JP2006228604A - Anode active substance for lithium ion secondary batterry, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode active substance which has proper heat stability and is cheap, and further whose initial discharge capacity is sufficiently large that can withstand the use as a real battery, as the anode active substance for a lithium ion secondary batterry. <P>SOLUTION: A composite hydroxide shown by general Formula Mn<SB>(1-Y-Z)</SB>Ni<SB>Y</SB>Al<SB>Z</SB>(OH)<SB>2</SB>is heat-treated at 900-1,000°C to produce a manganese-nickel-aluminium composite oxide, and the manganese-nickel-aluminium composite oxide and a lithium compound produced are mixed and heat-treated at 650-850°C, to produce a lithium-manganese-nickel-aluminium composite oxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery and a method for producing the same, and more particularly, to a positive electrode active material for a lithium ion secondary battery comprising a lithium manganese nickel aluminum composite oxide having a hexagonal layered crystal structure. The present invention relates to a substance and a manufacturing method thereof.

  In recent years, with the widespread use of portable devices such as mobile phones and laptop computers, there is an increasing demand for small and lightweight secondary batteries with high energy density. There is a non-aqueous electrolyte type lithium ion secondary battery as such, and research and development have been actively conducted and put into practical use. This lithium ion secondary battery uses a positive electrode having a lithium-containing composite oxide as an active material and a material capable of inserting and extracting lithium, such as lithium, a lithium alloy, a metal oxide, or carbon, as an active material. The main component is a negative electrode and a separator or solid electrolyte containing a non-aqueous electrolyte.

Among these components, those studied as positive electrode active materials include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ), and the like. There is. In particular, a battery using lithium cobalt composite oxide as a positive electrode has been developed to obtain excellent initial discharge capacity characteristics and cycle characteristics, and various results have already been obtained and put into practical use. Has reached.

  However, the demand for higher energy density for secondary batteries is increasing year by year, and in lithium ion secondary batteries using a lithium cobalt composite oxide that is currently in practical use as a positive electrode, cobalt is scarce and expensive. Therefore, there is a demand for an alternative material that can be realized at a lower cost and higher energy density.

Therefore, as a positive electrode active material for a non-aqueous electrolyte secondary battery, lithium manganese composite oxide (LiMn ₂ O ₄ ) using inexpensive manganese or lithium nickel composite oxide (LiNiO) using nickel instead of LiCoO _{2 2} ).

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

On the other hand, lithium nickel composite oxide (LiNiO ₂ ) has substantially the same theoretical capacity as lithium cobalt composite oxide (LiCoO ₂ ), and shows a slightly lower battery voltage than lithium cobalt composite oxide. For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance. However, when a lithium-ion secondary battery is made using a lithium-nickel composite oxide composed solely of nickel as a positive electrode active material without replacing nickel with other elements, the cycle is higher than that of lithium-cobalt composite oxide. Inferior properties. In addition, the battery performance is relatively easily lost when used or stored in a high temperature environment (for example, about 60 ° C.).

In order to solve such drawbacks, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 8-45509), as a positive electrode active material capable of maintaining good battery performance even in storage and use under a high temperature environment, Li _w Ni _x Co _y B _z O ₂ (0.05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, x + y + z = 1) Nickel composite oxides have been proposed.

In Patent Document 2 (JP-A-8-213015), for the purpose of improving the self-discharge characteristics and cycle characteristics of the lithium ion secondary _{battery, Li x Ni a Co b M} c O 2 (0.8 ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al , V, Mn, Fe, Cu, and Zn) have been proposed.

  The lithium nickel composite oxide proposed in Patent Document 1 and Patent Document 2 is higher in charge capacity and discharge capacity than the cobalt-based composite oxide, even if manufactured by a conventional manufacturing method. The characteristics are also improved. However, in the case of a product manufactured by a conventional manufacturing method, when it is left in a high temperature environment in a fully charged state, decomposition starts with oxygen release from a lower temperature than that of a cobalt-based composite oxide. There is a risk that the internal pressure will rise and the battery will explode in the worst case. There is also a danger that the released oxygen causes the electrolyte to oxidize and the temperature of the battery rises rapidly.

In order to solve such a problem, for example, in Patent Document 3 (Japanese Patent Laid-Open No. 5-242891), Li _a M _b Ni is used for the purpose of improving the thermal stability of the positive electrode material of a lithium ion secondary battery. _c Co _d O _e (M is at least one metal selected from the group consisting of Al, Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn, and Mo, and 0 <a <1. 3, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1)). Yes.

  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. When nickel is replaced with an amount of aluminum necessary to ensure the safety, the amount of nickel contributing to the oxidation-reduction reaction accompanying the charge / discharge reaction is reduced, so the initial discharge capacity, which is the most important for battery performance, is greatly reduced. Has the problem.

  When manganese is selected as the additive element M, for example, a lithium manganese nickel cobalt composite oxide is obtained. As a material of this system, a material having a 1: 1 ratio of manganese, nickel, and cobalt is generally known. However, although it is a material excellent in thermal stability, there is a problem that the cobalt used is expensive.

  Patent Documents 4 and 5 also disclose lithium manganese nickel aluminum composite oxides in which cobalt of lithium manganese nickel cobalt composite oxide is replaced with inexpensive aluminum. However, the initial discharge capacity is not specifically shown, and it is unclear whether it has an initial discharge capacity that can withstand use as an actual battery.

JP-A-8-45509

Japanese Patent Laid-Open No. 8-213015

Japanese Patent Laid-Open No. 5-242891

JP 2004-281253 A

JP 2000-223122 A

  The present invention has been made in view of such problems, and as a positive electrode active material for a lithium ion secondary battery, the thermal stability is good and inexpensive, and the initial discharge capacity is used as a real battery. It aims at providing the positive electrode active material which is a magnitude | size which can endure.

  The charge / discharge reaction of the battery proceeds as lithium ions in the positive electrode active material reversibly enter and exit. The positive electrode active material from which lithium has been extracted by charging is unstable at high temperatures, and when heated, the active material decomposes and releases oxygen, which causes oxidation of the electrolyte and causes an exothermic reaction.

