JPS5945180B2 - Manufacturing method for anodes for non-aqueous batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an anode for a nonaqueous battery using a light metal such as lithium, sodium, or calcium as a negative electrode active material and an organic electrolyte, which has excellent high rate discharge and storage stability. The present invention provides an anode that provides a non-aqueous battery with excellent mass productivity.

The battery system to which the present invention can be applied uses koji light metal as a negative electrode active material as described above, and uses γ-butyrolactone, tetrahydrofuran, propylene carbonate, dimethoxyethane, etc. alone or in a mixed solvent as an electrolyte, and lithium perchlorate, lithium borofluoride, etc. as an electrolyte. This battery uses a so-called organic electrolyte in which silver iodide, silver nitrate, etc. are dissolved, or a solid electrolyte such as silver iodide or silver nitrate.

Further, the positive electrode active material is a metal oxide obtained by thermally decomposing a thermally decomposable salt such as manganese, ruthenium, copper, lead, nickel, and silver. Manganese oxide, which is the most typical of these, will be explained below. Conventionally, manganese dioxide, an anode active material for organic electrolyte batteries, is produced by heat-treating electrolytically collected γ-MnO2 at 250°C to 450°C to produce β-MnO2.
nO2 or γ-' thick phase MnO2 is used.

The electrowinning γ-MnO2 has 3 to 4 weights of attached water,
Since it contains water of crystallization, it is subjected to the heat treatment described above for dehydration. However, even with such heat treatment, this type of MnO2 is highly hygroscopic, so the relative humidity is 1.
Even in a drying room controlled to ~3%, moisture in the air is adsorbed in a short time, resulting in a moisture content of 0.8 to 2.0% by weight. Thus, the trace amount of water contained in MnO2 has an adverse effect on the shelf life of the battery. In other words, water reacts with the lithium negative electrode and decomposes the organic electrolyte, and this tendency is particularly noticeable during high-temperature storage. This is the main cause. As a measure to prevent the heat-treated manganese dioxide from absorbing moisture, a method has been proposed in which a mixture of γ-βMnO, graphite, and a binder is reheated at 200 to 350°C.

However, considering that MnO2 is an excellent oxidizing agent and oxidation catalyst, this method is extremely dangerous. In addition, a method has been proposed in which the surface of activated carbon, graphite, etc. is impregnated with manganese nitrate and thermally decomposed at high temperature to produce manganese dioxide. It is considered extremely dangerous to use it industrially.

In view of the above points, the present invention provides an anode for non-aqueous batteries that is suitable for mass production and has low water absorption.

That is, the present invention involves thermally decomposing a metal salt attached to a metal substrate that becomes an anode current collector in a semi-closed furnace by radiant heat transfer from the furnace wall to generate a metal oxide that becomes an anode active material. It is characterized by The details of the present invention will be explained below.

The anode active materials to which the present invention can be applied are oxides of manganese, ruthenium, copper, lead, nickel, etc., and suitable thermally decomposable salts include nitrates, acetates, and hydrochlorides of these metals, with nitrates being particularly suitable. is the best.

Since ruthenium is often commercially available as a chloride, it is preferable to use it after anion exchange with a nitrate. It may also be used in the form of a double salt consisting of nitrate ions, ammonia ions, and water. As the metal substrate used for the current collector, nickel, chromium, stainless steel, steel, silver, etc. used in conventional current collectors can be used. However, in the present invention, aluminum, tantalum, titanium, hafnium,
Preferably, valve metals such as niobium (alloys based on these metals) are used. Among these, aluminum, titanium, tantalum, and niobium are particularly economical and effective. The shape of this metal base can be appropriately selected, such as a disc-shaped, cylindrical, or rod-like shape, depending on the shape of the intended battery.

In this case, the metal powder is molded together with a lead piece,
It is preferable to sinter it to make it polymorphic. Its porosity is 4
0-90% is preferred, and 50-80% is most preferred.
Note that aluminum is difficult to obtain in powder form and difficult to sinter, so when aluminum or its alloys are used, it is best to make them porous by etching.

