JPH04282570A - Alkali metal-metal chloride battery - Google Patents

Abstract

PURPOSE:To prevent precipitation by a reducing discharge product so as to improve energy density and output density by using specific cerium as a positive pole active material. CONSTITUTION:Alkali metal is used as a negative pole active material, and melted sodium 302, positive pole active material tetravalent cerium-contained melted tetrachloro aluminate sodium 304 and a positive pole tungsten electrode 305 are separated by a selective ion conductive separator 303. These materials are stored in a carbon-steel vessel 301, functioning as a negative pole collecting unit, to separate positive-negative pole collecting units 305, 301 by an electric insulator 306. Thus by using tetravalent cerium for a positive pole active material, energy density and output density can be improved by suppressing precipitation by a reducing discharge product.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to an alkali metal-metal chloride battery, and focuses on the use of tetravalent cerium (Ce4+) produced from CeCl3 as a positive electrode active material.

0002

SUMMARY OF THE INVENTION The present invention provides high energy density and
In order to obtain a battery with a power density exceeding 0W/Kg,
Tetravalent cerium (Ce4) produced from CeCl3 is used as a soluble positive electrode active material in alkali metal-metal chloride batteries.
+) is used.

0003

BACKGROUND OF THE INVENTION High temperature sodium-metal chloride battery systems are attractive battery systems for both electric drives and load leveling devices. It is similar when compared to the more well-known high temperature sodium-sulfur battery system in that both cells use a sodium-conducting sodium aluminate electrolyte to separate molten sodium from the cathode material. The cathode material in sodium-sulfur cells is liquid sulfur, whereas (in sodium-metal chloride cells) metal chloride suspended or dissolved in molten sodium chloroaluminate is used as the cathode material. The use of molten sodium chloroaluminate and metal chloride as cathode materials has a few advantages over sulfur. Sulfur has a high vapor pressure and the discharge product, sodium polysulfide, is extremely corrosive even to high grade steels. Additionally, sulfur is a poor conductor in the fully charged state, requiring the addition of a conductive material such as carbon felt. Sodium tetrachloroaluminate melts at 153° C. and is much less corrosive to container materials and sealants than sodium polysulfide. Its high sodium conductivity is independent of the charge state of the active metal chloride.

The choice of metal chloride to be suspended or dissolved in molten sodium chloroaluminate determines the open circuit potential and theoretical energy density of the cell. In the suspended structure, the metal chloride is insoluble in the molten electrolyte, and the active metal chloride and reaction products must be in intimate contact with the current collecting electrode. In reality, the current collecting electrode is
It is a complex of reduced metal and activated metal chloride. An example of this structure is shown in FIG. 101 is a metal container that functions as a current collector for the negative electrode. 102 is molten sodium. 103 is a sodium conductive solid electrolyte, typically beta double prime alumina (actual composition approximately Na6Al32O51). 104 is molten sodium tetrachloroaluminate. 105 is a complex mixture of iron and iron(II) chloride. 106 is an electrically insulating material, typically alpha alumina, for separating the negative and positive current collectors. 107 is a positive electrode current collector. For this type of structure to produce high power density,
It is necessary that the composite electrode have sufficient porosity to allow diffusion of alkali metal and chloride ions into and out of the active material. Additionally, the composite electrode must retain structural strength as the battery cycles between charged and discharged states. Metal and chloride metal couples usually have different densities, so the composite electrode
It must be able to withstand expansion and contraction during charging and discharging.

Ideally, in the dissolved configuration, both the active metal chloride and its corresponding reduction product are soluble in the molten alkali metal chloroaluminate salt. An inert current collecting electrode is used in this case, which donates electrons to the metal chloride during discharge. Therefore, in this case, the active material and the reaction product are not limited to being part of the current collecting electrode, so that a larger amount of active material can be filled into the positive electrode compartment of this structure. If on the anode side the active material or its reduced discharge products precipitates out of solution, the cell capacity decreases as the cycle progresses because transfer of material or charge to the current collecting electrode cannot easily occur. Metal chloride or its reduction reaction product is
It may also react with the ion-conducting separator and cause damage. As the ionic conductivity of the separator decreases, there will be less theoretical energy in the cell available for useful work. Another embodiment is shown in FIG. 201 is a metal container that functions as a current collector for the negative electrode. 202
is molten sodium. 203 is a sodium conductive solid electrolyte, typically beta double prime alumina (actual composition approximately Na6Al32O).
51). 204 is molten sodium tetrachloroaluminate containing molten SCl4. 205 is a platinum current collecting electrode. and 206 is an electrically insulating material to separate the negative and positive electrode current collectors, typically alpha alumina.

