JP2014131947A - Manganese dioxide, method of producing the same and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide manganese dioxide with high filling properties and including α-type crystal phases.SOLUTION: Manganese dioxide has 1.0 g/cmor more of a bulk density, and also has 2.5 or less of a (110) plane peak intensity of a γ phase relative to a (110) plane peak intensity of an α phase in a powder X-ray diffraction pattern.

Description

  The present invention relates to manganese dioxide containing an α-type crystal phase. More specifically, the present invention relates to manganese dioxide containing an α-type crystal phase used for electrochemical applications and a method for producing the same.

Manganese dioxide is a manganese oxide having a crystal structure in which MnO ₆ octahedrons are formed as one unit and are continuously crosslinked. Since the crystal structure differs depending on the cross-linked state of the unit, manganese dioxide has a plurality of types having different crystal structures. For example, α-type manganese dioxide composed of α-type crystal phase (tunnel structure expressed as 2 × 2), β-type manganese dioxide composed of β-type crystal phase (tunnel structure expressed as 1 × 1), and Γ-type manganese dioxide composed of γ-type crystal phase (two types of mixed structure of 1 × 1 tunnel structure and 1 × 2 tunnel structure) is known as a kind of manganese dioxide Yes.

  Among these crystal structures, the α-type crystal phase is a crystal structure having a large void. Therefore, α-type manganese dioxide is expected to be applied as an electrode material for next-generation batteries such as multivalent cation batteries such as magnesium ion batteries and calcium ion batteries (Non-patent Document 1).

  α-type manganese dioxide is also called hollandite-type manganese dioxide and is produced naturally. In addition, manganese dioxide having an α-type crystal structure obtained by various production methods has been reported so far. For example, Patent Document 1 reports that manganese dioxide chemically synthesized using a manganese inorganic acid salt and a permanganate, and that this becomes a positive electrode active material of a lithium secondary battery.

  In Patent Document 2, it is reported that mesoporous manganese dioxide synthesized hydrothermally by reduction of permanganate, oxidation of manganese salt, or the like, and this becomes an electrode material of a supercapacitor.

  Patent Document 3 reports manganese dioxide containing ammonia obtained by using manganese sulfate containing ammonia and a solution of sulfuric acid as an electrolyte. It has been reported that the manganese dioxide can be an excellent positive electrode active material for a lithium secondary battery by containing lithium and then firing it.

Japanese Patent No. 2711624 Special table 2011-520744 gazette Japanese Patent Laid-Open No. 05-21062

Masaru Miyayama, FC Report, 30 (3), 86-89 (2012)

  The manganese dioxide disclosed in Patent Documents 1 and 2 is manganese dioxide containing a large amount of α phase, but both have low filling properties. Therefore, when used in an electrochemical device having a limited volume such as a lithium secondary battery or a capacitor, there is a problem that the charge / discharge capacity per unit volume is low. Furthermore, these methods for producing manganese dioxide are production methods involving chemical reactions using expensive reducing agents and oxidizing agents, and have a problem that they are difficult to apply to production on an industrial scale.

  Further, the manganese dioxide disclosed in Patent Document 3 has a high filling property. However, most of the manganese dioxide was γ-type manganese dioxide, and was manganese dioxide substantially free of α-type manganese dioxide. Manganese dioxide is considered to have extremely low ion movement in electrochemical reactions involving movement of ions larger than that of lithium, for example, in charge / discharge of a multivalent cation battery or a multivalent cation capacitor.

  An object of the present invention is to solve these problems and to provide manganese dioxide having a high filling property and having an α-type crystal phase.

The present inventor has repeatedly studied manganese dioxide having an α-type crystal phase (hereinafter referred to as “α-phase”). As a result, the present inventors have found manganese dioxide that has a high electrochemical activity as an electrochemically active material and has a high filling property, and has led to the present invention. That is, in the present invention, the bulk density is 1.0 g / cm ³ or more, and the (110) plane peak intensity of the γ phase with respect to the (110) plane peak intensity of the α phase in the powder X-ray diffraction pattern is 2.5 or less. Manganese dioxide characterized by

  Hereinafter, the present invention will be described in detail.

The manganese dioxide of the present invention is manganese dioxide having an α phase. Manganese dioxide contains an α phase, which tends to improve the electrochemical characteristics, and only the movement of alkali metal ions such as lithium ion (Li ⁺ ), sodium (Na ⁺ ), and potassium (K ⁺ ) in the manganese dioxide crystal structure. In addition, the migration of polyvalent cations such as magnesium ions (Mg ²⁺ ) and calcium ions (Ca ²⁺ ) is facilitated.

  The manganese dioxide of the present invention is manganese dioxide containing an α phase, preferably manganese dioxide having an α phase as a main crystal, and may be manganese dioxide consisting essentially of an α phase. On the other hand, the γ phase has a structure that allows easy movement of alkali metal ions and the like. Therefore, the manganese dioxide of the present invention may be manganese dioxide containing an α phase and a γ phase, and may further be manganese dioxide substantially consisting of only two phases of an α phase and a γ phase. .

