JP2007055887A - Manganese dioxide, method and apparatus for producing the same, and battery active material manufactured by using the same and battery prepared using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manganese dioxide product that improves discharge characteristics and the long time reliability of a battery. <P>SOLUTION: The manganese dioxide comprises single crystal particles having a β-type crystal structure. The manganese dioxide can be produced by a producing method including a process in which an aqueous solution containing manganese ions is converted into a subcritical or supercritical state, to thereby deposit the manganese dioxide. The aqueous solution containing manganese ions is mixed with the water in a subcritical or supercritical state at the end portion of the entrance side of a reaction tube. The inside wall portion of the reaction tube is made of an insulating inorganic material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to manganese dioxide, a production method and production apparatus thereof, a battery active material produced using the same, and a battery using the same.

  Since manganese dioxide is abundant in resources and inexpensive, it is widely used as a positive electrode active material for batteries. For example, manganese dioxide is used for positive electrodes such as manganese batteries or alkaline batteries using zinc as a negative electrode, or lithium batteries using lithium metal as a negative electrode. In particular, since lithium batteries have excellent storage characteristics, they are not only used as a main power source but also widely used as a backup power source.

Conventionally, as a method for producing manganese dioxide for batteries, an electrolytic method in which a manganese mineral is dissolved in an acidic aqueous solution such as an aqueous sulfuric acid solution and the solution is electrolyzed is used (see Patent Document 1). It has been reported that secondary particles of several tens of μm can be obtained by the electrolytic method.
JP-A-6-150914

  As electronic devices have become more portable and multifunctional in recent years, there has been a demand for higher performance of batteries, such as improved discharge characteristics and long-term reliability. However, it cannot be said that conventional manganese dioxide obtained by an electrolytic method or a solid phase method sufficiently satisfies the above demand. For example, manganese dioxide obtained by the electrolytic method has a polycrystalline structure, and crystal defects and / or grain boundaries exist. For this reason, it is considered that hydrogen ions, lithium ions and the like are prevented from diffusing in the manganese dioxide solid phase, and the discharge characteristics of the battery are deteriorated.

  The particle size of the positive electrode active material is considered to affect the discharge characteristics of the battery. Manganese dioxide obtained by the electrolytic method or the solid phase method has a large average particle diameter of several tens of μm, and thus the movement distance of hydrogen ions and lithium ions in manganese dioxide is long. For this reason, for example, if the manganese dioxide is refined by pulverization, an improvement in discharge characteristics can be expected. However, the average particle size can only be reduced to about 1 μm by miniaturization. Furthermore, this miniaturization also causes an increase in cost.

  For example, it is possible to produce fine particles having a particle size of 1 μm or less by using a sol-gel method or a spray pyrolysis method. However, since these processes are complicated and it takes time to synthesize manganese dioxide, it is considered difficult to mass-produce manganese dioxide using these methods.

  Accordingly, the present invention provides manganese dioxide that can improve the discharge characteristics and long-term reliability of a battery, a method and apparatus for producing the same, an active material for a battery produced using the same, and a battery using the same. For the purpose.

  The present invention relates to manganese dioxide containing single crystal particles having a β-type crystal structure. The average particle size of the single crystal particles of manganese dioxide is preferably 0.1 μm or more and 1 μm or less. The single crystal particles preferably have a needle-like particle shape. The manganese dioxide preferably contains 70% by weight or more of single crystal particles having a β-type crystal structure. Here, the average particle diameter of the single crystal particles refers to the average value of the maximum width of the manganese dioxide single crystal particles. For example, in the case of acicular particles, the average particle diameter of single crystal particles refers to the average value of the lengths of single crystal particles in the crystal growth direction (length direction).

  Moreover, this invention relates to the manufacturing method of the said manganese dioxide. This manufacturing method includes a step of depositing manganese dioxide in an aqueous solution containing manganese ions in a subcritical state or a supercritical state.

  In the above production method, the aqueous solution containing manganese ions is preferably heated to a subcritical state or a supercritical state by heating at a temperature rising rate of 300 ° C./sec or more. At this time, it is more preferable to heat the aqueous solution containing manganese ions at a heating rate of 300 ° C./sec or more by directly mixing the aqueous solution containing manganese ions with water in a subcritical state or a supercritical state.

  In the above production method, an oxidizing agent is dissolved in the aqueous solution containing manganese ions, and the oxidizing agent preferably contains at least one selected from the group consisting of oxygen gas, ozone gas, hydrogen peroxide, and nitrate ions. .

  When an aqueous solution containing manganese ions is directly mixed with subcritical or supercritical water, an oxidizing agent may be dissolved in the subcritical or supercritical water. As the oxidizing agent, the same ones as described above can be used.

  Moreover, this invention relates to the manufacturing apparatus of the said manganese dioxide. This apparatus is connected to a reaction tube, a first tube connected to an inlet side of the reaction tube, supplying an aqueous solution containing manganese ions to the reaction tube, and connected to an inlet side of the reaction tube. A second pipe for supplying water in a critical state and a manganese dioxide recovery means provided on the outlet side of the reaction pipe are provided. The aqueous solution containing manganese ions and the water in the subcritical state or the supercritical state are mixed at the end on the inlet side of the reaction tube. The inner wall portion of the reaction tube is made of an insulating inorganic material. The insulating inorganic material is preferably quartz or alumina.

  Moreover, this invention relates to the positive electrode active material for batteries synthesize | combined by heat-firing the said manganese dioxide and a lithium compound. In addition, the said manganese dioxide can also be used as a positive electrode active material.

  Moreover, this invention relates to the battery containing the positive electrode containing the said manganese dioxide or the said positive electrode active material for batteries, a negative electrode, a separator, and electrolyte solution.

  By using the manganese dioxide of the present invention as a battery active material, it becomes possible to improve the discharge characteristics and long-term reliability of the battery. Similarly, when an active material synthesized using the manganese dioxide of the present invention as a starting material is used, the discharge characteristics and long-term reliability of the battery can be improved.

The manganese dioxide of the present invention includes single crystal particles having a β-type crystal structure. By using such manganese dioxide as the positive electrode active material for a battery, it becomes possible to improve the discharge characteristics and long-term reliability of the battery.
That is, conventional polycrystalline manganese dioxide has crystal defects and crystal grain boundaries, and these crystal defects and crystal grain boundaries prevent hydrogen ions and lithium ions from diffusing in the active material particles. . However, the manganese dioxide of the present invention is a single crystal as described above, and mainly contains particles containing almost no crystal defects, so that the discharge characteristics can be improved as compared with conventional manganese dioxide having a polycrystalline structure. it can. That is, by using the manganese dioxide of the present invention, for example, an increase in the internal resistance of the battery during discharge can be suppressed.

