JP3856015B2 - Positive electrode secondary active material for nonaqueous electrolyte secondary battery, positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery (hereinafter also simply referred to as “positive electrode active material”), a positive electrode active material for a nonaqueous electrolyte secondary battery ( Hereinafter, it is also simply referred to as a “positive electrode active material”) and a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a positive electrode secondary active material, a positive electrode active material, and a non-aqueous electrolyte secondary battery having a spinel-structure lithium transition metal composite oxide having excellent overdischarge characteristics and the like and having a high charge / discharge capacity per unit volume of the battery.

Nonaqueous electrolyte secondary batteries are characterized by a higher operating voltage and higher energy density than conventional nickel cadmium secondary batteries, and are widely used as power sources for electronic devices. As the positive electrode active material of the non-aqueous electrolyte secondary battery, lithium transition metal composite oxides typified by LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are used.
In particular, LiMn ₂ O ₄ is easily available as a raw material at low cost because manganese, which is a constituent element, is present in a large amount as a resource. In addition, there is a feature that the load on the environment is small. Furthermore, even if all the Li ions in the crystal are desorbed by the deintercalation reaction, the crystal structure exists stably. For this reason, the nonaqueous electrolyte secondary battery using LiMn ₂ O ₄ is excellent in thermal stability as compared with LiCoO ₂ and LiNiO ₂ .

Non-aqueous electrolyte secondary batteries using LiMn ₂ O ₄ having the advantages as described above have been used for mobile electronic devices such as mobile phones, notebook computers, digital cameras, etc. Battery characteristics sufficient for these applications were exhibited.
However, at present, the required characteristics of mobile electronic devices are becoming more severe due to high functionality such as various functions added and use at high and low temperatures. In addition, application to power sources such as batteries for electric vehicles is expected.

  By the way, in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a protection circuit is conventionally incorporated in the battery in order to prevent overdischarge. However, if this protection circuit can be eliminated, the space is reduced. The capacity can be increased by adding an active material to the. Further, the manufacturing cost can be reduced by omitting the protection circuit. Therefore, means for eliminating the protection circuit have been studied.

In order to eliminate the protection circuit, it is necessary to prevent various problems from occurring even when overdischarge occurs. In general, when overdischarge occurs, the potential of the negative electrode rises, and Cu used as a current collector for the negative electrode is eluted, so that battery characteristics are significantly deteriorated. The reason why Cu elutes will be specifically described.
FIG. 1 is a graph schematically showing changes in potential of the positive electrode and the negative electrode during a charge / discharge cycle of a lithium ion secondary battery. As shown in FIG. 1, in the conventional example, when the battery is charged, the potential of the positive electrode rises along the path indicated by arrow a, and the potential of the negative electrode falls along the path indicated by arrow b.
When the battery is discharged after charging, the potential of the negative electrode increases, but retention (a phenomenon in which lithium ions are not released) occurs in the negative electrode, and the path is as indicated by an arrow c. On the other hand, the potential of the positive electrode falls along the path indicated by the arrow d. Therefore, when overdischarge occurs, the potentials of the positive electrode and the negative electrode become equal at point A. Here, since the potential at point A is higher than the potential at which Cu used as the negative electrode current collector is eluted, Cu is eluted.

On the other hand, as a technique for preventing Cu from eluting even when overdischarged, Patent Document 1 discloses a main active material made of a first lithium compound having a potential nobler than the potential of the negative electrode current collector, and a negative electrode current collector. A positive electrode active material including a secondary active material made of a second lithium compound having a base potential lower than that of the electric body is described. Specifically, LiCoO ₂ is used as a main active material, and Li _x MoO ₃ A positive electrode active material having (x = 1 to 2) as a secondary active material is described.
However, in the positive electrode active material described in Patent Document 1, although improvement of overdischarge characteristics is observed, improvement of high temperature characteristics and improvement of electrode plate density that are currently required for mobile electronic devices can be realized. could not.

JP-A-2-265167

  An object of the present invention is to provide a positive electrode secondary active material for a non-aqueous electrolyte secondary battery, a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte solution having excellent battery characteristics even in a more severe use environment. The next battery is to provide. That is, a positive electrode active material for a non-aqueous electrolyte secondary battery and a positive electrode for a non-aqueous electrolyte secondary battery having excellent battery characteristics, particularly overdischarge characteristics, and having a high charge / discharge capacity per unit volume of the battery. An object is to provide an active material and a non-aqueous electrolyte secondary battery.

Nonaqueous electrolyte cathode active material for a secondary battery described in the present invention includes a main active material having a first lithium transition metal composite oxide, a subsidiary active substance having a second lithium-transition metal composite oxide The second lithium transition metal composite oxide has a form of particles composed of one or both of primary particles and secondary particles that are aggregates thereof. In the particle size distribution of the particles, when the particle sizes at which the volume cumulative frequency reaches 10%, 50% and 90% are D10, D50 and D90, respectively, 0 <(D10 / D50) <1, 1 <(D90 / D50) satisfies all ≦ 5 and 5 [mu] m ≦ D50 ≦ 40 [mu] m, the second lithium-transition metal composite oxides, there are lithium 16c site and lithium man having a spinel structure Characterized in that it is a down composite oxide.

