JP2001163700A - Lithium-based composite metal oxide and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lithium composite metal oxide which prevents decrease in the electric capacitance in the cycles of charging and discharging when the oxide is used for the positive pole of a lithium ion cell. SOLUTION: The crystal defects on the surface of the lithium-based composite metal oxide are suppressed by forming a single crystal structure for at least a part of the crystal structure of the lithium-based composite metal oxide which can store and discharge lithium ions. When the obtained oxide is used for a positive pole of a lithium ion cell, for example, a catalytic effect such as oxidation on an organic nonwater-based electrolyte solution during charging can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium cobalt oxide (LiC) capable of occluding and releasing lithium ions, which is mainly used as a cathode material of a lithium ion battery.
The present invention relates to an improvement of a lithium-based composite metal oxide exemplified by oO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) and a production method capable of suitably producing the improved lithium-based composite metal oxide.

[0002]

2. Description of the Related Art In recent years, lithium-based composite metal oxides capable of occluding and releasing lithium ions have been known as LiC,
oO ₂ , LiNiO ₂ or LiMn ₂ O ₄ or the like can be used as a positive electrode material, and a lithium ion battery can be formed using a carbon-based material such as graphite for a negative electrode. The possible power capacity is large and the voltage per cell is 2
Compared to secondary batteries such as nickel cadmium batteries and nickel-metal hydride rechargeable batteries, their use is rapidly expanding as a battery having a high energy density because the device can be operated without boosting the voltage. Demand for lithium-based composite metal oxides is also expanding.

[0003] As a method for producing these lithium-based composite metal oxides, there is a conventional method known as UnderLundblad B.
ill Bergman, "Sold State
Ionics "96 (1997) 173-181,18.
As shown in 3-193, Li as a lithium raw material
2CoO ₃ , CoCO ₃ was used as a cobalt raw material, these were adjusted so that Li / Co = 1.14, molded into pellets, reacted at 700 ° C. for 5 hours, and calcined at 800 ° C. for 3 hours. After that, the calcined pellets are pulverized and washed with water to collect the particles, whereby a lithium-based composite metal oxide having an average particle diameter of 1 μm or more is produced.

As another method for producing a lithium-based composite metal oxide, T.I. Ogiwara, Y .; Sai
to, et. al, "Journal of the
Society of Japan "101 (199
8) As shown in 1159-1163, LiNO _{3 is used} as a lithium source, and Co (N
Using O ₃ ) ₂ , these are adjusted to Li / Co = 1 and dissolved in distilled water, and the raw material solution is adjusted to a concentration of 0.05 to 1.0 mol / liter. The raw material liquid thus adjusted is supplied to the ultrasonic spray pyrolysis apparatus at 25 ° C. by atomizing with air, and the dry pyrolysis is performed at a drying temperature of 400 ° C. and a pyrolysis temperature of 500 to 900 ° C. By that
There is a liquid phase method described as a spray pyrolysis method for obtaining LiCoO ₂ having an average particle size of 0.56 μm.

Further, as another liquid phase method, YK.su
n, "journal of Materials
As shown in Sciencen. (1996) 3617-3621, LiNO ₃ is used as a lithium raw material and Co (NO ₃ ) ₂ .6H ₂ O is used as a cobalt raw material.
These were adjusted so that Li / Co = 1, and the pH was 1
The mixture was stirred and mixed with polyacrylic acid (PAA) while adjusting with nitric acid so that
In the evening, after the sol is dried until a sol is obtained, the resulting sol is dried at 70 to 80 ° C. while stirring to remove water to obtain a gel, and at 300 ° C. for the purpose of removing organic components in the gel. For 1 hour, then 400-65
There is a sol-gel method in which heat treatment is performed at 0 ° C. to obtain LiCoO ₂ .

[0006]

However, the crystal structure of the conventional lithium-based composite metal oxide obtained by each of the above-mentioned methods has a polycrystalline structure having a polycrystalline or partially amorphous phase in any of the methods. These are particles, and the strain at the crystal grain boundaries increases with the charge-discharge cycle and the crystal structure is destroyed, so the amount of lithium ions that can be stored or released decreases, and for example, manganese used is In the LiMn ₂ O ₄ , which is relatively abundant and can be obtained at a low cost, the elution of Mn is increased, and the organic nonaqueous electrolyte solution such as ethylene carbonate is oxidized. However, there is a problem that the electric capacity gradually decreases.

Further, the following problems are involved in each of the conventional manufacturing methods.
There are points. First, in the solid phase method, unreacted residual
LiCO₃It is difficult to get rid of this
Not only is it difficult, but also
I have to. In addition, the reaction time is long and
There is also a problem that the reaction temperature is high. In addition, the spray pyrolysis
In the method, LiCoO₂The higher the temperature, the better the crystallinity
High quality LiCoO ₂To get a fairly high temperature
However, it is difficult to process at these high temperatures.
The resulting product particles are particles having a polycrystalline structure.
You. Further, the particle size is set to 0.56 μm or less.
Is considered almost difficult. Further, the sol-gel method
Needs a very long time treatment and considered industrialization
At times, there is a problem that the manufacturing cost increases.
And the sol-gel contains non-
Always fine LiCoO₂It is possible to obtain a precursor of
However, by removing these hydroxyl groups, LiCoO₂Got
In order to achieve this, the fine particles LiCoO₂The precursor of
It is necessary to perform firing, and during the firing,
This causes polycrystallization and generation of aggregated particles,
Fine particles having a crystal structure cannot be obtained.

Accordingly, the present invention has been made in view of the above problems. First, when a lithium-based composite metal oxide is used for a positive electrode of a lithium ion battery,
A second aspect of the present invention is to provide an improved lithium-based composite metal oxide capable of preventing a decrease in electric capacity in a charge / discharge cycle. An object of the present invention is to provide a method for producing a lithium-based composite metal oxide that can be efficiently produced in a short time.