  Manganese dioxide of the present invention does not substantially contain impurities such as lower oxides, acid components and crystal water, so that manganese ions are not easily eluted from manganese dioxide even during storage. Furthermore, since the manganese dioxide of the present invention mainly contains single crystal particles, corrosion at the grain boundaries and the like are suppressed, and the surface energy is low. For this reason, it is stable and difficult to decompose as compared with manganese dioxide mainly composed of conventional polycrystalline structure particles. Therefore, long-term reliability can be improved.

  The average particle diameter of the single crystal particles of manganese dioxide is preferably 0.1 μm or more and 20 μm or less, and more preferably 0.1 μm or more and 1 μm or less. When the average particle size of the single crystal particles is 20 μm or less, it is not necessary to pulverize manganese dioxide into fine particles. In particular, when the average particle diameter of the single crystal particles is 1 μm or less, the diffusion distance of hydrogen ions and lithium ions in the single crystal particles is shortened. For this reason, it becomes possible to further improve the discharge characteristics of the battery. However, manganese dioxide having a single crystal particle having an average particle size of less than 0.1 μm may be difficult to mix with a conductive additive and a binder during electrode production.

  The manganese dioxide of the present invention preferably contains 70% by weight or more of single crystal particles having a β-type crystal structure.

The manganese dioxide of the present invention can be produced by bringing an aqueous solution containing manganese ions (Mn ²⁺ ) into a subcritical state or a supercritical state. For example, when the aqueous solution containing manganese ions contains hydrogen peroxide as an oxidizing agent for promoting the oxidation of manganese ions, manganese dioxide has the following reaction formula:
Mn ²⁺ + 2H ₂ O ₂ + 2e ⁻ → MnO ₂ + 2H ₂ O
Is generated by

  By setting the temperature of the aqueous solution containing manganese ions to 250 ° C. or higher and the pressure to 20 MPa or higher, the aqueous solution containing manganese ions can be at least in a subcritical state. Furthermore, by setting the temperature of the aqueous solution containing manganese ions to 374 ° C. or higher and the pressure to 22 MPa or higher, the aqueous solution can be brought into a supercritical state.

Ions having a charge such as Mn ^{2+ tend} to exist stably in the liquid. On the other hand, nonpolar substances such as produced manganese dioxide tend to exist stably in the gas. Therefore, particularly in the supercritical state, a solvent such as water changes from a liquid state to a gaseous state, so that nonpolar manganese dioxide is rapidly generated.

  In the supercritical state, the solubility of a metal oxide such as manganese dioxide in water rapidly decreases as the temperature of the water increases under a constant pressure. Therefore, in the supercritical state, it is possible to promote precipitation of manganese dioxide as a reaction product by increasing the temperature under a constant pressure.

When a metal oxide is produced by performing hydrothermal synthesis at a relatively low temperature of about 100 to 200 ° C., the produced oxide generally incorporates crystal water and / or a compound containing a hydroxyl group. On the other hand, when synthesizing a metal oxide in a high temperature state such as a supercritical state, since water is in a gaseous state, crystal water or the like is hardly taken into the generated oxide. Furthermore, in such a high temperature state, it is possible to synthesize fine particles and highly crystalline manganese dioxide.
Therefore, it is considered that the synthesis in the subcritical state or the supercritical state as in the present invention promotes the formation of an oxide with a high degree of crystallinity and makes it easy to obtain oxide single crystal fine particles.

In particular, manganese dioxide, which is a single crystal particle having a β-type crystal structure and an average particle diameter of 0.1 μm or more and 1 μm or less, heats an aqueous solution containing manganese ions at a heating rate of 300 ° C./sec or more. Then, it can be produced by setting it to a subcritical state or a supercritical state.
Hereinafter, the method for producing manganese dioxide of the present invention will be specifically described.

(Production Method 1)
The manganese dioxide of the present invention, in particular, manganese dioxide mainly containing single crystal particles having an average particle diameter of more than 1 μm and not more than 20 μm, for example, can be used to substantiate an aqueous solution containing manganese ions using an apparatus as shown in FIG. It can be produced by setting it to a critical state or a supercritical state.
The apparatus shown in FIG. 1 comprises a tubular furnace 2 provided with a heating wire 4 and a tube 1 arranged in the tubular furnace 2. The tube 1 is filled with an aqueous solution (raw material aqueous solution) containing manganese ions. The tube 1 is fixed in the tubular furnace 2 by a holder 6. The space in which the tube 1 in the tubular furnace 2 is arranged is sealed with a stopper 5. The heating wire 4 passes through a portion in the vicinity of the space where the pipe is arranged in the main body of the tubular furnace 2. A thermocouple 3 is disposed in the tubular furnace 2, and the temperature inside the tubular furnace 2 is measured by the thermocouple 3.

Manufacture of manganese dioxide using such an apparatus can be performed as follows.
First, the raw material aqueous solution is put into the tube 1 and the tube 1 is sealed. The raw material aqueous solution is prepared, for example, by dissolving a water-soluble manganese salt in distilled water. Various manganese salts can be used. Examples include Mn (NO ₃ ) ₂ and MnSO ₄ .

  The concentration of manganese ions contained in the raw material aqueous solution is preferably 0.01 to 5 mol / L. When the concentration of manganese ions is smaller than 0.01 mol / L, the production amount of manganese dioxide decreases. When the manganese ion concentration is higher than 5 mol / L, the yield of manganese dioxide decreases.

After the raw material aqueous solution is sealed in the tube 1, the tube 1 is inserted into the tubular furnace 2. The amount of the raw material aqueous solution sealed in the tube 1 is adjusted to a target pressure at a predetermined temperature in the tubular furnace 2. Here, this pressure can be calculated by a steam table assuming that the raw material aqueous solution is pure water. For example, reaction temperature 400 ° C., since the density of water in the reaction pressure 30MPa is 0.35 g / cm ^3, if the volume is, for example 10 cm ³ of the tube 1, the tube 1, the raw material aqueous solution of 3.5g Enclosed.

Next, the tube 1 is heated in the tubular furnace 2 to a predetermined temperature, and the aqueous raw material solution is brought into a subcritical state or a supercritical state. The temperature is maintained for a predetermined reaction time (for example, about 5 to 20 minutes) to synthesize manganese dioxide. Although depending on conditions such as the type of the raw material aqueous solution, the raw material aqueous solution can be at least in a subcritical state by setting the temperature to 250 ° C. or higher and the pressure to 20 MPa or higher. It is preferable to adjust the heating temperature and the amount of the raw material aqueous solution enclosed in the tube 1 to bring the raw material aqueous solution into a supercritical state. In addition, raw material aqueous solution can be made into a supercritical state by setting temperature to 374 degreeC or more and a pressure to 22 Mpa or more. The heating rate up to the predetermined temperature is determined by the performance of the tubular furnace and the like. The time required to raise the temperature of the raw material aqueous solution to the predetermined temperature is generally about 30 seconds to 2 minutes. For example, in the above apparatus, the rate of temperature rise can be 4 ° C./sec.
The heating temperature by the tubular furnace 2 is controlled while measuring the temperature in the tubular furnace using the thermocouple 3.