When the battery voltage is reduced to around 0 V due to overdischarge, the potential of the negative electrode rises, and copper used in the negative electrode current collector is precipitated, so that the battery characteristics are remarkably deteriorated.
In the present invention, lithium is present at the 16c site, and the lithium present at the 16c site is supplied to the negative electrode as the retention amount of the negative electrode during the first charge, whereby the balance between the positive electrode and the negative electrode can be maintained. It is possible to suppress an increase in the potential of the negative electrode during overdischarge. Accordingly, the overdischarge characteristics are improved.
In FIG. 1, when the battery is discharged after charging, the potential of the negative electrode of the example of the present invention rises along the path indicated by the arrow c as in the conventional example, while the potential of the positive electrode falls along the path indicated by the arrow e. This is because lithium ions exist at the 16c site of the positive electrode as compared with the conventional example. Therefore, when overdischarge occurs, the potentials of the positive electrode and the negative electrode become equal at point B. Here, since the potential at point B is lower than the potential at which Cu used as the negative electrode current collector elutes, the elution of Cu is suppressed. That is, the nonaqueous electrolyte secondary battery using the positive electrode secondary active material of the present invention is excellent in overdischarge characteristics.
In addition, although the case where a collector is Cu is demonstrated using FIG. 1, it is not limited to the case where a collector is Cu.

However, although lithium is present at the 16c site and the lithium present at the 16c site is supplied to the negative electrode as the amount of retention of the negative electrode during the first charge, the potential of the negative electrode can be prevented from increasing during overdischarge. It is difficult to improve the charge / discharge capacity.
By controlling the variation in the size of each particle, it is possible to improve the electrode plate density when the positive electrode active material of the present invention is applied to the positive electrode plate without impairing the improvement of the overdischarge characteristics. Therefore, the charge / discharge capacity per unit volume of the battery can be improved by improving the electrode plate density.
In addition, by controlling the variation in the size of each particle so as to satisfy a specific relational expression regarding the volume cumulative frequency of the particle size distribution, it is possible to achieve both improvement of the overdischarge characteristics and improvement of the electrode plate density. it can.

The standard deviation of the particle size in the particle size distribution of the particles is preferably 0.6 or less.
By making the standard deviation of the particle diameter of the secondary active material 0.6 or less, both improvement of overdischarge characteristics and improvement of electrode plate density can be achieved.

The second lithium transition metal composite oxide is preferably 1 to 30% by weight with respect to the positive electrode active material composed of the main active material and the sub active material.

The first lithium transition metal composite oxide is preferably at least one of lithium cobaltate, lithium manganate, lithium nickelate, and lithium / nickel / cobalt composite oxide.

  The non-aqueous electrolyte secondary battery described in the present invention has a positive electrode active material layer using the positive electrode active material for a non-aqueous electrolyte secondary battery described in the present invention as a positive electrode active material on both sides of a strip-shaped positive electrode current collector. And forming a negative electrode active material layer using metal lithium, a lithium alloy or a compound capable of occluding and releasing lithium ions as a negative electrode active material, on both sides of the negative electrode current collector, respectively. A spiral in which a strip separator is interposed between the strip positive electrode and the strip negative electrode by winding a number of times in a state where the strip positive electrode and the strip negative electrode are stacked via the strip separator. It forms a wound body of a mold.

  By comprising in this way, while a manufacturing process is simple, it can make it hard to produce the crack of a positive electrode active material layer and a negative electrode active material layer, and peeling from a strip | belt-shaped separator. In addition, the battery capacity can be increased and the energy density can be increased. In particular, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a high electrode plate density, excellent filling properties, and is easily compatible with a binder. Therefore, the positive electrode has a high charge / discharge capacity and excellent binding properties and surface smoothness, so that the positive electrode active material layer can be prevented from being cracked or peeled off.

  As described above, the overdischarge characteristics and the electrode plate density of the nonaqueous electrolyte secondary battery can be improved by using the positive electrode secondary active material and the positive electrode active material of the present invention. As a result, a non-aqueous electrolyte secondary battery having excellent battery characteristics that could not be achieved in the past can be put into practical use, and can be applied to various fields.

  Hereinafter, a positive electrode active material for a nonaqueous electrolyte secondary battery, a positive electrode active material for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery according to the present invention will be described with reference to the embodiments, examples, and FIGS. This will be described with reference to FIG. However, the present invention is not limited to this embodiment, examples, and FIGS.

The positive electrode active material and the positive electrode active material of the present invention have at least a lithium transition metal composite oxide having a spinel structure (spinel crystal structure). The “spinel structure” is one of the typical crystal structure types found in double oxide AB ₂ O ₄ type compounds (A and B are metal elements).
FIG. 2 is a schematic diagram showing a crystal structure of a spinel-structure lithium transition metal composite oxide. In FIG. 2, lithium atom 1 occupies a tetrahedral site of 8a site, oxygen atom 2 occupies 32e site, and transition metal atom 3 occupies an octahedral site of 16d site.

  Examples of the spinel structure lithium transition metal composite oxide include lithium manganese composite oxide, lithium titanium composite oxide, lithium / manganese / nickel composite oxide, and lithium / manganese / cobalt composite oxide. Among these, lithium manganese composite oxide is preferable.

  In the positive electrode side active material of the present invention, the lithium transition metal composite oxide is present in the form of particles composed of one or both of primary particles and secondary particles that are aggregates thereof. That is, the lithium transition metal composite oxide exists in the form of particles, and the particles may be composed only of primary particles, or may be composed only of secondary particles that are aggregates of primary particles. It may consist of both particles and secondary particles.

In the present invention, in the particle size distribution of the particles, when the particle size at which the volume cumulative frequency reaches 10%, 50%, and 90% is D10, D50, and D90, respectively,
0.1 ≦ (D10 / D50) ≦ 1,
1 <(D90 / D50) ≦ 3 and 5 μm ≦ D50 ≦ 40 μm
It is preferable to satisfy all of the following.
When D10, D50 and D90 satisfy the above relational expression, the electrode plate density can be further improved without impairing the improvement of the overdischarge characteristics.

Further, D10, D50, and D90 are expressed by a more preferable relational expression according to the purpose and application. For example, in order to further improve the electrode plate density,
0.2 ≦ (D10 / D50) ≦ 0.9,
1.2 <(D90 / D50) ≦ 2 and 7 μm ≦ D50 ≦ 30 μm
It is preferable to satisfy all of the following.