  In the manganese dioxide of the present invention, the (110) plane peak intensity of the γ phase relative to the (110) plane peak intensity of the α phase in the powder X-ray diffraction pattern is 2.5 or less, preferably 2 or less, and preferably 1 or less. It is more preferable that it is 0.5 or less. If the (110) plane peak intensity of the γ phase relative to the (110) plane peak intensity of the α phase in the powder X-ray diffraction pattern is in the above range, the movement of lithium ions, polyvalent cations, etc. is mainly the tunnel structure of the α phase. It tends to occur. Thereby, the manganese dioxide of the present invention tends to easily develop a high electric capacity in an electrochemical reaction using lithium ions or polyvalent cations.

  Here, the (110) plane peak of the α phase in the powder X-ray diffraction pattern (hereinafter referred to as “α (110)”) is 2θ = 13 ± 2 ° in the powder X-ray diffraction pattern using CuKα rays as a light source. Corresponding peak. Further, the (110) plane peak of the γ phase in the powder X-ray diffraction pattern (hereinafter referred to as “γ (110)”) corresponds to 2θ = 22 ± 2 ° in the powder X-ray diffraction pattern using CuKα rays as a light source. It is a peak.

The more α phases, the easier the movement of polyvalent cations such as magnesium ions (Mg ²⁺ ) and calcium ions (Ca ²⁺ ). Therefore, the manganese dioxide of the present invention preferably has a high proportion of α phase contained in its crystal structure.

  Furthermore, a crystal structure other than the α phase and the γ phase may be included as long as the filling property and the electrochemical reaction are not adversely affected. However, the β-type crystal phase (hereinafter referred to as “β phase”) has a lower theoretical density than the other crystal phases. Therefore, when a lot of β phases are contained, the filling property of manganese dioxide tends to be particularly low. Therefore, it is preferable that the manganese dioxide of the present invention has a small β phase and further substantially does not contain a β phase.

  The crystal structure of manganese dioxide can be identified by using each powder X-ray diffraction pattern of JCPDS 53-633 for α phase, JCPDS 14-644 for γ phase, and JCPDS 24-735 for β phase.

  In the manganese dioxide of the present invention, the full width at half maximum of α (110) (hereinafter referred to as “FWHM”) in the powder X-ray diffraction pattern is preferably 1.8 or less, and is preferably 1.5 ° or less. More preferred. In general, when FWHM is large, crystallinity is lowered. The manganese dioxide of the present invention has a moderately low FWHM, so that the α-phase structure is easily stabilized.

The manganese dioxide of the present invention has a bulk density of 1.0 g / cm ³ or more, preferably 1.2 g / cm ³ or more, and more preferably 1.7 g / cm ³ or more. . When the bulk density is less than 1.0 g / cm ³ , when the manganese dioxide of the present invention is used, the amount that can be filled decreases. The bulk density need not be higher than necessary, and examples include 3.0 g / cm ³ or less, 2.5 g / cm ³ or less, and 2.0 g / cm ³ or less.

The manganese dioxide of the present invention preferably has an apparent particle density of 2.6 g / cm ³ or more, more preferably 3.0 g / cm ³ or more, and 3.4 g / cm ^3. It is still more preferable that it is above. When the apparent particle density of manganese dioxide is 2.6 g / cm ³ or more, not only the packing property but also the activity for the electrochemical reaction tends to be high.

  Here, the bulk density is a density represented by a filling mass with respect to a filling volume of manganese dioxide. This is an indicator of the filling properties of manganese dioxide, but is unlikely to be an indicator of electrochemical reactivity. On the other hand, the apparent particle density is a density based on a macroscopic form including fine cracks and cracks of manganese dioxide. This can be used as an indicator of the density of manganese dioxide that contributes to the electrochemical reaction. Therefore, even if the bulk density is high, if the apparent particle density is low, the electrochemical reactivity of manganese dioxide becomes low, and the direct relationship between the bulk density and the electrochemical reactivity of manganese dioxide is Absent. A conceptual diagram of bulk density and apparent particle density ((a) bulk density, (b) apparent particle density) is shown in FIG.

In the manganese dioxide of the present invention, the area of pores having an average pore diameter of 2 nm or more and 50 nm or less (hereinafter referred to as “mesopores”) is preferably 10 m ² / g or more, and 14 m ² / g or more. More preferably. When the area of the mesopores is 10 m ² / g or more, when the manganese dioxide of the present invention is used as a battery material or a capacitor material, the surface that can contribute to the electrochemical reaction increases. This facilitates the progress of the electrochemical reaction.

Further, the mesopore volume is preferably 0.045 cm ³ / g or more, and more preferably 0.05 cm ³ / g or more.

