JP5109447B2 - Cathode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery using the same - Google Patents

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. The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery made of nickel 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, a lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, which is cheaper than cobalt, or a lithium nickel composite oxide (LiNiO ₂ ) using nickel as a positive electrode active material for a lithium ion secondary battery. ) 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 lithium ion secondary battery positive electrode material, Li _{a Mb} Ni _c Co _d O _e (wherein 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.

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)

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

In order to achieve the above object, the present inventors have conducted extensive research on a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel composite oxide powder and a non-aqueous electrolyte secondary battery using the same. As a result, a positive electrode active material composed of a composite oxide represented by a composition formula showing lithium and titanium at a specific atomic ratio, and when a battery is charged, a crystal structure composed of a specific two phase is formed. While ensuring a high charge / discharge capacity, it is possible to improve thermal stability by suppressing rapid oxygen release during heating in a charged state, good thermal stability, and high charge / discharge capacity. It has been found that a positive electrode active material for a non-aqueous electrolyte secondary battery can be obtained, and that a high-capacity and high-safety non-aqueous electrolyte secondary battery can be obtained.
In addition, in the production method including a step of obtaining a nickel cobalt titanium composite hydroxide having a controlled atomic ratio of nickel, cobalt and titanium, and a step of obtaining a lithium nickel cobalt titanium composite oxide having a controlled atomic ratio of lithium, It has been found that by using titanyl sulfate as a titanium salt to obtain a composite oxide in which titanium is uniformly dissolved, the positive electrode active material is industrially efficiently produced. Thus, the present invention has been completed.

That is, according to the first invention of the present invention, a positive electrode active material for a nonaqueous electrolyte secondary battery comprising a composite oxide represented by the following composition formula (1) containing lithium, nickel, cobalt and titanium: There,
The crystal structure is a single phase of a complex oxide having a hexagonal layered structure, and a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° in the X-ray diffraction measurement by Cu—Kα ray when the battery is charged. And a composite oxide phase having a layered structure in which a diffraction peak appears at 2θ = 17 to 19 °, and a positive electrode active material for a non-aqueous electrolyte secondary battery. .
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y and z satisfy the requirements shown in the following (a) to (c).)
(A) 0.10 ≦ x ≦ 0.21
(B) 0.01 ≦ y ≦ 0.08
(C) 0.03 ≦ z ≦ 0.14

  According to the second invention of the present invention, in the first invention, a phase having a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° in an X-ray diffraction measurement by Cu—Kα ray, and 2θ = The composite oxide phase having a layered structure in which a diffraction peak appears at 17 to 19 ° has a temperature range (A) of 120 to 180 ° C. and a temperature range (B) of 200 to 270 ° C. by TG-DTA measurement upon heating, respectively. Provided is a positive electrode active material for a non-aqueous electrolyte secondary battery characterized by exhibiting weight reduction.

  Moreover, according to the third invention of the present invention, in the second invention, the weight reduction is TG-DTA measurement of the positive electrode after charging the battery, and is 3.5 mass% or less in the temperature region (A). And a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by being 5.2 mass% or less in the temperature region (B).

  According to the fourth invention of the present invention, in any one of the first to third inventions, the initial discharge capacity when used for the positive electrode of the nonaqueous electrolyte secondary battery is 190 mAh / g or more. A positive electrode active material for a non-aqueous electrolyte secondary battery is provided.

According to a fifth aspect of the present invention, there is provided a positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of the first to fourth aspects, comprising the following steps (a) and (b): A manufacturing method is provided.
Step (I): A mixed aqueous solution of nickel salt and cobalt salt, an aqueous solution of titanyl sulfate, and an aqueous alkali solution are simultaneously added dropwise to a reaction vessel, and they are stirred, and the pH is adjusted to 10 to 11 at a temperature of 60 to 80 ° C. Hold, co-precipitate, and after reaching a steady state in the reaction vessel , the overflowed precipitate is collected, filtered, washed with water, and dried to control the atomic ratio of nickel, cobalt, and titanium. Obtain a hydroxide.
Step (b): The nickel-cobalt-titanium composite hydroxide and lithium hydroxide or hydrate thereof are mixed, and the mixture is baked in an oxygen stream at a temperature of 700 to 800 ° C. to determine the atomic ratio of lithium. A controlled lithium nickel cobalt titanium composite oxide is obtained.

