TWI487679B - Crystallized glass and its manufacturing method - Google Patents

Description

Crystallized glass and method of producing the same

The present invention relates to a production method for crystallizing glass by microwave irradiation, and a crystallized glass obtained by the production method.

In general, crystallization of glass is performed by external heating using an electric furnace or the like or direct heating by laser irradiation or the like. For example, Patent Document 1 discloses that a surface portion containing a rare earth element is irradiated with an ultrashort pulse laser to form a crystal phase containing a rare earth element.

On the other hand, the industry has been studying the application of microwave irradiation to the processing of various materials such as inorganic material synthesis or ceramic sintering, bonding, and crystallization. These applications utilize self-heating phenomena caused by the loss of electromagnetic wave energy that penetrates into the interior of the material. Since only the transition metal oxide or the semiconductor material which absorbs microwaves and the reaction component which is a metal conductive substance generate|occur|produce heat by the heating by microwave irradiation, it heat-processes by the external external heating for short time and energy saving.

Patent Document 2 discloses that, after manufacturing a precursor solution for synthesizing various inorganic materials, it is continuously injected into a tubular microwave reactor and synthesized and crystallized, thereby different from the previous crystallization. The long-term hydrothermal treatment process takes a short time to several minutes to tens of minutes.

Patent Document 3 discloses that an amorphous titanium oxide is heated and crystallized while irradiating ultraviolet rays or visible rays having energy having a band gap or more, thereby producing an anatase-containing titanium oxide. Photocatalyst.

In the case where the glass was previously crystallized by external heating using heat transfer from a heat source or direct heating by laser irradiation or the like, since crystals in a thermodynamic equilibrium state are all precipitated, there is an unnecessary crystal. The problem of precipitation.

On the other hand, in the case of heating by microwave irradiation (microwave heating), a reaction in a thermal non-equilibrium state caused by a difference in microwave absorption of a material component occurs. Therefore, the inventors and the like conceived that there is a possibility that crystals containing a material component which easily absorbs microwaves are preferentially precipitated from the glass. However, since ordinary glass is an insulator and a non-magnetic body, and does not absorb microwaves, there is no report example in which microwave irradiation is applied to crystallization of glass.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-83044

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-186849

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-294744

An object of the present invention is to provide a method for producing crystallized glass which selectively precipitates only desired crystals, and a crystallized glass obtained by the method.

The method for producing crystallized glass of the present invention is characterized in that the glass is irradiated with microwaves to crystallize at least a part of the glass.

Further, the "glass" in the present invention is defined as a solid which exhibits a glass transition phenomenon having a network structure in which atoms are randomly arranged.

The present invention can provide a crystallization method capable of selectively depositing a desired crystal having conductivity or magnetic properties from a glass containing a transition metal element, a crystallized glass having conductivity or magnetic properties, and applying the crystallized glass. An electrode active material for a secondary battery or a thermoelectric conversion element.

Hereinafter, the present invention will be described in detail.

The present inventors have found that a glass containing a transition metal element is heated by microwaves, and a high conductivity crystal or a magnetic crystal containing a transition metal element is selectively precipitated into the amorphous material. The term "microwave" as used herein refers to an electromagnetic wave of UHF (Ultra High Frequency) to EHF (Extremely High Frequency) with a frequency of 0.3 GHz to 3 THz and a wavelength of 0.1 to 1000 mm.

Further, it has been found that a mixture of a compound powder containing a Group 1 element or a Group 2 element and a glass powder containing a transition metal element is heated by microwave, and the Group 1 element or the Group 2 element is doped in the glass in an ionic state.

Further, it has been found that the crystallized glass which is at least partially crystallized by microwave heating can be applied to an electrode active material for a secondary battery or a thermoelectric conversion element.

Hereinafter, the present invention will be described in detail.

