JP4673451B2 - Method for producing lithium transition metal oxide - Google Patents

Description

  The present invention relates to a method for producing a lithium transition metal oxide, particularly a lithium transition metal oxide that can be used as a positive electrode active material of a lithium secondary battery.

  Lithium batteries, especially lithium secondary batteries, have features such as high energy density and long life, and power supplies for home appliances such as video cameras, portable electronic devices such as notebook computers and mobile phones. Is widely used. Recently, application to large batteries mounted on electric vehicles (EV), hybrid electric vehicles (HEV), and the like is expected.

  A lithium secondary battery is a secondary battery with a structure in which lithium is extracted as ions from the positive electrode during charging, moves to the negative electrode and is stored, and reversely, lithium ions return from the negative electrode to the positive electrode during discharging. It is known to be due to the potential of the material.

Examples of the lithium transition metal oxide that can be used as the positive electrode active material of the lithium secondary battery include lithium transition metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMnO ₂ having a layer structure, LiMn ₂ O ₄ , and LiNi _0.5 Mn. A lithium transition metal oxide having a manganese-based spinel structure (Fd-3m) such as _1.5 O ₄ (also referred to as “spinel-type lithium transition metal oxide” or “LMO” in the present invention) is known.

Manganese spinel-type lithium transition metal oxide (LMO) is a positive electrode for large batteries such as electric vehicles (EV) and hybrid electric vehicles (HEV) because of its low raw material price, non-toxicity, and high safety. It is attracting attention as an active material. Moreover, excellent output characteristics are particularly required for batteries for EVs and HEVs. In this regard, insertion and desorption of Li ions are three-dimensionally compared with lithium transition metal oxides such as LiCoO ₂ having a layer structure. A possible spinel type lithium transition metal oxide (LMO) has excellent output characteristics.

By the way, in a normal spinel type lithium transition metal oxide (LMO), when cycles are repeated in a high temperature region (for example, 45 to 60 ° C.), Mn ²⁺ is easily eluted, and the eluted Mn ²⁺ is deposited on the negative electrode. Since this becomes a resistance and causes capacity deterioration, it is said that the problem in practical use of the spinel type lithium transition metal oxide (LMO) is the cycle life characteristic in a high temperature region (for example, 45 to 60 ° C.). I have been.
Since the skeleton of LMO is composed of oxygen (O), if O is lost, the skeleton becomes weak, and the life, in particular, the high-temperature cycle life characteristics is deteriorated. In particular, spinel-type lithium transition metal oxides (LMO) fired at high temperatures have large oxygen vacancies and large crystal structure distortion, resulting in low Li-Mn-O bond strength and manganese during charge / discharge cycles. It is known that the elution of the battery becomes remarkable and the deterioration of the battery is promoted.
For this reason, with respect to the production of LMO, means for reducing oxygen vacancies or crystal structure distortion have been studied.

For example, Patent Document 1 discloses a method of suppressing oxygen deficiency by adding lithium hydroxide after high-temperature baking and re-baking at a lower temperature.
In Patent Document 2, the starting material is baked in an oxidizing atmosphere at a temperature in the range of 900 to 1000 ° C. for 5 to 50 hours, and then in an oxidizing atmosphere at 600 to 900 ° C. A method for suppressing oxygen deficiency is disclosed by re-baking at a temperature in the range of 1 to 50 hours.
Patent Document 3 proposes a method for producing a lithium composite oxide in which a mixture of raw materials is fired at a high temperature to produce a fired product, and the fired product is refired while flowing.

JP 2001-335323 A JP 2006-252940 A JP 2007-149414 A

  An object of the present invention is to provide a lithium transition metal oxide that can achieve both output characteristics (rate characteristics) and high-temperature cycle life characteristics, and can increase the crystallite size and suppress the distortion of the crystal structure. Another object of the present invention is to provide a new method for producing a lithium transition metal oxide.

  In order to solve this problem, the present invention provides a method for producing a lithium transition metal oxide comprising a raw material mixing step, a firing step, and a heat treatment step, in an atmosphere having an oxygen partial pressure of 0.015 MPa to 0.15 MPa. And heat treatment at a primary oxygen release temperature of ± 50 ° C. in an atmosphere having an oxygen partial pressure of 0.03 MPa or more after baking at 850 ° C. in a method for producing a lithium transition metal oxide This is a proposal.

  According to the production method of the present invention, since the crystallite size can be increased and the distortion of the crystal structure can be suppressed, the distortion is reduced and the skeleton is strengthened. For example, as a positive electrode active material of a lithium secondary battery When used, it is possible to provide a new lithium transition metal oxide capable of achieving both output characteristics (rate characteristics) and high-temperature cycle life characteristics.