  To improve the thermal stability of the positive electrode material means to suppress the decomposition reaction of the positive electrode active material from which lithium has been extracted. As a method for suppressing the decomposition reaction of the positive electrode active material disclosed heretofore, it has been generally performed that a part of nickel is substituted with an element having strong covalent bond with oxygen such as aluminum. Certainly, if the amount of substitution from nickel to aluminum is increased, it is confirmed that the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved, but nickel that contributes to the oxidation-reduction reaction accompanying the charge / discharge reaction As a result, the charge / discharge capacity is reduced. Therefore, in order to suppress the decrease in charge / discharge capacity within a certain range, it is necessary to keep the substitution amount with aluminum within a certain range. In other words, thermal stability must be sacrificed in order to obtain a certain level of charge / discharge capacity.

  In addition, in order to obtain a lithium manganese nickel aluminum composite oxide, manganese nickel aluminum composite hydroxide and a lithium compound are mixed and fired in a predetermined amount. When sulfate is used as a raw material, sulfuric acid contained in a large amount Lithium is consumed by the roots, resulting in a lithium-deficient lithium-manganese-nickel-aluminum composite oxide. Therefore, the initial discharge capacity is greatly reduced, and there is a problem that the material cannot be charged and discharged as an actual battery. Found.

In light of the above problems, the present inventor has a hexagonal layered structure, good thermal stability, is inexpensive, and has an initial discharge capacity that can withstand use as a real battery. Research and development for obtaining lithium-manganese-nickel-aluminum composite oxide, which is the same size, has been advanced. As a result, the general formula Li _{1 + X} Mn _(1-YZ) Ni _Y Al _Z O ₂ (where X, Y, and Z are −0.05 ≦ X ≦ 0.10 and 0.33 ≦ Y, respectively) ≦ 0.50, 0 <Z ≦ 0.24) A method for producing a positive electrode active material for a lithium ion secondary battery containing a lithium manganese nickel aluminum composite oxide having a hexagonal layered structure represented by It is found that a lithium manganese nickel aluminum composite oxide having good thermal stability and low cost and having an initial discharge capacity that can withstand use as a real battery can be obtained. It came to.

First, an aqueous solution in which a nickel salt, an aluminum salt, and a manganese salt are mixed so that the atomic ratio of manganese, nickel, and aluminum is the atomic ratio of the above general formula is continuously poured into the reaction vessel together with the alkaline solution, and mixed and stirred. To do. Then, coprecipitation is performed without using a complexing agent, and the resulting precipitate is filtered and washed with water to obtain a composite hydroxide Mn _(1-YZ) Ni _Y Al _Z (OH) ₂ . Next, the obtained composite hydroxide Mn _(1-YZ) Ni _Y Al _Z (OH) ₂ is heat-treated to make a manganese nickel aluminum composite oxide, and then mixed with a lithium compound and heat-treated, A lithium manganese nickel-aluminum composite oxide having good stability and low cost and having an initial discharge capacity that can withstand use as a real battery is obtained.

That is, the lithium manganese nickel aluminum composite oxide according to the present invention has a general formula Li _{1 + X} Mn _(1-YZ) Ni _Y Al _Z O ₂ (wherein X, Y, and Z are each -0.05 ≦ X ≦ 0.10, 0.33 ≦ Y ≦ 0.50, 0 <Z ≦ 0.24), and is used as a positive electrode active material for lithium ion secondary batteries. The initial discharge capacity of the lithium ion secondary battery is 100 mAh / g or more, and the calorific value in the safety evaluation test of the positive electrode is 500 J / g or less. Here, the measurement of the initial discharge capacity and the safety evaluation test of the positive electrode are performed as follows.

  70% by mass of lithium manganese nickel aluminum composite oxide powder is mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg is taken out from the resulting mixture to produce a pellet, which is used as a positive electrode.

Lithium metal is used for the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting salt is used for the electrolyte. Then, a 2032 type coin battery as shown in FIG. 1 is manufactured in an Ar atmosphere glove box whose dew point is controlled to −80 ° C.

The produced battery is left for about 24 hours, and after OCV (open circuit voltage) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm ^{2 and} is charged to a cutoff voltage of 4.3 V. The capacity when discharged to an off voltage of 3.0 V is defined as the initial discharge capacity.

The safety evaluation test of the positive electrode is a CCCV charge (constant current-constant voltage charge) of a 2032 type coin battery manufactured as described above up to a cutoff voltage of 4.5V. And then charge the positive electrode that is disassembled and taken out with care so as not to short-circuit. Specifically, 3.0 mg of the extracted positive electrode was weighed, and 1.3 mg of an electrolytic solution (a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in an equal amount using 1 M LiClO ₄ as a supporting salt) was added. Then, the sample was sealed in an aluminum measurement container and heated from 80 ° C. to 400 ° C. at a temperature rising rate of 10 ° C./min using a differential scanning calorimeter (DSC) PTC-10A (manufactured by Rigaku). This is done by measuring the amount.

In the lithium manganese nickel aluminum composite oxide according to the present invention, the average particle diameter d50 is preferably 7 to 12 μm, the tap density is preferably 1 to 1.5 g / cm ³ , and the sulfate group (SO ₄ ²⁻ ) is used. The content is preferably 0.35% by mass or less. Here, the average particle size d50 is a particle size when the cumulative mass from the minimum particle size occupies 50% of the total mass of all powders in the particle size distribution of the powder. The tap density is determined by putting 12 g of powder in a 20 ml glass graduated cylinder and dividing the powder mass 12 g by the volume after tapping 500 times.

  The positive electrode active material for lithium ion secondary batteries according to the present invention contains the lithium manganese nickel aluminum composite oxide, and the lithium ion secondary battery according to the present invention contains the positive electrode active material for lithium ion secondary batteries. To do.

The method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention has a general formula Li _{1 + X} Mn _(1-YZ) Ni _Y Al _Z O ₂ (wherein X, Y and Z are each − 0.05 ≦ X ≦ 0.10, 0.33 ≦ Y ≦ 0.50, 0 <Z ≦ 0.24) containing a lithium manganese nickel aluminum composite oxide having a hexagonal layer structure A method for producing a positive electrode active material for a lithium ion secondary battery, wherein an aqueous solution and an alkaline solution in which a nickel salt, an aluminum salt and a manganese salt are mixed so that the atomic ratio of manganese, nickel and aluminum is the atomic ratio of the above general formula And continuously co-precipitated without using a complexing agent, with the resulting reaction solution having a pH of 10 to 11 and a reaction temperature of 60 to 80 ° C. Step 1 to obtain a precipitate and obtained in step 1 Step 2 for obtaining a composite hydroxide represented by the general formula Mn _(1-YZ) Ni _Y Al _Z (OH) ₂ by filtering and washing the precipitate, and the composite hydroxide obtained in Step 2 Step 3 in which heat treatment is performed to obtain a manganese nickel aluminum composite oxide, and a step in which the manganese nickel aluminum composite oxide obtained in step 3 is mixed with a lithium compound and heat treatment is performed to obtain a lithium manganese nickel aluminum composite oxide. 4.

