JP2008198364A - Positive electrode active material for nonaqueous electrolyte secondary battery, its manufacturing method, and nonaqueous electrolyte secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, made from lithium nickel cobaltate titanium composite oxide powder which is excellent in thermal stability, and provides high charge/discharge capacitance, and also to provide its manufacturing method suitable for industrial production and a nonaqueous electrolyte secondary battery of high capacitance and safety which uses the same. <P>SOLUTION: After the surface of nickel cobaltate composite hydroxide (A) is coated with titanium compound, or after it is further roasted at 700°C or less, it is mixed with lithium compound, and the resultant mixture is baked at 650-850°C in the oxygen atmosphere, to provide the powder of lithium nickel cobaltate titanium composite oxide (B) represented by a composition formula (1): Li<SB>1+z</SB>Ni<SB>1-x-y</SB>Co<SB>x</SB>Ti<SB>y</SB>O<SB>2</SB>(where x, y, and z represent 0.10≤x≤0.21, 0.01≤y<0.04, and -0.05≤z≤0.10, respectively). <P>COPYRIGHT: (C)2008,JPO&INPIT

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 positive electrode active material. More specifically, the lithium is excellent in thermal stability and provides high charge / discharge capacity. TECHNICAL FIELD The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery made of nickel-cobalt-titanium composite oxide powder, a manufacturing method suitable for industrial production thereof, and a high-capacity, high-safety 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 personal computers, development of non-aqueous electrolyte secondary batteries having high energy density, small size and light weight is strongly desired. As such a secondary battery, a lithium ion secondary battery can be cited, and research and development are currently 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 to be a battery having a high density and is being put to practical use. With respect to lithium ion secondary batteries using this lithium cobalt composite oxide, many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained.

  However, since the lithium cobalt composite oxide uses rare and expensive cobalt as a raw material, it has been a cause of cost increase of the battery. For this reason, what is cheaper than a lithium cobalt complex oxide as a positive electrode active material is desired. In addition, recently, as a use of lithium ion secondary batteries, not only small secondary batteries for portable electronic devices but also expectation to be applied as large secondary batteries for power storage, electric vehicles, etc. Yes. Therefore, reducing the cost of the active material and making it possible to manufacture a cheaper lithium ion secondary battery can be expected to have a large ripple effect in these wide fields. Furthermore, when used as a power source for a hybrid vehicle or an electric vehicle, it is a big problem to solve the problem of the lithium nickel composite oxide that is inferior in safety.

Under such circumstances, as a positive electrode active material for a lithium ion secondary battery, lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, or lithium nickel composite oxide (LiNiO ₂ ) using nickel. ) Has been proposed as a new material. Here, the lithium manganese composite oxide is an effective alternative to the lithium cobalt composite oxide because its raw material is inexpensive and has excellent thermal stability, in particular, safety with respect to ignition and the like. However, since its theoretical capacity is only about half that of the lithium cobalt composite oxide, 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 a temperature of 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, the lithium nickel composite oxide has almost the same theoretical capacity as the lithium cobalt composite oxide, and shows a slightly lower battery voltage than the lithium cobalt composite oxide. Therefore, decomposition due to oxidation of the electrolyte is less likely to be a problem. Since high capacity can be expected, development is actively conducted. However, when a lithium-ion secondary battery is produced using a lithium-nickel composite oxide composed only of nickel as a positive electrode active material without replacing a part of nickel with another element, compared to lithium cobalt composite oxide There is a problem that the cycle characteristics are inferior. In addition, when used or stored in a high-temperature environment, the battery performance is relatively easily lost.

As this solution, for example, Li _w Ni _x Co _y B _Z O ₂ (wherein w, x, y) can be used as a positive electrode active material capable of maintaining good battery performance during storage and use in a high temperature environment. , Z is 0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, and x + y + z = 1.) That is, a lithium nickel composite oxide to which cobalt and boron are added has been proposed (for example, see Patent Document 1).
Further, for the purpose of improving the self-discharge characteristics and cycle characteristics of the lithium ion secondary battery, Li _z Ni _a Co _b M _c O _z (wherein M is Al, V, Mn, Fe, Cu or Zn). X, a, b, c are 0.8 ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, Lithium-nickel based composite oxide represented by 0.01 ≦ c ≦ 0.3 and 0.8 ≦ a + b + c ≦ 1.2 is proposed (for example, see Patent Document 2).
However, in these lithium nickel composite oxides, both the charge capacity and the discharge capacity are higher than those of the lithium cobalt composite oxide, and the cycle characteristics are improved, but when left in a fully charged state in a high temperature environment, There is a problem of thermal stability that involves oxygen release from a lower temperature than lithium cobalt composite oxide.

In order to solve such a problem, for example, for the purpose of improving the thermal stability of the positive electrode material of the lithium ion secondary battery, Li _a M _b Ni _c Co _d O _e (where M is Al, It is at least one element selected from Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn or Ti, and a, b, c, d and e are 0 <a <1.3, 0. 02 ≦ b ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1)) (For example, see Patent Document 3). Here, 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, if nickel is replaced with an effective amount of aluminum to ensure sufficient stability, the amount of nickel that contributes to the oxidation-reduction reaction accompanying the charge / discharge reaction decreases, so the initial capacity, which is the most important for battery performance, is large. It had the problem of being lowered. This is because Al is stable at trivalent, and Ni also stabilizes at trivalent in order to match the charge, so that a portion that does not contribute to the oxidation-reduction reaction (Redox reaction) occurs, resulting in a decrease in capacity. Conceivable. Therefore, even in this proposal, it cannot be said that the problems of securing charge / discharge capacity and improving thermal stability are solved.

In general formula _{LiNi 1-x Co y M z} O 2 ( where, M is made Mg, Al, Ca, Ti, V, Cr, Mn, or at least one selected from Fe, x, y, z Is 0.1 ≦ x ≦ 0.3, 0.05 ≦ y ≦ 0.28, 0.02 ≦ z ≦ 0.25, and x = y + z.) It has been proposed (see, for example, Patent Document 4).

