Extending the range of electric vehicles

The possibility of achieving high-energy, long-life storage batteries has tremendous scientific and technological significance. An example is the Li–S cell that offers higher energy density compared with conventional Li-ion cells at a low cost. Despite significant advances, there are major challenges regarding its wide-scale implementation. These include sulphur's low intrinsic conductivity as well as undesirable molecules stemming from cathode disintegration — called polysulphides — that dissolve into the battery electrolyte liquid.

In the EU-funded project 'Advanced European lithium sulphur cells for automotive applications' (EUROLIS), researchers are seeking to stabilise Li–S cathodes by using polysulphide reservoirs with modified surfaces. The proposed system with a high surface area should enable weak adsorption of polysulphide intermediates and also reversible desorption. The active material is therefore fully utilised.

To further understand the impact of the surface area and the interactions between electrolyte and sulphur-based cathode composites, reliable characterisation techniques are required. EUROLIS has developed a number of different in situ and ex situ tools for analysing Li–S batteries at different stages of discharge and charge. This has helped further understand the electrochemical properties of the Li–S battery. EUROLIS used these to effectively monitor polysulphide formation and diffusion or migration in different parts of the Li–S battery.

Ultraviolet-visible spectroscopy and the four-electrode modified Swagelok cells could find use in quantitatively determining polysulphides in the separator in addition to distinguishing different polysulphide types. Another spectroscopic tool — sulphur K-edge X-ray absorption spectroscopy — has enabled partners to qualitatively and quantitatively determine polysulphides in the composite cathode.

The electrode composition has been defined to maximise sulphur loading on the positive electrode. Separators, lithium and electrolyte filling were adapted to prepare 12 prototype cells in a standard configuration. Other activities involved benchmarking alternative Li–S technologies. Focus has been placed on solid-state or polymer batteries since both can efficiently prevent polysulphide migration.

EUROLIS activities are significantly contributing to developing know-how regarding Li–S battery production. Dissemination activities include the project website, publications in peer-reviewed scientific journals and conference attendances.