  Next, after elapse of a predetermined reaction time, the tube 1 is taken out from the tubular furnace 2 and put in a cold water bath or the like to quickly stop the reaction. Subsequently, the solid content deposited in the tube 1 is filtered and washed to obtain manganese dioxide fine particles as a reaction product.

By the above preparation method, manganese dioxide fine particles having an average particle size of single crystal particles of more than 1 μm and 20 μm or less, preferably more than 1 μm and 10 μm or less can be obtained. For this reason, it is not necessary to pulverize the obtained manganese dioxide into fine particles. Furthermore, manganese dioxide can be produced with high yield by the above production method.
Here, the average particle diameter of the single crystal particles means an average value of the maximum diameters of the manganese dioxide single crystal particles. For example, in the case of acicular particles, the average value of the lengths of single crystal particles in the crystal growth direction (length direction).

The raw material aqueous solution may contain an oxidizing agent for promoting the oxidation of manganese ions. As the oxidizing agent, for example, oxygen gas, ozone gas, hydrogen peroxide, and nitrate ions can be used. These may be used alone or in combination of two or more. By including such an oxidizing agent, Mn ²⁺ can be rapidly oxidized to Mn ⁴⁺ .
For example, by using Mn (NO ₃ ) ₂ , NO ₃ ⁻ ions can be added to the raw material aqueous solution. Oxidation of Mn ²⁺ ions to Mn ⁴⁺ ions can be promoted by the presence of NO ₃ ⁻ ions.

  Furthermore, air is present in the tube 1. At this time, oxygen in the air also functions as an oxidant. Therefore, it is more preferable that oxygen gas is present in the gas phase in the reaction tube 1. In order to promote the oxidation reaction, it is preferable to increase the amount of oxygen gas contained in the gas phase in the tube 1.

  As the oxidizing agent, it is preferable to use nitrate ions and hydrogen peroxide in combination. Hydrogen peroxide is easily decomposed into oxygen gas and water by heating. In particular, under supercritical conditions, oxygen gas and the raw material aqueous solution form a uniform phase, so that the oxidizing agent contains nitrate ions and hydrogen peroxide, so that a better oxidation reaction field can be formed. Become.

(Production method 2)
Manganese dioxide mainly containing single crystal particles having an average particle size of 0.1 μm or more and 1 μm or less is heated in an aqueous solution (raw aqueous solution) containing manganese ions at a heating rate of 300 ° C./sec or more to form a subcritical state. Or it can produce by making it into a supercritical state.
Such manganese dioxide can be produced, for example, using the apparatus shown in FIG. In the apparatus of FIG. 2, distilled water is heated to a predetermined temperature under a predetermined pressure to produce subcritical or supercritical water. The obtained subcritical or supercritical water is directly mixed with the raw material aqueous solution, and the raw aqueous solution is heated at a temperature rising rate of 300 ° C./sec or more, so that the raw aqueous solution is brought into the subcritical or supercritical state. To do.

  The apparatus of FIG. 2 includes a reaction tube 26, a first supply device 21 for supplying an aqueous solution containing manganese ions to the reaction tube 26 through the first tube 23, and a subcritical state or a supercritical state to the reaction tube 26 through the second tube 24. The 2nd supply apparatus 22 which supplies this water is provided. The apparatus further includes a tubular electric furnace 25 provided in the middle of the second tube 24, a manganese dioxide recovery means 29 provided on the outlet side of the reaction tube 26, and a tube type provided in the middle of the reaction tube 26. An electric furnace 27, a heat exchanger 28 for cooling the reaction liquid, a back pressure valve 30 for reducing the pressure of the reaction liquid, and a reservoir 31 are provided. The inner wall portion of the reaction tube 26 is made of an insulating inorganic material.

  The first supply device 21 includes a tank 21a for storing an aqueous solution containing manganese ions and a pump 21b for supplying the aqueous solution containing manganese ions at a predetermined pressure. The second supply device 22 includes a tank 22a for storing distilled water and a pump 22b for supplying distilled water at a predetermined pressure. As the pumps 21b and 22b, for example, a non-pulsating pump can be used.

  Distilled water supplied into the second pipe 24 by the second supply device 22 is heated to 250 ° C. or more by a tubular electric furnace 25 provided in the middle of the second pipe 24 to be in a subcritical state or supercritical state. Of water. At this time, a predetermined pressure of 20 MPa or more is applied to the distilled water by the second supply device 22 according to the subcritical state or supercritical state to be formed.

The first tube 23 and the second tube 24 are connected to the inlet side of the reaction tube 26. An aqueous solution containing manganese ions and water in a subcritical state or a supercritical state are mixed at the end on the inlet side of the reaction tube. FIG. 3 shows an example of the joining portion MP of the first tube 23, the second tube 24, and the reaction tube 26.
In FIG. 3, the raw material aqueous solution supplied from the first pipe 23 and the subcritical or supercritical water supplied from the second pipe 24 are the first pipe 23, the second pipe 24, and the reaction pipe 26. The reaction liquid is formed by mixing at the merging portion MP. The aqueous raw material solution is heated at a temperature rising rate of 300 ° C./sec or more by being brought into contact with subcritical or supercritical water to be in a subcritical state or a supercritical state. A predetermined pressure of 20 MPa or more is also applied to the raw material aqueous solution by the first supply device 21 so as to be in a subcritical state or a supercritical state. The connection mode of the first tube, the second tube, and the reaction tube is that the raw material aqueous solution flowing through the first tube and the subcritical or supercritical water flowing through the second tube are at the upstream end of the reaction tube. 3 is not limited to the style shown in FIG.

  The obtained reaction liquid moves through the reaction tube 26. At this time, the reaction solution is heated by the tubular electric furnace 27 so that the subcritical state or the supercritical state is maintained.

After the reaction solution has moved through the reaction tube 26 having a predetermined length, the reaction solution is cooled by a double tube heat exchanger 28 provided on the downstream side of the reaction tube 26. The cooled reaction liquid passes through a recovery means 29 such as an inline filter. A solid content is deposited on the recovery means 29. Manganese dioxide can be obtained by washing the solid content. The pressure of the reaction liquid that has passed through the recovery means 29 is reduced by a back pressure valve 30 provided on the downstream side of the recovery means 29. The reaction liquid after the pressure reduction is stored in the reservoir 31.
In the above apparatus, as shown in FIG. 3, the inner wall portion 32 of the reaction tube 26 is made of an insulating inorganic material. When using an insulating inorganic material, unlike the case of using a metal material such as stainless steel, crystal nucleation of manganese dioxide does not occur at the interface between the reaction solution and the reaction tube, and crystal nucleation occurs only in the reaction solution. Happens. For this reason, obstruction | occlusion of an apparatus can be prevented.

  More preferably, the insulating inorganic material is quartz glass or alumina. Since these materials are insulators and are stable even in a supercritical state, by using these materials, it is possible to stably perform continuous synthesis of manganese dioxide over a long period of time.