According to the sixth aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of the first to fourth aspects as a positive electrode.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a positive electrode active material 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. The manufacturing method is a manufacturing method suitable for industrial production of the positive electrode active material, and the non-aqueous electrolyte secondary battery of the present invention is obtained from the lithium nickel cobalt titanium composite oxide powder of the present invention. Since the non-aqueous electrolyte secondary battery has a high capacity and high safety using the positive electrode active material for a non-aqueous electrolyte secondary battery, the industrial value is extremely large.
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. Positive electrode active material for non-aqueous electrolyte secondary battery The positive electrode active material for non-aqueous electrolyte secondary battery of the present invention comprises a composite oxide represented by the following composition formula (1) containing lithium, nickel, cobalt and titanium. A positive electrode active material for a non-aqueous electrolyte secondary battery, the crystal structure of which is a single phase of a complex oxide having a hexagonal layered structure, and X-ray diffraction by Cu-Kα rays during battery charging It is characterized by comprising two phases: a phase having a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° in measurement and a complex oxide phase having a layered structure in which a diffraction peak appears at 2θ = 17 to 19 °. To do.
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y and z satisfy the requirements shown in the following (a) to (c).)
(A) 0.10 ≦ x ≦ 0.21
(B) 0.01 ≦ y ≦ 0.08
(C) 0.03 ≦ z ≦ 0.14

In the present invention, the positive electrode active material, lithium, nickel, formula containing cobalt and _titanium: it consists _{Li 1 + z Ni 1-x} -y Co x M y O 2 composite oxide expressed, and wherein X, y, and z of the above satisfy the requirements shown in the above (a) to (c), and the crystal structure is a complex oxide single phase having a hexagonal layered structure, and During charging, a complex oxide having a phase having a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° and a layered structure in which a diffraction peak appears at 2θ = 17 to 19 ° in X-ray diffraction measurement by Cu-Kα ray It is important to consist of two phases with a phase. Thereby, the thermal stability can be remarkably improved.

These points will be described below in relation to the charge / discharge reaction of the non-aqueous electrolyte secondary battery.
In general, the charge / discharge reaction of a non-aqueous electrolyte secondary battery proceeds by reversibly entering and exiting lithium ions in the positive electrode active material. It is said that the positive electrode active material from which lithium is extracted by charging becomes unstable at high temperatures, so that when heated, the active material decomposes and releases oxygen, which causes combustion of the electrolyte and an exothermic reaction. . Here, if the heat dissipation rate to the outside of the battery is larger than the internal heat generation rate, the temperature of the battery will not rise, but if the reverse, the temperature of the battery will rise and lead to thermal runaway. Therefore, improving the safety of the battery means that, from the standpoint of the positive electrode side, the decomposition reaction of the positive electrode active material from which lithium is extracted is suppressed or the reaction rate is reduced.

By the way, conventionally, as a method for suppressing the decomposition reaction of the LiNiO ₂ type positive electrode active material, it has been disclosed and generally carried out that a part of nickel is replaced by an element having strong covalent bonding with oxygen such as aluminum. I came. According to this method, if the amount of substitution from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material can surely be suppressed and the thermal stability can be improved, but on the other hand, the redox reaction accompanying the charge / discharge reaction As a result, the amount of nickel that contributes to the decrease is reduced, leading to a decrease in charge / discharge capacity. Therefore, the amount of substitution with aluminum at this time had to be limited to some extent. As a result, such a replacement with aluminum cannot provide a sufficient reversible capacity if sufficient thermal stability is ensured, and at the expense of thermal stability to obtain a certain level of capacity. There was a technical problem that had to be done.

In contrast, in the present invention, the general formula (1): Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (however, 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0. 08, 0.03 ≦ z ≦ 0.14) is used as the positive electrode active material.
First, tetravalent and stable titanium (Ti) is used as an additive element, so that part of nickel (Ni) substituted with Ti is stable from trivalent to divalent, and lithium (Li) is extracted during charging. In this case, Ni can be stabilized.

