Versatilely tuned vertical silicon nanowire arrays by cryogenic reactive ion etching as a lithium-ion battery anode

Andam Deatama Refino,Iqbal Syamsu,Erwin Peiner,Andika Pandu Nugroho,Naufal Hanif Hawari,Tobias Voss,Nursidik Yulianto,Hutomo Suryo Wasisto,Afriyanti Sumboja,Alina Syring,Evvy Kartini,Ferry Iskandar

doi:10.1038/s41598-021-99173-4

Abstract

Production of high-aspect-ratio silicon (Si) nanowire-based anode for lithium ion batteries is challenging particularly in terms of controlling wire property and geometry to improve the battery performance. This report demonstrates tunable optimization of inductively coupled plasma reactive ion etching (ICP-RIE) at cryogenic temperature to fabricate vertically-aligned silicon nanowire array anodes with high verticality, controllable morphology, and good homogeneity. Three different materials [i.e., photoresist, chromium (Cr), and silicon dioxide (SiO2)] were employed as masks during the subsequent photolithography and cryogenic ICP-RIE processes to investigate their effects on the resulting nanowire structures. Silicon nanowire arrays with a high aspect ratio of up to 22 can be achieved by tuning several etching parameters [i.e., temperature, oxygen/sulfur hexafluoride (O2/SF6) gas mixture ratio, chamber pressure, plasma density, and ion energy]. Higher compressive stress was revealed for longer Si wires by means of Raman spectroscopy. Moreover, an anisotropy of lattice stress was found at the top and sidewall of Si nanowire, indicating compressive and tensile stresses, respectively. From electrochemical characterization, half-cell battery integrating ICP-RIE-based silicon nanowire anode exhibits a capacity of 0.25 mAh cm−2 with 16.67% capacity fading until 20 cycles, which has to be improved for application in future energy storage devices.

Highlights

Production of high-aspect-ratio silicon (Si) nanowire-based anode for lithium ion batteries is challenging in terms of controlling wire property and geometry to improve the battery performance
Vertical Si nanowire arrays have been successfully fabricated by inductively coupled plasma reactive ion etching (ICP-RIE) at cryogenic temperature and subsequently utilized as an anode for half-cell lithium-ion battery
Among the investigated mask materials, the S iO2 mask has exhibited good selectivity and the lowest effect of undercuts on the nanowires demonstrating its suitability for realizing ICP-RIE-based Si anodes

Summary

Introduction

Production of high-aspect-ratio silicon (Si) nanowire-based anode for lithium ion batteries is challenging in terms of controlling wire property and geometry to improve the battery performance. It was demonstrated that heavily-n-doped Si nanowires could exhibit high conductivity, and ultrafast charging compared to their intrinsic counterparts[16] When they were fabricated using the MACE method, a drawback in terms of balancing the possible amount of dopants in Si nanowires and the resulting porosity was revealed[13]. Since the doping atoms act as nucleation sites for pore formation on the Si nanowire surface during chemical etching, higher doping concentrations yield more porous structures This porosity is beneficial to increase the active surface area and provide buffer space during the volume change of Si. excessive porosity in heavily doped Si nanowires facilitates more oxide formation, leading to lower battery performance

Methods

Results

Conclusion