JP5435810B2 - Lithium nickel manganese composite oxide, positive electrode active material for secondary battery containing the same, and production method thereof - Google Patents

Description

  The present invention relates to a lithium nickel manganese composite oxide, a positive electrode active material for a secondary battery including the same, and a method for producing the same.

  Lithium batteries have a high energy density compared to other batteries, are light and can be used for a long time, and are power sources for portable devices such as mobile phones, PHS and small computers, power storage power sources, electric vehicles Development is underway for use as a power source for automobiles.

Such a lithium battery includes a positive electrode made of a positive electrode active material containing a lithium-containing composite oxide, a negative electrode made of a material capable of occluding and releasing lithium such as carbon, and a separator containing a non-aqueous electrolyte. Alternatively, a solid electrolyte is provided as a main component.
Among these constituent elements, those studied as positive electrode active materials include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O _4). ) Etc. In particular, a battery using a lithium cobalt composite oxide as a positive electrode has been developed to obtain excellent initial capacity characteristics and cycle characteristics, and has already been put into practical use.
However, since cobalt is a rare resource, a lithium ion secondary battery using a lithium cobalt composite oxide as a positive electrode is expensive, and an alternative material that is cheaper than cobalt and can realize a high energy density is required.
Therefore, lithium nickel manganese composite oxide having a spinel type crystal structure has attracted attention instead of lithium cobalt composite oxide, and some proposals have already been made.

For example, Patent Document 1, the general _{formula: Li a (Ni x Mn 2} -xy Y y) (O 4-z Z z) [ wherein, x, y, z, the valence of a and Y are within a specific range And Y is at least one selected from the group consisting of B and the like. Z is at least one of F or Cl. ] The positive electrode active material for secondary batteries characterized by including the spinel type lithium manganese complex oxide represented by this is described.

Patent Document 2 includes a step of mixing a lithium source, a metal source and a doping solution containing a doping element, and a step of heat-treating the mixture, and the doping solution is volatile with an alkoxide containing the doping element. Li _x Mn _{2 -y} M _y M ′ _z A ₄ (x, y, z are within a specific range, and M and M ′ are the same as each other. Or at least one element selected from the group consisting of B, Ni and the like, and A is an element selected from the group consisting of O, F, S and P). A method for producing a positive electrode active material for a secondary battery is described.

Patent Document 3 has a spinel structure represented by the general formula: Li _{(1 + X)} Mn _(2-YX) Ni _Y O ₄ (wherein X and Y are numerical values within a specific range, respectively). Lithium manganese nickel composite oxide, cubic unit cell lattice constant is 8.17-8.18〜, specific surface area 0.2-1.0 m ² / g, tap density 1.52 g / cm ³ or more Further, a positive electrode for a non-aqueous electrolyte secondary battery characterized in that a region exceeding 4.5 V in the discharge curve is 120 mAh / g or more and a potential region shelf is excluded from 3.5 to 4.5 V An active material and its manufacturing method are described.

Further, Patent Document 4 discloses Li _X2 Mn _(2-Y2) R _Y2 O ₄ (wherein X2 and Y2 represent numbers within a specific range. R is at least one element selected from the group consisting of Ni and the like. The positive electrode material for a lithium secondary battery containing a spinel type lithium manganese composite oxide represented by:

Japanese Patent No. 3675439 Japanese Patent No. 4031939 JP 2004-303710 A JP 2003-92108 A

  However, the present inventor has found that the positive electrode active materials described in Patent Documents 1 to 4 have a problem that the capacity density (mAh / cc) is low. Here, the capacity density means the product of the tap density of the positive electrode active material and the initial discharge capacity of the secondary battery using the positive electrode active material. For example, when it is used as a battery for an electric vehicle, it is important how much electricity can be stored in a limited space. Therefore, a capacity density indicating “how much capacity can be stored in a volume of 1 cc” is High is important. The positive electrode active material does not have to have either a high discharge capacity or a tap density, but it is important that both of them exhibit a high value.

The positive electrode active materials described in Patent Documents 1 to 4 have a low capacity density. For example, Patent Document 3 describes an example in which when the tap density of a positive electrode active material is 1.58 g / cm ³ , the discharge capacity of a secondary battery using the positive electrode active material is about 130 mAh / g. In this case, however, the capacity density is as low as 1.58 × 130 = 205.4 mAh / cc. Patent Document 4 describes, as Example 1, a layered lithium nickel manganese composite oxide having a tap density of 0.9 g / cc and a spinel type lithium manganese composite oxide having a tap density of 1.7 g / cc. A positive electrode material was obtained by mixing in the above, and a secondary battery was prepared and the initial discharge capacity was measured. As a result, it was described that it was 124 mAh / g. The tap density of this positive electrode was assumed to be 1.18 g / cc. Then, the capacity density is as low as 146.3 mAh / cc.

  Thus, in the conventional positive electrode active material, at least one of the tap density and the discharge capacity is low, and the capacity density that is the product of the tap density and the initial discharge capacity is low.

  The object of the present invention is that both the tap density of the positive electrode active material containing the same and the initial discharge capacity of the secondary battery using the positive electrode active material are both high, so that the capacity density is high and at the same time the positive electrode active material An object of the present invention is to provide a lithium-nickel-manganese composite oxide having practically excellent cycle characteristics of a secondary battery comprising Another object is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery containing the lithium nickel manganese composite oxide, a positive electrode for a secondary battery using the positive electrode active material, and a secondary battery having the positive electrode. . Furthermore, it is providing the manufacturing method of the lithium nickel manganese complex oxide and the positive electrode active material for non-aqueous electrolyte secondary batteries containing it.

