Low viscosity/high conductivity sodium haloaluminate electrolyte

Abstract

An additive that is added to the NaAlX.sub.4 electrolyte for use in a ZEBRA battery (or other similar battery). This additive has a moiety with a partial positive charge (+) that attracts the negative charge of the [AlX.sub.4].sup. moiety and weakens the ionic bond between the Na.sup.+ and [AlX.sub.4].sup. moieties, thereby freeing some Na.sup.+ ions to transport (move). By using a suitable NaAlX.sub.4 electrolyte additive, the battery may be operated at much lower temperatures than are typical of ZEBRA batteries (such as, for example, at temperatures between 150 and 200 C.). Additionally, the additive also lowers the viscosity of the electrolyte solution and improves sodium conductivity. Non-limiting examples of the additive SOCl.sub.2, SO.sub.2, dimethyl sulfoxide (DMSO, CH.sub.3SOCH.sub.3), CH.sub.3S(O)Cl, SO.sub.2Cl.sub.2. A further advantage of using this additive is that it allows the use of a NaSICON membrane in a ZEBRA-type battery at lower temperatures compared to a typical ZEBRA battery.

Claims

1. A molten sodium battery cathode electrolyte consisting of: a quantity of molten sodium haloaluminate having a viscosity and a sodium ion conductivity, wherein the sodium haloaluminate is represented by the formula Na.sup.+[AlX.sub.4].sup., where X is a halogen, wherein an ionic bond exists between the Na.sup.+ and [AlX.sub.4].sup. moieties; and a quantity of an additive that lowers the viscosity of the sodium haloaluminate and increases the sodium ion conductivity of the sodium haloaluminate at a temperature in the range from 150 to 200 C., wherein the additive is present in an amount less than 50 mole % of the sodium haloaluminate.

2. The molten sodium battery cathode electrolyte of claim 1, wherein the additive has a moiety with a partial positive charge (+) that attracts the negative charge of the [AlX.sub.4].sup. moiety and weakens the ionic bond between the Na.sup.+ and [AlX.sub.4].sup. moieties.

3. The molten sodium battery cathode electrolyte of claim 1, wherein the additive is selected from the group consisting of SOCl.sub.2, SO.sub.2, DMSO (CH.sub.3SOCH.sub.3), CH.sub.3S(O)Cl, and SO.sub.2Cl.sub.2.

4. The molten sodium battery cathode electrolyte of claim 1, wherein X is selected from chlorine, bromine, and iodine.

5. The molten sodium battery cathode electrolyte of claim 1, wherein the viscosity of the electrolyte is lowered by about 50%.

6. The molten sodium battery cathode electrolyte of claim 1, wherein the sodium conductivity is increased by at least 10%.

7. A molten sodium battery comprising: a molten sodium metal negative electrode, which electrochemically oxidizes to release sodium ions during discharge and electrochemically reduces sodium ions to sodium metal during recharging; a positive electrode compartment comprising a positive electrode disposed in a positive electrolyte, wherein the positive electrolyte consists of: a quantity of molten sodium haloaluminate having a viscosity and a sodium ion conductivity, wherein the sodium haloaluminate is represented by the formula Na.sup.+[AlX.sub.4].sup., where X is a halogen, wherein an ionic bond exists between the Na.sup.+ and [AlX.sub.4].sup. moieties; and a quantity of an additive that lowers the viscosity of the sodium haloaluminate and increases the sodium ion conductivity of the sodium haloaluminate, wherein the additive is present in an amount less than 50 mole % of the sodium haloaluminate; and a sodium ion conductive electrolyte membrane that separates the molten sodium metal negative electrode from the positive electrolyte, wherein the sodium metal negative electrode is in contact with the conductive electrolyte membrane as the battery operates, and wherein the battery functions at an operating temperature between about 150 C. and about 200 C.

8. The molten sodium battery of claim 7, wherein the positive electrolyte additive has a moiety with a partial positive charge (+) that attracts the negative charge of the [AlX.sub.4].sup. moiety and weakens the ionic bond between the Na.sup.+ and [AlX.sub.4].sup. moieties.

9. The molten sodium battery of claim 7, wherein the positive electrolyte additive is selected from the group consisting of SOCl.sub.2, SO.sub.2, DMSO (CH.sub.3SOCH.sub.3), CH.sub.3S(O)Cl, and SO.sub.2Cl.sub.2.

10. The molten sodium battery of claim 7, wherein the sodium ion conductive electrolyte membrane comprises a NaSICON-type material.

11. The molten sodium battery of claim 10, wherein the NaSICON-type material comprises a composite membrane having a porous layer and a dense functional layer.