  In this manufacturing method, the aqueous solution containing manganese is heated at a temperature increase rate of 300 ° C./sec or more. Thereby, since the high supersaturation state of manganese dioxide can be achieved instantaneously, a crystal nucleus of 1 μm or less can be generated. In addition, since a plurality of manganese dioxide crystal nuclei are simultaneously generated, it is possible to prevent crystallization due to aggregation of the nuclei and secondary nucleation on the crystal surface. Particularly in the supercritical state, it is possible to suppress the growth of manganese dioxide crystals due to re-dissolution precipitation of crystals (Ostwal tripping phenomenon). For this reason, it becomes possible to produce manganese dioxide single crystal particles having an average particle diameter of 1 μm or less in a high yield.

  In the apparatus of FIG. 2, the raw material aqueous solution and the subcritical or supercritical water can be continuously mixed. For this reason, manganese dioxide can be continuously synthesized.

  In the above method, since manganese dioxide fine particles having an average particle diameter of 1 μm or less can be synthesized, it is not necessary to subject the obtained manganese dioxide to pulverization treatment. However, if the heating rate of the aqueous solution containing manganese ions is less than 300 ° C./sec, crystal nuclei are likely to grow, and the average particle size may be greater than 1 μm.

  As described above, the aqueous solution containing manganese ions may be directly mixed with subcritical or supercritical water and heated at a temperature increase rate of 300 ° C./sec or more. Subcritical or supercritical water can be produced using methods known in the art. Alternatively, an aqueous solution containing manganese ions may be directly heated using a heating device at a temperature increase rate of 300 ° C./sec or more.

Also in this production method, as the aqueous solution containing manganese ions, an aqueous solution in which a water-soluble manganese salt is dissolved in distilled water can be used as in Production Method 1. Similarly, the concentration of manganese ions contained in the aqueous solution containing manganese ions is preferably 0.01 to 5 mol / L.
The aqueous solution containing manganese ions may contain an oxidizing agent for promoting the oxidation of manganese ions. When an aqueous solution containing manganese ions is directly mixed with subcritical or supercritical water, the aqueous solution containing manganese ions may contain an oxidizing agent, or subcritical or supercritical water An oxidizing agent may be included. As the oxidizing agent, the same material as that in Preparation Method 1 can be used.

When producing manganese dioxide in a reaction field where a gas phase exists, not only an oxidizing agent is added to the raw material aqueous solution but also oxygen gas is contained in the gas phase in order to promote oxidation of Mn ²⁺ as described above. You may not. At this time, in order to promote the oxidation reaction, it is preferable to increase the amount of oxygen gas contained in the gas phase in the reaction tube. In particular, in the supercritical state, an aqueous solution containing manganese ions and a gas such as oxygen gas can form a uniform phase. For this reason, oxidation of manganese ions occurs easily, and manganese dioxide can be produced in a high yield.

  As described above, according to the manufacturing method of the present embodiment, manganese dioxide, which is a single crystal particle having a β-type crystal structure and having an average particle diameter of 0.1 μm to 1 μm, can be manufactured with high yield.

  Manganese dioxide obtained by the production method 1 and the production method 2 can be used as a positive electrode active material of a battery. Further, a compound synthesized using the obtained manganese dioxide as a starting material can be used as a positive electrode active material of a battery. The compound synthesized using manganese dioxide as a starting material has high purity and high crystallinity, and further has a small average particle size. For this reason, a battery including such a compound as an active material can improve charge / discharge characteristics and long-term reliability.

For example, by mixing the manganese dioxide and the lithium compound and firing the mixture, a high-purity, high-crystalline lithium-containing manganese oxide or spinel-like lithium manganese oxide can be obtained. As the lithium compound, lithium hydroxide, lithium oxide, or the like can be used.
Such manganese oxide can also be used as an active material of a battery.

Manganese dioxide and / or manganese oxide as described above can be used, for example, as a positive electrode active material for lithium primary batteries, lithium secondary batteries, alkaline batteries, and manganese batteries.
Hereinafter, the present invention will be described based on examples. However, this example shows one embodiment of the present invention, and the present invention is not limited to these examples.

<< Example 1-1 >>
(Production of manganese dioxide)
Manganese dioxide was produced using an apparatus as shown in FIG.
The tube volume 5 cm ³ made of stainless steel (SUS316), aqueous solution of manganese nitrate (Mn ion concentration: 1 mol / L) of 1.31cm ³ (1.31g) was encapsulated. A tube filled with an aqueous manganese nitrate solution was inserted into a tubular furnace and reacted at a reaction temperature of 400 ° C. for 10 minutes. The pressure at this time was 28 MPa. Moreover, the temperature increase rate at this time was 4 degree-C / sec.
After the end of the reaction time of 10 minutes, the tube was put into a water bath to stop the reaction. Next, the contents of the tube were taken out, and the contents were filtered and washed with water to obtain manganese dioxide. The average particle diameter of the obtained manganese dioxide single crystal particles was 8 μm.

(Preparation of positive electrode)
Manganese dioxide obtained as described above, carbon black as a conductive agent, and fluorine resin as a binder were mixed at a weight ratio of 90: 5: 5 to obtain a positive electrode mixture. This positive electrode mixture was pressure-molded to produce a cylindrical positive electrode. In addition, the positive electrode was heat-treated at 250 ° C. to remove adhering water before use.

(Preparation of negative electrode)
A lithium rolled plate was punched into a disk shape to obtain a negative electrode.

(Preparation of electrolyte)
Lithium perchlorate (LiClO ₄ ) was dissolved at a concentration of 1 mol / L in a mixed solvent in which propylene carbonate and 1,2-dimethoxyethane were mixed at a volume ratio of 1: 1 to prepare an electrolytic solution.

(Battery assembly)
Using the positive electrode, the negative electrode, and the electrolytic solution obtained as described above, a coin-type battery having the structure shown in FIG. 4 was produced as follows. The outer diameter of the coin battery was 20.0 mm and the thickness was 3.2 mm.
The negative electrode 42 was pressure-bonded to the sealing plate 45 combined with the gasket 44. Next, a separator 43 made of a polypropylene non-woven fabric punched out in a circular shape was placed in contact with the negative electrode 42. The positive electrode 41 was disposed so as to face the negative electrode 42 with the separator 43 interposed therebetween, and then a predetermined amount of electrolyte was injected. After covering the positive electrode case 46 so as to be in contact with the positive electrode 41, these are put in a sealing mold, and the opening end of the positive electrode case 46 is caulked to the sealing plate 45 via the gasket 44 by a press machine. 46 openings were sealed. A carbon paint 47 is applied between the positive electrode case 46 and the positive electrode 41.
The battery thus obtained was designated as battery 1-1.