The inventor has intensively studied to solve the above-mentioned problems, and has completed the present invention.
The present invention includes the following (1) to (11).
(1) formula _{(I): Li 1 + x} Ni 0.5-1 / 4x-1 / 4y Mn 1.5-3 / 4x-3 / 4y B y O 4 ( provided that Formula (I) medium-x, y is A lithium nickel manganese composite oxide having a spinel structure represented by 0 ≦ x ≦ 0.025, 0 <y ≦ 0.01),
The median diameter is 5-20 μm,
The particle size variation coefficient is 2.0 to 3.5%,
A lithium nickel manganese composite oxide having a BET specific surface area of 0.30 to 1.30 m ² / g.
(2) A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising the lithium nickel manganese composite oxide according to (1) above.
(3) A secondary battery including the lithium nickel manganese composite oxide according to the above (1) having a tap density of 1.84 g / cc or more and having an initial discharge capacity of 126 mAh / g or more is obtained. The positive electrode active material for a non-aqueous electrolyte secondary battery according to (2) above.
(4) A lithium source, a nickel source, a manganese source and a boron source are introduced into a solvent so as to have an atomic ratio of lithium, nickel, manganese and boron represented by the above formula (I), and an average particle size is 0.40 μm. The first step of pulverizing and mixing until the following is obtained, spray-drying the obtained slurry to obtain a precursor,
And a second step of firing the precursor at 800 to 950 ° C., wherein the lithium nickel manganese composite oxide according to (1) above is obtained.
(5) The method for producing a lithium nickel manganese composite oxide according to (4) above, wherein at least one selected from the group consisting of lithium hydroxide and lithium carbonate is used as the lithium source.
(6) The method for producing a lithium nickel manganese composite oxide according to (4) or (5) above, wherein at least one selected from the group consisting of nickel oxide and nickel hydroxide is used as the nickel source.
(7) The method for producing a lithium nickel manganese composite oxide according to any one of (4) to (6) above, wherein at least one selected from the group consisting of manganese oxide and manganese carbonate is used as the manganese source.
(8) A nonaqueous electrolyte secondary that obtains a positive electrode active material for a nonaqueous electrolyte secondary battery using the lithium nickel manganese composite oxide obtained by the production method according to any of (4) to (7) above A method for producing a positive electrode active material for a battery.
(9) A positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the production method according to (8) above.
(10) A positive electrode for a secondary battery, wherein the positive electrode active material for a nonaqueous electrolyte secondary battery according to (2), (3) or (9) is bound with a binder.
(11) A secondary battery comprising the secondary battery positive electrode according to (10), a negative electrode, and an electrolyte solution.

  According to the present invention, both the tap density of the positive electrode active material containing it and the initial discharge capacity of the secondary battery using the positive electrode active material are both high, so that the capacity density is high and at the same time the positive electrode active material. It is possible to provide a lithium nickel manganese composite oxide that has practically excellent cycle characteristics of a secondary battery using the above. In addition, a positive electrode active material for a non-aqueous electrolyte secondary battery containing the lithium nickel manganese composite oxide, a positive electrode for a secondary battery using the positive electrode active material, and a secondary battery having the positive electrode can be provided. . Furthermore, the manufacturing method of the lithium nickel manganese complex oxide and the positive electrode active material for non-aqueous electrolyte secondary batteries containing the same can be provided.

The present invention will be described.
The present invention provides a compound of formula _{(I): Li 1 + x} Ni 0.5-1 / 4x-1 / 4y Mn 1.5-3 / 4x-3 / 4y B y O 4 ( provided that Formula (I) medium-x, y Is a lithium nickel manganese composite oxide having a spinel structure represented by 0 ≦ x ≦ 0.025 and 0 <y ≦ 0.01), having a median diameter of 5 to 20 μm and a particle diameter variation coefficient of 2 The lithium-nickel-manganese composite oxide has a BET specific surface area of 0.30 to 1.30 m ² / g.
Hereinafter, the lithium nickel manganese composite oxide of the present invention is also referred to as “the composite oxide of the present invention”.

<Composite oxide of the present invention>
The composite oxide of the present invention will be described.
The composite oxide of the present invention is represented by the following formula (I) and has a spinel structure.
Formula _{(I): Li 1 + x} Ni 0.5-1 / 4x-1 / 4y Mn 1.5-3 / 4x-3 / 4y B y O 4
In the formula (I), x satisfies 0 ≦ x ≦ 0.025, preferably 0 ≦ x ≦ 0.020, and more preferably 0 ≦ x ≦ 0.015.
In the formula (I), y satisfies 0 <y ≦ 0.01, preferably 0 <y ≦ 0.0075, more preferably 0 <y ≦ 0.0050.
The composite oxide of the present invention has a spinel structure, in which a part of Mn atoms in the crystal structure is substituted with Ni atoms, and a part of Ni atoms and Mn atoms are further substituted with Li atoms and B atoms. It is estimated that

The composite oxide of the present invention has a median diameter of 5 to 20 μm, preferably 5 to 15 μm, more preferably 5 to 10 μm.
The composite oxide of the present invention has a particle size variation coefficient of 2.0 to 3.5%, preferably 2.5 to 3.5%, more preferably 3.0 to 3.5%.
Further, the composite oxide of the present invention, BET specific surface area of 0.30~1.30m ² / g, preferably 0.30~1.13m ² / g, more preferably 0.30~1.00m ² / g, more preferably 0.30 to 0.85 m ² / g.