  Here, the following method is disclosed as a manufacturing method of this lithium nickel type complex oxide. In the reaction vessel, a nickel-cobalt-added element (M) aqueous solution whose salt concentration is adjusted, a complexing agent that forms a complex salt with the aqueous solution, and an alkali metal hydroxide are continuously supplied to each of the nickel, A complex salt containing cobalt and the additive element (M) is produced. Next, the complex salt is decomposed with an alkali metal hydroxide to precipitate a nickel-cobalt-added element (M) hydroxide, and the formation and decomposition of the complex salt is repeated while circulating in the tank to form a particle shape. A hydroxide containing nickel, cobalt, and additive element (M) having a substantially spherical shape is taken out by overflowing. The obtained hydroxide containing nickel, cobalt and additive element (M) is used as a raw material, or it is further baked to obtain an oxide containing nickel, cobalt and additive element (M). A lithium salt is mixed and fired to obtain a lithium nickel cobalt composite oxide. This method improves the polarization characteristics of the lithium-containing composite oxide active material by coprecipitation of two or more hydroxides in nickel hydroxide and restricts one of them to cobalt. The additive element (M) was coprecipitated in the hydroxide to stabilize the lattice. When the hydroxide in which the additive element (M) is co-precipitated is used as a positive electrode active material of a lithium ion secondary battery, when a cobalt-nickel hydroxide that is a two-element co-precipitated hydroxide is used. In comparison, the initial capacity increases and cycle deterioration due to repeated charge and discharge is suppressed.

  However, this proposal also describes the effect of increasing the discharge capacity and suppressing cycle deterioration due to repeated charge and discharge, but there is no description regarding the improvement of thermal stability, ensuring the charge and discharge capacity and thermal stability. It is not enough as a solution to the important problem of improving the performance. Moreover, when titanium sulfate is used as the additive element (M) salt, titanium sulfate is almost insoluble in water at trivalent and water-soluble at tetravalent, but is dissolved in a large amount of sulfuric acid. Lithium nickel cobalt is obtained because of the necessity of an extra neutralizing agent to neutralize the sulfuric acid and the tendency to hydrolyze, which causes segregation and obstructs nickel cobalt hydroxide particle growth. Since the titanium compound segregates in the composite oxide, there is a problem that an effective effect cannot be obtained and it is not suitable for industrial production.

  From the above, in a positive electrode active material for a non-aqueous electrolyte secondary battery made of lithium nickel cobalt titanium composite oxide powder, it is required to secure charge / discharge capacity and further improve thermal stability.

JP-A-8-45509 (first page, second page) Japanese Patent Laid-Open No. 8-213015 (first page, second page) JP-A-5-242891 (first and second pages) JP 10-27611 A (first page, second page)

  In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a positive electrode active for a non-aqueous electrolyte secondary battery comprising a lithium nickel cobalt titanium composite oxide powder that is excellent in thermal stability and obtains a high charge / discharge capacity. It is an object of the present invention to provide a material and a production method suitable for industrial production thereof, and a non-aqueous electrolyte secondary battery having high capacity and high safety using the material.

In order to achieve the above object, the present inventors have conducted intensive research on a positive electrode active material for a non-aqueous electrolyte secondary battery made of lithium nickel cobalt titanium composite oxide powder and a non-aqueous electrolyte secondary battery using the same. As a result, the nickel-cobalt composite hydroxide (A) was coated with a lithium compound after the surface was coated with a titanium compound, or subsequently baked at a specific temperature. When subjected to firing at a temperature to obtain a powder of lithium nickel cobalt titanium composite oxide represented by a specific composition formula, lithium nickel cobalt titanium composite oxide (B) in which titanium is uniformly dissolved is produced. The present inventors have found that a positive electrode active material for a non-aqueous electrolyte secondary battery having excellent thermal stability and high charge / discharge capacity can be obtained.
Conventionally, in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, in order to produce a uniform nickel-cobalt composite hydroxide as an intermediate material, a mixed solution containing nickel and cobalt, an aqueous sodium hydroxide solution, etc. In the case of producing a composite hydroxide containing titanium, the mixed solution containing titanium together with nickel and cobalt is neutralized as described above. In this method, a composite hydroxide in which a sufficient amount of titanium is uniformly dissolved cannot be obtained.

That is, according to the first invention of the present invention, after the surface of the nickel cobalt composite hydroxide (A) is coated with a titanium compound, or subsequently roasted at a temperature of less than 700 ° C. The lithium nickel cobalt titanium composite oxide (B) represented by the following composition formula (1) is subjected to firing at a temperature of 650 to 850 ° C. in an oxygen atmosphere. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel cobalt titanium composite oxide powder is provided.
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y, and z are 0.10 ≦ x ≦ 0.21, 0.01 ≦ y <0.04, and −0.05 ≦ z ≦ 0.10).

  According to the second invention of the present invention, in the first invention, the nickel cobalt composite hydroxide (A) is added to an aqueous solution containing a nickel salt and a cobalt salt at a temperature of 50 to 80 ° C. at a pH of 50 to 80 ° C. A positive electrode for a non-aqueous electrolyte secondary battery prepared by adding a complexing agent and an alkaline aqueous solution so that the pH becomes 10.0 to 12.5 and coprecipitating nickel and cobalt hydroxides A method for producing an active material is provided.

  According to a third aspect of the present invention, there is provided the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the second aspect, wherein the complexing agent is an ammonium ion supplier. Provided.

  According to a fourth invention of the present invention, in the first invention, the nickel cobalt composite hydroxide (A) is added to an aqueous solution containing a nickel salt and a cobalt salt at a temperature of 60 to 80 ° C. at a pH of 60 ° C. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery is provided, which is prepared by adding an alkaline aqueous solution so as to be 10 to 11 and coprecipitating nickel and cobalt hydroxides. The

  According to a fifth aspect of the present invention, in the first aspect, the coating treatment is performed by simultaneously adding a titanium salt aqueous solution and an alkaline aqueous solution to the nickel cobalt composite hydroxide (A) slurry to adjust the pH. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries characterized by adjusting to 8-11 is provided.