<< Example 1-2 >>
Manganese nitrate and hydrogen peroxide were dissolved in distilled water at 1 mol / L and 2 mol / L, respectively, to obtain a raw material aqueous solution. Manganese dioxide was produced in the same manner as in Example 1-1 except that this raw material aqueous solution was used. The average particle diameter of the obtained manganese dioxide single crystal particles was 8 μm.
A battery 1-2 was produced in the same manner as in Example 1-1 except that the manganese dioxide thus obtained was used as the positive electrode active material.

<< Example 1-3 >>
A battery 1-3 was produced in the same manner as in Example 1-2 except that the amount of the raw material aqueous solution sealed in the tube was 4.12 cm ³ (4.12 g) and the reaction temperature was 250 ° C. The pressure during the reaction was 28 MPa. The average particle diameter of the obtained manganese dioxide single crystal particles was 20 μm.

<< Example 1-4 >>
A battery 1-4 was fabricated in the same manner as in Example 1-2 except that the amount of the raw material aqueous solution sealed in the tube was 3.74 cm ³ (3.74 g) and the reaction temperature was 300 ° C. The pressure during the reaction was 28 MPa. The average particle diameter of the obtained manganese dioxide single crystal particles was 15 μm.

<< Example 1-5 >>
Manganese dioxide obtained in Example 1-1 and lithium hydroxide were mixed at a molar ratio of 1: 0.5. The obtained mixture was heat-treated at 400 ° C. to obtain lithium-containing manganese oxide (Li _0.5 MnO ₂ ). The obtained lithium-containing manganese oxide was used as a positive electrode active material. Except that the obtained lithium-containing manganese oxide, carbon black as a conductive agent, and fluororesin as a binder were mixed at a weight ratio of 90: 5: 5 to obtain a positive electrode mixture. A battery 1-5 was produced in the same manner as in Example 1-1. The battery 1-5 is a secondary battery.

<< Example 1-6 >>
Manganese dioxide obtained in Example 1-1 and lithium hydroxide were mixed at a molar ratio of 1: 0.5 to obtain a mixture. The obtained mixture was heat-treated at 850 ° C. to obtain manganese spinel (LiMn ₂ O ₄ ). The obtained manganese spinel was used as a positive electrode active material. Example 1 except that the obtained manganese spinel, carbon black as a conductive agent, and fluororesin as a binder were mixed at a weight ratio of 90: 5: 5 to obtain a positive electrode mixture. In the same manner as in Example 1, a battery 1-6 was produced. The battery 1-6 is a secondary battery.

<< Comparative Example 1-1 >>
Electrolytic manganese dioxide (average particle size 30 μm) was used as the positive electrode active material. Since electrolytic manganese dioxide has a γ-type crystal structure containing a large amount of crystal water, the electrolytic manganese dioxide was heat-treated at 400 ° C. to change the phase to a β-type crystal structure. Electrolytic manganese dioxide whose crystal structure is changed to β-type, carbon black as a conductive agent, and fluororesin as a binder are mixed at a weight ratio of 90: 5: 5 to obtain a positive electrode mixture A comparative battery 1-1 was produced in the same manner as in Example 1-1 except that.

<< Comparative Example 1-2 >>
Electrolytic manganese dioxide (average particle size 30 μm) and lithium hydroxide were mixed in a molar ratio of 1: 0.5. The obtained mixture was heat-treated at 400 ° C. to obtain lithium-containing manganese oxide (Li _0.5 MnO ₂ ). Comparative battery 1-2 was produced in the same manner as in Example 1-1 except that the obtained lithium-containing manganese oxide was used as the positive electrode active material. The comparative battery 1-2 is a secondary battery.

<< Comparative Example 1-3 >>
Electrolytic manganese dioxide (average particle size 30 μm) and lithium hydroxide were mixed in a molar ratio of 1: 0.5. The obtained mixture was heat-treated at 850 ° C. to obtain manganese spinel (LiMn ₂ O ₄ ). Comparative battery 1-3 was produced in the same manner as in Example 1-1 except that the obtained manganese spinel was used as the positive electrode active material. Comparative battery 1-3 is a secondary battery.

  The electrolytic manganese dioxide used in the comparative batteries 1-1 to 1-3 was massive secondary particles and had a polycrystalline structure. The average particle size of crystallites contained in the electrolytic manganese dioxide having a polycrystalline structure was about 0.2 μm. Here, the average particle diameter of the crystallite refers to the average particle diameter of the primary particles contained in the secondary particles.

(Evaluation method of fabricated sample)
Crystal structure of manganese dioxide produced in Examples 1-1 to 1-4 above, crystal structure of positive electrode active material produced in Examples 1-5 to 1-6, and produced in Comparative Examples 1-1 to 1-3 The crystal structure of the positive electrode active material was measured by an X-ray diffraction method (XRD) using CuKα. The shape of the produced manganese dioxide or the like was observed with a scanning electron microscope (SEM).

(Evaluation results)
As an example, an SEM photograph of manganese dioxide produced in Example 1-2 is shown in FIG. 5, and an X-ray diffraction chart is shown in FIG. From the SEM photograph of FIG. 5 and the X-ray diffraction chart of FIG. 6, it can be seen that manganese dioxide used for the battery 1-2 has very few impurities and extremely high crystallinity. Therefore, the manganese dioxide of the present invention is very suitable as a positive electrode material for a lithium primary battery, for example.

The shape of the single crystal particles of manganese dioxide obtained in Example 1-2 was mainly acicular as seen in the SEM photograph of FIG. The length of the needle crystal was in the range of 5 μm to 10 μm, and the average length (average particle diameter) was 8 μm. The width of the needle crystal was in the range of 1 μm to 2 μm. In Examples 1-3 and 1-4 in which the reaction temperature was 374 ° C. or lower, the average particle sizes of the obtained manganese dioxide single crystal particles were 20 μm and 15 μm, respectively. That is, the average particle size of the manganese dioxide single crystals obtained in Examples 1-3 and 1-4 was larger than the average particle size of the manganese dioxide single crystal particles of Example 1-2.
Conventionally, most of manganese dioxide having a β-type crystal structure is polycrystalline particles, and there is no manganese dioxide containing 70% by weight or more of single crystal particles.

Table 1 shows the presence / absence of addition of H ₂ O ₂ , the reaction temperature, and the yield of manganese dioxide when producing manganese dioxide used in batteries 1-1 to 1-4. The yield of manganese dioxide is a value representing the percentage of the amount of manganese dioxide actually obtained with respect to the amount of manganese dioxide theoretically obtained.

From the results of the batteries 1-1 and 1-2 shown in Table 1, it can be seen that the yield of manganese dioxide is higher in the battery 1-2 to which H ₂ O ₂ is added. From this, it is considered that H ₂ O ₂ functions as an oxidizing agent.

  From the results of the batteries 1-2 to 1-4, it can be seen that in the temperature range of 250 to 400 ° C., the higher the temperature, the higher the yield of manganese dioxide. From this, it is understood that manganese dioxide can be easily obtained by bringing the raw material aqueous solution to the subcritical state or the supercritical state.