The appropriate etching ratio is 5 to 50 times, especially 10 to 30 times.
It is preferable to double the amount in terms of mechanical strength, mass productivity, and battery performance. The etching solution is selected depending on the substrate, but in the case of aluminum, 10-20t/t of sodium chloride and 5-20t/t of sodium chloride
An aqueous solution containing 20t/t of ammonium borate
Preferably it is used at a temperature of 50°C. The present invention is characterized in that the anode active material is formed directly on the surface of the metal substrate by thermal decomposition. It is preferable to use a valve metal such as the following, and to form a dielectric film on the surface thereof by an anodization method.

This anode chemical conversion film serves to prevent the substrate surface from being chemically degraded during thermal decomposition, and also to suppress self-discharge due to the formation of local cells when the battery is stored at high temperatures. The method for forming a chemical conversion film on the surface of the valve metal is selected depending on the method for preparing the substrate.

For aluminum substrates, ammonium borate 5-
An aqueous solution of 10 f7/t is preferred, and in the case of tantalum or titanium, a 5 to 10 f/t solution of phosphoric acid or nitric acid is preferred.
When a chemical conversion film is formed on the surface of a substrate, in the case of an aluminum substrate, an n layer, an i layer, and a p layer are formed in order from the base side. Accordingly, in anode polarization, no current flows, but in cathodic polarization, it exhibits a valve action that allows current to flow freely, so it can be used as an anode for a battery system.

On the other hand, metals such as nickel, chromium, and silver can also be used as current collectors; This results in disadvantages such as weakening the adhesion strength of the active material, lowering the contact strength, forming local batteries, and increasing the internal resistance of the battery.

Therefore, it is preferable to use a porous body of valve metal as the metal substrate. In order to generate an active material on a metal substrate by thermal decomposition, it takes 2 to 10 steps of impregnation with a thermally decomposable salt and thermal decomposition, depending on the shape, size, porosity, etc. of the substrate.
need to be repeated several times.

Taking manganese dioxide as an example of the active material, it is preferable to repeat the following steps: impregnation of the substrate with a manganese nitrate solution, thermal decomposition, reconversion of the dielectric film, impregnation with manganese mononitrate, and thermal decomposition. After the active material is formed on the metal substrate by pyrolysis, it is impregnated with a conductive material such as colloidal graphite to further improve conductivity, dried and baked. As described above, the present invention is a method for manufacturing an anode that is different from the conventional method of mixing graphite powder and active material, pre-pressing the mixture, and then molding the mixture. The active material formed on the surface of the metal substrate has differences in electrical resistance, bulk specific gravity, etc. depending on its thermal decomposition method.

Conventional pyrolysis furnaces are usually open type, with hot air heated by a heater being supplied through one opening and exhausted through the other exhaust port.

This is to make the temperature distribution inside the furnace uniform and to dissipate gases produced by thermal decomposition such as water vapor and nitrogen oxides out of the furnace as quickly as possible during thermal decomposition. However, metal oxides obtained using such a furnace, such as β-MnO2 obtained by thermally decomposing manganese nitrate, are porous, as shown in the electron micrograph shown in Figure 2 (magnification: 1000). Although it has a lower adsorbed water content than γ-MnO2, it also has a large equilibrium adsorbed water content, high electrical resistance, and low bulk specific gravity. Moreover, even when considering the operability of the furnace, the energy cost and equipment cost are large. On the other hand, the present invention uses a semi-closed furnace that does not perform forced circulation of hot air inside the furnace, and unlike conventional furnaces that use heat insulating materials for the main parts of the furnace, aluminum and aluminum alloys, which are good conductors of heat, are used. ,
It uses stainless steel, copper, cast metal, etc., and utilizes the radiant heat of the furnace. It decomposes thermally.

An example of the structure of a semi-closed furnace suitable for use in the present invention is shown below.

In FIG. 3, 1 is the furnace body, 2 is its lid, and has a small hole 3. 4 is a temperature control sensor, 5 is a heating device equipped with a heater 6, and 7 is a live material. This is a holding rod that holds the metal base 8 that forms the structure.

