JP2009135067A - Electrolytic manganese dioxide, method for producing the same, and use thereof - Google Patents

Abstract

Disclosed is an electrolytic manganese dioxide used as an active material for a positive electrode of an alkaline manganese dry battery. The electrolytic manganese dioxide has a high alkali potential and has high reactivity and filling properties as a positive electrode of a battery.
Electrolysis having an alkali potential of 310 mV or more, a FWHM of 2.2 ° or more and 2.9 ° or less, and a peak intensity ratio of (110) / (021) in an X-ray diffraction peak of 0.50 or more and 0.80 or less. Manganese dioxide is used. It is preferable that the interval between the (110) planes of electrolytic manganese dioxide is 4.00 mm or more and 4.06 mm or less. Manganese dioxide having a high alkali potential and high filling property can be produced by electrolysis at a low sulfuric acid concentration in the first electrolysis and a high sulfuric acid concentration in the second half in sulfuric acid-manganese sulfate bath electrolysis.
[Selection] Figure 1

Description

  The present invention relates to electrolytic manganese dioxide used as a positive electrode active material in, for example, a manganese dry battery, particularly an alkaline manganese dry battery, a method for producing the same, and an application thereof.

  Manganese dioxide is known as a positive electrode active material of, for example, a manganese dry battery or an alkaline manganese dry battery, and has an advantage of being excellent in storage stability and being inexpensive. In particular, alkaline manganese batteries using manganese dioxide as the positive electrode active material have excellent discharge characteristics under heavy loads, so they are widely used in electronic cameras, portable tape recorders, portable information devices, game machines, and toys. In recent years, the demand has been increasing rapidly.

  However, the alkaline manganese battery has a problem that the substantial discharge capacity is greatly impaired because the utilization rate of manganese dioxide, which is a positive electrode active material, decreases as the discharge current increases and cannot be used in a state where the discharge voltage decreases. was there. In other words, when an alkaline manganese battery is used in a device that uses a large current (high rate discharge), the charged positive electrode active material manganese dioxide is not fully utilized, and the usable time is short. It was.

  Thus, an excellent manganese dioxide capable of exhibiting a high capacity and a long life under high-rate intermittent discharge conditions in which a large current is taken out in a short time, that is, manganese dioxide excellent in so-called high-rate characteristics is desired.

  In applications where high rate characteristics are required, in order to increase the voltage when the battery is discharged, the potential (hereinafter referred to as the alkali potential) when measured with a mercury / mercury oxide reference electrode as a standard in a 40% KOH aqueous solution is used. Although high electrolytic manganese dioxide can be used as the positive electrode active material, the alkaline potential of conventional electrolytic manganese dioxide has not been sufficiently high.

  Further, as electrolytic manganese dioxide having a high alkali potential, electrolytic manganese dioxide obtained by controlling electrolysis conditions, for example, electrolytic manganese dioxide produced by increasing the acid concentration of sulfuric acid in an electrolytic solution has been proposed. (Non-patent document 1, Patent document 1) However, in the electrolysis under the production conditions where the acid concentration of the electrolytic solution is high, the electrolytic manganese dioxide electrodeposited during the electrolysis peels off from the electrolytic electrode. Since the crystallite diameter of the obtained electrolytic manganese dioxide is small and the BET surface area is large, there is a problem that the filling property cannot be improved when the battery is constructed, and the volumetric energy density is low.

  On the other hand, a method for producing electrolytic manganese dioxide having a high alkali potential by electrolysis at a low current density has been reported (Patent Document 2). However, electrolytic manganese dioxide by electrolysis with low current density is low in productivity due to slow electrodeposition rate, the crystallite diameter of electrolytic manganese dioxide is too large, and the reactivity of electrolytic manganese dioxide becomes poor, and the positive electrode active material for batteries As a result, there was a problem that the discharge capacity decreased.

