WO2015111658A1 - Positive electrode active material, positive electrode material using same, positive electrode for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

Provided are: a positive electrode active material which has high capacity and excellent load characteristics; a positive electrode material which uses this positive electrode active material; a positive electrode for nonaqueous electrolyte secondary batteries; and a nonaqueous electrolyte secondary battery. A positive electrode active material which is composed of a composite oxide having a lamellar structure and represented by general formula (1), and which satisfies (i) and/or (ii) described below. Li[Li_aMn_bMe_c]O_2-d (1) (In the formula, Me represents at least one element selected from among transition metals other than Mn, and a, b, c and d satisfy 0 < a < 1/3, 0 < b < 2/3, 0 < c < 1 and 0 ≤ d ≤ 0.2). (i) The average primary particle diameter is 150 nm or less; and the ratio of the diffraction peak intensity I(020) around 2θ = 20.8° to the diffraction peak intensity I(003) around 2θ = 18.6° in an X-ray diffraction pattern, namely I(020)/I(003) is 0.5 or less. (ii) The lamellar structure has a stacking fault density of 0.4 or less.

Description

Cathode active material, cathode material using the same, cathode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

The present invention relates to a positive electrode active material, a positive electrode material using the same, a positive electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

In recent years, non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries, are widely used as power sources for personal computers and portable devices because they have high voltage and high energy density. Lithium secondary batteries are also promising as power sources for environmentally friendly electric vehicles and hybrid vehicles.

Current positive electrode active materials for lithium secondary batteries mainly use lithium-containing transition metal oxide materials that exhibit a battery voltage of about 4 V. Specifically, lithium cobaltate, lithium nickelate, lithium manganate Etc. are used.

However, the available capacity of the lithium-containing transition metal oxide material currently used is as small as 100 to 200 mAh / g. Therefore, in order to realize further higher energy density of the lithium secondary battery, a positive electrode active material having a larger capacity per unit weight is required.

In recent years, as a positive electrode active material having a possibility of meeting this requirement, electrochemically inactive layered Li ₂ MnO ₃ and electrochemically active layered LiMO ₂ (M is Co, Ni, etc.). Since a Li-excess solid solution with a transition metal has a high capacity exceeding 200 mAh / g and a relatively high true density, it has been studied as a next-generation high-capacity positive electrode active material.

For example, Patent Document 1 describes the necessity of controlling an excess amount of Li for the purpose of controlling the valence of Ni in order to improve the load characteristics of an excess Li solid solution. However, as far as the examples are concerned, the discharge capacity at 1 C (150 mA / g) is in the 150 to 160 mAh / g level, and it cannot be said that it has practical load characteristics.

In Patent Document 2, X-ray diffraction measurement using a CuKα ray is performed on an Li-excess solid solution, and (003) diffraction peak intensity (p) derived from a complex oxide structure at a diffraction angle 2θ = 18.3 ± 1 °. And the ratio (q / p) of the diffraction peak intensity (q) of (020) derived from the Li ₂ MnO ₃ structure at the diffraction angle 2θ = 21.1 ± 1 ° is 0.04 or less, or 0.04 It is described that when ≦ q / p ≦ 0.07, the volume change rate of the crystal lattice due to charge / discharge is small, which is effective for extending the life of the lithium secondary battery. However, there is no mention of a technique for improving the load characteristics.

In Patent Document 3, 2θ = 21 ± 1.5 with respect to the diffraction line intensity (m) of 2θ = 18.6 ± 0.3 ° in a powder X-ray diffraction diagram using CuKα rays for Li-excess solid solution. A positive electrode active material for a lithium secondary battery is described, wherein the ratio (s / m) of diffraction line intensity (s) at 0 ° is less than 0.04. It is described that a lithium secondary battery using a positive electrode active material having a ratio (s / m) of less than 0.04 exhibits high charge / discharge cycle performance. However, there is no mention of a technique for improving the load characteristics.

Patent Document 4 discloses a general formula Li [Li _a Mn _b Me _c ] O _2-d having a layered structure (Me includes at least one element selected from transition metals) (0 <a <1 / 3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2) The shape of the Li excess solid solution is an acicular particle having an average diameter of 5 nm or more and less than 50 nm A positive electrode active material for a non-aqueous secondary battery is described.

Patent Document 5 discloses a general formula Li [Li _a Mn _b Me _c ] O _2-d having a layered structure (Me includes at least one element selected from transition metals) (0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2), and the crystallite size in the powder X-ray diffraction pattern is 2 nm or more and 19 nm A positive electrode active material for a non-aqueous secondary battery characterized by the following is described.

Further, Patent Documents 4 and 5 disclose a next-generation high energy density non-aqueous secondary battery that exhibits high capacity even under high current density conditions by using the above positive electrode active material for a positive electrode for a non-aqueous secondary battery. It is described that construction is possible. However, only the effect of improving the rate characteristics by making the crystallite size and the particle size nano-sized so that the diffusion distance of lithium ions in the solid is shortened and the shape is needle-like is described. Moreover, since nano needle-like particles are extremely high in volume, it is considered extremely difficult to design a practical bulk density electrode.

As described above, in order to increase the energy density of lithium ion secondary batteries, a high-capacity positive electrode material has been demanded. As a technology for realizing this, as described in Patent Documents 1 to 5, a Li-excess solid solution is used. Improvement research is actively conducted. Various inventions are finding the direction of higher capacity and longer life, but no practical solution has been found for load characteristics, which are the weak points of solid solutions.

In this specification, capacity characteristics under high current density conditions are also referred to as “load characteristics”.

Japanese Patent No. 5157071 JP 2007-184145 A Japanese Patent No. 4956883 JP 2013-4401 A JP 2013-73826 A

The present invention relates to a positive electrode active material for a lithium secondary battery having high capacity and practical load characteristics, a method for producing the same, a positive electrode material for a lithium secondary battery, and a lithium secondary battery including the positive electrode for the lithium secondary battery. Next battery.

Accordingly, an object of the present invention is to provide a positive electrode active material having high capacity and excellent load characteristics, a positive electrode material using the positive electrode active material, a positive electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery. .

As a result of diligent research to solve the above-mentioned problems, the present inventors have a high-capacity and practical load characteristic for a lithium secondary battery because the positive electrode active material has the following characteristics. The inventors have found that a positive electrode active material can be obtained, and have completed the present invention.