  According to a sixth aspect of the present invention, there is provided the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the fifth aspect, wherein the titanium salt aqueous solution is a titanyl sulfate aqueous solution. Is done.

  According to a seventh aspect of the present invention, in the sixth aspect, the aqueous solution of titanyl sulfate is obtained by previously neutralizing an excessive amount of sulfuric acid. A method for producing a positive electrode active material for an aqueous electrolyte secondary battery is provided.

  According to an eighth aspect of the present invention, in the seventh aspect, the neutralization treatment is carried out by adjusting the pH to 0 to 2, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery is produced. A method is provided.

  According to a ninth aspect of the present invention, in the first aspect, the lithium compound is lithium carbonate, lithium hydroxide, or a hydrate thereof. A method for producing a positive electrode active material is provided.

  According to the tenth aspect of the present invention, the lithium nickel cobalt titanium composite oxide powder is obtained by the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of the first to ninth aspects. A positive electrode active material for a non-aqueous electrolyte secondary battery is provided.

  According to an eleventh aspect of the present invention, in the tenth aspect, the initial discharge capacity when used for the positive electrode of the nonaqueous electrolyte secondary battery is 180 mAh / g or more. A positive electrode active material for an electrolyte secondary battery is provided.

  According to the twelfth aspect of the present invention, there is provided a nonaqueous electrolyte secondary battery using the positive electrode active material for a nonaqueous electrolyte secondary battery according to the tenth or eleventh aspect of the present invention as a positive electrode.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is for a non-aqueous electrolyte secondary battery comprising a lithium nickel cobalt titanium composite oxide powder having excellent thermal stability and high charge / discharge capacity. This is a manufacturing method suitable for industrial production of a positive electrode active material, and the non-aqueous electrolyte secondary battery of the present invention has a high capacity and safety using the positive electrode active material of the present invention obtained by the above manufacturing method. The non-aqueous electrolyte secondary battery has a high industrial value.
As a result, it is possible to meet the demand for higher capacity in small secondary batteries such as portable electronic devices, and to ensure the safety required for large secondary batteries that are power sources for hybrid vehicles and electric vehicles. It is more advantageous because it can.

Hereinafter, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the production method thereof, and the non-aqueous electrolyte secondary battery using the same will be described in detail.
1. Method for producing positive electrode active material for non-aqueous electrolyte secondary battery The method for producing a positive electrode active material for non-aqueous electrolyte secondary battery according to the present invention comprises coating the surface of nickel-cobalt composite hydroxide (A) with a titanium compound. Or subsequent baking at a temperature of less than 700 ° C., followed by mixing with a lithium compound, and subjecting the resulting mixture to firing at a temperature of 650 to 850 ° C. in an oxygen atmosphere. It is a manufacturing method of the positive electrode active material which consists of lithium nickel cobalt titanium complex oxide powder characterized by obtaining the powder of lithium nickel cobalt titanium complex oxide (B) represented by Formula (1).
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y, and z are 0.10 ≦ x ≦ 0.21, 0.01 ≦ y <0.04, and −0.05 ≦ z ≦ 0.10).

  In the present invention, the surface of the nickel-cobalt composite hydroxide is coated with a predetermined proportion of the titanium compound, or subsequently roasted at a temperature of less than 700 ° C., and then the lithium compound is added and mixed and fired. It is important to. Thereby, a lithium nickel cobalt titanium composite oxide in which titanium is uniformly dispersed is obtained, and securing of charge / discharge capacity and improvement of thermal stability are achieved at the same time.

  That is, generally, the charge / discharge reaction of the nonaqueous electrolyte secondary battery proceeds by reversibly entering and exiting lithium ions in the positive electrode active material. The positive electrode active material from which lithium is extracted at the time of charging is unstable at a high temperature, and when heated, the active material is decomposed to release oxygen, so that this oxygen causes combustion of the electrolyte and an exothermic reaction occurs. Therefore, improving the thermal stability of the positive electrode material is nothing but suppressing 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, in order to suppress the release of oxygen, it has been generally performed to replace nickel with an element having a strong covalent bond with oxygen such as aluminum. It was. If the amount of substitution from nickel to aluminum is increased in this way, the decomposition reaction of the positive electrode active material is surely suppressed and the thermal stability is improved, but the amount of nickel contributing to the oxidation-reduction reaction accompanying the charge / discharge reaction is small. In order to reduce the charge / discharge capacity, the amount of replacement with aluminum had to be kept below a certain level. As a result, when sufficient thermal stability was ensured, sufficient charge / discharge capacity could not be obtained, and conversely, thermal stability had to be sacrificed in order to obtain a certain level of capacity. .

In contrast, in the lithium-nickel-cobalt-titanium composite oxide obtained in the production method of the present invention have 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 <0.04, −0.05 ≦ z ≦ 0.10) In the powder of lithium metal composite oxide, the additive element (M) is replaced with tetravalent Ti. Thus, a part of the trivalent Ni is divalent and stabilized, and the decomposition reaction is suppressed. For this reason, since nickel substituted for the additive element (M) can be reduced to improve the thermal stability, it is possible to prevent a decrease in the initial capacity of the battery. Moreover, since the titanium compound is added by surface coating of nickel cobalt composite hydroxide or is further baked to form a nickel cobalt composite oxide containing titanium, titanium in the conventional nickel cobalt composite hydroxide is formed. Compared with the method of coprecipitation, segregation of the titanium compound is prevented and it works effectively, so that an excessive amount of addition that causes a decrease in battery capacity is unnecessary.

  As described above, in the production method of the present invention, a nickel-cobalt composite hydroxide having a predetermined composition is prepared, and then a titanium compound is coated on the surface of the nickel-cobalt composite hydroxide, or roasted under predetermined conditions. It is characterized in that a nickel cobalt titanium composite oxide powder obtained by firing and a method of mixing a lithium compound are employed, and the solid solution is uniformly dissolved by subsequent firing.