  Furthermore, a method for producing manganese dioxide having a high alkaline potential using hydrochloric acid instead of the sulfuric acid normally used for the electrolytic solution has been proposed (Patent Document 1). However, electrolysis using hydrochloric acid is accompanied by the generation of chlorine during electrolysis, so there are many inconveniences in production, such as the need to take further measures, and the obtained electrolytic manganese dioxide has a small crystallite size and a battery. There is a problem in that the filling property cannot be improved when the is formed, and the volumetric energy density is low.

Furukawa Electric Times, No. 43, p. 91-102 (May 1967) JP 2007-141463 A US Pat. No. 6,527,941

  An object of the present invention is manganese dioxide used as a positive electrode active material of an alkaline manganese dry battery that is particularly excellent in high-rate characteristics, and particularly has a high potential in an alkaline electrolyte and has high reactivity and filling properties. Electrolytic manganese dioxide, a method for producing the same, and uses thereof are provided.

  As a result of intensive studies on manganese dioxide used as a positive electrode active material for alkaline manganese dry batteries, the present inventors have determined that 2θ is 22 ± 1 ° in XRD measurement using an alkali potential of 310 mV or higher and CuKα rays as a light source. The full width at half maximum (hereinafter referred to as FWHM) of the diffraction line of the (110) plane appearing in the vicinity is 2.2 ° or more and 2.9 ° or less, and the (110) / (021) peak intensity ratio of X-ray diffraction is 0. It was found that electrolytic manganese dioxide having a value of .50 or more and 0.80 or less is a positive electrode material particularly excellent in high-rate characteristics, and the present invention has been completed.

  Hereinafter, the present invention will be described in more detail.

  The electrolytic manganese dioxide of the present invention has an alkali potential of 310 mV or more, a full width at half maximum (FWHM) of a diffraction line of (110) plane of 2θ around 22 ± 1 °, 2.2 ° to 2.9 °, X-ray This is manganese dioxide having a diffraction (110) / (021) peak intensity ratio of 0.50 or more and 0.80 or less.

  When the alkaline potential is 310 mV or more, when used as a positive electrode material of an alkaline manganese dry battery, the open circuit voltage of the battery increases, and the discharge time to the lower limit of usable discharge voltage can be extended. The alkali potential is particularly preferably 330 mV or higher, more preferably 340 mV or higher.

  The electrolytic manganese dioxide of the present invention has a full width at half maximum (FWHM) of a diffraction line on the (110) plane of 2θ of around 22 ± 1 ° in a normal XRD measurement pattern using CuKα rays as a light source. Although it is .9 ° or less, it is particularly preferably 2.4 ° or more and 2.8 ° or less, more preferably 2.5 ° or more and 2.8 ° or less. In such FWHM, the filling property is improved and the discharge capacity is increased.

  On the other hand, when the FWHM is larger than 2.9 °, when the battery is configured as the positive electrode material, the packing density is lowered, and the discharge capacity is lowered accordingly. When the FWHM is smaller than 2.2 °, the crystal grows too much, the reactivity of the electrolytic manganese dioxide becomes worse, and the discharge capacity as the positive electrode active material for the battery decreases.

  The reason why the lower limit of FWHM is as small as 2.2 ° is that the electrolytic manganese dioxide of the present invention is electrolyzed using, for example, electrolysis with an electrolyte containing low-concentration sulfuric acid, which will be described later, and subsequently using an electrolyte containing high-concentration sulfuric acid. This is because manganese dioxide having a low FWHM and a high alkali potential is obtained particularly when the ratio of electrolysis time in an electrolytic solution containing a low concentration of sulfuric acid is large.

  The crystallite diameter of the electrolytic manganese dioxide of the present invention is obtained by conversion according to Scherrer's formula from the FWHM and the (110) peak position, and the average crystallite diameter corresponds to 29 to 37 mm. Electrolytic manganese dioxide having an average crystallite size larger than 37 mm has low reactivity as described above, and has a low discharge capacity. If it is smaller than 29 mm, the packing property is poor and the capacity energy density is low.

