Silicon nanowires for Li-based battery anodes: a review

Abstract

After more than 20 years of steady progress, lithium-ion batteries still exhibit modest energy capacities that seem to have reached their asymptotic values with the present combination of graphite at the anode and insertion oxide or phosphate materials at the cathode. New applications, particularly for all-electric vehicles are pushing the development of electrode materials with higher Li storage capabilities, for both electrodes.Silicon, which exhibits the highest known Li-alloying capacity is one of the most promising anode materials.However, Li alloying with Si is accompanied by a large volume change which induces cracking and rapid pulverization of Si-based anodes. Significant improvements in the anode's lifetime as well as chargedischarge rates have been obtained over the past few years by employing Si nanostructures, particularly nanowires. In this paper, we present the main synthesis methods for Si nanowires as well as the alloying properties of Li with Si and review how the use of Si-based nanowires has evolved, thanks to sophisticated material/structure combinations, including core-shell nanowires, composites as well as hollowed nanotube-like approaches.

In situ methods for Li-ion battery research: A review of recent developments

“…However, many authors recognize the difference in configuration as well as testing methods, between the investigated nano-batteries and bulk-size batteries that are used in practice [41,42,44]. For instance, due to the required nano-sized configuration of the batteries, the contacts are very small and often non-optimized, inducing significant overpotentials during battery operation, which might influence their characteristics.…”

Si-containing precursors for Si-based anode materials of Li-ion batteries: A review

“…SiOx is at the bottom of the Ag clusters and can be easily dissolved by HF, leading to the production of nanocups right under the Ag clusters. The formation and subsequent dissolution of SiOx can proceed continuously, due to the further deposition of Ag, thus further "digging" the holes in the Si substrate underneath the Ag particles, 52 resulting an array of Si nanowires. For example, large-area, oriented Si nanowire arrays formed on the Si wafer at near room temperature by localized chemical etching were reported by Zhu's group (Figure 1a and 1b).…”

“…51,52 The galvanic displacement reaction between Ag + ions and Si can create Ag clusters and SiOx simultaneously. SiOx is at the bottom of the Ag clusters and can be easily dissolved by HF, leading to the production of nanocups right under the Ag clusters.…”

“…During the VLS reaction, the silane decomposes, releasing silicon atoms which alloy with the metal, inducing eutectic formation, followed by silicon precipitation and nanowire growth from the silicon saturated nanoparticles. 52 For example, Chen's group 26 used SiH4 as the silicon precursor along with a templating method to synthesize hollow silicon using the CVD process (Figure 6a and 6b). They found that a silicon shell could be created on the outer surface of the templates and showed a uniform thickness distribution.…”

“…49,[74][75][76] The temperatures used in this VLS-CVD process range from 300 up to well above 1000 o C, depending on the types of gas precursors and metal catalysts that are employed. 49,52 The gaseous silicon-bearing precursors, such as silane (SiH4), disilane (Si2H6), dichlorosilane (SiH2Cl2), and tetrachlorosilane (SiCl4), are always employed as the silicon sources for synthesizing silicon nanowires, and gold (Au) is the most popular metallic catalyst for the VLS growth of nanosized silicon. [77][78][79][80][81] The name "VLS mechanism" refers, of course, to the fact that silicon from the vapor passes through a liquid droplet and finally ends up as a solid.…”