Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing inorganic compound
Reexamination Certificate
2001-08-30
2003-10-07
Phasge, Arun S. (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing inorganic compound
C205S541000, C429S224000
Reexamination Certificate
active
06630065
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a powder of electrolytic manganese dioxide which has specific properties and is suitable for use as a positive-electrode active material in, e.g., manganese dry cells, in particular, alkaline manganese dry cells. The invention further relates to a process for producing the powder.
DESCRIPTION OF THE RELATED ART
Powders of electrolytic manganese dioxide are known as the positive-electrode active material of, e.g., manganese dry cells or alkaline manganese dry cells, and have advantages of excellent storage stability and inexpensiveness.
In particular, the alkaline manganese dry cells employing a powder of electrolytic manganese dioxide as the positive-electrode active material have excellent discharge characteristics in heavy discharge use. Because of this, these dry cells are extensively used in applications ranging from electronic cameras, portable tape recorders, and portable information apparatus to game machines and toys, and there is a rapidly growing demand for these. However, the alkaline manganese dry cells have a drawback that as the discharge current increases, the amount of the powder of electrolytic manganese dioxide which can be utilized as a positive-electrode active material decreases and the discharge voltage becomes low, resulting in a considerably reduced discharge capacity. In other words, the alkaline manganese dry cells have a drawback that when the cells are used in apparatus operated at a high current, the electrolytic manganese dioxide packed as a positive-electrode active material is not sufficiently utilized, resulting in a reduced operating time.
The most effective means for overcoming the drawback described above is to employ a powder of electrolytic manganese dioxide which has a higher potential in terms of the potential of a suspension thereof in 40% aqueous KOH solution as measured using a mercury/mercury oxide reference electrode as a base (hereinafter referred to as “alkali potential”) so as to heighten the discharge voltage of a cell. The higher the alkali potential of electrolytic manganese dioxide, the more the time period can be prolonged in which an allowable discharge voltage can be maintained in actual use. Furthermore, by packing a powder of electrolytic manganese dioxide in a sufficient amount into a cell, the substantial cell capacity can be increased and, hence, the time period in which an allowable discharge voltage can be maintained in actual use can be further prolonged. Namely, the powders of electrolytic manganese dioxide especially for use in alkaline manganese dry cells are required to have a sufficiently high alkali potential or have both a high alkali potential and high packability.
However, the conventional powders of electrolytic manganese dioxide have an insufficient alkali potential and it has been difficult to attain high packability.
The potential of conventional powders of electrolytic manganese dioxide in an alkaline electrolyte is 250 mV when measured using a mercury/mercury oxide reference electrode as a base. This value of potential corresponds to a voltage of 1.55 V in the case of alkaline manganese dry cells employing zinc metal as a negative-electrode active material. When a current of 1 A is taken out of such an alkaline manganese dry cell, the cell voltage decreases by 350 mV to 1.20 V. Since the minimum voltage required for an alkaline manganese dry cell to operate an instrument is generally 0.9 V, the width of the usable discharge voltage is about 300 mV at the most, ranging from about 1.20 V to 0.9 V, because the potential of the powder of electrolytic manganese dioxide in an alkaline electrolyte is 250 mV at the most.
Especially for use as the positive-electrode active material of an alkaline manganese dry cell, a powder of electrolytic manganese dioxide is compacted into a disk or ring form and this powder compact is used as the positive electrode of the cell.
When this powder compact has a high density &rgr;, the powder of electrolytic manganese dioxide can be packed in an increased amount into the cell to thereby increase the cell capacity. However, the powder compacts formed from the conventional powders of electrolytic manganese dioxide by compacting 5 g of the powder at a pressure of 3 ton into a disk having a diameter of 2 cm have a density &rgr; of 3.2 g/cm
3
at the most. Namely, the conventional powders have had a drawback of insufficient packability.
Furthermore, the powder of electrolytic manganese dioxide disclosed in PCT International Publication WO 00/37714 (Karr Mcgee, U.S.A.) has the following and other drawbacks. Since this powder is produced through low-current-density electrolysis, it has such a particle constitution that the content of particles not smaller than 74 &mgr;m in terms of particle diameter is as high as 9%. The presence of such coarse particles results in a reduced coefficient of use during discharge at a high current. Moreover, the powder necessitates a compaction pressure of 4.5 ton for obtaining a necessary packing density, so that the impregnation of the resulting positive-electrode mix with water, which is necessary for discharge from the powder of electrolytic manganese dioxide, is insufficient and, hence, a sufficient coefficient of use cannot be obtained. In addition, the conventional powder has poor productivity because the electrolysis is conducted at a low current density.
SUMMARY OF THE INVENTION
One object of the invention is to provide a powder of electrolytic manganese dioxide which is especially for use as the positive-electrode active material of an alkaline manganese dry cell, and which has a high alkali potential in an alkaline electrolyte or has a high potential in an alkaline electrolyte and high packability.
Another object of the invention is to provide a process for producing the powder.
The present inventors made intensive investigations. As a result, they have succeeded in producing a powder of electrolytic manganese dioxide which has a high potential in an alkaline electrolyte or has a high potential in an alkaline electrolyte and high packability. Furthermore, a process for producing this powder of electrolytic manganese dioxide has been completed as a result of investigations on conditions for electrolysis for producing electrolytic manganese dioxide, i.e., electrolysis temperature and electrolyte concentration.
The invention provides a powder of electrolytic manganese dioxide which has a high potential in an alkaline electrolyte or has a high potential in an alkaline electrolyte and high packability. Specifically, the invention provides a powder of electrolytic manganese dioxide which has a maximum particle diameter of 100 &mgr;m or smaller, a content of 1 &mgr;m and smaller particles of lower than 15% by number, and a median diameter of from 20 to 60 &mgr;m, and which has a potential of 270 mV or higher in terms of the potential of a suspension of the powder in 40% aqueous KOH solution as measured using a mercury/mercury oxide reference electrode as a base. This powder of electrolytic manganese dioxide is preferably one which, when compacted at a pressure of 3 ton/cm
2
, gives a compact having a density (&rgr;) in the range of from 3.20≦&rgr;≦3.35.
The invention further provides a process for producing the powder of electrolytic manganese dioxide which comprises preparing an aqueous solution of manganese sulfate and sulfuric acid which has a bivalent manganese concentration of from 35 to 60 g/L, a sulfuric acid concentration of from 35 to 60 g/L, and a temperature of 90° C. or higher, using the aqueous solution as an electrolyte to conduct electrolysis in an electrolytic cell equipped with an anode and a cathode at a current density of from 70 to 100 A/m
2
to electrolytically deposit manganese dioxide on the anode, removing the electrolytic manganese dioxide deposit from the anode, pulverizing the resulting solid masses of the electrolytic manganese dioxide, and then classifying the resulting particles.
DETAILED DESCRIPTION OF THE INVENTION
In the case where the powder of electrol
Chiba Kazuyuki
Ichida Masanori
Takahashi Ken'ichi
Tsuyoshi Toru
Phasge Arun S,.
Tosoh Corporation
LandOfFree
Powder of electrolytic manganese dioxide and process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Powder of electrolytic manganese dioxide and process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Powder of electrolytic manganese dioxide and process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3153156