Among advanced materials studied to enhance the performance and energy storage of Li-ion batteries, silicon was found to be the most promising next-generation anode material with its exceptional theoretical gravimetric capacity of approximately 4200 mAh/g which is ~10 times higher than that of the commercially used anode material graphite and the proper working voltage range. However, the dramatic volume expansion of ~400% during the lithiation and delithiation process 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 the surface of silicon nanoparticles that will reduce the strain caused by volume variation due to lithiation and delithiation in the cycling process.<br/>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. Full cells with LiCoO<sub>2</sub> also show a similar trend as the half cells. Chemical and surface analytical techniques such as Fourier transformation infrared spectroscopy(FTIR), x-ray photoelectron spectroscopy (XPS), hard x-ray photoelectron spectroscopy (HAXPES), thermogravimetric analysis (TGA), scanning electron microscopy, 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 improves the performance and the results of this study will be discussed.

Use of citric acid to form an artificial SEI on silicon nanoparticles to enhance the performance of lithium-ion battery anodes

256th National Meeting (2018)

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