In addition, in order for the nonaqueous electrolyte secondary battery using the positive electrode secondary active material of the present invention and the positive electrode active material to be suitably used for stationary use such as residential use and home use,
0.7 ≦ (D10 / D50) ≦ 1,
1 <(D90 / D50) ≦ 1.3 and 7 μm ≦ D50 ≦ 15 μm
It is preferable to satisfy all of the following. In this case, not only the overdischarge characteristics and the electrode plate density are improved, but also the cycle characteristics, storage characteristics, load characteristics and output characteristics are excellent.

Furthermore, in order that the non-aqueous electrolyte secondary battery using the positive electrode active material of the present invention and the positive electrode active material can be suitably used for applications such as a mobile phone, an electric tool, and an electric vehicle,
0.2 ≦ (D10 / D50) ≦ 0.7,
1.3 <(D90 / D50) ≦ 2 and 15 μm ≦ D50 ≦ 36 μm
It is preferable to satisfy all of the following. In this case, the overdischarge characteristics, cycle characteristics, storage characteristics, load characteristics and output characteristics are excellent, and the electrode plate density is also excellent.

  In the present invention, examples of the method for measuring the particle size distribution of the particles include a sieving method, an image analysis method, a sedimentation method, a laser diffraction scattering method, and an electrical detection method.

In the lithium transition metal composite oxide of the secondary active material of the present invention, lithium is present at the 16c site. Lithium is present at the 16c site, and the lithium present at the 16c site is supplied to the negative electrode as the retention amount of the negative electrode during the first charge, so that the potential of the negative electrode increases due to overdischarge, and the core material of the negative electrode current collector It is possible to prevent elution of copper.
In the present invention, a Rietveld analysis method is an example of a method for measuring the presence of lithium at the 16c site of the lithium transition metal composite oxide.
Lithium may be present in any state. It may exist in a lithium atom state or may exist in a lithium ion state.

  In the particle size distribution of the positive electrode side active material of the present invention, the standard deviation of the particle size is preferably 0.6 or less, more preferably 0.36 or less, and 0.07 or more. Is preferred. Within the above range, the electrode plate density can be increased without impairing the overdischarge characteristics.

In the positive electrode side active material of the present invention, in the particle size distribution of the particles, the ratio of the particles having a volume-based particle diameter of 50 μm or more is preferably 10% by volume or less, and 7% by volume or less. Is more preferable.
By controlling the particle size distribution of the particles as described above, coarse particles composed of secondary aggregates can be prevented from being included, and thus a positive electrode coated surface with excellent smoothness can be obtained.

  In the positive electrode side active material of the present invention, the lithium transition metal composite oxide preferably has a (400) crystallinity of 600 to 1200 angstroms. The (400) crystallinity is more preferably 700 angstroms or more, and more preferably 1100 angstroms or less.

  The larger the crystallinity, the better the crystallinity and the less the distortion of the crystal structure. In the lithium transition metal composite oxide having a spinel structure as used in the present invention, the degree of regularity of unit cell arrangement can be shown by the following (400) crystallinity.

  The (400) crystallinity of the lithium transition metal composite oxide can be determined by, for example, an X-ray diffraction method. The X-ray diffraction method can be performed, for example, under conditions of a tube current of 100 mA and a tube voltage of 40 kV. From the diffraction peak derived from the (400) plane determined by the X-ray diffraction method, the crystallite diameter is calculated by the Scherrer equation represented by the following equation (1).

  D = Kλ / (βcos θ) (1)

In the above formula, D represents (400) crystallinity (Å), K represents Scherrer constant (K is sintered Si for optical system adjustment (manufactured by Rigaku Corporation), and diffraction is caused by the (400) plane. Λ represents the wavelength of the X-ray source (1.540562 場合 in the case of CuKα1), β represents β = By (B represents the width of the observation profilm) , Y is calculated by y = 0.9991-0.019505b-2.8205b ² + 2.878b ³ -1.0366b ⁴ where b means the width of the device constant profile. θ represents a diffraction angle (degree).

In the positive electrode side active material of the present invention, the specific surface area is preferably 0.2 to 1.5 m ² / g. The specific surface area is more preferably 0.25 m ² / g or more, more preferably 1.2 m ² / g or less, and still more preferably 0.9 m ² / g or less. When the specific surface area is too small, the discharge capacity decreases. If the specific surface area is too large, the cycle characteristics are not excellent.
The specific surface area can be measured by a nitrogen gas adsorption method.

  In the positive electrode side active material of the present invention, the transition metal is preferably manganese. When the transition metal is manganese, the non-aqueous electrolyte secondary battery using the positive electrode secondary active material and the positive electrode active material of the present invention is particularly excellent in improving the overdischarge characteristics and the electrode plate density. It can be particularly suitably used for applications such as electric tools. Moreover, since it becomes the thing excellent also in the output characteristic, it can use especially suitably also for the use of an electric vehicle.

In the positive electrode side active material of the present invention, the lithium transition metal composite oxide is lithium represented by the general formula Li _a Mn ₂ O ₄ (a represents a number satisfying 1.0 <a <2.0). Manganese composite oxide is preferred. The lithium manganese composite oxide may be partially substituted with at least one selected from the group consisting of magnesium, aluminum, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, zirconium, boron, and fluorine. Good.

  In the positive electrode side active material of the present invention, the lithium transition metal composite oxide preferably has an iron content of 25 ppm or less, more preferably 20 ppm or less, and even more preferably 18 ppm or less. If the iron content is too high, it may cause an internal short circuit of the battery.

The positive electrode active material of the present invention has a main active material having a first lithium transition metal composite oxide and a secondary active material having a second lithium transition metal composite oxide.
In the positive electrode active material of the present invention, the first lithium transition metal composite oxide is not particularly limited.

