizes the composition of Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ synthesized in each Example and Comparative Example and the evaluation results.

  Prepare a mixed solution of nickel sulfate and cobalt sulfate and a niobium caustic potash aqueous solution so that the molar ratio of nickel: cobalt: niobium is 80: 15: 5, and simultaneously add 12.5% sodium hydroxide solution to the reaction vessel Then, the pH was kept in the range of 10 to 11 and the reaction temperature was kept in the range of 50 to 80 ° C., and nickel cobalt niobium composite hydroxide particles were formed by the coprecipitation method. Thereafter, the entire amount of hydroxide slurry in the reaction vessel was recovered, filtered, washed with water and dried to obtain a dry powder of nickel cobalt niobium composite hydroxide. This metal composite hydroxide is composed of spherical secondary particles in which a plurality of primary particles of 1 μm or less are aggregated.

  After weighing the nickel cobalt niobium composite hydroxide and commercially available lithium carbonate (manufactured by FMC) so that the atomic ratio of nickel cobalt niobium and lithium is 1: 1.05, the shape of spherical secondary particles is The mixture was sufficiently mixed using a shaker mixer apparatus (TURBULA Type T2C manufactured by WAB Co., Ltd.) at such a strength as to be maintained. 20 g of this mixture was inserted into a 5 cm × 12 cm × 3 cm magnesia firing vessel, and heated to 730 ° C. at a heating rate of 5 ° C./min in an oxygen stream with a flow rate of 3 L / min using a closed electric furnace. The mixture was baked for 10 hours and then cooled to room temperature.

The obtained fired product was analyzed by X-ray diffraction. As shown in FIG. 1, the fired product had a hexagonal layered structure that did not contain a heterogeneous phase, and a chemical analysis method (for Ni, Co, and Nb, an ICP emission analyzer) (OPTIMA 3300DV manufactured by PERKINELMER) and Li were analyzed by atomic absorption analysis (analyzed by VARIAN, Spectr AA-40 atomic absorption method). The composition formula (Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 It was found to be a positive electrode active material that becomes O ₂ ). The particle size distribution d50 measured by Microtrac was 6.6 μm, and the tap density was 0.93 g / ml.
Moreover, about the positive electrode active material which consists of this metal complex oxide, the dispersion | variation in a composition was judged by the energy dispersion method using the energy dispersion measuring apparatus (EDX apparatus FALCON by EDAX). The measurement was carried out by placing the composite oxide on a conductive double-sided tape on a sample stage with a thickness of several particles, applying a vacuum, checking the image with an SEM, setting a measurement target, and measuring.
The measurement conditions were a voltage of 15 kV, a current of 10 ⁻⁹ to 10 ⁻¹⁰ A, an electron beam diameter of 3 to 5 nm, and an extraction angle of 20 °. In this measurement, information on a thickness of several μm is picked up by a part of the composite oxide particles. In the above measurement, the average value and standard deviation of n = 10 measurements of the intensity ratio I _Nb / I _Ni when the peak intensity of Nb K-line is I _Nb and the peak intensity of Ni L-line is I _Ni. Judged by.
As a result of measuring at n = 10, the positive electrode active material made of this metal composite oxide and the positive electrode active material made of this metal composite oxide were measured by the energy dispersion method. Even when measured, the average value of the intensity ratio I _Nb / I _Ni when the peak intensity of the Nb L line is I _Nb and the peak intensity of the Ni L line is I _Ni is 0.173, The standard deviation was 0.044, which always satisfied the composition formula Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 O ₂ .
The above measurement method was also used in other examples and comparative examples.

The initial capacity evaluation of the obtained positive electrode active material was performed as follows. 70% by mass of the active material powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg was taken out from this to produce a pellet to obtain a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (made by Toyama Pharmaceutical Co., Ltd.) using 1M LiClO ₄ as a supporting salt was used as the electrolyte. A 2032 type coin battery as shown in FIG. 1 was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The prepared battery is left for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) is stabilized, the current density with respect 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 the battery was discharged to a cutoff voltage of 3.0 V after a one hour rest was defined as the initial discharge capacity.

