JPH04343B2 - - Google Patents

Description

[Detailed Description of the Invention] In recent years, with the development of electronic devices, there has been an increasing demand for batteries that are small, lightweight, and have a long shelf life.
Nonaqueous batteries with lithium, sodium, or magnesium as negative electrodes are attracting attention as suitable batteries for this purpose. Although various oxidizing agents have been proposed as positive electrode active materials for this battery, only (CF)n, Ag ₂ CrO ₄ and MnO ₂ are in the stage of practical application.

Recently, substances produced by anodic oxidation of electrodes made of nickel, titanium, graphite, etc. using an acidic bath containing cobalt salts contain cobalt oxides, etc., and are extremely electrochemically active in alkaline aqueous solutions. It has been revealed that this material has a high carbon content and can be used as a positive electrode active material for alkaline batteries.

The present invention is based on the discovery that this material heated at 800° C. or higher can be used as a positive electrode active material for nonaqueous batteries using lithium, sodium, magnesium, or the like as the negative electrode.

The active material according to the invention can basically be made by anodic oxidation using electrodes such as nickel in an oxidation bath containing a cobalt salt such as cobalt nitrate.

This material is stable in acidic baths, and the rate of formation increases with increasing current density. The form of formation of this substance varies depending on the material of the electrode.
When a titanium or graphite electrode is used as an electrode, it is obtained as a deposit on the surface of the electrode, but when a nickel plate is used as an electrode, this substance formed on the nickel plate becomes small flakes and peels off in the bath liquid.

In the former case, it can be obtained by applying vibration to the electrode or scraping off deposits, and in the latter case, it can be obtained by filtering the bath liquid.
The substance produced by this method can be easily made into a fine powder of several microns using a grinder or the like. According to the BET method, its surface area is extremely large, approximately 200 m ² /g. Chemical analysis of the materials produced in this way reveals that those using titanium or graphite for the electrodes have cobalt oxides and hydroxides as the main components, while those using nickel for the electrodes have cobalt oxides and hydroxides as the main components, although this varies depending on the bath composition. contains 1 to 50% nickel to cobalt.

When thermogravimetric analysis and differential thermal analysis of the latter material with a cobalt to nickel ratio of approximately 2:1 are performed at a heating rate of 10°C/min, the results are as shown in Figure 1. From the figure, a weight loss is observed at around 800°C, and an endothermic peak is also clearly observed. 900 of this substance
After heat treatment at ℃ for 10 minutes and X-ray diffraction analysis using CoKα rays, clear diffraction peaks were observed at 2θ of 43.0°, 50.05°, 73.50°, and 89.05°. It can be considered that this diffraction peak appeared because CoO and NiO formed a solid solution.
It was also found that in materials with a low nickel content, almost all CoO is formed when the temperature exceeds 800°C.

A specific method for producing this substance will be described below. Using a platinum plate as a counter electrode in a 3M cobalt nitrate aqueous solution adjusted to pH = 2, a nickel plate with a thickness of 3 mm was stirred at a current density of 3 A/dm ² and a bath temperature of 80°C. energize the nickel plate so that the anode current flows through it. When the current is continued, a black film is formed on the surface of the nickel board and then peeled off.The nickel board gradually becomes thinner, and the film becomes flakes with a diameter of 0.5 to 3 mm and floats in the bath liquid.
After the energization ends, the substances thus produced are filtered and collected using a filter. In this case, if a titanium or graphite electrode is used instead of the nickel plate, this substance will adhere to the surface, so it can be scraped off and collected after electricity is applied. The material thus obtained is a substance containing cobalt as a main component, as described above. As for the bath solution, a nitric acid aqueous solution has the best yield, but a sulfuric acid bath, a hydrochloric acid bath, or a mixed bath solution thereof can also be used. Furthermore, a similar substance can be produced by adding not only a cobalt salt but also a nickel salt to the bath solution, but as the nickel content increases, the nickel content tends to increase in the resulting product. When the material thus produced is heat-treated at 800°C or higher in the air range, CoO or a solid solution of CoO and NiO is formed.

Next, a non-aqueous solution battery using the material of the present invention obtained by this heat treatment, for example, Li,
Among batteries using Na, Mg, Al, etc., lithium, which exhibits the lowest potential, is used as a representative example of the negative electrode active material, and examples and effects thereof will be described in detail.

Example 1 Fine powder according to the present invention with a nickel content of 10 wt% based on cobalt obtained by heat treatment at 900°C
After thoroughly mixing 0.4g with 10wt% of graphite as a conductive agent and 5wt% of polytetrafluoroethylene powder as a binder, the mixture was molded into a disk shape (11mmφ) at a pressure of 500Kg/ ^cm2 to make a positive electrode plate. The negative electrode plate was manufactured by punching out a disk shape (7.5 mmφ) from a 1.25 mm sheet obtained by rolling metallic lithium. This lithium negative electrode plate was crimped to a stainless steel current collector welded to a stainless steel negative electrode can, and the positive electrode plate was similarly crimped to the positive electrode can. Propylene carbonate in which 1 mol/mol of lithium perchlorate (LiClO ₄ ) was dissolved was used as the electrolytic solution, and this was used by impregnating a polypropylene nonwoven fabric separator. A button-shaped battery A according to the present invention having an outer diameter of 11.6 mm and a height of 4.2 mm was manufactured by using these elements with insulating packing made of polypropylene.

Figure 2 shows the discharge characteristics when this battery was discharged at 25°C through a constant resistance of 15KΩ. For comparison, batteries C and D, which were manufactured in the same manner as in the example using commercially available CoO powder and NiO powder as positive electrode active materials, are also shown.

From the figure, battery A of the present invention is different from conventional batteries C and D.
It can be seen that the discharge voltage is clearly higher and the discharge duration is longer. The reason why the battery according to the present invention has extremely high performance compared to conventional batteries is that the conventional CoO and NiO are manufactured by thermally decomposing chemically created hydroxides and nitrates, or are made from metals. In contrast to those produced by oxidizing cobalt and nickel, CoO and Co
(Ni)O is produced by heating a material with an extremely large surface area obtained using electrochemical means, which is a completely new production method, at 800°C or higher, so it has no electrochemical activity. It is considered expensive.

As described above, the present invention produces a material produced by anodic oxidation using an electrode such as nickel in an acidic bath containing a cobalt salt, and then heat-treats the material at 800°C or higher to produce a positive electrode active material for a non-aqueous electrolyte battery. By using this method, it is possible to provide a battery with excellent performance.

[Brief explanation of drawings]

Figure 1 shows the results of thermogravimetric analysis and differential thermal analysis of the electrochemically produced cobalt-nickel mixed oxide used in the present invention, and Figure 2 shows the results of battery A according to the present invention and conventional batteries C and D. It is a comparison diagram of discharge characteristics.

Claims (1)

[Claims] 1. A method for producing a positive electrode active material for a non-aqueous electrolyte battery, which comprises heat-treating a material produced by anodizing using a nickel electrode in an acidic bath containing a cobalt salt at 800°C or higher. .