Here, it is essential that the above x, y, and z satisfy the following requirements (a) to (c).
The requirement (a) is that the Co substitution amount (x) is 0.10 ≦ x ≦ 0.21 in atomic ratio with respect to the total amount of nickel, cobalt and titanium. That is, a pure lithium nickel composite oxide (LiNiO ₂ ) that does not perform element substitution has a disadvantage that it is inferior in cycle characteristics, but in order to solve this, it is useful to substitute a part of Ni with Co. It is known that there is. Here, in particular, sufficient cycle characteristics can be obtained by setting the value of x to 0.10 or more. On the other hand, if the amount of substitution of Co is increased, the initial capacity is significantly lowered, and the high capacity, which is the greatest merit of the positive electrode active material made of nickel-based composite oxide, is sacrificed. .21.

The requirement (b) is that the Ti substitution amount (y) is 0.01 ≦ y ≦ 0.08 in atomic ratio with respect to the total amount of nickel, cobalt and titanium. That is, if the value of y is less than 0.01, the amount of Ni that can be stabilized from trivalent to divalent decreases, and the two-phase formation of the crystal structure described later is not sufficient, and a sufficient thermal stability effect is obtained. On the other hand, when the value of y exceeds 0.08, Ni substituted by Ti increases and the charge / discharge capacity decreases.
The requirement (c) is that the variation amount (z) of Li is 0.03 ≦ z ≦ 0.14 in atomic ratio with respect to the total amount of nickel, cobalt and titanium. That is, if the value of z is less than 0.03, the two-phase structure of the crystal structure described later is not sufficient, and the effect of dispersing the decomposition reaction temperature causing oxygen release is not sufficient. On the other hand, when it exceeds 0.14, excessive Li becomes too much, and the charge / discharge capacity decreases.

When these requirements are satisfied, the crystal structure of the lithium nickel cobalt titanium composite oxide is a composite oxide single phase having a hexagonal layered structure. Moreover, when the Ti substitution amount (y) is 0.01 or more in atomic ratio and the variation amount (z) of Li corresponding to the excess amount of Li as the LiNiO ₂ type positive electrode active material is 0.03 or more in atomic ratio, When charging a secondary battery using this lithium nickel cobalt titanium composite oxide as a positive electrode active material, for example, after charging to 4.5 V, it is diffracted to 2θ = 12 to 14 ° in an X-ray diffraction measurement by Cu-Kα ray. Two phases are formed: a phase having a crystal structure in which a peak appears and a complex oxide phase having a layered structure in which a diffraction peak appears at 2θ = 17 to 19 °.
The phase having a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° in the X-ray diffraction measurement by Cu-Kα ray decomposes in the temperature region (A): 120 to 180 ° C. by TG-DTA measurement upon heating. Thus, the weight decrease with the release of oxygen is shown. On the other hand, the complex oxide phase having a layered structure decomposes in the temperature region (B): 200 to 270 ° C., and shows a weight reduction accompanying the release of oxygen. That is, since the decomposition reaction temperature causing oxygen release is dispersed in two stages as described above, it is possible to suppress the temperature rise of the electrolytic solution due to a rapid exothermic reaction and to prevent the battery from running out of heat. In addition, when the conventional positive electrode active material is subjected to TG-DTA measurement under the same conditions, weight loss is observed only at 200 ° C. to 270 ° C., and the decomposition reaction temperature causing oxygen release is concentrated. The exothermic reaction of the liquid tends to occur, and there is a risk that the battery will run out of heat.

  Although the weight reduction is not particularly limited, it is 3.5% by mass or less in the temperature region (A) and 5% in the temperature region (B) by TG-DTA measurement of the positive electrode after charging the battery. .2% by mass or less is preferable. Thereby, the safety | security as a battery improves. That is, when the weight loss in each temperature region exceeds 3.5% by mass or 5.2% by mass, a rapid exothermic reaction of the electrolytic solution may occur even when the decomposition reaction temperature is dispersed. The TG-DTA measurement of the positive electrode was performed using the positive electrode taken out after charging the secondary battery to 4.5V. This detailed condition will be described in Examples.

