Effect of Li–Si composites on electrochemical properties of silicon-based anode materials

Abstract

Metal silicides are considered promising candidates for the replacement of graphite due to their larger capacity than graphite used in Li-ion batteries. In this work, a type of lithium silicide composite material consisting of LixSi, graphite (G), and porous carbon (PC) together with carbon coating treatment, denoted as (LS-G-PC)@C, was prepared by high-energy ball milling and subsequent pitch pyrolysis. This type of material is used as a pre-lithiation additive to improve the initial Coulombic efficiency (ICE) of Si-based anodes. The microstructural characteristic of (LS-G-PC)@C composite material was analyzed by x-ray diffraction and scanning electron microscopy. The electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and capacity cycling tests. It has been found that the irregular particles of LS compounds are uniformly dispersed on the graphite sheet, which constitutes an effective conductive network together with PC. The addition of a 5 wt. % (LS-G-PC)@C pre-lithiation additive makes the ICE of a low ICE silicon-based composite material increase by 16%. At a current density of 100 mA g−1, the discharge capacity retention rate of the silicon-based composite increased from 86.1% to 91% after the 19th cycle, showing good cycle stability. Further work is to add higher levels of our pre-lithiation additive in order to improve the ICE significantly.