The nickel-cobalt composite hydroxide (A) is not particularly limited. Crystallization in which a precipitate having good crystallinity is produced using an aqueous solution containing nickel salt and cobalt salt mixed in a predetermined ratio as a raw material. Although those prepared by the method are used, for example, those obtained by the following preparation methods (a) and (b) are preferable.
(A) A complexing agent and an alkaline aqueous solution are added to an aqueous solution containing a nickel salt and a cobalt salt at a temperature of 50 to 80 ° C. so that the pH is 10.0 to 12.5. Prepared by co-precipitation.
(B) Prepared by adding an aqueous alkaline solution to an aqueous solution containing nickel salt and cobalt salt at a temperature of 60 to 80 ° C. so that the pH becomes 10 to 11, and coprecipitating nickel and cobalt hydroxides. The

  The difference between the preparation methods (a) and (b) is in the presence or absence of addition of a complexing agent and the conditions in the pH region and the temperature region. Here, the complexing agent has an action of increasing the solubility of nickel and cobalt in the liquid, and affects the formation rate of hydroxide or the shape control of the crystallized product. Therefore, by adding a complexing agent, the upper limit of the pH range and the lower limit of the temperature range can be controlled so that the composition and shape of the produced nickel cobalt composite hydroxide particles have a desired composition and become substantially spherical. Can be spread

That is, in the preparation method (a), when the pH is less than 10.0, the rate of hydroxide formation is remarkably slow, nickel remains in the filtrate, and the amount of nickel precipitated deviates from the target composition. A composite hydroxide of a ratio cannot be obtained. On the other hand, if the pH exceeds 12.5, the crystallized product becomes fine particles, the filterability also deteriorates, and spherical particles cannot be obtained.
In addition, when the temperature of the aqueous solution is less than 50 ° C., the solubility of nickel is small, so that the precipitation amount of nickel deviates from the target composition and does not coprecipitate. On the other hand, when the temperature exceeds 80 ° C., the slurry concentration becomes high due to a large amount of evaporation of water, so that the solubility of nickel decreases, crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration increases. There arises a problem that the charge / discharge capacity of the positive electrode material is lowered.

  On the other hand, in the preparation method (b), since a complexing agent is not added, a preferable pH region and temperature region are narrowed. That is, when the pH exceeds 11, the crystallized product becomes fine particles, the filterability also deteriorates, and spherical particles cannot be obtained. In addition, when the temperature of the aqueous solution is less than 60 ° C., the solubility of nickel is small, so that the amount of nickel precipitated deviates from the target composition and does not coprecipitate.

  The aqueous solution containing a nickel salt and a cobalt salt used in the above method is not particularly limited, and an aqueous solution in which a water-soluble salt such as sulfate, chloride or nitrate is dissolved in a desired composition is used. Further, the concentration of the aqueous solution is not particularly limited, and a saturated concentration is desirable for the purpose of reducing the amount of the solution, but a concentration that does not cause crystals to precipitate when left at room temperature is preferable. For example, the total of nickel and cobalt is preferably 1 to 2 mol / L, and more preferably 1.5 to 2 mol / L.

  As a mixing ratio of the nickel salt and the cobalt salt, cobalt is contained in a molar ratio of 0.10 to 0.21 with respect to the total amount of nickel, cobalt and titanium in the obtained lithium nickel cobalt titanium composite oxide powder. Adjust to This means that x in the composition formula (1) is performed so as to satisfy the range of 0.10 ≦ x ≦ 0.21. That is, when the molar ratio of cobalt is less than 0.10, the thermal stability decreases, and when the molar ratio of cobalt exceeds 0.21, the charge / discharge capacity decreases.

  The aqueous alkali solution used in the above method is not particularly limited, and a solution in which an alkali metal hydroxide such as sodium hydroxide is dissolved is used. The concentration of the alkaline aqueous solution is not particularly limited, and is preferably 12% by weight or more and not more than a saturated concentration for the purpose of suppressing the liquid amount.

  The complexing agent used in the above method is not particularly limited, and a drug having an action of increasing the solubility of nickel and cobalt is used. Among them, ammonium chloride, ammonium carbonate, ammonium carbonate, Examples thereof include ammonium fluoride, and an ammonium ion supplier is preferable.

  As a more specific method of both the above methods, first, an alkaline aqueous solution and, if necessary, a complexing agent are simultaneously added to an aqueous solution containing a nickel salt and a cobalt salt so that the atomic ratio becomes a predetermined ratio in a reaction vessel. While stirring, coprecipitate at a constant speed. Thereafter, after the product in the reaction vessel reaches a steady state, a precipitate is collected, filtered and washed with water to obtain a nickel cobalt composite hydroxide.

  The coating treatment is not particularly limited. For example, the titanium salt aqueous solution and the alkaline aqueous solution are simultaneously added to the nickel cobalt composite hydroxide (A) slurry to adjust the pH to 8 to 11. Is done. Thereafter, the hydroxide slurry is filtered and washed with water, whereby a nickel cobalt composite hydroxide whose surface is coated with a titanium compound so as to contain titanium in a predetermined ratio is obtained.

  As content of titanium in the said titanium salt aqueous solution, 0.01 mol or more of titanium is molar ratio with respect to the total amount of nickel, cobalt, and titanium in lithium nickel cobalt titanium complex oxide (C) powder obtained, and 0.00. It adjusts so that it may contain in less than 04 range. This is performed so that y in the composition formula (1) satisfies a range of 0.01 ≦ y <0.04. That is, when the molar ratio of titanium is less than 0.01, the effect of improving the thermal stability is small. On the other hand, when the molar ratio of titanium is 0.04 or more, sulfate groups and the like that are derived from the titanium compound and exist on the particle surface. Sufficient charge / discharge capacity cannot be obtained due to inorganic ions or the like.

