Abstract
The X-ray absorption spectroscopy technique has been applied to study different stages of the lithium/sulfur (Li/S) cell life cycle. We have investigated how speciation of S in Li/S cathodes changes upon the introduction of CTAB (cetyltrimethylammonium bromide, CH3(CH2)15N+(CH3)3Br−) and with charge/discharge cycling. The introduction of CTAB changes the synthesis reaction pathway dramatically due to the interaction of CTAB with the terminal S atoms of the polysulfide ions in the Na2Sx solution. For the cycled Li/S cell, the loss of electrochemically active sulfur and the accumulation of a compact blocking insulating layer of unexpected sulfur reaction products on the cathode surface during the charge/discharge processes make the capacity decay. A modified coin cell and a vacuum-compatible three-electrode electro-chemical cell have been introduced for further in-situ/in-operando studies.
Highlights
Sustainable and clean energy technologies are highly desirable due to the increasing global energy consumption
It is well established that X-ray absorption absorption spectroscopy spectroscopy (XAS) allows us to determine the chemical bonding, oxidation states, band structures and local symmetries of materials [13,15]
In an X-ray absorption process, a core-hole is first created when a core-electron is excited up to an unoccupied state above the Fermi energy. This transition is governed by the dipole-selection rules that limit the available final states
Summary
Sustainable and clean energy technologies are highly desirable due to the increasing global energy consumption. The widespread applications of the Li/S cells are limited by some issues, such as low electronic conductivity and lithium ion diffusion rate for S and sulfides; volume expansion (~76%) and the polysulfide shuttle effect [4,5]. To address these challenges, a melt-diffusion assistance method was developed to load sulfur onto conductive porous carbon materials, such as microporous carbon spheres, porous hollow carbon, porous carbon nanofibers, and graphene oxide (GO) [5,6,7,8].
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