Production of silicon-graphene based hybrid nano composite anode electrodes and li-ion battery applications

Due to the high energy density and long cycling life, lithium ion batteries (LIBs) have been utilized as promising power sources for mobile devices, electric vehicles, and energy storage systems. Anode materials plays an important role in determining the overall performance of LIBs. In face of the increasing demand for next generation lithium ion batteries, Si has attracted much attention owing to its ultra high theoretical capacity (4.200 mAh/g, lithiated to Li4.4Si). At the same time, Si is world's second most abundant element and harmless to the environment. Nonetheless, there are still some disadvantages for the practical applications of Si as anode materials, including low intrinsic electric conductivity and large volume change (about %300) during the lithiation/delithiation process, which result in fast capacity fading and poor rate capability. Moreover, this large volume expansion will destroy the solid electrolyte interphase (SEI) protective layer on the surface of Si, which will result in a low Coulombic efficiency. Consequently, aggregation results in pulsing Si nanoparticles and loss of contact with the existing collector, resulting in poor electrochemical performance. In order to solve these problems carbon mainly serves as a protecting matrix for the volume change of Si particle. In this master thesis study, commercial silicon were coated with tetraethyl orthosilicate (TEOS) and carbon to produce yolk Shell nanoparticles and Si-C/Graphene hybrid composite free electrodes. The chemical and physical properties of the as-produced electrodes were analyzed with several testing methods. The electrochemical properties of the as-produced electrode materials were evaluated by assembling those electrodes in a CR2016 coin cell. The electrochemical tests were shown that the electrochemical performance of freestanding Si/C/Graphene and Yolk Shell Si-C/Graphene hybrid electrodes are far beyond the commercial graphite.