<1> A positive electrode active material having a layered structure and comprising a composite oxide represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2)
A positive electrode active material that satisfies the following (i) and / or (ii):
(I) A diffraction peak intensity I (020) near 2θ = 20.8 ° and a diffraction peak intensity I (003) near 2θ = 18.6 ° in an X-ray diffraction pattern having an average primary particle size of 150 nm or less. ) (I (020) / I (003) ratio) is 0.5 or less,
(Ii) The stacking fault density in the layered structure is 0.4 or less.
<2> The positive electrode active material according to <1>, which satisfies the above (i).
<3> The positive electrode active material according to <2>, wherein the I (020) / I (003) ratio is 0.01 or more.
<4> The positive electrode active material according to <3>, wherein the composite oxide has an average primary particle size of 10 to 150 nm.
<5> The positive electrode active material according to any one of <1 to 4, which satisfies the above (ii).
<6> The positive electrode active material according to any one of <1> to <5>, wherein the composite oxide is in the form of spherical particles.
<7> The positive electrode active material according to <6>, wherein the composite oxide spherical particles form an aggregate.
<8> The positive electrode active material according to <7>, wherein the aggregate has a three-dimensional network structure.
<9> A positive electrode material comprising the positive electrode active material according to any one of the above items <1> to <8>, a conductive auxiliary agent, and a binder.
<10> A positive electrode for a nonaqueous electrolyte secondary battery, comprising the positive electrode material according to <9> above and a current collector.
<11> A nonaqueous electrolyte secondary battery including the positive electrode for a nonaqueous electrolyte secondary battery according to <10>.
<12> A method for producing a positive electrode active material comprising a composite oxide having a layered structure and represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2)
(I) a step of obtaining a mixture of manganese compound particles having an average primary particle diameter of 5 to 120 nm, a transition metal salt and a lithium salt, or a precursor oxide particle containing Mn having an average primary particle diameter of 5 to 120 nm and Me / Or a step of obtaining a mixture in which precursor hydroxide particles and a lithium salt are mixed,
(Ii) A method for producing a positive electrode active material by a solid phase method including a step of heat-treating the mixture at 600 ° C. to 720 ° C.
<13> The method according to <12>, wherein the precursor oxide particles are obtained by oxidizing particles comprising carbonate containing Mn and Me at 100 to 550 ° C.
<14> A method for producing a positive electrode active material comprising a composite oxide having a layered structure and represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2)
(I) a step of obtaining a mixture obtained by mixing manganese compound particles having an average primary particle size of 5 to 120 nm, a transition metal salt, a lithium salt, and a flux, or a precursor containing Mn having an average primary particle size of 5 to 120 nm and Me Obtaining a mixture in which oxide particles and / or precursor hydroxide particles, a lithium salt, and a flux are mixed;
(Ii) A method for producing a positive electrode active material by a molten salt method including a step of heat-treating the above mixture at 510 to 560 ° C.

If the positive electrode active material of the present invention and the positive electrode for a nonaqueous electrolyte secondary battery using the same are applied, a nonaqueous electrolyte secondary battery having high capacity and practical load characteristics can be provided.

1A is a SEM photograph (50000 times) of the positive electrode active material of Example 1, FIG. 1B is a STEM secondary electron image of the positive electrode active material of Example 1, and FIG. It is a STEM dark field image, (D) is an enlarged view of (B), and (E) is an enlarged view of (C). FIG. 2 (A) is a TEM photograph of the positive electrode active material of Example 1, and (B) is an enlarged view of (A). FIG. 3 is an X-ray diffraction pattern of the positive electrode active material of Example 1. FIG. 4 is an initial discharge curve using the positive electrode active material of Example 1. FIG. 5 is a SEM photograph (50000 times) of the positive electrode active material of Example 2. FIG. 6 is an X-ray diffraction pattern of the positive electrode active material of Example 2. FIG. 7 is an initial discharge curve using the positive electrode active material of Example 2. FIG. 8 is an SEM photograph (50000 times) of the positive electrode active material of Example 3. FIG. 9 is an X-ray diffraction pattern of the positive electrode active material of Example 3. FIG. 10 is an initial discharge curve using the positive electrode active material of Example 3. FIG. 11 is an SEM photograph (50000 times) of the positive electrode active material of Example 4. FIG. 12 is an X-ray diffraction pattern of the positive electrode active material of Example 4. FIG. 13 is an initial discharge curve using the positive electrode active material of Example 4. FIG. 14 is an SEM photograph (50000 times) of the positive electrode active material of Comparative Example 1. FIG. 15 is an X-ray diffraction pattern of the positive electrode active material of Comparative Example 1. FIG. 16 is an initial discharge curve using the positive electrode active material of Comparative Example 1. FIG. 17 is an SEM photograph (50000 times) of the positive electrode active material of Comparative Example 2. FIG. 18 is an X-ray diffraction pattern of the positive electrode active material of Comparative Example 2. FIG. 19 is an initial discharge curve using the positive electrode active material of Comparative Example 2. FIG. 20 is an SEM photograph (50000 times) of the positive electrode active material of Example 5. FIG. 21 is a TEM photograph of the positive electrode active material of Example 5. FIG. 22 is an X-ray diffraction pattern of the positive electrode active material of Example 5. FIG. 23 is an initial discharge curve using the positive electrode active material of Example 5. FIG. 24 is a SEM photograph (50000 times) of the positive electrode active material of Example 6. FIG. 25 is an X-ray diffraction pattern of the positive electrode active material of Example 6. FIG. 26 is an initial discharge curve using the positive electrode active material of Example 6. FIG. 27 is a SEM photograph (50000 times) of the positive electrode active material of Comparative Example 3. FIG. 28 (A) is a TEM photograph of the positive electrode active material of Comparative Example 3, and (B) is an enlarged view of (A). FIG. 29 is an X-ray diffraction pattern of the positive electrode active material of Comparative Example 3. FIG. 30 is an initial discharge curve using the positive electrode active material of Comparative Example 3. FIG. 31 is a SEM photograph (50000 times) of the positive electrode active material of Example 7. FIG. 32 is an X-ray diffraction pattern of the positive electrode active material of Example 7. FIG. 33 is an initial discharge curve using the positive electrode active material of Example 7. FIG. 34 is an SEM photograph (50000 times) of the positive electrode active material of Comparative Example 4. FIG. 35 is an initial discharge curve using the positive electrode active material of Comparative Example 4. FIG. 36 is an SEM photograph (50000 times) of the positive electrode active material of Comparative Example 5. FIG. 37 is an initial discharge curve using the positive electrode active material of Comparative Example 5. 38 is a SEM photograph (50000 times) of the positive electrode active material of Example 8. FIG. FIG. 39 is a TEM photograph of the positive electrode active material in Example 8. 40 shows the X-ray diffraction pattern of the positive electrode active material of Example 8. FIG. FIG. 41 is an initial discharge curve using the positive electrode active material of Example 8. 42 is a SEM photograph (50000 times) of the positive electrode active material of Example 9. FIG. 43 (A) and (C) are TEM photographs of the positive electrode active material of Example 9, (B) is an enlarged view of A, and (D) is an enlarged view of (C). 44 is an X-ray diffraction pattern of the positive electrode active material of Example 9. FIG. FIG. 45 is an initial discharge curve using the positive electrode active material of Example 9. 46 is an SEM photograph (50000 times) of the positive electrode active material of Example 10. FIG. 47 is an X-ray diffraction pattern of the positive electrode active material of Example 10. FIG. FIG. 48 is an initial discharge curve using the positive electrode active material of Example 10.

<Positive electrode active material of the present invention>
Hereinafter, the positive electrode active material of the present invention will be described.

The positive electrode active material of the present invention is a composite oxide having a layered structure and represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2).

Here, the composite oxide in the present invention has a layered structure. The structure of the composite oxide mainly includes a layered rock salt type, a spinel type, an olivine type, etc., but the composite oxide in the present invention is based on a close-packed layered rock salt type structure, and has a cubic rock salt type structure <111. It has a structure in which a transition metal and lithium are regularly arranged in the> direction to form a two-dimensional plane. In other words, the composite oxide in the present invention includes a crystal structure belonging to a layered structure, and has a structure in which a lithium layer, a transition metal layer, and an oxygen layer are repeatedly laminated in a uniaxial direction. (See Patent Document 1).

The composite oxide represented by the above formula (1) is a Li-excess solid solution, and the operating voltage and capacity differ depending on the type of the metal element Me. Therefore, the battery voltage can be arbitrarily set depending on the metal element species and the ratio of the Me element. It is known that the theoretical capacity is as high as 300 mAh / g or more.

Me in the general formula (1) is at least one element selected from transition metals such as Ni, Co, Zr, Zn, Cr, Fe, Ti, and V. From the point of obtaining a higher capacity positive electrode active material, Me is preferably Ni, Co or a combination thereof.