  According to the manufacturing method of the present invention, it is possible to suppress the distortion of the crystal structure while increasing the crystallite size as described above, the strain is 0.05 or less, and the crystallite size is 250 nm to A 1000 nm spinel lithium transition metal oxide can be obtained. Such spinel-type lithium transition metal oxides are not recognized as publicly known in Japan at the time of this application.

In order to demonstrate a primary oxygen release temperature and a secondary oxygen release temperature, it is the figure which showed the TG curve of the spinel type lithium transition metal oxide of Example 1. FIG. It is the figure which showed the structure of the cell for electrochemical produced in order to evaluate the battery characteristic of the sample obtained by the Example and the comparative example.

  Hereinafter, embodiments of the present invention will be described. However, the scope of the present invention is not limited to the following embodiment.

<Manufacturing method>
The present embodiment is an embodiment relating to a method for producing a spinel (Fd-3m) lithium transition metal oxide.

The manufacturing method of this embodiment is characterized in that after the raw materials are mixed, calcined at 850 ° C. or higher in a predetermined oxygen partial pressure atmosphere, and then heat-treated in an atmosphere having a higher oxygen partial pressure than the atmosphere. .
Hereinafter, the details will be described in order.

(material)
As the starting material, at least a lithium material and a manganese material may be appropriately selected.

The lithium raw material is not particularly limited. For example, lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), LiOH.H ₂ O, lithium oxide (Li ₂ O), and others Examples include lithium fatty acid and lithium halide. Of these, lithium hydroxide salts, carbonates and nitrates are preferred.

As the manganese raw material, any of manganese dioxide, trimanganese tetroxide, dimanganese trioxide, manganese carbonate, or a mixture of two or more selected from these can be used.
As manganese dioxide, chemically synthesized manganese dioxide (CMD), electrolytic manganese dioxide (EMD) obtained by electrolysis, manganese carbonate, or natural manganese dioxide can be used.

In the present embodiment, in addition to the lithium raw material and the manganese raw material, for example, a magnesium raw material, an aluminum raw material, and other substances known as starting materials for lithium transition metal oxides can be blended.
In this case, the magnesium raw material is not particularly limited. For example, magnesium oxide (MgO), magnesium hydroxide (Mg (OH) ₂ ), magnesium fluoride (MgF ₂ ), magnesium nitrate (Mg (NO ₃ ) ₂ Etc.), among which magnesium oxide is preferred.
The aluminum raw material is not particularly limited. For example, aluminum hydroxide (Al (OH) ₃ ), aluminum fluoride (AlF ₃ ), or the like can be used, and aluminum hydroxide is particularly preferable.

  Examples of other substances known as starting materials for lithium transition metal oxides include elements such as Ti, Ni, Co and Fe, and the starting materials are not particularly limited. For example, an oxide or hydroxide may be blended.

(Mixing of raw materials)
The method of mixing raw materials is not particularly limited as long as it can be uniformly mixed. For example, the respective raw materials may be added simultaneously or in an appropriate order using a known mixer such as a mixer, and mixed by stirring in a wet or dry manner. When adding an element that is difficult to replace, such as aluminum, it is preferable to employ wet mixing.

Examples of the dry mixing include a mixing method using a precision mixer that rotates mixed powder at a high speed.
On the other hand, examples of the wet mixing include a mixing method in which a liquid medium such as water or a dispersant is added and wet mixed to form a slurry, and the resulting slurry is pulverized with a wet pulverizer. It is particularly preferable to grind to submicron order. After pulverizing to the submicron order, granulation and baking can increase the uniformity of each particle before the baking reaction, and the reactivity can be increased.

(Granulation)
The raw materials mixed as described above may be granulated to a predetermined size, if necessary, and then fired. However, granulation is not necessarily performed.
The granulation method may be wet or dry as long as the various raw materials pulverized in the previous step are dispersed in the granulated particles without being separated, and the extrusion granulation method, rolling granulation method, fluidized granulation method, A mixed granulation method, a spray drying granulation method, a pressure molding granulation method, or a flake granulation method using a roll or the like may be used. However, when wet granulation is performed, it is necessary to sufficiently dry before firing.
As a drying method, it may be dried by a known drying method such as a spray heat drying method, a hot air drying method, a vacuum drying method, a freeze drying method, etc. Among them, the spray heat drying method is preferable. The spray heat drying method is preferably performed using a heat spray dryer (spray dryer). By granulating with a thermal spray dryer (spray dryer), the particle size distribution can be made sharper, and the secondary particles can be formed so as to contain agglomerated particles (secondary particles) formed by agglomeration. Forms can be prepared.

