TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The secondary cell (S1) is able to operate when a temperature of the negative electrode is: below 150 degrees C, or below 250 degrees C, preferably below 60 degrees C; and above 100 degrees C. The negative electrode remains solid as the secondary cell operates. The secondary cell (S1) further comprises: a non-aqueous anolyte solution disposed between the negative electrode and the electrolyte membrane; and (a1) a first reservoir in fluid communication with the positive electrode compartment, and (b1) 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. The current collector comprises a metal comprising copper, nickel, and/or zinc. The secondary cell (S2) is able to operate when a temperature of the negative electrode is 100-150 degrees C. The secondary cell (S2) further comprises (a1) and (b1) as above per se. The secondary cell (S3) is able to operate when a temperature of the negative electrode is below 60 degrees C. The secondary cell (S3) further comprises: a reservoir in fluid communication with the positive electrode compartment; and a pumping mechanism configured to cause the liquid positive electrode solution to flow from the reservoir into the positive electrode compartment and past the current collector.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The negative electrode comprises molten sodium metal. The negative electrode comprises a material comprising a sodium metal or sodium intercalating carbon anode. The electrolyte membrane comprises a sodium super ion conductors-type material. The sodium super ion conductor type material comprises a composite membrane having a porous layer and a dense functional coating layer. The negative electrode comprises molten sodium metal, where the secondary cell further comprises a second fluid reservoir in fluid communication with the negative electrode compartment, and a second pumping mechanism configured to cause the molten sodium metal to flow from the second reservoir into the negative electrode compartment. The current collector comprises a sodium intercalation material.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The liquid positive electrode solution comprises solvent comprising N-methyl formamide or dimethyl sulfoxide. The liquid positive electrode solution comprises a compound comprising sodium bromide, sodium iodide, or sodium chloride. The liquid positive electrode solution comprises sufficient amount of at least one of sodium halide or an elemental halogen to form a sodium polyhalide as the secondary cell operates. The liquid positive electrode solution comprises a complexing agent that is capable of forming a complex with at least one of a halogen, sodium halide, and polyhalide in the liquid positive electrode solution. The complexing agent comprises a tetramethyl ammonium halide compound. The liquid positive electrode solution comprises a molten sodium halide dissolved in a molten fluorosulfonyl amide, where the fluorosulfonyl amide comprises 1-ethyl-3-methylimidazolium-(bis(fluorosulfonyl) amide. The complex-agent comprises an N-methyl-N-methylmorpholinium halide material.