  The particle size distribution of the positive electrode active material is not particularly limited, but preferably, the particle size distribution D50 by laser scattering particle size measurement is 2 to 13 μm, and the tap density is 1.2 to 3.0 g / mL. Thereby, when producing a positive electrode, excellent filling properties of the positive electrode active material can be obtained.

  When the positive electrode active material is used for the positive electrode, the initial discharge capacity of the battery is 190 mAh / g or more, preferably 190 to 200 mAh / g, which is a capacity sufficient to be a substitute for the conventional material.

2. Manufacturing method of positive electrode active material for nonaqueous electrolyte secondary battery The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and the following steps (A) and (B) It is characterized by including.
Step (I): A mixed aqueous solution of nickel salt and cobalt salt, an aqueous solution of titanyl sulfate, and an aqueous alkali solution are simultaneously added dropwise to a reaction vessel, and they are agitated. Nickel-cobalt-titanium composite hydroxide with controlled atomic ratio of nickel, cobalt and titanium by holding, co-precipitating, collecting the precipitate after reaching steady state in the reaction vessel, filtering, washing and drying Get.
Step (b): Lithium having a nickel atomic ratio controlled by mixing the nickel cobalt titanium composite hydroxide and a lithium compound, and firing the mixture at a temperature of 650 to 850 ° C. in an oxidizing atmosphere. A nickel cobalt titanium composite oxide is obtained.

Or in the said manufacturing method, it can replace with the said process (I) and can include the following process (I ').
Step (I ′): Mixing aqueous solution of nickel salt and cobalt salt, aqueous solution of titanyl sulfate, aqueous alkali solution and complexing agent are added dropwise to the reaction vessel at the same time while stirring them, and the pH is adjusted at a temperature of 50-80 ° C. Nickel with the atomic ratio of nickel, cobalt and titanium controlled by holding it at 10 to 12.5, co-precipitation, collecting the precipitate after reaching a steady state in the reaction vessel, filtering, washing with water and drying A cobalt titanium composite hydroxide is obtained.

  In the production method of the present invention, a mixed hydroxide of nickel salt and cobalt salt, an aqueous solution of titanyl sulfate, an aqueous alkaline solution, and if necessary, a complexing agent is dropped simultaneously into a reaction tank to obtain and use a composite hydroxide. As the titanium salt, it is important to use titanyl sulfate having high solubility in water. In addition, about these action mechanisms, it explains in full detail in description of each process.

(1) Process (I), (I ')
Step (I) or (I ′) is a composition formula in which the atomic ratio of nickel, cobalt and titanium is controlled using a mixed aqueous solution of nickel salt and cobalt salt and an aqueous solution of titanyl sulfate: Ni _1-xy Co _x This is a step of obtaining a nickel cobalt titanium composite hydroxide represented by Ti _y (OH) ₂ .
The differences between the steps (A) and (I ') are the presence or absence of the addition of the complexing agent and the conditions of 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 the 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 nickel-cobalt composite hydroxide particles to be produced are approximately spherical with a desired composition. Can be spread

That is, in the step (ii), when the pH is less than 10.0, the rate of hydroxide formation is remarkably slow, nickel remains in the filtrate, the amount of nickel precipitated deviates from the target composition, and the target ratio is reached. It becomes impossible to obtain the composite hydroxide. On the other hand, if 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 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 step (ii '), since a complexing agent is added, a preferable pH region and temperature region are widened. However, if the pH exceeds 12.5, the crystallized product becomes fine particles, the filterability deteriorates, and spherical particles cannot be obtained. Further, 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 does not shift from the target composition and does not coprecipitate.

  Here, a mixed aqueous solution of nickel salt and cobalt salt, an aqueous solution of titanyl sulfate, an aqueous alkali solution and, if necessary, a complexing agent are simultaneously added dropwise to the reaction vessel at a predetermined ratio, while stirring them, and at a predetermined temperature and a predetermined pH. Holding, co-precipitate, and after collecting the precipitate after reaching a steady state in the reaction vessel, a nickel-cobalt-titanium composite hydroxide in which three elements of nickel, cobalt and titanium are uniformly dispersed is obtained. Therefore, in the step (b), securing of charge / discharge capacity and improvement of thermal stability are achieved at the same time.