12. The molten sodium battery of claim 7, wherein X is selected from chlorine, bromine, and iodine.

13. A method of lowering the viscosity and increasing the sodium ion conductivity of a molten sodium battery, molten sodium haloaluminate cathode electrolyte comprising: obtaining a quantity of sodium haloaluminate cathode electrolyte consisting of sodium haloaluminate, wherein the sodium haloaluminate is represented by the formula Na.sup.+[AlX.sub.4].sup., wherein an ionic bond exists between the Na.sup.+ and [AlX.sub.4].sup. moieties; adding a quantity of an additive to the sodium haloaluminate to lower the viscosity of the sodium haloaluminate and increase the sodium ion conductivity of the sodium haloaluminate, wherein the additive is added in an amount that is less than 50 mole % of the sodium haloaluminate; and heating the sodium haloaluminate to temperature in the range from 150 to 200 C.

14. The method of claim 13, wherein the additive has a moiety with a partial positive charge (+) that attracts the negative charge of the [AlX.sub.4].sup. moiety and weakens the ionic bond between the Na.sup.+ and [AlX.sub.4].sup. moieties.

15. The method of claim 13, wherein the additive is selected from the group consisting of SOCl.sub.2, SO.sub.2, DMSO (CH.sub.3SOCH.sub.3), CH.sub.3S(O)Cl, and SO.sub.2Cl.sub.2.

16. The method of claim 13, wherein X is selected from chlorine, bromine, and iodine.

17. The method of claim 13, wherein the viscosity of the electrolyte is lowered by about 50%.

18. The method of claim 13, wherein the sodium conductivity is increased by at least 10%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the manner in which the above-recited and other features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

(2) FIG. 1 shows an example of a battery, and more specifically, a ZEBRA battery;

(3) FIG. 2 shows the chemical interactions between an additive (SOCl.sub.2) and the NaAlX.sub.4 species, as described herein.

(4) FIG. 3 shows the chemical interactions between an additive (SO.sub.2) and the NaAlX.sub.4 species, as described herein.

(5) FIG. 4 shows the chemical interactions between an additive (DMSO, CH.sub.3SOCH.sub.3) and the NaAlX.sub.4 species, as described herein.

(6) FIG. 5 shows the chemical interactions between an additive (CH.sub.3S(O)Cl) and the NaAlX.sub.4 species, as described herein.

(7) FIG. 6 shows the chemical interactions between an additive (SO.sub.2Cl.sub.2) and the NaAlX.sub.4 species, as described herein.

DETAILED DESCRIPTION OF THE INVENTION

(8) The present embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the methods and batteries of the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of present embodiments of the invention.

(9) The present embodiments relate to additives that may be added to a sodium haloaluminate (NaAlX.sub.4) electrolyte as a means of lowering the viscosity of this material, and thereby lowing the temperature required to operate the battery.

(10) Specifically, as shown in FIG. 2, the electrolyte will include NaAlX.sub.4. (In the embodiments shown in FIG. 2, the halide (X.sup.) moiety is a chloride (Cl.sup.) moiety; however, a bromide (Br.sup.) moiety or an iodide (I.sup.) moiety may likewise be used as the halide (X.sup.) moiety. The electrolyte also includes an additive, which in the embodiment of FIG. 2 comprises thionyl chloride (SOCl.sub.2). Because the O and Cl moieties of the thionyl chloride are more electronegative than the sulfur, these moieties withdraw electrons from the sulfur (e.g., are electron withdrawing groups). This causes a slight positive charge on the sulfur atom (as represented by the + superscript). This slight positive charge of the sulfur is attracted to the negatively charged X.sup. moiety of the [AlX.sub.4].sup. ion. In turn, this attraction between the S and the halide moiety of the [AlX.sub.4].sup. ion weakens the bond between the sodium ion and the [AlX.sub.4].sup. ion, thereby allowing some of the Na.sup.+ ions to move throughout the electrolyte. At the same time, the additive SOCl.sub.2 also operates to decrease the viscosity of the electrolyte. This reduction in viscosity further allows the Na.sup.+ ions to flow through the system.

(11) FIG. 3 shows the chemical interactions between an additive, sulfur dioxide (SO.sub.2) and the NaAlX.sub.4 species, in a manner similar to thionyl chloride described above. The sulfur atom has a slight positive charge on the sulfur atom (as represented by the + superscript). This slight positive charge of the sulfur is attracted to the negatively charged X.sup. moiety of the [AlX.sub.4].sup. ion. In turn, this attraction between the S and the halide moiety of the [AlX.sub.4].sup. ion weakens the bond between the sodium ion and the [AlX.sub.4].sup. ion, thereby allowing some of the Na.sup.+ ions to move throughout the electrolyte. At the same time, the additive SO.sub.2 also operates to decrease the viscosity of the electrolyte. This reduction in viscosity further allows the Na.sup.+ ions to flow through the system.

