Silicon/polypyrrole nanocomposite wrapped with graphene for lithium ion anodes
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Silicon/polypyrrole nanocomposite wrapped with graphene for lithium ion anodes Changling Li1, Chueh Liu 1, Zafer Mutlu1, Yiran Yan1, Kazi Ahmed2, Mihri Ozkan2 and Cengiz S. Ozkan1,3 1 Materials Science and Engineering Program, University of California Riverside, CA 92521 2 Department of Electrical and Computer Engineering, University of California, Riverside, CA 92521 3 Department of Mechanical Engineering, University of California Riverside, CA 92521
ABSTRACT Herein, silicon nanoparticles (SiNPs) are coated with conducting hydrogel and wrapped with reduced graphene oxide (rGO) sheets via a facile and scalable solution-based sol-gel process. The in-situ polymerized polypyrrole (PPy) hydrogel forms an interconnected threedimensional (3D) fiber matrix. Amine and hydroxyl groups from the hydrogel assist the encapsulation of the SiNPs through hydrogen bonding. The electro-conductive PPy fiber network and the wrapping of rGO offer efficient electron and ion transport pathways. 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 current density of 2.1 A g-1, respectively.
INTRODUCTION The tremendous demand for improvement of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) has promoted extensive research into new generation energy storage devices[1-4]. Silicon (Si) is considered to be a promising alloy anode material for the next generation lithium ion batteries (LIBs) and has been utilized in several commercial anodes[5, 6]. This is due to its low discharge potential relative to Li/Li+ and the high theoretical capacity of 3572 mAh g-1 corresponding to the ambient temperature formation of a Li15Si4 phase[7]. However, Si suffers from poor capacity retention due to its large volume expansion in excess of 300% resulting from alloying with large amounts of Li during lithiation. Nano-materials synthesized by advanced technologies, such as atomic layer deposition[810], electrospinning[11, 12], and self-assembly[13, 14] are used for the production of novel structures. Several nanostructured silicon and their composites such as SiNPs, double-walled Si nanotubes/nanowires, porous silicon have been verified to create the void spaces necessary for volume change during alloying and dealloying[15-17]. Moreover, silicon-carbon composites are proposed as high-performance anodes for LIBs[18-20]. Recently, gel-like conductive polymers, such as polyaniline (PANI) and PPy have adjustable conductivity and excellent mechanical properties[21]. Those polymers not only act as adhesive to bind Si but also offer continuous electro-conductive frameworks, which can substitute traditional resistive binders (e.g. polyvinlidene difluoride (PVDF), polyacrylic acid (PAA)) and carbon black. In this work, we report on the synthesis of hierarchically nanostructured PPy hydrogel to encapsulate SiNPs with the wrapping of rGO sheets via a simple and scalable in-situ polymerization process. The continuous and seamless PPy coating wrapped with rGO sheets
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