The safety evaluation of the positive electrode is performed by CCCV charging (constant current-constant voltage charging. First, charging is operated at a constant current) to a cutoff voltage of 4.5V using a 2032 type coin battery manufactured by the same method as described above. Then, the charging method using a charging process of two phases of ending charging at a constant voltage.), And then disassembling with care not to short-circuit, and taking out the positive electrode. 3.0 mg of this electrode was measured, 1.3 mg of the electrolyte was added, sealed in an aluminum measurement container, and a temperature increase rate of 10 ° C./degree using a differential scanning calorimeter (DSC) PTC-10A (manufactured by Rigaku). The heat generation behavior was measured from room temperature to 400 ° C. in min.
Table 1 shows the elemental analysis values of the obtained lithium nickel cobalt niobium composite oxide, the initial discharge capacity obtained by battery evaluation, and the heat generation rate obtained by DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 78: 15: 7 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material having a hexagonal layered structure containing no heterophase (Li _1.05 Ni _0.78 Co _0.15 Nb _0.07 O ₂ ). The particle size distribution d50 measured by Microtrac was 6.1 μm, and the tap density was 0.85 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.242, a standard deviation is 0.088, always compositional formula Li _{1 .05} Ni _0.78 Co _0.15 Nb _0.07 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 80: 15: 5 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 800 ° C. and baking for 10 hours, the furnace was cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material (Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 having a hexagonal layer structure not containing a heterogeneous phase) O ₂ ). D50 of the particle size distribution measured by Microtrac was 4.3 μm, and the tap density was 1.07 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.162, a standard deviation is 0.041, always compositional formula Li _{1 .05} Ni _0.80 Co _0.15 Nb _0.05 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 80: 15: 5 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. The temperature was raised to 650 ° C., baked for 10 hours, and then cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material (Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 having a hexagonal layer structure not containing a heterogeneous phase) O ₂ ). D50 of the particle size distribution measured by Microtrac was 3.2 μm, and the tap density was 1.56 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.178, a standard deviation is 0.051, always compositional formula Li _{1 .05} Ni _0.80 Co _0.15 Nb _0.05 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 84: 15: 1 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature.
When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material (Li _1.05 Ni _0.84 Co _0.15 Nb _0.01 having a hexagonal layer structure not containing a heterogeneous phase) was obtained. O ₂ ). D50 of the particle size distribution measured by Microtrac was 6.1 μm, and the tap density was 1.56 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the peak intensity of the L line of the Ni is the average value of the intensity ratio _{I Nb} / _{I Ni} is 0.035 when the _{I Ni,} the standard deviation is 0.010, always compositional formula Li _{1 .05} Ni _0.84 Co _0.15 Nb _0.01 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium is 75: 21: 4 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature.
When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material (Li _1.05 Ni _0.75 Co _0.21 Nb _0.04 having a hexagonal layer structure not containing a heterogeneous phase) was obtained. O ₂ ). D50 of the particle size distribution measured by Microtrac was 5.3 μm, and the tap density was 0.89 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.185, a standard deviation is 0.047, always compositional formula Li _{1 .05} Ni _0.75 Co _0.21 Nb _0.04 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 85: 10: 5 was prepared by the same method as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 730 ° C. and baking for 10 hours, the furnace was cooled to room temperature.
When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material (Li _1.05 Ni _0.85 Co _0.10 Nb _0.05 having a hexagonal layer structure not containing a heterogeneous phase) O ₂ ). D50 of the particle size distribution measured by Microtrac was 7.2 μm, and the tap density was 1.00 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, an average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.162, the standard deviation is 0.040, always composition formula Li _1.05 Ni _0.85 Co _0.10 Nb _0.05 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

A mixed solution of nickel sulfate and cobalt sulfate and a niobium hydrochloric acid solution were prepared so that the molar ratio of nickel: cobalt: niobium was 80: 15: 5, and the metal composite hydroxide was prepared in the same manner as in Example 1. Prepared. This was mixed in the same manner as in Example 1 so that the molar ratio of lithium to metal was 1.05: 1, and using an enclosed electric furnace, in an oxygen stream at a flow rate of 3 L / min at 500 ° C. for 2 hours. After calcination, the temperature was raised to 730 ° C. at a temperature rising rate of 5 ° C./min, baked for 10 hours, and then cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material (Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 having a hexagonal layer structure not containing a heterogeneous phase) O ₂ ). D50 of the particle size distribution measured by Microtrac was 3.3 μm, and the tap density was 0.90 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, an average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.182, the standard deviation is 0.062, always composition formula Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 O ₂ was satisfied.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 1]