In the step 3, the temperature at which the composite hydroxide represented by the general formula Mn _(1-YZ) Ni _Y Al _Z (OH) ₂ is heat-treated is preferably 900 to 1000 ° C.

  Moreover, in the said process 4, it is preferable that the temperature which mixes and heat-processes a manganese nickel aluminum complex oxide and a lithium compound is 650-850 degreeC.

  According to the present invention, as a positive electrode active material for a lithium ion secondary battery, a positive electrode active material that has good thermal stability, is inexpensive, and has an initial discharge capacity that can withstand use as a real battery. Can be provided.

(1) Lithium Manganese Nickel Aluminum Composite Oxide First, the reasons for limiting the numerical values in the constituent requirements of the lithium manganese nickel aluminum composite oxide according to the present invention will be described.

The lithium manganese nickel aluminum composite oxide according to the present invention has a general formula Li _{1 + X} Mn _(1-YZ) Ni _Y Al _Z O ₂ (wherein X, Y and Z are each -0.05 ≦ X ≦ 0.10, 0.33 ≦ Y ≦ 0.50, 0 <Z ≦ 0.24) When used as a positive electrode active material of a lithium ion secondary battery The initial discharge capacity of the lithium ion secondary battery is 100 mAh / g or more, and the calorific value in the safety evaluation test of the positive electrode is 500 J / g or less.

  The atomic ratio of lithium needs to be 0.95 or more and 1.10 or less. When the atomic ratio of lithium is less than 0.95, lithium is insufficient, so that a complete hexagonal layered structure is not obtained, resulting in a decrease in discharge capacity due to residual unreacted oxide. On the other hand, when the atomic ratio of lithium exceeds 1.10, lithium is excessive, so that the particles grow excessively and it becomes difficult to move lithium ions during charge / discharge, resulting in a decrease in discharge capacity. .

  The atomic ratio of manganese needs to be 0.26 or more and less than 0.67. If the atomic ratio of manganese is less than 0.26, the amount of manganese that contributes to thermal stability decreases, so the calorific value in the safety evaluation test of the positive electrode is 500 J / g or more. On the other hand, when the atomic ratio of manganese is 0.67 or more, the amount of nickel contributing to the charge / discharge capacity is reduced, and the initial discharge capacity is 100 mAh / g or less.

  The atomic ratio of nickel needs to be 0.33 or more and 0.50 or less. When the atomic ratio of nickel is less than 0.33, the amount of nickel contributing to the charge / discharge capacity is reduced, and the initial discharge capacity is 100 mAh / g or less. On the other hand, if the atomic ratio of nickel exceeds 0.50, the amount of manganese that contributes to thermal stability decreases, so the calorific value in the safety evaluation test of the positive electrode is 500 J / g or more.

  The atomic ratio of aluminum needs to be larger than 0 and 0.24 or less. If aluminum is not contained at all, elution of manganese into the electrolytic solution that occurs when charging / discharging, which is a weak point of the manganese system, cannot be suppressed, and cycle characteristics deteriorate. On the other hand, when the atomic ratio of aluminum exceeds 0.24, the amount of elements that do not contribute to the charge / discharge capacity increases, so the initial discharge capacity becomes 100 mAh / g or less.

  The crystal structure needs to have a hexagonal layered structure. By having a hexagonal layered structure, the initial discharge capacity is increased.

  The initial discharge capacity measured by producing a 2032 type coin battery as described above needs to be 100 mAh / g or more. Whether or not the initial discharge capacity is 100 mAh / g or more is a measure of whether or not the battery can withstand use as an actual battery.

  The calorific value in the safety evaluation test of the positive electrode described above needs to be 500 J / g or less. When the calorific value exceeds 500 J / g, safety when used as an actual battery is not sufficient.

Note that the present inventors have confirmed that there is no practical problem in safety if the calorific value is 500 J / g or less in lithium cobalt composite oxide (LiCoO ₂ ) that has been put into practical use.

The average particle diameter d50 is preferably 7 to 12 μm. When the average particle diameter d50 is less than 7 μm, it is not preferable in that the tap density is 1 g / cm ³ or less. When the thickness exceeds 12 μm, a positive electrode mixture paste prepared by mixing a conductive material and a binder to produce a positive electrode is uniformly applied, for example, on the surface of a current collector made of aluminum foil. It is not preferable in that it cannot be performed.

The tap density is preferably 1 to 1.5 g / cm ³ . When the tap density is less than 1 g / cm ³ , the amount that can be filled in the production of a battery is reduced, which is not preferable in that a certain capacity cannot be satisfied. Moreover, when it exceeds 1.5 g / cm < ³ >, it is unpreferable at the point from which the average particle diameter d50 will exceed 12 micrometers.

  The content of sulfate radicals is preferably 0.35% by mass or less. This is because if the sulfate group content exceeds 0.35% by mass, the sulfate group is combined with the lithium compound, resulting in an incomplete hexagonal layered structure.

  Next, a method for producing a lithium manganese nickel aluminum composite oxide according to the present invention will be described below.

  In the method for producing a lithium manganese nickel aluminum composite oxide having a hexagonal layered structure represented by the general formula described above, the hydroxide as the raw material is a mixed aqueous solution of nickel salt, manganese salt and aluminum salt, and alkali. The solution is obtained simultaneously and continuously into the reaction vessel, mixed and stirred, and precipitated, and is obtained by a so-called coprecipitation method.

  The conditions used for the coprecipitation were not using a complexing agent, and the pH range of the reaction solution in a reaction vessel in which a mixed aqueous solution of nickel salt, manganese salt and aluminum salt and an alkaline solution were mixed was pH = 10 to 11 And the temperature of the reaction solution was in the range of more than 60 ° C. and 80 ° C. or less.