[Example 1] (production of glass)

200 g of a mixed powder prepared by mixing Cu ₂ O, V ₂ O ₅ , Fe ₂ O ₃ , and P ₂ O ₅ at a molar fraction of 10%, 70%, 10%, and 10%, respectively, into platinum In the crucible, use an electric furnace to heat to 1373 K at a heating rate of 5 to 10 K/min for 1 hour. Stir in the formation to form a uniform glass. Next, the platinum crucible was taken out from the electric furnace, and the mixture was poured into a stainless steel plate previously heated to 473 to 573 K. Furthermore, the coagulum exhibits a glassy luster.

(crystallization of glass)

The obtained glass was processed into a size of about 10 × 10 × 2 mm to prepare a sample piece, and subjected to crystallization treatment by microwave irradiation and ordinary electric furnace heating under the conditions shown in Table 1. Microwave irradiation is carried out in the following two ways. Furthermore, heating is carried out in the atmosphere. Further, the crystallization start temperature of the above-mentioned glass used in the present study was confirmed to be 633 K by differential thermal analysis (DTA).

[1] single mode

The self-magnetizing oscillator introduces a microwave of 2.45 GHz into the waveguide blocked by one end of the reflector, and the microwave propagates in the waveguide in a TE (Transverse Electric) mode 10, and the sample piece placed in the waveguide is placed. Single mode microwave irradiation is performed. Furthermore, in order to be able to independently control the electric field and magnetic field of a specific sample position, microwaves can be irradiated from both systems. That is, a strong electric field is generated by the irradiation of the first system at the position of the sample, and a strong magnetic field is formed by the irradiation of the second system, and the outputs of the two systems are respectively adjusted, thereby changing the electric field and the magnetic field of the sample position. The output ratio.

[2] Multimode mode

Microwave irradiation was carried out by a commercially available microwave oven. Since the electromagnetic wave of 2.45 GHz in the microwave oven randomly flies around, the electromagnetic wave is irradiated to the sample piece from various directions.

(Identification of crystallized glass by precipitation of X-ray diffraction)

The test piece subjected to microwave irradiation was measured by using a thin film X-ray diffraction apparatus (manufactured by Rigaku, RINT 2500HL) so that X-rays were incident on the microwave incident surface. Furthermore, the measurement conditions are as follows. The X-ray source is Cu, and its output is set to 50 kV, 250 mA. Using an optical system with a parallel beam of single light, the divergence slit is chosen to be 0.2 mm. The scanning axis of the X-ray diffraction is a 2θ single mode, and continuous scanning is performed at a scanning speed of 0.5 deg/min in the range of 5 ≦ 2 θ ≦ 100 deg, and sampling is performed at 0.02 deg/step. The identification of precipitated crystals was carried out using the ICDD (The International Centre for Diffraction Data) data as an X-ray diffraction standard data set.

In the test piece which was heated by the electric furnace, the test piece was pulverized into a powder form, and it measured by the wide-angle X-ray diffraction apparatus (Rig 2500HL, Rigaku). Furthermore, the measurement conditions are as follows. The X-ray source is Cu, and its output is set to 50 kV, 250 mA. Using an optical system with a concentrated beam of single light, a 0.5 deg divergence slit, a 0.15 mm receiving slit, and a 0.5 deg scattering slit were selected. The scanning axis of the X-ray diffraction is a 2θ/θ linkage type, and continuous scanning is performed at a scanning speed of 0.5 deg/min in the range of 5 ≦ 2 θ ≦ 100 deg, and sampling is performed at 0.01 deg/step. The identification of precipitated crystals was carried out using ICDD data as a standard data set for X-ray diffraction.

The results of the identification of the precipitated crystals of each sample are shown in Table 1. When heated in an electric furnace, in addition to confirmation of the precipitated desired high conductivity of the Cu _x V ₂ O ₅ (monoclinic system), likewise the degree of precipitation of lower conductivity than Cu _x V V ₂ O ₅ of the ₂ O ₅ ( Orthorhombic system). On the other hand, in the case of microwave irradiation, only the desired Cu _x V ₂ O ₅ is precipitated regardless of the irradiation mode. This result suggests that high conductivity crystals can be selectively precipitated from the glass by microwave heating.