The lithium nickel manganese composite oxide having the structure of the formula (I) as described above and further satisfying all the requirements of the median diameter, the particle diameter variation coefficient and the BET specific surface area as described above has a high tap density. The present inventors have found that a secondary battery using this as at least a part of the positive electrode active material has an increased initial discharge capacity, and that the cycle characteristics of the secondary battery are particularly excellent.
Specifically, the composite oxide of the present invention can have a tap density of 1.84 g / cc or more, preferably 1.90 g / cc or more, more preferably 2.00 g / cc or more.
The initial discharge capacity of the secondary battery using the composite oxide of the present invention as the positive electrode active material can be 126 mAh / g or more, preferably 130 mAh / g or more, more preferably 135 mAh / g or more.
In particular, the tap density may be 1.84 g / cc, and the initial discharge capacity may be 126 mAh / g or more.
The capacity density, which is the product of the tap density and the initial discharge capacity, can be 242 mAh / cc or more, preferably 250 mAh / cc or more, more preferably 255 mAh / cc or more, and even more preferably 260 mAh / cc or more.
Furthermore, the cycle capacity maintenance rate of the secondary battery using the composite oxide of the present invention as at least a part of the positive electrode active material is 42.0% or more, preferably 60.0% or more, more preferably 62.0%. % Or more.

In addition, as described above, the inventor sets the BET specific surface area to 1.30 m ² / g or less and further sets the particle diameter variation coefficient to 2.0% or more, so that elution of Mn, decomposition of the electrolyte, etc. It is estimated that side reactions that lead to performance degradation are suppressed and the cycle capacity retention rate is increased.

A method for measuring the median diameter of the composite oxide of the present invention will be described.
First, the composite oxide of the present invention is dispersed in an aqueous sodium hexametaphosphate solution by ultrasonic dispersion and stirring in a room temperature atmosphere to form a slurry. Next, after adjusting this slurry to have a transmittance of 80 to 90%, the particle size distribution is measured using a laser diffraction / scattering type particle size distribution measuring apparatus.
The median diameter in the composite oxide of the present invention is determined from the particle size distribution thus measured.

A method for measuring the particle size variation coefficient of the composite oxide of the present invention will be described.
The particle diameter variation coefficient (CV value) of the composite oxide of the present invention was measured using a scanning electron microscope (for example, JSM-6701, manufactured by JEOL Ltd.) (for example, magnification is 5,000 times). Then, 19 radii are measured for each particle, the relative standard deviation is obtained, and the average value of the obtained relative standard deviations for 250 particles is obtained.

A method for determining the BET specific surface area of the composite oxide of the present invention will be described.
The BET specific surface area of the composite oxide of the present invention is a value obtained by BET one-point measurement by a continuous flow method. Specifically, both the adsorption gas and the carrier gas used are a mixed gas of nitrogen, air, and helium, and the powder sample is degassed by heating with the mixed gas at a temperature of 450 ° C. or lower, and then cooled with liquid nitrogen. Then, the mixed gas is adsorbed, and the adsorbed nitrogen gas is desorbed by returning it to room temperature, detected by a thermal conductivity detector, the amount is obtained as a desorption peak, and is calculated as the specific surface area of the sample.
Such a BET specific surface area can be measured using a known BET powder specific surface area measuring device.

A method for measuring the tap density of the composite oxide of the present invention will be described.
The tap density of the composite oxide of the present invention is calculated by measuring 10 g of the composite oxide of the present invention in a 20 ml glass graduated cylinder and measuring the volume after tapping 300 times.

A method for measuring the initial discharge capacity of a secondary battery using the composite oxide of the present invention as at least a part of the positive electrode active material will be described.
At first, 70% by mass of the composite oxide of the present invention, 25% by mass of acetylene black, and 5% by mass of polytetrafluoroethylene powder were thoroughly mixed in a mortar to make a thin sheet. Punched with a 14 mmφ punch, this is the positive electrode. At this time, the punched sheet is adjusted to about 70 mg.
Next, LiPF ₆ is added to a non-aqueous solvent obtained by mixing 50% by mass of ethylene carbonate and 50% by mass of diethyl carbonate to obtain a non-aqueous electrolyte having a concentration of 1 M / L.
Next, the obtained positive electrode (test electrode) was placed in a stainless steel container, and the non-aqueous electrolyte was added to a polypropylene nonwoven fabric (lithium battery separator) and a Li metal (counter electrode) laminated as a negative electrode. After sufficiently impregnating, it is sealed with an upper part made of stainless steel to obtain a semi-open lithium battery.
The lithium battery thus obtained was subjected to a constant current charge of 0.5 mA / cm ² , that is, a reaction for releasing lithium ions from the positive electrode at an upper limit of 5.0 V, and 0.5 mA / cm ² (0 0.1C equivalent) constant current discharge, that is, the initial discharge capacity per unit mass of the positive electrode active material (mAh / g) when a reaction for occluding lithium ions in the positive electrode is performed at a lower limit of 3.0 V.
In the present invention, the value obtained by measuring in this way is defined as the initial discharge capacity.