[0009]

In order to solve the above-mentioned problems, a lithium-based composite metal oxide of the present invention is a lithium-based composite metal oxide capable of occluding and releasing lithium ions, and has a crystal structure. Has a single crystal structure. According to this feature, since at least a part of the lithium-based composite metal oxide has a single crystal structure, crystal defects on the surface of the lithium-based composite metal oxide are suppressed. When used for the positive electrode of a lithium-ion battery, it is possible to suppress catalytic effects such as oxidation on the organic non-aqueous electrolyte solution during charging. Can be prevented from decreasing in electric capacity. Further, by making at least a part of the single crystal structure, the surface energy of the particles can be reduced, and even if the particle size is reduced, the metal in the lithium-based composite metal oxide, in particular, Mn in LiMn ₂ O ₄
Can be kept low.

[0010] In the lithium-based composite metal oxide of the present invention, the metal component in the lithium-based composite metal oxide is preferably at least one of nickel, cobalt, manganese, and iron. In this way, by setting the metal component to at least one of nickel, cobalt, manganese, and iron, each of these metals is relatively abundant in resources and can be obtained at low cost. A lithium ion battery can be manufactured.

The lithium-based composite metal oxide according to the present invention is characterized in that the lithium-based composite metal oxide has an average particle size of about 0.1 to 1;
It is preferably a fine powder of μm. In this case, the surface area of the lithium-based composite metal oxide can be increased by reducing the average particle size to 0.1 to 1 μm as compared with the conventional one. When used as a positive electrode of a lithium ion battery, not only can a lithium ion battery having a high charge / discharge rate be provided, but by setting the average particle size to 0.1 to 1 μm, a binder or a conductive material can be provided. Mixing with carbon or the like can be performed relatively easily, and a good positive electrode material can be obtained.

The method for producing a lithium-based composite metal oxide according to the present invention is a method for producing a lithium-based composite metal oxide capable of inserting and extracting lithium ions, wherein at least lithium ions and other metal ions are supercritical. Alternatively, the method is characterized in that a hydrothermal reaction is performed in water in a subcritical state to produce a lithium-based composite metal oxide at least partially having a single crystal structure. According to this feature, in order to obtain a lithium-based composite metal oxide having a single-crystal structure at least in part, while suppressing aggregation of nuclei generated by the reaction,
It is necessary to suppress the generation of secondary nuclei on the crystal surface, and it is desirable to perform high-temperature treatment to increase crystallinity.
In a high-pressure supercritical or subcritical state, water becomes a nonpolar gaseous state, and the generation rate of a nonpolar lithium-based composite metal oxide becomes extremely high and the dissolved ion concentration becomes extremely low. Generation and excessive crystal growth are unlikely to occur, so that not only can lithium-based composite metal oxide particles having a single crystal structure be efficiently obtained, but also the diameter of the generated particles can be reduced. Oxides synthesized by a hydrothermal reaction at about 200 to 300 ° C. generally contain water of crystallization or hydroxyl groups inside the crystal or on the surface of the crystal. By synthesizing or treating by a hydrothermal reaction in water in a state, a lithium-based composite metal oxide containing no crystallization water or a hydroxyl group and having high crystallinity can be obtained.

In the method for producing a lithium-based composite metal oxide according to the present invention, the hydrothermal reaction may be carried out at a predetermined temperature at which a supercritical or subcritical state can be obtained by dissolving the aqueous solution dissolving at least the lithium ions and metal ions of other metals. Preferably, the temperature is raised rapidly. By doing so, the aqueous solution is rapidly brought into a supercritical or subcritical state by a rapid temperature rise, and the hydrothermal reaction is carried out. Can be prevented, or the crystal state can be prevented from deteriorating due to aggregation of nuclei and generation of secondary nuclei on the crystal surface. With this configuration, the rapid temperature increase can be efficiently performed.

In the method for producing a lithium-based composite metal oxide according to the present invention, the fine particles of the lithium-based composite metal oxide are subjected to a hydrothermal treatment under a subcritical or supercritical condition for a predetermined time even after the fine particles are formed, so that the crystalline fine particles are grown. It is preferable to improve the crystallinity without increasing the crystallinity. By doing so, it is possible to improve single crystallization without increasing the fine particle size of the lithium-based composite metal oxide to be generated.

In the method for producing a lithium-based composite metal oxide according to the present invention, an oxidizing agent is dissolved in an aqueous solution for dissolving the lithium ion and a metal ion of another metal, and the oxidizing agent is oxygen gas, ozone gas, Preferably, it is a simple substance or a mixture of two or more of hydrogen and nitrate ions. With this configuration, when the metal ion reacts with lithium ion to form a lithium-based composite metal oxide, when it is necessary to appropriately increase the oxidation number by oxidation, under the subcritical or supercritical condition The oxidation of the metal ions can be suitably performed.

In the method for producing a lithium-based composite metal oxide according to the present invention, when at least one of oxygen gas and ozone gas is used as the oxidizing agent, the hydrothermal reaction conditions are preferably supercritical. In this way, under subcritical conditions, an effective oxidation reaction cannot be obtained because the gas becomes bubbles and phase separation occurs, whereas under the supercritical water conditions, the oxidation reaction occurs in a uniform phase. Is possible,
The oxidation reaction can be advanced to an effect.

In the method for producing a lithium-based composite metal oxide according to the present invention, it is preferable that the rapid heating hydrothermal reaction is performed under conditions to which hydroxyl ions are appropriately added. In this way, if the aqueous solution is appropriately added with hydroxide ions to make it alkaline, the by-products (for example, Co ₃ O ₄ ) that are easily generated in the temperature raising process are easily dissolved, and therefore, these temperature rising By-reactants generated in the process can be prevented from remaining in the reaction product, adversely affecting the crystal quality, and preventing the yield of the target lithium-based composite metal oxide from decreasing.

In the method for producing a lithium-based composite metal oxide according to the present invention, the addition of the hydroxide ion is preferably carried out by the addition of lithium hydroxide. In this case, the hydroxyl ions can be added together with lithium ions as a raw material.

In the method for producing a lithium-based composite metal oxide according to the present invention, when the above-mentioned hydroxide ions are appropriately added, the aqueous solution to which the hydroxide ions are added is directly mixed with supercritical water to rapidly increase the temperature. It is preferred to warm. By doing so, it is possible to suppress the generation of impurity oxides such as the above-mentioned Co ₃ O ₄ at the time of raising the temperature by rapidly raising the temperature.
The amount of hydroxyl ions to be added can be kept lower, and the incorporation of hydroxyl groups into crystals can be suppressed.