  When hydrogen peroxide was allowed to coexist in the raw material aqueous solution to bring the raw material aqueous solution into a supercritical state (Example 1-2), the yield of manganese dioxide was high. This result is considered to be because the oxygen gas generated by thermal decomposition of hydrogen peroxide and the raw material aqueous solution formed a homogeneous phase and oxidation of manganese ions proceeded well.

(Evaluation of primary battery)
Discharge per unit weight of manganese dioxide by discharging each of the batteries 1-1 to 1-4, which are primary batteries, and the comparative battery 1-1 at 10 load resistors each at a load resistance of 15 kΩ until the battery voltage drops to 2.0 V. The capacity was determined. In each battery, the obtained 10 discharge capacity values were averaged to obtain an average value.

  The batteries 1-1 to 1-4 and the comparative battery 1-1 were each discharged in advance to 75% of the discharge capacity of the battery. After discharging, by applying an AC voltage of 1 kHz for each battery (AC impedance method), the internal resistance was measured, and the average value was obtained. Each battery was then stored at 60 ° C. for 40 days. Storage under these conditions is considered to correspond to storage for 2 years at room temperature.

After storage, the internal resistance was measured in the same manner as before storage, and the average value was obtained. The obtained results are shown in Table 2. Table 2 shows the average value of discharge capacity per unit weight of manganese dioxide (in Table 2, the discharge capacity), the average value of internal resistance before storage and the average value of internal resistance after storage (Table 2). Shows the internal resistance value). Table 2 also shows the presence or absence of addition of H ₂ O ₂ , the reaction temperature, and the average particle diameter of the manganese dioxide single crystal particles.

  From the results of the batteries 1-1 to 1-4 and the comparative battery 1-1 in Table 2, the manganese dioxide of the present invention has a discharge capacity per unit weight increased by about 10 mAh or more as compared with the conventional manganese dioxide. I understand that. It is considered that the manganese dioxide of the present invention has a single crystal or a structure close to a single crystal, and there are almost no grain boundaries in the particles, so that lithium ions are smoothly diffused in the solid phase.

It can be seen that the discharge capacity of the battery 1-2 is larger than the discharge capacity of the battery 1-1. It is thought that by adding H ₂ O ₂ to the raw material aqueous solution, the crystallinity of the produced manganese dioxide was further increased, and the utilization rate was improved.

  From the results of the batteries 1-2 and 1-3, it can be seen that the discharge capacity increases as the reaction temperature during synthesis of manganese dioxide increases. This is considered to be because the crystallinity of manganese dioxide was increased and its utilization rate was improved by making the aqueous raw material solution in a subcritical state or even a supercritical state when producing manganese dioxide.

  The batteries 1-1 to 1-4 have a lower internal resistance value after storage than the comparative battery 1-1. Therefore, it can be seen that the manganese dioxide used in the batteries 1-1 to 1-4 is more stable than the conventional manganese dioxide used in the comparative battery 1-1. The manganese dioxide of the present invention has a single crystal or a structure close to a single crystal, hardly contains crystal defects and lower oxides, and hardly contains sulfate radicals and crystal water in the crystal structure. For this reason, it is thought that the elution of manganese from manganese dioxide was suppressed, and the increase in internal resistance was suppressed.

It can be seen that the internal resistance value after storage of the battery 1-2 is smaller than the internal resistance value after storage of the battery 1-1. When producing manganese dioxide, the crystallinity of manganese dioxide becomes higher by adding H ₂ O ₂ to the raw material aqueous solution. For this reason, it is thought that elution of manganese is suppressed.

  From the results of the battery 1-2 and the battery 1-3, it can be seen that the higher the reaction temperature, the smaller the internal resistance value after storage. It is considered that by making the raw material aqueous solution into a subcritical state or a supercritical state, the produced manganese dioxide has higher crystallinity and the elution of manganese is suppressed.

(Evaluation of secondary battery)
Regarding the batteries 1-5 and the comparative battery 1-2, which are secondary batteries, 10 batteries are repeatedly charged and discharged at a current value of 0.1 mA in a battery voltage range of 2.5 to 3.5 V. It was. The number of cycles at which the discharge capacity was 50% of the discharge capacity at the first cycle (hereinafter also referred to as initial discharge capacity) was determined.

  Similarly, for the batteries 1-6 and the comparative battery 1-3, which are secondary batteries, 10 batteries are charged at a current value of 0.1 mA in a battery voltage range of 3.5 to 4.5V. The discharge was repeated. The number of cycles at which the discharge capacity was 50% of the initial discharge capacity was determined.

  The number of cycles until the discharge capacity of the battery 1-5 decreased to 50% of the initial discharge capacity was increased by about 20% compared to the comparative battery 1-2. The number of cycles until the discharge capacity of the battery 1-6 decreased to 50% of the initial discharge capacity was increased by about 25% compared to the comparative battery 1-3.

<< Example 2-1 >>
Manganese dioxide was produced using the apparatus shown in FIGS. Quartz glass was used as the insulating inorganic material constituting the inner wall portion 32 of the reaction tube 26. Stainless steel was used as a constituent material of the first tube 23 and the second tube 24 and a constituent material of the outer portion of the reaction tube 26.

  A 0.05 mol / L manganese nitrate aqueous solution was used as the raw material aqueous solution. This manganese nitrate aqueous solution was supplied at a predetermined pressure by the first supply device 21. Hydrogen peroxide solution in which hydrogen peroxide as an oxidizing agent was dissolved in distilled water at a concentration of 0.1 mol / L was supplied by the second supply device 22 at a predetermined pressure. On the way, the hydrogen peroxide solution was heated by the electric furnace 25 to obtain supercritical water.

  The manganese nitrate aqueous solution and the supercritical water were joined at the joining part MP to obtain a reaction solution. At this time, the electric furnaces 25 and 27 and the back pressure valve 30 were adjusted so that the temperature of the reaction solution at the junction MP was 400 ° C. and the pressure was 30 MPa. The temperature rising rate of the raw material aqueous solution was 322 ° C./sec.

Next, the solid content deposited on the recovery means 29 was washed to obtain manganese dioxide. The obtained manganese dioxide single crystal particles had a β-type crystal structure, and the average particle size was 0.4 μm.
Using the manganese dioxide obtained as described above, a battery 2-1 was produced in the same manner as in Example 1-1.

<< Example 2-2 >>
When producing manganese dioxide, a battery 2-2 was produced in the same manner as in Example 2-1, except that an 0.05 mol / L manganese nitrate aqueous solution was used and no oxidizing agent was added to distilled water. . Note that the temperature and pressure of the reaction solution at the junction MP were the same as those in Example 2-1. The average particle size of the manganese dioxide single crystal particles obtained in this example was 0.4 μm.

<< Example 2-3 >>
A battery 2-3 was produced in the same manner as in Example 2-1, except that the temperature of the reaction solution at the junction MP was 300 ° C. when producing manganese dioxide. In addition, the pressure of the reaction liquid in the junction part MP was made the same as Example 2-1. The average particle size of the manganese dioxide single crystal particles obtained in this example was 0.7 μm.

