Development of nanostructured silicon/carbon composites as advanced anodes for lithium ion batteries

Graphite has dominated the market for anode materials of lithium ion batteries (LIBs) for more than two decades owing to its low working potential, excellent cyclic stability, low cost and environmental friendliness. Nevertheless, the capacity delivered by graphite with a theoretical specific capacity of 372 mAh g-1 is far from sufficient to satisfy today’s demanding and emerging applications like electric vehicles (EVs) and smart grids, which require much higher energy/power densities, longer cyclic life and lower costs than current LIBs can offer. Exploring and developing alternative electrodes to meet the above requirements become exigent and imperative. Si has long been identified as one of the most promising alternatives to graphite owing to its high theoretical capacity of ~4200 mAh g-1, a low working potential of ~370 mV and abundance in nature. Despite these intriguing benefits, Si electrodes suffer from important drawbacks, like fast capacity degradation, potential pulverization and the formation of unstable solid electrolyte interface (SEI) along with huge volume expansion of ~300 % during discharge. This thesis is dedicated to mitigating the above challenges and developing advanced Si/C composites with excellent electrochemical property. The research objectives include not only designing novel nanostructures but also understanding the lithiation mechanisms by special techniques like in-situ microscopy. Carbon nanofibers (CNFs) containing uniformly dispersed Si nanoparticles (NPs) are synthesized via one-pot electrospinning and carbonization as free-standing electrodes for LIBs. As a prerequisite, monodispersion of Si NPs in aqueous solution is obtained via amino-silane functionalization followed by F ion mediation. The graphene oxide sheets and graphene-covered Ni particles are further introduced to improve the ionic/electronic conductivities of Si/CNF composites, the resultant Si/CNF/G, Si/CNF/Ni electrodes deliver remarkable electr