  The reason for not using a complexing agent is that when a complexing agent such as ammonia is used, manganese does not form a complex, and therefore the pH region in which nickel precipitates as a hydroxide fluctuates, which is not preferable. .

  When a complexing agent is not used, when the reaction solution in the reaction tank is crystallized in the pH range of pH = 11 to 13, fine particles are obtained, filterability is deteriorated, and spherical particles cannot be obtained. For this reason, the problem that cleaning becomes insufficient and the impurity concentration increases occurs. In addition, if the pH of the reaction solution in the reaction tank is less than 10, the production rate of manganese hydroxide is remarkably slow, manganese ions remain in the filtrate, and the amount of manganese hydroxide precipitated is less than the intended composition. As a result, the mixed hydroxide having the desired ratio cannot be obtained. Therefore, the pH range of the reaction solution in the reaction tank is set to pH = 10 to 11, the precipitation amount of manganese hydroxide is increased, and the temperature of the reaction solution is maintained at a temperature exceeding 60 ° C. To suppress the nickel hydroxide precipitation reaction. Thereby, the precipitation amount of manganese hydroxide and nickel hydroxide becomes the target amount, and it can be avoided that the precipitate deviates from the target composition, and a nickel aluminum manganese composite hydroxide having the target composition is obtained. be able to.

  When the temperature of the reaction solution in the reaction vessel exceeds 80 ° C., the amount of water evaporation increases, so the slurry concentration increases, and sodium sulfate produced in the neutralization reaction becomes supersaturated, and sodium sulfate is added to the filtrate. This causes a problem that the concentration of impurities in the hydroxide increases. Further, since the precipitation rate of the hydroxide is increased, the particle growth is insufficient and the particles have a small average particle diameter d50. Further, when the temperature of the reaction solution in the reaction vessel is lower than 60 ° C., the growth of particles in the pH range of pH = 10 to 11 is caused by the decrease in the precipitation rate even if the precipitation amount of manganese hydroxide and nickel hydroxide is the same. Occurs, resulting in coarse particles having an average particle diameter d50 exceeding 15 μm. When such a problem arises, the charge / discharge capacity of the obtained positive electrode material decreases, which is not preferable.

  This manganese nickel aluminum composite hydroxide must be heat-treated before mixing with the lithium compound to form a composite oxide. The reason why it is necessary to heat-treat the composite oxide is that manganese, nickel and aluminum are completely dissolved, and manganese nickel aluminum when sulfate is used as the raw material for manganese nickel aluminum composite hydroxide This is for removing sulfate radicals contained in the composite hydroxide out of the system in the form of sulfurous acid gas. The heat treatment is preferably performed at 900 to 1000 ° C.

Even if the obtained manganese nickel aluminum composite hydroxide was directly mixed with a lithium compound and baked without heat treatment to obtain a lithium manganese nickel aluminum composite, manganese, nickel, and aluminum were not sufficiently dissolved. In addition, if the composite hydroxide contains a sulfate radical (SO ₄ ²⁻ ), the sulfate radical (SO ₄ ²⁻ ) is bonded to the lithium compound, so that a hexagonal layered structure is formed. The structure will be incomplete. For this reason, even if it uses the obtained lithium manganese nickel aluminum complex oxide as a positive electrode material, since initial stage charge / discharge capacity will become remarkably low, it cannot be used as a positive electrode material.

On the other hand, when the manganese nickel aluminum composite hydroxide is heat-treated into a manganese nickel aluminum composite oxide before mixing with the lithium compound as in the present invention, manganese, In addition to the solid solution of nickel and aluminum, sulfate radical (SO ₄ ^2- ) is removed from the system in the form of SO ₂ gas during heat treatment, and the content of sulfate radical (SO ₄ ^2- ) Becomes 0.35 mass% or less. Therefore, after that, if the lithium compound is mixed and subjected to a predetermined heat treatment, a lithium manganese nickel aluminum composite oxide having a hexagonal layered structure can be obtained. When used as a positive electrode material, charge and discharge are possible. Become a material. In addition, in the manganese nickel aluminum composite oxide obtained by heat treatment, in order to sufficiently dissolve manganese, nickel, and aluminum, the heat treatment temperature of the manganese nickel aluminum composite hydroxide is preferably 900 ° C. or higher. In addition, when the sulfate group (SO ₄ ²⁻ ) is present in the manganese nickel aluminum composite hydroxide at a heat treatment temperature of less than 900 ° C., the sulfate group (SO ₄ ²⁻ ) can be sufficiently removed. It is not possible and not preferable. On the other hand, if the heat treatment temperature exceeds 1000 ° C., the sintering of the manganese nickel aluminum composite oxide proceeds and pulverization is required, which is not preferable.

  The manganese nickel aluminum composite oxide obtained by heat treating the manganese nickel aluminum composite hydroxide is mixed with a predetermined amount of lithium compound and subjected to a predetermined heat treatment to obtain the lithium manganese nickel aluminum composite oxide according to the present invention. be able to.

  As the lithium compound, lithium carbonate, lithium hydroxide and hydrates thereof are preferable. As the nickel compound, nickel sulfate, nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide, and the like can be used. Carbon dioxide or the like can be used. However, as described above, it is more preferable that nickel, manganese, and aluminum are mixed with a lithium compound after being subjected to a predetermined heat treatment in the form of a composite hydroxide and then subjected to a heat treatment.

  The heat treatment after mixing a predetermined amount of the lithium compound and the manganese nickel aluminum composite oxide obtained as described above may be performed in an oxygen stream at a temperature of about 650 to 850 ° C. for about 10 to 20 hours. .

  When the firing temperature is lower than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium manganese nickel aluminum composite oxide having a desired layered structure. Further, if the temperature exceeds 850 ° C., Ni is mixed into the Li layer, Li is mixed into the Ni layer and the layered structure is disturbed, and the site occupancy rate of metal ions other than lithium at the 3a site becomes larger than 2%. For this reason, the mixing rate of metal ions at the 3a site, which is the lithium site, is increased, the lithium ion diffusion path is obstructed, and the battery using the lithium manganese nickel aluminum composite oxide has a reduced initial discharge capacity and output. This is not preferable.