The positive electrode active material of the present invention satisfies the following (i) and / or (ii):
(I) A diffraction peak intensity I (020) near 2θ = 20.8 ° and a diffraction peak intensity I (003) near 2θ = 18.6 ° in an X-ray diffraction pattern having an average primary particle size of 150 nm or less. ) (I (020) / I (003) ratio) is 0.5 or less,
(Ii) The stacking fault density in the layered structure is 0.4 or less.

The stacking fault density in the layered structure of the positive electrode active material may be 0.4 or less, preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less.

If the stacking fault density is too high, the lattice constant (unit length, axis ratio, axis angle) of the unit cell changes due to the ordering of the transition metal atom arrangement. In order to inhibit diffusion, it is assumed that the load characteristic is lowered. On the other hand, if the stacking fault density is sufficiently small, in addition to high capacity characteristics at a low current density, lithium ions can be diffused in the crystal, so that practical load characteristics can be obtained. Therefore, the lower the stacking fault density, the better the load characteristics.

Here, in this specification, “stacking fault density in a layered structure” refers to a composite oxide that is a Li-excess solid solution observed by a transmission electron microscope (TEM) and selects five or more arbitrary layers from the layered structure. And it calculates by calculating | requiring the ratio of the number of layers containing the stacking fault per selected number of layers. Specifically, when five arbitrary layers are selected from the layered structure and checked, stacking faults exist only in one of the layers, and stacking faults do not exist in the other four sets. The “stacking fault density in the layered structure” is (one layer in which stacking faults are present) / (5 layers examined for stacking faults), which is 0.2. A stacking fault is a kind of planar lattice defect (plane defect). When a complete crystal is considered to be formed by periodically stacking (several types of) atomic planes, this stacking rule is used. It means that the sex (order) goes wrong.

The positive active material may have an average primary particle size of 150 nm or less, preferably 100 nm or less, more preferably 80 nm or less, for example, 10 to 150 nm or 20 to 80 nm. The average primary particle size was determined by observing the positive electrode active material with a scanning electron microscope (SEM), picking up 10 or more primary particles randomly from an image of 50000 times, and measuring the diameter (x) and length (y ) Is measured and calculated as an average value (x + y) / 2.

The above I (020) / I (003) ratio is 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less, such as 0.01 to 0.4 or 0.1 to 0.27. It may be.

A practical load characteristic can be obtained because the positive electrode active material of the present invention has an average primary particle size that is not too large. Specifically, when the average primary particle size is larger than 150 nm, a capacity of 200 mAh / g or more can be obtained at a low current density (48 mA / g or less), but at a high current density (240 mA / g or more), the capacity is greatly increased. It will drop to. This is because when the average primary particle size increases, the lattice constant (axis length, axis ratio, axis angle) of the unit cell changes due to the regularization of the transition metal atom arrangement, thereby increasing the stacking fault density. This is thought to be due to the inability to diffuse lithium ions.

In addition, the positive electrode active material of the present invention can obtain practical load characteristics because the I (020) / I (003) ratio is not too large. Specifically, when the I (020) / I (003) ratio is greater than 0.5, the load characteristics are degraded. This decrease in load characteristics is due to the change in the lattice constant of the unit cell (axis length, axis ratio, axis angle) of the unit cell due to the ordering of the transition metal atomic arrangement, thereby narrowing the interlayer, thereby causing lithium ions to This is thought to be due to the inability to diffuse.

Note that the regularization of the transition metal atom arrangement means that there is a high possibility that a regular lattice having a triple period and / or a double period of the basic lattice exists. The basic lattice consists of transition metal atoms and lithium atoms. In other words, it suggests that the degree of crystallinity is increased by ordering the transition metal atom arrangement.

In the positive electrode active material having a specific composition, the present inventors correlate the average primary particle diameter and the I (020) / I (003) ratio of the positive electrode active material with the stacking fault density in the layered structure of the positive electrode active material. It has been found that That is, when the average primary particle diameter and the ratio of I (020) / I (003) are within the above ranges, the stacking fault density in the layered structure of the positive electrode active material can be reduced, thereby increasing the lithium ion storage capacity (high (Capacitance characteristics) and practical load characteristics can be combined.

The crystal size of the (020) plane of the positive electrode active material of the present invention is preferably 5 to 30 nm, more preferably 7 to 25 nm, and even more preferably 10 to 20 nm. When the crystal size of the (020) plane is in the above range, more excellent load characteristics can be obtained.

In the positive electrode active material of the present invention, the shape of the primary particles of the composite oxide that is a Li-excess solid solution is not particularly limited, and is spherical, acicular, plate-like, polyhedral (pentahedral, hexahedral, etc.), and these Examples include combinations. Among these, it is preferable that spherical particles are included because an electrode having a high bulk density can be obtained. Here, in this specification, the spherical particles may be not only true spheres but also ellipsoids, and the ratio of the lengths of the major axis and the minor axis may be 1/1 to 4/1.

In the positive electrode active material of the present invention, it is preferable to form aggregates of spherical particles of composite oxide particles. According to this, the handleability of the positive electrode active material is improved, and the existing facilities related to the positive electrode active material can be used in many cases.

The aggregate can have an arbitrary size, but the average particle size is preferably 40 nm to 100 μm, more preferably 500 nm to 50 μm, and further preferably 1 μm to 10 μm. .

It is preferable that the aggregate has a three-dimensional network structure. The three-dimensional network structure is formed by causing spherical primary particles to undergo grain boundary melting and joining. In an agglomerate having a three-dimensional network structure, stress is relieved, so that an ideal crystal structure having no stacking fault or having a very low stacking fault density can be produced. Furthermore, since lithium ions can enter three-dimensionally from the vacancies, the diffusion time of lithium ions is shortened and the load characteristics are improved.

<Method for producing positive electrode active material>
Although the manufacturing method of the positive electrode active material of this invention is not specifically limited, It is preferable that it is a solid-phase method or a molten salt method. First, the manufacturing method of the positive electrode active material of this invention using a solid-phase method is demonstrated.

(Solid phase method)
The positive electrode active material of the present invention includes (i) a step of obtaining a mixture of manganese compound particles having an average primary particle size of 5 to 120 nm, a transition metal salt and a lithium salt, or Mn having an average primary particle size of 5 to 120 nm and the above Me. By a solid phase method including a step of obtaining a mixture in which precursor oxide particles and / or precursor hydroxide particles containing lithium and lithium salt are mixed, and (ii) heat-treating the mixture at 600 ° C. to 720 ° C. can get. Here, the precursor oxide particles are preferably obtained by oxidizing particles made of carbonate containing Mn and Me at 100 to 550 ° C.

Examples of the manganese compound particles in the step (i) include manganese sulfate, manganese nitrate, manganese acetate, manganese oxalate, manganese hydroxide, manganese oxyhydroxide, manganese sulfate, manganese oxide, and manganese oxide. The metal salt is selected according to the intended composition, but two or more kinds of transition metal salts can be mixed and used.

Examples of the transition metal salt include nitrates such as Ni, Co, Zr, Zn, Cr, Fe, Ti, and V, acetates, oxalates, carbonates, hydroxides, oxyhydroxides, sulfates, oxides, Examples thereof include peroxides and halides such as chlorides, and these transition metal salts are selected according to the intended composition, but two or more kinds of transition metal salts can also be mixed and used.

Examples of the lithium salt include lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate, lithium hydroxide, lithium carbonate, lithium peroxide, lithium sulfate, lithium fluoride, lithium chloride, lithium iodide, and the like. It is possible to use at least one selected salt, which can be used alone or in combination of two or more. Lithium carbonate can maintain a solid phase because it has a melting point of 724 ° C. when heat-treated in a predetermined temperature range in step (ii). Other lithium salts can also maintain a solid phase by heat treatment below the melting point.