<< Example 2-4 >>
A battery 2-4 was produced in the same manner as in Example 2-1, except that when the manganese dioxide was produced, the temperature of the reaction solution at the junction MP was 250 ° C. and the pressure was 30 MPa. The average particle size of the manganese dioxide single crystal particles obtained in this example was 0.9 μm.

<< Example 2-5 >>
Manganese dioxide obtained in Example 2-1 and lithium hydroxide were mixed at a molar ratio of 1: 0.5 to obtain a mixture. The obtained mixture was heat-treated at 400 ° C. to obtain lithium-containing manganese oxide (Li _0.5 MnO ₂ ). A battery 2-5 was produced in the same manner as in Example 2-1, except that the obtained lithium-containing manganese oxide was used as a positive electrode active material. The battery 2-5 is a secondary battery.

<< Example 2-6 >>
Manganese dioxide obtained in Example 2-1 and lithium hydroxide were mixed at a molar ratio of 1: 0.5 to obtain a mixture. The obtained mixture was heat-treated at 850 ° C. to obtain manganese spinel (LiMn ₂ O ₄ ). A battery 2-6 was produced in the same manner as in Example 2-1, except that the obtained manganese spinel was used as the positive electrode active material. The battery 2-6 is a secondary battery.

(Production sample evaluation method)
The crystal structure and shape of the manganese dioxide prepared in Examples 2-1 to 2-4 and the positive electrode active materials prepared in Examples 2-5 to 2-6 were measured in the same manner as described above.

(Evaluation results)
As an example, the SEM photograph and X-ray diffraction chart of the manganese dioxide produced in Example 2-1 are shown in FIGS. 7 and 8, respectively.
7 and 8, it can be seen that the manganese dioxide obtained in Example 2-1 has almost no impurities and mainly contains acicular fine particles having high single crystallinity. Furthermore, the average particle diameter of the manganese dioxide single crystal particles of Example 2-1 was 0.4 μm. On the other hand, as shown in FIG. 5, the average particle size of the manganese dioxide single crystal particles obtained in Example 1-2 was 8 μm. Accordingly, the manganese dioxide obtained in Example 2-1 is a fine particle having a smaller average particle diameter, and is thus very suitable as a positive electrode material for a lithium primary battery.
When the reaction temperature was 374 ° C. or lower, the average particle size of the produced manganese dioxide tended to increase.

Next, Table 3 shows the presence / absence of addition of H ₂ O ₂ , the reaction temperature, and the yield of manganese dioxide in the production of manganese dioxide in Examples 2-1 to 2-4.

The results of Example 2-1 and Example 2-2 show that the yield of manganese dioxide is higher in Example 2-1 in which the reaction solution contains H ₂ O ₂ . From this, it is considered that H ₂ O ₂ functions as an oxidizing agent. That is, it is considered that oxygen gas generated by thermal decomposition of hydrogen peroxide in a supercritical state and an aqueous solution containing manganese ions formed a uniform phase and oxidation of manganese ions proceeded well.

  From the results of Example 2-1, Example 2-3, and Example 2-4, it can be seen that the higher the temperature, the higher the yield in the temperature range of 250 to 400 ° C. Therefore, it can be understood that manganese dioxide having a small average particle diameter of single crystal particles can be easily obtained by bringing the aqueous solution containing manganese ions into a subcritical state or a supercritical state.

(Evaluation method of primary battery)
For batteries 2-1 to 2-4, which are primary batteries, the discharge capacity and the internal resistance value before and after storage were determined in the same manner as described above. Table 4 shows the obtained results. Table 4 also shows the results of Battery 1-2 and Comparative Battery 1-1. Further, Table 4 also shows the presence / absence of addition of H ₂ O ₂ , reaction temperature, and average particle diameter of manganese dioxide single crystal particles.

  From the results of the batteries 2-1 to 2-4 and the comparative battery 1-1, a battery using manganese dioxide mainly containing single crystal particles having an average particle diameter of 0.1 μm or more and 10 μm or less uses conventional electrolytic manganese dioxide. It can be seen that the discharge capacity is increased by about 20 mAh or more as compared with the comparative battery 1-1. Since the manganese dioxide used has a single crystal or a structure close to a single crystal, there are almost no grain boundaries in the manganese dioxide particles. Furthermore, the average particle diameter of the manganese dioxide particles is small. It is considered that the discharge capacity was improved because the movement distance of lithium ions in the manganese dioxide particles was shortened and the lithium ions could be smoothly diffused in the manganese dioxide particles.

Further, the discharge capacity of the battery 2-1 is larger than the discharge capacity of the battery 2-2. It is considered that when the reaction solution contains H ₂ O ₂ , the crystallinity of manganese dioxide is increased and the utilization rate is improved.

  From the results of the battery 2-1, the battery 2-3, and 2-4, it can be seen that the discharge capacity of the battery increases as the reaction temperature increases. It is considered that by making the aqueous solution containing manganese ions into a subcritical state or a supercritical state, the crystallinity of manganese dioxide is increased and the utilization rate is improved.

  The discharge capacity of the batteries 2-1 to 2-4 is approximately the same as or higher than the discharge capacity of the battery 1-2. It is considered that by setting the average particle diameter of the manganese dioxide single crystal particles to 0.1 to 1 μm, the diffusion distance of lithium ions is shortened and the utilization rate is improved.

  It can be seen that the batteries 2-1 to 2-4 have lower internal resistance values after storage than the comparative battery 1-1. Similarly to the above, the manganese dioxide of the present invention has a single crystal or a structure close to a single crystal, does not contain crystal defects or lower oxides, and does not contain sulfate radicals or crystal water in the crystal structure. For this reason, it is thought that elution of manganese is suppressed and an increase in internal resistance value is suppressed.

It can be seen that the internal resistance value after storage of the battery 2-1 is smaller than the internal resistance value after storage of the battery 2-2. It is considered that when the reaction solution contains H ₂ O ₂ , the crystallinity of manganese dioxide is increased and elution of manganese is suppressed.

  From the results of the batteries 2-1, 2-3, and 2-4, it can be seen that the higher the reaction temperature, the smaller the internal resistance value after storage. It is considered that by bringing the aqueous solution containing manganese ions into a subcritical state or a supercritical state, the crystallinity of manganese dioxide is increased and the elution of manganese is suppressed.

(Evaluation of secondary battery)
For batteries 2-5 and 2-6, which are secondary batteries, the number of cycles at which the discharge capacity was 50% of the initial discharge capacity was determined in the same manner as described above.
The number of cycles in which the discharge capacity of the battery 2-5 was 50% of the initial discharge capacity was increased by about 20% compared to the comparative battery 1-2. The number of cycles in which the discharge capacity of the battery 2-6 was 50% of the initial discharge capacity was increased by about 25% compared to the comparative battery 1-3.