Further, when the glass material to a change in the above case, microwave heating is also confirmed by selectively precipitated ₂ O ₅ in addition to the single Cu _x V M of the monoclinic crystal _x V ₂ O ₅ (M represents iron, Sb Any one of metal elements such as yttrium, tungsten, molybdenum, manganese, nickel, silver, alkali metal or alkaline earth metal, 0<x<1)

[Table 1]

(observed by SEM (Scanning Electron Microscope))

The difference in the structure crystallized by electric furnace heating and microwave heating was examined by SEM. Fig. 1 is a cross-sectional SEM image of the surface and the inside of a glass crystallized by the heating conditions of No. 1 and No. 3 in Table 1. Compared with the electric furnace heating material, the crystal grain boundary of the microwave heating material is clearer and the crystal grain size is larger. The reason for this is that since the heating rate of microwave heating is much larger than that of the electric furnace heating material, the number of crystal nuclei is small, thereby promoting crystal growth.

(Evaluation of thermoelectric characteristics)

The Westeck coefficient and the resistivity were measured by a thermoelectric property evaluation device (ZEM-3) manufactured by ULVAC. The shape of the sample was set to a prism of about 3 × 3 × 10 mm, and it was measured in a low-pressure helium gas at a temperature ranging from room temperature to 723 K. Again, all samples were tested twice under the same conditions.

Fig. 2 shows the temperature dependence of the electrical conductivity of the glass crystallized under the heating conditions of No. 1 (MW) and No. 3 (EF) in Table 1. In either case, the conductivity increases with an exponential function as the temperature rises. Also, the microwave heating material has a high electrical conductivity. The reason for this is that Cu _x V ₂ O _{5 having a} conductivity higher than V ₂ O ₅ is selectively precipitated by microwave heating.

Fig. 3 shows the temperature dependence of the Westeck coefficient (temperature difference electromotive force: S) of the glass crystallized by the heating conditions of No. 1 (MW) and No. 3 (EF) in Table 1. It can be seen that in either case, since the Westeck coefficient becomes a negative value, it is an n-type semiconductor. Moreover, the absolute value of the Western White coefficient increases as the temperature rises. Moreover, the Western White coefficient (absolute value) of the microwave heating material is large.

Fig. 4 shows the electrical conductivity (σ), the Western White coefficient (S), and the thermal conductivity of the glass crystallized according to the heating conditions of No. 1 (MW) and No. 3 (EF) in Table 1. κ) The result of the calculated Dimensionless figure of merit (ZT) of the thermoelectric conversion material. Further, ZT is provided by the following formula (1). In either case, the high temperature shows a higher ZT. Moreover, comparing the ZT of the electric furnace heating material and the microwave heating material, the ZT of the microwave heating material is relatively high, and is 16 times that of the electric furnace heating material at room temperature.

Further, the vanadium-based glass produced in the present embodiment can be an n-type semiconductor or a p-type semiconductor by preparing a valence of vanadium ions in the glass. When the ratio of the number of vanadium ions to the number of vanadium ions is greater than 1 ([V ⁺⁵ ] / [V ⁺⁴ ]>1), it is n-type, and when it is less than 1 ([V ⁺⁵ ] When /[V ⁺⁴ ]<1), it is p type. Specifically, the polarity of the glass can be controlled by controlling the composition of the glass or the environment at the time of the crystallization treatment.

The p-type glass can be produced by including at least one selected from the group consisting of iron, ruthenium, osmium, tungsten, molybdenum, manganese, and nickel in addition to vanadium and phosphorus. Further, the p-type glass can also be formed by crystallizing the n-type glass in a reducing atmosphere.

Further, the n-type glass can be produced by including at least one selected from the group consisting of copper, silver, an alkali metal, and an alkaline earth metal in addition to vanadium and phosphorus. Further, the n-type glass can be formed by crystallizing the p-type glass in an oxidizing atmosphere.