The production method of the precursor oxide particles and / or precursor hydroxide particles containing Mn and Me is not particularly limited, and a known method can be used. The Me is the same as that described in the general formula (1).

When the shape of the primary particles of the complex oxide that is an Li-excess solid solution is made spherical, needle-like, plate-like, polyhedral (pentahedral, hexahedral, etc.), and combinations thereof, the precursor containing Mn and Me It is preferable that the body oxide particles and / or the precursor hydroxide particles have a spherical shape, a needle shape, a plate shape, a polyhedral shape (pentahedron, hexahedron, etc.), and a combination thereof. Therefore, when the spherical particles of the composite oxide particles form an aggregate, the precursor oxide particles and / or the precursor hydroxide spherical particles containing Mn and Me form an aggregate. It is preferable to do so. Similarly, the primary particle size of the composite oxide can be adjusted by selecting the primary particle size of the precursor oxide particles and / or the precursor hydroxide particles. Specifically, in order to obtain the desired primary particle size of the composite oxide of the present invention, it is necessary to adjust the primary particle size of the precursor oxide particles and / or precursor hydroxide particles in advance. It is.

The average primary particle diameter of the manganese compound particles, precursor oxide particles and precursor hydroxide particles is preferably 5 to 120 nm, more preferably 7 to 100 nm, and more preferably 10 to 80 nm. Further preferred.

When the average primary particle size of the precursor oxide particles or the like is smaller than 5 nm, the target load characteristics may not be obtained as an active material when heat treatment is performed. In addition, when the average primary particle diameter of the precursor oxide particles or the like is larger than 120 nm, the obtained solid solution has an ordered structure. As a result, the lattice constant of the unit cell (crystal axis (Axial length, axial ratio, axial angle) may change, thereby increasing stacking fault density and reducing load characteristics.

The mixing method is not particularly limited, and a known method can be used. For example, the method of dry-mixing using a mortar is mentioned.

Next, in the step (ii), the mixture obtained in the step (i) is heat-treated at 600 ° C. to 720 ° C. This step is performed by a solid phase method.

When the heat treatment temperature is less than 600 ° C., the heat treatment is insufficient, so that the crystallinity is low and the desired load characteristics may not be obtained. When the heat treatment temperature is higher than 720 ° C., the resulting solid solution has developed a regular structure. As a result, the lattice constant of the unit cell (the axial length of the crystal axis, the axial ratio, the axial angle) is obtained by ordering the transition metal atom arrangement. ) May change, thereby increasing the stacking fault density and reducing the load characteristics.

The heat treatment temperature is preferably 600 ° C. to 700 ° C., and more preferably 610 to 660 ° C.

The heat treatment temperature means the maximum temperature under the firing conditions.

As the pre-heat treatment, firing may be performed at 100 ° C. to 550 ° C. before reaching the maximum temperature for firing, or may be performed in stages. More preferably, it is 150 ° C. to 500 ° C., which is a heat treatment temperature that does not transfer to oxide crystals, and more preferably 200 ° C. to 400 ° C.

The gas atmosphere at the time of heat treatment is not particularly limited as long as an oxidizing atmosphere is secured. For example, air, oxygen, and a mixed gas with oxygen can be used.

(Molten salt method)
Next, the manufacturing method of the positive electrode active material of this invention using a melting method is demonstrated.

The positive electrode active material of the present invention comprises (i) a step of obtaining a mixture of manganese compound particles having an average primary particle size of 5 to 120 nm, a transition metal salt, a lithium salt, and a flux, or an average primary particle size of 5 to 120 nm. A step of obtaining a mixture in which precursor oxide particles and / or precursor hydroxide particles containing Mn and Me are mixed, a lithium salt, and a flux, and (ii) a step of heat-treating the mixture at 510 to 560 ° C. Obtained by the molten salt method.

The above step (i) is the same as the above-described step (i) of the solid phase method except that a flux is further added and mixed.

Examples of the flux include nitrates, nitrites, acetates, phosphates, borates, sulfates, hydroxides, carbonates, etc., whose cation is lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, etc. And various halides such as oxyacid salts and chlorides, peroxides, oxides and the like. As the flux, it is possible to use at least one salt selected from among the flux according to the temperature at which crystal growth of the target crystal occurs.

The lithium salt can also serve as a flux, and lithium nitrate is preferably used.

Next, in the step (ii), the mixture obtained in the step (i) is heat-treated at 510 to 560 ° C. This step is performed by a molten salt method in which a desired crystal is obtained in a melt melted at a temperature equal to or higher than the melting point of the above-mentioned flux. This method can increase the speed of the target crystal growth by selecting a flux having a melting point lower than the temperature at which the target crystal growth occurs.

When the heat treatment temperature is less than 510 ° C., the heat treatment is insufficient, so that the crystallinity is low and the target load characteristic may not be obtained. On the other hand, when the heat treatment temperature is higher than 560 ° C., the resulting solid solution has developed a regular structure. As a result, the lattice constant of the unit cell (the axial length of the crystal axis, the axial ratio) is determined by ordering of the transition metal atom arrangement. , Axial angle) may change, which may increase the stacking fault density and reduce load characteristics. The heat treatment temperature is preferably 520 ° C. to 550 ° C.

Prior to reaching the maximum temperature for firing as pre-heat treatment, firing may be performed at 100 ° C. to 510 ° C., or may be performed stepwise. The gas atmosphere during the heat treatment is the same as described above.

The positive electrode active material of the present invention obtained by the solid phase method or the molten salt method described above has a layered structure, is composed of a complex oxide represented by the above general formula (1), and has excellent load characteristics.

<Positive electrode material of the present invention>
The positive electrode material of the present invention includes the above-described positive electrode active material of the present invention, a conductive additive, and a binder.

The positive electrode active material of the present invention may at least partially contain a carbon-based material or may be coated (coated). The carbon-based material is not particularly limited, and conventionally known materials can be used. For example, carbon such as amorphous carbon, carbon black such as acetylene black, graphite fine particles, graphite on scale, carbon fiber, etc. Materials can be mentioned.

The production method is not particularly limited as long as at least a part of the positive electrode active material for a lithium ion secondary battery according to the present embodiment includes a carbon-based material for the purpose of improving conductivity. There are CVD, mechanical milling, and a method of compounding by a mechanochemical method using a solid medium. As a carbon source for thermal CVD, an organic solvent, for example, an aromatic hydrocarbon compound such as benzene or toluene, or an aliphatic hydrocarbon compound such as gaseous methane, ethylene or acetylene can be used. In order to obtain composite particles coated with a high carbon layer, it is more preferable to use an aromatic hydrocarbon compound because the conductivity becomes higher. The compounding by the mechanochemical method is compounding using a medium stirring type mixer such as a bead mill, a vibration mill, or a ball mill, and can be further complexed by heat treatment.

The positive electrode active material according to the present invention has no particular problem even if other positive electrode active materials are used in combination as long as the composite oxide which is the Li-excess solid solution of the present invention is contained as an essential component. Examples thereof include lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, and spinel Mn series.

Examples of the lithium-transition metal composite oxide include LiCoO ₂ , Li (Co, Mn) O ₂ , Li (Co, Mg) O ₂ , LiNiO ₂ , Li (Ni, Al) O ₂ , Li (Ni, Mn , Co) O ₂ , Li (Li, Ni, Mn, Co) O _{2 and the} like. Examples of the lithium-transition metal phosphate compound include LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiVPO _4, and those in which some of these transition metals are substituted with other elements. Examples of the spinel Mn system include LiMn ₂ O ₄ and Li (Mn, Ni) ₂ O ₄ . Moreover, you may add oxides and sulfur, such as MnO and vanadium pentoxide, as a positive electrode active material which does not contain lithium. By adding these lithium-free positive electrode active materials, it becomes possible to suppress irreversible capacity. These positive electrode active materials can also be used in combination.