  The electrolytic manganese dioxide of the present invention has a (110) / (021) peak intensity ratio of X-ray diffraction of 0.50 to 0.80, preferably 0.53 to 0.80.

  The intensity ratio of each diffraction surface of the X-ray diffraction pattern of electrolytic manganese dioxide varies depending on the electrolysis conditions and the physical properties of the resulting manganese dioxide. Manganese dioxide obtained by electrolyzing only an electrolytic solution having a high sulfuric acid concentration satisfies the above-described conditions and has a (110) / (021) peak intensity ratio of less than 0.50, while electrolysis is performed at a low current density. The high alkaline potential product exceeds 0.8, which is different from the manganese dioxide of the present invention.

  As described above, the (110) plane in the X-ray diffraction of electrolytic manganese dioxide is the main X-ray diffraction peak of the manganese dioxide crystal that appears in the vicinity of 22 ± 1 ° and the (021) plane in the vicinity of 37 ± 1 °.

  In the electrolytic manganese dioxide of the present invention, it is preferable that the (110) plane spacing of the X-ray diffraction is 4.00 mm or more and 4.06 mm or less in order to satisfy the above conditions.

  Here, the (110) plane spacing is an index representing the spacing between (110) crystal planes of manganese dioxide belonging to orthorhombic crystals.

  Conventional manganese dioxide having an alkaline potential higher than 310 mV has a (110) plane spacing greater than 4.06 mm. In the electrolytic manganese dioxide of the present invention, since the (110) plane spacing is small, the stability of the crystal is high.

The electrolytic manganese dioxide of the present invention preferably has a BET specific surface area of 22 m ² / g or more and 32 m ² / g or less.

When the BET specific surface area is lower than 22 m ² / g, the reactivity of electrolytic manganese dioxide is deteriorated, the discharge capacity as the positive electrode active material for the battery is lowered, and when the BET specific surface area is higher than 32 m ² / g, The filling capacity of manganese dioxide is poor, and the discharge capacity when the battery is configured is likely to decrease.

  The electrolytic manganese dioxide of the present invention is characterized by alkali potential, (110) plane FWHM, (110) plane spacing, (110) / (021) peak intensity ratio, and the like. By mixing the obtained electrolytic manganese dioxide, it is different from the one in which only the alkali potential or the filling property is adjusted, and can be easily distinguished.

Next, the manufacturing method of the electrolytic manganese dioxide of this invention is demonstrated.
Conventional methods for producing electrolytic manganese dioxide are performed so as to keep the sulfuric acid concentration of the electrolytic solution constant during electrolysis. The production method of the present invention is characterized by changing the sulfuric acid concentration in the electrolytic solution during electrolysis, which is completely different from the conventional method. The detailed method of the present invention will be described below.

  In the present invention, manganese dioxide having a high alkaline potential and crystallinity is obtained by electrolysis under the condition that the sulfuric acid concentration is kept low and constant in the first half and then adjusted under the condition that the sulfuric acid concentration is increased from the middle. In addition, manganese dioxide does not peel from the electrode during electrolysis, and high-grade manganese dioxide can be produced stably.

  In the production of manganese dioxide by electrolysis, if the sulfuric acid concentration in the electrolyte is lowered, the electrolytic manganese dioxide is strongly deposited on the anode and there is no problem of delamination, but that alone can only provide electrolytic manganese dioxide with a low alkaline potential. .

  Electrolysis with a high concentration of sulfuric acid provides manganese dioxide with a high alkali potential, but it peels off during electrodeposition, and stable high-potential manganese dioxide cannot be obtained, resulting in smaller crystallites and a high BET surface area. Only low ones can be obtained.

  In the present invention, in addition to obtaining manganese dioxide having a large crystallite diameter and a low BET surface area and high filling properties by electrolysis at a low sulfuric acid concentration in the first half, it is obtained by electrolysis at the first half by further electrolyzing at a high sulfuric acid concentration. It has been found that the potential can be increased by including the produced manganese dioxide.