(Baking)
Firing is preferably performed in an atmosphere having an oxygen partial pressure of 0.015 MPa to 0.15 MPa, for example, in an air atmosphere. If the oxygen partial pressure is higher than 0.15 MPa, crystal growth cannot be promoted and the crystallite size cannot be increased. In addition, as will be described later, in order to promote crystal growth by firing, it is preferable that the oxygen partial pressure in the atmosphere is low. However, if the oxygen partial pressure during firing is too low, oxygen deficiency will increase and heat treatment will also occur. Since the strain cannot be recovered, baking is preferably performed at an oxygen partial pressure of 0.015 MPa or more.
From this point of view, the oxygen partial pressure during firing is more preferably 0.015 MPa to 0.13 MPa, particularly 0.015 MPa to 0.12 MPa, more preferably 0.015 MPa or more, or less than 0.08 MPa. preferable.

The firing temperature can be increased at 850 ° C., particularly 910 to 1,050 ° C., particularly 910 to 980 ° C., because the crystallite size can be increased by promoting the crystal growth by firing at a high temperature. preferable.
The firing temperature means the product temperature of the fired product measured by bringing a thermocouple into contact with the fired product in the firing furnace.
The firing time, that is, the time for maintaining the firing temperature may be 0.5 to 30 hours, although it depends on the firing temperature.

  The kind of baking furnace is not specifically limited. For example, it can be fired using a rotary kiln, a stationary furnace, or other firing furnace.

(Heat treatment)
Next, it is important to perform heat treatment at a temperature of primary oxygen release temperature ± 50 ° C. in an atmosphere having an oxygen partial pressure higher than that of air.
By performing the heat treatment in this manner, crystal distortion can be reduced.

  The atmosphere for the heat treatment is preferably such that the oxygen partial pressure is 0.03 MPa or higher and the oxygen partial pressure is higher than that during firing, particularly 0.05 MPa or higher, particularly 0.08 MPa or higher. By performing heat treatment in an atmosphere having a high oxygen partial pressure, oxygen can be easily taken in equilibrium, and oxygen vacancies can be suppressed to reduce strain.

  Further, it is preferable to perform heat treatment while flowing oxygen gas having an oxygen concentration of 80% to 100%. By performing heat treatment while always supplying fresh oxygen, oxygen can be easily taken in, and oxygen vacancies can be further suppressed.

Furthermore, the pressure of the atmosphere during the heat treatment is preferably controlled to a pressure higher than atmospheric pressure, for example, 0.1 MPa to 1.5 MPa. Thus, by pressurizing the oxygen atmosphere, it becomes easier to take in oxygen and oxygen deficiency can be further suppressed.
From this point of view, the pressure of the atmosphere during the heat treatment is preferably controlled to 0.1 MPa to 1.5 MPa, particularly 0.1 MPa to 1.3 MPa, and particularly preferably 0.1 MPa to 1.0 MPa.

The heat treatment preferably maintains the primary oxygen release temperature ± 50 ° C., particularly ± 35 ° C., especially ± 30 ° C., and especially ± 20 ° C. Among these, it is more preferable to maintain a temperature range higher than the primary oxygen release temperature in each of the above temperature ranges from the viewpoint that energy exceeding the primary oxygen release temperature can be given.
The temperature of this heat treatment means the product temperature of the processed material measured by bringing a thermocouple into contact with the processed material in the furnace.
When the lithium transition metal oxide is heated to around the primary oxygen release temperature, the thermal vibration of Mn—O becomes large and becomes unstable by antagonizing the bonding force of Mn—O. By performing heat treatment while forcibly supplying oxygen within a temperature range of ± 50 ° C., oxygen can be taken into the crystal structure and distortion can be effectively reduced.
At this time, the rate of temperature rise is preferably 0.5 ° C./min to 4 ° C./min, particularly 0.5 ° C./min to 3 ° C./min, particularly 0.5 ° C./min to 2 ° C./min. More preferably, it is set to min.
The primary oxygen release temperature can be obtained as the starting temperature at which the spinel-type lithium transition metal oxide after heating is heated and the weight is reduced in the range of 600 ° C. to 900 ° C. (see FIG. 1).