  The amount of water contained in the manganese dioxide of the present invention is not particularly limited, but the amount of water is 2.0% by weight in order to quickly move ions accompanying the electrochemical reaction and maintain a high bulk density. It is preferably not less than 8.0% by weight, and more preferably not less than 2.7% by weight and not more than 8.0% by weight because the hydrophilicity between the electrolytic solution and manganese dioxide is further increased and ion migration is facilitated. .

The manganese dioxide of the present invention preferably has a BET specific surface area of 50 m ² / g or more and 150 m ² / g or less, more preferably 120 m ² / g or less. When the BET specific surface area is 50 m ² / g or more, the electric double layer capacity tends to increase particularly when the manganese dioxide of the present invention is used as a capacitor material. If the BET specific surface area is 150 m ² / g or less, the filling property of manganese dioxide can be maintained higher, and the filling property becomes sufficient when used as an electrochemically active material.

The manganese dioxide of the present invention may contain a third component that contributes to the maintenance of the α-phase crystal skeleton structure. Examples of the third component include alkali metal ions such as sodium ion (Na ⁺ ) and potassium ion (K ⁺ ), alkaline earth metal ions such as barium ion (Ba ²⁺ ) and magnesium ion (Mg ²⁺ ), and ammonium ions. One or more cations selected from the group (NH ₄ ⁺ ), and any one or more of ammonium ions and potassium ions can be mentioned.

  When the manganese dioxide of the present invention contains ammonium ions as the third component, its content exceeds 0.6% by weight, further 1.2% by weight or more, and further 1.6% by weight or more. Also good. In addition, ammonium ion content (weight%) is the ratio of the weight of the ammonium ion in the weight of the manganese dioxide of this invention.

  When the manganese dioxide of the present invention contains potassium ions as the third component, the content may be 1.6% by weight or more. In addition, potassium ion content (weight%) is the ratio of the weight of the potassium ion in the weight of the manganese dioxide of this invention.

  The manganese dioxide of the present invention has a potential (hereinafter referred to as “alkali potential”) of 400 mV or less, preferably 300 mV or less, as measured with a mercury / mercury oxide reference electrode as a standard in a 40 wt% aqueous potassium hydroxide solution. Preferably, it is 260 mV or less, further 250 mV or less, and further 240 mV or less. Manganese dioxide tends to be stable when the alkali potential is 400 mV or less. Moreover, 180 mV or more can be illustrated as a lower limit of an alkaline potential.

  The particle diameter of the manganese dioxide of the present invention can be appropriately adjusted according to the application. Examples of the average particle diameter of the manganese dioxide of the present invention include 1 μm or more and 50 μm or less.

  The manganese dioxide of the present invention may be either chemical manganese dioxide or electrolytic manganese dioxide as long as it has the crystal structure and filling properties described above. In general, since the filling property is high, the manganese dioxide of the present invention is preferably electrolytic manganese dioxide.

  The manganese dioxide of the present invention includes, for example, a positive electrode active material for a primary battery such as a lithium primary battery and an alkaline battery, a positive electrode active material for a lithium secondary battery, and a multivalent cation secondary battery such as a magnesium ion battery and a calcium ion battery. The positive electrode active material for secondary batteries, capacitor electrode active materials such as Redox capacitors, electric double layer capacitors or supercapacitors, and various electrochemical active materials such as oxygen reduction catalysts for metal-air secondary batteries . These electrochemically active materials may be produced by using the manganese dioxide of the present invention as it is, but may also be produced by mixing, baking, etc. with other compounds such as lithium as necessary. Good.

  Next, the manufacturing method of the manganese dioxide of this invention is demonstrated.

  The manufacturing method of the manganese dioxide of the present invention may be either a chemical method or an electrolytic method as long as it has the above crystal structure and filling properties.

  As a preferred method for producing manganese dioxide according to the present invention, electrolysis is performed by electrolyzing a sulfuric acid-manganese sulfate mixed solution in which the cation concentration of at least one of ammonium ions and potassium ions is 1.2 or more in molar ratio with respect to the manganese ion concentration. The manufacturing method of manganese dioxide characterized by having a process can be mentioned.

  In the electrolysis step in the above production method, a sulfuric acid-manganese sulfate mixed solution is used as an electrolytic solution. Unlike the electrolytic method in which the electrolytic solution is an aqueous manganese sulfate solution, in the electrolytic method in which the electrolytic solution is a sulfuric acid-manganese sulfate mixed solution, the sulfuric acid concentration during electrolysis is constant. Thereby, the variation in the physical property of the obtained manganese dioxide tends to become small.

  The sulfuric acid concentration of the sulfuric acid-manganese sulfate mixed solution is preferably 15 g / L or more and 40 g / L or less, and more preferably 20 g / L or more and 35 g / L or less. In addition, the sulfuric acid concentration here is a value excluding the divalent anion of manganese sulfate.

The sulfuric acid-manganese sulfate mixed solution contains one or more cations of ammonium ions (NH ₄ ⁺ ) or potassium ions (K ⁺ ) (hereinafter simply referred to as “cations”). It is considered that when the sulfuric acid-manganese sulfate mixed solution contains cations, manganese dioxide is electrolytically precipitated while taking in cations, and the manganese dioxide of the present invention has a crystal structure containing a large amount of α phase.