  The aqueous solution containing the nickel salt and cobalt salt used in the above process is not particularly limited, and a solution obtained by dissolving a water-soluble salt such as sulfate, chloride or nitrate in a desired composition is used. A sulfate aqueous solution is more preferable from the viewpoint of impurities. Further, the concentration of the aqueous solution is not particularly limited, and a saturated concentration is preferable for the purpose of reducing the amount of the solution, but a concentration at which crystals do not precipitate even 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 blending ratio of the nickel salt and the cobalt salt, cobalt is contained in an atomic ratio in the range 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.

  As a titanyl sulfate aqueous solution used for the said process, the titanyl sulfate aqueous solution which contains a sulfuric acid 10 mass% or more is preferable. That is, in an aqueous solution of titanyl sulfate having a sulfuric acid content of less than 10% by mass, hydrolysis occurs during storage to precipitate titanium hydroxide, and segregation of titanium occurs in the nickel cobalt titanium composite hydroxide. As described above, when titanium chloride or titanium sulfate, which represents a titanium salt, is used, hydrolysis or oxidation proceeds in an aqueous solution, and titanium hydroxide or titanium oxide is generated to cause segregation of titanium. Use is preferred.

  The addition ratio of the aqueous titanyl sulfate solution is such that titanium is contained in an atomic ratio of 0.01 to 0.08 with respect to the total amount of nickel, cobalt and titanium in the obtained lithium nickel cobalt titanium composite oxide powder. Adjust to. This is performed so that y in the composition formula (1) satisfies a range of 0.01 ≦ y ≦ 0.08.

  The aqueous alkali solution used in the above step 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 mass or more and a saturated concentration or less for the purpose of suppressing the liquid amount.

  The complexing agent used in the above step (ii ') is not particularly limited, and a drug having an action of increasing the solubility of nickel and cobalt is used. Among them, ammonium chloride in addition to ammonia and ammonium sulfate. , Ammonium carbonate, ammonium fluoride, and the like, and an ammonium ion supplier is preferred.

  The nickel-cobalt-titanium composite hydroxide obtained by the above steps (a) and (ii ′) is composed of substantially spherical secondary particles in which a plurality of primary particles of 1 μm or less are assembled, and has good handling properties such as filterability. .

(2) Process (b)
In the step (b), the nickel cobalt titanium composite hydroxide and the lithium compound were mixed, and the mixture was baked at a temperature of 650 to 850 ° C. in an oxidizing atmosphere to control the atomic ratio of lithium. This is a step of obtaining a lithium nickel cobalt titanium composite oxide.
Accordingly, the general formula (1): Li _{1 + Z} Ni _1-xy Co _x Ti _y O ₂ (however, 0.10 ≦ x ≦ 0.21, 0.01 ≦ y ≦ 0.08, 0.03 ≦ A powder of lithium nickel cobalt titanium composite oxide represented by z ≦ 0.14) is obtained.

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

  As the addition ratio of the lithium compound, lithium was added in an atomic ratio of 1. with respect to the total amount of nickel, cobalt, and titanium in the obtained lithium nickel cobalt titanium composite oxide powder. Adjust to contain 3 to 1.14. This is performed so that z in the composition formula (1) satisfies the range of 0.03 ≦ z ≦ 0.14.

The firing temperature of the mixture used in the step (b) is 650 to 850 ° C., preferably 700 to 800 ° C. The firing time is not particularly limited, but should be about 5 to 20 hours. Is preferred. In addition, the firing atmosphere is performed in an oxidizing atmosphere such as an oxygen stream. However, firing in an oxygen stream is more preferable because impurities are not mixed.
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 hindered, and the battery using the positive electrode active material has reduced initial capacity and output.

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. That is, when the battery is charged, the decomposition reaction temperature causing oxygen release is dispersed in two stages, so that the temperature rise of the electrolytic solution due to a rapid exothermic reaction can be suppressed, and the battery can be prevented from thermal runaway.
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.