In addition, in the case where the optimum particle diameter is different in expressing the respective intrinsic effects of these positive electrode active materials, the optimum particle diameters may be blended and used for expressing the respective intrinsic effects, It is not always necessary to make the particle sizes of all active materials uniform.

The conductive auxiliary agent used in the positive electrode material of the present invention is not particularly limited, and conventionally known ones can be used, for example, carbon black such as acetylene black, graphite fine particles, graphite on scale, carbon fiber, etc. A carbon material can be mentioned. In particular, it is considered preferable to use ultrafine fibrous carbon having an average fiber diameter of 10 to 900 nm in terms of improving cycle characteristics.

With respect to such ultrafine fibrous carbon, for example, the description in JP-A-2010-245423 can be referred to. JP 2010-245423 discloses fine carbon fibers having a specific surface area in the range of 5 to 20 m ² / g, an average fiber diameter in the range of 5 to 900 nm, and having no branched structure. Yes.

The binder used in the positive electrode material of the present invention is added for the purpose of maintaining the electrode structure by binding the positive electrode active materials or between the positive electrode active material and the current collector.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamideimide, polyamide (PA), wholly aromatic polyamide (aramid), polyvinyl chloride ( PVC), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN), thermoplastic resins, epoxy resins, polyurethane resins , And thermosetting resins such as urea resins.

A water-based emulsion may be used as a binder, and examples thereof include rubber-based materials such as styrene-butadiene rubber (SBR), fluorine-modified styrene-butadiene rubber, olefin copolymer, and acid-modified olefin copolymer. it can.

In the case of using an aqueous binder emulsion, a thickener such as carboxymethyl cellulose (CMC), polyvinyl alcohol, polyvinyl pyrrolidone or the like can be used as necessary.

<Positive electrode for non-aqueous electrolyte secondary battery of the present invention>
The positive electrode for a nonaqueous electrolyte secondary battery of the present invention comprises the above-described positive electrode material of the present invention and a current collector. The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is preferably formed by forming the positive electrode material of the present invention on the surface of a current collector. The positive electrode for a non-aqueous electrolyte secondary battery of the present invention can increase the capacity of the non-aqueous electrolyte secondary battery and can further enhance load characteristics.

The current collector used in the positive electrode for a non-aqueous electrolyte secondary battery of the present invention can be formed from any conductive material. Thus, for example, the current collector can be formed from a metallic material such as aluminum, nickel, stainless steel, titanium, etc., in particular aluminum, stainless steel.

The positive electrode for a non-aqueous electrolyte secondary battery of the present invention can be manufactured by any method. The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is prepared by, for example, dispersing a positive electrode material containing a positive electrode active material, a binder, a conductive additive, etc. in a dispersion medium, and applying the dispersed positive electrode material to a current collector. It can be obtained by drying, pressurizing with a roll press machine or the like, and adjusting the thickness of the positive electrode active material layer to an appropriate thickness.

The dispersion medium in this case is not limited as long as the object and effect of the present invention are not impaired, and for example, an organic solvent can be used. Specifically, the dispersion medium may be a non-aqueous solvent such as alcohol, alkane, alkene, alkyne, ketone, ether, ester, aromatic compound, or nitrogen-containing ring compound, particularly isopropyl alcohol (IPA), or N-methyl-2-pyrrolidone (NMP), dimethylacetamide, and dimethylformamide can be suitably used.

Further, the drying temperature can be appropriately selected in consideration of the boiling point of the dispersion medium to be used. For example, it can be selected to be 50 ° C or higher, 70 ° C or higher, or 90 ° C or higher and 100 ° C or lower, 150 ° C or lower, 200 ° C or lower, or 250 ° C or lower.

<Nonaqueous electrolyte secondary battery of the present invention>
Examples of the nonaqueous electrolyte secondary battery of the present invention include a lithium ion secondary battery, a lithium battery, a lithium ion polymer battery, a lithium all solid battery, and the like, and a lithium ion secondary battery is preferable.

In the non-aqueous electrolyte secondary battery of the present invention, a positive electrode for the non-aqueous electrolyte secondary battery of the present invention, an electrolyte layer containing an electrolyte or an electrolyte, and a negative electrode formed by forming a negative electrode material layer on the surface of the current collector, The positive electrode material layer and the negative electrode material layer are laminated facing each other. Further, when the electrolyte layer is liquid or kel-like, it may be laminated via a separator.

As the non-aqueous electrolyte, a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-polar solvent having a high polarity can be used. Examples of the lithium salt (electrolyte salt) used include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO _{2 3} ), lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate, and the like. These ionic compounds can be used alone or in admixture of two or more.

Non-aqueous solvents used for the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and chloroethylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate Chain carbonates such as ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, Ethers such as 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof alone or A mixture of two or more of these may be mentioned, but the invention is not limited to these. In particular, at least one solvent selected from chain carbonates such as propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferably used.

Also, for the purpose of improving the cycle characteristics and storage characteristics of the battery, it is also effective to contain additives that improve reduction resistance and oxidation resistance in the non-aqueous electrolyte. Examples thereof include reduction polymerization compounds such as vinylene carbonate and vinyl acetate, and oxidizing compounds such as biphenyl, terphenyl, pyrrole, aniline, and thiophene. The amount of the additive to be contained is preferably 0.1 to 3% by weight.

Moreover, a flame retardant may be contained from the viewpoint of improving the safety of the battery. Examples of the flame retardant include phosphazene compounds and phosphate ester compounds. The preferred content is 1 to 20% by weight.

The concentration of the electrolyte salt (lithium salt) in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.1 mol / l in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. 5 mol / l to 2.5 mol / l. The electrolytic solution is characterized by comprising a lithium salt and a nonaqueous solvent soluble in the lithium salt.

Also, it is possible to use a room temperature molten salt (ionic liquid) made of a lithium salt as the non-aqueous electrolyte. In order to adjust the viscosity, the ionic liquid may be mixed with the nonaqueous electrolytic solution.

These liquid electrolytes function as an electrolyte layer by being impregnated and held in a separator having a porous structure. It can be said that the thinner the thickness of the electrolyte layer (that is, the thickness of the separator) is, the better it is to reduce the internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm. The porosity of the separator is preferably 90% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

As the separator, it is preferable to use a microporous film or a nonwoven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the microporous film include a single layer or laminated film of polyolefin resin typified by polyethylene, polypropylene, etc., polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride. Perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, Vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinyl fluoride Den - ethylene - fluorine-based microporous films such as tetrafluoroethylene copolymer and the like.

Further, as the nonwoven fabric separator, it is possible to use nanofibers or papers using fiber materials such as polyester resins represented by polyethylene terephthalate, polybutylene terephthalate, etc., cellulose, aramid, glass fiber and the like.

From the viewpoint of withstand voltage, separators with good oxidation resistance are particularly preferred, and fluororesins, aramids, or ceramic-coated ones are preferably used on substrates such as porous membranes and nonwoven fabrics. The

Also, from the viewpoint of preventing battery leakage, a gel polymer electrolyte obtained by gelling a non-aqueous electrolyte may be applied. The gel polymer electrolyte can be produced by combining a polymer that swells and gels with the non-aqueous electrolyte and the non-aqueous electrolyte.

Specific examples of the polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), and polyethylene glycol (PEG). ), Polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polysiloxane and copolymers thereof, and cross-linked products thereof.