Using the lithium manganese nickel aluminum composite oxide produced as described above as a positive electrode active material, a 2032 type coin battery as shown in FIG. 1 is produced and left for about 24 hours, and the OCV (open circuit voltage) is After stabilization, assuming that the current density with respect to the positive electrode is 0.5 mA / cm ² and charging to a cut-off voltage of 4.3 V, and the capacity when discharged to a cut-off voltage of 3.0 V after a pause of 1 hour is the initial discharge capacity, The initial discharge capacity is 100 mAh / g or more. Therefore, the lithium ion secondary battery configured using the lithium manganese nickel aluminum composite oxide produced as described above as the positive electrode active material has an initial discharge capacity large enough to withstand use as an actual battery.

  In addition, the safety evaluation of the positive electrode is performed by charging a 2032 type coin battery created by the same method as described above to CCCV charge (constant current-constant voltage charge) up to a cut-off voltage of 4.5V. A charging method using a two-phase charging process that is performed at a constant current and then terminated at a constant voltage.) Then, 3.0 mg of the positive electrode taken out and disassembled with care so as not to be short-circuited is measured. 1.3 mg of the solution was added, sealed in an aluminum measuring container, and heated from 80 ° C. to 400 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC) PTC-10A (manufactured by Rigaku). And the calorific value can be measured. When the calorific value is 500 J / g or less, the present inventors have confirmed that there is no practical problem in safety as an actual battery as described above. A lithium ion secondary battery constructed using manganese nickel aluminum composite oxide as a positive electrode active material has a small calorific value of 500 J / g or less, and there is no problem in safety.

In addition, the average particle diameter d50 (particle diameter in which the cumulative mass is 50%) in the particle size distribution of the obtained lithium manganese nickel aluminum composite oxide is 7.0 to 12.0 μm, and the tap density is 1.0 to 1.5 g. / Cm ³ is preferable. If it is out of the above range, it becomes difficult to properly produce the positive electrode, for example, it becomes difficult to sufficiently fill the positive electrode active material when producing the positive electrode.

(2) Positive electrode Next, the preparation method of a positive electrode, the positive electrode compound material which forms a positive electrode, and each material which comprises it are demonstrated.

Formula _{Li 1 + X Mn (1-} YZ) Ni Y Al Z O 2 ( where wherein X, Y, Z are each -0.05 ≦ X ≦ 0.10,0.33 ≦ Y ≦ 0 A positive electrode using a lithium manganese nickel aluminum composite oxide having a hexagonal layered structure represented by .50, 0 <Z ≦ 0.24) as a positive electrode active material is produced, for example, as follows.

  A powdery positive electrode active material, a conductive material, and a binder are mixed, and activated carbon and a target solvent such as viscosity adjustment are added as necessary, and kneaded to prepare a positive electrode mixture paste.

  The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass and the content of the conductive material is the same as the positive electrode of a general lithium secondary battery. 1 to 20% by mass, and the binder content is preferably 1 to 20% by mass.

  The positive electrode is produced by applying the obtained positive electrode mixture paste to the surface of a current collector made of aluminum foil, for example, and drying to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode is produced. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

  In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluororubber, styrene butadiene, cellulose resin, polyacrylic acid, and the like can be used.

  The binder plays a role of holding the active material particles, and for example, fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, and thermoplastic resins such as polypropylene and polyethylene can be used. If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Moreover, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(3) Negative electrode For the negative electrode, a negative electrode mixture formed by mixing metallic lithium, lithium alloy, etc., and a negative electrode active material capable of inserting and extracting lithium ions with a binder and adding an appropriate solvent to form a paste. In addition, it is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

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

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

(5) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used.

  Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(6) Shape and configuration of battery The shape of the lithium secondary battery according to the present invention composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above is various, such as a cylindrical type and a laminated type. be able to.

  In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolyte. The positive electrode current collector and the positive electrode terminal communicating with the outside, and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like. The battery having the above configuration can be sealed in a battery case to complete the battery.

(7) Assumed Field of Application As described above, the positive electrode active material for a lithium ion secondary battery according to the present invention has an initial discharge capacity that can withstand use as a real battery, and safety. It is made of inexpensive materials such as manganese, nickel, and aluminum.

  Therefore, it is considered that the nonaqueous electrolyte secondary battery according to the present invention is suitable for use in a field where high safety and low cost are required, such as a power source for an electric vehicle.

  On the other hand, in a power source for an electric vehicle, since a large output is required, an increase in size of a battery is inevitable, and it is difficult to ensure safety. In addition, it is indispensable to install an expensive protection circuit for ensuring a higher level of safety.

  On the other hand, since the lithium ion secondary battery according to the present invention has excellent safety, it is easy to ensure safety, simplify an expensive protection circuit, and reduce costs. it can. Therefore, the nonaqueous electrolyte secondary battery according to the present invention is suitable as a power source for electric vehicles.

  The electric vehicle power source described here includes not only an electric vehicle driven purely by electric energy but also a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

  Hereinafter, the present invention will be described in detail by way of examples. Table 1 summarizes the composition, production conditions, and evaluation results of the lithium manganese nickel aluminum composite oxide synthesized in each Example and Comparative Example.

Example 1
Manganese sulfate (manufactured by Shinyo Co., Ltd.), nickel sulfate (manufactured by Sumitomo Metal Mining Co., Ltd.) and aluminum sulfate (manufactured by Wako Pure Chemical Industries, Ltd.) so that the molar ratio of manganese: nickel: aluminum is 47: 47: 6 ) And a 12.5% aqueous sodium hydroxide solution are simultaneously added to the reaction vessel, and the pH of the resulting reaction solution is kept in the range of 10 to 11 and the reaction temperature in the range of 65 to 70 ° C. Then, manganese nickel aluminum composite hydroxide particles were formed by a coprecipitation method. Thereafter, the entire amount of hydroxide slurry in the reaction vessel was recovered, filtered, washed with water and dried to obtain a dry powder of manganese nickel aluminum composite hydroxide. This metal composite hydroxide is composed of secondary particles in which a plurality of primary particles of 1 μm or less are aggregated.

In order to completely dissolve this manganese nickel aluminum composite hydroxide and to remove sulfate radicals (SO ₄ ²⁻ ) contained in the hydroxide, the dried powder was pulverized and passed through a sieve having a sieve size of 106 μm. The obtained sieving powder was baked in an air stream at 1000 ° C. for 10 hours in an electric furnace, and then cooled to room temperature to obtain a manganese nickel aluminum composite oxide.

