Crystalline-Amorphous Core−Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes

Abstract

Silicon is an attractive alloy-type anode material for lithium ion batteries because of its highest known capacity (4200 mAh/g). However silicon's large volume change upon lithium insertion and extraction, which causes pulverization and capacity fading, has limited its applications. Designing nanoscale hierarchical structures is a novel approach to address the issues associated with the large volume changes. In this letter, we introduce a core-shell design of silicon nanowires for highpower and long-life lithium battery electrodes. Silicon crystalline-amorphous core-shell nanowires were grown directly on stainless steel current collectors by a simple one-step synthesis. Amorphous Si shells instead of crystalline Si cores can be selected to be electrochemically active due to the difference of their lithiation potentials. Therefore, crystalline Si cores function as a stable mechanical support and an efficient electrical conducting pathway while amorphous shells store Li(+) ions. We demonstrate here that these core-shell nanowires have high charge storage capacity ( approximately 1000 mAh/g, 3 times of carbon) with approximately 90% capacity retention over 100 cycles. They also show excellent electrochemical performance at high rate charging and discharging (6.8 A/g, approximately 20 times of carbon at 1 h rate).

Solution-Grown Silicon Nanowires for Lithium-Ion Battery Anodes

“…Our previous EPS studies 44,45 on VLS SiNWs found that lithiation of the crystalline SiNW occurs at 0.125 V vs Li/Li ϩ , whereas lithiation of amorphous Si occurs at higher potentials (ϳ0.22 V vs Li/Li ϩ ). During the first lithiation step, a small peak at about 0.6 V is observed from initiation of the SEI formation 29 due to the reduction of the electrolyte.…”

“…This shell is composed of polyphenylsilanes that form as a reaction byproduct during the large-scale SFLS growth of SiNWs (Ͼ10 mg). 15 Carbon coating 21 of battery materials has been frequently used to improve the electron flux to the surface of the Li insertion material, aid electron transport between particles, and to improve rate performance. For Si, carbon coating may also be used to buffer the large volume changes and control the solid electrolyte interphase (SEI) formation, as well as improve the electronic conductivity of the electrode.…”

Tailoring the shape of amorphous nanomaterials: recent developments and applications

“…The long-range disorder of amorphous materials generally makes them unable to form 1D nanostructures, which have obvious anisotropy, without any attached host [62] or particular guiding technique [63][64][65][66][67]. Nanotubes, NWs, and nanofibers are three typical types of 1D nanomaterials.…”

Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium–Sulfur Battery Cathode Material with High Capacity and Cycling Stability

“…It is worth noting that the graphene-sulfur composite could be coupled with silicon based anode materials for rechargeable batteries with significantly higher energy density than currently possible. [31][32][33] In such batteries, Li + could be preloaded into either sulfur or silicon. 11,33 In summary, we have developed a graphene-sulfur composite material by synthesizing submicron sulfur particles coated with PEG containing surfactants and graphene sheets.…”