The first lithium transition metal composite oxide is not limited to one type of lithium transition metal composite oxide.
In the positive electrode active material of the present invention, the first lithium transition metal composite oxide is at least one selected from the group consisting of lithium cobaltate, lithium manganate, lithium nickelate, and lithium / nickel / cobalt composite oxide. Is preferred.
Thereby, not only the improvement of the overdischarge characteristic and the electrode plate density, but also the charge / discharge capacity is increased, and a nonaqueous electrolyte secondary battery excellent in load characteristic and output characteristic can be obtained.

  The first lithium transition metal composite oxide includes lithium cobaltate and lithium manganate, lithium cobaltate and nickel cobalt lithium manganate, lithium cobaltate and lithium nickel cobalt aluminate, lithium manganate and nickel cobalt lithium manganate, manganese It is preferably one selected from the group consisting of lithium acid lithium and nickel cobalt lithium aluminate and nickel cobalt lithium manganate and nickel cobalt lithium aluminate.

Lithium cobaltate represented by the general formula Li _{1 + x} CoO ₂ (x represents a number satisfying −0.5 ≦ x ≦ 0.5) is preferable. The lithium cobaltate is at least partly selected from the group consisting of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. It may be substituted with one kind.

Represented by the general formula Li _a Mn _3−a O _{4 + f} (a represents a number satisfying 0.8 ≦ a ≦ 1.2, and f represents a number satisfying −0.5 ≦ f ≦ 0.5). Lithium manganate is preferred. This lithium manganate is at least partly selected from the group consisting of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin It may be substituted with one kind.

Lithium nickelate represented by the general formula Li _{1 + x} NiO ₂ (x represents a number satisfying −0.5 ≦ x ≦ 0.5) is preferable. This lithium nickelate is at least partly selected from the group consisting of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. It may be substituted with one kind.

Formula _{Li x Ni y Co z X (} 1-y-z) O w (X represents Al or Mn, x is a number satisfying 0.95 ≦ x ≦ 1.10, y is 0.1 ≦ and y represents a number satisfying 0.1 ≦ z ≦ 0.9, and w represents a number satisfying 1.8 ≦ w ≦ 2.2. Lithium / nickel / cobalt composite oxide is preferred. This lithium / nickel / cobalt composite oxide is partially composed of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. It may be substituted with at least one selected from the group.

In the positive electrode active material of the present invention, the first lithium transition metal composite oxide is selected from the group consisting of lithium cobaltate, lithium nickelate, and lithium / nickel / cobalt composite oxide, where the amount of lithium manganate is A. When at least one amount is B, it is preferable to mix so as to be in the range of 0.2 ≦ B / (A + B) ≦ 0.8.
As a result, it is possible to obtain a non-aqueous electrolyte secondary battery with improved load characteristics and output characteristics as well as improved overdischarge characteristics and electrode plate density.
The first lithium transition metal composite oxide is more preferably mixed so as to be in the range of 0.4 ≦ B / (A + B) ≦ 0.6. This is because within this range, load characteristics and output characteristics are remarkably improved.

In the positive electrode active material of the present invention, the lithium manganate that is the first lithium transition metal composite oxide preferably contains lithium at the 16d site.
The presence of lithium at the 16d site of the first lithium transition metal composite oxide improves the cycle characteristics without impairing the overdischarge characteristics and the electrode plate density.
Lithium may be present in any state. It may exist in a lithium atom state or may exist in a lithium ion state.

  The second lithium transition metal composite oxide is the same as the lithium transition metal composite oxide in the positive electrode side active material described in the present invention.

  The amount of the secondary active material having the second lithium transition metal composite oxide is preferably 1 to 30% by weight with respect to the amount of the positive electrode active material. The amount of the secondary active material is more preferably 3% by weight or more, and more preferably 15% by weight or less. If the amount of the secondary active material is too small, elution of Cu as the negative electrode current collector occurs during overdischarge. If the amount of the secondary active material is too large, the cycle characteristics deteriorate.

  Although the manufacturing method of the positive electrode secondary active material of the present invention is not particularly limited, for example, it can be manufactured as in the following (1) to (3).

(1) Preparation of raw material mixture The compounds described later are mixed so that each constituent element has a predetermined composition ratio to obtain a raw material mixture. The compound used for the raw material mixture is selected according to the elements constituting the target composition.
The mixing method is not particularly limited, for example, a method of mixing powdery compounds as they are to obtain a raw material mixture; mixing in a slurry form using water and / or an organic solvent, and then drying to obtain a raw material mixture Method: A method in which an aqueous solution of the above-mentioned compound is mixed and precipitated, and the resulting precipitate is dried to obtain a raw material mixture; a method in which these are used in combination.

Below, the compound used for a raw material mixture is illustrated.
Lithium compound is not particularly limited, for _{example, Li 2 CO 3, LiOH,} LiOH · H 2 O, Li 2 O, LiCl, LiNO 3, Li 2 SO 4, LiHCO 3, Li (CH 3 COO), fluoride Examples include lithium, lithium bromide, lithium iodide, and lithium peroxide. Among these, Li ₂ CO ₃ , LiOH, LiOH · H ₂ O, Li ₂ O, LiCl, LiNO ₃ , Li ₂ SO ₄ , LiHCO ₃ , and Li (CH ₃ COO) are preferable.