The titanium salt aqueous solution is not particularly limited, and for example, a titanyl sulfate aqueous solution is preferable. That is, as the titanium salt, titanyl sulfate having high solubility in water and an aqueous sulfuric acid solution are preferable because industrial handling is easy. This is because in general titanium chloride or titanium sulfate, a titanium compound or titanium oxide is generated by hydrolysis or oxidation at that time, and segregation of titanium occurs.
At this time, as the above-mentioned titanyl sulfate aqueous solution, a solution obtained by previously neutralizing an excessively contained sulfuric acid is preferable. Here, as the neutralization treatment, the pH is preferably adjusted to 0 to 2, more preferably about 1. That is, the neutralization treatment can prevent the hydroxide from dissolving.

  In the coating treatment, it is preferable to adjust the pH by simultaneously adding a titanyl sulfate aqueous solution and an alkaline aqueous solution in a state where the pH of the nickel cobalt composite hydroxide (A) slurry is not adjusted in advance. That is, when a titanyl sulfate aqueous solution is added to a solution having a high pH by addition separately, neutralization proceeds rapidly, so that it becomes difficult to coat all titanium hydroxide on the surface of the nickel cobalt composite hydroxide (A). .

  As the raw material of the above mixture, either a nickel cobalt composite hydroxide whose surface is coated with a titanium compound or a nickel cobalt titanium composite oxide obtained by baking this is used, and the resulting lithium nickel cobalt titanium composite oxide In order to stabilize (B), the nickel cobalt titanium complex oxide baked on predetermined conditions is more preferable. That is, since the composite hydroxide is bulky due to its crystal water, the filling amount in the firing container is less than the composite oxide after firing, the production amount decreases, and the moisture varies depending on the dry state. There are also problems such as large shrinkage after firing.

  The nickel-cobalt-titanium composite oxide powder is obtained by roasting nickel-cobalt composite hydroxide whose surface obtained by coating treatment is coated with a titanium compound at a temperature of less than 700 ° C., preferably 300 ° C. or more and less than 700 ° C. Obtained by baking. Here, when the roasting temperature is 700 ° C. or higher, separation of titanium as titanium oxide proceeds, segregation of titanium occurs, and the discharge capacity decreases. In order to sufficiently decompose the hydroxide, the roasting temperature is preferably 300 ° C. or higher. Further, the roasting atmosphere is not particularly limited, and there is no problem in an oxidizing atmosphere such as an air stream or an oxygen stream.

  The lithium compound is not particularly limited, and at least one selected from the group consisting of lithium hydroxide, oxyhydroxide, oxide, carbonate, nitrate and halide is used. Among these, lithium carbonate, lithium hydroxide, or a hydrate thereof is preferable.

  The mixing ratio of the lithium compound is adjusted so that lithium is contained in a molar ratio of 0.95 to 1.10 with respect to the total amount of nickel, cobalt and titanium in the obtained lithium nickel cobalt titanium composite oxide powder. This is performed so that z in the composition formula (1) satisfies the range of −0.05 ≦ z ≦ 0.10. That is, when the molar ratio of lithium is less than 0.95, nickel is present at a site where lithium should originally exist in forming a layered structure, and the crystallinity of the obtained powder becomes very poor. Moreover, since the lithium related to charging / discharging is insufficient, it causes a large decrease in battery capacity during the charging / discharging cycle. On the other hand, when the molar ratio of lithium exceeds 1.10, lithium is present at a site where nickel should originally exist in forming a layered structure, and the crystallinity of the obtained powder becomes very poor. Further, a large amount of excess lithium compound is present on the surface of the obtained powder, and it becomes difficult to remove this by washing with water.

The firing temperature of the mixture is 650 to 850 ° C., preferably 700 to 800 ° C. The firing time is not particularly limited, but is preferably about 10 to 20 hours. In addition, the firing atmosphere is performed in an oxidizing atmosphere such as an oxygen stream.
That is, when the firing temperature is less 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. On the other hand, when the temperature exceeds 850 ° C., Ni is mixed into the Li layer, Li is mixed into the Ni layer, the layered structure is disturbed, and the site occupancy rate of metal ions other than lithium at the 3a site becomes larger than 2%. The mixing rate of metal ions at the 3a site, which is the site, is increased, the lithium ion diffusion path is obstructed, and the battery using the positive electrode has a reduced initial capacity and output.

  Furthermore, the process of attaching | subjecting the powder of the obtained lithium nickel cobalt titanium complex oxide (B) to water washing, and filtering and drying as needed can be performed. Conventionally, washing with water has not been performed, but by washing with water, inorganic ions such as sulfate groups derived from titanium compounds present on the surface of the particles of the lithium nickel cobalt titanium composite oxide (B) after firing are removed. High charge / discharge capacity can be obtained stably.

2. Positive electrode active material for nonaqueous electrolyte secondary battery The positive electrode active material for nonaqueous electrolyte secondary battery of the present invention is obtained by the above production method, has excellent thermal stability and high charge / discharge capacity. It is a positive electrode active material made of lithium nickel cobalt titanium composite oxide powder represented by the composition formula (1).
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y, and z are 0.10 ≦ x ≦ 0.21, 0.01 ≦ y <0.04, and −0.05 ≦ z ≦ 0.10.)
Here, if the value of y is less than 0.01, the effect of improving the thermal stability is small, while if it is 0.04 or more, sufficient charge / discharge capacity cannot be obtained. Moreover, if the value of x is less than 0.10, thermal stability will fall, and when it exceeds 0.21, charging / discharging capacity will fall. On the other hand, if the value of z is less than −0.05, the charge / discharge capacity decreases, whereas if it exceeds 0.10, the thermal stability decreases.

As a particle size distribution of the positive electrode active material for a non-aqueous electrolyte secondary battery, D50 is 5 to 15 μm, a tap density is 1 to 3 g / mL, and more preferably 2 to 3 g / mL. If it is out of the above range, the filling property of the positive electrode active material is lowered when the positive electrode is produced.
Moreover, 180 mAh / g or more is obtained as an initial discharge capacity when the positive electrode active material for a non-aqueous electrolyte secondary battery is used for a positive electrode. Furthermore, the heating rate by a differential scanning calorimeter (DSC) when heated after charging is 11 W / g or less. Thereby, there is no practical problem in safety as a battery.

3. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention has a high capacity and high safety using the positive electrode active material for a non-aqueous electrolyte secondary battery.
Here, the configuration of the lithium ion secondary battery 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 forms described below are merely examples, and the nonaqueous electrolyte secondary battery of the present invention should be implemented in various modified and improved forms based on the knowledge of those skilled in the art, including the following forms. Can do. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.

As described above, the positive electrode active material has a composition formula: Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (where x, y, and z are 0.10 ≦ x ≦ 0.21, 0 .01 ≦ y <0.04, −0.05 ≦ z ≦ 0.10.) Lithium nickel cobalt titanium composite oxide powder.

The positive electrode is not particularly limited, and is produced, for example, as follows. The powdered positive electrode active material, conductive material, binder, and binder are mixed, and if necessary, the target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare the positive electrode mixture paste. Make it. The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery. For example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass, as in the case of the positive electrode of a general lithium secondary battery. It is desirable that the content of the material 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. Moreover, it may pressurize with a roll press etc. to raise an electrode density as needed. In this way, a sheet-like positive electrode can be produced. The obtained sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production.

As the conductive agent, for example, carbon black materials such as graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, ketjen black and the like can be used. Examples of the binder that can be used include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluororubber, styrene butadiene, cellulose resin, and polyacrylic acid. Moreover, as the binder, it plays a role of keeping the active material particles together, and for example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene is used. be able to.
Furthermore, 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 this solvent. Moreover, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

Next, components other than the positive electrode used in the nonaqueous electrolyte secondary battery of the present invention will be described.
However, the nonaqueous electrolyte secondary battery of the present invention is characterized in that the positive electrode active material is used, and other components are not particularly limited.
Examples of the negative electrode include metallic lithium, lithium alloys, and the like, and a negative electrode mixture in which a binder is mixed with a negative electrode active material capable of inserting and extracting lithium ions, and an appropriate solvent is added to form a paste. 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, a fired organic compound such as natural graphite, artificial graphite, or a 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.

  The separator is disposed between the positive electrode and the negative electrode. This separator separates a positive electrode and a negative electrode and retains an electrolyte. For example, a thin film of polyethylene, polypropylene or the like and a film having many minute holes can be used.

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, ethyl methyl carbonate, and dipropyl carbonate, tetrahydrofuran, and 2-methyl. At least one selected from ether compounds such as tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, or phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof. Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  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 can be various, such as a cylindrical type and a laminated type. In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and this 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.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the composition, crystal structure, particle size distribution, powder packing density, charge / discharge capacity and positive electrode safety evaluation method used in Examples and Comparative Examples are as follows.

(1) Composition analysis: The analysis was performed using an ICP emission spectrometer (Plasma Spectrometer SPS3000 manufactured by Seiko Instruments Inc).
(2) Analysis of crystal structure of positive electrode active material: Analysis was performed with an X-ray diffractometer (manufactured by Rigaku Electric Co., Ltd .: RINT-1400).
(3) Measurement of the particle size distribution of the positive electrode active material: The particle size at a D50 (cumulative distribution rate of 50% by mass) was determined from the particle size distribution measured with a laser scattering particle size measuring device (Nikkiso Microtrac HRA).
(4) Measurement of powder packing density (tap density) of positive electrode active material: 12 g of powder was put into a 20 ml glass graduated cylinder and tapped 500 times with a shaking specific gravity measuring instrument (KRS-409 manufactured by Kuramochi Scientific Instruments). After that, the powder packing density was determined.

(5) Evaluation of charge / discharge capacity of positive electrode active material: 70 parts by mass of active material powder was mixed with 20 parts by mass of acetylene black and 10 parts by mass of PTFE. 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 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C. FIG. 1 shows a schematic structure of a 2032 type coin battery. Here, the coin battery includes a positive electrode (evaluation electrode) 3 in a positive electrode can 6, a lithium metal negative electrode 1 in a negative electrode can 5, an electrolyte-impregnated separator 2, a gasket 4, and a current collector 7.
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. A multi-channel voltage / current generator (R6741A) manufactured by ADVANTEST was used for measuring the charge / discharge capacity.

(6) Evaluation of safety of positive electrode: CCCV charging (constant current-constant voltage charging. First, charging is operated at a constant current) for a 2032 type coin battery manufactured by the same method as above. Then, a charging method using a two-phase charging process of terminating 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 heated at a rate of temperature increase of 10 ° C./min using a differential scanning calorimeter (PTC-10A, manufactured by Rigaku). The heat generation behavior was measured from room temperature to 400 ° C., and the heat generation rate was determined.

(Example 1)
(1) Preparation of nickel-cobalt composite hydroxide Nickel sulfate (made by Wako Pure Chemical Industries, reagent grade) and cobalt sulfate (made by Wako Pure Chemical Industries) so that the mixing ratio of nickel and cobalt is 84:15. , Reagent special grade) mixed aqueous solution was prepared. Next, in the reaction tank, together with the mixed solution, a sodium hydroxide aqueous solution having a concentration of 25% by weight prepared using sodium hydroxide (made by Wako Pure Chemical Industries, Ltd., reagent grade), and a 25% by weight aqueous ammonia solution as a complexing agent. (Wako Pure Chemical Industries, reagent special grade) was added simultaneously. At this time, the pH was maintained in the range of 10 to 12.5, and the reaction temperature was maintained in the range of 50 to 80 ° C. Then, after the inside of the reaction vessel was in a steady state, the overflowed precipitate was collected, filtered and washed with water to obtain a nickel cobalt composite hydroxide.

