Surface Functionalization of Silicon Nanoparticles with Citric Acid for Enhanced Performance As Lithium Ion Battery Anodes

Among advanced materials studied to enhance the performance and energy storage of Li ion batteries, silicon nanoparticles have shown great potential as an anode material with its high theoretical gravimetric capacity of approximately 4200 mAh/g which is ~10 times higher than that of the commercially used anode material graphite. Nevertheless, the volume expansion of ~400% during the lithiation causes the electrode to suffer from rapid degradation, thus leading to poor cycle life. In this study we discuss the surface modification of silicon nanoparticles with citric acid for better cycling performance and capacity retention of silicon based electrodes. The objective of the study is to form a protective layer on silicon nanoparticles that will reduce the strain caused by volume variation due to lithiation and delithiation in the cycling process. Cycling performance studies have been conducted on 50% silicon containing electrodes as well as graphite silicon composite electrode (70:15 weight % respectively). Both types of electrodes have shown promising cycling performance data when the surface of was functionalized with citric acid. The results indicate good capacity retention of ~60% after 50 cycles from surface modified silicon electrodes as opposed to 45% with the surface unmodified electrode. Chemical and surface analytical techniques such as Fourier transformation infrared spectroscopy(FTIR), Xray photoelectron spectroscopy (XPS), hard x-ray photoelectron spectroscopy (HAXPES), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), electrochemical impedance spectroscopy was used to analyze the nanoparticle surface as well as the solid electrolyte interphase formed on the electrodes to further understand how this protective layer improve the performance and the results of this study will be discussed. Figure 1