JPH075319B2 - Method for producing beta manganese dioxide - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for producing beta-manganese dioxide. Specifically, the present invention converts gamma-manganese dioxide into a beta crystalline phase in a very short time, and uses the beta-manganese dioxide as a cathode active material in a non-aqueous battery. Regarding the method to use.

DESCRIPTION OF THE PRIOR ART Manganese dioxide manufacturers generally use the aqueous method of electrolytes to produce manganese dioxide with a gamma crystal structure. It has long been known that before gamma-manganese dioxide can be used as a cathode material in lithium batteries, it must be heated to remove water and convert the crystal structure from the gamma phase to the beta-dominant phase. U.S. Pat. Nos. 4,133,856 and 4,297,231 disclose heating manganese dioxide in the temperature range of 250 ° C to 430 ° C for 2 hours or more to remove water and convert it to the beta crystalline phase. Some manufacturers perform heat treatment for up to 20 hours (see “8. Lithium-Manganese D
ioxide Cells "by H.Ikeda, Lithium Batteries, ed.jPG
abano, Academic Press, (New York, 1988)). When manganese dioxide decomposes, lower or lower oxides
Therefore, until now, it was said that the treatment had to be performed at a temperature of 450 ° C. or lower. To support this,
U.S. Pat. No. 4,133,856 states that heat treatment at 430 ° C or above
It is disclosed that Mn ₂ O ₃ is generated, and when Mn ₂ O ₃ is used as a positive electrode of a battery, this Mn ₂ O ₃ has an adverse effect. Figures 1 and 2 of this U.S. patent show that the utilization of heat treatment temperatures is low above 375 ° C.

In the case of this heat treatment, there is a problem that mass production cannot be performed because the time required for heating to a predetermined temperature is too long. In the conventional method, many ovens must be prepared to produce the required amount. Therefore, it is required to shorten the conventional heat treatment time which requires several hours.

In the present specification, the terms "beta manganese dioxide" and "beta conversion" mean that gamma manganese dioxide is 100%.
It should be understood that it does not mean that it is converted into beta, but that most of the gamma crystal phase is converted into beta crystal phase by the heat treatment of manganese dioxide. As described below, manganese dioxide is preferably less than 100% beta. Thus, "beta manganese dioxide" herein is actually a "mix" of gamma and beta.

The present invention is a short-term heat treatment of manganese dioxide,
It is an object of the present invention to provide a method capable of obtaining beta manganese dioxide having substantially the same performance as that of manganese dioxide obtained by a conventional heat treatment when used in a battery.

A further object of the present invention is to provide a method capable of continuously producing the manganese dioxide.

(Technical Means) The present invention is based on the finding that heating at a temperature of 450 ° C. or higher does not adversely affect the battery performance. This is because the conversion rate of manganese dioxide from gamma to beta is much faster than the decomposition rate of manganese dioxide to low oxides in this temperature range. Therefore, according to the present invention, granular manganese dioxide at 1
Gamma MnO ₂ can be converted to beta by heating for less than an hour, and the decomposition of manganese dioxide at this time is also minimized.

The heat treatment process is composed of the following three time sections.

(1) Time required to heat MnO ₂ from room temperature to heat treatment temperature ... tr (2) Time to heat MnO ₂ at heat treatment temperature ... th (2) Temperature rise to cool MnO ₂ from heat treatment temperature to room temperature Time ... tc To shorten the total heat treatment time, it is important to shorten the time of tr and tc. Thus, th becomes the rate-determining time of the entire heat treatment process.

Gamma MnO ₂ is available in the form of fine powder. In order to shorten the tr time, it is necessary to increase the heat transfer efficiency from the heating furnace to the individual particles of MnO ₂ powder. Furthermore, in order to be able to perform a uniform beta transformation,
The whole mass of MnO ₂ must be heated uniformly. The method of the present invention is carried out by passing the MnO ₂ powder through a multi-zone rotary tube furnace (also known as a rotary kiln or rotary dryer), thus achieving uniform heating in a very short time. it can.

Description of Embodiments The features and advantages of the present invention will be described with reference to the drawings.

