Mechanisms

Understanding the mechanism of a lithium–sulfur cell at the molecular level is important on a number of fronts. Firstly, knowledge of the chemistry and physical mechanisms at play within the lithium–sulfur system is the key to focusing on and accelerating materials research efforts (Part I). Secondly, this knowledge can be used to develop a range of physical models at varying levels of detail to further explain and predict the performance of a lithium–sulfur cell (Part III). Such models have practical application forming the basis of battery management systems for applications to realize the potential of lithium–sulfur technology (Part IV).

Unlike well‐studied lithium ion intercalation mechanisms, lithium–sulfur technology has a much more complex and intriguing mechanism from dissolution of the active sulfur into the electrolyte. The transition moves from solid sulfur through soluble polysulfides to solid lithium sulfide. An ever‐changing equilibrium exists between lithium polysulfides that readily interconvert through association and disassociation reactions via neutral, ionic, and radical species from long chain to the more nucleophilic short chain polysulfides, and the reactivity of polysulfides with cathode, electrolyte, and anode components.

There are many theories around the mechanism of a lithium–sulfur cell and elucidation of that mechanism; reading literature on the subject is perhaps like reading a good murder mystery novel. The mechanism is elusive, ...

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