Moreover, it is also possible to apply an all-solid electrolyte containing no liquid to the electrolyte used in the present invention. When an all solid electrolyte is applied, the above separator need not be used in combination. Examples of the all solid electrolyte include an intrinsic polymer electrolyte not containing a solvent (plasticizer) and an inorganic solid electrolyte. Examples of the intrinsic polymer electrolyte include a crosslinked polymer having a molecular structure that is flexible and soluble in lithium salt, and examples of the inorganic solid electrolyte include a lithium-containing oxide and a lithium-sulfur compound.

The negative electrode active material used for the negative electrode of the lithium ion secondary battery of the present invention is not particularly limited as long as it can reversibly occlude and release lithium, and a conventionally known negative electrode active material can be used.

For example, graphite (natural graphite, artificial graphite, etc.) that is highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), low-temperature calcined carbon, carbon black (Ketjen black, acetylene black, channel black, lamp black, Oil furnace black, thermal black, etc.), carbon materials such as fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, etc. And oxides containing these elements (silicon monoxide (Si _{), SiO x (0 <x} <2), tin dioxide _{(SnO 2), SnO x (} 0 <x <2), etc. SnSiO ₃₎ and nano-iron oxide, a metal material such as lithium metal, a lithium - titanium composite oxide And lithium-transition metal composite oxides such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ). In addition, these negative electrode active materials can be used alone or in the form of a mixture of two or more.

The conductive additive, binder and current collector used for the negative electrode are the same as those described in the positive electrode for nonaqueous electrolyte secondary batteries of the present invention, except that copper can be used as the current collector.

(Calculation of average primary particle size)
The positive electrode active materials obtained in the following examples and comparative examples were observed with a scanning electron microscope (SEM), and 10 or more primary particles were randomly selected from a 50000 times image, and the diameter (x) and length thereof were selected. (Y) was measured and an average value (x + y) / 2 was calculated. The results are shown in Table 1 below.

(Observation of laminated structure)
The positive electrode active materials obtained in the following examples and comparative examples were observed with a transmission electron microscope (TEM), and the stacking fault density was calculated. For observation, a field emission transmission electron microscope JEM-2100F manufactured by JEOL Ltd. was used. The observation method was a TEM bright field method. Five or more arbitrary layers were selected from the observed layered structure, and the stacking fault density was calculated as the ratio of the number of layers including stacking faults per the selected number of layers. The results are shown in Table 1 below.

(Confirmation method of composition)
In order to confirm the composition of the positive electrode active material obtained in the following examples and comparative examples, the Li, Ni, Co, and Mn ratios were measured by chemical analysis. The chemical analysis was performed with an ICP emission photometric analyzer (ICP-AES 720-ES, manufactured by Agilent Technologies).

(X-ray diffraction measurement)
Powder X-ray diffraction measurement (SmartLab, manufactured by Rigaku) using CuKα rays of the positive electrode active materials obtained in the following Examples and Comparative Examples was performed, and from the diffraction pattern, the diffraction peak intensity around 2θ = 20.8 ° The ratio (I (020) / I (003) ratio) between I (020) and the diffraction peak intensity I (003) near 2θ = 18.6 ° was determined. In addition, the crystallite size was calculated.

(Electrochemical evaluation of positive electrode active material for lithium ion secondary battery)
Using the positive electrode active materials obtained in the following examples and comparative examples, an evaluation cell was prepared by the following procedure, and the initial charge / discharge characteristics and the discharge characteristics under high current density conditions were evaluated.

75 parts by mass of the positive electrode active material obtained in Examples and Comparative Examples, 10 parts by mass of acetylene black (Denka Black (trademark) manufactured by Denki Kagaku Kogyo) as a conductive material, and polytetrafluoroethylene (manufactured by Daikin, F104 as a binder) ) 15 parts by mass were mixed to prepare an electrode sheet so that the positive electrode active material weight was a predetermined amount.

The produced electrode sheet was punched into a circle having a diameter of 17 mm, and then adhered to a 20 μm Al foil using a conductive paste (manufactured by Nippon Graphite Industry Co., Ltd., Bunny Height T-602), followed by vacuum drying at 170 ° C. for 10 hours. A positive electrode for battery characteristic evaluation was obtained by pressing. The physical properties of the produced positive electrode are shown in Table 1 below.

For the positive electrode, the prepared positive electrode, for the negative electrode, a metal lithium foil having a thickness of 200 μm (Honjo Chemical Co., Ltd.), and for the electrolyte solution, 1 mol / l LiPF ₆ , ethylene carbonate and ethyl methyl carbonate (volume ratio 30:70). ) (Manufactured by Kishida Chemical Co., Ltd.), an evaluation cell using a separator of glass nonwoven fabric (thickness 400 μm) (manufactured by Advantech, GB-100R) and commercially available polyethylene microporous membrane (thickness 20 μm) Was made.

The initial charge / discharge characteristics at 25 ° C. of the prepared cell were evaluated by performing charge / discharge under the following charge / discharge conditions.

-Charging / discharging conditions The charging upper limit voltage was set to 4.8V, the discharge lower limit voltage was set to 2.0V, and constant current / constant voltage charging / discharging was performed. The initial test was carried out at a current density of 48 mA / g (about 5 hours), followed by the second cycle at 120 mA / g, the third cycle at 240 mA / g, and the fourth cycle at 480 mA / g (2C).

The initial charge / discharge capacity was measured by charging to 4.8 V at a constant current of 48 mA / g (about 5 hours rate), followed by discharging to 2.0 V at a constant current of 48 mA / g. I went.

The capacity (%) of the fourth cycle (480 mA / g) relative to the initial capacity (48 mA / g) is shown in Table 1 below as “2C”.

The positive electrode active material of the present invention was produced by the following method.

(Example 1: Solid phase method)
(Preparation of precursor oxide particles)
Oxide particles (precursor oxide particles) containing manganese, cobalt, and nickel, which are precursors of the positive electrode active material of this example, were prepared as follows.

Manganese sulfate pentahydrate (Wako Pure Chemical Industries, first grade reagent) 13.64 g, cobalt nitrate hexahydrate (Wako Pure Chemical Industries, special grade reagent) 2.06 g, and nickel nitrate hexahydrate ( 5.04 g (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 100 ml of distilled water to prepare an aqueous solution. Next, 26.9 g of sodium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) was dissolved in 1000 ml of distilled water to prepare an aqueous solution. While stirring this aqueous sodium hydrogen carbonate solution, the prepared aqueous solution was added dropwise to obtain a milky white precipitate which was carbonate particles containing manganese, cobalt and nickel. Then, it filtered by suction and dried at 120 degreeC. Furthermore, the precursor oxide particle containing manganese, cobalt, and nickel was obtained by oxidizing at 200 degreeC. The average primary particle diameter of the precursor oxide particles was 38 nm. Further, this precursor oxide is an aggregate of spherical particles and forms a three-dimensional network structure.

(Preparation of positive electrode active material)
The positive electrode active material of this example was produced as follows.

1.94 g of lithium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent, melting point 723 ° C.) and 2.03 g of the prepared precursor oxide particles were weighed and dry-mixed using an agate mortar.

Next, this mixture was placed in a 50 ml alumina crucible and heat-treated in a firing furnace. In heat treatment, the temperature was raised to 620 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 12 hours, and then lowered to room temperature.

Distilled water was added to the obtained powder, sufficiently stirred, washed with distilled water 5 times, then suction filtered, dried at 100 ° C. for 5 hours, and 200 ° C. for 5 hours to obtain the positive electrode of Example 1. An active material was obtained.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . 1 to 4 show SEM photographs, TEM photographs, X-ray diffraction patterns, and initial discharge curves measured by the above method. 1B to 1E suggest that the positive electrode active material of Example 1 is an aggregate of spherical particles and forms a three-dimensional network structure.