The positive electrode is not particularly limited except that the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is used as the positive electrode active material. For example, the positive electrode is produced as follows.
Mix the powdered positive electrode active material, conductive material, binder, and binder, and add the desired solvent such as activated carbon and viscosity adjustment, if necessary, and knead them to prepare the positive electrode mixture paste. To do. 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. The nonaqueous electrolyte secondary battery of the present invention is characterized in that the positive electrode active material is used. The components of 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, and separates the positive electrode and the negative electrode to hold the electrolyte. Examples of the separator include a thin film such as polyethylene and polypropylene, Can be used.

The non-aqueous electrolyte is a solution 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.
The TG-DTA measurement was performed by washing the positive electrode with acetone to remove the attached electrolyte, weighing 15 mg, filling the aluminum measurement container, and using TG-DTA at a heating rate of 10 ° C./min. The weight reduction due to oxygen release from room temperature to 350 ° C. was measured, and the weight reduction rate of the positive electrode in the temperature region (A): 120 ° C. to 180 ° C. and the temperature region (B): 200 ° C. to 270 ° C. was determined. In DSC measurement, 3.0 mg of this positive electrode was measured, 1.3 mg of electrolyte was added, sealed in an aluminum measurement container, and the temperature was raised using a differential scanning calorimeter (PTC-10A, manufactured by Rigaku). The exothermic behavior was measured from room temperature to 300 ° C. at a rate of 10 ° C./min.

Example 1
First, a mixed aqueous solution of 2 mol / L in total concentration of nickel and cobalt to which nickel sulfate (made by Wako Pure Chemical Industries, reagent special grade) and cobalt sulfate (made by Wako Pure Chemical Industries, reagent special grade) are added, and sulfuric acid content 13 A mass% titanyl sulfate aqueous solution was prepared. Next, in the reaction vessel, sodium hydroxide (Wako Pure Chemical Industries, Ltd.) together with the mixed aqueous solution and the titanyl sulfate aqueous solution so that the atomic ratio of nickel, cobalt and titanium is Ni: Co: Ti = 81: 14: 5. A sodium hydroxide aqueous solution having a concentration of 12.5% by mass prepared by using a special grade reagent (manufactured by Renesas) was simultaneously added dropwise. At this time, the pH was maintained in the range of 10-11, and the reaction temperature was maintained in the range of 60-80 ° C. Then, after the inside of the reaction vessel was in a steady state, the overflowed precipitate was collected, filtered, washed with water and dried to obtain spherical particles of nickel cobalt titanium composite hydroxide.
The obtained composite hydroxide and commercially available lithium hydroxide (manufactured by FMC) were so adjusted that the atomic ratio of lithium to nickel, cobalt and titanium in the composite hydroxide was 1: 1.09. After weighing, using a shaker mixer device (TURBULA Type T2C manufactured by WAB), the mixture was sufficiently mixed with such a strength that the shape of spherical secondary particles was maintained. The mixture was heated to 730 ° C. at a rate of temperature increase of 5 ° C./min in an oxygen stream, fired at that temperature for 10 hours, cooled to room temperature in the furnace, and calcined powder of lithium nickel cobalt titanium composite oxide A positive electrode active material was obtained.
The composition of the obtained positive electrode active material, crystal structure, D50 of 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 Table 1. An example of TG-DTA measurement is shown in FIG. 2, and an example of DSC measurement is shown in FIG. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Example 2)
The positive electrode active material was obtained in the same manner as in Example 1 except that the fired product was obtained so that the atomic ratio of lithium to the total amount of nickel, cobalt and titanium in the nickel cobalt titanium composite hydroxide was 1: 1.03. The material was obtained, and the composition, crystal structure, particle size distribution D50, powder packing density (tap density), charge / discharge capacity, and positive electrode safety of the obtained positive electrode active material were evaluated by the above evaluation methods. The results are shown in Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Example 3)
The positive electrode active material was obtained in the same manner as in Example 1 except that the calcined product was obtained so that the atomic ratio of lithium to the total amount of nickel, cobalt and titanium in the nickel cobalt titanium composite hydroxide was 1: 1.14. The material was obtained, and the composition, crystal structure, particle size distribution D50, powder packing density (tap density), charge / discharge capacity, and positive electrode safety of the obtained positive electrode active material were evaluated by the above evaluation methods. The results are shown in Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