The manganese compound is not particularly limited. For example, manganese metal, oxide (eg, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ ), hydroxide, nitrate, carbonate (MnCO ₃ ), chloride salt, Examples thereof include manganese iodide, manganese sulfate, and manganese nitrate. Among these, manganese metal, MnCO ₃ , MnSO ₄ , and MnCl ₂ are preferable.
Manganese compounds have a particle size distribution in which the particle size at which the volume cumulative frequency reaches 10%, 50% and 90% is d10, d50 and d90, respectively, d10 is 5 to 25 μm, d50 is 7 to 40 μm, It is preferable to use one having d90 of 10 to 60 μm. In order to obtain a manganese compound having such a particle size distribution, a rough mortar, ball mill, vibration mill, jet mill or the like can be used. Various classifiers can also be used.

Magnesium compound is not particularly limited, for _{example, MgO, MgCO 3, Mg (} OH) 2, MgCl 2, MgSO 4, Mg (NO 3) 2, Mg (CH 3 COO) 2, magnesium iodide, perchlorate Examples include magnesium. Among these, MgSO ₄ and Mg (NO ₃ ) ₂ are preferable.

The boron compound is not particularly limited, and examples thereof include B ₂ O ₃ (melting point: 460 ° C.), H ₃ BO ₃ (decomposition temperature: 173 ° C.), lithium boron composite oxide, orthoboric acid, boron oxide, and boron phosphate. It is done. Among these, H ₃ BO ₃ and B ₂ O ₃ are preferable.

The fluorine compound is not particularly limited, and examples thereof include NH ₄ F, LiF, LiCl, LiBr, MnF ₂ , hydrogen fluoride, oxygen fluoride, hydrofluoric acid, chlorine fluoride oxide, and bromine fluorosulfate. Of these, NH ₄ F, LiF, and MnF ₂ are preferable.

The titanium compound is not particularly limited, and examples thereof include titanium fluoride, titanium chloride, titanium bromide, titanium iodide, titanium oxide, titanium sulfide, and titanium sulfate. Of these, TiO, TiO ₂ , Ti ₂ O ₃ , TiCl ₂ , and Ti (SO ₄ ) ₂ are preferable.

The zirconium compound is not particularly limited, and examples thereof include zirconium fluoride, zirconium chloride, zirconium bromide, zirconium iodide, zirconium oxide, zirconium sulfide, and zirconium carbonate. Of these, ZrF ₂ , ZrCl, ZrCl ₂ , ZrBr ₂ , ZrI ₂ , ZrO, ZrO ₂ , ZrS ₂ , Zr (OH) _{3 and the} like are preferable.

The hafnium compound is not particularly limited, and examples thereof include hafnium fluoride, hafnium chloride, hafnium bromide, hafnium iodide, hafnium oxide, and hafnium carbonate. Among these, HfF ₄ , HfCl ₂ , HfBr ₂ , HfO ₂ , Hf (OH) ₄ , Hf ₂ S and the like are preferable.

The sulfur compound is not particularly limited. For example, Li ₂ SO ₄ , MnSO ₄ , (NH ₄ ) ₂ SO ₄ , Al ₂ (SO ₄ ) ₃ , MgSO ₄ , sulfide, sulfur iodide, hydrogen sulfide, sulfuric acid and The salt and nitrogen sulfide are mentioned. Among these, Li ₂ SO ₄ , MnSO ₄ , (NH ₄ ) ₂ SO ₄ , Al ₂ (SO ₄ ) ₃ , and MgSO ₄ are preferable.

Sodium compound is not particularly limited, for _{example, Na 2 CO 3, NaOH,} Na 2 O, NaCl, NaNO 3, Na 2 SO 4, NaHCO 3, CH 3 CONa the like.

Calcium compound is not particularly limited, for _{example, CaO, CaCO 3, Ca (} OH) 2, CaCl 2, CaSO 4, Ca (NO 3) 2, Ca (CH 3 COO) 2 and the like.
Moreover, you may use the compound containing 2 or more types of each element mentioned above.

Hereinafter, a preferred method for obtaining a raw material mixture will be described in detail by taking as an example a positive electrode secondary active material which is a lithium manganese composite oxide having magnesium and boron.
An aqueous solution containing manganese ions and magnesium ions having a predetermined composition ratio prepared from the above-described manganese compound and magnesium compound is dropped into the stirring pure water.
Next, an aqueous ammonium hydrogen carbonate solution is added dropwise to precipitate manganese and magnesium to obtain manganese and magnesium salts. In place of the ammonium hydrogen carbonate aqueous solution, an alkali solution such as a sodium hydroxide aqueous solution, a sodium hydrogen carbonate aqueous solution, a potassium hydroxide aqueous solution, or a lithium hydroxide aqueous solution can also be used.

  Next, the aqueous solution is filtered to collect a precipitate. The collected precipitate is washed with water and heat-treated, and then mixed with the above-described lithium compound and boron compound to obtain a raw material mixture.

(2) Firing and grinding of raw material mixture Next, the raw material mixture is fired. The firing temperature, time, atmosphere, and the like are not particularly limited, and can be appropriately determined according to the purpose.
The firing temperature is preferably 650 ° C. or higher, and more preferably 700 ° C. or higher. If the firing temperature is too low, unreacted raw materials may remain in the positive electrode active material, and the original characteristics of the positive electrode active material may not be utilized. The firing temperature is preferably 1100 ° C. or lower, and more preferably 950 ° C. or lower. If the firing temperature is too high, the particle size of the positive electrode active material may become too large, and the battery characteristics may deteriorate. In addition, by-products such as Li ₂ MnO ₃ and LiMnO ₂ are likely to be generated, which may lead to a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage.
In general, the firing time is preferably 1 to 24 hours, and more preferably 6 to 12 hours. When the firing time is too short, the diffusion reaction between the raw material particles does not proceed. If the firing time is too long, firing after the diffusion reaction is almost completed is wasted, and coarse particles may be formed by sintering.

  The firing may be divided into a plurality of firing steps. For example, a 1st baking process can be performed at 350-550 degreeC for 1 to 24 hours, and a 2nd baking process can be performed at 650-1000 degreeC for 1 to 24 hours.