Production of the lithium-based composite metal oxide of the present invention
The method is to appropriately add an acid or alkali to the aqueous solution.
To adjust the pH of the aqueous solution to either acidic or alkaline.
It is preferable to carry out the hydrothermal reaction as a state. This
By the way, by-products that are likely to be generated during the heating process
(For example, Co₃O ₄) Etc. are easily dissolved,
As a result, by-products produced during these heating processes react.
It may remain in the product and adversely affect crystal quality,
To prevent reduction in yield of lithium-based composite metal oxide
Can be

In the method for producing a lithium-based composite metal oxide according to the present invention, the alkali molar ratio in the aqueous solution may be 1 to 20.
It is preferred that By doing so, the intended lithium-based composite metal oxide can be efficiently obtained.

In the method for producing a lithium-based composite metal oxide according to the present invention, the other metal ion may be nickel, cobalt,
It is preferably at least one of manganese and iron.
In this way, by setting the metal component to at least one of nickel, cobalt, manganese, and iron, each of these metals is relatively abundant in resources and can be obtained at low cost. A lithium ion battery can be manufactured.

In the method for producing a lithium-based composite metal oxide according to the present invention, when the metal ion is a divalent cobalt ion and the hydrothermal reaction is carried out in the presence of the oxidizing agent, the reaction is as rapid as possible. Preferably, the temperature is raised. In this way, divalent cobalt ions can be easily obtained, and the presence of an oxidizing agent at the time of the hydrothermal reaction allows LiCoO 2 to be oxidized into trivalent cobalt ions while oxidizing the divalent cobalt ions. ₂ can be effectively produced, and by performing the temperature increase to the subcritical or supercritical where the hydrothermal reaction is performed as quickly as possible, the oxidizing agent is decomposed at the time of the temperature increase, Consumption can be prevented, and a more effective oxidation reaction can be performed.

In the method for producing a lithium-based composite metal oxide according to the present invention, the value of the lithium ion / cobalt ion ratio is preferably in the range of 1 to 20. In this way, by increasing the amount of lithium ions present in the aqueous solution as compared with cobalt ions, the desired LiCoO 2
₂ can be obtained efficiently.

In the method for producing a lithium-based composite metal oxide according to the present invention, the range of the lithium ion concentration in the aqueous solution is 0.5.
It is preferably from 05 mol / liter to 2 mol / liter. In this case, since the lithium ion concentration is relatively low, it is possible to appropriately prevent the crystal state from deteriorating due to aggregation of nuclei and the like, and it is possible to efficiently obtain fine particles having a good single crystal structure. it can.

In the method for producing a lithium-based composite metal oxide according to the present invention, the reaction conditions in the hydrothermal reaction are such that the lithium-based composite metal oxide having a single crystal structure at least partially has an average particle size of about 0. It is preferable that the thickness be set to 0.1 to 1 μm. In this way, the surface area of the lithium-based composite metal oxide can be increased by reducing the average particle size to 0.1 to 1 μm as compared with the conventional one, and thus the lithium ion having a high charge / discharge rate can be obtained. Not only can a battery be provided, but by setting the average particle size to 0.1 to 1 μm in this way, it is possible to relatively easily carry out mixing with a binder or carbon as a conductive material to obtain a good positive electrode material. Can also.

In the method for producing a lithium-based composite metal oxide of the present invention, it is preferable that the production of the lithium-based composite metal oxide by the hydrothermal reaction is continuously performed. In this manner, in the batch method, the temperature rise is slow, the oxidizing agent is decomposed at the time of the temperature rise, and the oxidation reaction does not sufficiently occur, so that impurities are easily generated, and the target lithium-based composite metal oxide is efficiently produced. In comparison with the case where the lithium-based composite metal is not obtained well, for example, the temperature can be increased at a high speed by contact with the subcritical water or the supercritical water, and a sufficient oxidation reaction can be obtained. An oxide can be obtained efficiently, and fine particles having a smaller particle size can be produced at a low cost as compared with a batch method.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an apparatus for producing a lithium-based composite metal oxide used in the present embodiment. In the metal salt melting bath 10, a metal salt solution that is stable even at high temperatures (for example, KNO ₃ —NaNO ₃ 50 w manufactured by Shin-Nichika Chemical Co., Ltd.)
t% nitrates Metal heat treatment agent Tempering agent T-3) is contained. The electric heater 12 is immersed therein for heating, and the thermoelectric body 14 for temperature measurement is disposed therein. By controlling the heating by the electric heater 12 while measuring the temperature with the thermoelectric body 14, the metal salt solution in the metal salt molten bath 10 is controlled to a predetermined temperature.

Then, the reaction tube 16 is immersed in the metal salt melting bath 10, and LiCo is
To generate O _2. The stop valve 18 connected to the reaction tube 16 is provided for collecting the generated gas generated in the reaction tube 16 after the reaction.

When LiCoO ₂ is produced by such an apparatus, first, a raw material aqueous solution is charged into the reaction tube 16. The raw material aqueous solution is, for example, LiOH and Co (NO ₃ ).
₂ dissolved in distilled water is used. Where LiC
The ratio Li / Co for producing oO ₂ is not a theoretical ratio of 1, but LiCoO is set in a state where Li ions are present in excess in the raw material aqueous solution in excess of Co ions.
₂ is preferable because the yield can be increased. In the present embodiment, Li / Co is set to about 15.

As described above, it is preferable to use LiOH as a raw material because both Li ions and hydroxyl ions can be supplied to the aqueous solution, but the present invention is not limited to this.

Further, by using Co (NO ₃ ) ₂ ,
NO ₃ ions can be added to the raw material aqueous solution. This NO ₃
Functions as an oxidizing agent. Therefore, Co ²⁺ supplied as Co (NO ₃ ) ₂ due to the presence of this NO ₃ ion →
The oxidation reaction to Co ³⁺ can be promoted. Further, the reaction tube 1
Since air exists in 6, oxygen in the air also functions as an oxidizing agent. As described above, it is preferable that oxygen is present in the gas phase in the reaction tube 16. The oxidizing agent in the present invention is not limited to the above-mentioned NO ₃ ion and oxygen in the air, and other oxidizing agents such as ozone gas and hydrogen peroxide may be used alone or in combination as described above. Can be.

