Fe3C doped modified nano-Si/C composites as high-coulombic-efficiency anodes for lithium-ion batteries

Abstract

Silicon is considered to be the most promising candidate for the anode of high energy density lithium-ion batteries. Nanometerization has been proven to be an effective method for improving the stress accumulation caused by the volume expansion of silicon. However, new issues such as poor initial coulombic efficiency (ICE) need to be solved because nanostructure silicon has an increased specific surface area. Here, a doping modification strategy is developed by a solvothermal combined with low-pressure gas–solid conversion reaction, and innovatively formed an Fe₃C/N co-doped carbon coating on the nano-silicon surface. The doping of Fe₃C in the composite material can catalyze the formation of a thin and stable solid electrolyte interphase (SEI) on the electrode surface and serve as a framework to stabilize the electrode structure during charge and discharge. As a result, Fe₃C doping can significantly increase the ICE of the electrode from 66.4% to 87.1%, and the stable efficiency exhibited a rapid increase upwards of 99.5% after only 6 cycles including the first formation cycle, compared to the non-doped structure. The modified nano-silicon with Fe₃C doping can provide high reversible capacity (1443.3 mA h g⁻¹ after 200 cycles at 0.2 A g⁻¹) and long cycle life (74% capacity retention after 1000 cycles at 0.5 A g⁻¹).