Carbon precursor coated iron monosulphide (CP@FeS) microcrystals are synthesized by a facile one-pot solvothermal reaction of FeSO₄ and two moles of Na₂S with sucrose as the carbon source, and evaluated as the cathode material of rechargeable lithium batteries. The results show that the obtained CP@FeS microcrystals consist of two FeS phases and contain a small amount of sulphur. In storage, FeS transforms into Fe₃S₄, which is further oxidized by oxygen in air to release elemental sulphur. Interestingly, such transformation and oxidation are found to affect only the first discharge voltage profile with negligible impact on the specific capacity and cycling performance of a Li/FeS battery. It is shown that the cyclability of the Li/FeS battery is greatly affected by the electrolyte solvent and charging cutoff voltage. In this paper, we discuss the chemical stability and redox mechanism of the FeS cathode material, and investigate the factors that affect the cycling performance of Li/FeS batteries.