  The time for maintaining the primary oxygen release temperature ± 50 ° C. in the heat treatment needs to be at least 1 minute. In order to fully incorporate oxygen into the crystal structure, at least one minute is considered necessary. From this viewpoint, the time for maintaining the primary oxygen release temperature ± 50 ° C. is preferably 5 minutes or more, particularly preferably 10 minutes or more.

The temperature lowering rate after the heat treatment is preferably slow cooling at a cooling rate of 10 ° C./min or less up to at least 500 ° C., particularly 0.1 ° C./min to 8 ° C./min, especially 0.5 ° C./min to More preferably, it is controlled to 5 ° C./min.
Since the oxygen taken in near the primary oxygen release temperature is considered to be stabilized, the oxygen is slowly cooled at a temperature lowering rate of 10 ° C./min or less until the temperature close to the primary oxygen release temperature, that is, at least 500 ° C. Can be considered preferable.

<Lithium transition metal oxide>
According to the manufacturing method of the present embodiment described above, a spinel type lithium transition metal oxide (also referred to as “present LMO”) having the characteristics described below can be obtained.

(composition)
The present LMO is a spinel (Fd-3m) lithium transition metal oxide containing, in addition to Li and Mn, any one of Ti, Ni, Mg, Co, and Fe, or a combination of two or more thereof.
The content of substitutional elements other than Li and Mn is preferably 0 to 1.8 wt%, particularly 0.2 to 1.0 wt%, particularly 0.4 to 0.6 wt% from the viewpoint of strain removal. Is even more preferable.

(distortion)
According to the production method of the present embodiment, the strain of the obtained spinel-type lithium transition metal oxide can be adjusted to 0.05 or less, preferably 0.02 or less, and more preferably 0.009 or less. By reducing the strain to this extent, the skeleton of the spinel lithium transition metal oxide becomes stronger, and when used as a positive electrode active material for a lithium secondary battery, the output characteristics (rate characteristics) and high-temperature cycle life characteristics It can be compatible.

(Crystallite size)
According to the manufacturing method of the present embodiment, the crystallite size of the obtained spinel-type lithium transition metal oxide is 250 nm to 1000 nm, particularly 300 to 1000 nm, preferably 350 nm to 900 nm, and particularly preferably 420 nm to 750 nm. Can be adjusted.
By setting the crystallite size of the present LMO to 250 nm to 1000 nm, the high temperature cycle life characteristics can be improved, and both the output characteristics and the high temperature cycle life characteristics can be achieved.
Here, “crystallite” means the largest group that can be regarded as a single crystal, and can be obtained by XRD measurement and Rietveld analysis.

(Characteristics / Applications)
The present LMO can be effectively used as a positive electrode active material of a lithium battery after being crushed and classified as necessary.
For example, the positive electrode mixture can be manufactured by mixing the present LMO, a conductive material made of carbon black or the like, and a binder made of Teflon (registered trademark) binder or the like. Such a positive electrode mixture is used for the positive electrode, for example, a material that can occlude / desorb lithium such as lithium or carbon is used for the negative electrode, and a lithium salt such as lithium hexafluorophosphate (LiPF6) is used for the non-aqueous electrolyte. A lithium secondary battery can be formed using a material in which is dissolved in a mixed solvent such as ethylene carbonate-dimethyl carbonate. However, the present invention is not limited to the battery having such a configuration.

  A lithium battery equipped with the present LMO as a positive electrode active material has both excellent life characteristics (cycle life characteristics) and output characteristics when repeatedly used for charge / discharge in the central region of charge / discharge depth (eg, SOC 50-80%). Since it exhibits, it is particularly excellent in the use of a positive electrode active material of a large-sized lithium battery used as a power source for driving a motor mounted on an electric vehicle (EV) or a hybrid electric vehicle (HEV).

<Explanation of words>
In the present invention, “HEV” means an automobile using two power sources, that is, an electric motor and an internal combustion engine.
The term “lithium battery” is intended to encompass all batteries containing lithium or lithium ions in the battery, such as lithium primary batteries, lithium secondary batteries, lithium ion secondary batteries, and lithium polymer batteries.

In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  Next, the present invention will be further described based on examples and comparative examples, but the present invention is not limited to the examples shown below.