The cation concentration (hereinafter referred to as “cation / manganese ratio”) relative to the manganese ion concentration (Mn ²⁺ concentration) in the sulfuric acid-manganese sulfate mixed solution is 1.2 or more in molar ratio. When the cation / manganese ratio is less than 1.2 in terms of molar ratio, the resulting manganese dioxide is manganese dioxide having a significantly low α-phase content. The cation / manganese ratio is preferably 1.5 or more, more preferably 1.7 or more, and still more preferably 1.9 or more in terms of molar ratio. On the other hand, if the cation / manganese ratio becomes too high, the content of the α phase of the resulting manganese dioxide tends to decrease. Therefore, the upper limit of the cation / manganese ratio can be exemplified as 13 or less, further 10 or less, and further 8 or less in molar ratio.

  If the above cation / manganese ratio is satisfied, the cation concentration of the sulfuric acid-manganese sulfate mixed solution can be set to an arbitrary concentration. Examples of the cation concentration of the sulfuric acid-manganese sulfate mixed solution include 10 g / L or more, further 15 g / L or more, and further 17 g / L or more.

  On the other hand, if the cation concentration becomes too high, precipitates are generated in the sulfuric acid-manganese sulfate mixed solution, and electrolysis may not be possible. Therefore, the cation concentration is preferably such that no precipitate is generated. Examples of the concentration at which no precipitate is generated include 140 g / L or less when the cation is an ammonium ion, and 75 g / L or less when the cation is a potassium ion.

If the above cation / manganese ratio is satisfied, the manganese ion concentration (Mn ²⁺ concentration) in the sulfuric acid-manganese sulfate mixed solution can be set to an arbitrary value. Examples of the manganese ion concentration in the sulfuric acid-manganese sulfate mixed solution include 20 g / L or more and 40 g / L or less.

  In the electrolysis step, it is preferable to add a cation-containing manganese sulfate aqueous solution to the sulfuric acid-manganese sulfate mixed solution during electrolysis in order to keep the cation concentration constant.

  The cation-containing manganese sulfate aqueous solution can be exemplified as a manganese sulfate aqueous solution containing a cation sulfate. For example, when the cation is an ammonium ion, examples of the cation-containing manganese sulfate aqueous solution include an ammonium sulfate-containing manganese sulfate aqueous solution. Moreover, when a cation is a potassium ion, potassium sulfate containing manganese sulfate aqueous solution can be illustrated as a cation containing manganese sulfate aqueous solution.

The electrolysis current density in the electrolysis process is preferably less than 1.0 A / dm ² , and more preferably 0.9 A / dm ² or less. Electrolysis with an electrolytic current density of 1.0 A / dm ² or more tends to oxidize the electrolytic electrode and degrade it. In addition to this, the efficiency of electrolytic deposition of manganese dioxide, so-called current efficiency, tends to decrease. In order to suppress deterioration of the electrolytic electrode and achieve efficient electrolysis, and to obtain manganese oxide containing a large amount of α phase, the electrolysis current density is preferably 0.3 A / dm ² or more, and 0.45 A / dm ² or more. It is more preferable that

  The electrolysis temperature in the electrolysis step is, for example, more than 90 ° C. and 98 ° C. or less, and further 93 ° C. or more and 97 ° C. or less.

  In the production method of the present invention, after the electrolysis step, any one or more of a washing step, a neutralization step and a pulverization step may be included.

  The cleaning process is performed to remove impurities adhering to manganese dioxide and impurities contained therein. Examples of the cleaning method include a method of immersing manganese dioxide in water such as a water bath or a warm bath while stirring for a certain time.

  In the neutralization step, manganese dioxide obtained by the electrolysis step may be acidic. This is carried out for neutralization depending on the purpose. Examples of the neutralization method include a method of washing this with an aqueous solution of an alkali metal hydroxide or the like so that the manganese dioxide has a desired pH.

  In the pulverization step, manganese dioxide obtained in the electrolysis step is performed to obtain a desired particle size. The pulverization method may be either dry pulverization or wet pulverization, and examples thereof include a method using a general pulverizer such as a mortar or a roller mill.

  In the production method of the present invention, the amount of water contained in manganese dioxide can be further increased through a hydrophilization treatment step. Examples of the hydrophilization method include a method of immersing manganese dioxide in an acid solution, stirring the solution for a certain period of time under heating, and then filtering and separating. The hydrophilization treatment step is performed, for example, after the electrolysis step or after the pulverization step of pulverizing manganese dioxide obtained in the electrolysis step. For the acid solution, for example, 1-8 mol / L sulfuric acid, 1-8 mol / L nitric acid or the like is used, and the heating is performed, for example, at 40 ° C. to 80 ° C., and the stirring time is, for example, 0.5 hours to 6 hours.