  In the method of the present invention, the sulfuric acid concentration in the electrolytic solution is preferably 25 to 40 g / L at the start of electrolysis, and the sulfuric acid concentration in the latter half is preferably increased to exceed 40 g / L and 75 g / L at the end of electrolysis. Furthermore, it is particularly preferable that the sulfuric acid concentration in the electrolytic solution at the start of electrolysis is 29 to 40 g / L, and the sulfuric acid concentration in the latter half is increased to 44 to 75 g / L at the end of electrolysis. The sulfuric acid concentration mentioned here excludes the divalent anion of manganese sulfate.

  Although there is no limitation on the manganese concentration in the electrolytic replenisher in the present invention, for example, 40 to 60 g / L can be exemplified.

There is no particular limitation on the electrolysis temperature, and for example, a temperature range of 94 to 98 ° C. can be applied. Moreover, as a current density, 0.4-0.6 A / dm < ² > is applicable, for example.

  There is no limitation on the ratio of electrolysis in the first period and electrolysis in the second half, but for example, the ratio of electrolysis time at low sulfuric acid concentration and high sulfuric acid concentration is in the range of 1: 9-9: 1, especially 3: 7-7: 3. preferable.

  The electrolytic manganese dioxide of the present invention can be used particularly as a positive electrode active material for alkaline manganese dry batteries.

  There is no restriction | limiting in particular in the method used as a positive electrode active material of an alkaline manganese battery, It can mix and use with an additive by a well-known method.

  For example, a mixed powder obtained by adding carbon or the like in order to impart conductivity to electrolytic manganese dioxide can be prepared, and the battery positive electrode can be formed as a powder molded body obtained by pressure molding this into a disk shape or a ring shape.

  When the electrolytic manganese dioxide of the present invention is used as a positive electrode material, in an LR6 type battery specified by JIS-C8511, a high potential with an open circuit voltage (OCV) before discharge exceeding 1.649 V can be obtained. The open circuit voltage (OCV) before discharge is particularly 1.67V, and more than 1.68V.

  The electrolytic manganese dioxide of the present invention is uniform and has a high potential in an unprecedented alkaline electrolyte.

  In particular, the characteristics of an alkaline manganese dry battery used as an active material for a positive electrode of an alkaline manganese dry battery are evaluated by a discharge time until reaching a final voltage of 0.9 V, with a cycle of 10 seconds of discharge at 1000 mA followed by a pause of 50 seconds as one pulse. In the high-rate discharge characteristic evaluation, a discharge life longer by 10% or more than that obtained when conventional electrolytic manganese dioxide is used can be obtained.

  Further, the AA alkaline manganese dry battery using the electrolytic manganese dioxide of the present invention as the positive electrode active material is continuously discharged at a load of 1 watt, and the discharge capacity of the battery is calculated from the amount of discharge current until reaching the final voltage of 0.9 V. A high discharge capacity of 70 mAh / g or more, particularly 72 mAh / g or more, obtained in terms of the electrolytic manganese dioxide weight can be obtained.

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

(Measurement of potential of electrolytic manganese dioxide)
The potential of electrolytic manganese dioxide was measured in a 40% KOH aqueous solution as follows.

  0.9 g of carbon as a conductive agent was added to 3 g of electrolytic manganese dioxide to obtain a mixed powder, and 4 ml of 40% KOH aqueous solution was added to this mixed powder to obtain a mixture slurry of electrolytic manganese dioxide, carbon and KOH aqueous solution. The alkaline potential of the electrolytic manganese dioxide was measured with respect to the potential of the mixture slurry with reference to a mercury / mercury oxide reference electrode.

(Measurement of full width at half maximum (FWHM) in XRD measurement)
The full width at half maximum (FWHM) of a diffraction line having 2θ of about 22 ± 1 ° of electrolytic manganese dioxide was measured 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

(Calculation of (110) spacing by XRD measurement)
The diffraction line of electrolytic manganese dioxide with 2θ of around 22 ± 1 ° was Gaussian treated to determine the peak top 2θ. From the obtained 2θ value, d was calculated from the Bragg equation (nλ = 2dsinθ, n = 1) to obtain the (110) plane spacing.

