| Among all the anode materials, silicon is one of the most attractive anode materials for lithium-ion batteries because of its highest capacity of4200mAh g-1, satisfactory voltage window for lithium insertion and extraction (<0.5V vs. Li/Li+), high safety and low cost. However, the practical utilization of Si as anode material is hindered by its huge volume changes (300%) induced by the lithium-ion insertion and extraction processes, culminating in the pulverization of electrode structure as well as the poor cycling performance. In addition, the low electrical conductivity of pristine Si and the difficulty in the formation of stable solid-electrolyte interface (SEI) films have also restrained the commercialization of Si anode material. In this paper, we have prepared a series of porous silicon based composites, aiming at solving the problems of current silicon anode materials. Those porous silicon based anode materials have demonstrated to be effective in maintaining good electronic contact among particles and accommodating the mechanical stresses experienced by the huge volume change of active silicon associated with Li insertion/extraction processes.1. Firstly, we have designed a three dimensional porous carbon-silicon (PC/Si) nanocomposite, in which Si nanoparticles were coated with a uniform porous carbon shell via self-assembly of a phenol formaldehyde resin by the assistance of triblock PEO-PPO-PEO copolymers. As expected, the as-prepared PC/Si exhibited a higher reversible specific capacity (1000mAh g-1at100mA g-1after100cycles) with stable coloumbic efficiency in the range of98-99%. The PC/Si composites suggest a much more stable cycling and enhanced capacitance compared to Si with direct carbon coating.2. Diatomite, a natural clay mineral, which contains a large number of fine microscopic pores. In the present work, we have synthesized a series of porous Si/C composites by employing diatomite as a raw material, followed by low temperature magnesiothermic reduction, impregnation and carbonization of phenolic resin. The optimized67%Si-33%C exhibits the highest reversible capacity of about1628mAh g-1at the first cycle with excellent capacity retention in the following cycles (759mAh g-1after30cycles) and high rate capacity of776mAhg-1at2A g-1. The present work has proposed an environmental friendly and price competitive approach for the production of porous Si/C anode materials. 3. Novel silicon nanoparticle/porous carbon nanofiber (Si/PCNF) hybrids with high Si loading (52wt.%) have been designed and fabricated through a simple electrospinning. With the presence of F127, which serves as both surfactant and template, the Si nanoparticles of high loading were found to be homogeneously dispersed in the as-spun carbon nanofibers. As a result, the free-standing Si/PCNF electrodes, serving as both anode-active materials and current collectors, exhibit stable cycling performance (ca.870mAh g-1at0.1A g-1after100cycles) and high rate capability (405mAh g-1at5A g-1). The mechanical flexibility of the Si/PCNF hybrids demonstrate that the film materials can be used as free-standing electrode with large-scale production for lithium ion batteries.4. By taking advantage of the robust and conductive TiOx/C frameworks, unique three-dimensional porous carbon/TiOx/silicon (C/T/Si,0<x<2) hybrid frameworks were scalable fabricated by current industrial techniques for electrodes of lithium ion batteries followed by heat treatment. Si nanoparticles are conformably encapsulated in the conducting TiOx/C matrix. As a consequence, the Si/TiOx/C exhibits a stable reversible specific capacity of1696mAh g-1at0.1A g-1after100cycles,87%capacity retention, and superior rate capability (754mAh g-1at15A g-1). |
