FeNi2S4 QDs @C composites as a high capacity and long life anode material for lithium ion battery and ex situ investigation of electrochemical mechanism

Abstract

Nowadays, exploiting electrode materials with high energy density and long cycling life is crucial for meeting the urgent requirement of ever-growing energy storage for EV/HEV. Herein, we introduced a simple synthetic route to prepare FeNi2S4 QDs @C composites on a large scale. By means of suitable design, the ultra-small FeNi2S4 quantum dots (QDs) were encapsulated in the carbon matrix, and the forming FeNi2S4 QDs @C composites exhibit excellent electrochemical performances. When tested as anode materials for lithium ion battery, the high capacity of 920 mAhg−1 at 0.1 Ag-1 could be achieved. Except the high capacity, the FeNi2S4 QDs @C composites present the enhancing cycling stability, which demonstrated more than 700 cycles with twice capacity of graphite and capacity retention of almost 100% could be achieved, compared to the capacity of second cycle. Detailed investigations of phase evolutions by XRD patterns and TEM indicate the phase segregation of FeSx and NiSy during the charge/discharge process. The conversion reactions between Fe/Ni and FeSx/NiSy took place in the carbon matrixes, which would hinder the aggregation and grow-up of nanoparticles, resulting in the structure stability. Hence, the ultra-small size, self-doping and stable structure led to the superior electrochemical properties. We believe that the FeNi2S4 @C composites would be an alternative anode material for next generation lithium ion battery.