Example 4
A positive electrode active material was prepared in the same manner as in Example 1 except that the nickel / cobalt / titanium atomic ratio was Ni: Co: Ti = 84: 15: 1 to obtain a nickel cobalt titanium composite hydroxide. The composition of the obtained positive electrode active material, crystal structure, D50 of 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 Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Example 5)
A positive electrode active material was obtained in the same manner as in Example 1 except that the nickel cobalt titanium composite hydroxide was obtained so that the atomic ratio of nickel, cobalt and titanium was Ni: Co: Ti = 80: 12: 8. The composition of the obtained positive electrode active material, crystal structure, D50 of 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 Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 1)
Instead of using a mixed aqueous solution to which nickel sulfate and cobalt sulfate are added and a titanyl sulfate aqueous solution, a mixed aqueous solution of nickel sulfate, cobalt sulfate and titanium sulfate (however, the total concentration of nickel, cobalt and titanium is 2 mol / L To obtain the nickel cobalt titanium composite hydroxide, and the atomic ratio of lithium to the total amount of nickel, cobalt and titanium in the nickel cobalt titanium composite hydroxide is 1: 1.02. The positive electrode active material was obtained in the same manner as in Example 1 except that the fired product was obtained. The composition, crystal structure, particle size distribution D50, and powder packing density (tap density) of the obtained positive electrode active material The charge / discharge capacity and the safety of the positive electrode were evaluated by the above evaluation methods. The results are shown in Table 1. An example of TG-DTA measurement is shown in FIG. 2, and an example of DSC measurement is shown in FIG. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 2)
The positive electrode active material was obtained in the same manner as in Example 1 except that the calcined product was obtained so that the atomic ratio of lithium to the total amount of nickel, cobalt and titanium in the nickel cobalt titanium composite hydroxide was 1: 1.15. The material was obtained, and the composition, crystal structure, particle size distribution D50, powder packing density (tap density), charge / discharge capacity, and positive electrode safety of the obtained positive electrode active material were evaluated by the above evaluation methods. The results are shown in Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 3)
Except that the nickel cobalt titanium composite hydroxide was obtained so that the atomic ratio of nickel, cobalt and titanium was Ni: Co: Ti = 84.5: 15: 0.5 A positive electrode active material was obtained, and the composition, crystal structure, particle size distribution D50, powder packing density (tap density), charge / discharge capacity, and positive electrode safety of the obtained positive electrode active material were evaluated by the above evaluation methods. The results are shown in Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

(Comparative Example 4)
A positive electrode active material was obtained in the same manner as in Example 1 except that the nickel cobalt cobalt composite hydroxide was obtained so that the atomic ratio of nickel, cobalt and titanium was Ni: Co: Ti = 79: 12: 9. The composition of the obtained positive electrode active material, crystal structure, D50 of 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 Table 1. The crystal structure was a complex oxide single phase having a hexagonal layered structure.

  From Table 1, in Examples 1 to 5, cobalt and titanium are used as additive elements. In the composition of the positive electrode active material, particularly the atomic ratio of lithium and titanium, and the crystal structure, and the crystal structure at the time of charging the battery, Since it was carried out in accordance with the invention, the positive electrode active material 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 and a high capacity using the same It can be seen that a highly safe non-aqueous electrolyte secondary battery can be obtained. That is, the initial discharge capacity exceeds 190 mAh / g, and the weight loss due to TG-DTA measurement of the positive electrode after charging the battery is in two temperature ranges, so the decomposition reaction temperature causing oxygen release is dispersed in two stages. Thus, since the battery can be prevented from thermal runaway by suppressing the temperature rise of the electrolytic solution due to a rapid exothermic reaction, it is an excellent material as a new battery material that replaces the lithium cobalt composite oxide. Moreover, since the manufacturing method was performed according to the manufacturing method of the present invention in the step of obtaining the nickel cobalt titanium composite hydroxide and the step of obtaining the lithium nickel cobalt titanium composite oxide, the positive electrode active material is obtained. I understand.