  According to the present invention, manganese dioxide having an α-type crystal phase can be provided. Furthermore, according to the present invention, manganese dioxide having high filling properties and possibly having excellent characteristics as an electrochemically active material can be provided.

  Furthermore, the manufacturing method of the present invention can provide a method for manufacturing manganese dioxide having an α-type crystal phase that can be applied to industrial-scale production.

It is a conceptual diagram ((a) bulk density, (b) apparent particle density) of a bulk density and an apparent particle density. 2 is a scanning electron micrograph of the electrolytic manganese dioxide of Example 1 (the scale is 50 μm in the figure). 2 is a pore size distribution of Example 1. 3 is a powder X-ray diffraction pattern of Example 3. FIG. 4 is a powder X-ray diffraction pattern of Comparative Example 3. It is a scanning electron micrograph of the chemical manganese dioxide of Comparative Example 6 (scale in the figure is 10 μm).

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited to these Examples.

(Powder X-ray diffraction measurement)
The powder X-ray diffraction measurement of the sample was performed using a general X-ray diffractometer (MXP-3 manufactured by Mac Science). A CuKα ray (λ = 1.5405 mm) is used as the radiation source, the measurement mode is step scan, the scan condition is 0.04 ° per second, the measurement time is 3 seconds, and the measurement range is 2 ° to 5 ° to 80 °. Measured with

  The obtained powder X-ray diffraction pattern was compared with the powder X-ray diffraction pattern of each JCPDS, and the crystal phase of the sample was identified. The powder X-ray diffraction patterns of JCPDS 53-633, JCPDS 24-735 for identification of the β phase, and JCPDS 14-644 for identification of the γ phase were used for the α phase identification.

(Calculation of γ (110) / α (110))
The peak intensity of 2θ = 13 ± 2 ° of the powder X-ray diffraction pattern obtained by the above powder X-ray diffraction measurement is regarded as α (110) intensity (I _α ), and the peak intensity of 2θ = 22 ± 2 ° is determined. The intensity (I _γ ) of γ (110) was considered. From the obtained I _α , I _γ , and the peak intensity (I ₀ ) of 2θ = 37 ± 2 °, γ (110) / α (110) was determined from the following equation.

γ (110) / α (110) = {(I _γ ) / (I ₀ )} / {(I _α ) / (I ₀ )}
(Measurement of FWHM)
The 2θ = 13 ± 2 ° peak of the powder X-ray diffraction pattern obtained by the above powder X-ray diffraction measurement was regarded as α (110), and the FWHM of the peak was measured.

(Measurement of pore area and pore volume)
The pore area and pore volume of the mesopores were determined by mercury porosimetry (measuring device: pore sizer 9510, manufactured by Micromeritics).

  As a pretreatment for the measurement, the sample was left to dry at 80 ° C. The sample after drying was filled into a measurement container, and mercury was introduced into the container while gradually changing the pressure range from atmospheric pressure to 414 MPa, thereby measuring the pore area and pore volume of the sample.

  The pore distribution (volume distribution) was obtained by this measurement, and pores having a pore diameter of 2 nm or more and 200 nm or less were designated as “secondary pores”, and pores having a pore diameter of 2 nm or more and 50 nm or less were designated as “mesopores”. .

(Measurement of bulk density and apparent particle density)
The bulk density and the apparent particle density were measured by a mercury intrusion method (measuring device: Pore Sizer 9510, manufactured by Micromeritics) in the same manner as the pore area and pore volume of mesopores.

The bulk density was determined from the following formula. That is, the volume obtained by removing the mercury volume (V _Hg ) introduced into the sample at atmospheric pressure from the volume (V _c ) of the measurement container was regarded as the sample volume (V _Mn ). The mass (W _Mn ) of the sample with respect to the sample volume was determined and used as the bulk density (ρ _B ).

V _Mn = V _c -V _Hg
ρ _B = W _Mn / V _Mn
Furthermore, the apparent particle density was determined from the following equation. That is, the volume obtained by removing the mercury volume (V _Hg ′) introduced into the sample at a pressure of 414 MPa from the volume (V _c ) of the measurement container was regarded as the sample volume (V _Mn ′). The mass (W _Mn ) of the sample with respect to the sample volume was determined and used as the apparent particle density (ρ _A ).

V _Mn '= V _c -V _Hg '
ρ _A = W _Mn / V _Mn '
Note that the mercury volume introduced into the sample at atmospheric pressure corresponds to the volume formed between the particles. On the other hand, the volume of mercury introduced into the sample at a pressure of 414 MPa corresponds to the total volume between the particles and the pore volume with a pore diameter of 200 nm. A conceptual diagram of the apparent particle density and bulk density is shown in FIG.

(Measurement of BET specific surface area)
The BET specific surface area of electrolytic manganese dioxide was measured by nitrogen adsorption using the BET one-point method. A gas adsorption type specific surface area measuring device (Flowsorb III, manufactured by Shimadzu Corporation) was used as a measuring device. Prior to the measurement, the measurement sample was deaerated by heating at 150 ° C. for 40 minutes.

