TECHNOLOGY FOCUS - ELECTRONICS - Preferred Electrode: The electrode further comprises a fluid. The sulfur or metal sulfide is suspended and/or dissolved in the fluid. The electronically conductive particles are suspended in the fluid. The concentration of the first material is 2-10 M. The second electrode comprises an electro-active material comprising lithium. Preferred Device: In the energy storage device, the second electrode is in electrochemical communication with the first electrode. The second electrode comprises a second electro-active material comprising an electro-active metal or metal alloy of a non-sulfur element. At least one of the electrodes of the device is substantially fluid prior to first use; or both electrodes of the device are substantially fluid prior to first use. The device further comprises a layer adjacent the second electrode. The layer comprises lithium nitrite (LiNO3), a ceramic and/or a polymer. The energy storage device further comprises an ionically conductive membrane separating the first and second electrodes; and a metal salt. The concentration of the first material in the fluid is at least 1 M, preferably at least 2 M, especially at least 5 M. The concentration of the first material in the carrier fluid is at least 10 M, preferably at least 15 M, especially 1-20 M, particularly 2-10 M. Preferred Method: During reversible cycling of the energy storage device, a second metal sulfide is precipitated and subsequently dissolved. The first metal sulfide and the second metal sulfide are the same or different. The second metal sulfide is Li2S. The method of operating energy storage device, involves: reversibly cycling the device containing flowable electrode such that a metal sulfide is precipitated and subsequently dissolved in the electrode during the cycling. The precipitated and dissolved metal sulfide comprises Li2S. The reversible cycling occurs over a voltage of 0.45 V to 2.7 V. The electrode of the device is in motion during at least a portion of the cycling. The reversible cycling of the device involves: transporting the electrode through an electrode compartment; inhibiting the flow of the electrode; at least partially charging or discharging a portion of the electrode; and transporting the electrode out of the electrode compartment.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The electrode composition further comprises a metal salt dissolved and/or suspended in the fluid. The electronically conductive particles make up less than or equal to 0.5, preferably less than or equal to 1.5, especially 0.5-5, particularly 1.5-5 vol.%, of the electrode composition. Preferred Components: The metal sulfide comprises lithium sulfide, sodium sulfide, magnesium sulfide, aluminum sulfide, zinc sulfide, manganese sulfide, titanium sulfide, and/or an iron sulfide, preferably Li2S8 and/or Li2S6. The metal salt comprises bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), lithium triflate, sodium triflate, lithium perchlorate, sodium perchlorate, lithium tetrafluoroborate, and/or sodium tetrafluoroborate. The electronically conductive particles comprise carbon black particles. The concentration of sulfur in the fluid is at least 1 M, preferably at least 10 M, especially 1-20 M, particularly 2-10 M. The percolation threshold is less than or equal to 10, preferably less than or equal to 5, especially 0.5-10, particularly 1-3 vol.%, of the electronically conductive particles in the electrode composition. The percolating conductive network has a fractal dimension of 1.7-2.2, preferably 1.8-2.1. The ratio of the concentration of electronically conductive particles suspended in the fluid to the concentration of the sulfur or metal sulfide electro-active material dissolved and/or suspended in the fluid is less than or equal to 0.5 M.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The fluid is an ionically conductive fluid. The fluid comprises tetraethylene glycol dimethyl ether (TEGDME), dimethyl ether (DME), diglyme, triglyme, dioxolane (DOL), tetrahydrofuran (THF), methyl-THF, and/or gamma-butyrolactone (GBL). EXAMPLE - No suitable example given.