By adding LiOH, the alkali molar ratio [OH ⁻ ] / [NO ₃ ⁻ ] can be increased. By increasing the alkali molar ratio, the production of LiCoO ₂ can be promoted. Furthermore, the alkali molar ratio can be further increased by adding ammonia.
That is, it is considered that one molecule of ammonia [NH ₃ ] generates one OH ^- 1 molecule. The addition of ammonia can raise the pH of the raw material aqueous solution, thereby suppressing the production of Co ₃ O _{4 and the} like in the temperature raising process and improving the yield of LiCoO ₂ .

The aqueous solution of the raw material is adjusted to a desired pressure at the temperature in the metal salt melting bath 10. Here, as for this pressure, assuming that the raw material aqueous solution is pure water, a steam table (Steam Tabl) is used.
e) is calculated. For example, reaction temperature 400 ° C., the density of water in the reaction pressure 30MPa, since it is 0.35 g / cm ^3, the volume of the reaction tube 16 is as long as 10 cm ^3,
The raw material aqueous solution is charged so that the total amount of the raw material aqueous solution in the reaction tube 16 becomes 3.5 cm ³ .

The supercritical point of water is 374 ° C., 22M
Pa, and the reaction conditions are set to be in a subcritical or supercritical state. Although it depends on other conditions such as the concentration of the raw material solution, it is preferable that the temperature is at least 250 ° C. or more, and the pressure is 20 MPa or more so that the water is in a subcritical state. It is particularly preferable to set the conditions.

After charging the raw material aqueous solution into the reaction tube 16,
The reaction tube 16 is immersed in the metal salt melting bath 10 and kept in that state for a predetermined reaction time (for example, about 5 to 20 minutes). Next, the reaction tube 16 is taken out of the metal salt melting bath 10 and put in a cold water bath to immediately stop the reaction.

Then, the contents of the reaction tube 16 are taken out,
By washing with water after filtration, the reaction product LiC
Fine particles of oO ₂ are obtained.

The LiCoO ₂ thus obtained is:
As shown in the transmission electron micrograph of FIG. 5 (a), it has a small amount of impurities, a small particle size, and is a single crystal or a material close to a single crystal, which is very suitable as a battery material. Therefore, it can be suitably used as a positive electrode material of a lithium ion battery.

These lithium-based composite metal oxides, L
Regarding the formation temperature of iCoO ₂ , Li ⁺ , Co ²⁺ ,
Ions having a charge such as NO ₃ ^— tend to be more stably present in the liquid. On the other hand, a nonpolar substance such as LiCoO ₂ , which is a metal oxide after the reaction, originally tends to exist more stably in a gas. Furthermore, the solubility of the metal oxide drops sharply as the temperature of the supercritical water increases under a constant pressure. Therefore, as the temperature of water in the supercritical state, which is the generation temperature of the lithium-based composite metal oxide, is increased, the solvent changes from a liquid state to a gaseous state, and the solute reacts from a polar ionic state to a nonpolar oxide. Is faster. Further, since the solubility of the oxide is reduced, the precipitation of the oxide (in this case, LiCoO ₂ ) as a reaction product is promoted. At this time, the nucleus generation rate of oxide generation is increased, and the particle diameter of the generated oxide is reduced.

When the solvent is liquid, the precipitated oxide is
It takes in water of crystallization and hydroxyl groups, but not when the solvent is gaseous. Therefore, it is considered that generation of an oxide having a high degree of crystallinity is promoted and single-crystal oxide fine particles are easily obtained. Further, the conditions such that the water becomes supercritical state, the CO ²⁺ due to the presence of nitrate Co ^{3 +}
Oxidation can be suitably performed.

Further, when producing these lithium-based composite metal oxides, it is better to increase the Li / Co ratio in the aqueous solution of the raw materials and to make the condition of excess Li ions so that LiCoO ₂
Has a good yield. That is, when the Li / Co ratio is reduced, the amount of Co ₃ O ₄ that is not the target substance in the reaction product increases. This is probably because the presence of a large amount of Li during the deposition of the oxide facilitates the production of LiCoO ₂ more equilibrium than Co ₃ O ₄ . Raw material aqueous solution concentration,
Depending on other conditions such as temperature and pressure, Li / Co is 1
-20, especially 15-20. Further, the overall concentration of the raw material aqueous solution, that is, the concentration of lithium ions and cobalt ions is reduced to increase the concentration range of lithium ions from 0.05 mol / liter to 2 m.
When the amount is ol / liter, the yield of LiCoO ₂ increases, but the present invention is not limited to these conditions.

In addition, the production of the lithium-based composite metal oxide
At the time of formation, ammonia is added and an alkali molar ratio ([N
H₃] 10 [OH⁻]) / [NO₃ ⁻]
LiCoO₂Yield is high. This is the
By increasing the pH, Co ₃O₄Precipitates, especially overheating
It is considered that precipitation during the process became difficult to occur. Manufacturing method
In the method, the raw material aqueous solution is charged into the reaction tube 16 at normal temperature,
Immersed in a metal melting bath 10. Therefore, the supercritical
Before the state is created, Co₃O₄Generates
It remains as it is even in the supercritical state. That is,
After warming, LiCoO₂Condition that generates
Even before that, Co₃O₄Is generated
This remains in the reaction product as it is.

By increasing the alkali molar ratio and the pH of the raw material aqueous solution, Co ₃ O ₄ in the solution is increased.
, The precipitation is suppressed, the generation of Co ₃ O ₄ in the temperature raising process is suppressed, and the C in the reaction product is reduced.
It is considered that generation of o ₃ O ₄ is suppressed.

By increasing the amount of LiOH added, it is possible to increase Li and increase the concentration of OH ⁻ .
Thus, it can be seen that adding a large amount of LiOH is also preferable from this point.