(Measurement of alkali potential)
The alkali potential of the sample was measured in a 40% aqueous potassium hydroxide solution as follows.

  0.9 g of carbon as a conductive agent was added to 3 g of the sample to obtain a mixed powder. 4 ml of 40% potassium hydroxide aqueous solution was added to this mixed powder to prepare a mixture slurry of the sample, carbon and potassium hydroxide aqueous solution. Using the mercury / mercury oxide reference electrode as a standard, the potential of the mixture slurry was measured to obtain the alkali potential of the sample.

(Measurement of water content)
The water content of electrolytic manganese dioxide is determined by measuring the weight loss (ΔTa) from room temperature to 110 ° C with a thermal analyzer (TG-DTA6300, manufactured by Seiko Instruments Inc.) and dividing by the weight at 1000 ° C (T1000). It was. The measurement conditions were a temperature increase rate of 10 ° C./min under a stream of nitrogen gas of 100 CC / min.

Water content (% by weight) = ΔTa / T1000 × 100
Example 1
Manganese sulfate and ammonium sulfate were dissolved in water to obtain an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 27.6 g / L and an ammonium ion concentration of 18 g / L.

The obtained ammonium ion-containing sulfuric acid-manganese sulfate mixed solution was used as an electrolytic solution, and electrolysis was performed while continuously adding the ammonium sulfate-containing manganese sulfate solution so that the ammonium ion concentration in the electrolytic solution was constant at 18 g / L. An electrodeposit was obtained. The electrolysis current density was 0.88 A / dm ² , the electrolysis temperature was 96 ° C., and the electrolysis time was 24 hours.

The molar ratio between the ammonium ion concentration and the manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 1.99, and the electrolysis voltage at the end of electrolysis was 1.89 V.

  The obtained electrodeposit was peeled from the electrode, pulverized, and washed with water to obtain electrolytic manganese dioxide having an average particle size of 40 μm. The obtained electrolytic manganese dioxide had a main crystal phase of γ phase, but contained a lot of α phase.

  The electrolytic conditions are shown in Table 1, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, respectively. A scanning electron micrograph of electrolytic manganese dioxide is shown in FIG. 2, and the pore size distribution is shown in FIG.

Example 2
The electrolyte used was an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 27.5 g / L and an ammonium ion concentration of 36 g / L, and the ammonium ion concentration in the electrolyte was constant at 36 g / L. Thus, electrolytic manganese dioxide was obtained under the same conditions as in Example 1 except that the ammonium sulfate-containing manganese sulfate solution was continuously added. The obtained electrolytic manganese dioxide contained an α phase and a γ phase, and the α phase was the main crystal phase.

The molar ratio of the ammonium ion concentration to the manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 3.99, and the electrolysis voltage at the end of electrolysis was 1.79V.

  The electrolytic conditions are shown in Table 1, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, respectively.

Example 3
As an electrolytic solution, an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 32.3 g / L and an ammonium ion concentration of 72 g / L was used, so that the ammonium ion concentration in the electrolytic solution was constant at 72 g / L. An electrolytic manganese dioxide was obtained under the same conditions as in Example 1, except that the ammonium sulfate-containing manganese sulfate solution was continuously added to the sample, and the electrolytic current density was 0.5 A / dm ³ . The obtained electrolytic manganese dioxide contained an α phase and a γ phase, and the α phase was the main crystal phase.

The molar ratio between the ammonium ion concentration and the manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 6.80, and the electrolysis voltage at the end of electrolysis was 1.77 V.

  The electrolytic conditions are shown in Table 1, the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, and the powder X-ray diffraction pattern is shown in FIG.

Example 4
Manganese sulfate and potassium sulfate were dissolved in water to obtain a potassium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 32.0 g / L and a potassium ion concentration of 39 g / L.

  The obtained potassium ion-containing sulfuric acid-manganese sulfate mixed solution was used as an electrolytic solution, and a potassium sulfate-containing manganese sulfate solution was continuously added so that the potassium ion concentration in the electrolytic solution was constant at 39 g / L. Except that, electrolytic manganese dioxide was obtained under the same conditions as in Example 1. The obtained electrolytic manganese dioxide contained an α phase and a γ phase, and the α phase was the main crystal phase.

The molar ratio of the potassium ion concentration to the manganese ion concentration in the electrolytic solution was K ⁺ / Mn ²⁺ = 1.72, and the electrolysis voltage at the end of electrolysis was 2.25V.

  The electrolytic conditions are shown in Table 1, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, respectively.

Comparative Example 1
Manganese sulfate and sulfuric acid were dissolved in water to obtain a sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 27.7 g / L. The mixed solution contains neither ammonium ions nor potassium ions.

  Except that the obtained sulfuric acid-manganese sulfate mixed solution was used as the electrolytic solution and that the manganese sulfate solution was continuously added so that the manganese ion concentration in the electrolytic solution was constant at 27.7 g / L. Manganese dioxide was obtained under the same conditions as in Example 1.

