JPH0123899B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to organic electrolyte batteries, and particularly to a method for manufacturing an anode using manganese dioxide as an anode active material. When manganese dioxide is used as an anode active material in an organic electrolyte battery, the water contained therein has a negative effect on cathode active materials such as lithium, so it is necessary to heat-treat the manganese dioxide to remove the water content. Conventionally, the method for heat treatment of this anode was to mix and mold manganese dioxide, a conductive additive, and a binder to make an anode, and then place the anode in a sealed furnace and heat treat it at a predetermined temperature. There is. However, when an anode heat-treated in a sealed furnace is used, the internal resistance of the battery is high, resulting in performance problems. As a result of various studies on this increase in internal resistance, the present inventors found that when an anode is heat-treated in a sealed furnace, some of the conductive additives and binders mixed in the anode undergo thermal changes. It was revealed that this is due to the formation of metamorphic products. In other words, phosphorous graphite is used as a conductive agent, but there are functional groups such as carboxyl groups at the ends of the crystal lattice, and organic substances are attached to the surface of phosphorous graphite. Furthermore, although a synthetic resin is usually used as a binder, the functional groups, attached organic matter, and a part of the binder are thermally decomposed during heat treatment. The resulting modified product is incorporated into the battery while remaining attached to the anode, and the modified product is dissolved in an electrolytic solution containing an organic solvent, and transferred to the cathode side through the separator, forming a coating on the surface of the cathode. This is one of the reasons for the increase in internal resistance. Furthermore, during heat treatment in the furnace, some of the oxygen in the air inside the furnace is used to thermally decompose the functional groups, attached organic matter, and binders and disappears, resulting in an oxygen-deficient state in the furnace. Become. Then, the temperature inside the furnace was 430℃.
Even if this is not achieved, a portion of MnO ₂ is converted to lower manganese oxides such as Mn ₂ O ₃ , which also contributes to an increase in internal resistance and causes a decrease in discharge capacity. In addition, conventionally, manganese dioxide powder was processed in a furnace with a high oxygen concentration atmosphere of 50% by volume or more.
A method has been proposed in which the material is heat treated at a temperature of around 400°C, and then a conductive additive and a binder are mixed therein and pressure molded to form an anode. However, with this method, some of the manganese dioxide may reach a much higher temperature than the set furnace temperature, and therefore
A part of MnO ₂ changes to Mn ₂ O ₃ , causing an increase in internal resistance and variations in discharge performance. An object of the present invention is to provide a method for manufacturing an anode for an organic electrolyte battery that overcomes the drawbacks of the prior art and has excellent discharge performance. In order to achieve this object, the present invention involves forming an anode using manganese dioxide having a γ-type crystal structure, and then sequentially supplying and discharging oxygen-containing gas into the heated atmosphere of the anode to achieve a predetermined temperature. Heat treatment is performed to convert manganese dioxide in the anode to γ.
It is characterized by being transformed into an intermediate between the β-form and the β-form and used as an anode active material. Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an organic electrolyte battery according to an embodiment of the present invention. 100 parts by weight of electrolytic manganese dioxide and 10 parts by weight of phosphorous graphite
An anode 1 made of a mixture of 1 part by weight and 1 part by weight of polytetrafluoroethylene is inserted into the bottom of an anode can 2, and an electrolyte absorber 3 made of a nonwoven polypropylene fabric is placed thereon. The anode 1 and the electrolyte absorber 3 are each impregnated with a predetermined amount of an electrolyte in which 1 mole of lithium perchlorate is dissolved in a solvent in which propylene carbonate and dimethoxyethane are mixed at a volume ratio of 1:1. be done. A cathode terminal plate 5 is fitted into the opening of the anode can 2 via a gasket 4 made of polypropylene.
A stainless steel net 6 is welded to the inner surface of the cathode terminal plate 5, and a cathode 7 made of metallic lithium is pressed onto this.The cathode 7 faces the anode 1 with the separator 3 in between. Next, a method for manufacturing the anode 1 will be explained with reference to FIGS. 2 to 4. The anode 1, which is formed by mixing electrolytic manganese dioxide (γ-type MnO ₂ ), a conduction aid, and a binder in a predetermined ratio as described above and press-molding the mixture, is stored in a heat-resistant cassette 8 shown in FIG. 3. . A plurality of through holes 9 are provided on the outer peripheral wall of the cassette 8 to improve air circulation, and inside the cassette 8, as shown in FIG. A large number of anodes 10 and anodes 1 are stored so as to be alternately stacked on top of each other. The cassette 8 containing the anode 1 is stacked on a perforated plate 13 installed in the inner chamber 12 of the electric furnace 11, as shown in FIG. In this inner chamber 12,
An air supply pipe 14, an exhaust pipe 15, and a thermocouple 16 are inserted, respectively, and a heater 18 is arranged on the peripheral wall 17 of the electric furnace 11. This heater 18
The temperature inside the furnace in the inner chamber 12 is maintained at approximately 400°C,
Air 20 is sent from the air supply pipe 14 into the interior chamber 12 by a blower 19 at a rate of 1/min. The air 20 is heated by the heater 18, passes through the perforated plate 13, flows along the surface of the anode 1 housed in the cassette 8, and is discharged from the exhaust pipe 15. By performing this heat treatment for 4 hours, adhering water and crystal water of manganese dioxide are removed, and the crystal structure is changed to γ.
It becomes an intermediate between form and β form. The heat treatment temperature of the anode is suitably about 250-430°C, preferably about 370-430°C. In the above embodiments, air was used as the oxygen-containing gas, but if it is desired to increase the oxygen concentration in the gas, oxygen gas alone or a mixture of oxygen and other gases such as nitrogen gas may be used. It is preferable that the gas containing oxygen be supplied and discharged into the heating atmosphere continuously during the heat treatment of the manganese dioxide, but it may be carried out intermittently. The following table shows the performance of lithium batteries made using manganese dioxide treated under various conditions. The processing temperature and processing time were all 400℃.
The test time was 4 hours, and the performance test was conducted one day after the battery was assembled, and the number of samples was 30 for each type of battery. The range in the table indicates the variation range, and the numerical value in parentheses indicates the average value.

