Study on the nitrogen-doped carbon coated silicon nanoparticles for high performance lithium-ion battery anodes

Abstract

Lithium-ion batteries have been widely used as power sources for portable electronic devices such as cellular phones, digital cameras, and laptop computers in the past few decades. Recently, with the concern about environmental pollution and a spike in oil prices, much attention has been devoted to the large-scale lithium-ion batteries for electric vehicles (EV) and energy storage systems (ESS). Silicon is the most promising anode material for these future applications owing to its high specific capacity (4200 mA h g-1), low cost, and safety. However, the practical use of silicon anode has been impeded by several limitations. First, silicon experiences volume expansion by up to 300 % upon lithium insertion, which leads to the pulverization of active material and the disruption of solid electrolyte interphase (SEI) layer. It is well known that a SEI layer formed on silicon surface plays a critical role in achieving good cycle stability. Second, silicon shows poor rate capability due to its intrinsically low electronic conductivity. To overcome these limitations, many researchers have introduced effective SEI-forming electrolyte additives and conductive carbon coatings. In this work, silicon nanoparticles encapsulated with nitrogen-doped carbon (Si@N-C) was prepared and applied as an anode material. The nitrogen functionalities within the carbon lattice not only increase the electronic conductivity but also enhance the affinity to lithium ions. In addition, nitrogen-doped carbon actively reacts with fluoroethylene carbonate (FEC), which is one of the effective SEI-forming additives, results in a stable SEI layer. The effect of nitrogen-doped carbon on the electrochemical properties of silicon anodes was identified using galvanostatic charge/discharge tests. To explain the enhanced performance of Si@N-C anode, various techniques such as SEM, TEM, TGA, XPS, and EIS were conducted.