  The molar ratio of the cation concentration to the manganese ion concentration in the electrolytic solution was 0, and the electrolysis voltage at the end of electrolysis was 2.01V. The obtained electrolytic manganese dioxide had a γ phase as a main crystal phase.

  The electrolytic conditions are shown in Table 1, and the physical property evaluation results of manganese dioxide are shown in Table 2.

Comparative Example 2
The electrolyte used was an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 27.4 g / L and an ammonium ion concentration of 9 g / L, and the ammonium ion concentration in the electrolyte was constant at 9 g / L. Thus, manganese dioxide was obtained under the same conditions as in Example 1 except that the ammonium sulfate-containing manganese sulfate solution was continuously added. The molar ratio between the ammonium ion concentration and the manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 1.00, and the electrolysis voltage at the end of electrolysis was 1.93 V. The obtained electrolytic manganese dioxide was a γ phase slightly including an α phase.

  The electrolytic conditions are shown in Table 1, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, respectively.

Comparative Example 3
The electrolyte used was an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 51 g / L and an ammonium ion concentration of 10.9 g / L, and the ammonium ion concentration in the electrolyte was constant at 10.9 g / L. The same conditions as in Example 1 except that the ammonium sulfate-containing manganese sulfate solution was continuously added, the electrolysis current density was 1.0 A / dm ³ , and the electrolysis temperature was 95 ° C. Electrolytic manganese dioxide was obtained. The molar ratio of ammonium ion concentration to manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 0.65, and the electrolysis voltage at the end of electrolysis was 1.95V. The obtained electrolytic manganese dioxide had a γ phase as a main crystal phase and contained only a slight α phase.

  The electrolysis conditions are shown in Table 1, the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, and the powder X-ray diffraction pattern is shown in FIG.

Comparative Example 4
As the electrolyte, an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 52 g / L and an ammonium ion concentration of 16.4 g / L was used, and an ammonium sulfate-containing manganese sulfate solution having a manganese ion concentration of 58 g / L was used. The ammonium sulfate-containing manganese sulfate solution was continuously added so that the ammonium ion concentration in the electrolyte was constant at 16.4 g / L, the electrolysis current density was 1.0 A / dm ³ , and the electrolysis Electrolytic manganese dioxide was obtained under the same conditions as in Example 1 except that the temperature was 95 ° C. The molar ratio between the ammonium ion concentration and the manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 0.96, and the electrolysis voltage at the end of electrolysis was 1.89 V. The obtained electrolytic manganese dioxide had a γ phase as a main crystal phase and contained only a slight α phase.

  The electrolytic conditions are shown in Table 1, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 2, respectively.

Comparative Example 5
Manganese sulfate and potassium sulfate were dissolved in water to obtain a potassium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 32.2 g / L and a potassium ion concentration of 78 g / L.

  The obtained potassium-containing sulfuric acid-manganese sulfate mixed solution was used as an electrolytic solution. However, since white precipitation occurred in the sulfuric acid-manganese sulfate mixed solution immediately before the start of electrolysis, electrolysis could not be performed. The electrolysis conditions are shown in Table 1.

Comparative Example 6
Manganese sulfate and sulfuric acid were dissolved in pure water to obtain a sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 20 g / L and a sulfuric acid concentration of 490 g / L (5 mol / L). Under stirring at a temperature of 96 ° C., a 0.1 mol / L potassium permanganate (KMnO ₆ ) aqueous solution was added to the obtained mixture to obtain a precipitate. The precipitate was filtered and dried to obtain chemical manganese dioxide.

It was γ (110) / α (110) = 0.94 of the chemical manganese dioxide. However, the bulk density was 0.4 g / cm ³ and the filling property was low. The pore area of the mesopores was as small as 0.9 m ² / g. The obtained chemical manganese dioxide had a shape in which fine particles of 1 μm or less were aggregated. The physical property evaluation results of the obtained chemical manganese dioxide are shown in Table 2, and a scanning electron micrograph is shown in FIG.

Example 5
Manganese sulfate and ammonium sulfate were dissolved in water to obtain an ammonium ion-containing sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 27.3 g / L and an ammonium ion concentration of 36 g / L.

The obtained ammonium ion-containing sulfuric acid-manganese sulfate mixed solution was used as an electrolytic solution, and electrolysis was performed while continuously adding the ammonium sulfate-containing manganese sulfate solution so that the ammonium ion concentration in the electrolytic solution was constant at 36 g / L. An electrodeposit was obtained. The electrolysis current density was 0.88 A / dm ² , the electrolysis temperature was 96 ° C., and the electrolysis time was 24 hours.

The molar ratio between the ammonium ion concentration and the manganese ion concentration in the electrolytic solution was NH ₄ ⁺ / Mn ²⁺ = 4.03, and the electrolysis voltage at the end of electrolysis was 1.81V.

