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Advanced Nanomaterials for Renewable Energy and Sustainability

  • Author(s): Li, Changling
  • Advisor(s): Ozkan, Cengiz S.
  • et al.
Abstract

Lithium-ion batteries (LIBs) is believed to be one of the most promising alternatives to non-renewable fossil fuels for energy crisis, environmental protection and sustainable development. To further increase the energy and power densities of LIBs, nanostructured silicon and its nanocomposites were synthesized to achieve high-capacity, environmentally benign, and highly scalable candidates for the next generations of Li-Ion anodes. Herein, four distinct silicon-based nanostructures were synthesized and thoroughly characterized including silicon-carbon fabrics, nano-silicon from unrecycled glass bottles (gSi), conducting hydrogel coated silicon nanocomposites, and graphene wrapped conducting polymer-silicon hybrid structure. The electrochemical properties of silicon based nanomaterials were characterized in terms of cyclic voltammetry (CV), long-term capacity stability, rate capability and potentiostatic electrochemical impdedance spectroscopy (PEIS), and galvanostatic charge-discharge curves.

Highly flexible and free-standing silicon-carbon (Si/C) fabrics are synthesized via simultaneous double-nozzle electrospinning. The binderless and current collector-free fabrics are used as Li-ion anodes with an overall capacity of ~1000 mAh g-1. 92 % capacity retention after 100 cycles coupled with the excellent rate capability up to 9.3 A g-1 demonstrate its superior flexibility over the conventional electrodes.

A conversion from potential glass waste into high-purity nano-silicon is synthesized by a surface protected magnesiothermic reduction. Carbon-coated glass derived-silicon (gSi@C) anodes demonstrate excellent electrochemical performance with a capacity of ~1420 mAh g-1 at C/2 after 400 cycles. Full cells are assembled using gSi@C anodes and LiCoO2 cathodes, and achieve good cycling stability with high energy density.

Conducting hydrogels are formed to coat Si surfaces via an in-situ polymerization process. Functional groups from hydrogels chemically improve the adhesion of conducting coatings on Si surface, rendering the Si-hydrogel hybrid structure without resistive binders and carbon black. It is observed that the degree of enhancing the cycling stability and rate capability of the conductive hydrogels decrease in the order of polypyrrole (PPy) > polyaniline (PANI) > poly(acrylic acid) (PAA).

Silicon nanoparticles (SiNPs) are coated with polypyrrole-hydrogel and wrapped with reduced graphene oxide sheets (rGO) via an environmentally benign and scalable sol-gel process. The PPy/SiNPs/rGO electrodes can produce highly reversible capacities of 1312, 1285 and 1066 mAh g-1 at 100, 250 and 500 cycles at a high current density of 2.1 A g-1, respectively.

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