A method for measuring the cycle capacity retention rate of a secondary battery using the composite oxide of the present invention as at least part of the positive electrode active material will be described.
A positive electrode is prepared in the same manner as in the measurement of the initial discharge capacity except that the sheet thickness is reduced and a punch of 10 mmφ is used for punching. Adjust the punched sheet to about 13 mg. Then, the obtained positive electrode was used as a test electrode, a coin cell was assembled using Li metal as a counter electrode, and similarly, at an upper limit voltage of 5.0 V and a lower limit voltage of 3.0 V by 0.5 C constant current charge / discharge at 55 ° C. Repeat the cycle test. The ratio (%) of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle (initial discharge capacity) is defined as the cycle capacity maintenance rate.

<Method for producing composite oxide of the present invention>
Next, the method for producing the composite oxide of the present invention will be described.
Although the method for producing the composite oxide of the present invention is not particularly limited, the lithium source, the nickel source, the manganese source, and the boron source are used as a solvent so that the atomic ratio of lithium, nickel, manganese, and boron shown in the above formula (I) is obtained. The first step of obtaining a precursor by spray-drying the obtained slurry, and firing the precursor at 800 to 950 ° C. It is preferable that it is a manufacturing method of lithium nickel manganese complex oxide provided with 2 processes.
Hereinafter, such a production method is also referred to as “the preferred production method of the present invention”.

The 1st process in the suitable manufacturing method of the present invention is explained.
In the first step of the preferred production method of the present invention, first, a lithium source, a nickel source, a manganese source and a boron source are used as a solvent so that the atomic ratio of lithium, nickel, manganese and boron shown in the above formula (I) is obtained. Throw in. In particular, the boron source enhances the sinterability in the second step, promotes the growth of the particle diameter, contributes to the improvement of the tap density, the elution of Mn, and the reduction of the specific surface area causing side reactions, and the present invention. Estimate.

  Here, as the lithium source, an inorganic or organic compound containing a lithium atom can be used. For example, lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate can be used. Among these, it is preferable to use at least one selected from the group consisting of lithium hydroxide and lithium carbonate as the lithium source. The reason is that the generation of harmful gases can be suppressed.

  As the nickel source, an inorganic or organic compound containing nickel atoms can be used. For example, nickel oxide, nickel hydroxide, nickel carbonate, nickel carbonate hydrate, nickel oxyhydroxide can be used. Among these, it is preferable to use at least one selected from the group consisting of nickel oxide and nickel hydroxide as the nickel source. The reason is that it can be obtained at low cost as an industrial raw material.

  Further, as the manganese source, an inorganic or organic compound containing a manganese atom can be used. For example, manganese oxide, manganese carbonate, manganese carbonate hydrate, manganese hydroxide, manganese oxyhydroxide can be used. Among these, it is preferable to use at least one selected from the group consisting of manganese oxide and manganese carbonate as the manganese source. The reason is that it can be obtained at low cost as an industrial raw material.

Further, an inorganic or organic compound containing a boron atom can be used as the boron source. For example, boric acid (H ₃ BO ₃ ) or diboric acid triborate (B ₂ O ₃ ) can be used. Among these, it is preferable to use boric acid (H ₃ BO ₃ ) as a boron source. The reason is that it can be obtained at low cost as an industrial raw material.

Furthermore, at least one selected from the group consisting of lithium hydroxide and lithium carbonate is used as the lithium source, and at least one selected from the group consisting of nickel oxide and nickel hydroxide is used as the nickel source, and manganese oxide It is more preferable to use at least one selected from the group consisting of manganese carbonate and boric acid (H ₃ BO ₃ ) as the boron source because the capacity density tends to be higher.

The solvent into which these raw materials are added is not particularly limited, and for example, a conventionally known solvent such as water (pure water or the like), ethanol, acetone or the like can be used.
Moreover, it is preferable that the solid content concentration of the slurry obtained by putting each said raw material into a solvent is 20-35 mass%, and it is more preferable that it is 30-35 mass%. This is because a larger production capacity can be secured without impairing uniformity in this setting.

In the first step of the preferred production method of the present invention, each raw material is charged into the solvent as described above, and then pulverized and mixed until the average particle size is 0.40 μm or less.
The method of pulverization and mixing is not particularly limited, but a wet pulverization method using a wet pulverizer using a bead mill or the like is preferable. All raw materials (lithium source, nickel source, manganese source and boron source) can be pulverized and mixed at the same time in a solvent, so that they can be mixed more uniformly. Can be dissolved.
In addition, when pulverized and mixed so that the average particle size is 0.40 μm or less, the solid content tends to be uniform in the slurry. The average particle size is preferably 0.20 μm or more, and more preferably 0.30 μm or more. This is because if the particle size is too small by pulverization, handling in the subsequent steps will be worsened.
The average particle size is adjusted by adding a sodium hexametaphosphate aqueous solution to the slurry at room temperature in the atmosphere, and dispersing the slurry by ultrasonic dispersion and stirring, and adjusting the slurry to have a transmittance of 40 to 60%. The particle size distribution is measured using a diffraction / scattering type particle size distribution measuring device, and the median diameter obtained from the particle size distribution is meant.