  The obtained electrodeposit was peeled from the electrode and pulverized so as to have an average particle diameter of 40 μm. The pulverized product was then immersed in 3 mol / L sulfuric acid and stirred for 4.0 hours while heating at 62 ° C. And hydrophilized. Then, it washed with water and obtained the electrolytic manganese dioxide with an average particle diameter of 40 micrometers. The obtained electrolytic manganese dioxide contained an α phase and a γ phase, and the α phase was the main crystal phase.

  The electrolytic conditions and hydrophilization treatment conditions are shown in Table 3, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 4, respectively.

Comparative Example 7
Manganese sulfate and sulfuric acid were dissolved in water to obtain a sulfuric acid-manganese sulfate mixed solution having a manganese ion concentration of 27.5 g / L. The mixed solution contains neither ammonium ions nor potassium ions.

  Except that the obtained sulfuric acid-manganese sulfate mixed solution was used as an electrolytic solution, and the manganese sulfate solution was continuously added so that the manganese ion concentration in the electrolytic solution was constant at 27.5 g / L. Manganese dioxide electrodeposits were obtained under the same conditions as in Example 5.

  The molar ratio of the cation concentration to the manganese ion concentration in the electrolytic solution was 0, and the electrolysis voltage at the end of electrolysis was 2.05V.

  The obtained electrodeposit was peeled from the electrode and pulverized so as to have an average particle diameter of 40 μm, and the pulverized product was immersed in 3 mol / L sulfuric acid and stirred for 4.2 hours while heating at 58 ° C. And hydrophilized. Then, it washed with water and neutralized and obtained the electrolytic manganese dioxide with an average particle diameter of 40 micrometers. The obtained electrolytic manganese dioxide had a γ phase as a main crystal phase.

  The electrolytic conditions and hydrophilization treatment conditions are shown in Table 3, and the physical property evaluation results of electrolytic manganese dioxide are shown in Table 4, respectively.

From the above, the manganese dioxide of the examples has a high filling property with a bulk density of 1.3 g / cm ³ or more, and further 1.7 g / cm ³ or more, and γ (110) / α (110) is high. 2 or less. Furthermore, it has been found that the crystal structure is manganese dioxide containing an α phase and a γ phase and containing a large amount of the α phase. Also, the FWHM of these manganese dioxides is 1.64 ° (Example 1), 1.67 ° (Example 2), 1.17 ° (Example 3), 1.44 ° (Example 4) and It was found to be manganese dioxide having an α phase having moderately high crystallinity, such as 1.18 ° (Example 5) and 1 ° to 1.7 °. Furthermore, it was found that when the hydrophilization treatment was performed, the water content became 2.7% by weight or more.

When the electrolysis current density is as high as 1.0 A / dm ³ , γ (110) / α (110) is 2.7 or more, and the crystal structure of the γ phase is the main crystal phase, and α The phase content was very low. It has been found that the content of the α phase is significantly lower than that of the manganese dioxide of the present invention.

  The manganese dioxide of the present invention includes, for example, a positive electrode active material for a primary battery such as a lithium primary battery and an alkaline battery, a positive electrode active material for a lithium secondary battery, and a multivalent cation secondary battery such as a magnesium ion battery and a calcium ion battery. The positive electrode active material for secondary batteries, capacitor electrode active materials such as Redox capacitors, electric double layer capacitors or supercapacitors, and various electrochemical active materials such as oxygen reduction catalysts for metal-air secondary batteries .

1: Manganese dioxide (particles)
2: Pore in manganese dioxide (pore diameter 200 nm or more)
3: Pore in manganese dioxide (pore diameter less than 200 nm)
4: Mercury (Hg)

Claims (9)

Manganese dioxide having a bulk density of 1.0 g / cm ³ or more and a (110) plane peak intensity of the γ phase with respect to the (110) plane peak intensity of the α phase in the powder X-ray diffraction pattern is 2.5 or less . 2. The manganese dioxide according to claim 1, wherein an area of pores having an average pore diameter of 2 nm or more and 50 nm or less is 10 cm ³ / g or more. 3. The manganese dioxide according to claim 1, wherein the moisture content is 2.0% by weight or more and 8.0% by weight or less. The electrolytic process of electrolyzing a sulfuric acid-manganese sulfate mixed solution in which the cation concentration of at least one of ammonium ions and potassium ions with respect to the manganese ion concentration is 1.2 or more in molar ratio. The manufacturing method of the manganese dioxide of any one of Claims 1-3. 5. The method for producing manganese dioxide according to claim 4, wherein in the electrolysis step, electrolysis is performed at an electrolysis current density of less than 1.0 A / dm ³ . The method according to claim 4 or 5, wherein, in the electrolysis step, a cation concentration of at least one of ammonium ions and potassium ions is 10 g / L or more. The method for producing manganese dioxide according to any one of claims 4 to 6, further comprising a step of treating manganese dioxide with an acid solution after the electrolysis step. The method for producing manganese dioxide according to claim 7, wherein the acid is sulfuric acid. The manufacturing method of the electrochemically active material characterized by using the manganese dioxide of any one of Claims 1-3.

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