  The composite oxide and commercially available lithium carbonate (manufactured by FMC) were weighed so that the ratio of the total number of atoms of manganese, nickel and aluminum to the number of atoms of lithium was 1: 1.05, Thoroughly mixed with sufficient strength to maintain secondary particle morphology. 20 g of this mixture was put into a 5 cm × 12 cm × 3 cm magnesia firing container and heated to 900 ° C. at a heating rate of 5 ° C./min in an oxygen stream at a flow rate of 3 L / min using a closed electric furnace. After firing at 900 ° C. for 10 hours, the furnace was cooled to room temperature.

When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.07 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure. The average particle diameter d50 of the particle size distribution measured by Microtrac was 8.7 μm, and the tap density was 1.27 g / cm ³ . The tap density was determined by putting 12 g of powder in a 20 ml glass graduated cylinder and dividing the powder mass of 12 g by the volume after tapping 500 times.

  The initial discharge capacity evaluation of the obtained lithium manganese nickel aluminum composite oxide was performed as follows. 70% by mass of lithium manganese nickel aluminum composite oxide powder was mixed with 20% by mass of acetylene black and 10% by mass of PTFE, and 150 mg was taken out from the resulting mixture to produce a pellet, which was used as a positive electrode.

Lithium metal was used for 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 for the electrolyte. Then, a 2032 type coin battery as shown in FIG. 1 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.

The prepared battery is left for about 24 hours, and after OCV (open circuit voltage) is stabilized, the initial charge capacity is the capacity when the current density with respect to the positive electrode is 0.5 mA / cm ² and the battery is charged to a cutoff voltage of 4.3 V. The capacity when the battery was discharged to a cutoff voltage of 3.0 V after 1 hour of rest was defined as the initial discharge capacity.

The safety of the positive electrode is evaluated by CCCV charging (constant current-constant voltage charging) of a 2032 type coin battery made by the same method as described above up to a cutoff voltage of 4.5V. The charging method using a two-phase charging process in which charging is terminated at a constant voltage), and then the positive electrode was disassembled and taken out with care so as not to short-circuit. Specifically, 3.0 mg of the extracted positive electrode was weighed, and 1.3 mg of an electrolytic solution (a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in an equal amount using 1 M LiClO ₄ as a supporting salt) was added. The temperature is increased from 80 ° C. to 400 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC) PTC-10A (Rigaku) and the heat generation behavior is measured. It was done by doing.

  Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Example 2)
The composite hydroxide was coprecipitated in the same manner as in Example 1 except that an aqueous solution in which manganese sulfate, nickel sulfate, and aluminum sulfate were mixed so that the molar ratio of manganese: nickel: aluminum was 43:43:14 was used. Heat treatment, mixing with lithium carbonate, and firing. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.10 Mn _0.43 Ni _0.43 Al _0.14 O ₂ ) having a hexagonal layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 7.7 μm, and the tap density was 1.15 g / cm ³ . The initial discharge capacity was measured by battery evaluation, and the heat generation behavior was measured using a differential scanning calorimeter (DSC). Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Example 3)
The composite hydroxide was coprecipitated in the same manner as in Example 1 except that an aqueous solution in which manganese sulfate, nickel sulfate and aluminum sulfate were mixed so that the molar ratio of manganese: nickel: aluminum was 38:38:24 was used. Heat treatment, mixing with lithium carbonate, and firing.

When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.09 Mn _0.38 Ni _0.38 Al _0.24 O ₂ ) having a hexagonal layered structure. The average particle diameter d50 of the particle size distribution measured by Microtrac was 7.1 μm, and the tap density was 1.05 g / cm ³ . The initial discharge capacity was measured by battery evaluation, and the heat generation behavior was measured using a differential scanning calorimeter (DSC). Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

Example 4
The composite hydroxide obtained in Example 1 was mixed and fired with lithium carbonate under the same conditions as in Example 1 except that the composite hydroxide was heat-treated at 900 ° C. to obtain a composite oxide. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.07 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 8.5 μm, and the tap density was 1.25 g / cm ³ . The initial discharge capacity was measured by battery evaluation, and the heat generation behavior was measured using a differential scanning calorimeter (DSC). Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Example 5)
The composite hydroxide obtained in Example 1 was mixed and fired with lithium carbonate under the same conditions as in Example 1 except that the composite hydroxide was heat-treated at 890 ° C. to obtain a composite oxide. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.07 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 8.4 μm, and the tap density was 1.24 g / cm ³ . The initial discharge capacity was measured by battery evaluation, and the heat generation behavior was measured using a differential scanning calorimeter (DSC). Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Example 6)
The composite hydroxide obtained in Example 1 was mixed and fired with lithium carbonate under the same conditions as in Example 1 except that the composite hydroxide was heat-treated at 1010 ° C. to obtain a composite oxide. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.07 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 12.0 μm, and the tap density was 1.48 g / cm ³ . The initial discharge capacity was measured by battery evaluation, and the heat generation behavior was measured using a differential scanning calorimeter (DSC). Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Comparative Example 1)
The composite hydroxide was coprecipitated in the same manner as in Example 1 except that an aqueous solution in which manganese sulfate, nickel sulfate and aluminum sulfate were mixed so that the molar ratio of manganese: nickel: aluminum was 33:33:34 was used. , Heat treatment, mixing with lithium carbonate, and firing.

When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.09 Mn _0.33 Ni _0.33 Al _0.34 O ₂ ) having a hexagonal layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 12.3 μm, and the tap density was 1.43 g / cm ³ . The initial discharge capacity was measured by battery evaluation, and the heat generation behavior was measured using a differential scanning calorimeter (DSC). Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Comparative Example 2)
The composite hydroxide obtained in Example 1 was used in the same manner as in Example 1 except that the composite hydroxide was used without heat treatment, mixed with lithium carbonate, and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a positive electrode active material having a hexagonal layered structure, but having a lithium sulfate peak, and not a complete layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 9.8 μm, and the tap density was 1.48 g / cm ³ . Table 1 shows the elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide and the initial discharge capacities obtained by battery evaluation. In addition, since the initial discharge capacity was low, the heat generation behavior of the positive electrode was not measured.

