Rechargeable anion battery cell using a molten salt electrolyte

Abstract

A rechargeable electrochemical battery cell includes a molten carbonate salt electrolyte whose anion transports oxygen between a metal electrode and an air electrode on opposite sides of the electrolyte, where the molten salt electrolyte is retained inside voids of a porous electrolyte supporting structure sandwiched by the electrodes, and the molten salt includes carbonate including at least one of the alkaline carbonate including Li.sub.2Co.sub.2, NA.sub.2CO.sub.2, and K.sub.2CO.sub.2, having a melting point between 400 C. and 800 C.

Claims

1. A rechargeable battery cell comprising: an air electrode; a metal electrode; a molten salt electrolyte disposed between the air electrode and metal electrode and including a porous retaining material structured for accommodating a carbonate ion in a molten salt state, wherein at the air electrode a reduction-oxidation reaction between oxygen and the carbonate ion takes place, and wherein at the metal electrode, the carbonate ion interacts with metal for releasing/capturing oxygen during discharging/charging operation, respectively.

2. The rechargeable battery cell as claimed in claim 1, wherein an anion of the molten salt is a carrier for transporting oxygen between the air electrode and the metal electrode.

3. The rechargeable battery cell as claimed in claim 1, wherein the molten salt electrolyte comprises an alkali carbonate mixture of lithium carbonate (Li.sub.2CO.sub.3) and at least one material selected from the group consisting of sodium carbonate (Na.sub.2CO.sub.3), and potassium carbonate (K.sub.2CO.sub.3).

4. The rechargeable battery cell as claimed in claim 3, wherein the alkali carbonate mixture has a melting point between 400 C. and 800 C.

5. The rechargeable battery cell as claimed in claim 4, wherein the molten salt electrolyte consists essentially of lithium carbonate (Li.sub.2CO.sub.3) and potassium carbonate (K.sub.2CO.sub.3).

6. The rechargeable battery cell as claimed in claim 5, wherein the alkali carbonate mixture is transformed producing an eutectic molten salt when its composition ratio is constituted by 62 mol % of lithium carbonate (Li.sub.2CO.sub.3) and 38 mol % of potassium carbonate (K.sub.2CO.sub.3).

7. The rechargeable battery cell as claimed in claim 1, wherein the porous retaining material for the molten salt electrolyte is made of at least one material selected from the group consisting of lithium aluminate, lithium zirconate and stabilized zirconia.

8. The rechargeable battery cell as claimed in claim 1, wherein the metal of the metal electrode is selected from the group consisting of Sc, Y, La, Ti, Zr, Hf, Ce, Cr, Mn, Fe, Co, Ni, Cu, Nb, Ta, V, Mo, Pd and W.

9. The rechargeable battery cell as claimed in claim 1, wherein the reaction at the metal electrode is yCO.sub.3.sup.2+xMeMe.sub.xO.sub.y+yCO.sub.2+2ye.sup., wherein y=1-5 and x=1-4.

10. The rechargeable battery cell as claimed in claim 1, wherein the reaction at the air electrode is yCO.sub.2+y/2O.sub.2+2ye.sup.yCO.sub.3.sup.2, wherein y=1-5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention, reference may be made to the preferred embodiments exemplary of this invention, shown in the accompanying drawings in which:

(2) FIG. 1 illustrates the operation principles, generally, of prior art molten carbonate fuel cells;

(3) FIG. 2 illustrates the working principles of a rechargeable oxide-ion battery (ROB) cell; and