The furnace of FIG. 4 has a gap 915 between the end of the lid 2 and the main body 1.
This is an example of the formation. FIGS. 5 and 6 show an example in which both sides of the lid 2 are set so that gaps 10 and 10 are formed between the lid 2 and the main body. Note that, as in this example, the heater 6 may be incorporated into the bottomed main body 1 and the lid. Figure 7 shows an example in which a semi-closed furnace with the structure shown in Figure 3 is set inside a conventional hot air circulation type furnace. It has been done.

13 is a furnace body made of a heat insulating material, 14 is a thermometer, 15 is a distribution plate, 16 is a circulation fan, 17 is a fan motor, 18
19 is a cooling fan, 19 is a heater, 20 is a heat sensitive part for temperature adjustment, 21 is a cover, and 22 is a control equipment room.

The above pyrolysis furnaces all have small holes 3 or gaps 9 and 1.
It is a semi-closed type radiant furnace having a temperature of 0.0, and a slight pressure is applied by the gas produced by pyrolysis without forced circulation of hot air or stirring inside the furnace.

The heat source necessary for pyrolysis is preferably secured by directly heating the furnace body or by placing it in an atmosphere at a predetermined temperature of the furnace body.

The furnace body is preferably made of metal or an alloy, but may be made of other heat-resistant materials as long as machining accuracy can be achieved.

In order to improve the transfer and diffusion of heat, it is better to be a good conductor of heat.
The larger the heat capacity of the furnace body, the more stable performance can be obtained. When the furnace body is completely sealed, the interior is pressurized due to the gas generated by pyrolysis, which scatters pyrolytic salts, reduces the amount of oxides formed on the metal substrate, and also reduces the amount of oxides formed on the metal substrate. Yo~ You won't be able to get an oxide film.

Conversely, if the container is placed in an open state without being sealed with a lid, a dense oxide cannot be obtained. When hot air is circulated or stirred in the furnace, the oxide produced by thermal decomposition is sufficiently filled inside the porous substrate and becomes an uneven oxide with zero porosity that adheres only to the surface layer. On the other hand, when a semi-closed furnace as described above is used, the inside of the furnace has a temperature slightly below normal pressure (atmospheric pressure) due to decomposition gas generated from the surface of the porous substrate during thermal decomposition.
A slight pressure is applied, and thermal decomposition proceeds under the slight pressure caused by the autolytic gas, resulting in the following effects.
Note that the above-mentioned micropressure is suitably 5 to 100 tvnH20. 1. A concentrated manganese nitrate solution that forms manganese oxide inside the porous substrate can be used, and the number of repetitions of the pyrolysis process can be reduced.

(2) Oxides produced by thermal decomposition have a large bulk specific gravity. In the case of manganese dioxide, the surface of the porous substrate is smooth and exhibits a dense adhesion state, as if it had been electrolytically deposited. FIG. 8 shows an electron micrograph (magnification: 1000) obtained by thermally decomposing manganese nitrate. The MnO2 obtained in this manner has a bulk specific gravity two to three times that of that obtained in a conventional forced circulation furnace, and exhibits a silver-gray metallic luster in color, compared to the conventional black.

This is thought to be due to the fact that thermal decomposition is carried out by radiation conduction under the above-mentioned micropressure, so scattering due to nucleate boiling is prevented, and MnO2 is densely formed even inside the porous substrate. The size of each particle of MnO2 shown in Fig. 8 is 2 to 8.
The size is determined by the thermal decomposition conditions.

The preferred particle size is 0.1 to 50 ttm. (3) The obtained manganese dioxide has an electrical resistance of 0.01 to 1 ΩCm
It is smaller than that of a γ-β mixed phase obtained by heat-treating electrolytic manganese dioxide, and the amount of adsorbed water after heat treatment is about less than that of γ-βMnO2.

In addition, MnO2 obtained by thermal decomposition using a hot air circulation furnace
Compared to the above, it is superior in both electrical resistance and adsorbed water content as an anode active material for non-aqueous batteries. (4) The obtained manganese dioxide has extremely low hygroscopicity. This hygroscopicity can be compared based on the equilibrium adsorbed moisture content. Here, the amount of weight loss is expressed when various adjusted MnO2 are stored at room temperature for 48 hours and then heated to 250° C. using a differential thermal balance. Conventional electrowinning γ-MnO2 has a specific surface area of 30 to 60 i/f and contains 3 to 5% by weight of water.

