JPH06150905A - Composite metal electrode and method for manufacturing the same - Google Patents

Abstract

PURPOSE:To provide a high temperature type sodium-nickel chloride battery of high output density by applying the predetermined thickness of nickel plating to a carbon fiber body inactive to battery reaction and having a specific surface area equal to or above the predetermined value. CONSTITUTION:In a standard structure, an anode current collector 101 includes a metal vessel, a positive current collector 107, molten sodium 101, a sodium permeable solid electrolyte 103, molten tetrachlorosodium aluminate 104, a compound material of sodium and nickel chloride, and an electrical insulation ceramic 106. At a charging process, nickel turns into nickel chloride in a nickel positive electrode, and acts to collect electrons from a reaction section. Nickel directly involved in reaction, however, is located at depth up to approximately 0.2mum from the surface of the electrode and the nickel at a deeper position does not react, while acting as a conductor. Nickel plating of thickness equal to or less than 0.3mum is applied to a carbon body having a specific surface area equal to or above 0.55m<2>/g, and the surface of the body is evenly protected via decompression and deaeration at the plating process. When the plated body is used as a positive electrode, the utilization efficiency of a nickel positive electrode can be kept at 30% or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a nickel positive electrode for a sodium-nickel chloride secondary battery.

[0002]

2. Description of the Related Art A sodium-nickel chloride battery, which is a high-temperature type secondary battery, has the characteristics of high energy density and high output density and is attracting attention as a secondary battery for electric vehicles or power smoothing. A sodium-nickel chloride battery is composed of a conductive positive electrode having many fine holes, a liquid electrolyte composed of a molten salt of sodium-aluminum chloride, a solid electrolyte separating the positive electrode and the molten salt electrolyte from the negative electrode, and liquid sodium. To be done. (U.
S.Patent 4,626,483) The positive electrode is composed of nickel chloride, nickel or a metal whose main component is nickel, which is hard and insoluble to some extent, and a small amount of other transition metals. In this battery, the positive electrode active material during discharge is nickel chloride. Sodium aluminum halide electrolyte
It is NaAlCl ₄ and suspends sodium chloride. NaAlCl
_{4 The} electrolyte melts at 153 ° C. The solid electrolyte contains sodium ions, and a typical one is β ″ -alumina. (The actual composition is Na ₆ Al ₃₂ O ₅₁ ) A typical structure of a sodium nickel chloride battery is shown in FIG. 1. 101 is an anode A metal container functioning as a current collector of 102, 102 is molten sodium, 103 is a solid electrolyte permeable to sodium, and 104 is molten sodium tetrachloroaluminate.
105 is a composite of nickel and nickel chloride. 106 is an electrically insulating ceramic that insulates the current collectors of the anode and the cathode. 107 is a positive electrode current collector.

A conventionally reported method for producing a porous nickel positive electrode will be described below. First, a mixed powder of nickel powder and sodium chloride powder is sintered under reduced pressure. It is then placed in a new battery to electrochemically oxidize nickel into the active nickel chloride during the charging process.
(USPatent 4,626,483) About 100W by this manufacturing method
A battery having a high energy density of h / Kg can be obtained.

[0004]

However, in the electrode manufactured by the above-mentioned conventional manufacturing method, the maximum amount of nickel that can be electrochemically effectively utilized in the nickel-sodium chloride sintered body is 28% (this value). Is calculated from the measured values of cathode weight and charge / discharge capacity (hereinafter referred to as positive electrode utilization rate).

The ratio of the weight of the positive electrode Ni to the weight of the entire battery is large. Therefore, there are problems that a large amount of useless Ni that does not participate in the battery reaction, the Ni utilization rate is low, and the weight energy density is low.

Therefore, the present invention solves such a problem, and an object of the present invention is to achieve a high-temperature sodium-chloride having a high energy density and a high power density with a positive electrode utilization rate exceeding 30%. It is in the area of providing nickel batteries.

[0007]

[MEANS FOR SOLVING THE PROBLEMS] A composite metal electrode and a method for producing the same of the present invention for solving the problems are as follows: (1) 0.3 μm or less on a carbon fiber having a specific surface area of 0.55 m ² / g or more. Is coated with a metal having a thickness of.

(2) The metal is chromium, manganese, iron,
It contains one or more elements selected from cobalt, nickel, and copper.

(3) A metal is thinly coated on the surface of the carbon body having a large specific surface area by a plating method.

(4) It is characterized in that the carbon body is immersed in a plating solution, degassed under reduced pressure, and then plated.

[0011]

In the nickel positive electrode of the high temperature sodium-nickel chloride battery, nickel becomes nickel chloride during charging. At this time, nickel is a reactant and acts as a conductor for collecting electrons from the reaction part. Nickel, which is directly involved in the cell reaction, is about 0.2 μm from the surface. Nickel located deeper than this does not react with the battery and functions as a conductor.

The main causes of impeding the improvement of the utilization factor of the nickel electrode manufactured by the conventional sintering method are (1) nickel particles are larger than necessary (small specific surface area), (2)
There are two parts, that is, there is a part where the electrical continuity is interrupted in the constricted part of the particle assembly and it cannot be used. An ideal nickel electrode structure for solving the problem (1) is a fiber having a sufficiently thin and uniform thickness, or a sufficiently thin and uniform foil-like aggregate. In order to solve (2), a current collector that is inactive in the battery reaction is incorporated in the center of the nickel electrode.

The present invention solves these two problems at the same time and approaches the ideal state. That is, an electrode was obtained by uniformly coating nickel on a carbon fiber / body having a specific surface area of 0.55 m ² / g or more, which was inactive to the battery reaction, with a thickness of 0.3 μm or less by a plating method.

