JP2011169504A - Solid-phase reaction baking method for powder, and solid-phase reaction baking furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for quantity production capable of uniformly and economically performing solid-phase reaction baking on powder received in a sagger while preventing dispersion of baking quality between its surface layer and inside. <P>SOLUTION: In this solid-phase reaction baking method for the powder for performing solid-phase reaction baking on the powder received in the sagger 3 by heating the powder in a continuous furnace, the powder is heated to a temperature just before the maximum temperature by a resistance heater 8 disposed in a furnace body, then microwave is applied thereto by a microwave heating device 11 to make the powder generate heat, and to equally heat the surface layer and the inside, and then the maximum temperature is kept by the resistance heater 8 again. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a solid phase reaction firing method and a solid phase reaction firing furnace for powders used in the manufacture of lithium ion batteries, ceramic capacitors and the like.

  Various lithium compounds are used as a raw material for a positive electrode material of a lithium ion battery, and barium titanate is used as a raw material for a ceramic capacitor. Various methods have been proposed in the laboratory as these production methods. However, as an industrial production method capable of mass production, the precursor powder of these powders is placed in a container called a mortar and placed in a furnace. A general method is to heat and raise the temperature to a predetermined temperature determined by the compound, and maintain the maximum temperature for a predetermined time to advance the solid phase reaction.

  Although the furnace atmosphere varies depending on the type of powder, a resistance heater that does not cause contamination of the furnace atmosphere and is easy to control temperature is widely used as a heating means. The resistance heater is installed on the ceiling of the furnace and radiates and heats the mortar and the precursor powder. Further, since the furnace atmosphere is also heated, convection heating is also performed in the furnace.

  Usually, the thickness of the powder layer in the mortar is about 50 to 100 mm, and the heating is mainly performed from the surface layer portion. Moreover, these powders do not have a very high thermal conductivity. For this reason, although the temperature of the powder in the surface layer portion in the mortar tends to rise, the temperature of the powder inside becomes slow, and a temperature difference inevitably occurs in the temperature raising step. This temperature difference is gradually eliminated while the maximum temperature is maintained for a predetermined time, but the powder on the surface layer is maintained at the maximum temperature for a relatively long time, whereas the internal powder is the maximum. Since the time during which the temperature is maintained is shortened, the progress of the solid-phase reaction varies. In particular, recently, the required particle size of the powder is 10 μm or less, which is smaller than in the past. Therefore, accuracy is required for the temperature condition range for firing, and a slight difference in solid-phase reaction conditions greatly affects the firing quality. Tend to influence.

  In order to solve the above problem, the temperature raising rate may be lowered, but this causes a decrease in productivity and an increase in the size of the furnace body. Therefore, as shown in Patent Document 1, it has been proposed to heat powder using a microwave. Since the heating by the microwave is a method of causing the powder itself to generate heat, only the surface layer portion is not intensively heated unlike the heating by the resistance heater. However, in order to implement this heating method industrially, there are many problems as follows, and application to mass production facilities is not easy.

First, although microwaves are extremely effective for heating a substance containing water molecules, ceramic powders have a very small loss coefficient compared to water, so that they do not generate heat easily, especially in a low temperature range.
Secondly, since the loss factor of ceramic tends to increase with temperature, if a high temperature region is partially generated due to non-uniformity of microwave irradiation, a runaway phenomenon in which the temperature of that portion increases at an accelerated rate occurs.
Third, compared to resistance heaters, the microwave heating apparatus has an equipment cost of 10 times or more, and it is economically difficult to apply to mass production equipment.

JP 2004-168575 A

  Accordingly, the object of the present invention is to solve the above-mentioned conventional problems, and to uniformly and economically prevent the powder stored in the mortar from being uniform in the firing quality between the surface layer portion and the inside. It is to provide a mass production technique that can be fired by reaction.

  The solid phase reaction firing method of the powder of the present invention made to solve the above problems is a method of performing solid phase reaction firing by heating the powder stored in a mortar with a continuous furnace, The powder is heated to a temperature just before the maximum temperature by a resistance heater installed in the chamber, and the surface layer and the inside are soaked by irradiating microwaves to generate heat, and then the resistance heater is again heated It is characterized by maintaining at the maximum temperature. Is.

  The powder is, for example, a precursor powder for a positive electrode of a lithium ion battery or a precursor powder of barium titanate. Further, mullite cordierite, alumina, and carbon mortar can be used as the mortar. Further, the temperature immediately before the maximum temperature can be a temperature of (maximum temperature-30 ° C) to (maximum temperature-100 ° C).

  The solid phase reaction firing furnace of the powder of the present invention is a continuous furnace for heating and solid phase reaction firing while transporting the powder stored in the sagger, and in the temperature raising zone and the maximum temperature holding zone. A resistance heater is arranged, and a microwave heating device is arranged in a soaking zone sandwiched between them.