When this is heat-treated to form a γ-β mixed phase, the specific surface area becomes 10
~20d/f, and the equilibrium adsorbed water content is 0.9~1.
The amount is approximately 2% by weight. On the other hand, heat a manganese salt, such as manganese nitrate. Even in β-MnO2 obtained by decomposition, the equilibrium adsorbed water content is 0.6% by weight, although it varies depending on the thermal decomposition conditions.
The above is normal, and it is difficult to reduce it below this.

However, if the semi-closed furnace described above is used, the equilibrium adsorbed water content is 0.
．． Up to 5% by weight, in particular up to 0.2% by weight, of MnO can be obtained. Since its hygroscopicity is thus extremely low, it hardly absorbs moisture during battery assembly, improving battery storage stability. Next, examples of the present invention will be described.

A pure aluminum plate having a thickness of 1.2T1:m was used as the metal base, and was punched out so that the disc-shaped base portion 23 and the lead piece portion 24 were integrated with the support portion 25 as shown in FIG.

This was etched using an aqueous solution containing sodium chloride and ammonium borate at an etching rate of 23 times.
After washing with water and drying, an anodic chemical conversion film was formed in an aqueous solution containing 8 t/t of ammonium borate at 30°C. This aluminum base was impregnated with a manganese nitrate solution with a specific gravity of 1.6, and the process of thermally decomposing it in a semi-closed furnace at 350°C under a slight pressure of 50 TmH20 above normal pressure was repeated three times, and then the colloidal Impregnated with graphite and dried at 200℃, lead piece 2
There is a sound of separation from the support part 25 at part 4.

The anode thus obtained is designated as A. Moreover, as a comparative example, an anode obtained in the same manner as above except that the thermal decomposition was repeated seven times in a conventional hot air circulation furnace was designated as B.

Furthermore, the electrolytically extracted γ-MnO2 was placed in the air for 3
6 parts by weight of acetylene black and 3 parts by weight of a fluororesin binder were mixed with 90 parts by weight of the anode heat-treated at 00°C for 2 hours, and the anode was heat-treated at 250°C after molding. These anodes were sealed in a test cell in a dry box together with a disk-shaped lithium negative electrode and an organic electrolyte in which 1.0 mol/t of lithium perchlorate was dissolved in propylene carbonate.

The battery obtained in this way immediately after the prototype was rated at 5 mA/
C1! Comparing the anode utilization rate when discharging at i, the first
It was as shown in Figure 0. Further, the anode utilization rate under the same conditions after storage at 60° C. for 3 months is shown in FIG. Next, the equilibrium adsorption water content of MnO2 used in each anode is compared with the results shown in FIGS. 10 and 11. As described above, the anode according to the present invention provides a non-aqueous battery with low electrical resistance and excellent discharge utilization.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the electrical characteristics of an aluminum substrate on which a chemical conversion film was formed in an example of the present invention, Fig. 2 is an electron micrograph of MnO2 obtained by thermal decomposition in a hot air circulation furnace, and Fig. 3 -
FIG. 5 is a schematic vertical cross-sectional view showing an example of the configuration of a semi-closed furnace, FIG. 6 is a front view of the furnace shown in FIG. 5, FIG. 7 is a schematic vertical cross-sectional view showing another example of the configuration of the semi-closed furnace, and FIG. is an electron micrograph of MnO obtained by thermal decomposition in a semi-closed furnace, FIG. 9 is a front view of the metal substrate group used in the example, and FIGS. 10 and 11 are various MnO
A comparison of the utilization rates of lithium batteries using O2 anodes is shown.

Claims (1)

[Scope of Claims] 1. A method comprising the step of thermally decomposing a metal salt attached to the surface of a metal substrate in a semi-closed furnace by radiant heat transfer from the furnace wall to generate an anode active material made of a metal oxide. A method for manufacturing anodes for non-aqueous batteries. 2 Claim 1 in which the metal is a valve metal
A method for producing an anode for a non-aqueous battery as described in . 3. The method for manufacturing an anode for a non-aqueous battery according to claim 2, which comprises the step of forming a dielectric film on the surface of the metal substrate before forming the anode active material.