NOVELTY - A cathode composition (C1) comprises a first element selected from nickel or cobalt; a second element M selected from iron or cobalt, where the second element M is contained within a sulfide composition MxSy, where the ratio of x and y is between 0.5:1 and 1.5:1; at least one first alkali metal halide; and an electrolyte salt comprising a second alkali metal halide and a metal halide, where the electrolyte salt has a melting point of 150-300 degrees C; where the molar ratio of the first element to the sulfur in the sulfide composition is 1.5:1 to 50:1.    USE - In an energy storage device (Claimed) including primary battery, secondary battery, fuel cell, ultracapacitor, lithium battery, lithium ion battery, lithium polymer battery, or nickel metal hydride battery.    ADVANTAGE - The composition demonstrates advantageous retention of performance during repeated cycling. The energy storage device is rechargeable over several cycles. An improvement in the amount of energy per day is observed in the cells containing a higher percentage of FeS in relation to nickel.    DETAILED DESCRIPTION - A cathode composition (C1) comprises a first element selected from nickel or cobalt; a second element M selected from iron or cobalt, where the second element M is contained within a sulfide composition MxSy, where the ratio of x and y is between 0.5:1 and 1.5:1; at least one first alkali metal halide; and an electrolyte salt comprising a second alkali metal halide and a metal halide, where the electrolyte salt has a melting point of 150-300 degrees C; where the molar ratio of the first element to the sulfur in the sulfide composition is 1.5:1 to 50:1; where cobalt cannot be both the first element and the second element; and where the first alkali metal halide and the second alkali metal halide may be the same. INDEPENDENT CLAIMS are included for the following:    (1) an article comprising the cathode (C1);    (2) an energy storage device comprising first compartment comprising metallic alkali metal; second compartment comprising the cathode composition (C1); solid separator capable of transporting alkali metal ions between the first and second compartments.