Fig. 5 shows an example of a thermoelectric conversion element in which n-type and p-type crystallized glass are electrically bonded. FIG. 5( a ) shows an example of a thermoelectric conversion element in which an n-type crystallized glass 501 and a p-type crystallized glass 502 are connected in a type II via an electrode 503 such as copper or aluminum. Further, as shown in Fig. 5 (b), the crystallized glass of two polarities may be directly bonded. Further, by using either of the n-type and the p-type as the other thermoelectric conversion material or in the thermoelectric conversion material of each polarity, the crystallized glass of the present invention can be combined with other thermoelectric conversion materials to achieve high Conversion efficiency.

Fig. 6 is a view showing an example of a thermoelectric conversion module in which the thermoelectric conversion elements shown in Fig. 5 are electrically joined, respectively. The upper and lower insulating substrates 604 are used to retain the shape of the module, and may be omitted as needed.

[Embodiment 2] (production of glass)

200 g of a mixed powder prepared by mixing Fe ₂ O ₃ , Li ₂ CO ₃ , and SiO ₂ at a weight fraction of 40%, 10.8%, and 49.2%, respectively, in a platinum crucible, and using an electric furnace at 5 to 10 K The heating rate of /min was heated to 1573 K for 2 hours. Stir in the formation to form a uniform glass. Next, the platinum crucible was taken out from the electric furnace to cause the mixture to flow into the stainless steel plate. Furthermore, the coagulum exhibits a glassy luster.

(crystallization of glass)

The obtained glass was processed into a size of about 10 × 10 × 2 mm to prepare a sample piece, and subjected to microwave heating (magnetic field) by a single mode method and crystallization by ordinary electric furnace heating. Further, microwave heating and electric furnace heating were carried out in the atmosphere at about 1130 K × 3 min and 1123 K × 16 hr, respectively.

(Identification of crystallized glass by precipitation of X-ray diffraction)

Any of the samples was pulverized into a powder, and the precipitated crystals were identified by a wide-angle X-ray diffraction apparatus in the same manner as described above. When heating in an electric furnace, it was confirmed that in addition to the desired magnetic spinel crystals (LiFe ₅ O ₈ ), unnecessary non-magnetic Li ₂ SiO ₃ or Fe ₂ SiO _{4 was} precipitated. On the other hand, when microwave irradiation is performed, the desired LiFe ₅ O _{8 is} selectively deposited. This result suggests that the magnetic crystal can be selectively precipitated from the glass by microwave heating.

(Application to positive active material for lithium ion secondary battery)

The crystallized glass in which LiFe ₅ O ₈ crystallizes out into the amorphous state can be used as a positive electrode active material of a lithium ion secondary battery. Fig. 7 is a schematic view showing a three-pole battery performance evaluation unit using the positive electrode active material of the present invention. Hereinafter, description will be made with reference to this figure.

Using a mortar, a glass powder (positive electrode active material 202) crystallized by electric furnace and microwave heating, a Ketjen black as a conductive auxiliary agent 203, and a binder as a binder are mixed at a weight ratio of 85:5:10. 5 wt% of polyvinylidene fluoride (PVDF, Polyvinylidene Fluoride) N-methyl-2-pyrrolidone (NMP, N-methyl-2-pyrrolidone). At this time, in order to adjust the viscosity, the NMP was appropriately mixed while being slurryed. The obtained slurry was applied onto an aluminum alloy foil having a thickness of 20 μm as the positive electrode collector 201 using a knife coater having a gap of 200 μm. The film was dried in the air at 90 ° C × 2 hr to form a positive electrode layer 206, and then punched into a disk shape having a diameter of 15 mm. Next, after pressing at about 400 Mpa, it was vacuum dried at 120 ° C for 1 hour to prepare a positive electrode 207.