(Comparative Example 3)
The composite hydroxide obtained in Example 2 was used in the same manner as in Example 1 except that it was used without heat treatment, mixed with lithium carbonate, and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a positive electrode active material having a hexagonal layered structure, but having a lithium sulfate peak, and not a complete layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 11.4 μm, and the tap density was 1.50 g / cm ³ . Table 1 shows the elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide and the initial discharge capacities obtained by battery evaluation. In addition, since the initial discharge capacity was low, the heat generation behavior of the positive electrode was not measured.

(Comparative Example 4)
The composite hydroxide obtained in Example 3 was used in the same manner as in Example 1 except that the composite hydroxide was used without heat treatment, mixed with lithium carbonate, and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a positive electrode active material having a hexagonal layered structure, but having a lithium sulfate peak, and not a complete layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 13.0 μm, and the tap density was 1.69 g / cm ³ . Table 1 shows the elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide and the initial discharge capacities obtained by battery evaluation. In addition, since the initial discharge capacity was low, the heat generation behavior of the positive electrode was not measured.

(Comparative Example 5)
The composite hydroxide obtained in Comparative Example 1 was used in the same manner as in Example 1 except that the composite hydroxide was used without heat treatment, mixed with lithium carbonate, and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a positive electrode active material having a hexagonal layered structure, but having a lithium sulfate peak, and not a complete layered structure.

The average particle diameter d50 of the particle size distribution measured by Microtrac was 17.3 μm, and the tap density was 1.74 g / cm ³ . Table 1 shows the elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide and the initial discharge capacities obtained by battery evaluation. In addition, since the initial discharge capacity was low, the heat generation behavior of the positive electrode was not measured.

(Comparative Example 6)
Except that the reaction pH was 9 or more and less than 10, a manganese nickel aluminum composite hydroxide was obtained and heat-treated in the same manner as in Example 1, followed by mixing and baking with lithium carbonate. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.06 Mn _0.44 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure. The average particle diameter d50 of the particle size distribution measured by Microtrac was 15.1 μm, and the tap density was 1.43 g / cm ³ . Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Comparative Example 7)
Except that the reaction pH was more than 11 and 12 or less, a manganese nickel aluminum composite hydroxide was obtained and heat-treated in the same manner as in Example 1, followed by mixing and baking with lithium carbonate. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.06 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure. The particle size distribution d50 measured by Microtrac was 6.6 μm, and the tap density was 1.20 g / cm ³ . Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Comparative Example 8)
Except that the reaction temperature was 55 ° C., a manganese nickel aluminum composite hydroxide was obtained in the same manner as in Example 1, heat-treated, mixed with lithium carbonate, and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.07 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure. The average particle diameter d50 of the particle size distribution measured by Microtrac was 15.4 μm, and the tap density was 1.44 g / cm ³ . Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Comparative Example 9)
Except that the reaction temperature was 85 ° C., a manganese nickel aluminum composite hydroxide was obtained in the same manner as in Example 1, heat-treated, and then mixed with lithium carbonate and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.07 Mn _0.47 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure. The average particle diameter d50 of the particle size distribution measured by Microtrac was 6.8 μm, and the tap density was 1.26 g / cm ³ . Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

(Comparative Example 10)
Except that ammonia was added as a complexing agent, a manganese nickel aluminum composite hydroxide was obtained in the same manner as in Example 1, heat-treated, and then mixed with lithium carbonate and fired. When the obtained fired product was analyzed by X-ray diffraction, it was a lithium manganese nickel aluminum composite oxide (Li _1.06 Mn _0.42 Ni _0.47 Al _0.06 O ₂ ) having a hexagonal layered structure. The average particle diameter d50 of the particle size distribution measured by Microtrac was 10.5 μm, and the tap density was 1.33 g / cm ³ . Table 1 shows elemental analysis values of the obtained lithium manganese nickel aluminum composite oxide, initial discharge capacity obtained by battery evaluation, and calorific value of the positive electrode obtained by DSC measurement.

  Examples 1 to 6 within the scope of the present invention have good initial discharge capacities of 100 mAh / g or more. In addition, the present inventors have confirmed that if the calorific value measured by DSC by the above-described method is 500 J / g or less, there is no practical problem in safety as an actual battery. The lithium manganese nickel aluminum composite oxides shown in Examples 1 to 6 have a small calorific value of 500 J / g or less, and it can be seen that the material has no safety problem.

Furthermore, in Examples 1 to 4, since the heat treatment temperature for obtaining the manganese nickel aluminum composite oxide from the manganese nickel aluminum composite hydroxide is within a preferable temperature range (900 to 1000 ° C.), the obtained lithium manganese The content of sulfate radicals (SO ₄ ²⁻ ) contained in the nickel aluminum composite oxide is reduced, and the amount separated as lithium sulfate is reduced. Moreover, an average particle diameter is also 7.1-8.7 micrometers, and is less than 10 micrometers. For this reason, the initial discharge capacity of each of Examples 1 to 4 exceeds 110 (mAh / g), which indicates that the material is suitable as a battery material.

In the lithium manganese nickel aluminum composite oxide obtained in Example 5, the heat treatment temperature for obtaining the manganese nickel aluminum composite oxide from the manganese nickel aluminum composite hydroxide is 890 ° C., which is 900, which is the lower limit of the preferable temperature range. Since the temperature is lower than 0 ° C., the content of sulfate radical (SO ₄ ²⁻ ) is slightly high at 1.20% by mass, and the initial discharge capacity is slightly low at 105.2 mAh / g. However, it exceeds 100 mAh / g. Moreover, the calorific value measured by DSC is 500 J / g or less, and there is no problem in safety. Therefore, it is a material that can be used as a battery material.

In the lithium manganese nickel aluminum composite oxide obtained in Example 6, the heat treatment temperature for obtaining the manganese nickel aluminum composite oxide from the manganese nickel aluminum composite hydroxide is 1010 ° C., which is 1000, which is the upper limit of the preferable temperature range. Although the temperature is higher than ° C., the content of sulfate radical (SO ₄ ²⁻ ) is low because the heat treatment is performed at a higher temperature. However, since the heat treatment is performed at a higher temperature, the sintering proceeds, the average particle diameter d50 is as large as 12.0 μm, and the initial discharge capacity is slightly low at 104.0 mAh / g. However, it exceeds 100 mAh / g. Moreover, the calorific value measured by DSC is 500 J / g or less, and there is no problem in safety. Therefore, it is a material that can be used as a battery material.

