Facile conversion of waste laboratory glass to high purity silicon nanomaterial and its potential application as an anode material in lithium-ion batteries

Abstract

In the current global environment, the search for sustainable energy solutions has become crucial. As the demand for efficient energy storage is growing, Lithium ion (Li-ion) batteries have emerged as a key technological advancement. Li-ion batteries have become indispensable in the current days powering anything from electric vehicles to portable devices. Owing to the high energy density, extended cycle life and efficiency, it facilitates to shift towards the clean and sustainable energy technologies. Thus, the improvement of Li-ion batteries continues to be an essential topic of significant research interest. The performance, stability, and energy density of lithium-ion batteries are all significantly influenced by the anode material. Traditionally, graphite has been the most popular anode owing to its reversible Li-ion intercalation ability and structural stability. However, in order to meet the growing need for more faster charging, and more capacity alternative materials are being explored. Therefore, development of sophisticated anode materials is crucial for next generation Li-ion batteries. Silicon (Si) has been regarded as the promising anode material in Li ion batteries owing to the high theoretical specific capacity and low working potential. The scope of this report is to synthesize the Si nanomaterial from waste laboratory glass via facile magnesiothermic reduction method. The reason behind choosing the waste material as a precursor to produce high value nanomaterial is to emphasize more on the sustainable and circular approaches in material science. Discarded laboratory glassware is majorly composed of silica (SiO2) which is abundant and underused resource for the production of Si nanomaterial. To obtain pure Si nanomaterial, the various reaction parameters such as the feed particle size, weight ratio of the feed, acid leaching duration, reaction temperature and reaction time have been optimized as the reaction parameters vary with the different feed source. The synthesized Si has been well characterized using the sophisticated techniques such as X-ray Diffractometry, RAMAN Spectroscopy, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, Field-Emission Scanning Electron Microscopy and High-Resolution Transmission Electron Spectroscopy. After optimizing the above-mentioned parameters, the Si produced has been used as an anode material in Li-ion batteries. The initial specific capacity of Si as an active electrode exhibited 2200 mAh g-1 which faded drastically to around 80 mAh g-1. This rapid decay during cycling is attributed to the significant volume expansion that occurs during the Li-ion insertion and extraction. Consequently, this leads to the pulverization of the Si matrix, loss of the electrical contact and constant formation and breakdown of the SEI layer. To address the key issue of volume expansion, capacity fading, poor cycling stability, the Si-based anode during cycling, herein, Si embedded as an alloying material in electrospun polyacrylonitrile (PAN) based carbon nanofibers (CNF) has been developed. The combination of both Si (high Li storage capacity) and C (long cycle life) makes the anode material advantageous and also exhibit good and stable electrochemical performance. The bead-like Si nanomaterial is observed to be uniformly dispersed in the thread like CNF. Additionally, this composite material has acted as the free standing, flexible, binder free electrode material. In order to maintain the structural integrity and electrical contact, CNF serves as a flexible and conductive framework that helps in accommodating the mechanical stress caused by the lithiation induced expansion. The initial discharge capacity of the Si/CNF composite is 1065 mAh g-1 which becomes stable around 300 mAh g-1 after 100th cycle which is much higher in comparison with the bare Si. The loading of Si in Si/CNF composite has been further investigated where 30% loading of Si in the composite has exhibited significant improvement in the electrochemical performance. The initial specific capacity has been observed at 1057 mAh g-1 which became stable at 380 mAh g-1. Upon increasing the Si loading beyond 30% resulted in agglomeration of Si particles mostly exposed outside on the surface of the fibers that again weakening the mechanical integrity of the composite. The higher loading of Si exacerbates the volume expansion and results in the pulverization of the material which leads to the rapid decline in the capacity of the electrode material. Thus, after optimizing the Si loading in the composite, it has been observed that 30% Si loading in the CNF has exhibited high capacity and electrochemical stability of the Si/CNF composite anode.