<Measurement of primary oxygen release temperature>
40 mg of spinel-type lithium transition metal oxide after calcination was weighed and placed in an Al ₂ O ₃ deep dish container, and air was allowed to flow at a flow rate of 100 ml / min (oxygen partial pressure 0.021 MPa, oxygen concentration 21%). Then, the heating rate was increased to 1100 ° C. at a rate of temperature increase of 5 ° C./min. From the obtained TG curve (see FIG. 1), the starting temperature where the weight decreased in the range of 600 ° C. to 900 ° C. Calculated as “temperature”.
A TG-DTA apparatus (TG-DTA2000S) manufactured by Mac Science Co., Ltd. was used for thermal analysis.
In Japanese Patent Application No. 2009-159161, it was described that “O ₂ gas (purity 99.9%) was allowed to flow at a flow rate of 100 ml / min”, but this “O ₂ gas (purity 99 .9%) ”was an error in“ air ”.

<Measurement of XRD>
For the samples (powder) obtained in the examples and comparative examples, the crystallite size and strain were measured by the Rietveld method using the fundamental method described below.
The Rietveld method using the fundamental method is a method for refining the crystal structure parameters from the diffraction intensity obtained by powder X-ray diffraction or the like. This method assumes a crystal structure model, and refines various parameters of the crystal structure so that the X-ray diffraction pattern derived from the structure and the measured X-ray diffraction pattern match as much as possible.

For the measurement of the X-ray diffraction pattern, an X-ray diffraction apparatus (D8 ADVANCE manufactured by Bruker AXS Co., Ltd.) using Cu-Kα rays was used. The peak of the X-ray diffraction pattern obtained from the range of diffraction angle 2θ = 10 to 120 ° was analyzed using analysis software (product name “Topas Version 3”) to obtain the crystallite size and strain.
The crystal structure is attributed to a cubic crystal of the space group Fd-3m (Origin Choice 2), with Li occupied at the 8a site, Mn, Mg at the 16d site, excess Li content x, and O occupied at 32e. Assuming that the parameter Beq. Is fixed at 1 and the oxygen coordinate is a variable, the index Rwp <8.0, GOF <2.0 indicating the degree of agreement between the observed intensity and the calculated intensity as shown in the table The calculation was repeated until convergence was achieved. The crystallite size and strain were analyzed using a Gaussian function.

Other equipment specifications and conditions used for other measurements and Rietveld analysis are as follows.
Detector: PSD
Detector Type: VANTEC-1
High Voltage: 5616V
Discr. Lower Level: 0.35V
Discr. Window Width: 0.15V
Grid Lower Level: 0.075V
Grid Window Width: 0.524V
Flood Field Correction: Disabled
Primary radius: 250mm
Secondary radius: 250mm
Receiving slit width: 0.1436626mm
Divergence angle: 0.3 °
Filament Length: 12mm
Sample Length: 25mm
Receiving Slit Length: 12mm
Primary Sollers: 2.623 °
Secondary Sollers: 2.623 °
Lorentzian, 1 / Cos: 0.01630098Th

<Battery evaluation>
(Production of battery)
Li battery evaluation was performed by the following method.

PVDF (Kishida Chemical Co., Ltd.) in 8.80 g of positive electrode active material (spinel type lithium transition metal oxide obtained in Examples and Comparative Examples), 0.60 g of acetylene black (manufactured by Denki Kagaku Kogyo) and NMP (N-methylpyrrolidone) (Product made) 5.0 g of 12 wt% dissolved solution was accurately weighed and 5 ml of NMP was added and mixed well to prepare a paste. This paste is placed on an aluminum foil as a current collector, formed into a coating film with an applicator adjusted to a gap of 250 μm, vacuum-dried at 120 ° C. all day and night, punched out at φ16 mm, pressed thick at 4 t / cm ² , did. Immediately before producing the battery, it was vacuum-dried at 120 ° C. for 120 minutes or more to remove the adhering moisture and incorporated into the battery. In addition, the average value of the weight of φ16 mm aluminum foil is obtained in advance, the weight of the positive electrode mixture is obtained by subtracting the weight of the aluminum foil from the weight of the positive electrode, and the mixture of the positive electrode active material, acetylene black and PVDF The content of the positive electrode active material was determined from the ratio.
The negative electrode was made of metal Li having a diameter of 20 mm and a thickness of 1.0 mm, and an electrochemical evaluation cell TOMCEL (registered trademark) shown in FIG. 2 was produced using these materials.

In the electrochemical cell of FIG. 2, the positive electrode 3 made of the positive electrode mixture was disposed at the inner center of the lower body 1 made of organic electrolyte-resistant stainless steel. On the upper surface of the positive electrode 3, a separator 4 made of a microporous polypropylene resin impregnated with an electrolytic solution was disposed, and the separator was fixed with a Teflon (registered trademark) spacer 5. Further, on the upper surface of the separator, a negative electrode 6 made of metal Li was disposed below, a spacer 7 also serving as a negative electrode terminal was disposed, and the upper body 2 was placed thereon and tightened with screws to seal the battery.
The electrolytic solution used was a mixture of EC and DMC in a volume of 3: 7, and a solvent in which LiPF ₆ was dissolved in 1 mol / L as a solute.