  The manganese nickel aluminum composite oxide obtained in Comparative Example 1 has an aluminum atomic ratio of 0.34, which exceeds the upper limit of 0.24 in the range of the present invention. For this reason, initial discharge capacities are 67.8 mAh / g and 100 mAh / g or less, which is not preferable as a battery material. Further, the positive electrode active material shown in Comparative Example 1 has a calorific value measured by DSC of 571.3 J / g, a calorific value exceeding 500 J / g, and it can be seen that there is a problem with safety. .

In Comparative Examples 2 to 5, the obtained manganese nickel aluminum composite hydroxide is mixed and fired with lithium carbonate without any heat treatment. For this reason, in the obtained lithium manganese nickel aluminum composite oxide, the content ratio of sulfate radical (SO ₄ ²⁻ ) is considered to be increased and separated as lithium sulfate. As a result of analysis by X-ray diffraction, The peak of lithium sulfate is actually recognized, and it is considered that the lithium of the obtained lithium manganese nickel aluminum composite oxide is insufficient. Therefore, the initial discharge capacities are 3.5 to 89.4 mAh / g and 100 mAh / g or less. In particular, Comparative Examples 3 to 5 are as small as 3.5 to 19.2 mAh / g and are not suitable as battery materials. It is.

  In Comparative Example 6, the pH of the reaction solution in the reaction vessel at the time of forming the manganese nickel aluminum composite hydroxide particles is 9 ≦ pH <10, and in the direction of decreasing pH from the range of the present invention (10 ≦ pH ≦ 11). It is off. For this reason, the atomic ratio of Mn becomes smaller than the composition at the time of mixing, and the initial discharge capacity is reduced.

  In Comparative Example 7, the pH of the reaction solution in the reaction tank at the time of forming the manganese nickel aluminum composite hydroxide particles is 11 <pH ≦ 12, and the pH is increased from the range of the present invention (10 ≦ pH ≦ 11). It is off. For this reason, the average particle diameter d50 in the particle size distribution is as small as 6.6 μm, and the initial discharge capacity is reduced.

  In Comparative Example 8, the temperature of the reaction liquid in the reaction vessel at the time of forming the manganese nickel aluminum composite hydroxide particles is 55 ° C., and deviates from the range of the present invention (60 to 80 ° C.) in the direction of decreasing temperature. For this reason, the average particle diameter d50 in the particle size distribution is as large as 15.4 μm, and the initial discharge capacity is reduced.

  In Comparative Example 9, the temperature of the reaction liquid in the reaction vessel at the time of forming the manganese nickel aluminum composite hydroxide particles is 85 ° C., and deviates from the range of the present invention (60 to 80 ° C.) in the direction of increasing temperature. For this reason, the average particle diameter d50 in the particle size distribution is as small as 6.8 μm, and the initial discharge capacity is reduced.

  Comparative Example 10 uses a complexing agent (ammonia). For this reason, in the obtained lithium manganese nickel aluminum composite oxide, the atomic ratio of manganese is about 10% smaller than the atomic ratio of the target composition, and the initial discharge capacity is lowered. Therefore, it can be said that using a complexing agent (ammonia) is a method with poor mass productivity.

Cross section of coin battery used for battery evaluation

Explanation of symbols

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

Claims (8)

Formula _{Li 1 + X Mn (1-} YZ) Ni Y Al Z O 2 ( where wherein X, Y, Z are each -0.05 ≦ X ≦ 0.10,0.33 ≦ Y ≦ 0. 50, 0 <Z ≦ 0.24). When used as a positive electrode active material of a lithium ion secondary battery, the initial discharge capacity of the lithium ion secondary battery is 100 mAh. Lithium manganese nickel-aluminum composite oxide having a calorific value of 500 J / g or less in a positive electrode safety evaluation test. The lithium manganese nickel aluminum composite oxide according to claim 1, wherein the average particle diameter d50 is 7 to 12 µm and the tap density is 1 to 1.5 g / cm ³ .   The lithium manganese nickel aluminum composite oxide according to claim 1 or 2, wherein the sulfate group content is 0.35 mass% or less.   The positive electrode active material for lithium ion secondary batteries containing the lithium manganese nickel aluminum complex oxide in any one of Claims 1-3.   The lithium secondary battery which used the lithium secondary battery positive electrode active material of Claim 4 as a positive electrode active material. Formula _{Li 1 + X Mn (1-} YZ) Ni Y Al Z O 2 ( where wherein X, Y, Z are each -0.05 ≦ X ≦ 0.10,0.33 ≦ Y ≦ 0. 50, 0 <Z ≦ 0.24), a method for producing a positive electrode active material for a lithium ion secondary battery containing a lithium manganese nickel aluminum composite oxide having a hexagonal layered structure represented by: An aqueous solution in which a nickel salt, an aluminum salt and a manganese salt are mixed and an alkaline solution are continuously charged into the reaction vessel so that the atomic ratio of nickel and aluminum is the atomic ratio of the above general formula, and the pH of the resulting reaction liquid is obtained. In the range of 10 to 11 and the reaction temperature in the range of 60 to 80 ° C., coprecipitation without using a complexing agent to obtain a precipitate, and filtration of the precipitate obtained in step 1 By washing with water, the general formula Mn _(1-YZ) Ni _Y Al Obtained in Step 2 for obtaining a composite hydroxide represented by _Z (OH) ₂ , Step 3 for heat treating the composite hydroxide obtained in Step 2 to make a manganese nickel aluminum composite oxide, and Step 3 A method for producing a positive electrode active material for a lithium ion secondary battery, comprising the step 4 of mixing a manganese nickel aluminum composite oxide and a lithium compound and performing a heat treatment to obtain a lithium manganese nickel aluminum composite oxide . The temperature of heat-treating the composite hydroxide represented by the general formula Mn _(1-YZ) Ni _Y Al _Z (OH) ₂ in the step 3 is 900 to 1000 ° C. A method for producing a positive electrode active material for a lithium ion secondary battery.   8. The positive electrode for a lithium ion secondary battery according to claim 6, wherein a temperature at which the manganese nickel aluminum composite oxide and the lithium compound are mixed and heat-treated in the step 4 is 650 to 850 ° C. 8. A method for producing an active material.

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