It is preferable that the molar ratio of these alkalis is 1 to 20, especially about 5 or more. Thereby, the yield of LiCoO ₂ in the reaction product can be made sufficient.

It is to be noted that the deposition of Co ₃ O ₄ can be similarly suppressed by using an acid instead of an alkali. this is,
This is because the solubility of Co ₃ O ₄ is reduced even in the acidic condition. In this way, by lowering the pH of the raw material aqueous solution, the Co ₃ O ₄ generated in the temperature raising step is dissolved in water to efficiently generate LiCo ₂ during the reaction after the temperature is raised. Can be.

In addition, when generating the lithium-based composite metal oxide, by adding NO ₃ , an oxidizing agent is added to the raw material aqueous solution. That is, NO ₃ functions as an oxidizing agent for oxidizing Co ²⁺ to Co ³⁺ by being reduced to NO ²⁻ . Therefore, cobalt is changed to Co (NO
₃ ) It is understood that the addition in the form of ₂ is preferable. Therefore, it is also preferable to further add nitric acid or aqueous hydrogen peroxide to increase the amount of the oxidizing agent. For example, by adding nitric acid in the form of ammonium nitrate (NH ₄ NO ₃ )
The nitric acid can be increased while maintaining the alkali molar ratio at a predetermined value.

Further, for oxidation of Co ²⁺ , the reaction tube 16
The oxygen gas in the gas phase also contributes. Therefore, it is also preferable to increase the amount of oxygen in the gas phase or to add ozone gas.

In the above description of the embodiment,
Although the description has been made on the assumption that LiCoO ₂ is produced, the present invention is not limited to this. Instead of cobalt, a simple substance or a mixture of manganese, nickel, and iron can be used. As shown in b), manganese can be used to obtain single-crystal or nearly single-crystal LiMn ₂ O ₄ fine particles.

Example 1 Using the apparatus shown in FIG.
And LiCoO₂Was manufactured. Volume 10cm ³of
An experiment was performed using a reaction tube 16 made of SUS316. original
3.34mo1 / liter of LiOH
And 1.56 mo1 / liter of Co (NO₃)₂For
Was. Co (NO₃)₂Constant (0.097mo
1 / liter), and by changing the amount of LiOH,
The Co ratio was adjusted to (1, 5, 10, 15). Also the reaction
In order to investigate the effect of oxygen gas in the tube 16,
Part of the gas in the above was replaced with argon (48 Pa = 5 ber)
An experiment was also conducted in the case of doing this.

3.5 cm ³ of the raw material aqueous solution was charged into the reaction tube 16 and reacted in the metal salt melting bath 10 adjusted to 400 ° C. for a certain time (7 minutes or 10 minutes). After the reaction, the reaction tube 16 was put into a water bath to stop the reaction. The reaction solution was subjected to suction filtration to collect generated particles. The crystal structure of the resulting particles is
It was measured by powder XRD (X-ray analysis). The shape and size of the formed particles were observed by TEM and SEM.
Further, the resulting particles were dissolved in hydrochloric acid (6M) and quantified by ICP to determine the stoichiometric ratio Li / Co of the product. The filtrate of the reaction solution was diluted, and the concentrations of nitrate ion and nitrite ion were determined by ion chromatography, and the concentrations of residual Li and Co were determined by flame atomic absorption spectrophotometry.

Table 1 shows the experimental conditions and results. In addition,
In Table 1, the Li / Co molar ratio is a rough value, and the exact value is twice the alkali molar ratio. Also,
The alkali molar ratio is the [OH ⁻ ] / [NO 3 ⁻ ] ratio, and the relative intensity is the intensity ratio between the maximum peak of Co ₃ O _{4 and} the maximum peak of LiCoO _{2 in} the XRD chart. In addition, the reaction time includes a temperature raising time.

[0053]

[Table 1] LiCoO ₂ was obtained at a Li / Co ratio of 5 or more and an alkali molar ratio of 2.36 or more. From XRD chart Co
A peak derived from ₃ O ₄ can be confirmed, and the reactive product is LiCo.
O ₂ (Co is trivalent) and Co ₃ O ₄ (Co is divalent and trivalent)
Was a mixture with L of the largest peak derived from Co ₃ O ₄
The relative intensity with respect to the iCoO ₂ maximum peak becomes smaller as the raw material Li / Co ratio increases when viewed from XRD. Therefore, in the range of the Li / Co ratio of 1 to 15, the larger the ratio, the more easily LiCoO ₂ is generated.
Particles with small relative intensity (reaction time 7 minutes, Li / C
o = 15, air), (reaction time 10 minutes, Li / Co =
15, Air), the Li / Co ratio was measured to be 0.853 and 0.795, respectively. Generated particles are Li
Assuming only CoO ₂ and Co ₃ O ₄ , Li in the particles
The CoO ₂ yields are as high as 95 mol% and 93 mol%, respectively.

Here, the production of LiCoO ₂ is based on bivalent C
O is oxidized to trivalent Co. The nitrite ion concentration in the recovered liquid increases with the phenomenon of relative intensity. This suggests that divalent Co in the raw material aqueous solution is oxidized to nitrate ions. Furthermore, the result of replacing the gas in the reaction tube 16 with argon (48 Pa = 5 ber) shows that the presence of air increases the yield of LiCoO ₂ . This indicates that oxygen in the air also contributes to the oxidation of Co. In addition, SEM and TE
According to the observation result of M, the diameter of the produced particles was 400 nm to 1 nm.
It was about μm, and it was a very fine particle. The synthesis conditions were as follows: reaction temperature 400 ° C., pressure 30 MPa, cobalt nitrate 0.
Li at a concentration of 0.5 M and a LiOH concentration of 0.5 M
Electron micrographs of the CoO ₂ fine particles are shown in FIGS. FIG. 2 is a photograph at a magnification of 30,000 and FIG. 3 is a photograph at a magnification of 40,000.

Therefore, CoO ₃ O _{4 is obtained} by a method such as (i) further increasing the Li / Co ratio, (ii) increasing the alkali molar ratio, (iii) increasing the nitric acid concentration, or adding other oxidizing agents. And a single-phase LiCoO
₂ was obtained.