(Rate characteristics evaluation)
Using the electrochemical cell prepared as described above, the output characteristics were determined by the method described below.
From the content of the positive electrode active material in the positive electrode in a state charged at 0.1 C to 4.3 V at 20 ° C., a discharge rate of 0.1 C, 1.0 C, 3.0 C, 5.0 C, 7.0 C The current value was calculated so that Based on the current value, the discharge capacity (mAh / g) up to 3.0 V when constant current discharge was performed at each rate was measured. A rate-discharge capacity diagram was created, extrapolated by the least square method, a linear approximation equation was obtained to calculate a linear slope, and the relative values when the value of Example 3 was set to 100 are shown in Table 2.

(High temperature cycle life characteristics evaluation)
Using the electrochemical cell prepared as described above, a charge / discharge test was performed by the method described below, and the high-temperature cycle life characteristics were obtained.
Place the cell in an environmental tester set so that the environmental temperature for charging and discharging the battery is 45 ° C., prepare for charging and discharging, and let stand for 4 hours so that the cell temperature becomes the environmental temperature. After charging and discharging at 3.0C to 4.3V for 2 cycles at 0.1C, the charge / discharge cycle was performed 47 times at 1C at a charge / discharge depth of SOC 50-80%. The 50th cycle was for capacity confirmation. The charge / discharge was performed at 0.1 C in the charge / discharge range of 3.0 V to 4.3 V.
The high temperature cycle life characteristic value (0.1 C) was obtained by dividing the percentage (%) of the numerical value obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the second cycle. In addition, the same cycle condition was changed from 0.1 C to 1.0 C, and a high temperature cycle life characteristic value (1.0 C) was obtained. All are shown in Table 2 as relative values when the value of Example 3 is taken as 100.

<Example 1-3>
Lithium carbonate 1770.9 g, electrolytic manganese dioxide 7500 g, magnesium oxide 65.7 g were set at a high speed blade rotation speed 400 rpm cross screw with a precision mixer (vertical granulator (Fuji Sangyo Co., Ltd. (FM-VG-25)), Mix for 5 minutes.
The obtained mixed powder was placed in a firing container (alumina crucible size = vertical * width * warm = 10 * 10 * 5 (cm)) ratio of open area to filling height (open area cm ² / Filling height cm) was filled to 100. Then, using a static electric furnace, in the atmosphere shown in Table 1, the temperature is raised from room temperature to the firing setting temperature at a heating rate = 150 ° C./hr, and the firing temperature (holding temperature) shown in Table 1 is held for 14 hours. Thereafter, the temperature was lowered from the holding temperature to 600 ° C. at a temperature lowering rate = 20 ° C./hr, and then naturally cooled to room temperature. The temperature variation within the holding time was controlled within a range of ± 5 ° C.
The fired powder obtained by firing was crushed with a mortar, classified with a sieve having an opening of 53 μm, and the powder under the sieve was collected to obtain a crushed sample.

  Next, the obtained crushed sample was heat-treated using a tube furnace heating device (Koyo Thermo System Co., Ltd.). That is, 200 g of crushed samples were filled in a magnetic boat, and this magnetic boat was installed near the center of the tube furnace. Then, while flowing oxygen gas (oxygen concentration 100%) into the tube furnace at a flow rate of 0.5 l / min, the sample was heated to the set temperature shown in Table 1 at a heating rate of 1.7 ° C./min. Hold for a predetermined time. Then, while continuing oxygen inflow, it cooled to room temperature at the temperature-fall rate shown in Table 1, and obtained the spinel type lithium transition metal oxide (sample).

The oxygen concentration was measured using an oxygen concentration meter (XPO-318 (New Cosmos Electric Co., Ltd.)) (the same applies to comparative examples described later).
The temperature at the time of the firing and the heat treatment is the product temperature of the processed product measured by bringing a thermocouple into contact with the processed product in the furnace (the same applies to comparative examples described later).

<Comparative Example 1>
A spinel-type lithium transition metal oxide (sample) was obtained using the same raw materials as in Example 1 except that heat treatment was not performed, and mixing, firing, crushing, and classification were performed in the same manner as in Example 1.