In a rotary tube furnace, an elongated steel tube is rotatably arranged and a heating element is provided adjacent to a part of the outer surface of the tube. The tube is tilted downwards from the end for powder loading to the end for powder delivery. The powder is continuously fed from one end and rolls towards the longitudinal direction of the slowly rotating tube. With the rotation of the tube, the powder is constantly moving, and the particles in contact with the heated surface of the tube are constantly changing. Therefore, the thermal efficiency of the powder can be greatly improved. This makes tr very short. Once the powder reaches the heat treatment temperature, it passes through the remaining heating zone while rolling for a time corresponding to th. The powder then passes through the cooling zone and out of the tube.

As a rotary tube furnace suitable for the heat treatment for making the beta crystalline phase from gamma-manganese dioxide a main part, a rotary tube furnace manufactured by Harper Electric Furnace Company (Lancaster, NY) can be exemplified. The tubes of a rotary tube furnace are made of stainless steel and are about 3.5 meters long and 17.8 centimeters in diameter. The inner surface of the tube should be made smooth. The tube can be tilted within a range of 0-5 degrees. The tube rotation can be adjusted within the range of 0-18 RPM. The transit time of manganese dioxide is determined by the inclination angle of the tube and the rotation speed. The furnace has three independent heating zones formed in succession, each zone being 0.6 meters long. The first zone starts at a position 0.6 m downstream from the inlet of the pipe. Therefore, the final zone ends 2.4 meters downstream from the pipe entrance. The remaining 1.1 meters to the outlet of the pipe will be a cooling zone.

The temperature profile of the manganese dioxide as it passes through the tube will be explained based on the following experiments. Heat treatment temperature is 400
It carried out about three types, ℃, 450 ℃, and 500 ℃. Each heat treatment was performed as follows. All three heating zones were set to the same temperature. Manganese dioxide is 0.27 kg /
The tube was fed at a rate of minutes. The inclination angle of the pipe is 1 degree,
The rotation speed was 3 RPM. As a result, the powder passage speed is
It was 0.06 m / min. When the furnace is started from room temperature, it generally takes 2 to 3 hours to reach a so-called steady state condition. This is the condition that is believed to have reached thermal equilibrium between the heating element, tube and manganese dioxide. Install a thermocouple along the length of the tube 0.6
Since it is installed every meter, the manganese dioxide fills the thermocouple as the manganese dioxide powder passes through the tube. The steady state is the time when the temperature fluctuation of each thermocouple disappears. FIG. 1 shows temperature distributions in the longitudinal direction of the tube in a stable state for three kinds of heat treatment temperatures.
Each heat treatment was performed for about 2 hours after reaching steady state in order to collect sufficient material for analysis. As shown in FIG. 1, the third zone between the 6 foot and 2.4 meters downstream of the tube reaches the heat treatment temperature. Therefore, manganese dioxide is heated at the maximum heating temperature of each processing temperature for about 10 minutes. The gamma to beta conversion of the crystalline phase is believed to begin at about 350 ° C. First
The table shows that heating times above this temperature are longer than 10 minutes. Table 1 shows the times for the three heat treatment temperatures.

As shown in Table 1, the higher the temperature of the heating zone, the faster the heating time to reach the beta conversion temperature (350 ° C). As a result, the time above the beta conversion temperature will be longer than if the same material was treated at a lower temperature. Therefore, by keeping the temperature of the heating zone at 450 ° C. or higher, the total time of heat treatment can be shortened. If the heating is performed at a temperature of 500 ° C. or higher, the heat treatment time should be carefully considered and the heating should be performed in a short time so that a lower oxide of manganese is not formed. 500
After heat treatment at 60 ° C. for 60 minutes, X-ray analysis showed that low oxide was not formed, but after heat treatment for 105 minutes, the presence of low oxide was recognized. The figure also shows that the manganese dioxide did not reach the temperature of the heating zone. Therefore, in order to reach the predetermined heat treatment temperature, it is necessary to set the temperature slightly higher than the predetermined heat treatment temperature.

The materials obtained by the heat treatments at the three types of temperatures described above were analyzed to determine the beta conversion%. This analysis was performed using X-ray diffraction in the following manner. Take a sample of each powder,
X-ray diffraction patterns were determined using CuKα radiation. A monochromator is then placed between the sample and scintillation detector to remove the fluorescent radiation. 110 reflection line (refle
ction) was applied to the sample to determine the reflection count, and the beta conversion was determined by comparing with the reflection count of the 100% beta standard sample. The ratio of counts indicates the% beta conversion of the sample.