In the first step of the preferred production method of the present invention, the slurry obtained by pulverization and mixing as described above is spray-dried to obtain a precursor. That is, after the slurry is sprayed to form a mist or dried, the slurry is dried. By spray-drying under desired conditions, the particle size of the resulting precursor can be adjusted within a desired range.
The method of spray drying is not particularly limited. For example, the slurry is caused to flow into the atomizer rotating at high speed, thereby causing the slurry component droplets to be discharged from the slit of the atomizer, and then sprayed using an appropriate drying gas temperature or air flow rate. A method for quickly drying the droplets is mentioned. At this time, the slurry flow rate is preferably 2 kg / h or more, more preferably 3 kg / h or more, and the atomizer rotational speed is preferably 30,000 rpm or more, more preferably 36,000 rpm. A treatment such as an appropriate temperature and air blowing is performed so as to quickly dry the dispersed droplets, but it is preferable to introduce a dry gas in a downward flow from the upper part of the drying tower to the lower part.
Spray drying is preferably performed using a spray dryer. Moreover, it is preferable that the inlet temperature of the hot air for drying of a spray dryer is 190-210 degreeC, and outlet temperature is 110-120 degreeC.

Next, the 2nd process in the suitable manufacturing method of this invention is demonstrated.
In the second step in the preferred production method of the present invention, the precursor obtained by the first step as described above is baked at 800 to 950 ° C.
By firing the precursor in an oxygen-containing atmosphere at such a temperature, the solid-phase reaction in the precursor can be advanced, and the composite oxide of the present invention can be obtained.

  Here, the firing method is not particularly limited as long as it is performed in an oxygen-containing atmosphere, and examples thereof include conventionally known methods such as a firing method using a tunnel furnace, a muffle furnace, a rotary kiln, and the like.

Moreover, it is preferable that a calcination temperature is 830 degreeC or more. When the precursor contains boron, if the firing temperature is high, the cycle characteristics tend to be improved as a result of a decrease in the specific surface area and an increase in the particle size variation coefficient due to the promotion of sintering of the primary particles. The present inventors have found that. The present inventor presumes that when the specific surface area decreases, side reactions such as elution of Mn in the active material and the expected decomposition of the organic solvent are suppressed, thereby contributing to improvement of cycle characteristics. If the boron source is not included, there is a tendency that the growth of primary particles does not proceed even if the firing temperature is high.
Moreover, it is preferable that a calcination temperature is 900 degrees C or less, It is more preferable that it is 870 degrees C or less, It is further more preferable that it is 850 degrees C or less. If the firing temperature is too high, it is presumed that oxygen is released from the crystal structure and the battery performance is lowered.

  The time for firing the precursor at the firing temperature as described above is preferably 6 to 8 hours, and more preferably 6 to 7 hours.

  According to such a preferred production method of the present invention, the composite oxide of the present invention having a high capacity density and excellent cycle characteristics as described above can be produced relatively easily.

The composite oxide of the present invention can be produced by other methods.
For example, in the preferred production method of the present invention, a lithium source, a nickel source, a manganese source and a boron source are wet pulverized in a solvent, and dry pulverization is performed using an air-flow impact crusher such as a ball mill or a jet mill. You can also get a body.
For example, in the preferred production method of the present invention, all of the lithium source, nickel source, manganese source and boron source are put into a solvent and pulverized and mixed, but each raw material is dry pulverized or wet pulverized and then mixed. A precursor can be obtained.
For example, in the preferred production method of the present invention, a slurry obtained by wet pulverization is spray-dried to obtain a precursor, but the slurry is obtained by other drying methods, for example, a drying method using a band dryer, a shelf-type dryer or the like. Can be dried to obtain a precursor.

<Positive electrode active material of the present invention>
The positive electrode active material of the present invention will be described.
The positive electrode active material of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery containing the composite oxide of the present invention.
The positive electrode active material of the present invention preferably contains 80% by mass or more of the composite oxide of the present invention, more preferably 90% by mass or more, and substantially 100% by mass, that is, from the composite oxide of the present invention. More preferably.

<Method for Producing the Positive Electrode of the Present Invention>
The positive electrode of the present invention may be in the same mode as, for example, a conventionally known positive electrode, as long as the positive electrode active material of the present invention is used. For example, what formed the layer which consists of what added the conductive support agent, the binder, etc. and mixed with the positive electrode active material of this invention as needed on a collector is mentioned. Specifically, an ink (slurry) is prepared by kneading a conductive additive, a binder, and an organic solvent such as N-methylpyrrolidone with the positive electrode active material of the present invention, and this ink is applied to the aluminum foil of the current collector. After applying and drying, it can be obtained by applying to a roller press. By applying to a roller press, the contact between the positive electrode active material and the current collector can be improved and the density of the positive electrode active material can be increased. Moreover, after fully mixing a conductive support agent and a binder with the positive electrode active material of this invention, it shape | molds in a sheet form with a roller press, and can obtain a positive electrode.
Here, examples of the conductive assistant include graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and ketjen black.
Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine rubber, styrene butadiene, cellulose resin, and polyacrylic acid.
Further, the current collector is not limited, and for example, a conventionally known net shape, sheet shape, or film shape can be used.

<Secondary battery of the present invention>
The secondary battery of the present invention will be described.
The secondary battery of the present invention may have the same configuration as a normal lithium ion secondary battery except that the positive electrode of the present invention is used as a positive electrode, and may be a cylindrical type, a square type, a coin type, a button type, or the like. It's okay. That is, the positive electrode, the negative electrode, and the non-aqueous electrolyte are the main battery components, and these components are enclosed in, for example, a battery can. Each of the positive electrode and the negative electrode acts as a lithium ion carrier, and the lithium ions are occluded in the negative electrode during charging and detached from the negative electrode during discharging.