12. A mixed solution in which niobium metal is added to a mixed solution of nickel sulfate, cobalt sulfate, hydrofluoric acid, and sulfuric acid is simultaneously mixed so that the molar ratio of nickel: cobalt: niobium is 80: 15: 5. 5% sodium hydroxide solution is added to the reaction vessel, the pH is kept in the range of 10-11, the reaction temperature is kept constant in the range of 60-80 ° C, and nickel cobalt niobium composite hydroxide particles are formed by coprecipitation method I let you. The obtained metal composite hydroxide was prepared in the same manner as in Example 1, and this was mixed in the same manner as in Example 1 so that the molar ratio of lithium to metal was 1.05: 1. After calcining at 500 ° C. for 2 hours in an oxygen stream with a flow rate of 3 L / min using an electric furnace, the temperature was raised to 730 ° C. at a heating rate of 5 ° C./min, calcined for 10 hours, and then cooled to room temperature. did.
When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material having a hexagonal layered structure (Li _1.03 Ni _0.84 Co _0.16 O ₂ ) and lithium niobate ( Li ₈ Nb ₂ O ₉ ). D50 of the particle size distribution measured by Microtrac was 9.6 μm, and the tap density was 1.32 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.171, the standard deviation is 0.110, the positive electrode active material (Li _{1 0.03} Ni _0.84 Co _0.16 O ₂ ) and lithium niobate (Li ₈ Nb ₂ O ₉ ), which shows a large composition variation.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 2]

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 75:15:10 was prepared by the same method as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. And a calcining rate of 5 ° C./min after calcining at 500 ° C. for 2 hours in an oxygen stream with a flow rate of 3 L / min. Was heated to 730 ° C., baked for 10 hours, and then cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.75 Co _0.16 Nb _0.10 O ₂ ) was used. there were. The particle size distribution d50 measured by Microtrac was 2.2 μm, and the tap density was 0.80 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.764, the standard deviation is 0.480, the big composition variation Recognize.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 3]

A mixed solution of nickel sulfate and cobalt sulfate and a 12.5% sodium hydroxide solution were simultaneously added to the reaction vessel so that the molar ratio of nickel: cobalt was 81:19, and the pH was in the range of 10-11, reaction temperature. Is kept constant in the range of 60 ° C. to 80 ° C., nickel cobalt niobium composite hydroxide particles are formed by a coprecipitation method, and the metal composite hydroxide is obtained in the same manner as in Example 1 and lithium. The mixture was mixed so that the molar ratio with the metal was 1.05: 1, and calcined at 500 ° C. for 2 hours in an oxygen stream with a flow rate of 3 L / min using a sealed electric furnace. The temperature was raised to 730 ° C. for min and baked for 10 hours, followed by furnace cooling to room temperature.
When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, it was a positive electrode active material (Li _1.05 Ni _0.81 Co _0.19 O ₂ ) having a hexagonal layered structure. D50 of the particle size distribution measured by Microtrac was 9.0 μm, and the tap density was 1.54 g / ml.
Since the positive electrode active material made of this metal composite oxide did not contain niobium, measurement by the energy dispersion method was not performed.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 4]

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 80: 15: 5 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. The mixture was mixed so that the molar ratio thereof was 1.05: 1, and calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours using a sealed electric furnace. The temperature was raised to 900 ° C. for min, baked for 10 hours, and then cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, a positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.80 Co _0.15 Nb _0.05 O ₂ ) was obtained. there were. D50 of the particle size distribution measured by Microtrac was 7.3 μm, and the tap density was 1.62 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the average value of the intensity ratio _{I Nb} / _{I Ni} when the _I Nb, the peak intensity of the L line of Ni and _{I Ni} is 0.210, a standard deviation was 0.089.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 5]

