Extending lifetime with quasi-solid-state lithium-sulfur batteries

Lithium-sulfur batteries offer the promise of very high gravimetric energy density (the charge stored per unit mass), but their commercialisation has been hampered by comparatively poor lifetimes and the rate at which they can deliver their charge (the rate performance) compared to alternative technologies. This challenge is linked to a complex operating mechanism, where solid sulfur is dissolved in the liquid electrolyte to produce lithium polysulfides. These products then continue to react in the liquid phase before forming final, solid, discharge products. During these reaction steps polysulfides can react with the lithium electrode, which reduces the number of charge-discharge cycles the cells can achieve.

To overcome these limitations, researchers from University College London, Imperial College London and the University of Oxford have developed a new cell in which the sulfur does not readily dissolve in the liquid electrolyte, driving the discharge reaction towards a more solid-state mechanism. The work, detailed in Communications Materials, highlights the improved stability associated with this approach. Cells retained over 1,100 mAh/g of sulfur capacity after 200 cycles, a retention of 82% compared to a control cell that retained only 44% capacity over the same number of cycles. Also, with the addition of a lithium-ion conducting material into the electrode, the electrode showed impressive power delivery performance and resulted in a 200% improvement in capacity retention at high discharge rates.

This innovation in electrode design highlights new avenues to develop lithium-sulfur cells, which will be built upon as the project continues. The aim is to further increase the capacity of the electrode and extend the cycle life in this new ‘quasi-solid-state’ cell format.

Image: X-ray tomography image of the electrode showing the microstructure of the newly developed electrode.

Case study published December 2025.