SODIUM-HALOGEN SECONDARY CELL
A sodium-halogen secondary cell that includes a negative electrode compartment housing a negative, sodium-based electrode and a positive electrode compartment housing a current collector disposed in a liquid positive electrode solution. The liquid positive electrode solution includes a halogen and/or a halide. The cell includes a sodium ion conductive electrolyte membrane that separates the negative electrode from the liquid positive electrode solution. Although in some cases, the negative sodium-based electrode is molten during cell operation, in other cases, the negative electrode includes a sodium electrode or a sodium intercalation carbon electrode that is solid during operation.
1 . A sodium-halogen secondary cell, comprising:
a negative electrode compartment comprising a negative electrode that comprises sodium, wherein the negative electrode electrochemically oxidizes to release sodium ions during discharge and electrochemically reduces sodium ions to form sodium metal during recharge;
a positive electrode compartment comprising a current collector disposed in a liquid positive electrode solution that comprises at least one of a halogen and a halide, wherein the secondary cell is configured to perform one or more reactions in the positive electrode compartment selected from the following reactions:
NaX 3 +2 e − 3NaX
3X 2 +2Na + +2 e − 2NaX 3 ; and
a sodium ion conductive electrolyte membrane that separates the negative electrode from the liquid positive electrode solution.
2 . The secondary cell of claim 1 , wherein the negative electrode comprises molten sodium metal.
3 . The secondary cell of claim 1 , wherein the secondary cell operates when a temperature of the negative electrode is below about 150° C.
4 . The secondary cell of claim 3 , wherein the secondary cell operates when the temperature of the negative electrode is also above about 100° C.
5 . The secondary cell of claim 1 , wherein the electrolyte membrane comprises a NaSICON-type material.
6 . The secondary cell of claim 5 , wherein the NaSICON-type material comprises a composite membrane having a porous layer and a dense functional coating layer.
7 . The secondary cell of claim 1 , wherein liquid positive electrode solution comprises solvent selected to favor the reaction in the positive electrode compartment of 3X 2 +2Na + +2e − 2NaX 3 .
8 . The secondary cell of claim 1 , wherein liquid positive electrode solution comprises a dimethyl sulfoxide solvent.
9 . The secondary cell of claim 1 , wherein liquid positive electrode solution comprises a N-methyl formamide solvent.
10 . The secondary cell of claim 1 , wherein the liquid positive electrode solution comprises a compound selected from NaBr, NaI, and NaCl.
11 . The secondary cell of claim 1 , wherein the liquid positive electrode solution comprises a sufficient amount of at least one of the sodium halide and an elemental halogen to form a sodium polyhalide as the secondary cell operates.
12 . The secondary cell of claim 1 , wherein the liquid positive electrode solution comprises a complexing agent that is capable of forming a complex with at least one of a halogen, the sodium halide, and a polyhalide in the liquid positive electrode solution.
13 . The secondary cell of claim 1 , wherein the complexing agent comprises a tetramethyl ammonium halide compound.
14 . The secondary cell of claim 1 , wherein the current collector comprises a material selected from the group consisting of graphite, hard carbon, manganese, molybdenum, tungsten, titanium, tantalum, copper, nickel, zinc, and combinations thereof.
15 . The secondary cell of claim 1 , further comprising:
a first reservoir in fluid communication with the positive electrode compartment; and
a first pumping mechanism configured to cause the liquid positive electrode solution to flow from the first reservoir into the positive electrode compartment and past the current collector.