Polymer‐free Vertical Transfer of Silicon Nanowires and their Application to Energy Storage

Abstract

Silicon nanowires (SiNWs) for use as lithium-ion battery (LIB) anode materials have been studied for their one-dimensional (1D) properties and ability to accommodate large volume changes and avoid rapid capacity fading during cycling. Although the vertical transfer of SiNWs from their original substrate onto a conducting electrode is very important, to date, there has been no report of a direct integration method without polymer binders. Here, we propose for the first time a vertical transfer method for SiNWs grown on a Si substrate directly to the current-collecting electrode without using a polymer adhesive for the use as a binder-free LIB anode. The vertical SiNWs produced using a low-cost wafer-scale metal-assisted chemical etching (MaCE) process have been successfully transferred directly to a copper electrode coated with a thin Ag layer by using a simple hot pressing method. When evaluated as an LIB anode without using conventional polymeric binder and a conducting additive, the transferred vertically aligned SiNWs showed a high specific capacity (≈2150 mAh g(-1) ) and excellent rate performance. It is believed that the anode-manufacturing process is simple and fast, thus enabling a large-scale production that is of low-cost, broadly applicable, and provides new avenues for the rational engineering of Si-based electrode materials with enhanced power density and conductivity.

Design Considerations for Unconventional Electrochemical Energy Storage Architectures

“…The most straightforward approach for flexible electrodes fabrication is done by growing, functionalizing, or embedding active materials onto or within a flexible conductive scaffold that works as a current collector . Given the large availability and unique electrochemical properties, most of the methods exploit carbon‐based scaffolds such as woven fibers mats, nanotube forests, carbon cloth, Bucky papers, and others.…”

Rapid Low‐Temperature 3D Integration of Silicon Nanowires on Flexible Substrates

“…However, despite the importance of the polymer matrix in providing the mechanical support needed to allow the SiNWs to stand upright on the substrate, it also restricts their interaction with the surrounding environment. This has led to the development of polymer‐matrix‐free direct transfer methods based on using a polymer adhesive and thin metal film as an adhesive layer . For example, the direct transfer of SiNWs onto an Ag‐thin film that has been deposited on a Cu foil via thermo‐compression exposes the SiNWs to their surroundings, yet still provides a mechanically strong direct electrical contact with the substrate.…”

Facile Fabrication of Silicon Nanotube Arrays and Their Application in Lithium‐Ion Batteries

“…Many research reports have demonstrated that well‐aligned SiNWs with uniform length and diameter can be successfully fabricated using either bottom‐up or top‐down approaches, such as the vapor–liquid–solid (VLS) growth technique, metal‐assisted chemical etching (MaCE) process, and sidewall spacer method . However, SiNTs have been much less investigated than SiNWs because they have more difficult fabrication processes .…”

“…In addition, hollow‐structured Si nanomaterials, such as porous SiNWs, SiNTs, and porous Si nanoparticles have been widely studied as anode active materials for rechargeable lithium ion batteries (LIBs) that can accommodate large volume changes and avoid rapid capacity fading during cycling because of their 1D properties, including small size, large surface area, and stress alleviation induced by the distance between neighboring nanostructures . And, some research groups have proposed the surface coating technology of the Si‐based anode active materials for high‐performance LIBs …”

“…In order to check the feasibility of applying the fabricated SiNTs as lithium‐ion battery (LIB) anode materials, coin‐type half cells using SiNTs powder as the working electrode and lithium (Li) metal as the counter electrode were prepared under an Ar‐filled glove box. For comparison, SiNWs were also prepared by the same method (MaCE) under different conditions (metal catalyst: 5 nm thick platinum (Pt)) . For the LIB anode test, the active materials (SiNTs or SiNWs) were obtained from the Si wafer by ultra‐sonication treatment in ethanol solution .…”