(Example 2) In the same apparatus as in Example 1, ammonia was added to the raw material aqueous solution, and the effect was examined. Table 2 shows the conditions and results. Reaction time 10 minutes,
The reaction temperature is 400 ° C.

[0057]

[Table 2] From this, Li /
Even when the CO ratio is 1, LiCoO ₂ is generated. In addition, even when ammonia is added, Li
Increasing the / Co ratio increases the yield of LiCoO ₂ . Therefore, it was confirmed that the yield of LiCoO ₂ can be increased by adding ammonia.

Example 3 Further, the reaction temperature was set to 200,
The temperature was changed to 300 and 400 ° C., and an experiment was performed. Table 3 shows the experimental conditions and results.

[0059]

[Table 3] From this, it was confirmed that when the reaction temperature was lowered, it was difficult to generate LiCoO ₂ .

Example 4 FIG. 6 is a schematic view of a flow type experimental apparatus capable of continuously producing the lithium-based composite metal oxide used in Example 4 of the present invention. Starting material LiOH aqueous solution and C
Each o (NO ₃ ) ₂ or Mn (NO ₃ ) ₂ aqueous solution was flowed at a flow rate of 4 cm ³ / mi by a non-pulsating pump for HPLC.
n. The two solutions were mixed at mixing point MP1. On the other hand, the 0.14 M aqueous hydrogen peroxide solution is sent to the tubular electric furnace (FTO-16, manufactured by Seiwa Riko Co., Ltd.) 23 at 24 cm ³ / min by another pump, where H in the aqueous solution is added.
₂ O ₂ was completely thermally decomposed into oxygen-supercritical water. MP
The Li—Co mixed aqueous solution mixed in 1 is brought into contact with the oxygen-supercritical water mixed fluid at the mixing point MP2, rapidly heated to the reaction temperature, and the hydrothermal reaction is started. The reaction solution is
After cooling by the double-tube heat exchanger 21 at the outlet of the reaction tube 22, the mixture was passed through the in-line filter 24,
At 5 the pressure dropped.

The experimental results when LiCoO ₂ is continuously produced using cobalt as the metal ion in such a flow system will be described.

FIG. 7 shows an XRD chart of a product synthesized at a subcritical temperature of 350 ° C. and a supercritical temperature of 400 ° C. At 350 ° C., the oxidation state of cobalt is 2
400 ° C. while trivalent and trivalent Co ₃ O ₄ were produced.
Produced a single-phase LiCoO ₂ . This is because the oxygen gas and the aqueous solution phase-separated in the subcritical region, and the oxidation reaction of cobalt (II) did not sufficiently proceed. In the supercritical region, oxygen forms a homogeneous phase with the aqueous solution, so that the oxidation reaction of cobalt (II) proceeds rapidly and LiCoO ₂ is generated.

FIG. 8 shows the supercritical state (400
C) shows a SEM photograph of the product particles synthesized at (° C). For reference, particles synthesized by a batch reactor (slow temperature rising hydrothermal synthesis method) are also shown. As shown in FIG. 4, the particles synthesized by the ceramic method of firing a mixed salt of cobalt carbonate and lithium carbonate have a large size and size distribution of 1 to 10 μm and are agglomerated particles. In addition, according to the batch method, single crystal-like particles with clear crystal faces are obtained as crystals, but the particle size distribution is wide and the particle size is not necessarily small enough. On the other hand, the particles synthesized by the present distribution method are fine particles of 1 μm or less, and the particle size range is 0.5 to 1 μm, the particle size distribution is relatively small, and single crystal fine particles with clear crystal faces are obtained. Was done.

Also, an experiment was conducted on a manganese-based material in the same manner as the above-mentioned cobalt. As a result of TEM observation and electron beam diffraction of the obtained particles, it was found that the obtained particles had extremely high single crystallinity. FIG. 9 shows the results of a charge / discharge test performed using the obtained LiMn ₂ O ₄ as a positive electrode material of a lithium battery.
Shown in It can be seen that the deterioration due to charging and discharging is extremely low as compared with those using particles synthesized by the conventional ceramic method.

As described above, by performing hydrothermal synthesis in supercritical water while rapidly increasing the temperature using a flow-through apparatus for supercritical hydrothermal synthesis, lithium-based composite metal oxide fine particles having high single crystallinity can be obtained. I found that. In addition, they have found that the use of the single crystal fine particles as a positive electrode material of a lithium ion battery can provide an unprecedented extremely high degradation resistance while maintaining a high battery output.

The embodiments of the present invention have been described in the above embodiments with reference to the drawings. However, the present invention is not limited to these embodiments, and may be modified or changed without departing from the gist of the present invention. Needless to say, the addition is included in the present invention.

In the present invention, an example in which a lithium-based composite metal oxide is mainly used as a positive electrode material of a lithium ion battery is shown, but the present invention is not limited to this. The composite metal oxide can be used for other purposes as a material for storing and releasing lithium ions. The present invention relates to a lithium composite metal oxide used for these other uses and a method for producing the same. Needless to say, this is also applicable.

[0068]

The present invention has the following effects.

(A) According to the first aspect of the present invention, since at least a part of the lithium-based composite metal oxide has a single crystal structure, crystal defects on the surface of the lithium-based composite metal oxide are suppressed. When the lithium-based composite metal oxide is used for a positive electrode of a lithium-ion battery, it is possible to suppress catalytic effects such as oxidation on an organic non-aqueous electrolyte solution at the time of charging. It is possible to prevent a decrease in electric capacity in a charge / discharge cycle due to oxidative deterioration of the solution. Further, by making at least a part of the single crystal structure, the surface energy of the particles can be reduced, and even if the particle size is reduced, the metal in the lithium-based composite metal oxide, in particular, Mn in LiMn ₂ O ₄ Can be kept low.

(B) According to the second aspect of the present invention, since the metal component is at least one of nickel, cobalt, manganese, and iron, these metals are relatively abundant in resources and inexpensive. Because it is available, a lithium-ion battery can be manufactured at low cost.