(Calculation of (110) / (021) intensity ratio by XRD measurement)
By dividing the diffraction intensity of 2θ around 22 ± 1 ° as (110) and the diffraction line around 37 ± 1 ° as (021), the peak intensity of (110) is divided by the peak intensity of (021) (110). / (021) peak intensity ratio was determined.

(Measurement of BET specific surface area of electrolytic manganese dioxide)
The BET specific surface area of electrolytic manganese dioxide was measured by nitrogen adsorption according to the BET one-point method. The electrolytic manganese dioxide used for the measurement of the BET specific surface area was deaerated by heating at 150 ° C. for 40 minutes prior to the measurement of the BET specific surface area.

(High-rate characteristics evaluation for AA batteries)
Combined with two compacts made of 5g mixed powder composed of 85.8% electrolytic manganese dioxide, 7.3% graphite and 6.9% 40% potassium hydroxide electrolyte in a ring shape with a molding pressure of 2 tons AA type batteries were constructed using a negative electrode material containing zinc as a positive electrode. The AA batteries were left at room temperature for 24 hours, and then a discharge test was conducted. The discharge conditions were a relative discharge time until a final voltage of 0.9V was reached, with a cycle of 10 seconds of discharge at 1000 mA and a pause of 50 seconds as one pulse. In addition, the standard of the relative discharge time made the measurement result of the comparative example 1 100%.

(Battery characteristics evaluation at OCV and 1 Watt in AA batteries)
The LR6 type battery (AA size) was left at room temperature for 72 hours, and then the open circuit voltage (OCV) was measured with a voltmeter. Next, the AA battery was connected to a discharge test apparatus (BTS 2305 manufactured by Nagano), and a discharge test was performed with a 1 Watt load. The battery characteristics are evaluated by calculating the discharge capacity (mAh) per battery from the integrated amount of discharge current until the final voltage reaches 0.9 V, and converting it to the discharge capacity (mAh / g) per weight of electrolytic manganese dioxide in the battery. did. In addition, the battery characteristic in OCV measurement and 1 Watt produced and evaluated five batteries with respect to each electrolytic manganese dioxide sample, and made five average values the evaluation value of each electrolytic manganese dioxide.

Example 1
The current density is 0.5 A / dm ² , the electrolysis temperature is 96 ° C., the electrolytic replenisher is a manganese sulfate solution having a manganese concentration of 50.0 g / l, and the sulfuric acid concentrations in the early and late electrolysis are 29.2 g / l and 74. Electrolysis was performed for 16 days so as to be 8 g / l. Electrolysis was performed for 13 days at the first concentration and for 3 days at the second concentration.

The obtained electrolytic manganese dioxide had an alkali potential of 320 mV, a FWHM of 2.9 °, a (110) / (021) of 0.60, and a BET specific surface area of 29.8 m ² / g. The results are shown in Table 1 together with other evaluation results.

  Next, a molded product 2 in which 5 g of mixed powder obtained by mixing 85.8% of this electrolytic manganese dioxide, 7.3% of graphite and 6.9% of 40% potassium hydroxide electrolyte was molded into a ring shape with a molding pressure of 2 tons. AA batteries were assembled as a positive electrode by combining them, and the OCV measurement after leaving for 72 hours and the discharge test at 1 Watt load were performed. As a result, the OCV was 1.684 V and the discharge capacity was 70.4 mAh / g.

Example 2
The current density is 0.5 A / dm ² , the electrolysis temperature is 96 ° C., the electrolytic replenisher is a manganese sulfate solution having a manganese concentration of 40.0 g / l, and the sulfuric acid concentrations in the early and late electrolysis are 29.2 g / l and 49. Electrolysis was performed for 14 days so as to be 2 g / l. Electrolysis was carried out for 10 days at the former concentration and for 4 days at the latter concentration.

