Hollow and Silver-Cored Carbon Nanospheres as Effective Sulfur Hosts for Lithium-Sulfur Batteries

Abstract

Lithium sulfur (Li–S) batteries are considered to be one of the most promising “beyond lithium-ion” energy storage technologies and the development of alternative battery chemistries is required to alleviate our reliance on the burning of fossil fuels 1. The high theoretical specific capacity of sulfur (1672mAh g-1) leads to a theoretical specific energy of ~2510 Wh kg-1, which is significantly greater than the state-of-the-art lithium-ion batteries 2. Further to this, sulfur is environmentally benign, low cost, and Li–S batteries do not rely on cobalt, or manganese 3, which are expensive, toxic, and have known ethical implications associated with their extraction and refining 4.While Li–S batteries boast many theoretical advantages, their practical application has been plagued with an array of limitations, mainly attributed to the poor electrical conductivity of sulfur, the significant volumetric expansions (80%) that can occur during cycling, and the soluble polysulfide intermediates 5. To tackle this, current research efforts have focused on using porous carbon materials (PCMs) to prepare sulfur/carbon composite cathodes 6,7. PCMs offer improved electrical conductivity, a large specific surface area, and pore diameters that are less than 1nm—which may confine the soluble polysulfides within the cathode matrix 8.In this study, the synthesis of hollow and silver-cored carbon nanospheres (HCNS, Ag-CNS) is detailed and their use as a multifunctional sulfur host for Li–S batteries is assessed. Ag-CNS are synthesised via a hydrothermal procedure from a simple saccharide solution coupled with a silver precursor. These Ag-CNS are further processed to prepare HCNS by etching the internal silver nanoparticle with an acid solution. The hydrothermal procedure described in this study offers a simplification to traditional HCNS synthesis methods which typically require the removal of templates, such as silica nanospheres, through etching with hazardous chemicals such as hydrofluoric acid.In this work, the structural and physical properties of HCNS and Ag-CNS are characterised using transmission electron microscopy, scanning electron microscopy, nitrogen gas adsorption, X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The electrochemical performance of these materials, when used as a sulfur host, is investigated through the preparation, and testing of half cells with lithium metal anodes. Electrochemical testes include cyclic voltammetry and galvanostatic cycling data at different C-rates.