Uncovering a novel effect of continuous capacity rising performed by FeS/Fe3C/C composite electrodes for Lithium-ion Batteries.

FeS-based composites are sustainable conversion electrode materials for lithium-ion batteries combining features like low-cost, environmental friendliness and high capacities. However, they suffer from fast capacity decay and low electron conductivity. We open novel insights to a surprising phenomenon of this material. A FeS/Fe3C/C nanocomposite synthesized by a facile hydrothermal method is compared to pure FeS. When applied as anode materials for lithium-ion batteries, these two type of materials show different capacity evolution upon cycling. Surprisingly, the composite delivers a continuous increase of capacity instead of the expected capacity fading. This unique behavior is triggered by a catalyzing effect of Fe3C nanoparticles. The Fe3C phase is a beneficial by-product of the synthesis and was not intentionally obtained. In order to further understand the effect of interconnected carbon-balls on FeS-based electrodes, complementary analytic techniques are used. Ex situ X-ray radiation diffraction and ex situ scanning electron microscope are employed to track phase fraction and morphology structure. In addition, the electrochemical kinetics and resistance are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. These results reveal that the interconnected carbon balls have a profound influence on the properties of FeS-based electrodes resulting in an increased electrode conductivity, reduced particle size, and maintenance of the structure integrity.