In order for manganese dioxide to exhibit the desired performance as a positive electrode active material for lithium batteries, beta% is 60%.
% And above and below 90%. The use of manganese dioxide outside of this range has a positive electrode utilization (ut) higher than that within the range.
ilization) is inferior. The beta% is preferably in the range of about 65-85%. Table 1 shows beta conversion rates at three temperatures. Each numerical value shows the average value of three samples taken from those obtained under the same processing conditions. From this result, the heating zone was
When set to, manganese dioxide in the gamma crystal phase is about 60
It can be seen that the th required to convert to beta beta manganese dioxide is about 19 minutes. When the amount of change in manganese dioxide is within this range, it is suitable for use as a positive electrode active material in non-aqueous batteries. When the heating temperature is 400 ° C., it is suitable for a conventional heat treatment method that takes a long time, but in the case of the heat treatment that takes a short time as in the present invention, the beta conversion rate is about 40%, Not suitable.

The advantage of the present invention is that without forming harmful low oxides,
It is possible to continuously convert a large amount of gamma-manganese dioxide into the beta phase in a time shorter than the conventional treatment time. Next, a preferred embodiment when the processing time is extended to 48 hours will be shown. Each heating zone was set at 475 ° C. The angle of the tube is 1
The rotation speed of the tube was 3 RPM. The feeding speed of the heated object is
It was 0.27 kilograms / minute and the transit time through the length of the tube was 55 minutes. The time required to reach a steady state was about 2 hours. All the manganese dioxide collected during this time was slapped. Next, heat treatment was performed continuously for 46 hours, and samples were periodically taken. Thermocouples were installed every 0.6 meters along the length of the tube. Second temperature distribution of manganese dioxide
Shown in the figure. The heating temperature reaches a maximum of about 470 ° C, and the manganese dioxide is heated in the range of 450 to 470 ° C for about 10 minutes.

At the end of 46 hours, about 720 kilograms of manganese dioxide were collected. The beta conversion of the samples obtained through this treatment was about 80% on average. The x of MnOx indicates the oxidation state of manganese. The x value of gamma manganese dioxide is
Since other types of manganese exist before the heat treatment, x = 1.95. The value of x was determined by chemical analysis of the material prepared according to the present invention. When the value of x is 1.95, it indicates that decomposition of manganese dioxide has not occurred. For comparison,
When heated to 350 ℃ by the conventional batch method, 85.5 kg of about 75% beta manganese dioxide was obtained after 24 hours of heat treatment. On the other hand, in the case of the present invention, as described above,
The amount obtained in the same treatment time was 389 kilograms.
As described above, in the case of producing beta-manganese having a quality suitable for the positive electrode, according to the above-mentioned conditions of the present invention, a production amount about four times that of the conventional method can be achieved. In the case of the present invention,
At a temperature of 450 ° C or higher, th can be shortened, so that the production amount can be further increased.

FIG. 3A shows the X-ray diffraction pattern of manganese dioxide heat-treated according to the present invention, and FIG. 3B shows the X-ray diffraction pattern of manganese dioxide heat-treated by the conventional method. The diffraction pattern was determined by using CuKα radiation and scanning at an angle 2θ of 15 to 40 degrees. Beta phase lattice space is 110
It becomes the reflection position. In the conventional method, it was 81% beta, whereas in the method of the present invention, it was 82% beta. The diffraction pattern is substantially the same as that of the method of the present invention and that of the conventional method. The lack of reflection at about 33 degrees indicates the absence of harmful lower oxides.

The beta conversion can be improved by making the holding time of the manganese dioxide at the heat treatment temperature longer than 10 minutes. However, at the heat treatment temperatures mentioned above, most of the beta conversion is done in the first 10 minutes. For example, when the heat treatment temperature is 450 ° C, the beta conversion rate is about 60% in the first 10 minutes, whereas
Even if heated for 90 minutes, it only rises to about 65%. Thus, beta conversion is accelerated by heating at high temperature for a short time rather than heating at low temperature for a long time. In the case of the present invention, 450
Manganese dioxide can be heated at temperatures above ℃ for up to 1 hour, but heating time at temperatures above 450 ℃ is 30
It is desirable to be within minutes.