(2) Preparation of nickel-cobalt composite hydroxide coated with titanium compound After the obtained nickel-cobalt composite hydroxide was slurried with water at room temperature, the pH of the slurry was not adjusted, nickel, A titanyl sulfate aqueous solution adjusted to pH 1 with a sodium hydroxide aqueous solution and a sodium hydroxide aqueous solution with a concentration of 12% by weight so that the mixing ratio of cobalt and titanium is nickel: cobalt: titanium = 84: 15: 1 in molar ratio. Simultaneously added and stirred to adjust the pH to 8 to 10.5. Thereafter, the entire amount of the hydroxide slurry in the reaction tank was recovered, filtered, washed with water and dried to obtain a dry powder of nickel-cobalt composite hydroxide coated with a titanium compound.

(3) Synthesis of Lithium Nickel Cobalt Titanium Composite Oxide Dry powder of nickel cobalt composite hydroxide coated with the obtained titanium compound and commercially available lithium hydroxide (manufactured by FMC) were mixed with nickel, cobalt and titanium. After weighing so that the atomic ratio of the total to lithium is 1: 1.05, shaker mixer device (TURBULA Type T2C manufactured by WAB Co., Ltd.) is used with such a strength that the shape of spherical secondary particles is maintained. Used and mixed well.
Next, 30 g of the obtained mixture was put into a 5 cm × 12 cm × 3 cm magnesia firing container and calcined at 500 ° C. for 2 hours in an oxygen stream at a flow rate of 3 L / min using a sealed electric furnace. After heating up to 730 degreeC with the temperature increase rate of 5 degree-C / min and baking for 10 hours at the temperature, it cooled in the furnace to room temperature, and obtained the positive electrode active material.

(4) Evaluation of positive electrode active material and positive electrode The composition of the obtained positive electrode active material, D50 of the particle size distribution, powder packing density (tap density), charge / discharge capacity, and safety of the positive electrode were evaluated by the above evaluation methods. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Example 2)
In the preparation of the nickel-cobalt composite hydroxide, the mixing ratio of nickel and cobalt was set to 83:15, and in the preparation of the nickel-cobalt composite hydroxide coated with the titanium compound, nickel, cobalt And the mixing ratio of titanium was such that the molar ratio was nickel: cobalt: titanium = 83: 15: 2, and in the synthesis of the lithium nickel cobalt titanium composite oxide, the firing temperature was 780 ° C. The same procedure as in Example 1 was performed to obtain a positive electrode active material, and the composition of the obtained positive electrode active material, D50 of the particle size distribution, powder packing density (tap density), charge / discharge capacity, and safety of the positive electrode were evaluated as described above. The method was evaluated. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Example 3)
In the preparation of the nickel-cobalt composite hydroxide, the mixing ratio of nickel and cobalt was set to 82:15, and in the preparation of the nickel-cobalt composite hydroxide coated with the titanium compound, nickel, cobalt In addition, the mixing ratio of titanium and titanium was adjusted to be nickel: cobalt: titanium = 82: 15: 3, and the pH was adjusted to 10 to 11 when the titanyl sulfate aqueous solution and the sodium hydroxide aqueous solution were added. In addition, in the synthesis of lithium nickel cobalt titanium composite oxide, instead of nickel cobalt composite hydroxide coated with a titanium compound, nickel cobalt titanium composite oxide synthesized by the following roasting method was used. And the positive electrode active material in the same manner as in Example 1 except that the firing temperature was 760 ° C. Te, then further the obtained cathode active material, placed in a beaker of 50 mL, of pure water so that the slurry concentration becomes 1500 g / L was added, followed after stirring for 20 minutes with a stirrer, and filtered. The obtained filtrate was dried at 150 ° C. for 12 hours using a vacuum dryer. The composition of the obtained positive electrode active material after drying, D50 of the particle size distribution, powder packing density (tap density), initial discharge capacity, and safety of the positive electrode were evaluated by the above evaluation methods. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.
[Roasting method of nickel-cobalt composite hydroxide coated with titanium compound]
50 g of the composite hydroxide obtained by the preparation of the nickel-cobalt composite hydroxide coated with the titanium compound of Example 1 (2) was inserted into a 5 cm × 12 cm × 3 cm magnesia firing container, and sealed electric Using a furnace, the temperature was raised to 550 ° C. at a heating rate of 5 ° C./min in an air stream having a flow rate of 3 L / min, roasted at that temperature for 10 hours, and then cooled to room temperature in the furnace.

Example 4
In the preparation of the nickel-cobalt composite hydroxide, the mixing ratio of nickel and cobalt was adjusted to be 81:15, and in the preparation of the nickel-cobalt composite hydroxide coated with the titanium compound, the concentration was 12 wt. The pH of the slurry was adjusted to alkaline with an aqueous sodium hydroxide solution of 3% and then adjusted to a pH of 9 to 10 by adding a 3-fold diluted titanyl sulfate aqueous solution. Synthesis of lithium nickel cobalt titanium composite oxide In Example 1, except that the firing temperature was 760 ° C., a positive electrode active material was obtained in the same manner as in Example 1, the composition of the obtained positive electrode active material, D50 of the particle size distribution, powder packing density (tap density) The charge / discharge capacity and the safety of the positive electrode were evaluated by the above evaluation methods. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure. Moreover, the obtained composition shifted | deviated from preparation.