A hanging type 42Ah cell using iron(II) chloride as the active material and having an energy density exceeding 120Wh/Kg was fabricated (Tilley, A.
R. , Bull, R. N. ,Intersociety
Energy Conversion Eng
inering Conference), Philadelphia, August 1987, Paper No. 879227)
. Dissolved electroactive material type cell using SCl4 (Ma
mantov, G. , Marassi, R. ,Mats
unaga, M. , Ogata, Y. , Wiaux, J.
．． P. , Fraser, E. J. , Journal
of the ElectrochemicalS
ocity. , 127, 1980, 2319), but 2
It was demonstrated to have an energy density of over 50Wh/Kg. Together with both examples, they demonstrate the feasibility of achieving high energy densities in alkali metal-metal chloride battery systems without experiencing some of the same problems that have slowed the development of sodium-sulfur batteries.

[0007]

However, all known alkali metal-metal chloride battery systems are unable to achieve power densities exceeding 200 W/Kg, which are required for practical electric drives. Alkali metal-metal chloride cells with suspended cathode material cannot meet the power requirements due to mass transfer limitations and passivation of the electrode surface by the alkali metal chloride. (Ratnakumar
,B. V. , DiSefano, S. ,Halpert
,G. , J. Electrochem. Soc. ,13
7, 1990, 2991). Dissolved cathode material structures theoretically do not have the same mass transfer limitations as suspended cathode structures, and so far have not been able to approach the power density of suspended structures. Reasons for this include disturbances due to the reaction of dissolved metal chloride with the ion-conducting separator, and irreversible precipitation of reduction reaction products. These problems are addressed by FeCl3, SbCl3, and SCl4 (Dell, R.M., Bones, R.J.
,B. Electrochem. , 4, 1988, 31
9) has been observed for dissolved metal chlorides. By careful selection of the metal chloride, the common problems of molten electrode construction can be solved so that alkali metal-metal chloride batteries with high energy density and power density exceeding 200 W/Kg can be obtained. This is the object of the present invention.

[0008]

[Means for Solving the Problems] The present invention provides an alkali metal as a negative electrode active material, tetravalent cerium (Ce4+) produced from CeCl3 as a positive electrode active material, an electrolyte of molten alkali metal chloroaluminate, and a negative electrode and a positive electrode. An alkali metal-metal chloride battery comprising a selectively ion-conducting separator disposed between active materials.

[0009]

[Operation] Since both CeCl3 and its oxide, tetravalent cerium (Ce4+), are soluble in a molten salt solution, it is possible to select limited discharge conditions that do not cause precipitation of cerium metal. can. By preventing the precipitation of reduced discharge products, an alkali metal-metal chloride battery based on CeCl-derived tetravalent cerium (Ce4+) with high energy density and power density exceeding 200 W/Kg is obtained. .

0010

EXAMPLE An example of the alkali metal-metal chloride battery of the present invention is shown in FIG. 301 is a carbon-steel container that functions as a current collector for the negative electrode. 302 is molten sodium. 303 is beta double prime alumina (actual composition is approximately N), which is a sodium conductive solid electrolyte.
a6Al32O51). 304 is dissolved Ce
This is molten sodium tetrachloroaluminate containing tetravalent cerium (Ce4+) produced from Cl3. 305 is a tungsten current collecting electrode. 306 is alpha alumina, an electrically insulating material for separating the negative and positive electrode current collectors.