  Examples of the firing atmosphere include air, oxygen gas, a mixed gas of these with an inert gas such as nitrogen gas and argon gas, an atmosphere in which the oxygen concentration (oxygen partial pressure) is controlled, and a weak oxidizing atmosphere. Among these, an atmosphere in which the oxygen concentration is controlled is preferable.

  After firing, if desired, the powder may be pulverized using a rough mortar, ball mill, vibration mill, pin mill, jet mill or the like to obtain a powder having a desired particle size. Thus, the specific surface area can be set to the above-described preferred range by grinding after firing.

(3) Organic treatment The obtained lithium transition metal composite oxide is reacted with a lithium-containing organic solution. The solution obtained by the reaction is filtered and dried.
Drying may be performed in air, in a nitrogen gas atmosphere, in an argon gas atmosphere, or in a vacuum state.

  The positive electrode active material of the present invention can be obtained by the manufacturing method described above.

  The production method of the positive electrode active material of the present invention is not particularly limited, and can be produced, for example, as in the following (1) to (3).

(1) Preparation of main active material A compound is mixed so that each component may become a predetermined composition ratio, and a raw material mixture is obtained. The compound used for the raw material mixture is selected according to the elements constituting the target composition.
The mixing method is not particularly limited, for example, a method of mixing powdery compounds as they are to obtain a raw material mixture; mixing in a slurry form using water and / or an organic solvent, and then drying to obtain a raw material mixture Method: A method in which an aqueous solution of the above-mentioned compound is mixed and precipitated, and the resulting precipitate is dried to obtain a raw material mixture; a method in which these are used in combination.
Next, the raw material mixture is fired. The firing temperature, time, atmosphere, and the like are not particularly limited, and can be appropriately determined according to the purpose.
After firing, if desired, the powder may be pulverized using a rough mortar, ball mill, vibration mill, pin mill, jet mill or the like to obtain a powder having a desired particle size.

(2) Production of side active material A side active material can be obtained by the same manufacturing method as that of the positive electrode side active material described above.

(3) Mixing of main active material and sub-active material The obtained main active material and sub-active material can be mixed at a predetermined weight ratio to obtain the positive electrode active material of the present invention.
The method for mixing the main active material and the sub active material is not particularly limited. For example, it can mix with a high-speed stirrer.

The positive electrode active material of the present invention is suitably used for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and lithium ion polymer secondary batteries.
The non-aqueous electrolyte secondary battery may be the positive electrode active material of the present invention as at least part of the positive electrode active material in a conventionally known non-aqueous electrolyte secondary battery, and other configurations are not particularly limited. Hereinafter, a lithium ion secondary battery will be described as an example.

  As the negative electrode active material, metallic lithium, a lithium alloy, or a compound capable of occluding and releasing lithium ions can be used. Examples of the lithium alloy include a LiAl alloy, a LiSn alloy, and a LiPb alloy. Examples of the compound capable of occluding and releasing lithium ions include carbon materials such as graphite and graphite; and oxides such as tin oxide and titanium oxide.

The electrolyte solution is not particularly limited as long as it is a compound that does not change or decompose with the operating voltage.
Examples of the solvent include organic solvents such as dimethoxyethane, diethoxyethane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, γ-butyrolactone, 2-methyltetrahydrofuran, dimethyl sulfoxide, and sulfolane. Is mentioned. These can be used alone or in admixture of two or more.

Examples of the electrolyte include lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluorophosphate, and lithium trifluoromethanoate.
The above-described solvent and electrolyte are mixed to obtain an electrolytic solution. Here, a gelling agent or the like may be added and used as a gel. Moreover, you may make it absorb and use a hygroscopic polymer. Further, a solid electrolyte having conductivity of inorganic or organic lithium ions may be used.

  Examples of the separator include a porous film made of polyethylene or polypropylene.

  Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyamide acrylic resin, and the like.

Using the positive electrode active material of the present invention and the above-described negative electrode active material, electrolytic solution, separator, and binder, a lithium ion secondary battery can be obtained according to a conventional method.
Thereby, it is possible to realize excellent battery characteristics that could not be achieved conventionally.

A preferred method for producing a positive electrode using the positive electrode active material of the present invention will be described below.
A positive electrode mixture is prepared by mixing the positive electrode active material powder of the present invention with a carbon-based conductive agent such as acetylene black and graphite, a binder, and a binder solvent or dispersion medium. The obtained positive electrode mixture is made into a slurry or a kneaded product, applied to or supported on a current collector such as an aluminum foil, and press-rolled to form a positive electrode active material layer on the current collector.
FIG. 3 is a schematic cross-sectional view of the positive electrode. As shown in FIG. 3, the positive electrode 13 is obtained by holding the positive electrode active material 5 on the current collector 12 with the binder 4.

It is considered that the positive electrode active material of the present invention is excellent in mixing with the conductive agent powder and has a low internal resistance of the battery. Accordingly, the charge / discharge characteristics, particularly the discharge capacity, are excellent.
In addition, the positive electrode active material of the present invention is excellent in fluidity when kneaded with a binder, and is easily entangled with a polymer of the binder and has excellent binding properties.
Furthermore, since the positive electrode active material of the present invention does not contain coarse particles and is spherical, the surface of the coating film surface of the produced positive electrode has excellent smoothness. For this reason, the coating film surface of a positive electrode plate is excellent in binding property, and becomes difficult to peel off. In addition, since the surface is smooth and lithium ions are uniformly introduced and exited on the surface of the coating film accompanying charging / discharging, the cycle characteristics are remarkably improved.

