Sustainable SiO2 Nanostructures from Different Diatom Species As Anode Material for Future Generation Lithium-Ion Batteries

Abstract

Energy harvesting and storage devices occupy a more prominent place in the 21st century than at any time in the past. Intensive efforts have been devoted to next-generation energy storage devices such as rechargeable lithium-ion batteries (LIBs) to develop high energy density and long cycle life electrode materials from sustainable sources. In the present anode, graphite is severely restricted by capacity and unavoidable solid electrolyte interface (SEI) formation. Besides, it has been listed as a critical material by the European Commission. Recently, silicon-based electrodes have been pinpointed as promising anode candidates due to their high theoretical capacity (~4200 mAhg-1 for Li4.4Si), low operating voltage (0.4V/Li/Li+), abundant resources, and environmental friendliness. Interestingly, nanostructures of Silica (SiO2) can be extracted from the frustules (exoskeletons) of a type of microalgae called diatoms. In this current work, SiO2 frustules were grown from two different diatom species, constituting a sustainable source for producing nanostructured Si-based materials. Scanning electron microscopy (SEM) images confirmed the highly nanoporous structure of diatom silica, which was retained even after ball-milling. The electrochemical performance of SiO2 was investigated as an anode material for LIBs. Herein, we have tested both species A & B milled and un-milled samples (denoted as SPAUM, SPAM, SPBUM, and SPBM). The diatom SiO2 un-milled species A (SPAUM) exhibited a high specific capacity of ~ 810 mAhg-1 with remarkable capacity retention and coulombic efficiency even after 100 cycles at 0.1 Ag-1 and delivered a high specific capacity of ~ 400 mAhg-1 even at high current density 3 Ag-1. For comparison and understanding, commercially available diatomaceous earth milled, and un-milled silica (denoted as EDAM & EDAUM) has been subjected to the same cycling protocol. Results clearly showed species A & B milled and un-milled displaying better electrochemical performance than diatomaceous earth milled and un-milled silica. Such improved electrochemical properties like cycle life, and rate capability of SPAUM are mainly ascribed to their highly porous nature which significantly facilitates fast Li ion diffusion, its unique morphology, which favors a faster kinetics and its complete lithiation/de-lithiation after the initial activation cycle. In view of the superior electrochemical properties, such sustainably sourced SiO2 materials can be considered a potential anode material for future LIBs. Figure 1