As described above, it can be seen that the manganese dioxide of the present invention has an improved discharge capacity and a reduced internal resistance value after storage as compared with a conventional battery containing manganese dioxide. Furthermore, even when the positive electrode active material for secondary batteries obtained by processing or the like using the manganese dioxide of the present invention as a starting material, the characteristics of the manganese dioxide of the present invention are utilized, and the battery using the positive electrode active material is used. It can be seen that the charge / discharge cycle life is improved.
Even when the manganese dioxide of the present invention is mixed with other active materials, the above-described effects can be obtained. In this case, the manganese dioxide of the present invention preferably accounts for 10% by weight or more of the active material mixture.

<< Example 2-7 >>
Manganese dioxide was produced in the same manner as in Example 2-1, except that a reaction tube having an inner wall made of alumina was used. In this example, the temperature and pressure of the reaction solution at the junction MP were the same as those in Example 2-1. The average particle diameter of the manganese dioxide single crystal particles obtained in this example was 0.4 μm.

<< Comparative Example 2-1 and Comparative Example 2-2 >>
The apparatus shown in FIG. 2 was used. In Comparative Example 2-1, the reaction tube was composed only of stainless steel. In Comparative Example 2-2, the reaction tube was composed only of copper. A first tube and a second tube were connected to the inlet of the reaction tube as shown in FIG.
Manganese dioxide synthesis was started in the same manner as in Example 2-1, except that the above apparatus was used. However, in Comparative Example 2-1, 40 minutes after the start of synthesis, and in Comparative Example 2-2, 30 minutes after the start of synthesis, the apparatus (reaction tube) was blocked by the produced manganese dioxide.

  In the apparatuses used in Examples 2-1 and 2-7, no manganese dioxide was deposited on the inner wall surface of the reaction tube even after the synthesis of manganese dioxide for 5 hours. Therefore, as a material constituting the inside of the reaction tube, it is preferable to use an insulating inorganic material such as quartz glass or alumina because precipitation of manganese dioxide on the inner wall surface of the reaction tube can be suppressed.

As described above, the manganese dioxide of the present invention suppresses the elution of manganese at the time of discharge, so that the occurrence of defects such as an increase in battery internal resistance and defective discharge is reduced. By using such manganese dioxide, the life characteristics of the battery can be improved and the reliability of the battery can be improved.
By making an aqueous solution containing manganese ions into a subcritical state or a supercritical state, manganese dioxide having extremely high single crystallinity can be synthesized. In particular, in the supercritical state, when nitrate ions and oxygen gas, which are oxidizing agents, coexist in the reaction field, the aqueous solution containing manganese ions and the oxygen gas can further form a homogeneous phase. Manganese dioxide can be synthesized at a rate. Moreover, the particle | grains to produce | generate are 20 micrometers or less in average particle diameter, and do not require a grinding | pulverization process. For this reason, pulverization energy can be saved. Therefore, manganese dioxide single crystal particles that can improve battery characteristics can be synthesized at high speed, high efficiency, and low energy consumption by the method described above.

It is the schematic which shows an example of the apparatus for producing the manganese dioxide of this invention. It is the schematic which shows another example of the apparatus for producing the manganese dioxide of this invention. It is the schematic which shows the junction part of the 1st pipe | tube, the 2nd pipe | tube, and reaction tube which were provided in the apparatus shown by FIG. It is a longitudinal cross-sectional view which shows roughly the coin-type battery produced in the Example. It is an electron micrograph of manganese dioxide produced in Example 1-2. It is an X-ray diffraction chart of manganese dioxide produced in Example 1-2. It is an electron micrograph of manganese dioxide produced in Example 2-1. 3 is an X-ray diffraction chart of manganese dioxide produced in Example 2-1. It is the schematic which shows the confluence | merging part of the 1st pipe | tube of the manufacturing apparatus of the manganese dioxide used in Comparative Example 2-1 and Comparative Example 2-2, a 2nd pipe | tube, and a reaction tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction tube 2 Tubular furnace 3 Thermocouple 4 Heating wire 5 Plug 6 Holder 21 1st supply apparatus 22 2nd supply apparatus 21a, 22a Tank 21b, 22b Pump 23 1st pipe 24 2nd pipe 25, 27 Tube type electric furnace 26 Reaction tube 28 Heat exchanger 29 Recovery means 30 Back pressure valve 31 Reservoir 32 Insulating inorganic material 41 Positive electrode 42 Negative electrode 43 Separator 44 Gasket 45 Sealing plate 46 Positive electrode case 47 Carbon paint

Claims (14)

  Manganese dioxide containing single crystal particles having a β-type crystal structure.   The manganese dioxide according to claim 1, wherein the single crystal particles have an average particle size of 0.1 µm or more and 1 µm or less.   The manganese dioxide according to claim 1, wherein the single crystal particles have a needle-like particle shape. A method for producing manganese dioxide,
A production method comprising a step of depositing manganese dioxide in a subcritical state or a supercritical state of an aqueous solution containing manganese ions.   The method for producing manganese dioxide according to claim 4, wherein the aqueous solution containing manganese ions is heated at a heating rate of 300 ° C./sec or more to be in a subcritical state or a supercritical state.   6. The manganese dioxide according to claim 5, wherein the aqueous solution containing manganese ions is directly mixed with subcritical or supercritical water to heat the aqueous solution containing manganese ions at a temperature rising rate of 300 ° C./sec or more. Manufacturing method.   5. The manganese dioxide solution according to claim 4, wherein an oxidizing agent is dissolved in the aqueous solution containing manganese ions, and the oxidizing agent contains at least one selected from the group consisting of oxygen gas, ozone gas, hydrogen peroxide, and nitrate ions. Production method.   The oxidant is dissolved in the subcritical or supercritical water, and the oxidant includes at least one selected from the group consisting of oxygen gas, ozone gas, hydrogen peroxide, and nitrate ions. Of manufacturing manganese dioxide. A reaction tube, connected to the inlet side of the reaction tube and supplying an aqueous solution containing manganese ions to the reaction tube; connected to the inlet side of the reaction tube; A second pipe for supplying water in a critical state, and manganese dioxide recovery means provided on the outlet side of the reaction pipe;
At the inlet end of the reaction tube, the aqueous solution containing the manganese ions and the subcritical or supercritical water are mixed,
An apparatus for producing manganese dioxide, wherein an inner wall portion of the reaction tube is made of an insulating inorganic material.   The apparatus for producing manganese dioxide according to claim 9, wherein the insulating inorganic material is quartz or alumina.   The positive electrode active material for batteries containing the manganese dioxide of Claim 1.   A positive electrode active material for a battery, which is synthesized by firing the manganese dioxide according to claim 1 and a lithium compound.   The battery containing the positive electrode containing the positive electrode active material for batteries of Claim 11 or 12, a negative electrode, a separator, and electrolyte solution.   2. The manganese dioxide according to claim 1, comprising 70% by weight or more of single crystal particles having the β-type crystal structure.