A negative electrode is not specifically limited, For example, the aspect similar to a conventionally well-known negative electrode may be sufficient. For example, as the negative electrode active material, a lithium alloy represented by lithium or lithium-aluminum can be used, and graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Carbon-based materials that can reversibly occlude and release lithium ions such as mesocarbon microbeads, carbon fibers, and activated carbon can also be used. For example, the same current collector as that of the positive electrode can be used.
When the negative electrode active material is lithium or a lithium alloy, the negative electrode can be used as it is, or can be manufactured by pressure bonding to a current collector. In addition, when the negative electrode active material is a carbon-based material (graphite, carbon black, etc.) capable of occluding and releasing lithium ions, a binder similar to that for the positive electrode is added to the negative electrode active material and mixed as necessary. Then, paste it into a paste using a solvent, apply the obtained negative electrode mixture-containing paste to a negative electrode current collector made of copper foil, etc., dry it to form a negative electrode mixture layer, and press-mold as necessary It can manufacture by passing through a process.

  As the non-aqueous electrolyte, an organic electrolyte, a polymer electrolyte, a solid electrolyte, or the like can be used. Here, the organic electrolyte is a lithium salt added to a non-aqueous solvent, and the polymer electrolyte is a lithium salt added to a polymer compound.

Here, as the lithium salt, for example, LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Examples thereof include LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ . Among these, LiBF ₄ (lithium tetrafluoroborate) is less reactive with moisture present in the electrolyte, so it has better safety, cycle characteristics, rate characteristics (high rate discharge characteristics), initial characteristics, etc. It is easy to obtain an excellent lithium battery.
The concentration of the lithium salt in the organic electrolyte is preferably 0.1 to 3.0 mol / l, more preferably 0.2 to 2.0 mol / l. This is because the ionic conductivity of the non-aqueous electrolyte is increased, lithium salts are hardly precipitated in the non-aqueous electrolyte, and a lithium battery having high-performance battery performance can be obtained.

  As the non-aqueous solvent of the organic electrolyte, for example, a conventionally known one can be used, and a mixed solvent of ethylene carbonate, γ-butyrolactone, propylene carbonate and vinylene carbonate can be preferably used. Since ethylene carbonate, γ-butyrolactone and propylene carbonate have a high dielectric constant, they can reliably cause ionic conduction. Further, by containing vinylene carbonate in a non-aqueous solvent, ethylene carbonate, γ -Since the film | membrane derived from vinylene carbonate which can suppress reliably decomposition | disassembly of butyrolactone and propylene carbonate can be formed on a negative electrode, it can fully charge.

  The organic electrolyte may contain another organic solvent in addition to the lithium salt and the non-aqueous solvent.

When the non-aqueous electrolyte is a polymer electrolyte, it includes a matrix polymer compound that is gelled with a plasticizer (non-aqueous electrolyte). Examples of the matrix polymer compound include ethers such as polyethylene oxide and cross-linked products thereof. Fluorine-based resins such as vinyl resins, polymethacrylate resins, polyacrylate resins, polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers can be used alone or in combination.
Among these, from the viewpoint of oxidation-reduction stability, it is preferable to use a fluorine-based resin such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

The production of the polymer electrolyte is not particularly limited, and examples thereof include a method in which a polymer compound constituting a matrix, a lithium salt, and a solvent are mixed and heated to melt and dissolve. In addition, after dissolving a polymer compound, a lithium salt, and a solvent in an organic solvent for mixing, the organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a solvent are mixed, and ultraviolet rays, electron beams, or molecules are mixed. Examples include a method of polymerizing a polymerizable monomer by irradiating a line and the like to obtain a polymer.
10-90 mass% is preferable and, as for the ratio of the solvent in a polymer electrolyte, 30-80 mass% is more preferable. With such a ratio, the electrical conductivity is high, the mechanical strength is strong, and the film is easily formed.

Solid electrolytes include, for example, oxide-based quenching glasses containing lithium ions, glass-based solid electrolytes such as sulfide-based oxysulfide-based superionic conductive glasses, and high concentrations of Li salts dissolved and dispersed in polymers such as polyethers. Examples include molecular solid electrolytes.
The polymer solid electrolyte may be in the form of a gel containing a solvent component.

The secondary battery of the present invention preferably has a separator that prevents direct contact between the positive electrode and the negative electrode.
A separator is not specifically limited, For example, a conventionally well-known thing can be used, for example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.
In the case where an organic electrolyte or a polymer electrolyte is used as the nonaqueous electrolyte, a separator is usually used. However, in the case of a solid electrolyte, the solid electrolyte may be used without using the separator.

  The manufacturing method of the secondary battery of this invention is not specifically limited, For example, it can manufacture by a conventionally well-known method. For example, it can be manufactured by injecting a non-aqueous electrolyte before or after laminating the positive electrode of the present invention and the negative electrode via a lithium battery separator, and finally sealing with an exterior material. . Examples of the exterior material include a metal-resin composite film having a configuration in which nickel-plated iron, stainless steel, aluminum, and metal foil are sandwiched between resin films.

  Examples of the present invention and comparative examples will be described below, but the present invention is not limited to the following examples.