  According to the present invention, most of the process including the temperature raising step and the maximum temperature holding step of the powder is surface-heated using a resistance heater excellent in economic efficiency, and only the temperature region immediately before the maximum temperature is heated by the microwave. . For this reason, the temperature difference between the surface layer part in the mortar and the inside, which is inevitably generated by surface heating with a resistance heater, can be easily eliminated by heating the powder itself with microwaves, Uniform solid phase reaction firing can be performed.

  Moreover, since the loss factor of the ceramic increases at high temperatures, the heating efficiency by microwaves is also good. Moreover, an inexpensive resistance heater is disposed in the temperature raising zone and the maximum temperature holding zone, and the microwave heating device only needs to be disposed in the soaking zone sandwiched between them, so that the equipment cost and running cost are reduced, Implementation on an industrial scale is possible.

It is sectional drawing of the (fired temperature-time) curve and furnace body which shows embodiment of this invention. It is explanatory drawing of the effect of this invention. It is a (loss factor-temperature) curve of various substances.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic view showing an embodiment of the present invention, in which an upper stage shows a set temperature curve in the furnace, and a lower stage shows a cross section of the furnace body. In order to simplify the explanation, the set temperature shown in the figure is a simplified pattern in which the temperature is first raised to the maximum temperature, then maintained at the maximum temperature for a predetermined time, and then cooled. The solid-phase reaction firing furnace of this embodiment is a roller hearth kiln in which a large number of conveying rollers 2 are arranged at a constant pitch inside the furnace body 1, and the powder is placed in the sagger 3 and the furnace body 1 The inside is continuously fired while being conveyed at a constant speed in the right direction in FIG. 1 from the inlet side to the outlet side.

  Although the inside of the furnace body 1 which is a continuous furnace is divided roughly into the temperature rising zone 4, the maximum temperature holding zone 5, and the cooling zone 6, in this invention, between the temperature rising zone 4 and the maximum temperature holding zone 5 is provided. A soaking zone 7 is provided. The soaking zone 7 is a zone in which the temperature in the furnace is just before the maximum temperature. In the temperature raising zone 4 and the maximum temperature holding zone 5, a resistance heater 8 as an electric heater is provided in the furnace as in the conventional case. By energizing these, the resistance heater 8 generates heat, mainly radiant heating. To heat the powder stored in the mortar 3.

  However, the soaking zone 7 is provided with a microwave heating device 11 provided with a magnetron 9 and a waveguide 10, and the powder stored in the mortar 3 is microwave-heated. Although the resistance heater 8 is not provided in the soaking zone 7 in FIG. 1, it may be provided. The microwave heating device 11 irradiates microwaves of 2450 MHz toward the bowl 3 to generate heat and heat the powder itself.

  The present invention is suitable for solid-phase reaction firing of powders used in the production of lithium ion batteries, ceramic capacitors and the like. More specifically, the powder is a precursor powder for a positive electrode of a lithium ion battery, It is a ceramic powder that is a precursor powder of barium titanate. Precursor powders for positive electrodes of lithium ion batteries include cobalt-based, nickel-based, manganese-based, and iron-phosphorus-based (olivine-based), and solid phase reactions proceed when fired at a preferred firing temperature and firing atmosphere. Thus, a positive electrode material for a lithium ion battery is obtained. In the cobalt system, the firing temperature is 900 to 1000 ° C., and the firing atmosphere is an air atmosphere. The firing temperatures for nickel-based, manganese-based, and iron-phosphorus-based (olivine-based) are 700 to 800 ° C., 750 to 950 ° C., and 550 to 800 ° C., and each firing atmosphere includes an oxygen atmosphere, an air atmosphere, Nitrogen + hydrogen atmosphere. The precursor powder of barium titanate is barium carbonate and titanium oxide, and barium titanate is obtained by firing at 1100 to 1200 ° C. in an air atmosphere.

  Thus, although the firing temperature (maximum temperature) varies depending on the type of powder, the temperature immediately before the maximum temperature for microwave heating is within the range of (maximum temperature-30 ° C) to (maximum temperature-100 ° C). It is preferable to set the temperature. If the temperature is lower than this, the output of the microwave heating device 11 needs to be increased, which is not economical, and if the temperature is higher than this, the powder temperature of the surface layer portion increases excessively due to the microwave heating.

  Next, the function and effect of the present invention will be described with reference to FIG. When the furnace temperature is set as shown by the solid line, the powder temperature of the surface layer in the sagger rises almost the same as the set temperature, but the powder temperature inside the slag is delayed from the set temperature. Temperature. This is the actual situation in the conventional continuous furnace in which the resistance heater 8 is installed in the temperature raising zone 4 and the maximum temperature holding zone 5. However, in the present invention, since microwave heating is performed on the powder heated to the temperature just before the maximum temperature, the internal powder also generates heat and is heated as indicated by a broken line. For this reason, the internal powder temperature also rapidly approaches the set temperature, and the temperature difference between the surface layer portion in the mortar and the inside can be eliminated. In addition, although the powder temperature of the surface layer part also rises from the set temperature by microwave heating, it passes through the soaking zone 7 and is lowered to the furnace temperature (set temperature) due to radiation from the powder surface. There is no. When it is desired to suppress the increase in the powder surface temperature as much as possible, it can be sufficiently avoided by blowing a cooling gas onto the powder surface.

