Novel nanostructured composites materials for energy storage

The development of new carbon-based materials as electrode for lithium-ion batteries (LIBs) is a promising approach to challenge the limitations of the traditional electrodes and meet the ever-increasing demands for high energy and power densities for portable electronic devices. Due to their specific structures and unique properties, together with their easy syntheses and functionalization, nitrogen-containing porous carbons (NPCs) are recently receiving a great deal of attention in energy storage and conversion applications. This thesis reports on the design and evaluation of the electrochemical performance of macro and mesoporous nitrogen-doped carbons as anode material for LIBs. In this thesis work, the synthesis of nitrogen-doped porous carbon materials were performed successfully, using a polypyrrole and polyionic liquid (PIL) as the N-doped carbon precursor with polymer templated method to induce hierarchical porous structure in the carbon materials. Poly(methyl methacrylate) (PMMA) particles surrounded by graphene oxide sheets have been used as template. These particles are prepared by precipitation polymerization process in a water/methanol mixture in presence of graphene oxide sheets that stabilize the formation of polymer particles. This method has the advantage to not require the addition of a surfactant. Moreover, the GO sheets are reduced during the thermal treatment into graphene nanosheets (GNSs) which prevents the collapse of the pores, enhances the electrical conductivity and adds additional carbon source to the system. Practically, the pyrrole or the ionic liquid monomer is polymerized around the PMMA/GO particles followed by filtration and by an appropriate thermal treatment to decompose the PMMA template and to convert the graphene oxide into graphene and the polypyrrole or the PIL into N-doped carbon. These new NPCs materials, especially those prepared by using PIL as carbon source materials, demonstrated excellent performance as anode materials in the lithium and sodium-ion batteries, showing high potential applications in energy storage. In order to improve further the electrochemical performance of these electrodes, various inorganic nanoparticles, such as iron oxide and silicon NPs, have been introduced in the NPCs structure. Nanocomposites of N-doped carbon/Fe2O3 NPs with hierarchical and interconnected porous structures have been synthesized by simple addition of iron salts during the pyrrole polymerization. Anodes with 44 wt% of Fe2O3 NPs, exhibit a high reversible capacity of 930 mA h/g at a current density of 400 mA/g after 200 cycles based on the total mass loading of the composite. Furthermore, nanostructured 3D porous networks combining graphene, N-doped carbon and silicon NPs (G@Si@C) have been prepared in similar fashion and present an excellent reversible capacity of 740 mA h/g at a current density of 0.14 A/g in the potential range from 0.0 to 1.0 V after 125 cycles based on the total mass loading of the composite (include 30 wt% of Si NPs), with more than 99% coulombic efficiency, high rate capability and good cyclability. The excellent electrochemical performances exhibited by these different nanocomposites of NPCs/inorganic NPs demonstrate clearly that the resulting materials are promising candidates as anode materials for lithium-ion batteries.