<Example 1>
LiOH · H ₂ O as a lithium source, NiO as a nickel source, MnO ₂ as a manganese source, and H ₃ BO ₃ as a boron source were prepared. Then, each of the raw material, the formula _{(I): Li 1 + x} Ni 0.5-1 / 4x-1 / 4y Mn 1.5-3 / 4x-3 / 4y B y O 4 ( proviso that in formula (I) x, y are weighed so as to obtain a lithium nickel manganese composite oxide represented by 0 ≦ x ≦ 0.025, 0 <y ≦ 0.01) where x = 0 and y = 0.01. Then, after mixing these raw materials, pure water was added so that the solid content concentration was 33.3% by mass to prepare a slurry.

Next, while stirring this slurry, it was pulverized using a wet pulverizer (manufactured by Ashizawa Finetech Co., Ltd .: Star Mill Lab Star LMZ-06) until the average particle size of the solid content in the slurry became 0.37 μm. . A 600 ml vessel was used and the grinding time was 1 hour.
Here, the average particle size of the solid content in the slurry was determined using a laser diffraction / scattering particle size distribution measuring device (Horiba, Ltd .: LA-950 type particle size distribution measuring device). Specifically, an aqueous sodium hexametaphosphate solution is added to the slurry at room temperature in the atmosphere, dispersed by ultrasonic dispersion and stirring, adjusted to have a transmittance of 40 to 60%, and then the particle size using the above apparatus. It was determined by measuring the distribution.

  Next, the slurry after pulverization was spray-dried using a disk-type spray dryer (Okawara Kako Co., Ltd .: L-8 type spray dryer). Here, air was used as the drying gas. Further, the cyclone differential pressure was adjusted to 0.7 kPa, and the drying gas inlet temperature was adjusted to 200 ° C. The slurry flow rate was 3 kg / h, and the atomizer speed was 36,000 rpm.

  Then, the particulate precursor obtained by spray drying was fired in air at 850 ° C. for 6 hours to obtain a lithium nickel manganese composite oxide having a target composition.

  Next, powder X-ray diffraction was measured for the obtained lithium nickel manganese composite oxide. The obtained lithium nickel manganese composite oxide was found to have a cubic spinel structure.

Further, when the BET specific surface area of the obtained lithium nickel manganese composite oxide was measured, it was 0.45 m ² / g. The specific surface area was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd .: Macsorb HM model-1220).

The obtained lithium nickel manganese composite oxide particles had a median diameter of 15 μm, a maximum particle diameter of 44.9 μm, and a substantially spherical shape.
Here, the maximum particle diameter of the lithium nickel manganese composite oxide was determined from the measurement result of the particle size distribution obtained when measuring the median diameter.

  Moreover, the particle diameter variation coefficient (CV value) was calculated | required about the obtained lithium nickel manganese composite oxide. Specifically, using a scanning electron microscope (for example, JSM-6701, manufactured by JEOL Ltd.), the particles are photographed (magnification is 5,000 times), and 19 radii are measured for each particle. The relative standard deviation was obtained, and the average value of the obtained relative standard deviations for 250 particles was defined as a particle diameter variation coefficient (CV value). As a result, the particle diameter variation coefficient was 3.13%.

  In addition, 10 g of powdery lithium nickel manganese composite oxide was put in a 20 ml glass graduated cylinder, and the powder packing density (tap density) after tapping 300 times was measured. As a result, it was 2.00 g / cc.

Next, using the lithium nickel manganese composite oxide obtained by the above method as a positive electrode active material, a lithium secondary battery was prepared, and the initial discharge capacity and cycle capacity retention rate were measured by the above-described method to evaluate the battery. Went.
The measurement results are shown in Table 1.

<Example 2>
In the lithium nickel manganese composite oxide represented by the formula (I), the same operation as in Example 1 was performed except that the lithium nickel manganese composite oxide was weighed so as to obtain x = 0.025 and y = 0.01. The same measurement was performed by the same method.
The measurement results are shown in Table 1.

<Example 3>
In Example 1, the granulated particles obtained by spray drying were calcined at 850 ° C. All operations were the same as in Example 1 except that the calcining temperature was 800 ° C. to obtain a lithium nickel manganese composite oxide. The same measurement was performed by the same method.
The measurement results are shown in Table 1.

<Example 4>
In the lithium nickel manganese composite oxide represented by the formula (I), x = 0.025 and y = 0.01 are weighed to obtain a granulated particle obtained by spray drying. Except for calcining at 800 ° C. to obtain a lithium nickel manganese composite oxide, all operations were performed in the same manner as in Example 1, and the same measurement was performed in the same manner.
The measurement results are shown in Table 1.

<Comparative Example 1>
In Example 1, the granulated particles obtained by spray drying were calcined at 850 ° C. All operations were the same as in Example 1 except that the calcining temperature was 750 ° C. and a lithium nickel manganese composite oxide was obtained. The same measurement was performed by the same method.
The measurement results are shown in Table 1.

<Comparative example 2>
In the lithium nickel manganese composite oxide represented by the formula (I), all operations were performed in the same manner as in Example 1 except that x = 0 and y = 0 were obtained. The same measurement was performed by the method.
The measurement results are shown in Table 1.

<Comparative Example 3>
In Comparative Example 2, the granulated particles obtained by spray drying were calcined at 850 ° C. All operations were the same as in Comparative Example 2 except that the calcining temperature was 800 ° C. to obtain a lithium nickel manganese composite oxide. The same measurement was performed by the same method.
The measurement results are shown in Table 1.

<Comparative Example 4>
In Comparative Example 2, the granulated particles obtained by spray drying were calcined at 850 ° C. All operations were the same as in Comparative Example 2 except that the calcining temperature was 750 ° C. and a lithium nickel manganese composite oxide was obtained. The same measurement was performed by the same method.
The measurement results are shown in Table 1.