The obtained electrolytic manganese dioxide had an alkali potential of 343 mV, a FWHM of 2.6 °, a (110) / (021) of 0.68, and a BET specific surface area of 26.3 m ² / g. The results are shown in Table 1 together with other evaluation results.

  Next, a molded body 2 in which 5 g of mixed powder obtained by mixing 85.8% of this electrolytic manganese dioxide, 7.3% of graphite, and 6.9% of 40% potassium hydroxide electrolyte was molded into a ring shape with a molding pressure of 2 tons. As a result of assembling a single AA type battery as a positive electrode by combining them and conducting the above-described discharge test, the relative discharge time was 122%.

Example 3
Electrolytic manganese dioxide was prepared in the same manner as in Example 2 except that the sulfuric acid concentration in the electrolytic solution for the first 12 days of electrolysis was 29.2 g / l and the sulfuric acid concentration in the electrolytic solution for the latter 2 days of electrolysis was 44.7 g / l. Got.

The obtained electrolytic manganese dioxide had an alkali potential of 331 mV, a FWHM of 2.6 °, a (110) / (021) of 0.74, and a BET specific surface area of 28.4 m ² / g. . The results are shown in Table 1 together with other evaluation results.

Example 4
Electrolytic manganese dioxide was obtained in the same manner as in Example 2 except that the sulfuric acid concentration in the electrolytic solution during the latter 4 days of electrolysis was changed to 59.0 g / l. The results are shown in Table 1.

The obtained electrolytic manganese dioxide had an alkali potential of 341 mV, a FWHM of 2.7 °, (110) / (021) of 0.65, and a BET specific surface area of 30.4 m ² / g. . The results are shown in Table 1 together with other evaluation results.

  Next, an AA type battery was assembled from this electrolytic manganese dioxide under the same conditions as in Example 2, and the discharge test described above was conducted. As a result, the relative discharge time was 110%.

Example 5
Example except that a manganese sulfate solution having a manganese concentration of 45.0 g / l was used as the electrolytic replenishment solution, the sulfuric acid concentration in the initial 10 days of electrolysis was 32.9 g / l, and the sulfuric acid concentration in the late electrolysis was 48.8 g / l. Electrolytic manganese dioxide was obtained by the same method as 2.

The obtained electrolytic manganese dioxide had an alkali potential of 325 mV, a FWHM of 2.5 °, a (110) / (021) of 0.66, and a BET specific surface area of 31.4 m ² / g. . The results are shown in Table 1 together with other evaluation results.

Next, an AA type battery was assembled from this electrolytic manganese dioxide in the same manner as in Example 2, and the discharge test described above was conducted. As a result, the relative discharge time was 111%.
Further, two compacts in which 5 g of the mixed powder obtained by mixing 85.8% of this electrolytic manganese dioxide, 7.3% of graphite and 6.9% of 40% potassium hydroxide electrolyte was formed into a ring shape with a molding pressure of 2 tons. AA type batteries made up of positive electrodes were assembled and OCV measurement after standing for 72 hours and a discharge test at 1 Watt load were performed. As a result, the OCV was 1.684 V, and the discharge capacity was 76.1 mAh / g.

Example 6
Electrolytic manganese dioxide was obtained in the same manner as in Example 5 except that the sulfuric acid concentration in the electrolytic solution in the latter 4 days of electrolysis was changed to 66.7 g / l.

The obtained electrolytic manganese dioxide had an alkali potential of 330 mV, FWHM of 2.6 °, (110) / (021) of 0.53, and a BET specific surface area of 30.3 m ² / g. . The results are shown in Table 1 together with other evaluation results.

Examples 7 and 8
A lump obtained by electrolysis under the same conditions as in Example 1 was cut out, and electrolytic manganese dioxide deposited in the vicinity of the anode and on the electrolyte side was cut out.

  All portions had an alkaline potential of 310 mV or more and a uniform alkaline potential. From this result, the electrolytic manganese dioxide of the present invention is not a mixture of low-potential electrolytic manganese dioxide electrolyzed with low sulfuric acid concentration and high-potential electrolytic manganese dioxide with high sulfuric acid concentration, but a uniform high alkaline potential as a whole. The electrolytic manganese dioxide was confirmed.