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 80: 15: 5 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. Were mixed at a molar ratio of 1.05: 1, calcined in an oxygen stream at a flow rate of 3 L / min for 2 hours at 500 ° C. for 2 hours, and then heated at a rate of 5 ° C./min. After heating up to 600 ° C. and baking for 10 hours, the furnace was cooled to room temperature.
When the obtained fired product was analyzed by X-ray diffraction and chemical analysis, a positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.83 Co _0.12 Nb _0.05 O ₂ ) and It was a mixture of nickel oxide NiO. D50 of the particle size distribution measured by Microtrac was 3.2 μm, and the tap density was 1.31 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the _I Nb, the average value of the intensity ratio _{I Nb} / _{I Ni} when the peak intensity of the L line of Ni was _{I Ni} is 0.183, the standard deviation is 0.072, the positive electrode active material (Li _{1 .05} Ni _0.83 Co _0.12 Nb _0.05 O ₂ ) and nickel oxide NiO, the composition variation is relatively large.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 6]

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 73: 22: 5 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. And a calcining rate of 5 ° C./min after calcining at 500 ° C. for 2 hours in an oxygen stream with a flow rate of 3 L / min. Was heated to 730 ° C., baked for 10 hours, and then cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.73 Co _0.22 Nb _0.05 O ₂ ) was used. there were. The d50 of the particle size distribution measured with Microtrac was 4.3 μm, and the tap density was 0.83 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the average value of the intensity ratio _{I Nb} / _{I Ni} when the _I Nb, the peak intensity of the L line of Ni and _{I Ni} is 0.211, a standard deviation was 0.056.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.
[Comparative Example 7]

A metal composite hydroxide in which the molar ratio of nickel: cobalt: niobium was 86: 9: 5 was prepared in the same manner as in Example 1, and this was performed in the same manner as in Example 1 with lithium and metal. And a calcining rate of 5 ° C./min after calcining at 500 ° C. for 2 hours in an oxygen stream with a flow rate of 3 L / min. Was heated to 730 ° C., baked for 10 hours, and then cooled to room temperature.
The obtained fired product was analyzed by X-ray diffraction and chemical analysis. As a result, the positive electrode active material having a hexagonal layered structure (Li _1.05 Ni _0.86 Co _0.09 Nb _0.05 O ₂ ) was used. there were. D50 of the particle size distribution measured by Microtrac was 6.1 μm, and the tap density was 1.05 g / ml.
The positive electrode active material comprising this metal composite oxide was measured by the energy dispersion method in the same manner as in Example 1. As a result, the peak intensity of the Nb L-line was measured regardless of the range of the metal composite oxide. the average value of the intensity ratio _{I Nb} / _{I Ni} when the _I Nb, the peak intensity of the L line of Ni and _{I Ni} is 0.143, a standard deviation was 0.062.
The initial capacity evaluation of the obtained positive electrode active material was performed in the same manner as in Example 1. Table 1 shows the obtained initial discharge capacity and the heat generation rate of the positive electrode obtained from the DSC measurement.

［評価］

[Evaluation]

As shown in Table 1, since the lithium nickel cobalt niobium composite oxides obtained in Examples 1 to 8 were uniformly dissolved in niobium, the initial discharge capacity exceeded 180 (mAh / g), and lithium cobalt It can be seen that this is a material that can be used as a new battery material to replace the composite oxide (LiCoO ₂ ).
The present inventors have confirmed that there is no practical problem with safety as an actual battery if the calorific value is 11.00 mJ / sec / g or less in the safety evaluation using DSC, The positive electrode active materials shown in Examples 1 to 7 have a small calorific value of 11.00 mJ / sec / g or less, indicating that the material is highly safe.