(C) According to the third aspect of the invention, by reducing the average particle size to 0.1 to 1 μm as compared with the conventional one,
The surface area of the lithium-based composite metal oxide can be increased. For example, when the lithium-based composite metal oxide is used for a positive electrode of a lithium-ion battery, a lithium-ion battery having a high charge / discharge rate can be provided. By setting the average particle size to 0.1 to 1 μm, mixing with a binder, carbon as a conductive material, or the like can be performed relatively easily, and a favorable positive electrode material can be obtained.

(D) According to the fourth aspect of the present invention, in order to obtain a lithium-based composite metal oxide having a single crystal structure at least in part, aggregation of nuclei generated by the reaction is suppressed and the crystal surface It is necessary to suppress the generation of secondary nuclei, and it is desirable to perform high-temperature treatment to enhance the crystallinity. However, in a high-temperature, high-pressure supercritical or subcritical state, water becomes a nonpolar gaseous state, The generation rate of the lithium-based composite metal oxide is extremely high and the dissolved ion concentration is extremely low, so that secondary nucleation and excessive crystal growth are unlikely to occur, and therefore, the lithium-based composite metal oxide having a single crystal structure Not only can particles be obtained efficiently,
The size of the generated particles can be reduced. Also, 200-300
Oxides synthesized by hydrothermal reaction at about ℃ generally contain water of crystallization or hydroxyl groups inside the crystal or on the surface of the crystal, but in subcritical or supercritical water near the critical point. By synthesizing or treating by a hydrothermal reaction, it is possible to obtain a lithium-based composite metal oxide having high crystallinity and containing no crystallization water or hydroxyl group.

(E) According to the fifth aspect of the present invention, the aqueous solution is rapidly brought into a supercritical or subcritical state by rapid temperature rise, and a hydrothermal reaction is carried out. It is possible to prevent the yield of the resulting lithium-based composite metal oxide from lowering, and prevent the crystal state from deteriorating due to aggregation of nuclei and generation of secondary nuclei on the crystal surface.

(F) According to the invention of claim 6, the rapid temperature increase can be efficiently performed.

(G) According to the seventh aspect of the invention, the single crystallization can be improved without increasing the fine particle size of the lithium-based composite metal oxide to be produced.

(H) According to the invention of claim 8, when the metal ion reacts with lithium ion to form a lithium-based composite metal oxide, it is necessary to appropriately increase the oxidation number by oxidation. The oxidation of the metal ions under the subcritical or supercritical conditions can be suitably performed.

(I) According to the ninth aspect of the present invention, under subcritical conditions, gas becomes bubbles and phase separation occurs, so that an effective oxidation reaction cannot be obtained. , It is possible to cause an oxidation reaction in a homogeneous phase,
The oxidation reaction can be advanced to an effect.

(J) According to the tenth aspect, when the aqueous solution is made alkaline by appropriately adding hydroxyl ions,
Side reactants (for example, Co ₃
O ₄ ) is easily dissolved, and thus, by-products generated during these heating processes remain in the reaction product to adversely affect the crystal quality, and the yield of the intended lithium-based composite metal oxide The drop can be prevented.

(K) According to the eleventh aspect, the hydroxyl ions can be added together with lithium ions as a raw material.

(1) According to the twelfth aspect of the present invention, the rapid rise in temperature makes it possible to suppress the formation of impurity oxides such as the above-mentioned Co ₃ O ₄ at the time of temperature rise. It is possible to keep the amount of hydroxyl ions lower,
It is also possible to suppress the incorporation of hydroxyl groups into crystals.

(M) According to the thirteenth aspect of the present invention, a side reactant (eg, Co ₃ O ₄ ) which is easily generated during the temperature raising process
Etc. are easily dissolved, and therefore, by-products generated during these temperature raising processes remain in the reaction product, adversely affecting the crystal quality, or reducing the yield of the target lithium-based composite metal oxide. Can be prevented.

(N) According to the fourteenth aspect, the intended lithium-based composite metal oxide can be efficiently obtained.

(O) According to the invention of claim 15, the metal component is at least one of nickel, cobalt, manganese and iron.
Thus, since each of these metals is relatively abundant in resources and can be obtained at low cost, a lithium ion battery can be manufactured at low cost.

(P) According to the sixteenth aspect of the present invention, divalent cobalt ions can be easily obtained, and the presence of an oxidizing agent during the hydrothermal reaction reduces the divalent cobalt ions to three. LiCo while oxidizing to multivalent cobalt ions
O ₂ can be generated effectively, and by performing the temperature increase to the subcritical or supercritical in which the hydrothermal reaction is performed as quickly as possible, the oxidizing agent is decomposed at the time of the temperature increase. , Can be prevented from being consumed, and a more effective oxidation reaction can be performed.

(Q) According to the seventeenth aspect of the present invention, the target LiCoO ₂ can be obtained efficiently by making the lithium ions present in the aqueous solution excessive compared to the cobalt ions.

(R) According to the eighteenth aspect of the invention, since the lithium ion concentration is relatively low, it is possible to appropriately prevent the crystal state from deteriorating due to aggregation of nuclei and the like. Can be efficiently obtained.

(S) According to the nineteenth aspect, the surface area of the lithium-based composite metal oxide can be increased by reducing the average particle size to 0.1 to 1 μm as compared with the conventional one, Therefore, not only can a lithium-ion battery having a high charge / discharge rate be provided, but by setting the average particle size in this way to 0.1 to 1 μm, mixing with a binder or a conductive material such as carbon can be performed relatively easily. However, a good positive electrode material can be obtained.

(T) According to the twentieth aspect, in the batch method, the temperature rises at a low speed, and the oxidizing agent is decomposed at the time of the temperature rise, and the oxidation reaction does not sufficiently occur, so that impurities are easily generated. As compared with the case where a lithium-based composite metal oxide is not efficiently obtained, for example, the temperature can be increased at a high speed by contact with the subcritical water or supercritical water, and a sufficient oxidation reaction can be obtained. As a result, the intended lithium-based composite metal oxide can be efficiently obtained, and fine particles having a smaller particle size than the batch system can be produced at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a manufacturing apparatus used in Examples 1 to 3 for implementing a method for manufacturing a lithium-based composite metal oxide of the present invention.

FIG. 2 is an electron micrograph of LiCoO ₂ produced by the method for producing a lithium-based composite metal oxide of the present invention.