  On the other hand, in Comparative Examples 1 to 4, the composition of the positive electrode active material, particularly the atomic ratio of lithium and titanium, and in Comparative Example 1, the conditions for the process of obtaining the nickel cobalt titanium composite hydroxide are as follows. It can be seen that because the conditions are not met, satisfactory results are not obtained in either thermal stability or initial discharge capacity. That is, in Comparative Examples 1 and 2, since the atomic ratio of lithium or titanium is low and does not meet this condition, the weight reduction is only in the temperature region (B), and the thermal stability is insufficient. In No. 4, the weight loss is dispersed in two regions, but since the atomic ratio of lithium or titanium is high and does not meet this condition, the initial discharge capacity falls below 190 mAh / g, and the battery characteristics deteriorate.

As is clear from the above, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery that has excellent thermal stability and a high charge / discharge capacity, The non-aqueous electrolyte secondary battery using this is a high-capacity, high-safety non-aqueous electrolyte secondary battery, so that it can take advantage of the high charge / discharge capacity while being extremely safe. Therefore, it is suitable for use as a power source for small portable electronic devices that always require a 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. 4 is a diagram illustrating an example of TG-DTA measurement of positive electrode active materials of Example 1 and Comparative Example 1. FIG. 6 is a diagram illustrating an example of DSC measurement of the positive electrode active material of Example 1 and Comparative Example 1. FIG.

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)

A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a composite oxide represented by the following composition formula (1) containing lithium, nickel, cobalt and titanium,
The crystal structure is a single phase of a complex oxide having a hexagonal layered structure, and a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° in the X-ray diffraction measurement by Cu—Kα ray when the battery is charged. And a composite oxide phase having a layered structure in which a diffraction peak appears at 2θ = 17 to 19 °, and a positive electrode active material for a nonaqueous electrolyte secondary battery.
Composition formula (1): Li _{1 + z} Ni _1-xy Co _x Ti _y O ₂ (1)
(In the formula, x, y and z satisfy the requirements shown in the following (a) to (c).)
(A) 0.10 ≦ x ≦ 0.21
(B) 0.01 ≦ y ≦ 0.08
(C) 0.03 ≦ z ≦ 0.14   The complex oxide phase having a crystal structure in which a diffraction peak appears at 2θ = 12 to 14 ° and a layered structure in which a diffraction peak appears at 2θ = 17 to 19 ° in the X-ray diffraction measurement by the Cu—Kα ray is as follows. 2. The non-aqueous electrolyte according to claim 1, wherein in the heating, TG-DTA measurement shows weight loss in the temperature range (A): 120 to 180 ° C. and the temperature range (B): 200 to 270 ° C., respectively. Positive electrode active material for secondary battery.   The weight reduction is 3.5 mass% or less in the temperature region (A) and 5.2 mass% or less in the temperature region (B) by TG-DTA measurement of the positive electrode after charging the battery. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 2, wherein the positive electrode active material is a nonaqueous electrolyte secondary battery.   4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the initial discharge capacity when used for the positive electrode of the non-aqueous electrolyte secondary battery is 190 mAh / g or more. 5. . The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, comprising the following steps (A) and (B).
Step (I): A mixed aqueous solution of nickel salt and cobalt salt, an aqueous solution of titanyl sulfate, and an aqueous alkali solution are simultaneously added dropwise to a reaction vessel, and they are agitated. Hold, co-precipitate, and after reaching a steady state in the reaction vessel , the overflowed precipitate is collected, filtered, washed with water, and dried to control the atomic ratio of nickel, cobalt, and titanium. Obtain a hydroxide.
Step (b): The nickel-cobalt-titanium composite hydroxide and lithium hydroxide or hydrate thereof are mixed, and the mixture is baked in an oxygen stream at a temperature of 700 to 800 ° C. to determine the atomic ratio of lithium. A controlled lithium nickel cobalt titanium composite oxide is obtained.   A non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 as a positive electrode.

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