<Comparative Example 2>
Using the same raw materials as in Example 1, mixing, firing, crushing and classification were performed in the same manner as in Example 1 to obtain a crushed sample.
Next, the obtained crushed sample was heat-treated using a stationary electric furnace. That is, 200 g of the crushed sample was filled in a magnetic boat and shown in Table 1 at a temperature increase rate of 1.7 ° C./min in an air atmosphere (atmospheric pressure: 0.10 MPa, oxygen partial pressure: 0.021 MPa). Heated to the set temperature and held for a predetermined time after reaching. Then, while continuing oxygen inflow, it cooled to room temperature at the temperature-fall rate shown in Table 1, and obtained the spinel type lithium transition metal oxide (sample).

<Comparative Example 3>
A spinel type lithium transition metal oxide (sample) was obtained in the same manner as in Comparative Example 1 except that the atmosphere during firing was changed to an oxygen-pressurized atmosphere as shown in Table 1.

<Example 4-9>
Using the same raw materials as in Example 1, except for changing the atmosphere and heat treatment time in the heat treatment to the conditions shown in Table 3, the mixing of the raw materials to the heat treatment was performed in the same manner as in Example 1 to perform the spinel lithium transition. A metal oxide (sample) was obtained.

<Examples 10-22 and Comparative Example 4>
Using the same raw materials as in Example 1, except that the conditions at the time of firing and heat treatment were changed to the conditions shown in Table 3, the process from mixing of raw materials to heat treatment was carried out in the same manner as in Example 1 to spinel lithium transition A metal oxide (sample) was obtained.

<Example 23 and Comparative Example 5>
Example 1 except that the blending composition of the raw materials was changed to 1770.9 g of lithium carbonate, 7500 g of electrolytic manganese dioxide, and 129.0 g of titanium oxide, and the conditions at the time of firing and heat treatment were changed to the conditions shown in Table 3. The spinel type lithium transition metal oxide (sample) was obtained by carrying out from the mixing of the raw materials to the heat treatment in the same manner as described above.

<Example 24>
The raw material composition was changed to 1770.9 g of lithium carbonate, 7500 g of electrolytic manganese dioxide, 32.87 g of magnesium oxide, and 64.48 g of titanium oxide, and the conditions during firing and heat treatment were changed to the conditions shown in Table 3. The spinel type lithium transition metal oxide (sample) was obtained by carrying out from the mixing of the raw materials to the heat treatment in the same manner as in Example 1.

<Example 25>
Except for changing the composition of the raw materials to 1770.9 g of lithium carbonate, 7500 g of electrolytic manganese dioxide, 146.68 g of nickel hydroxide, and changing the conditions at the time of firing and heat treatment to the conditions shown in Table 3, Examples The spinel type lithium transition metal oxide (sample) was obtained by carrying out from the mixing of the raw materials to the heat treatment in the same manner as in 1.

<Example 26>
The raw material composition was changed to lithium carbonate 1770.9 g, electrolytic manganese dioxide 7500 g, cobalt oxyhydroxide 145.48 g, and the conditions at the time of firing and heat treatment were changed to the conditions shown in Table 3 The spinel type lithium transition metal oxide (sample) was obtained by carrying out from the mixing of the raw materials to the heat treatment in the same manner as in Example 1.

<Example 27>
The raw material composition was changed to lithium carbonate 1770.9 g, electrolytic manganese dioxide 7500 g, iron (iii) 132.99 g, and the conditions during firing and heat treatment were changed to the conditions shown in Table 3, In the same manner as in Example 1, mixing of raw materials to heat treatment was performed to obtain a spinel type lithium transition metal oxide (sample).

<Example 28>
Except for changing the composition of the raw materials to 1756.3 g of lithium carbonate, 7500 g of electrolytic manganese dioxide, 61.83 g of aluminum hydroxide, and changing the conditions at the time of firing and heat treatment to the conditions shown in Table 3, Example The spinel type lithium transition metal oxide (sample) was obtained by carrying out from the mixing of the raw materials to the heat treatment in the same manner as in 1.

(Discussion)
In the case of Comparative Example 1, since heat treatment was not performed, oxygen remained deficient by firing, so that the distortion of the crystal structure was increased, and the crystallite size was also reduced as compared with Example 1-3, and the rate characteristics. Both high temperature cycle life characteristics were inferior.
In the case of Comparative Example 2, since the heat treatment was performed under normal pressure and atmospheric atmosphere, the oxygen partial pressure was insufficient and the oxygen uptake was insufficient, resulting in large distortion of the crystal structure and particularly poor rate characteristics. By the way, Mn oxide (for example, MnO ₂ is reduced to Mn ₂ O ₃ at about 560 ° C.) has a thermal reduction property that releases oxygen when heated. It is presumed that the oxygen partial pressure at which oxygen could be sufficiently taken in was not reached.