As described above, it is desirable to make tr the shortest in order to shorten the total heat treatment time. In the above heat treatment, the time of tr was less than 1 hour. Even if this time is 1 hour or more, since the lower oxide is not formed at the heating temperature at this time, it does not adversely affect the finally produced manganese dioxide. However, to maximize manganese dioxide production,
It is desirable that the tr time does not exceed 1 hour. For example, the time to reach the temperature of gamma-manganese dioxide of 465 ° C or higher is tr within 1 hour, and manganese dioxide is converted to beta-phase to convert manganese dioxide to the beta phase.
The time th for holding at a temperature of 5 ° C or higher shall be within 30 minutes.

After heat-treating the gamma-manganese dioxide to convert it into the beta phase, the positive electrode can be produced in the conventional manner. For example,
The heat treated manganese dioxide is mixed with a conductive agent and a binder. Next, the mixture is formed into a positive electrode having a desired structure. In the case of a button type battery, the mixture is pressed into a disk shape, and the disk body is pressed into a positive electrode can of the button type battery to form a positive electrode. In the case of a spirally wound battery,
The mixture is applied to both sides of the conductive metal grid and compressed between the rollers to make a tight fit. By forming the positive electrode long and thin, the positive electrode can be spirally wound together with the negative electrode (anode) and the separator.

Any suitable conductive agent can be used as long as it is conventionally used in the art for the anode of a non-aqueous battery, for example, acetylene black or carbon black. Further, as the binder, any binder may be used as long as it is used for the anode of manganese dioxide in a non-aqueous battery and can exhibit sufficient bonding characteristics. As a suitable binder, polytetrafluoroethylene, tetrafluoroethylene / hexafluoroethylene copolymer,
There is a tetrafluoroethylene / ethylene / chlorotrifluoroethylene copolymer.

The positive electrode thus formed is subjected to heat treatment to remove the absorbed water. This heat treatment is generally 15
It is performed in a dry atmosphere or in a vacuum in the range of 0 to 300 ° C. After this heat treatment, the positive electrode is incorporated into the battery.

The composition of the mixture made is based on the previously mentioned beta-manganese dioxide 91
%, Carbon 6%, and polytetrafluoroethylene 3%. An expanded stainless steel grid is coated on both sides with this mixture and the coated grid is then compressed between rollers. The positive electrode thus formed is heat-treated in vacuum at a temperature of 200 ° C. next,
The dry cathode consists of a lithium foil anode and micropores (microp
orous) Wrap in a spiral with a polypropylene separator. The spirally wound electrode stack is inserted into a cylindrical can. Next, a known electrolyte is placed in the can and the lid is crimped at an appropriate position. A tab is attached to each electrode. One tab connects to the can and the other tab connects to the lid. In this way, the can and lid can function as electrode terminals.

The battery containing beta-manganese dioxide produced according to the method of the present invention as the positive electrode active agent, even compared to the battery containing manganese dioxide obtained by the conventional heat treatment,
It has substantially the same electrical discharge characteristics. in this way,
Rapid heating as in the present invention does not adversely affect the electrochemical properties of manganese dioxide.

Within the scope of the present invention, various modifications can be added to the heat treatment method described above. For example, gamma-manganese dioxide can be preheated at a temperature of 300 ° C. or lower before charging it into a rotary tube furnace. This has the effect of shortening the residence time of manganese dioxide in the heating zone and improving the production amount. If the heat released from manganese dioxide in the cooling zone is used for preheating manganese dioxide,
Energy efficiency can be further improved. Furthermore, by effectively removing the heat from the cooling zone, the overall processing time can be shortened.

Techniques related to rotary kilns are well known, and there is the following relationship between the tilt angle, the rotation speed, and the residence time in the pipe.

T = (KL) / (DRtan (A)) where T is the transit time, K is a constant, L is the length of the tube, R is the number of revolutions (RPM), and A is the angle of the tube. In the above-mentioned embodiment, the tube angle is 1 degree and the rotation speed is 3 RPM, but the same residence time can be obtained by using other conditions.
Also, the residence time can be changed. For the rotary tube furnace described above, the manganese dioxide feed rate is preferably 0.05 to 0.45 kilograms / minute, but can be increased up to 1.35 kilograms / minute. If a furnace larger than the one described above is used, the throughput can be further increased.