On the other hand, the lithium nickel cobalt niobium composite oxide obtained in Comparative Example 1 uses a mixed solution in which niobium metal is added to a hydrofluoric acid and sulfuric acid mixed solution as a niobium salt solution, and uses nickel sulfate, cobalt sulfate, and hydrogen fluoride. Since a mixed solution in which niobium metal was added to an acid and sulfuric acid mixed solution was mixed at the same time, a uniform coprecipitate was not obtained, and the positive electrode active material synthesized using this was analyzed by X-ray diffraction. However, it is a mixture of a positive electrode active material (Li _1.05 Ni _0.85 Co _0.15 O ₂ ) having a hexagonal layered structure and lithium niobate (Li ₈ Nb ₂ O ₉ ), and niobium segregates. You can see that It can be seen that the standard deviation is large even in the intensity ratio I _Nb / I _Ni by the energy dispersion method, and the composition variation is large. Therefore, it can be seen that the initial discharge capacity is 180 (mAh / g) or less, which is an undesirable material as a battery material. In addition, the initial discharge capacity is low and the calorific value exceeds 11.00 mJ / sec / g, indicating that the material is not desirable in terms of safety.

Comparative Example 2 is an example in which the molar ratio of nickel: cobalt: niobium was 75:15:10. Although the amount of niobium is large and safety is not a problem, the initial discharge capacity is low, and the voltage is lower than that of lithium cobalt composite oxide (LiCoO ₂ ). It can be seen that the standard deviation is large even in the intensity ratio I _Nb / I _Ni by the energy dispersion method, and the composition variation is large.
Moreover, although the comparative example 3 is an example which did not substitute with niobium, since the emitted-heat amount exceeds 11.00 mJ / sec / g, there exists a safety problem.
Comparative Examples 6 and 7 are cases where the amount of cobalt is outside the range of the present invention, and the initial discharge capacity is low.

  Comparative Example 4 is a case where the firing temperature was too high at 900 ° C., the initial discharge amount was low, the layered structure of the positive electrode active material was disturbed, and it was estimated that the diffusion path of lithium ions was inhibited. The On the other hand, in Comparative Example 5, since the firing temperature was as low as 600 ° C., the reaction with the lithium compound did not proceed sufficiently and nickel oxide was present in addition to the lithium nickel composite oxide having the desired layered structure. It was found from the analysis. For this reason, the initial discharge amount is low.

  In order to take advantage of the non-aqueous electrolyte secondary battery of the present invention that has high initial capacity while being excellent in safety, it is suitable for use as a power source for small portable electronic devices that always require high capacity It is. In addition, in the power source for electric vehicles, it is indispensable to ensure safety by increasing the size of the battery and to install an expensive protection circuit for ensuring higher safety. The secondary battery has excellent safety, so that not only is it easy to ensure safety, but it can also be used as a power source for electric vehicles in that it can simplify expensive protection circuits and reduce costs. Is preferred. The electric vehicle power source can be used not only for an electric vehicle driven purely by electric energy but also for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

X-ray diffraction diagram of Example 1 Cross section of coin battery used for battery evaluation

Explanation of symbols

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

Claims (6)

Lithium metal composite oxide Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ (however, 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0 .10) a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein an alkaline solution is added to a mixed aqueous solution of nickel salt and cobalt salt and a niobium salt solution at a temperature of 50 ° C. to 80 ° C., And a composite hydroxide Ni _1-xy Co _x Nb _y (OH) ₂ obtained by coprecipitation of hydroxides of nickel, cobalt, and niobium under conditions of pH 10 to 12.5, lithium A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising mixing a compound and heat-treating the mixture at a temperature of from 650 ° C to 850 ° C.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the niobium salt solution is a niobium caustic potash aqueous solution or a niobium hydrochloric acid solution.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium compound is lithium carbonate, lithium hydroxide, or a hydrate thereof. A lithium metal composite oxide Li _{1 + Z} Ni _1-xy Co _x Nb _y O ₂ (obtained by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1. However, a positive electrode for a non-aqueous electrolyte secondary battery, characterized by comprising a powder of 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10) Active material As a result of measuring the positive electrode active material for a non-aqueous electrolyte secondary battery by an energy dispersion method, the peak intensity of the _Nb L line is expressed as I _Nb , L of Ni, regardless of the range of the active material. the peak intensity of the lines is within 1/2 of the average value of the intensity ratio _{I Nb} / _I standard deviation intensity ratio of _{Ni I Nb} / _{I Ni} when the _{I Ni,} always, the composition formula _{Li 1} + Z _{Ni 1-x −y} Co _x Nb _y O ₂ (where 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, −0.05 ≦ z ≦ 0.10) Positive electrode active material for aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4 for a positive electrode.

Images