  As described above, in the present invention, the microwave heating device 11 only needs to be installed in the soaking zone 7, so that the equipment cost and running cost are not significantly different from those of the conventional furnace. Ceramics have a low loss factor in the low temperature range and are difficult to heat, but the loss factor increases with increasing temperature. Therefore, the ceramic can be efficiently heated by microwave heating in the high temperature range.

  In the present invention, the runaway phenomenon, which is a problem in microwave heating of ceramics, cannot be completely prevented, but the adverse effect is small because microwave heating is performed only for the time passing through the limited soaking zone 7. . Also, as shown in FIG. 3, the increase in loss factor with increasing temperature varies greatly depending on the type of powder, and powder showing rapid change such as chromium oxide is not suitable for the present invention because it tends to cause runaway phenomenon. . However, the present invention is particularly effective for powders that show a tendency to saturate due to a moderate increase in loss factor as the temperature rises, such as iron oxide, and is optimal for solid-phase reaction firing of olivine-based electrode materials. It is.

Furthermore, in order to eliminate the temperature difference of the powder inside the mortar 3, the mortar 3 is also preferably heated and heated in the same manner as the powder, and particularly iron-phosphorous (olivine) suitable for microwave heating. Is particularly preferable because it can be used in a nitrogen + hydrogen atmosphere, and a carbon sachet 3 can be used. However, even the conventional mullite cordierite or alumina mortar does not cause any serious trouble.
Next, examples of the present invention will be described.

Powders of Fe (CH ₃ COO) ₂ , Li ₂ CO ₃ and (NH ₄ ) ₂ HPO ₄ which are precursor powders for lithium ion battery cathodes are mixed at a molar ratio of 1: 1: 1. It is housed in a carbon bowl having dimensions of 330 mm × 330 mm × depth 100 mm and thickness 10 mm so that the thickness is about 70 mm, and the roller heater kiln equipped with the resistance heater shown in FIG. Continuous firing. The particle size of the powder is 5 to 10 μm.

  The temperature in the furnace was set so that the temperature was raised from room temperature to 750 ° C. in 1 hour, maintained at 750 ° C. over 1 hour, and then cooled to room temperature in 1 hour. A section 12 minutes before the set temperature reaches the maximum temperature is set as a soaking zone, and a microwave heating device with an oscillation frequency of 2450 MHz and an output of 5 kW is placed only in this soaking zone, and it is heated to the temperature just before the maximum temperature by a resistance heater. The powder was heated by microwave. The furnace temperature when entering the soaking zone is 700 ° C.

  In the case of heating only with a conventional resistance heater that does not perform microwave heating, when the powder of the surface layer is heated to 750 ° C., the powder temperature inside (50 mm depth from the surface layer) is The temperature difference was 600 ° C. and 150 ° C. However, if microwave heating is performed when the surface layer powder reaches 700 ° C. according to the present invention, the internal powder temperature rises rapidly, and the internal temperature when the surface layer powder is heated to 750 ° C. The powder temperature reached 745 ° C., and the temperature difference became 5 ° C.

  As described above, according to the present invention, the temperature difference between the surface layer portion in the mortar and the inside, which is inevitably generated by surface heating with a resistance heater, can be easily achieved by heating the powder itself with microwaves. And uniform solid phase reaction firing can be performed.

DESCRIPTION OF SYMBOLS 1 Furnace body 2 Roller 3 Conveyance bowl 4 Temperature rising zone 5 Maximum temperature holding zone 6 Cooling zone 7 Soaking zone 8 Resistance heater 9 Magnetron 10 Waveguide 11 Microwave heating device

Claims (6)

  In this method, the powder stored in the sagger is heated in a continuous furnace and solid-phase reaction firing is performed. The powder is heated to a temperature just before the maximum temperature by a resistance heater installed in the furnace body, and then microwaved. A method for solid-phase reaction firing of powder, characterized in that the surface layer portion and the inside are soaked by irradiating the powder to heat the powder, and then maintained at the maximum temperature again by a resistance heater.   2. The powder solid phase reaction firing method according to claim 1, wherein the powder is a precursor powder for a positive electrode of a lithium ion battery.   2. The powder solid-phase reaction firing method according to claim 1, wherein the powder is a precursor powder of barium titanate.   2. The powder solid phase reaction baking method according to claim 1, wherein a carbon sagger is used as the sagger.   The method for solid-phase reaction firing of powder according to claim 1, wherein the temperature immediately before the maximum temperature is a temperature of (maximum temperature-30 ° C) to (maximum temperature-100 ° C).   It is a continuous furnace for solid phase reaction firing by heating while transferring the powder stored in the mortar, where resistance heaters are placed in the temperature rising zone and the maximum temperature holding zone, and the soaking is sandwiched between them A solid phase reaction firing furnace for powder, characterized in that a microwave heating device is disposed in the zone.

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