<Comparative Example 5>
LiOH powder as a lithium source, NiO as a nickel source, and MnO ₂ as a manganese source were prepared. Then, only NiO and MnO ₂ are weighed so that Mn / Ni = 3.0 (molar ratio), and after mixing these raw materials, pure water is added so that the solid content concentration becomes 33.3 mass%. In addition, a slurry was prepared.
Next, this slurry was pulverized using a wet pulverizer (manufactured by Ashizawa Finetech Co., Ltd .: Star Mill Lab Star LMZ-06) while stirring. A 600 ml vessel was used and the grinding time was 1 hour.
Next, this slurry was spray-dried in the same manner as in Example 1, and the obtained granulated particles were fired at 890 ° C. for 2 hours under oxygen flow (100 mL / min) to obtain a fired powder. .
Next, the obtained fired powder is mixed with LiOH powder so that Li: (Ni + Mn) = 1: 2 (molar ratio), and fired at 750 ° C. for 6 hours to obtain a lithium nickel manganese composite oxide. It was.
The same measurement was performed by the same method as in Example 1.
The measurement results are shown in Table 1.
In addition, Comparative Example 5 and Comparative Examples 6, 7 and 8 to be described later were obtained by performing operations (used raw materials, mixing ratio, firing temperature, etc.) under conditions very similar to those of the example in Patent Document 3. .

<Comparative Example 6>
In Comparative Example 5, NiO was used as the nickel source, but all operations were performed in the same manner as in Comparative Example 5 except that Ni (OH) ₂ was used instead.
The measurement results are shown in Table 1.

<Comparative Example 7>
In Comparative Example 5, MnO ₂ was used as the manganese source, but all operations were performed in the same manner as in Comparative Example 5 except that MnCO ₃ was used instead.
The measurement results are shown in Table 1.

<Comparative Example 8>
In Comparative Example 5, NiO was used as the nickel source and MnO ₂ was used as the manganese source. All operations were the same as in Comparative Example 5 except that Ni (OH) ₂ and MnCO ₃ were used instead. The same measurement was performed by the method.
The measurement results are shown in Table 1.

Each of the lithium nickel manganese composite oxides according to Examples 1 to 4 within the scope of the present invention has a high tap density (1.84 g / cc or more), and an initial discharge of a secondary battery using the same. The capacity was also high (126 mAh / g or more). As a result, the capacity density was high, which was 242.5 to 260.4 mAh / g. In addition, the cycle capacity retention rate was high, specifically 42.5% or more (the maximum was 62.2% of Example 1).
On the other hand, the cycle capacity retention rate of the secondary battery using the lithium nickel manganese composite oxide according to Comparative Example 1 was very low, which was 3.9%.
In the case of the lithium nickel manganese composite oxide according to Comparative Examples 2 to 8, the capacity density is as low as 43.7 to 240.1 mAh / g, and in addition, the cycle capacity maintenance rate is also 2.4 to 33.8%. It became low.

Claims (11)

Formula _{(I): Li 1 + x} Ni 0.5-1 / 4x-1 / 4y Mn 1.5-3 / 4x-3 / 4y B y O 4 ( provided that Formula (I) medium-x, y is 0 ≦ x ≦ 0 .025, 0 <y ≦ 0.01), a lithium nickel manganese composite oxide having a spinel structure represented by:
The median diameter is 5-20 μm,
The particle size variation coefficient is 2.0 to 3.5%,
A lithium nickel manganese composite oxide having a BET specific surface area of 0.30 to 1.30 m ² / g.   A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising the lithium nickel manganese composite oxide according to claim 1.   The secondary battery including the lithium nickel manganese composite oxide according to claim 1 having a tap density of 1.84 g / cc or more and having an initial discharge capacity of 126 mAh / g or more is obtained. 2. A positive electrode active material for a non-aqueous electrolyte secondary battery according to 2. A lithium source, a nickel source, a manganese source and a boron source are introduced into a solvent so as to have an atomic ratio of lithium, nickel, manganese and boron represented by the above formula (I), and the average particle size becomes 0.40 μm or less. A first step of pulverizing and mixing until the obtained slurry is spray-dried to obtain a precursor;
A method for producing a lithium nickel manganese composite oxide, comprising: a second step of firing the precursor at 800 to 950 ° C., wherein the lithium nickel manganese composite oxide according to claim 1 is obtained.   The method for producing a lithium nickel manganese composite oxide according to claim 4, wherein at least one selected from the group consisting of lithium hydroxide and lithium carbonate is used as the lithium source.   The method for producing a lithium nickel manganese composite oxide according to claim 4 or 5, wherein at least one selected from the group consisting of nickel oxide and nickel hydroxide is used as the nickel source.   The method for producing a lithium nickel manganese composite oxide according to any one of claims 4 to 6, wherein at least one selected from the group consisting of manganese oxide and manganese carbonate is used as the manganese source.   A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein a positive electrode active material for a non-aqueous electrolyte secondary battery is obtained using the lithium nickel manganese composite oxide obtained by the production method according to claim 4. Production method.   A positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the production method according to claim 8.   A positive electrode for a secondary battery, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, 3 or 9 is bound with a binder.   A secondary battery comprising the positive electrode for a secondary battery according to claim 10, a negative electrode, and an electrolytic solution.