Since the carbon body is not a reactive substance, it does not react even if all the nickel reacts when fully charged, and functions as a stable current collector. However, if the amount is larger than necessary, the overall nickel utilization rate including the weight of carbon will decrease. As a result of our research, it has been found that when the specific surface area of the carbon body is set to 0.55 m ² / g or more, the excess weight of the carbon body is suppressed and the utilization factor is sufficiently improved. Further, in order to obtain a positive electrode utilization rate of 30% or more, the thickness of the coated nickel should be 0.3 μm.
It turned out that it was necessary to: It is speculated that this is related to the limit depth of reaction being 0.2 μm.

Since the carbon body has a large specific surface area, even if it is immersed in the plating solution, it has many bubbles on its surface. The bubbles prevent the formation of a uniform nickel coating on the entire surface of the carbon body. After immersing the carbon body in the plating solution and degassing under reduced pressure, the nickel plating solution comes into contact with the entire surface of the carbon body and a uniform nickel coating is formed.

[0016]

EXAMPLES The present invention will be described below based on examples.

First, carbon bodies having various specific surface areas are prepared. 2.67, 1.26, 0.55, 0.32, 0.2
Five levels of carbon fibers and carbon bodies having a specific surface area of m ² / g were prepared. The specific surface area of the carbon body was measured by krypton adsorption by the BET method.

A nickel film was coated on this carbon body by a plating method. In order to satisfactorily wet the surface of the carbon body with the plating solution, first, the carbon body was forcibly immersed in a plating bath, and then deaeration under reduced pressure was performed in the chamber to remove bubbles on the surface of the carbon body. The plating bath was mainly composed of nickel sulfamate, and the plating was performed while heating to about 50 ° C. and stirring. The current density on the carbon body electrode surface is 0.025
It was mA / cm ² , and the nickel coating thickness was controlled by controlling the plating time. The film thickness was measured by the amount of Coulomb required for plating and observation with a scanning electron microscope.

This nickel-coated electrode was incorporated and evaluated as a positive electrode of a sodium-nickel chloride battery. The cell is charged at a cutoff voltage of 2.8 volts at 0.1C and then discharged at 0.1C to a cutoff voltage of 2.0 volts. The utilization rate of the nickel positive electrode is calculated based on the Coulomb number of the electric charge obtained by the discharge. The utilization factor is the weight of nickel reacted in the battery divided by the total weight of the nickel-carbon composite electrode.

The results are shown in Table 1.

Table 1 shows the relationship between the oxygen content of the nickel electrode and the electrode utilization efficiency.

[0022]

[Table 1]

It is recognized that the higher the specific surface area of the carbon body and the smaller the coating thickness of nickel, the higher the nickel utilization rate is. The specific surface area of the carbon body is 0.55 m ² / g or more, and the coating thickness of nickel is 0. It can be seen that a utilization factor of 30% or more cannot be obtained unless the thickness is 0.3 μm or less.

In this embodiment, the effect was described only with respect to nickel, but the same effect can be obtained even if the positive electrode metal contains one or more elements of chromium, manganese, iron, cobalt, nickel and copper instead of nickel. You can get the effect.

Comparative Example 1 A nickel positive electrode is produced by a sintering method. Nickel powder (2 to 5 μm) and sodium chloride powder (53 to 125 μm) are mixed in a weight ratio of 3: 2. The mixture is press-molded with a nickel mesh sandwiched therebetween. Press the molded body for 30 minutes in a hydrogen reducing atmosphere for 7 minutes.
Sintered at 90 ° C.

This nickel sintered electrode was incorporated and evaluated as a positive electrode of a sodium-nickel chloride battery. The cell is charged at a cutoff voltage of 2.8 volts at 0.1C and then discharged at 0.1C to a cutoff voltage of 2.0 volts. The utilization rate of the nickel positive electrode is calculated based on the Coulomb number of the electric charge obtained by the discharge. The utilization factor is the weight of nickel reacted in the battery divided by the total weight of the nickel-carbon composite electrode. The utilization rate obtained was 29%.

(Comparative Example 2) Specific surface area of 0.55 m ² / g
An electrode was produced by omitting only the step of degassing under reduced pressure of the example for the carbon body of No. 3. The surface of the carbon body was coated with the same amount of nickel as the example in terms of Coulomb amount. Observation with a scanning electron microscope revealed that the nickel on the surface of the carbon body was non-uniform and the deposited nickel was thicker than in the examples.

When the utilization factor of this nickel-coated carbon electrode was evaluated in the same manner as in the examples, the utilization factor was 18%. Nickel adhered becomes too thick than the reaction limit depth,
It is presumed that the increase in nickel that did not react with the battery increased.

[0029]

The use of the electrode of the present invention as described above and the production method of the present invention have the effect of improving the nickel positive electrode utilization efficiency of a high temperature sodium-nickel chloride battery.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical structure of a sodium nickel chloride battery.

[Explanation of symbols]

 101 conductive container 102 sodium 103 sodium permeable solid electrolyte 104 molten sodium tetrachloroaluminate 105 composite of nickel and chloride 106 electrically insulating ceramics 107 positive electrode current collector

Claims (4)

[Claims] 1. A composite metal electrode, wherein a carbon body having a specific surface area of 0.55 m ² / g or more is coated with a metal having a thickness of 0.3 μm or less. 2. The composite metal electrode according to claim 1, wherein the metal contains one element or a plurality of elements selected from chromium, manganese, iron, cobalt, nickel and copper. 3. A method for producing a composite metal electrode, characterized in that the surface of a carbon body having a large specific surface area is thinly coated with a metal by a plating method. 4. The method for producing a composite metal electrode according to claim 3, wherein the carbon body is immersed in a plating solution, degassed under reduced pressure, and then plated.