Li2S4

Lithium tetrasulfide, with the chemical formula Li2S4, is an inorganic compound. It is a salt formed between lithium cations (Li+) and the tetrasulfide anion (S4^2-). This compound is typically encountered as a yellow or orange solid.

Li2S4 is not a commonly encountered standalone compound in bulk industrial applications. However, it plays a significant role as an intermediate species in certain electrochemical systems, most notably in lithium-sulfur (Li-S) batteries. During the discharge process of a Li-S battery, elemental sulfur (S8) reacts with lithium ions to form various lithium polysulfides, including Li2S4. These polysulfides are soluble in common organic electrolytes used in these batteries, leading to a phenomenon known as the "polysulfide shuttle."

The polysulfide shuttle refers to the diffusion of soluble lithium polysulfides, such as Li2S4, from the cathode to the anode and back. This process leads to several detrimental effects in Li-S batteries, including reduced coulombic efficiency, capacity fading, and self-discharge. Understanding the formation, dissolution, and redox behavior of Li2S4 is crucial for improving the performance and longevity of lithium-sulfur battery technology. Research efforts are focused on strategies to mitigate the polysulfide shuttle, such as modifying electrode materials or electrolytes.