The cells were assembled and tested as follows. First, the beta double prime alumina tube is
A boron oxide-alkali metal oxide based glass solder was used to bond to the alpha alumina ring. A platinum cathode compartment lid with a reactant filling site and a vertically disposed current collecting electrode was then bonded to the alpha alumina ring by thermopressure bonding. Thereafter, a carbon steel negative electrode compartment container having a reactant filling site was bonded to the cylindrical exterior of the alpha alumina ring by thermopressure bonding. The cathode compartment was filled with a 1:1 mixture of CeCl and NaCl (80% by weight) and sodium tetrachloroaluminate (20% by weight);
Thereafter, it was sealed under an argon atmosphere. The negative electrode compartment was filled with sufficient molten sodium, the beta double prime alumina tube and the carbon steel negative electrode compartment container were brought into electrical contact, and then sealed under an argon atmosphere. This cell was heated to 300°C and charged to 3.60V with constant current charging. Following this initial charging operation, the cell was repeatedly measured between 3.60 and 2.20V at 2/3 open circuit voltage and 70% depth of discharge, with an energy density greater than 100 Wh/Kg and 2
A power density exceeding 0.06 W/Kg was obtained. This cell was tested over 100 times, but only slight deterioration in cell performance was observed. When the cell was disassembled and inspected, no precipitation of metallic bismuth and no decolorization of the inner surface of the beta double prime alumina tubes were observed.

0012

[Comparative example] As a comparative example, antimony trichloride (SbCl
The cell was assembled by the same method as described in this example, except that 3) was used as the positive electrode active material and the negative electrode compartment was filled with 3 equivalents of sodium. There was no need to charge this cell initially. The reason is that in this case the cell was assembled in a charged state. It was tested under the same conditions used for the present invention. Initially energy density ratios greater than 100 Wh/Kg and power densities greater than 110 W/Kg were observed. However, below 10 cycles, these values clearly decreased. Inspection of the disassembled cell revealed that metallic antimony had precipitated and the internal surfaces of the beta double prime alumina tubes were clearly darkened.

[0013]

[Effect of the invention] Alkali metal as negative electrode active material, tetravalent cerium (Ce4+) derived from CeCl3 as positive electrode active material
By manufacturing an alkali metal-metal chloride secondary battery using an electrolyte of molten alkali metal chloroaluminate and a selectively ion-conducting separator placed between the anode and cathode active materials, high energy density and 200W A battery with a power density exceeding /Kg can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional hanging type alkali metal-metal chloride battery.

FIG. 2 is a schematic diagram of a conventional melt-type alkali metal-metal chloride battery.

FIG. 3 is a schematic diagram of an alkali metal-metal chloride battery of the present invention.

[Explanation of symbols]

101 Metal container 102 functioning as a negative electrode current collector
Dissolved Sodium 103 Sodium conductive solid electrolyte. Typically β
"Alumina (composition example: Na6Al32O51) 104
Dissolved sodium tetrachloroaluminate 105 Mixture of iron and iron(II) chloride 106 Electrical insulator for separating the negative and positive electrode current collectors. Typically, α-alumina 107 A positive electrode current collector 201 A metal container 202 that functions as a negative electrode current collector
Molten Sodium 203 Sodium conductive solid electrolyte. Typically β
"Alumina (composition example: Na6Al32O51) 204
Sodium tetrachloroaluminate containing dissolved SCl4 205 Platinum current collector 206 Electrical insulator for separating the negative and positive electrode current collectors. Typically alpha alumina 301 Carbon steel metal container 302 which functions as a current collector for the negative electrode Molten sodium 303 Sodium conductive solid electrolyte. Typically β
"Alumina (composition example: Na6Al32O51) 304
Tetravalent cerium (C
e4+) containing molten sodium tetrachloroaluminate 305 Platinum current collector electrode 306 Electrical insulator for separating the negative and positive electrode current collectors. Typically alpha alumina

Claims (1)

[Claims] Claim 1: Tetravalent cerium (C) produced from an alkali metal as a negative electrode active material and CeCl3 as a positive electrode active material.
e4+), an electrolyte of molten alkali metal chloroaluminate, and a selective ion conductive separator disposed between a negative electrode and a positive electrode active material.