【table】

[Table] As is clear from this table, batteries A and B using anodes heat-treated in a closed furnace have high internal resistance and a large variation range, which poses a quality problem. On the other hand, batteries C and D, which use anodes that have been heat-treated while supplying and discharging oxygen-containing gas into and out of the furnace, have low internal resistance, small variations in performance, and are stable in quality. The theoretical basis for why the performance is so good is not clear, but
By sequentially supplying and distributing oxygen-containing gas into the furnace, local overheating of the manganese dioxide is prevented and the temperature is kept almost constant. This is thought to be due to the fact that these thermal decomposition products are carried away by the circulating gas, and these products, which have an adverse effect on battery performance, do not enter the battery. The present invention has the above-described configuration, and can produce an anode for an organic electrolyte battery having excellent performance.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part of a lithium battery using an anode made according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of an electric furnace used in an embodiment of the present invention.
FIG. 3 is a perspective view of a heat treatment cassette used in the electric furnace, and FIG. 4 is a sectional view showing the state in which the anode is housed in the cassette. 1...Anode, 11...Electric furnace, 14...Air supply pipe, 15...Exhaust pipe, 19...Blower, 20...
…air.

Claims (1)

[Claims] 1. After forming an anode using manganese dioxide having a γ-type crystal structure, a predetermined heat treatment is performed while sequentially supplying and discharging oxygen-containing gas into the heated atmosphere of the anode, and the temperature inside the anode is A method for producing an anode for an organic electrolyte battery, which is characterized by converting manganese dioxide into a γ-form and a β-form intermediate to produce a positive electrode active material.