(Example 2: Solid phase method)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment conditions of the mixture of the precursor oxide particles and lithium carbonate were changed. In the heat treatment, the temperature was raised to 650 ° C. at a rate of temperature rise of 5 ° C./min in the air, heat treated for 6 hours, and then lowered to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 5 to 7, respectively.

(Example 3: Solid phase method)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment conditions of the mixture of the precursor oxide particles and lithium carbonate were changed. In the heat treatment, the temperature was raised to 650 ° C. at a rate of temperature rise of 5 ° C./min in the air, heat treated for 12 hours, and then lowered to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . 8 to 10 show SEM photographs, X-ray diffraction patterns, and initial discharge curves measured by the above method.

(Example 4: Solid phase method)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment conditions of the mixture of the precursor oxide particles and lithium carbonate were changed. In the heat treatment, the temperature was raised to 700 ° C. at a rate of temperature rise of 5 ° C./min in the air, heat treated for 6 hours, and then lowered to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 11 to 13, respectively.

(Comparative Example 1: Molten salt method)
A positive electrode active material was produced in the same manner as in Example 1 except that the heat treatment conditions of the mixture of the precursor oxide particles and lithium carbonate were changed. In the heat treatment, the temperature was raised to 750 ° C. at a rate of temperature rise of 5 ° C./min in the air, heat treated for 6 hours, and then lowered to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, TEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 14 to 16, respectively.

In addition, as a result of observing the positive electrode active material of Comparative Example 1 with a transmission electron microscope (TEM), it was confirmed that superlattice reflection appeared. This suggests that ordering of the transition metal atom arrangement is occurring. Moreover, as shown in Comparative Example 3, it is considered that the ordering of the transition metal atom arrangement causes an increase in stacking fault density.

(Comparative Example 2: Solid phase method)
The positive electrode active material was prepared in the same manner as in Example 2 except that the oxidation treatment temperature at the time of obtaining the precursor oxide particles by oxidizing the carbonate particles containing manganese, cobalt and nickel was 900 ° C. Produced. The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Also, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS.

(Example 5: Molten salt method)
7.25 g of lithium nitrate (manufactured by Nacalai Tesque, melting point 260 ° C.) and 2.0 g of precursor oxide particles prepared in the same manner as in Example 1, were weighed dry using an agate mortar, and then 50 ml of alumina It put in the crucible and heat-processed in the baking furnace. In heat treatment, the temperature was raised to 520 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 60 hours, and then lowered to room temperature. Distilled water was added to the obtained powder, sufficiently stirred, washed with distilled water 5 times, then suction filtered, dried at 100 ° C. for 5 hours, and 200 ° C. for 5 hours to obtain the positive electrode of Example 5. An active material was obtained.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, TEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 20 to 23, respectively.

(Example 6: Molten salt method)
A positive electrode active material was produced in the same manner as in Example 5 except that the heat treatment conditions of the mixture of the precursor oxide particles and lithium nitrate were changed. In heat treatment, the temperature was raised to 550 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 15 hours, and then cooled to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . In addition, SEM photographs, X-ray diffraction patterns, and initial discharge curves measured by the above method are shown in FIGS. 24 to 26, respectively.

(Comparative Example 3: Molten salt method)
A positive electrode active material was produced in the same manner as in Example 5 except that the heat treatment conditions of the mixture of the precursor oxide particles and lithium nitrate were changed. In heat treatment, the temperature was raised to 650 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 15 hours, and then lowered to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, TEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS.

In addition, as a result of observing the positive electrode active material of Comparative Example 3 with a transmission electron microscope (TEM), it was confirmed that superlattice reflection appeared. This suggests that there is a regular lattice having a triple period and double period of the basic lattice, that is, the transition metal atom arrangement is ordered. Moreover, since the positive electrode active material of Comparative Example 3 has a relatively large stacking fault density of 0.55, it is understood from this result that the ordering of the transition metal atom arrangement causes an increase in stacking fault density.

(Example 7: Molten salt method)
(Method for synthesizing manganese oxide (Mn ₃ O ₄ ))
Manganese oxide was produced as follows. Manganese sulfate pentahydrate (manufactured by Nacalai Tesque, first grade reagent, purity 98%), 12.1 g, was dissolved in 500 ml of distilled water to prepare an aqueous solution having a concentration of 0.1 mol / l. Next, a solution (concentration: 0.1 mol / l) of ammonia water (Nacalai Tesque, special grade reagent, 28% solution) diluted with 1000 ml of distilled water and hydrogen peroxide (Nacalai Tesque, first grade) A solution was prepared by mixing 14.1 g (reagent, 30% solution) (5 times in molar ratio with respect to manganese in the aqueous solution). While stirring the prepared mixed solution of aqueous ammonia and hydrogen peroxide, an aqueous manganese sulfate solution was added dropwise at a rate of 10 ml / min to obtain a brown precipitate. After the particles settled, decantation was performed three times with distilled water, suction filtered, and dried at 60 ° C. to obtain a target sample. As a result of SEM observation of the obtained sample, it was polyhedral particles having an average primary particle diameter of 55 nm.

Dry mixing of the produced Mn ₃ O ₄ 1.10 g, nickel nitrate (manufactured by Nacalai Tesque) 1.27 g, cobalt nitrate (manufactured by Nacalai Tesque) 0.524 g, and lithium nitrate 7.10 g using an agate mortar After that, it was put in a 50 ml alumina crucible and heat-treated in a firing furnace. In heat treatment, the temperature was raised to 520 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 60 hours, and then lowered to room temperature.

Distilled water was added to the obtained powder, sufficiently stirred, washed with distilled water 5 times, then suction filtered, dried at 100 ° C. for 5 hours, and 200 ° C. for 5 hours to obtain the positive electrode of Example 7. An active material was obtained.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 31 to 33, respectively.

(Comparative Example 4: Molten salt method)
1.10 g of manganese oxide prepared in Example 7, 1.27 g of nickel nitrate and 0.524 g of cobalt nitrate were weighed and dry-mixed using an agate mortar, and then heated to 750 ° C. at a heating rate of 5 ° C./min. Heat treated for 5 hours.

Next, 4.90 g of lithium nitrate and 2.0 g of the heat-treated precursor oxide particles were weighed and dry-mixed using an agate mortar, then placed in a 50 ml alumina crucible and heat-treated in a firing furnace. . In heat treatment, the temperature was raised to 520 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 60 hours, and then lowered to room temperature.

Distilled water is added to the obtained powder, and the mixture is sufficiently stirred. After washing with distilled water 5 times, suction filtration is performed, and the desired sample is obtained by drying at 100 ° C. for 5 hours and at 200 ° C. for 5 hours. It was.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 34 and 35, respectively.

(Comparative Example 5: Molten salt method)
Precursor oxide particles produced in the same manner as in Example 7 were heated to 800 ° C. at a heating rate of 5 ° C./min and heat-treated for 5 hours.

Next, 4.90 g of lithium nitrate and 2.0 g of the heat-treated precursor oxide particles were weighed and dry-mixed using an agate mortar, then placed in a 50 ml alumina crucible and heat-treated in a firing furnace. . In heat treatment, the temperature was raised to 520 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 60 hours, and then lowered to room temperature.

Distilled water is added to the obtained powder, and the mixture is sufficiently stirred. After washing with distilled water 5 times, suction filtration is performed, and the desired sample is obtained by drying at 100 ° C. for 5 hours and at 200 ° C. for 5 hours. It was.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 36 and 37, respectively.