(4) FIG. 3 is a schematic illustration of the electrochemical battery of this invention, using molten salt electrolyte.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) The working principles of a rechargeable oxide-ion battery (ROB) cell are schematically shown in FIG. 2, where metal electrode (anode) 22, electrolyte 24 and air electrode (cathode) 26 are shown. In discharge mode, oxide-ion anions migrate from the high partial pressure oxygen side (air electrode 26) to the low partial pressure oxygen side (metal electrode 22) under the driving force of gradient of oxygen chemical potential. There exist two possible reaction mechanisms to oxidize the metal. One of them, as designated as Path 1, is that oxide ion can directly electrochemically oxidize metal to form a metal oxide. The other, as designated as Path 2, involves generation and consumption of gaseous phase oxygen. The oxide ion can be initially converted to gaseous oxygen molecules on the metal electrode, and then further reacted with metal via a solid-gas phase mechanism to form metal oxide. In charge mode, the oxygen species, released by reducing metal oxide to metal via electrochemical Path 1 or solid-gas mechanism Path 2, are transported from the metal electrode back to the air electrode.

(6) FIG. 3 illustrates the operational principles of the invented electrochemical battery of this invention based on CO.sub.3.sup.2 ion, consisting of an air electrode 30, molten salt electrolyte 32, and a metal electrode 34, with interaction of metal electrode CO.sub.2, and air electrode 30 with O.sub.2, CO.sub.2 exit entry. Retained inside voids of a porous electrolyte supporting structure, which is sandwiched by the electrodes 30 and 34, the molten salt 32 comprises carbonate mixture of Li.sub.2CO.sub.3 and at least one alkaline carbonate selected from the group consisting of Na.sub.2CO.sub.3 and K.sub.2CO.sub.3. These alkaline carbonates, as electrolyte, have a melting point between 400 C. and 800 C. In discharging mode, the CO.sub.3.sup.2 ion, generated by the reduction reaction of yCO.sub.2+y/2O.sub.2+2ye.sup..fwdarw.yCO.sub.3.sup.2 on the air electrode where y=1-5, diffuses through molten salt and reaches the metal electrode where it oxidizes metal of the metal electrode following the reaction of yCO.sub.3.sup.2+xMe.fwdarw.Me.sub.xO.sub.y+yCO.sub.2+2ye.sup., where Me=a metal of the metal electrode selected from the group consisting of Sc, Y, La, Ti, Zr, Hf, Ce, Cr, Mn, Fe, Co, Ni, Cu, Nb, Ta, V, Mo, Pd and W and where y=1-5 and x=1-4.

(7) The total discharging reaction of the invention is expressed as y/2O.sub.2+xMe.fwdarw.Me.sub.xO.sub.y. In the charging mode, the metal oxide is reduced back into metal, by the reaction Me.sub.xO.sub.y.fwdarw.y/2O.sub.2+xMe. On the metal electrode, the metal oxide is reduced following the reaction of Me.sub.xO.sub.y+yCO.sub.2+2ye.sup..fwdarw.yCO.sub.3.sup.2+xMe. The produced CO.sub.3.sup.2 ion reverses back to the air electrode and forms CO.sub.2 and O.sub.2 by the reaction of yCO.sub.3.sup.2.fwdarw.yCO.sub.2+y/2O.sub.2+2ye.sup.. A discharging-charging cycle essentially is the metal oxidation and reduction reaction of y/2O.sub.2+xMeMe.sub.xO.sub.y, which is utilized for releasing and capturing electrical charges for energy storage, respectively.

(8) In the invention, the anion of a molten salt (CO.sub.3.sup.2) is a carrier for transporting oxygen between the electrodes. The preferred molten salt is an alkali carbonate mixture of (Li.sub.2CO.sub.3) and at least one material selected from the group consisting of sodium carbonate (Na.sub.2CO.sub.3), and potassium carbonate (K.sub.2CO.sub.3). These alkali carbonate mixtures can preferably be transformed producing an eutectic molten salt when its composition ratio is constituted by about 62 mol % of Li.sub.2CO.sub.3 and about 38 mol % of K.sub.2CO.sub.3. The electrolyte is contained in a porous retaining material preferably selected from the group consisting of lithium aluminate, lithium zirconate and stabilized zirconia.

(9) While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.