Sulfur Infilled Carbon Nanospheres As Cathode Materials for Lithium–Sulfur Batteries

Abstract

To date lithium-ion (Li-ion) batteries have been the de facto commercial battery type used in consumer electronics as well as in the first generation of electric vehicles (EVs). However, increases in the practical energy density of Li-ion batteries are too sluggish to keep pace with the demands of the next generation of portable electronics and EVs. Lithium Sulfur (Li–S) batteries are one of the most promising “beyond Li-ion” rechargeable battery systems in terms of both cost and specific energy density. (1, 2) Li–S batteries can deliver a practical specific energy density of 600 Wh/kg, which is more than double the values offered by state-of-the-art Li-ion batteries. (3, 4) However, there are still issues, which need to be addressed before widespread commercialization of Li–S batteries can be possible. Sulfur (S) and lithium sulfide (Li2S) have intrinsically low electronic conductivity. (5) Furthermore, the high-order lithium polysulfides (Li2Sx (6 < x ≤ 8)), which are formed upon first lithiation, are highly soluble in the standard liquid Li–S battery electrolyte. These various polysulfide anions are mobile and can be partially reduced and oxidized multiple times in the vicinity of the anode and cathode, respectively, leading to a so-called polysulfide shuttle phenomenon. (6) Additionally, the large volume changes (80%) which are associated with conversion reactions can lead to electrode disintegration and electrical isolation issues, resulting in severe capacity decay. (7) Various methods have been explored in an attempt to tackle these detrimental issues. Sulfur-carbon composites have been investigated to improve conductivity, following the pioneering work of the Nazar Group. (8) Efforts to reduce the polysulfide shuttle have been made via the application of various polysulfide-trapping interlayers, the use of functional separators and the exploitation of solid-state electrolytes.In this work, we detail the preparation of carbon nanospheres (CNS) with application as conductive sulfur host materials for Li–S batteries. CNS are prepared via facile hydrothermal treatment with different cost-effective precursors and the influence of each precursor on the structural and physical properties of the nanospheres is determined through examination of electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy and gas adsorption data. The electrochemical performance of sulfur infilled CNS samples is evaluated through comparison of cyclic voltammetry and galvanostatic cycling data. We demonstrate that the choice of carbon precursor can have a significant influence on the performance of the CNS-based sulfur electrodes. Sulfur infilled CNS materials, which are morphologically similar, can have significantly different electrochemical response due to differences in their physical properties such as pore volume and pore structure.