The shape of the lithium ion secondary battery is not particularly limited, and may be a cylindrical shape, a coin shape, a square shape, a laminate shape, or the like.
FIG. 4 is a schematic cross-sectional view of a cylindrical battery. As shown in FIG. 4, in the cylindrical battery 20, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12, and the negative electrode 11 in which the negative electrode active material layer is formed on the current collector 12. Are repeatedly laminated via the separator 14.
FIG. 5 is a schematic partial cross-sectional view of a coin-type battery. As shown in FIG. 5, in the coin-type battery 30, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12 and the negative electrode 11 are stacked via the separator 14.
FIG. 6 is a schematic perspective view of a prismatic battery. As shown in FIG. 6, in the square battery 40, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12, and the negative electrode 11 in which the negative electrode active material layer is formed on the current collector 12. However, they are repeatedly laminated via the separator 14.

A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the following I is used as the positive electrode active material of the positive electrode and the following II is used as the negative electrode active material of the negative electrode Can be obtained.
I: The positive electrode active material for nonaqueous electrolyte secondary batteries as described in this invention.
II: A negative electrode active material for a non-aqueous electrolyte secondary battery comprising at least one selected from the group consisting of metallic lithium, lithium alloys and compounds capable of occluding and releasing lithium ions.
This non-aqueous electrolyte secondary battery has a high electrode plate density and is extremely excellent in overdischarge characteristics.

The application of the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention is not particularly limited. For example, notebook computers, pen input computers, pocket computers, notebook word processors, pocket word processors, electronic book players, mobile phones, cordless phones, electronic notebooks, calculators, LCD TVs, electric shavers, electric tools, electronic translators, car phones , Portable printer, transceiver, pager, handy terminal, portable copy, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, handy cleaner, portable compact disc (CD) player, video movie, navigation system, etc. It can be used as a power source for equipment.
Also, lighting equipment, air conditioner, TV, stereo, water heater, refrigerator, oven microwave, dishwasher, washing machine, dryer, game machine, toy, road conditioner, medical equipment, automobile, electric car, golf cart, It can be used as a power source for electric carts, power storage systems and the like.
Furthermore, the application is not limited to consumer use, and may be used for military use or space.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

1. Preparation of cathode active material [Example 1]
Manganese carbonates with particle sizes (d10, d50 and d90) reaching 10%, 50% and 90% in the particle size distribution of the particles were 10 μm, 13 μm and 17 μm, respectively, washed with water and dried. Thereafter, 2500 g of this dried product and 393 g of lithium carbonate were mixed. The resulting mixture was calcined at about 800 ° C. for about 10 hours. The fired product obtained was pulverized.
100 g of the baked product after pulverization was reacted with 69.1 ml of n-butyllithium (1.6 mol / L) in 100 ml of hexane solution. The obtained reaction solution was filtered and dried in a nitrogen gas atmosphere to obtain a positive electrode side active material.

[Example 2]
Manganese carbonates whose particle size (d10, d50 and d90) in which the volume cumulative frequency in the particle size distribution of the particles reaches 10%, 50% and 90% are 9 μm, 12 μm and 16 μm, respectively, were washed with water and dried. Thereafter, 2500 g of this dried product and 393 g of lithium carbonate were mixed. The resulting mixture was calcined at about 800 ° C. for about 10 hours. The fired product obtained was pulverized.
100 g of the baked product after pulverization was reacted with 69.1 ml of n-butyllithium (1.6 mol / L) in 100 ml of hexane solution. The obtained reaction solution was filtered and dried in a nitrogen gas atmosphere to obtain a positive electrode side active material.

[Comparative Example 1]
500.0 g of manganese dioxide having d10, d50, and d90 of 0.3 μm, 2.1 μm, and 6.1 μm, respectively, and 101.5 g of lithium carbonate were dry-mixed for 5 minutes to obtain a raw material mixture powder. The obtained raw material mixture was baked at about 800 ° C. for about 10 hours in an air atmosphere. The fired product obtained was pulverized.
100 g of the baked product after pulverization was reacted with 69.1 ml of n-butyllithium (1.6 mol / L) in 100 ml of hexane solution. The obtained reaction solution was filtered and dried in a nitrogen gas atmosphere to obtain a positive electrode side active material.

[Comparative Example 2]
500.0 g of manganese dioxide having d10, d50 and d90 of 1.4 μm, 3.9 μm and 8.0 μm, respectively, and 101.5 g of lithium carbonate were dry mixed for 5 minutes to obtain a powder of the raw material mixture. The obtained raw material mixture was baked at about 800 ° C. for about 10 hours in an air atmosphere. The fired product obtained was pulverized.
100 g of the baked product after pulverization was reacted with 69.1 ml of n-butyllithium (1.6 mol / L) in 100 ml of hexane solution. The obtained reaction solution was filtered and dried in a nitrogen gas atmosphere to obtain a positive electrode side active material.

2. Properties of Positive Electrode Side Active Material (1) Particle Size Distribution of Positive Electrode Side Active Material The particle size distribution of the obtained positive electrode side active material was measured by a laser diffraction scattering method to obtain D10, D50, and D90.

(2) Electrode plate density of positive electrode secondary active material 90 parts by weight of positive electrode secondary active material powder, 5 parts by weight of carbon powder as conductive agent, and a normal methylpyrrolidone solution of polyvinylidene fluoride (5 parts by weight as the amount of polyvinylidene fluoride) are kneaded. A paste was prepared and applied to an aluminum current collector by the doctor blade method, followed by drying to obtain a positive electrode plate. After the positive electrode plate was cut into a predetermined size (5 cm ² ), the electrode plate was compressed with a uniaxial press. The electrode plate density was calculated from the thickness and weight of the electrode plate after compression.

The results are shown in Table 1.
It can be seen that the positive electrode side active material of the present invention has an improved electrode plate density as compared with the positive electrode side active material of the example.

