Investigating Magnesium Ion Intercalation in WS2 Cathodes

Abstract

Due to an unmatched combination of energy density, power output, and charge/discharge stability, lithium-ion batteries remain the energy storage technology of choice for a diverse and growing ecosystem of electronic devices, from mobile phones to electric vehicles. However, as the number of applications continues to rise, limitations of Li-ion concerning achievable capacity, cost, and environmental pollution have become increasingly apparent. Divalent Mg-ion chemistries present an intriguing alternative to lithium; however, studies of sulfur-containing chalcogenide cathodes reveal no clear path to commercial adoption. MoS2 and Chevrel-type cathodes do not currently meet anticipated energy density targets, while TiS2, Ti2S4, and Chevrel compounds use volatile electrolyte solutions.While exhibiting an atomic structure and interlayer spacing similar to TiS2 and MoS2, the electrochemical properties of WS2 cathodes remain largely unexplored in the context of Mg-ion intercalation. Here, we study a magnesium ion half-cell constructed from mechanically flexible materials, chosen for their low cost, simple fabrication steps, and separator-free reaction chemistry. Cathodes were fabricated from WS2 powder and electrolyte binder, while a polymer-based electrolyte made of PVDF-HFP and magnesium perchlorate dissolved in ethylene carbonate/propylene carbonate was chosen for its high ionic conductivity and low volatility. Analysis using cyclic voltammetry shows a reversible redox reaction involving Mg species at the cathode/electrolyte interface, indicating presence of an intercalation reaction. Additional cathode surface data is provided by XPS, Powder XRD, and Raman spectroscopy. Cell fabrication details and analysis of reacted cathodes in the context of Mg intercalation will be discussed.