Pyrite FeS2–C composite as a high capacity cathode material of rechargeable lithium batteries

Abstract

Pyrite FeS₂ is a promising cathode material for rechargeable lithium batteries because of its high theoretical capacity (894 mA h g⁻¹), low cost and near-infinite earth abundance. However, the progress in developing viable Li/FeS₂ batteries has been hampered by the poor cyclability of the FeS₂ cathode. Aiming to improve the cyclability of the FeS₂ cathode, we here report a facile method for the synthesis of FeS₂–C composites by a one-pot hydrothermal reaction of FeSO₄ and Na₂S₂ in the presence of carbon black, and examine the effect of composition on the structure of FeS₂–C composites and the cycling performance of Li/FeS₂ cells. It is shown that the added carbon not only surrounds the FeS₂ surface but also penetrates into the entire FeS₂ particle, forming continuously conductive networks throughout the FeS₂ particle. However, introduction of carbon meanwhile increases the particle size of the FeS₂ active material. These two factors lead to an improvement in the rate capability of Li/FeS₂ cells while having little effect on the specific capacity and capacity retention of the FeS₂ cathode. On the other hand, we show that the electrolyte plays an important role in affecting the cyclability of Li/FeS₂ cells, and that the ether- and carbonate-based electrolytes affect the cycling performance of Li/FeS₂ cells in their unique manners.