(12) FIG. 4 shows the chemical interactions between an additive, dimethyl sulfoxide (DMSO, CH.sub.3SOCH.sub.3) and the NaAlX.sub.4 species, in a manner similar to thionyl chloride described above. The sulfur atom has a slight positive charge on the sulfur atom (as represented by the + superscript). This slight positive charge of the sulfur is attracted to the negatively charged X.sup. moiety of the [AlX.sub.4].sup. ion. In turn, this attraction between the S and the halide moiety of the [AlX.sub.4].sup. ion weakens the bond between the sodium ion and the [AlX.sub.4].sup. ion, thereby allowing some of the Na.sup.+ ions to move throughout the electrolyte. At the same time, the additive DMSO also operates to decrease the viscosity of the electrolyte. This reduction in viscosity further allows the Na.sup.+ ions to flow through the system.

(13) FIG. 5 shows the chemical interactions between an additive, CH.sub.3S(O)Cl and the NaAlX.sub.4 species, in a manner similar to thionyl chloride described above. The sulfur atom has a slight positive charge on the sulfur atom (as represented by the + superscript). This slight positive charge of the sulfur is attracted to the negatively charged X.sup. moiety of the [AlX.sub.4].sup. ion. In turn, this attraction between the S and the halide moiety of the [AlX.sub.4].sup. ion weakens the bond between the sodium ion and the [AlX.sub.4].sup. ion, thereby allowing some of the Na.sup.+ ions to move throughout the electrolyte. At the same time, the additive CH.sub.3S(O)Cl also operates to decrease the viscosity of the electrolyte. This reduction in viscosity further allows the Na.sup.+ ions to flow through the system.

(14) FIG. 6 shows the chemical interactions between an additive, sulfuryl chloride (SO.sub.2Cl.sub.2) and the NaAlX.sub.4 species, in a manner similar to thionyl chloride described above. The sulfur atom has a slight positive charge on the sulfur atom (as represented by the + superscript). This slight positive charge of the sulfur is attracted to the negatively charged X.sup. moiety of the [AlX.sub.4].sup. ion. In turn, this attraction between the S and the halide moiety of the [AlX.sub.4].sup. ion weakens the bond between the sodium ion and the [AlX.sub.4].sup. ion, thereby allowing some of the Na.sup.+ ions to move throughout the electrolyte. At the same time, the additive sulfuryl chloride (SO.sub.2Cl.sub.2) also operates to decrease the viscosity of the electrolyte. This reduction in viscosity further allows the Na.sup.+ ions to flow through the system.

(15) By having the Na.sup.+ ions transport through the system, the ZEBRA battery can be used to store power and subsequently release power, as desired. At the same time, the fact that the Na.sup.+ ions can transport through the system means that the battery can be operated at lower temperatures (of between 150 to 200 C.) rather than the traditional temperature of 300 C. or greater. This lower operating temperature is much easier to achieve and maintain. Furthermore, a lower operating temperature results in costs savings as less resources need to be devoted to heating the battery to the proper temperature.

(16) Further, because lower temperatures are available, the sodium ion conductive electrolyte membrane is no longer required to be Beta Alumina. Rather, embodiments may be constructed in which the membrane is made of NaSICON. NaSICON is a membrane material that is commercially available from Ceramatec, Inc. of Salt Lake City, Utah. U.S. Patent Application Publication No. 20070138020 describes the structure and properties of NaSICON as well as other membrane materials that may be used in the present embodiments. The entire disclosure of this published U.S. application is expressly incorporated herein by reference.

(17) One of the features of NaSICON is the ability to create two distinctive environments on different sides of the membrane. This means that the solutions for the anolyte and catholyte may be different, the pressures on each side of the membrane may be different, the reactants and reaction conditions on each side of the membrane may be different, etc. In other words, the designer of the battery or secondary cell can tailor/select reactants/conditions for both the anolyte and catholyte that optimize each specific reaction. In some embodiments, the NaSICON membrane may have excellent conductivity (such as up to 100 mS/cm at 175 C.). The NaSICON membrane can be a supported membrane that is between 50-25 microns thick.

(18) Additional embodiments may be designed in which the additive is a different chemical other than thionyl chloride, SOCl.sub.2, SO.sub.2, dimethyl sulfoxide (DMSO, CH.sub.3SOCH.sub.3), CH.sub.3S(O)Cl, SO.sub.2Cl.sub.2, described above. It is understood that corresponding chemicals using a different halogen other than chlorine may be used. Moreover, other suitable additive chemicals may be used that have a moiety with a partial positive charge (+) that attracts the negative charge of the [AlX.sub.4].sup. moiety and weakens the ionic bond between the Na.sup.+ and [AlX.sub.4].sup. moieties. Thus, other chemicals (such as polar chemicals) that can interact with the [AlX.sub.4].sup. moieties in the manner outlined above and allow the Na.sup.+ ions to transport may be used as the electrolyte additive. These electrolyte additives may operate to lower the viscosity of the electrolyte.

(19) It should be noted that with respect to SO.sub.2, this chemical may be used as either a gas or a liquid. Since the NaSICON membrane allows for different reaction conditions on either side of the membrane, the side with the SO.sub.2 could be pressurized so that the SO.sub.2 is in the liquid form.

(20) All the patent applications and patents listed herein are expressly incorporated herein by reference.