The charge and discharge characteristics of the positive electrode 207 were evaluated using the three-pole model unit shown in FIG. The positive electrode 207, the Li plate of the negative electrode 208, and the Li plate of the reference electrode 209 are laminated via a separator 204 having a thickness of 30 μm impregnated in the electrolytic solution, and sandwiched between two SUS (Special Utility Steel) splints 205. After that, it is placed in a glass container to form a battery unit. The electrolyte used was prepared by dissolving 1 mol/l of lithium hexafluorophosphate (LiPF ₆ ) in a ratio of 1:2 by volume of ethylene carbonate (ethylene carbonate) and ethyl methyl carbonate (EMC, ethyl). Methyl carbonate) is a solvent.

Charging and discharging are performed in CC (Constant Current) mode, and the battery voltage is set to 1.5 to 4.2 V, starting from self-discharge. The current density at the time of the first charge and discharge was set to 0.057 mA/cm ² , and was 0.28 mA/cm ² after the second loop. As a result, reversible charge and discharge characteristics were obtained. Compared with the crystallized glass formed by heating in an electric furnace, the crystallized glass formed by microwave heating had a higher charge and discharge capacity, and the capacity retention rate was also higher.

[Example 3] (production of glass)

The mixed powder prepared by mixing V ₂ O ₅ , Li ₂ O, Fe ₂ O ₃ and P ₂ O ₅ at a molar ratio of 70.3%, 10.7%, 10.0%, and 9.0%, respectively, is heated in an electric furnace. Platinum crucible. The temperature increase rate was set to 5 ° C / min, and the glass was heated and kept warm for 1 hour from the time when the target temperature (1000 to 1100 ° C) was reached. Thereafter, the platinum crucible was taken out from the dissolution furnace, and the mixture was cast into a graphite mold which was previously heated and held at 150 to 300 °C. The obtained glass block was pulverized, and the characteristic points of the glass were measured by differential thermal analysis (DTA). The glass transition point (Tg) was 252 ° C, the deformation point (Mg) was 271 ° C, the first crystallization starting temperature was 315 ° C, and the second crystallization starting temperature was 428 ° C.

(crystallization of glass)

The glass powder obtained is placed in a quartz crucible, and microwave heating is performed in the atmosphere by a single mode (magnetic field) or a multimode method. The heating temperature of the glass powder was monitored by a radiation thermometer, and the irradiation time and output of the microwave were controlled so that the glass powder temperature became about 370 ° C above the glass crystallization temperature. Furthermore, for comparison, electric furnace heating is also performed at the same temperature.

(Identification of crystallized glass by precipitation of X-ray diffraction)

Similarly to the above, the precipitated crystal was identified by a wide-angle X-ray diffraction apparatus, and the degree of crystallinity was determined from the integral intensity ratio of the full peak and the broad peak derived from amorphous. It was confirmed that the glass crystallized by heating in an electric furnace precipitates an orthorhombic V ₂ O _{5 in} addition to the monoclinic Li _0.3 V ₂ O ₅ , but the glass crystallized by microwave heating only Li _0.3 V ₂ O ₅ crystals were selectively precipitated. Further, the degree of crystallization was 90%.

(Application to positive active material for lithium ion secondary battery)

A positive electrode was produced using the obtained crystallized glass powder in the same manner as in Example 2, and a charge and discharge test was carried out under the same conditions as in Example 2. As a result, reversible charge and discharge characteristics were obtained, and the loop retention ratio of the capacity of the crystallized glass formed by microwave heating was higher than that of the crystallized glass formed by heating in an electric furnace. Furthermore, the charge and discharge capacities of the two are approximately equal.

(ion doping of glass)

A compound powder containing a first group element (lithium or sodium or the like) or a second group element (magnesium or the like), and an amorphous glass in a molten or solidified state, or a part of the present embodiment is crystallized by cold pressing The mixture of glass powders becomes granular. Using TEM/EELS (transmission electron microscope/electron energy loss spectrometer) analysis, it was found that by heating the particles by microwave, the first group element or the second group element is in the state of ions. Doped into the glass.

