Tracking sulfur species to improve understanding of cell behaviour

While lithium-sulfur batteries offer substantial gravimetric energy density (the amount of charge a battery can store per unit mass) benefits over current Li-ion batteries, their lifetime remains a barrier to widespread commercialisation. The cell chemistry utilises a complex reaction mechanism in which sulfur is dissolved and reacts in the electrolyte producing lithium polysulfides. These further react in the liquid phase before reforming as solids at the end of discharge. During this process polysulfides can be lost by reacting with the lithium electrode, which reduces the number of charge-discharge cycles the cells can achieve.

LiSTAR project researchers from University College London and the University of Oxford have developed a new method of tracking the dissolved polysulfides in real time utilising optical fluorescence microscopy. The research, detailed in ACS Applied Materials and Interfaces, uses a fluorescent dye that binds to the polysulfides. Using this technique, the team has been able to spatially track the evolution of lithium polysulfides and observe benefits offered by electrolyte additives.

The new diagnostic technique will be leveraged to develop enhanced electrode architectures and electrolyte compositions. It is also providing new insights into the mechanisms of operation of Li-S cells, which could be leveraged in developments aimed at extending cell lifetime.

Image: The electrolyte of a lithiumsulfur battery is imaged using optical fluorescence microscopy. The colour seen in the images correlates to localised polysulfide concentration – enabling direct observation of the polysulfide shuttle effect.

Case study published December 2024.