(Example 8: Molten salt method)
(Synthesis Method of MnNiCo (OH) ₂ )
Manganese-nickel-cobalt hydroxide was prepared as follows. Manganese sulfate pentahydrate (Nacalai Tesque, primary reagent, purity 98%) 10.0 g, Nickel sulfate hexahydrate (Nacalai Tesque, primary reagent, purity 98-102%) 3.53 g, cobalt sulfate 1.46 g of heptahydrate (manufactured by Nacalai Tesque, first grade reagent, purity 98%) was dissolved in 600 ml of distilled water to prepare an aqueous solution having a concentration of 0.1 mol / l.

Next, a solution (concentration: 0.1 mol / l) of 7.16 g of ammonia water (Nacalai Tesque, special grade reagent, 28% solution) diluted with 1180 ml of distilled water and hydrogen peroxide (Nacalai Tesque, first grade) A solution was prepared by mixing 3.34 g (reagent, 30% solution) (1/2 times the molar ratio with respect to the transition metal in the aqueous solution).

While stirring the prepared manganese-nickel-cobalt aqueous solution at a rotational speed of 400 rpm, a mixed solution of ammonia water and hydrogen peroxide was dropped at a rate of 10 ml / min. After the particles settled, decantation was performed three times using distilled water, suction filtration and drying at 60 ° C. to obtain the desired precursor hydroxide particles containing manganese, cobalt and nickel. As a result of SEM observation of the obtained sample, it was a polygon having an average primary particle size of 32 nm.

Next, 4.90 g of lithium nitrate and 2.0 g of the synthesized precursor hydroxide particles were weighed and dry-mixed using an agate mortar, then placed in a 50 ml alumina crucible and heat treated in a firing furnace. . In heat treatment, the temperature was raised to 520 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 15 hours, and then lowered to room temperature.

Distilled water was added to the obtained powder, sufficiently stirred, washed with distilled water 5 times, then suction filtered, dried at 100 ° C. for 5 hours, and 200 ° C. for 5 hours to obtain the positive electrode of Example 8. An active material was obtained.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, TEM photographs, X-ray diffraction patterns, and initial discharge curves measured by the above method are shown in FIGS. 38 to 41, respectively.

(Example 9: Molten salt method)
A positive electrode active material was produced in the same manner as in Example 8 except that the heat treatment conditions were changed. In heat treatment, the temperature was raised to 520 ° C. at a rate of temperature rise of 5 ° C./min, heat treated for 60 hours, and then lowered to room temperature.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . 42 to 45 show SEM photographs, TEM photographs, X-ray diffraction patterns, and initial discharge curves measured by the above method, respectively.

(Example 10: Molten salt method)
To a solution obtained by dissolving 7.2 g of potassium permanganate (Nacalai Tesque, special grade reagent) in 200 ml of distilled water and stirring at 40 ° C. for 1 hour, 2.1 g of fumaric acid (Nacalai Tesque, special grade reagent) was added. The mixture was stirred in a state maintained at 40 ° C. to prepare a gel, and baked at 400 ° C. for 6 hours and at 700 ° C. for 10 hours to obtain K _x MnO ₂ .

Thereafter, 3.48 g of lithium nitrate (manufactured by Nacalai Co., Ltd., special grade reagent), 1.12 g of the produced manganese oxide, cobalt nitrate hexahydrate (manufactured by Nacalai Tesque Co., Ltd., 0.26 g of special grade reagent, nickel nitrate hexahydrate) 0.62 g of a product (manufactured by Nacalai Tesque Co., Ltd., special grade reagent) was weighed and dry-mixed using an agate mortar, then placed in a 50 ml alumina crucible and heat-treated in a firing furnace. The temperature was raised to 520 ° C. at 15 ° C./min, heat-treated for 15 hours, and then lowered to room temperature.

Distilled water was added to the obtained powder, sufficiently stirred, washed with distilled water 5 times, suction filtered, dried at 100 ° C. for 5 hours, and 200 ° C. for 5 hours to obtain the positive electrode of Example 10. An active material was obtained.

The composition of the positive electrode active material measured by the above method was Li [Li _0.2 Co _0.07 Ni _0.17 Mn _0.56 ] O ₂ . Further, SEM photographs, X-ray diffraction patterns and initial discharge curves measured by the above method are shown in FIGS. 46 to 48, respectively.

　＊表中、「２Ｃ」とは、初期（４８ｍＡ／ｇ）の容量に対する４サイクル目（４８０ｍＡ／ｇ）の容量（％）を示す。

* In the table, “2C” indicates the capacity (%) of the fourth cycle (480 mA / g) with respect to the initial capacity (48 mA / g).

Claims (14)

A positive electrode active material having a layered structure and comprising a composite oxide represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2)
A positive electrode active material that satisfies the following (i) and / or (ii):
(I) A diffraction peak intensity I (020) near 2θ = 20.8 ° and a diffraction peak intensity I (003) near 2θ = 18.6 ° in an X-ray diffraction pattern having an average primary particle size of 150 nm or less. ) (I (020) / I (003) ratio) is 0.5 or less,
(Ii) The stacking fault density in the layered structure is 0.4 or less. The positive electrode active material according to claim 1, wherein the positive electrode active material satisfies the above (i). The positive electrode active material according to claim 2, wherein the I (020) / I (003) ratio is 0.01 or more. The positive electrode active material according to claim 3, wherein the composite oxide has an average primary particle size of 10 to 150 nm. The positive electrode active material according to any one of claims 1 to 4, which satisfies the above (ii). The positive electrode active material according to any one of claims 1 to 5, wherein the composite oxide is in the form of spherical particles. The positive electrode active material according to claim 6, wherein the spherical particles of the composite oxide form an aggregate. The positive electrode active material according to claim 7, wherein the aggregate has a three-dimensional network structure. A positive electrode material comprising the positive electrode active material according to any one of claims 1 to 8, a conductive additive, and a binder. A positive electrode for a non-aqueous electrolyte secondary battery, comprising the positive electrode material according to claim 9 and a current collector. A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 10. A method for producing a positive electrode active material having a layered structure and comprising a composite oxide represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2)
(I) a step of obtaining a mixture of manganese compound particles having an average primary particle diameter of 5 to 120 nm, a transition metal salt and a lithium salt, or precursor oxide particles containing Mn having an average primary particle diameter of 5 to 120 nm and Me / Or a step of obtaining a mixture in which precursor hydroxide particles and a lithium salt are mixed,
(Ii) A method for producing a positive electrode active material by a solid phase method including a step of heat-treating the mixture at 600 ° C. to 720 ° C. The method according to claim 12, wherein the precursor oxide particles are obtained by oxidizing particles made of carbonate containing Mn and Me at 100 to 550 ° C. A method for producing a positive electrode active material having a layered structure and comprising a composite oxide represented by the following general formula (1):
Li [Li _a Mn _b Me _c ] O _2-d (1)
(Wherein Me is at least one element selected from transition metals other than Mn, and a, b, c and d are 0 <a <1/3, 0 <b <2/3, 0 <c <1, 0 ≦ d ≦ 0.2)
(I) a step of obtaining a mixture obtained by mixing manganese compound particles having an average primary particle size of 5 to 120 nm, a transition metal salt, a lithium salt, and a flux, or a precursor containing Mn having an average primary particle size of 5 to 120 nm and Me Obtaining a mixture in which oxide particles and / or precursor hydroxide particles, a lithium salt, and a flux are mixed;
(Ii) A method for producing a positive electrode active material by a molten salt method including a step of heat-treating the mixture at 510 to 560 ° C.

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