Cu silicide nanowires: Fabrication, characterization, and application to Li-Ion batteries

Document Type

Article

Publication Date

1-1-2017

Abstract

© 2013 by Taylor & Francis Group, LLC. Although batteries are inherently simple in concept, surprisingly, their development has progressed much more slowly than other areas of electronics [1]. The slow progress is due to the lack of suitable electrode materials and electrolytes, together with difficulties in mastering the interfaces between them. Traditional lithium-ion batteries employ carbonaceous anodes with a capacity of 372 mAhg-1. To obtain a substantial improvement in the specific capacity of Li-ion cells, it is essential to replace carbonaceous anodes with anodes having greater capacity. The most attractive candidate to replace carbonaceous anodes is silicon (Si), which has the highest known capacity, in excess of 4000 mAhg-1 [2,3]. Two major drawbacks have hindered the application of Si structures as anodes for Li-ion batteries. One is related to its electrical conductivity, which is much lower than graphite anodes. Consequently, during the charging process, the Li-ions cannot penetrate deep into the active Si anodes. As such, it is highly desirable to dope Si with other elements and improve its electrical transport. Among these dopants, alloying with copper (Cu) is favorable due to the fact that the current collector is also made of Cu [4]. In addition to the electrical conductivity drawback, the mechanical stresses associated with silithiation can be problematic. It is observed that upon driving Li-ions into Si, a volume expansion on the order of 300-400% [5,6] occurs due to the formation of various phases like Li12Si7, Li7Si3, Li13Si4, and Li22Si5 [7]. This leads to mechanical stresses large enough to fracture and pulverize Si into powder after the first few cycles of charging/discharging and eventually capacity fade during cycling [8]. To address this issue, it is suggested that a nanowire morphology 628will facilitate the lateral expansion of Si and enhance their fracture resistance [9]. In particular, single crystalline nanowires have the potential to exhibit ideal material characteristics for the design of nanotechnology-based fuel cells. For example, single crystalline nanowires may have a lower electrical resistivity and a higher tolerance to failure as compared to polycrystalline nanowires [10]. Recently, the fabrication of single crystalline freestanding Cu3Si nanowires was reported in Ref. [11] by the annealing of Cu/Ge bilayer films on a SiO2/Si substrate. However, obtaining the high-density coverage of single crystalline nanowires needed for anode materials remains a technical challenge.

Publication Title

Nanoelectronic Device Applications Handbook

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