High-Performance Lithium Battery Anodes Using Silicon Nanowires

Nature Nanotechnology (Impact Factor: 34.05). 01/2008; 3(1):31-5. DOI: 10.1038/nnano.2007.411
Source: PubMed


There is great interest in developing rechargeable lithium batteries with higher energy capacity and longer cycle life for applications in portable electronic devices, electric vehicles and implantable medical devices. Silicon is an attractive anode material for lithium batteries because it has a low discharge potential and the highest known theoretical charge capacity (4,200 mAh g(-1); ref. 2). Although this is more than ten times higher than existing graphite anodes and much larger than various nitride and oxide materials, silicon anodes have limited applications because silicon's volume changes by 400% upon insertion and extraction of lithium which results in pulverization and capacity fading. Here, we show that silicon nanowire battery electrodes circumvent these issues as they can accommodate large strain without pulverization, provide good electronic contact and conduction, and display short lithium insertion distances. We achieved the theoretical charge capacity for silicon anodes and maintained a discharge capacity close to 75% of this maximum, with little fading during cycling.

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    • "However, Si is subjected to extremely large volume change ($400%) during lithiation/delithiation process, which causes the pulverization of Si particles and loss of the electrical connection with current collector, resulting in rapid capacity fading. In addition, the severe volume change also brings about the repeated formation of solid electrolyte interphase (SEI) layer on Si surface, leading to low Coulombic efficiency (CE) during cycling process [4] [5] [6]. Moreover, the low intrinsic electrical conductivity of Si further compromises its cyclic stability and rate performance [7] [8]. "
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    ABSTRACT: Graphene and other carbon materials have been combined with various silicon (Si) nanostructures to accommodate the volume change of Si and enhance their electrical conductivity. However, for most of the formed hybrids, their low initial Coulombic efficiency (CE), fragile structures and poor stability cannot meet the practical application of battery. In this work, inspired by the structure and composition of reinforced concrete, a Si nanoparticles embedded in porous carbon/graphene (Si-C/G) electrode is fabricated through directly calcining a Si-polyacrylonitrile/graphene oxide precursor on a current collector. In this concrete-like structure, amorphous carbon, the carbonization product of polyacrylonitrile, acts as the “cement” and binds all components together. The flexible graphene network effectively enhances the strength, flexibility and conductivity of the electrode, as does the reinforcing rod framework in concrete. This carbon/graphene scaffold can accommodate the volume expansion of Si and isolate Si from electrolyte. Such Si-C/G electrode with small surface area and compact structure achieves a high initial CE of 78% and a reversible capacity of 1711 mAh g−1, as well as outstanding rate and cycling performances.
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    • "The major Li insertion occurred between $0.5 to 0.050 V and extraction between 0.15 and 0.6 V. Both the insertion and extraction curves showed tilt plateaus with larger slopes comparing to those of crystalline Si nanowires [12] [19], indicating that the Si-VACNF electrode is dominated by a battery behavior (represented by the flat plateau) but mixed with some pseudocapacitive contributions (represented by the tilt linear lines) due to the nanostructured Si shell. This can be attributed to the increase of the fast reactions at the Si surface, similar to the nanoscale size effects observed in high-rate Li intercalation in LiCoO 2 electrodes [7] [10]. "
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    • "Furthermore, these free spaces provide large active sites to accommodate lithium (Li + ) and create an easy path for electrolyte to access the entire electrode surface while reducing polarization which otherwise forms on the anode surface due to SEI (solid electrolyte interface) formation, hence improve the electrode service life eventually [10]. Within this scope, various studies have been conducted to form Si based nanorods such as laser irradiation [11], chemical vapor deposition [12], catalyst-free reactions [13] and lithography-based ion etching methods [14]. Other than that ''oblique angle deposition'' (OAD) via electron beam evaporation method has also become remarkable as it has the ability of avoiding the hazardous handling of flammable, explosive or cancerogen nanoparticles. "
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