The tube inner surface of the above rotary tube furnace is finished to be a smooth surface. The manganese dioxide powder can be mixed better by changing the shape of the inner surface of the tube. For example, it is possible to provide long fins (longitudinal fins) at intervals of 90 degrees in parallel with the longitudinal direction of the tube. This fin functions as a lifter for picking up manganese dioxide, and picks up manganese dioxide higher than in the case of a smooth inner surface and returns it to the center of the tube. Further, by forming the inner surface of the pipe in a corrugated shape, it is possible to collect and move the material while rotating and return it to the center of the pipe.

The water content of gamma-manganese dioxide is less than 5% when it is obtained from the manufacturer. Since most of this water is removed during the heat treatment, it is necessary to take measures to allow the water to escape from the furnace. Tilting the rotating tube has the additional advantage that water vapor can escape from the upper end of the tube by the so-called "chimney effect". By passing the inert gas from the lower end to the upper end of the tube, the vapor removal effect of water can be enhanced. However, if the gas flow rate is too high, the manganese dioxide particles will ride on the gas flow and pass through the tube, so the flow rate should not be increased too much.

Other than the rotary tube furnace, there is a means for rapidly heating manganese dioxide. For example, a fluidized bed (flui) that allows heated air to pass through.
Rapid heating can also be performed with a dized bed). In this method, gamma manganese dioxide powder is transferred to a fluidized bed chamber. The manganese dioxide powder is dispersed in the fluidized bed by the rapid upward flow of hot air, and the powder is heated to the heat treatment temperature in a short time. The powder is allowed to remain in the chamber for a sufficient time to be beta converted.
The converted powder is then collected, removed from the chamber and cooled. This heating method may be a continuous type or a batch type.

Modifications may be made to the method described above within the scope of the invention. The specific description of the method of the present invention is illustrative and should not be construed as limiting the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the position and temperature of a rotary tube furnace plotted under three different heat treatment temperatures.
FIG. 2 is a graph showing the relationship between the position and temperature of the rotary tube furnace when the temperature inside the furnace is 475 ° C. FIG. 3A is a diagram showing an X-ray diffraction pattern of manganese dioxide treated by the method of the present invention. FIG. 3B is a diagram showing an X-ray diffraction pattern of manganese dioxide treated by the conventional method.

Claims (10)

[Claims] 1. Granular gamma-manganese dioxide is supplied to a chamber, and while the gamma-manganese dioxide is heated in the chamber at a temperature of 450 ° C. or higher, the relative position of MnO ₂ granules is continuously changed to 450 ° C. or higher. The method for producing beta-manganese dioxide, wherein manganese dioxide is held at the temperature for a predetermined time, manganese dioxide is converted into a beta crystalline phase without producing harmful amounts of lower oxides, and the heat-treated manganese dioxide is taken out of the chamber. 2. The time required for the manganese dioxide to reach a temperature of 450 ° C. or higher is 1 hour or less, and the average manganese dioxide granules are kept at a temperature of 450 ° C. or higher for 1 hour or less. The method according to 1. 3. The time required for the gamma-manganese dioxide to reach a temperature of 465 ° C. or higher is 1 hour or less, and the manganese dioxide can be converted to the beta phase in an amount of 46 hours.
The method according to claim 1, wherein the holding time at a temperature of 5 ° C or higher is within 30 minutes. 4. The method of claim 1, wherein manganese dioxide is continuously fed into the chamber. 5. The method according to claim 4, wherein gamma manganese dioxide is supplied to the chamber at a rate of 0.05 to 1.3 Kg / min. 6. The gamma-manganese dioxide is preheated at a temperature of 300 ° C. or lower before being supplied to the chamber.
The method described in. 7. The method according to claim 1, wherein the beta crystal phase of manganese dioxide after heat treatment is 60 to 90%. 8. The method of claim 1, wherein the chamber is a rotary tube furnace. 9. A cathode which is produced by further producing a mixture of manganese dioxide, a conductive agent and a binder after heat treatment, coating the mixture on an expanded metal grid and compressing the coated grid between the rollers. The method according to claim 7, wherein the cathode is heated and the cathode is heated at a temperature of 150 to 300 ° C. to remove absorbed water. 10. The method according to claim 9, wherein the conductive agent is selected from the group consisting of carbon black, acetylene black, and mixtures thereof, and the binder is polytetrafluoroethylene.