FIG. 3 is an electron micrograph of LiMn ₂ O ₄ manufactured by the method of manufacturing a lithium-based composite metal oxide according to the present invention.

FIG. 4 is an electron micrograph of LiCoO ₂ produced by a conventional solid-phase method.

FIG. 5 (a) shows Li obtained by the production method of the present invention.
Shows a transmission electron micrograph of CoO _2.
(B) is the LiMn ₂ O obtained by the production method of the present invention.
FIG. ₄ is a diagram showing a transmission electron micrograph of FIG.

FIG. 6 is a diagram showing the configuration of a flow-type manufacturing apparatus used in Example 4 for implementing the method for manufacturing a lithium-based composite metal oxide of the present invention.

FIG. 7 is an XRD chart of an oxide obtained at each temperature of 350 ° C. and 400 ° C. in Example 4.

FIG. 8 is a photomicrograph showing a lithium-based composite metal oxide obtained by the flow-type production apparatus and the batch-type production apparatus of Example 4.

FIG. 9 is a diagram showing a change in battery capacity of a lithium battery using a LiMn ₂ O ₄ obtained by a conventional ceramic method and a LiMn ₂ O ₄ as a cathode material, which is obtained by a flow-type manufacturing apparatus of Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Metal salt melting bath 12 Heater 14 Thermocouple 16 Reaction tube 21 Heat exchanger 22 Reaction tube 23 Tube type electric furnace 24 In-line filter 25 Back pressure valve

Continued on the front page F-term (reference) 4G048 AA04 AB02 AC06 AD03 AD07 AE05 4G077 AA01 BC60 CB03 HA20 KA01 KA03 5H029 AJ01 AJ14 AK03 CJ00 CJ02 CJ28 DJ12 DJ16 DJ17 HJ02 HJ05 HJ10 HJ13 HJ14 FA17 GA17 A17A17A17 HA05 HA10 HA13 HA14 HA20

Claims (20)

[Claims] 1. A lithium-based composite metal oxide capable of occluding and releasing lithium ions, wherein at least a part of the crystal structure has a single crystal structure. 2. The lithium-based composite metal oxide according to claim 1, wherein the metal component in the lithium-based composite metal oxide is at least one of nickel, cobalt, manganese, and iron. 3. The lithium composite metal oxide is a fine powder having an average particle size of about 0.1 to 1 μm.
3. The lithium-based composite metal oxide according to item 1. 4. A method for producing a lithium-based composite metal oxide capable of inserting and extracting lithium ions, wherein at least lithium ions and other metal ions are hydrothermally reacted in water in a supercritical or subcritical state. And a method for producing a lithium-based composite metal oxide having a single crystal structure at least in part. 5. The hydrothermal reaction is performed by rapidly raising the temperature of an aqueous solution dissolving at least lithium ions and metal ions of another metal to a predetermined temperature at which a supercritical or subcritical state is obtained. 3. The method for producing a lithium-based composite metal oxide according to item 1. 6. A rapid solution by directly mixing an aqueous solution in which at least the metal ion of the other metal is dissolved with subcritical or supercritical water or subcritical or supercritical water containing lithium ions. The method for producing a lithium-based composite metal oxide according to claim 5, wherein the temperature is raised. 7. The crystallinity is improved without growing crystal fine particles by subjecting the lithium-based composite metal oxide fine particles to hydrothermal treatment under a subcritical or supercritical condition for a predetermined time even after generation. 7. The method for producing a lithium-based composite metal oxide according to any one of 6. 8. An oxidizing agent is dissolved in an aqueous solution for dissolving the lithium ion and a metal ion of another metal, and the oxidizing agent is a single or a mixture of two or more of oxygen gas, ozone gas, hydrogen peroxide, and nitrate ion. The method for producing a lithium-based composite metal oxide according to any one of claims 4 to 7, which is a body. 9. The method for producing a lithium-based composite metal oxide according to claim 8, wherein when at least one of oxygen gas and ozone gas is used as the oxidizing agent, hydrothermal reaction conditions are supercritical. 10. The method for producing a lithium-based composite metal oxide according to claim 5, wherein the rapid heating hydrothermal reaction is performed under conditions to which hydroxyl ions are appropriately added. 11. The method for producing a lithium-based composite metal oxide according to claim 10, wherein the addition of the hydroxide ion is performed by adding lithium hydroxide. 12. The lithium system according to claim 10, wherein when the hydroxyl ions are appropriately added, the temperature is rapidly raised by directly mixing the aqueous solution to which the hydroxyl ions are added with supercritical water. A method for producing a composite metal oxide. 13. The hydrothermal reaction according to claim 4, wherein an acid or an alkali is appropriately added to the aqueous solution to adjust the pH of the aqueous solution to either an acidic or alkaline state.
3. The method for producing a lithium-based composite metal oxide according to any one of 2. 14. The method for producing a lithium-based composite metal oxide according to claim 13, wherein the alkali molar ratio in the aqueous solution is 1 to 20. 15. The method according to claim 4, wherein the other metal ion is at least one of nickel, cobalt, manganese, and iron.
15. The method for producing a lithium-based composite metal oxide according to any one of items 14 to 14. 16. The lithium system according to claim 15, wherein when the metal ion is a divalent cobalt ion and the hydrothermal reaction is performed in the presence of the oxidizing agent, the temperature is raised as quickly as possible. A method for producing a composite metal oxide. 17. The method for producing a lithium-based composite metal oxide according to claim 15, wherein the value of the lithium ion / cobalt ion ratio is in the range of 1 to 20. 18. The method for producing a lithium-based composite metal oxide according to claim 4, wherein the concentration of lithium ions in the aqueous solution is 0.05 mol / L to 2 mol / L. 19. The reaction conditions in the hydrothermal reaction are set such that the lithium-based composite metal oxide having a single crystal structure in at least a part thereof has an average particle size of about 0.1 to 1 μm. A method for producing a lithium-based composite metal oxide according to any one of claims 4 to 18. 20. The method for producing a lithium-based composite metal oxide according to claim 4, wherein the lithium-based composite metal oxide is continuously produced by the hydrothermal reaction.