Example 9
The current density is 0.5 A / dm ² , the electrolysis temperature is 96 ° C., the electrolytic replenisher is a manganese sulfate solution having a manganese concentration of 42.0 g / l, and the sulfuric acid concentrations in the initial and second half of the electrolysis are 40.0 g / l, 70. Electrolysis was performed for 17 days so as to be 0 g / l. Electrolysis was performed for 12 days at the first concentration and for 5 days at the second concentration.

The obtained electrolytic manganese dioxide had an alkali potential of 319 mV, FWHM of 2.4 °, (110) / (021) of 0.78, and a BET specific surface area of 28.0 m ² / g. The results are shown in Table 1 together with other evaluation results.
Next, a molded product 2 in which 5 g of mixed powder obtained by mixing 85.8% of this electrolytic manganese dioxide, 7.3% of graphite and 6.9% of 40% potassium hydroxide electrolyte was molded into a ring shape with a molding pressure of 2 tons. AA batteries were assembled as a positive electrode by combining them, and the OCV measurement after leaving for 72 hours and the discharge test at 1 Watt load were performed. As a result, the OCV was 1.682 V and the discharge capacity was 72.8 mAh / g.

Example 10
Electrolytic manganese dioxide was prepared in the same manner as in Example 9 except that electrolysis was carried out for 15 days so that the sulfuric acid concentration in the latter half of the electrolysis was 72.0 g / l, and electrolysis was carried out in the first half for 9 days and the latter half for 6 days. Got.

The obtained electrolytic manganese dioxide had an alkali potential of 313 mV, a FWHM of 2.2 °, a (110) / (021) of 0.80, and a BET specific surface area of 26.0 m ² / g. The results are shown in Table 1 together with other evaluation results.

Comparative Example 1
The current density is 0.5 A / dm ² , the electrolysis temperature is 96 ° C., the manganese concentration of the electrolytic replenisher is 40.0 g / l, and the sulfuric acid concentration in the electrolyte is constant 32.9 g / l throughout the electrolysis. Electrolytic manganese dioxide was obtained.

The obtained electrolytic manganese dioxide had an alkali potential of 274 mV, a FWHM of 2.3 °, a crystallite diameter calculated from FWHM of 37.3 mm, and a BET specific surface area of 28.5 m ² / g. . The results are shown in Table 1 together with other evaluation results.

  Manganese dioxide obtained by electrolysis at a constant low sulfuric acid concentration had a large crystallite size and a low alkali potential.

  Next, an AA type battery was assembled from this electrolytic manganese dioxide in the same manner as in Example 2, the above-described discharge test was performed, and the discharge time was set to 100%.

  Further, two compacts in which 5 g of the mixed powder obtained by mixing 85.8% of this electrolytic manganese dioxide, 7.3% of graphite and 6.9% of 40% potassium hydroxide electrolyte was formed into a ring shape with a molding pressure of 2 tons. AA type batteries made up of positive electrodes were assembled and OCV measurement after standing for 72 hours and a discharge test at 1 Watt load were performed. As a result, the OCV was 1.635 V, and the discharge capacity was 67.6 mAh / g.

Comparative Example 2
Electrolytic manganese dioxide was obtained in the same manner as in Example 2 except that the sulfuric acid concentration in the electrolytic solution was kept high at 48.5 g / l throughout the entire period during electrolysis. Electrodeposited electrolytic manganese dioxide fell off.

The obtained electrolytic manganese dioxide had an alkali potential of 324 mV, a FWHM of 3.1 °, and a BET specific surface area of 35.1 m ² / g. The results are shown in Table 1 together with other evaluation results.

Although the alkali potential was high, the crystallite diameter calculated from FWHM was smaller than 29 mm, the BET specific surface area was larger than 32 m ² / g, and the filling property was low.