Therefore, the positive electrode active material 309 containing the glass powder pre-doped with lithium ions was used to produce the positive electrode 309, and the charge and discharge characteristics of the positive electrode 309 were evaluated using a two-pole model cell as shown in FIG. Hereinafter, description will be made with reference to this figure.

The negative electrode is used by coating a PIC (Pseudo Isotropic Carbon) as a negative electrode active material 305 on a copper foil as the negative electrode current collector 306, and drying it to form a negative electrode layer 308, which is punched into a diameter. 15 mm disc shape and pressed.

As shown in FIG. 8, the positive electrode 309 and the negative electrode 310 were laminated via a separator 304 having a thickness of 30 μm impregnated with an electrolytic solution, and the two SUS jigs 311 were used to sandwich the positive electrode 309 and the negative electrode 310, and then placed in a glass container. Into a battery unit. The electrolyte used was prepared by dissolving 1 mol/l of lithium hexafluorophosphate (LiPF ₆ ) in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:2. The addition of 0.8 wt% of vinylidene carbonate (VC) was added to the product.

The charge and discharge evaluation was carried out at room temperature and started from charging. The charge and discharge are performed in CC (Constant Current) mode, and the battery voltage is set to 1.5 to 4.2 V. Further, the current density at the time of the first charge and discharge was set to 0.057 mA/cm ² , and after the second loop, it was set to 0.28 mA/cm ² . As a result, reversible charge and discharge characteristics were obtained.

201, 301. . . Positive current collector

202, 302. . . Positive active material

203, 303. . . Conductive additive

204, 304. . . Spacer

205, 311. . . Splint

206, 307. . . Positive layer

207, 309. . . Positive electrode

208, 310. . . Negative electrode

209. . . Reference electrode

305. . . Negative electrode active material

306. . . Negative current collector

308. . . Negative electrode layer

501, 601. . . N-type crystallized glass

502, 602. . . P-type crystallized glass

503, 603. . . electrode

604. . . Insulating substrate

Fig. 1 is a cross-sectional SEM image of the crystallized glass of Example 1.

Fig. 2 is a graph showing the temperature dependence of the electrical conductivity of the crystallized glass of Example 1.

Figure 3 is a graph showing the temperature dependence of the Westeck coefficient of the crystallized glass of Example 1.

Figure 4 is a dimensionless performance index of the thermal energy of the crystallized glass of Example 1.

5(a) and 5(b) are schematic views showing thermoelectric conversion elements in which n-type and p-type crystallized glass are electrically bonded in the first embodiment.

Fig. 6 is a schematic view showing a thermoelectric conversion module in which the thermoelectric conversion elements are electrically bonded to each other in the first embodiment.

Fig. 7 is a schematic view showing a three-pole battery performance evaluation unit using the positive electrode active material of the present invention in Example 2.

Fig. 8 is a schematic view showing a two-pole battery performance evaluation unit of the third embodiment using the positive electrode active material doped with lithium ions of the present invention.

Claims (10)

A crystallized glass obtained by irradiating a glass containing a transition metal with microwaves to obtain at least a part of the glass, and having conductivity. A crystallized glass obtained by irradiating a glass containing a transition metal with microwaves to obtain at least a part of the glass, and having magnetic properties. A crystallized glass obtained by irradiating a glass containing a transition metal with microwaves to obtain at least a part of the glass, and at least a part of the crystallized glass is amorphous. The crystallized glass of claim 1 or 3, wherein the crystallized glass contains vanadium. The crystallized glass of any one of 3, 4, wherein the precipitated crystal is a monoclinic system. The crystallized glass according to any one of 3, 4, 5, which comprises any one of a lithium ion, a sodium ion, and a magnesium ion. An electrode active material for a secondary battery, characterized by using the crystallized glass according to any one of claims 1 to 6. A thermoelectric conversion material characterized by using the crystallized glass according to any one of claims 1, 3, and 5. A thermoelectric conversion element characterized by using the thermoelectric conversion material of claim 8. A thermoelectric power generation module characterized by using the thermoelectric conversion element of claim 9.