Silicon-based Nanocomposite Materials For Anode In Lithium-ion Batteries

Solid-state rechargeable batteries, especially, lithium ion batteries, are principle and promising power sources for a wide variety of electronics. Electrode material is a key for developing further lithium ion batteries, which are likely to require good reliability and high energy density. In recent years, silicon has attracted considerable attention as a potential Li-ion battery anode material to replace the current graphite anode due to its high capacity (specific capacity of4200mAhg corresponding to the Li22Si5, the maximum lithium containing alloy phase in the Li□Si system). However, the commercial application of the silicon anode in current lithium-ion batteries is hindered by the rapid capacity decay during cycling because of the enormous volume changes associated with the various phase transitions known to occur during the lithium alloying and de-alloying processes resulting in decrepitating of the particles comprising the electrode finally leading to electrode failure. Several strategies have been explored in recent years to overcome this problem. The use of nanoparticles in composite electrodes for lithium-ion batteries may have considerable kinetic advantages due to the reduction of the diffusion length for lithium-ion insertion into the active mass, and also because of the reduction of the overall charge transfer resistance of the electrodes. In this doctoral work, several silicon-based nanostructured composite materials were examined and characterized for possible application as anode materials for lithium-ion batteries.Carbon-coated silicon nanoparticles (Si@C) composite was synthesized by the polymerization of dopamine onto Si nanoparticles and carbonization of the polymer. Silicon nanoparticles were thus coated by amorphous carbon to reduce silicon volume expansion upon cycling, also to avoid aggregation of silicon nanoparticles. The composite material as anode in LIB retains a discharge capacity of376mAhg-1after67cycles, at current density100mAg-1. The main reason for this markedly improved electrochemical performance appears to be the beneficial effect of the carbon shell which enhances the dimensional stability of the silicon nanoparticles.Silicon-carbon nanotube (Si/CNT) composite was prepared by chemical vapor deposition (CVD), by growing CNTs onto silicon nanoparticles. This composite presents good cycling stability; it retains450mAhg-1after100cycles at current densities of100mA/g. This relative improve cycle performance can be ascribed to the maintenance of a good electronic conducting network due to the robust adherence of CNTs on Si and the excellent flexibility of CNTs, which can accommodate the severe volume change of Si upon lithium insertion and extraction.Finally graphene encapsulated silicon nanoparticles (GE-Si) composite was prepared in a two-steps process; first self-assembling of APS modified Si@SiO2and graphene oxide (GO), secondly, reduction of the graphene oxide to graphene. The Si/graphene composites exhibit relative improved cycling performance,426mAhg-1after100cycles at current density166mAg, which is better than that of bare Si nanoparticles. The highly compliant and flexible graphene layers could offer enhanced stress and strain resilience during charge/discharge cycling and thereby improve the structural stability and integrity of the composite anodes.