Comparative Example 3
Electrolytic manganese dioxide was obtained in the same manner as in Comparative Example 2 except that a carbon plate was used as the anode.

The obtained electrolytic manganese dioxide had an alkali potential of 319 mV, a FWHM of 3.0 °, and a BET specific surface area of 33.4 m ² / g. The results are shown in Table 1 together with other evaluation results.

  The crystallite diameter calculated from FWHM was close to 29 mm, and the filling property was low.

Comparative Example 4
Electrolytic manganese dioxide was obtained in the same manner as in Example 2 except that the current density was 0.3 A / dm ² and the sulfuric acid concentration in the electrolytic solution was kept constant at 48.5 g / l over the entire period of electrolysis. .

The obtained electrolytic manganese dioxide had an alkali potential of 338 mV, a FWHM of 2.4 °, and a BET specific surface area of 21.7 m ² / g. The results are shown in Table 1 together with other evaluation results.

Contrary to Comparative Example 2, the BET specific surface area was smaller than 22 m ² / g and the reactivity was low.

Comparative Example 5
Electrolytic manganese dioxide was obtained in the same manner as in Example 2 except that the current density was 0.3 A / dm ² and the sulfuric acid concentration in the electrolytic solution was kept constant at 53.7 g / l over the entire period of electrolysis. .

The obtained electrolytic manganese dioxide had an alkali potential of 305 mV, a FWHM of 2.1 °, and a BET specific surface area of 25.3 m ² / g. The results are shown in Table 1 together with other evaluation results.

  Next, an AA type battery was assembled from this electrolytic manganese dioxide, and the discharge test described above was conducted. As a result, the relative discharge time was 104%, and the improvement in discharge characteristics was small.

It is an XRD diffraction pattern of the electrolytic manganese dioxide of the present invention. (Example 5) It is a XRD diffraction pattern of electrolytic manganese dioxide obtained by electrolysis under conventional low sulfuric acid concentration conditions. (Comparative Example 1) It is an XRD diffraction pattern of electrolytic manganese dioxide obtained by electrolysis through a conventional high sulfuric acid concentration. (Comparative Example 3) It is an XRD diffraction pattern of electrolytic manganese dioxide obtained by electrolysis at a conventional low current density. (Comparative Example 4)

Claims (9)

Alkaline potential is 310 mV or more, full width at half maximum (FWHM) of (110) plane in XRD measurement using CuKα ray as light source is 2.2 ° or more and 2.9 ° or less, and X-ray diffraction peak (110) / An electrolytic manganese dioxide, wherein the peak intensity ratio of (021) is 0.50 or more and 0.80 or less. 2. The electrolytic manganese dioxide according to claim 1, wherein the peak intensity ratio of (110) / (021) in the X-ray diffraction peak is 0.53 or more and 0.80 or less. 3. The electrolytic manganese dioxide according to claim 1, wherein an interval between (110) planes in an X-ray diffraction peak is 4.00 to 4.06 mm. 4. The electrolytic manganese dioxide according to claim 1, wherein the BET specific surface area is 22 m ² / g or more and 32 m ² / g or less. In the method for producing manganese dioxide by electrolysis in a sulfuric acid-manganese sulfate mixed aqueous solution, the electrolytic manganese dioxide characterized in that the sulfuric acid concentration in the electrolytic solution at the end of electrolysis is higher than the sulfuric acid concentration in the electrolytic solution at the start of electrolysis Manufacturing method. The method for producing electrolytic manganese dioxide according to claim 5, wherein the sulfuric acid concentration at the start of electrolysis is 25 to 40 g / L, and the sulfuric acid concentration at the end of electrolysis exceeds 40 g / L and reaches 75 g / L. A positive electrode active material for a battery, comprising the electrolytic manganese dioxide according to claim 1. A battery comprising the battery active material according to claim 7. The battery according to claim 8, wherein an open circuit voltage (OCV) before discharge exceeds 1.649V in an LR6 type battery defined by JIS-C8511.

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