(Comparative Example 1)
In the preparation of the nickel-cobalt composite hydroxide, the mixing ratio of nickel and cobalt was adjusted to 81:15, and in the preparation of the nickel-cobalt composite hydroxide coated with the titanium compound, nickel, cobalt In addition, in the synthesis of lithium nickel cobalt titanium composite oxide, the calcining temperature is 450 ° C. and the calcining temperature is 780. Except that it was set to ° C., the same procedure as in Example 1 was performed to obtain a positive electrode active material, the composition of the obtained positive electrode active material, D50 of particle size distribution, powder packing density (tap density), charge / discharge capacity, and The safety of the positive electrode was evaluated by the above evaluation method. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 2)
In [Roasting Method of Nickel Cobalt Composite Hydroxide Coated with Titanium Compound], a positive electrode active material was obtained and obtained in the same manner as in Example 1 except that it was heated to 800 ° C. and roasted. The composition of the positive electrode active material, D50 of the particle size distribution, powder packing density (tap density), initial discharge capacity, and safety of the positive electrode were evaluated by the above evaluation methods. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 3)
In the preparation of the nickel-cobalt composite hydroxide, the mixing ratio of nickel and cobalt was 75:15 in molar ratio, and in the preparation of the nickel-cobalt composite hydroxide coated with the titanium compound, nickel, A positive electrode active material was obtained in the same manner as in Example 1 except that the mixing ratio of cobalt and titanium was such that the molar ratio was nickel: cobalt: titanium = 75: 15: 10. , D50 of particle size distribution, powder packing density (tap density), initial discharge capacity, and positive electrode safety were evaluated by the above evaluation methods. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 4)
In the preparation of nickel-cobalt composite hydroxide, the mixing ratio of nickel and cobalt was 84.5: 15, and in the preparation of nickel-cobalt composite hydroxide coated with a titanium compound, nickel The mixing ratio of cobalt and titanium was such that the molar ratio was nickel: cobalt: titanium = 84.5: 15: 0.5, and the calcining temperature was 450 in the synthesis of lithium nickel cobalt titanium composite oxide. The positive electrode active material was obtained in the same manner as in Example 1 except that the temperature and the baking temperature were 780 ° C. The positive electrode active material was obtained, the composition of the obtained positive electrode active material, the particle size distribution D50, and the powder packing density (tap density). The charge / discharge capacity and the safety of the positive electrode were evaluated by the above evaluation methods. The results are shown in Tables 1 and 2. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

  From Tables 1 and 2, in Examples 1 to 4, preparation of nickel cobalt composite hydroxide, roasting method of nickel cobalt composite hydroxide coated with titanium compound, synthesis of lithium nickel cobalt titanium composite oxide, and The composition of the lithium nickel cobalt titanium composite oxide, in particular the content of titanium, was carried out according to the method of the present invention, so that the lithium nickel cobalt titanium composite oxide powder has excellent thermal stability and high charge / discharge capacity. It can be seen that a positive electrode active material for a non-aqueous electrolyte secondary battery and a high-capacity, high-safety non-aqueous electrolyte secondary battery using the same can be obtained. That is, the initial discharge capacity exceeds 180 mAh / g, and the heat generation rate by DSC measurement is 11 W / g or less, which indicates that the material can be used as a new battery material in place of the lithium cobalt composite oxide.

  On the other hand, in Comparative Examples 1 to 4, either the content ratio of titanium of the lithium nickel cobalt titanium composite oxide or the roasting temperature of the nickel cobalt composite hydroxide coated with the titanium compound satisfies these conditions. Since it does not match, it can be seen that either thermal stability or initial discharge capacity does not give satisfactory results.

As is clear from the above, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a non-lithium nickel cobalt titanium composite oxide powder having excellent thermal stability and high charge / discharge capacity. This is a manufacturing method suitable for industrial production of a positive electrode active material for an aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery of the present invention is the lithium nickel cobalt titanium of the present invention obtained by the above manufacturing method. High capacity and high safety non-aqueous electrolyte secondary battery using a positive electrode active material for non-aqueous electrolyte secondary battery made of composite oxide powder. In order to take advantage of the advantages, it is suitable for use as a power source for small portable electronic devices that always require high capacity.
Moreover, in the power supply for electric vehicles, it is indispensable to install an expensive protection circuit for ensuring higher safety in addition to ensuring safety by increasing the size of the battery. However, since the non-aqueous electrolyte secondary battery of the present invention has excellent safety, not only is it easy to ensure safety, but also an expensive protection circuit can be simplified and the cost can be reduced. It is suitable as a power source for automobiles. The electric vehicle power source includes not only an electric vehicle driven purely by electric energy but also a so-called hybrid vehicle power source used in combination with a combustion engine such as a gasoline engine or a diesel engine.

It is the schematic of the cross section of the 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 (12)

After the surface of the nickel cobalt composite hydroxide (A) is coated with a titanium compound, or subsequently roasted at a temperature of less than 700 ° C., mixed with the lithium compound, and the resulting mixture is Lithium nickel cobalt titanium, characterized by obtaining a powder of lithium nickel cobalt titanium composite oxide (B) represented by the following composition formula (1) by firing at a temperature of 650 to 850 ° C. in an oxygen atmosphere A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a composite oxide powder.
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y, and z are 0.10 ≦ x ≦ 0.21, 0.01 ≦ y <0.04, and −0.05 ≦ z ≦ 0.10).   The nickel-cobalt composite hydroxide (A) is prepared by adding a complexing agent and an aqueous alkaline solution to an aqueous solution containing a nickel salt and a cobalt salt so that the pH becomes 10.0 to 12.5 at a temperature of 50 to 80 ° C. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the method is prepared by adding and coprecipitating nickel and cobalt hydroxides.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the complexing agent is an ammonium ion supplier.   The nickel-cobalt composite hydroxide (A) is prepared by adding an alkaline aqueous solution to an aqueous solution containing a nickel salt and a cobalt salt at a temperature of 60 to 80 ° C. so as to have a pH of 10 to 11. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the method is prepared by coprecipitation of an oxide.   2. The non-aqueous system according to claim 1, wherein the coating treatment is performed by simultaneously adding a titanium salt aqueous solution and an alkaline aqueous solution to the slurry of nickel cobalt composite hydroxide (A) to adjust the pH to 8 to 11. A method for producing a positive electrode active material for an electrolyte secondary battery.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the titanium salt aqueous solution is a titanyl sulfate aqueous solution.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the aqueous solution of titanyl sulfate is obtained by neutralizing an excessive amount of sulfuric acid in advance.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the neutralization treatment adjusts the pH to 0 to 2. 9.   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.   It consists of the powder of the lithium nickel cobalt titanium complex oxide obtained by the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries in any one of Claims 1-9, For nonaqueous electrolyte secondary batteries characterized by the above-mentioned Positive electrode active material.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein the initial discharge capacity when used for the positive electrode of the non-aqueous electrolyte secondary battery is 180 mAh / g or more.   A non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10 or 11 as a positive electrode.

Images