3. Evaluation of Positive Electrode Subactive Material Using each of the positive electrode subactive materials obtained in Example 1 and Comparative Example 1, a test secondary battery in which the negative electrode was lithium metal was produced and evaluated as follows.
A secondary battery for testing in which the negative electrode was lithium metal was produced as follows.
A paste was prepared by kneading 90 parts by weight of the positive electrode active material powder, 5 parts by weight of carbon powder to be a conductive agent, and a normal methylpyrrolidone solution of polyvinylidene fluoride (5 parts by weight of polyvinylidene fluoride), This was applied onto an Al foil of a positive electrode current collector and dried to obtain a positive electrode plate. Using the obtained positive electrode plate, a test secondary battery in which the negative electrode was lithium metal was obtained.

(1) Initial discharge capacity Under the conditions of a charging potential of 4.3 V, a discharging potential of 2.75 V, and a discharging current of 0.2 mA / cm ² , the test secondary battery in which the negative electrode was lithium metal was discharged. The discharge capacity at this time was defined as the initial discharge capacity.

(2) Initial charge capacity The battery was charged at a constant voltage of 4.3 V under the condition of a current value of 0.2 mA / cm ² . The charge capacity at this time was defined as the initial charge capacity.

Next, using each positive electrode secondary active material obtained in Example 2 and Comparative Example 2, a laminated battery was produced and evaluated as follows.
Using the positive electrode active material obtained by mixing 90 parts by weight of lithium cobaltate as the main active material and 10 parts by weight of each positive electrode sub active material obtained in Example 2 and Comparative Example 2 as the sub active material, A positive electrode plate was obtained by the same method as in the case of the secondary battery. Also, graphite was used as the negative electrode active material, and was applied onto the Cu foil of the negative electrode current collector and dried in the same manner as in the case of the positive electrode plate to obtain a negative electrode plate. A porous polyethylene film was used as the separator. As the electrolytic solution, a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate = 3/7 (volume ratio) to a concentration of 1 mol / L was used. The positive electrode plate, negative electrode plate and separator are molded into a thin sheet, stacked and stored in a laminated film battery case, and a Ni lead with Li metal attached as a reference electrode is inserted into the center of the laminated battery. After that, an electrolytic solution was injected into the battery case, heat sealed, and the laminate film was adhered to obtain a laminated battery.

(3) Negative electrode potential at 0V overdischarge The laminate battery was charged at a constant voltage of 4.2V at a current value of 0.1C, and a constant current discharge at a final voltage of 2.75V was performed at a current value of 0.2C. Next, overdischarge was performed so that the battery voltage was 0 V, and the Li metal inserted using the negative electrode potential at this time as a reference electrode was measured as a reference voltage. The smaller the negative electrode potential, the better the overdischarge characteristics.

The results are shown in Table 1.
From Table 1, it can be seen that the positive electrode secondary active material of the present invention has an improved initial discharge capacity and initial charge capacity compared to the comparative example. Moreover, since the negative electrode potential at the time of 0V overdischarge is small compared with a comparative example, it turns out that the positive electrode secondary active material of this invention is excellent in the overdischarge characteristic. Furthermore, in the positive electrode secondary active material of the present invention, gas generation during overdischarge was suppressed as compared with the positive electrode secondary active material of the comparative example.

FIG. 1 is a graph schematically showing changes in potentials of the positive electrode and the negative electrode during a charge / discharge cycle of a lithium ion secondary battery. FIG. 2 is a schematic diagram showing a crystal structure of a spinel-structure lithium transition metal composite oxide. FIG. 3 is a schematic cross-sectional view of the positive electrode. FIG. 4 is a schematic cross-sectional view of a cylindrical battery. FIG. 5 is a schematic partial cross-sectional view of a coin-type battery. FIG. 6 is a schematic perspective view of a prismatic battery.

Explanation of symbols

1 8a site 2 32e site 3 16d site 4 binder 5 positive electrode active material 11 negative electrode 12 current collector 13 positive electrode 14 separator 20 cylindrical battery 30 coin-type battery 40 square battery

Claims (5)

A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a main active material having a first lithium transition metal composite oxide; and a secondary active material having a second lithium transition metal composite oxide,
The second lithium transition metal composite oxide exists in the form of particles composed of one or both of primary particles and secondary particles that are aggregates thereof,
In the particle size distribution of the particles, when the particle sizes at which the volume accumulation frequency reaches 10%, 50%, and 90% are D10, D50, and D90, respectively,
0 <(D10 / D50) <1,
1 <(D90 / D50) ≦ 5 and 5 μm ≦ D50 ≦ 40 μm are all satisfied,
The positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the second lithium transition metal composite oxide is a lithium manganese composite oxide having lithium in the 16c site and having a spinel structure . The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein a standard deviation of the particle size in the particle size distribution of the particles is 0.6 or less. The said 2nd lithium transition metal complex oxide is 1-30 weight% with respect to the positive electrode active material which consists of the said main active material and the said subactive material, The Claim 1 thru | or 2 characterized by the above-mentioned. Positive electrode active material for non-aqueous electrolyte secondary battery . The first lithium transition metal composite oxide is at least one of lithium cobaltate, lithium manganate, lithium nickelate, and lithium / nickel / cobalt composite oxide. Positive electrode active material for non-aqueous electrolyte secondary battery . A strip-shaped positive electrode configured by forming positive electrode active material layers using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 as a positive electrode active material on both surfaces of the strip-shaped positive electrode current collector,
A negative electrode active material layer using a metal lithium, a lithium alloy or a compound capable of occluding and releasing lithium ions as a negative electrode active material;
A spiral wound body in which a strip separator is interposed between the strip positive electrode and the strip negative electrode is formed by winding the strip positive electrode and the strip negative electrode in a state of being stacked with a strip separator interposed therebetween. Non-aqueous electrolyte secondary battery.

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