  It was found that when firing with oxygen pressure as in Comparative Example 3, the crystallite size was reduced, and both the rate characteristics and the high temperature cycle life characteristics were inferior. The reaction to be heated to around 900 ° C. is a reaction in which particles are grown while releasing oxygen at the primary oxygen release temperature, the secondary oxygen release temperature, and the like. The secondary oxygen release temperature and the secondary oxygen release temperature shift to the high temperature side. As a result, it can be considered that the crystal growth reaction does not proceed and the crystallite size is reduced.

  Compared to Comparative Examples 1 to 3, after firing at 850 ° C. or higher in an atmosphere having an oxygen partial pressure of 0.015 MPa to 0.15 MPa as in Examples 1 to 3, the oxygen partial pressure was higher than that of the atmosphere. By heat-treating in a high atmosphere, the crystallite size can be increased and the distortion of the crystal structure can be suppressed, so the distortion is reduced and the skeleton is strengthened, and the output characteristics (rate characteristics) and high-temperature cycle are reduced. It was found that both life characteristics can be achieved.

Regarding the oxygen partial pressure during firing, as described above, the lower the oxygen partial pressure, the more the particle growth can be promoted. From this point of view, it is necessary to be 0.15 MPa or less in order to grow particles to the same extent as in the examples. Moreover, if it is about 0.015 Mpa, it can be considered that distortion can be recovered to about the level of the embodiment by heat treatment.
Regarding the firing temperature at the time of firing, it can be considered from the examples and past experience that particles of 850 ° C. or higher can be sufficiently grown. In addition, since firing at a high temperature exceeding 1050 ° C. may cause phase separation in terms of crystal structure, firing at 1050 ° C. or less is preferable.

  The oxygen partial pressure in the heat treatment is higher than that in the atmosphere (0.021 MPa), particularly an oxygen content of 0.03 MPa or more, from the viewpoint of recovering strain by incorporating oxygen into the crystal structure from Example 1-22. It is considered preferable to perform the heat treatment under pressure. In addition, it can be considered that it is preferable that the oxygen partial pressure is higher than that at the time of firing as compared with the atmosphere at the time of firing.

From the results of Examples 10-22 and Comparative Example 4, the heating temperature in the heat treatment is heated to near the primary oxygen release temperature at which oxygen can easily be taken in, specifically, to the primary oxygen release temperature ± 50 ° C. In particular, from the viewpoint of providing energy exceeding the primary oxygen release temperature, the primary oxygen release temperature to the primary oxygen release temperature + 50 ° C., that is, higher than the primary oxygen release temperature. It can be considered that heat treatment is preferably performed in the temperature range on the side.
From the results of the examples, regarding the pressure of the atmosphere at the time of heat treatment, it can be considered that oxygen of 0.10 MPa or more is more preferable because it is easier to take in oxygen. 5 MPa or less.

Regarding the temperature lowering rate after the heat treatment, oxygen taken in the vicinity of the primary oxygen release temperature is stabilized, so that it slowly passes 10 ° C./min or less until the temperature close to the primary oxygen release temperature, that is, at least up to 500 ° C. It is considered preferable to cool at a temperature drop rate.

Claims (5)

  In a method for producing a lithium transition metal oxide comprising a raw material mixing step, a firing step, and a heat treatment step, after firing at 850 ° C. or higher in an atmosphere with an oxygen partial pressure of 0.015 MPa to 0.15 MPa, oxygen A method for producing a lithium transition metal oxide, comprising performing heat treatment at a primary oxygen release temperature of ± 50 ° C in an atmosphere having a partial pressure of 0.03 MPa or more.   The method for producing a lithium transition metal oxide according to claim 1, wherein the oxygen partial pressure of the atmosphere during the heat treatment is 0.08 MPa or more.   The method for producing a lithium transition metal oxide according to claim 1 or 2, wherein the heat treatment is performed while flowing a gas having an oxygen concentration of 80 to 100%.   The method for producing a lithium transition metal oxide according to any one of claims 1 to 3, wherein after the heat treatment, cooling is performed to at least 500 ° C at a temperature lowering rate of 10 ° C / min or less.   The method for producing a lithium transition metal oxide according to claim 1, wherein the lithium transition metal oxide is a spinel type lithium transition metal oxide.